CA1122779A - Amorphous silica, products thereof and methods of preparing the same - Google Patents
Amorphous silica, products thereof and methods of preparing the sameInfo
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- CA1122779A CA1122779A CA358,846A CA358846A CA1122779A CA 1122779 A CA1122779 A CA 1122779A CA 358846 A CA358846 A CA 358846A CA 1122779 A CA1122779 A CA 1122779A
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- particles
- amorphous silica
- opsil
- shaped body
- crystals
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Abstract
ABSTRACT OF THE DISCLOSURE
The present invention provides a shaped body of amorphous silica comprising primary particles of amorphous silica randomly three-dimensionally interlocked with one another integrally into the body and voids interspersed therebetween, each of the primary particles having a crystalline appearance, at least two surfaces in symmetric relation, a length of about 1 to about 500µ, and a thickness of about 50 .ANG. to about 1µ, the length being at least about 10 times the thickness. The silica particles are useful for the adsorption of gases and water, have high oil adsorbing capacity and provide light weight shaped bodies of high mechanical strength and acid resistance.
The present invention provides a shaped body of amorphous silica comprising primary particles of amorphous silica randomly three-dimensionally interlocked with one another integrally into the body and voids interspersed therebetween, each of the primary particles having a crystalline appearance, at least two surfaces in symmetric relation, a length of about 1 to about 500µ, and a thickness of about 50 .ANG. to about 1µ, the length being at least about 10 times the thickness. The silica particles are useful for the adsorption of gases and water, have high oil adsorbing capacity and provide light weight shaped bodies of high mechanical strength and acid resistance.
Description
~Z2~7~
This inventlon relates to novel amorphous silicas having a crystalline appearance, products thereof and methods of preparing the silicas and their products.
This application is a divisional application of copending application No. 248,633 filed March 24, 1966.
Silica gel which is known as a representative example of amorphous silicas is mainly produced by neutralizing an aqueous solution of sodium silicate with an acid such as hydrochloric acid or sulfuric acid to form a precipitate, and washing and drying the precipitate. When desired, the silica gel obtained is heated at reduced pressure for activation.
Depending on the method of production, silica gel is obtained in an indefinite or spherical shape. Furthermore when required, silica gel is shaped to tablets and the li];e using a binder.
Silica gel is used for example as a drying agent, adsorbent, dehydrant, deodorant, catalyst carrier, etc. because of its hygroscopicity and large specific surface area.
However, silica gel readily adsorbs water upon contact therewith and collapses. It is therefore impossible or difficult to use silica gel in a system in which it is directly exposed to water. Generally silica gel has a average pore diameter of 20 to 220 A. Silica gel with a relatively small average pore diameter usually has a great bulk density of about 0.7 g/cm3, whereas conversely one possessing a bulk density of about 0.2 g/cm3 invariably has a large average pore diameter of about 180 to about 220 A in general. Accordingly, the silica gel with an average pore diameter of the order of 20 to 40 A suitable for use as an adsorbent for gases and ~.
This inventlon relates to novel amorphous silicas having a crystalline appearance, products thereof and methods of preparing the silicas and their products.
This application is a divisional application of copending application No. 248,633 filed March 24, 1966.
Silica gel which is known as a representative example of amorphous silicas is mainly produced by neutralizing an aqueous solution of sodium silicate with an acid such as hydrochloric acid or sulfuric acid to form a precipitate, and washing and drying the precipitate. When desired, the silica gel obtained is heated at reduced pressure for activation.
Depending on the method of production, silica gel is obtained in an indefinite or spherical shape. Furthermore when required, silica gel is shaped to tablets and the li];e using a binder.
Silica gel is used for example as a drying agent, adsorbent, dehydrant, deodorant, catalyst carrier, etc. because of its hygroscopicity and large specific surface area.
However, silica gel readily adsorbs water upon contact therewith and collapses. It is therefore impossible or difficult to use silica gel in a system in which it is directly exposed to water. Generally silica gel has a average pore diameter of 20 to 220 A. Silica gel with a relatively small average pore diameter usually has a great bulk density of about 0.7 g/cm3, whereas conversely one possessing a bulk density of about 0.2 g/cm3 invariably has a large average pore diameter of about 180 to about 220 A in general. Accordingly, the silica gel with an average pore diameter of the order of 20 to 40 A suitable for use as an adsorbent for gases and ~.
-2-~2~77~
water has a great bulk density and an inherently limited adsorbing capacity per unit weight. Although the capacity to - adsorb oils increases with decreasing bulk density and increasing specific surface area, silica gel having a large specific surface area also has a high bulk density and therefore invariably possesses an insufficient or no oil adsorbing capacity.
Particles o~f silica gel in themselves are not shapable without the use of a binder; in fact it is impossible to obtain a strong shaped body without using any binder. In addition, silica gel has not been used for the production of heat-resistant glass, refractory heat insulator, heat-resistant filter, etc.
The primary object of this invention is to provide a novel and useful amorphous silica, products thereof and methods of preparing the silica and its products.
Another object of this invention is to provide a novel amorphous silica which pos~esses various useful properties ~nd which are therefore usable in place of known 2~ silica ge] and also applicable to uses for which the known silica gel is unserviceable.
Another object of this invention is to provide a novel amorphous silica which has a high capacity to adsorb water but outstanding resistance to water and remains un-collapsible despite the adsorption of water and wh~ch is therefore usable in a system in which it is directly exposed to water.
1~2'7~9 Another object of this invention is to provide a novel amorphous silica which has a small average pore diameter of about 20 to about 40 ~ and also a small bulk density although none of silica gels heretofore known do not possess both the characteristics and which is suitable for the adsorp-tion of gases and water.
Another object of this invention is to provide a novel amorphous silica having a small bulk density and a large specific surface arPa and accordingly a high oil adsorbing capacity.
Another object of this invention is to provide an amorphous silica readily dispersible in water to give an aqueous slurry from which a lightweight and strong shaped body can be obtained by shaping and drying without using any binder and also to provide the aaueous slurry.
Another object of this invention is to provide a light-weight shaped body of amorphous silica which has high mechanical strength and acid resistance and which is therefore usable as a heat insulator, filter medium, catalyst carrier, etc.
Another object of this invention is to provide a novel amorphous silica suitable as a material for the product-ion of heat-resistant glass.
Another object of this invention is to provide a novel amorphous silica which readily permits the passage ~,.
~lZ~79 of water, therefore can be drained easily and is uncollapsible when in contact with water, the amorphous silica thus being serviceable for various uses wherein these character-istics are advantageously utilized.
S Another object of this invention is to provide methods of preparing the novel amorphous silicas having the foregoing excellent properties and products thereof.
Another object of this invention is to provide a novel composite material composed of the novel amorphous silica and extremely fine particles of calcium carbonate at-tached to the silica.
Another object of this invention is to provide a method of preparing a novel composite material of amorphous silica and calcium carbonate which is useful as a filler and reinforcing agent and also to provide a method of preparing products from the composite material.
These and other features of this invention will become apparent from the following description.
Basically, the amorphous silicas of this invention are in the form of primary particles and characterized in that the particles having a crystalline appearance and has at least two surfaces in symmetric relation, a lenght of about 1 to about 500~ and a thickness of about 50~ A to about l~
the lenght being at least about lO times the thickness. The amorphous silicas of this invention include, ,,,'~.
2~
in addition to those having the form of primary particles described above, those in the form of secondary particles and those in the form of a shaped body.
The term "Opsil" as used in the specification refers to the amorphous silica of this invention. Thus by the term l'Opsil-I" is meant an amorphous sil.ica of this invention having the form of primary particles, and by the term "Opsil-II" is meant an amorphous silica of this invention having the form of secondary particles.
Opsil-I of this invention is amorphous silica of high purity and therefore does not display and X-ray diffract-ion phenomenon and, when dehydrated by ignition and then chem-ically analyzed, is found to contain at least 98~ by weight of SiO2. Observation under an electron microscope has revealed that the primary particle, the basic form of Opsils, has a crystalline appearance and at least two surfaces in symmetric relation, although it is amorphous.
The crystalline appearance, the most distinct feature of Opsils of this invention, is attributable to the fact that they are derived from silicate crystals by the conversion of the silicate crystals into amorphous silica which retains the original configuration of the crystals. Accordingly, the crystalline appearance and size of -the particles of Opsil-I
are substantially in 7~7~
conformity with the appearance and size of the silicate crystals from which they are derived, and Opsil-I particles have varying configurations and sizes in corresponding relation to the original crystals. For example, the lath-like crystals of wollastonite, xonotlite, foshagite or like calcium silicate are converted into the particles of Opsil-I having a lath-lik~
configuration. The particles of Opsil-I have a plate-like con-figuration if they are derived from the plate-like crystals of tobermorite, gyrolite, a-dicalcium silicate hydrate (N-C2SH) or like calcium silicate. The particles of Opsil-I derived from the foil-like crystals of calcium silicate such as CSHn have a foil-like configuration. The sizes of these lath-like, plate-like and foil-like Opsil-I particles range from about l to about 500~, preferably about l to about 300~, in lengt~
and from about 50 A to about l~, preferably about 100 ~ to about l~ in thickness, the lenght being at least about 10 times, preferably about 10 to about 5,000 times the thickness.
The lath-like particles of Opsil-I derived from primary part-icles of xonotlite crystals have the configuration of the pri-mary particles and are about l to about 50~ in length, about 100 ~ to about 0.5~ in thickness and about 100 A to about 2~ in width, the length being about 10 to about 5,000 times the thick-ness. the plate-like particles of Opsil-I derived from primary ,~.`
1122~79 particles of tobemorite crystals have the configuration of the primary particles and are about 1 to about 50~ in length about 100 ~~ to about 0.5~ in thickness and about 0.2 to about 20~ in width, the length being about 10 to about 5,000 times the thickness. The lath-like particles of Opsil-I derived from primary particles of wollastonite crystals have the con-figuration of the pximary particles and are about 1 to about 500~ in length, about 100 ~ to about 1~ in thickness and about 100 A to about 5~ in width, the length being about 10 to about 5,000 times the thickness. The foil-like particles of Opsil-I
derived from primary particles of CSHn crystals have the con-figuration of the primary particles and are about 1 to about 20~ in length, about 50 ~ to about 500 ~ in thickness and about 100 ~ to about 20~ in width, the length being about 50 to about 5,000 times the thickness. The plate-like particles of Opsil-I derived from primary particles of gyrolite crystals have the configuration of the primary particles and are about 1 to about 50~ in length, about 100 A to about 0.5~ in thick-ness and about 1 to about 20~ in width, the length being about 20 10 to about 5,000 times the thickness. The plate-like particles of Opsil-I derived from primary particles of ~-dicalcium silicate hydrate crystlas have the configuration of the primary part-icles and are about 1 to about 300~ in lengtll, about ~2~
500 A to abou-t 1~ in thickness and about 1 to about 50~ in width, the length being about 10 to about 5,000 times the thick-ness.
Table 1 gives the chemical composition of Opsil-I, which is subjected to ignition dehydration and thereafter to elementary analysis, and Table 2 shows the physical properties of Opsil-I in comparison with those of silica gel.
Table 1 Ig. loss 4-7 wt. %
SiO2 > 98.0 wt. %
A123 < 1.0 wt. %
Fe23 < 0.01 wt. %
CaO < 0.02 wt. %
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~able 2 -Opsil-I Silica gel ~D(l) ID(2) LD(3) :
Bulk density (g/cm3)0.04-0.30 0.67-0.75 0.~5-0.40 0.12-0.17 ~rue specifiC~ 1.9-2.2 2.2 2.2 2.2 gravity (g/cm ) Specific surface area 250-600 750-800 300-350 100-200 (m2 /g) Pore volume0.1-0.5 0.~7-0.40 0.9-1.1 1.4-2.0 diameter (A) 20-40 22-26 120-160 180-220 Particle size 1-500 1,000-5,000 1,000-5,000 1-5 Oi( a/10Opt)on ~oO_90o 0 0 <300 gro(soc/)picit~ 220 45 110 150 Water No Collapse Coll~pse resiatancecha~ge Thermal oonductivity o . o~
(Kcal/m.h.
deg.) P~ 6-7 .
Note: (1) RD stands for regular density.
(2) ID stands for intermediate density.
water has a great bulk density and an inherently limited adsorbing capacity per unit weight. Although the capacity to - adsorb oils increases with decreasing bulk density and increasing specific surface area, silica gel having a large specific surface area also has a high bulk density and therefore invariably possesses an insufficient or no oil adsorbing capacity.
Particles o~f silica gel in themselves are not shapable without the use of a binder; in fact it is impossible to obtain a strong shaped body without using any binder. In addition, silica gel has not been used for the production of heat-resistant glass, refractory heat insulator, heat-resistant filter, etc.
The primary object of this invention is to provide a novel and useful amorphous silica, products thereof and methods of preparing the silica and its products.
Another object of this invention is to provide a novel amorphous silica which pos~esses various useful properties ~nd which are therefore usable in place of known 2~ silica ge] and also applicable to uses for which the known silica gel is unserviceable.
Another object of this invention is to provide a novel amorphous silica which has a high capacity to adsorb water but outstanding resistance to water and remains un-collapsible despite the adsorption of water and wh~ch is therefore usable in a system in which it is directly exposed to water.
1~2'7~9 Another object of this invention is to provide a novel amorphous silica which has a small average pore diameter of about 20 to about 40 ~ and also a small bulk density although none of silica gels heretofore known do not possess both the characteristics and which is suitable for the adsorp-tion of gases and water.
Another object of this invention is to provide a novel amorphous silica having a small bulk density and a large specific surface arPa and accordingly a high oil adsorbing capacity.
Another object of this invention is to provide an amorphous silica readily dispersible in water to give an aqueous slurry from which a lightweight and strong shaped body can be obtained by shaping and drying without using any binder and also to provide the aaueous slurry.
Another object of this invention is to provide a light-weight shaped body of amorphous silica which has high mechanical strength and acid resistance and which is therefore usable as a heat insulator, filter medium, catalyst carrier, etc.
Another object of this invention is to provide a novel amorphous silica suitable as a material for the product-ion of heat-resistant glass.
Another object of this invention is to provide a novel amorphous silica which readily permits the passage ~,.
~lZ~79 of water, therefore can be drained easily and is uncollapsible when in contact with water, the amorphous silica thus being serviceable for various uses wherein these character-istics are advantageously utilized.
S Another object of this invention is to provide methods of preparing the novel amorphous silicas having the foregoing excellent properties and products thereof.
Another object of this invention is to provide a novel composite material composed of the novel amorphous silica and extremely fine particles of calcium carbonate at-tached to the silica.
Another object of this invention is to provide a method of preparing a novel composite material of amorphous silica and calcium carbonate which is useful as a filler and reinforcing agent and also to provide a method of preparing products from the composite material.
These and other features of this invention will become apparent from the following description.
Basically, the amorphous silicas of this invention are in the form of primary particles and characterized in that the particles having a crystalline appearance and has at least two surfaces in symmetric relation, a lenght of about 1 to about 500~ and a thickness of about 50~ A to about l~
the lenght being at least about lO times the thickness. The amorphous silicas of this invention include, ,,,'~.
2~
in addition to those having the form of primary particles described above, those in the form of secondary particles and those in the form of a shaped body.
The term "Opsil" as used in the specification refers to the amorphous silica of this invention. Thus by the term l'Opsil-I" is meant an amorphous sil.ica of this invention having the form of primary particles, and by the term "Opsil-II" is meant an amorphous silica of this invention having the form of secondary particles.
Opsil-I of this invention is amorphous silica of high purity and therefore does not display and X-ray diffract-ion phenomenon and, when dehydrated by ignition and then chem-ically analyzed, is found to contain at least 98~ by weight of SiO2. Observation under an electron microscope has revealed that the primary particle, the basic form of Opsils, has a crystalline appearance and at least two surfaces in symmetric relation, although it is amorphous.
The crystalline appearance, the most distinct feature of Opsils of this invention, is attributable to the fact that they are derived from silicate crystals by the conversion of the silicate crystals into amorphous silica which retains the original configuration of the crystals. Accordingly, the crystalline appearance and size of -the particles of Opsil-I
are substantially in 7~7~
conformity with the appearance and size of the silicate crystals from which they are derived, and Opsil-I particles have varying configurations and sizes in corresponding relation to the original crystals. For example, the lath-like crystals of wollastonite, xonotlite, foshagite or like calcium silicate are converted into the particles of Opsil-I having a lath-lik~
configuration. The particles of Opsil-I have a plate-like con-figuration if they are derived from the plate-like crystals of tobermorite, gyrolite, a-dicalcium silicate hydrate (N-C2SH) or like calcium silicate. The particles of Opsil-I derived from the foil-like crystals of calcium silicate such as CSHn have a foil-like configuration. The sizes of these lath-like, plate-like and foil-like Opsil-I particles range from about l to about 500~, preferably about l to about 300~, in lengt~
and from about 50 A to about l~, preferably about 100 ~ to about l~ in thickness, the lenght being at least about 10 times, preferably about 10 to about 5,000 times the thickness.
The lath-like particles of Opsil-I derived from primary part-icles of xonotlite crystals have the configuration of the pri-mary particles and are about l to about 50~ in length, about 100 ~ to about 0.5~ in thickness and about 100 A to about 2~ in width, the length being about 10 to about 5,000 times the thick-ness. the plate-like particles of Opsil-I derived from primary ,~.`
1122~79 particles of tobemorite crystals have the configuration of the primary particles and are about 1 to about 50~ in length about 100 ~~ to about 0.5~ in thickness and about 0.2 to about 20~ in width, the length being about 10 to about 5,000 times the thickness. The lath-like particles of Opsil-I derived from primary particles of wollastonite crystals have the con-figuration of the pximary particles and are about 1 to about 500~ in length, about 100 ~ to about 1~ in thickness and about 100 A to about 5~ in width, the length being about 10 to about 5,000 times the thickness. The foil-like particles of Opsil-I
derived from primary particles of CSHn crystals have the con-figuration of the primary particles and are about 1 to about 20~ in length, about 50 ~ to about 500 ~ in thickness and about 100 ~ to about 20~ in width, the length being about 50 to about 5,000 times the thickness. The plate-like particles of Opsil-I derived from primary particles of gyrolite crystals have the configuration of the primary particles and are about 1 to about 50~ in length, about 100 A to about 0.5~ in thick-ness and about 1 to about 20~ in width, the length being about 20 10 to about 5,000 times the thickness. The plate-like particles of Opsil-I derived from primary particles of ~-dicalcium silicate hydrate crystlas have the configuration of the primary part-icles and are about 1 to about 300~ in lengtll, about ~2~
500 A to abou-t 1~ in thickness and about 1 to about 50~ in width, the length being about 10 to about 5,000 times the thick-ness.
Table 1 gives the chemical composition of Opsil-I, which is subjected to ignition dehydration and thereafter to elementary analysis, and Table 2 shows the physical properties of Opsil-I in comparison with those of silica gel.
Table 1 Ig. loss 4-7 wt. %
SiO2 > 98.0 wt. %
A123 < 1.0 wt. %
Fe23 < 0.01 wt. %
CaO < 0.02 wt. %
llZZ~7~
~able 2 -Opsil-I Silica gel ~D(l) ID(2) LD(3) :
Bulk density (g/cm3)0.04-0.30 0.67-0.75 0.~5-0.40 0.12-0.17 ~rue specifiC~ 1.9-2.2 2.2 2.2 2.2 gravity (g/cm ) Specific surface area 250-600 750-800 300-350 100-200 (m2 /g) Pore volume0.1-0.5 0.~7-0.40 0.9-1.1 1.4-2.0 diameter (A) 20-40 22-26 120-160 180-220 Particle size 1-500 1,000-5,000 1,000-5,000 1-5 Oi( a/10Opt)on ~oO_90o 0 0 <300 gro(soc/)picit~ 220 45 110 150 Water No Collapse Coll~pse resiatancecha~ge Thermal oonductivity o . o~
(Kcal/m.h.
deg.) P~ 6-7 .
Note: (1) RD stands for regular density.
(2) ID stands for intermediate density.
(3) LD stands for low density.
(Literature: Encyclopedia of Cnemical Technology 18, (1969) p 61-67) 1~ .
llZZ~77~
The characteristic values in Table 2 are determined by the following methods.
Bulk density: A 10 g quantity of particles are placed in a cylinder 5 cm2 in cross sectional area and subjected to a load of 250 g by a 50 g/cm2 capacity piston-- cylinder device. The volume of the coMpressed mass is then measured. Bulk den~ity is given by Bulk density - 10 (~
Volume (cm ) True specific gravity: l~e~sured by air compariSsn pycnometer Model 930, Bec~nann Co., with air replaced by He gas.
Average pore diameter: By BET nitrogen adsorption method.
Specific surface area; Same as above.
; Pore volume: Same as above.
Particle size: Determined under optical and electron microscopes.
Oil adsorption: Dioctyl phthalate (C6H4(COOC8H17)2) is \ added dropwise to 100 g of particles to cause the particles to adsorb the phthalate, and the amount of the phthalate is measured when the mass of the particels starts to become markedly viscous.
Hygroscopicity: Particles are placed in a container at R.H. 100% and maintained at 25 C, allowing the partlcles to adsorb moisture until an equilibrium i5 established.
77~
Hygro6coplcity i~ expressed in terms of the weight by % of the moisture adsorbed based on the particles.
~ The values listed are obtained using Opsil_I having a bulk density of 0.1 g/cm3, and silica gels with a bulk density of 0.7 g/cm3 for RD type, a bulk den~ity of 0.4 g/cm3 for ID type and a bulk density of 0.15 g/cm3 for LD type.
Table 2 s~ows that Opsil-I has a small average pore diameter and a large specific .urface area despite its Small bulk density, does not collapse when immersed in water because of its good resistance to water and is highly oil-adsorbent, remarkably hygroscopic and extremely low in thermal conductivity. Further, Opsil has an approximately neutral pH of 6 to 7 and high resistance to chemicals and will not be decomposed with hydrochloric acid and like acid~, These properties are very advantageous over the propertie5 of calcium silicate crystals from which they are derived; the crystals have a high pH of 10 to ll~ are decomposable with an acid such as hydro-chloric acid and therefore find limited uses~
Moreover, Opsil_I is easily dispersible in water to form an aqueous ~lurry thereof and has a peculiar shapability that the slurry gives, when shaped and dried, a light weight shaped body composed of Opsil-I randomly three-z5 dimensionally ~nterlocked with one another integrally into ...
~ 2 1~277~
the body and having a high mechanical strength The aqueous slurry to be shaped may preferably have a water to solid ratio of 4 - 50 : 1 by weight. When desired, the slurry may in-corporate therein a fibrous reinforcing material such as as-bestos, glass fibers, rock wool, synthetic fibers, naturalfibers, pulp, carbon fibers, stainless steel fibers, alumina sol, colloidal silica sol, clay, cement, coloring agent, filler and various other additives. The shaped body is usable variously for example as a heat insulating material, filtration medium, catalyst carrier, etc.
Because of the unique particulate shape and proper-ties described above, Opsil-I is serviceable as a substitute for silica gel in uses for which s lica gel is usually employed and is also serviceable in other uses to which silica gel is not applicable. For example, Opsil-I is useful as a filler, drying agent, adsorbent, deodorant, filter medium, heat-resist-ant filter, additive for adhesives, heat-resistant agent, delustering agent for paper making, emulsifier for cosmetics, abrasion-resistant agent, heat insulator, viscosity imparting agent, pigment, tooth powder, carrier for agricultural chem-icals, carrier for pharmaceuticals, catalyst, catalyst carrier, material for heat-resistant glass, absorbent for gas chroma-tography, excipient, anticaking agent, fixing agent for volatile , 7~9 substances, molecular sieve, shaped body, etc.
Opsil-II is in the form of substantially globular secondary particles of the amorphous silica of this invention.
Each of the secondary particles is composed of numerous pri-mary particles of amorphous silica randomly three-dimensionally interlocked with one another and voids interspersed therebetween and has a diameter of about 10 to about 150~l, preferably about 10 to about 80~, the primary particle having a crystalline appearance, at least two surfaces in symmetric relation, a length of about 1 to about 500~, preferably about 1 to about 300~, and a thickness of about 50 to about 1~, preferably about 100 to about 1~, the length being at least about 10 times, preferably about 10 to about 5,000 times, the thickness. Opsil-II usually has the porosity of at least about 75% preferably about 80 to about 98%.
Since Opsil-II is composed of Opsil-I described above, it has the foregoing properties of Opsil-I and finds the same uses as Opsil-I.
Moreover, Opsil-II is readily dispersible in water to form an aqueous slurry and has the peculiar shapability that the slurry gives a light-weight shaped body having high mechanical strength, when shaped and dried. Generally, the shaped body obtained from Opsil-II has higher mechanical strength than that obtained from Opsil-I having the same bulk density therewith. More specifically, when the aqueous slurry of ~2~779 Ops~ I is subjected to pressure for shaping~ the particles are cornpressed in the direction of pressure applied in the ihapingstep Namely, the particles of Opsil-II in the present shaped body are compressed more or less in at least one direction due to the pressure applied in the shaping step.
The compre&sed particles are interlocked with one another and shaped to an integral body in this state when dried.
The bulk density of the shaped body, v~hich i5 controllable as desired by altering the shaping pressure, can vary over a wide range. Preferably, the bulk density is in the range of about 0.1 g/cm3 to about 1.0 g/cm3. The shaped body is usable variously for example as a heat insulating material~ filtration medium, catalyst carrier, etc.
Generally~ the aqueous slurry of Opsil-II to be shaped may preferably have a water to solids ratio of 8 - 50 : 1 by weight. When desired, the aqueou; slurry may incorporate therein a fibrous reinforcing mate~~ial such as asbestos, ~lass fibers, rock wool~ synthetic fibers, ~ natural fibers, pulp, carbon fibers or stainless steel fibers, alumina sol,colloidal silica sol, clay, cement, coloring agent, filler and various other additives.
These additives afford useful properties to the shaped body.
Table 3 glves the propertie~; of Opsil-II.
c`
~2Z~'79 ~able 3 Bulk den~ity (g/cm3) 0.03~0.5 Specific surface area (m2/g) 250-600 Specific surface area (m2/~) after heating at 400 C 200-550 Porosity (%) prefer~bly at least 75 Oil adsorption (cc/100 g) 5U0-1200 pH 6-7 Heat resistance Secondary particlesO
retain shape at 950 C
The properties listed above are determined by the same methods as in Table 2, ~Iherein the porosity is given by Apparent specific gravity of Opsil -II
True specific gravity of Opsil-II
- 5 . The heat resistance i5 determined with the unaided eyeS -This invention further provides novel sh~ped bodies of amorphous silica which include a ~haped body composed of Opsil-I (hereinafter referred to as "Opsil-IS") and a shaped body composed of Opsil-II (hereinafter referred to as "Opsil-IIS"). Opsil-IS i5 a ;h~ped body WhiCh i6 integrally formed from the particles of Opsil-I
randomly three-dimensionally interlocked with one another.
,6 ~`
~z~
That is to say, Opsil-IS compri~e~ primary particle.5 of amorphous silica randomly three-dimen ionally i.nterlocked with one another integrally inlo ihe bou~
and voids interspersed therebetween, each of the ;5 primary particles having a crystalline appearance~ at least two surfaces in symmetric relation, a length of about 1 to about ~00~ , preferably about 1 to about 30~ , and a thickness of about ~50 ~ to about 1~1, preferably about 100 ~ to about 1~ , the length being at least about lO tiMes, preferably about 10 to about ~,000 times, the thickness~
~he shaped body usuall~ h~s a Porosit~ of ~t le~st about 50%, ~refer~bly ~b~ut ~ to abollt 95 opsil-IIs is a ~haped body in ~hich the particle~
of Opsil-II are interlocked with one another into the integral . 15 body. Namely, Opsil-IIS comprises secondary particles of amorphous silica compressed in at least one direction and interlocked with one another integrally into the body and voids inters~ersed therebetweenl the secondar~ ~article : '~ being composed of numerous primary particles of amorphous 6ilica randomly three-dimensionally interlocked with one another, each of the primary particles having a crystalline . - 17 -~.
~' I
- ~227~9 appearance~ at least two surfaceS insymmetric rela'cion~ !
a length of about 1 to 500 ~ , prefelably about 1 to about 300~ , and a thickness of about 50 ~ to about 1~ , preferably about 100 R to about 1~ , the length being at least 10 times, preferably about lO to about 5,000 times, the thickness. O~sil-IIS ususll~ h~s a poresit~ of at least _ . . . .
- about 50~, preferably about 60/~ to ~bout 97/n.
-- . . .
Both OpsiI-IS and Opsil-IIS have a large porosity, are lightweight and have high mechanical strength. More specifically, they have a low bulk density of about 0.1 to about 0.4 g/cm3 and high bending strength of,about 3 to 30 kg/cm2. The bulk density can be increased. The mechanical strength of the shaped body increases ~lith ; increasir~ bulk density. ~or example, shaped bodies with a bulk density of 0.4 g/cm3 to 1.0 g/cm3 possess hiGh bending strength of 20 to 100 kg/cm3. The lightvJeight and mechanlcally strong characteristics of ~uch shaped bodies are at~ribut~ble to the fact'that t,he component \ particles of,Opsil_I and/or Ops-il_II are firmly jolned to one anoth~r and have a'large porosity. The porosity lncreases with decreasing bulk density.
These shaped bodies, i.e. Opsil-IS and Opsil-IIS, may be composed of Opsil_I and Opsil_II or may further contaln any of various fibrous reinforcin~ materials such as glass fibers~ ceramic fibers, asbesto~, rock wool, , synthetic fibers (polyamide fiber, poly~inylalchol fiber, etc.), natural fibers, pulp, stainless steel fibers, metal fibers and carbon fibers, clay, cement~ coloring agent~ filler and like additives. The shaped bodies may incorporate therein iron reinforcing rods, wire nets, fabrics, etc Because of the properties deGcribed above, Opsil-IS
and Opsil-IIS are useful as heat insulators, refractories, filter media, catalyst carriers, etc.
~ Opsils of~the present invention can be prepared from various natural or synthetic silicate crystals having - 10 the network or chain structure of SiO4 tetrahedrons. The method for preparing Opsils of the invention is not limitative and optional methods are applicable, as far as the present Opsils are obtained. According to one of the preferred methods~ Opsils are prepared from calcium silicate crystals -by contacting the crystals with carbon dioxide gas in the presence of water to convert the calcium silicate to ; amorphous sllica and extremely fine particles of calcium - carbonate~ treatlng the resulting product with an acid to ~ decompose the calcium carbonate into carbon dioxide and calcium salt and separating the amorphous ~ilica from the calcium salt.
The most distinct feature of this method is that calcium sllicate can be converted to amorphous silica without entailing a substantlal change in the configuration of the component crystals of calcium silicate. Consequently, ~.
! 9 l~Z2779 the amorphous silica thus obtained, namely opsil~ substantially retains the original configuration of calcium silicate crystals and therefore possesses the foregoing variou5 useful properties as distinct from the properties of conventional amorphous Silica.
The calcium silicate crystals usable a~ the starting cry~tals include crystals of wollastonite-type calcium silicates such as wollastonite, xonotlite, foshagite~ hillebrandite, rohsenhanite, etc., crystals of tobermorite-type calcium silicate~ such as tobermorite, crystals of gyrolite-type calcium si]icateS such as gyrolite~ truscottite, reyerite, etc.~ crystals of ~
dicalcium silicates hydrate such as calcio-condrodite, kilchoanite, afwillite~ etc., crystals of a-dicalcium fiilicate hydrate~ tricalcium silicate hydrate, CSHn, - CSH(I), CSH(II), etc.
These crystals are used as a starting material - in the form of primary particles, secondary particles or ~ a ~haped body. Since Opsils as~ume the original configuration of the crystals without any substant~al change~ the forms of the starting crystal5 are retained ln Opsils free of any substantlal change. Put in detail, primary particles of crystalline calcium silicate (having at least two surfaces in symmetric relation, a length of about 1 to about 500 ~ and a thicl~ness of about 50 A to ~ 0 - ~ZZ~79 about 1~ ~ the length being at least about 10 times the thickness) give Opsil-I in which the configuration of the - crystalline particles remain intact. Secondary pàrticles of crystalline calcium silicate, each composed of numerous primary particles of silicate randomly thrce-dimensionally interlocked together into a substantially globular form D~
about 10 to about 150~ in diarnete~l and voids interspersed therebetween, afford Opsil-II substantially retaining the same form or structure. Secondary particles of crystalline calcium silicate having a poro~ity of about 50% or more are preferably used to obtain Opsil-II
having a porosity of about 75% or more. In this case-the secondary particles of crystalline calcium silicate having a porosity of at least about 60,~ are most preferable.
Further Opsil-IS is obtained from a .haped body of calcium silicate crystals which is intergrally formed from primary particles of crystalline calcium silicate randomly three-dimensionally interlocked with one anothe-. ~, , ; ~ and has voids inter~per~ed therebetween. Op~ IS
7 ,.................... .
having a porosity of about 50% or more can be prepared from a shaped body of calcium silicate crystals having a porosity of about 40% or more, preferably at least about 50%~ Opsil-IS can also be prepared from aqueoui slurry of Opsil_I a disclosed before. In this ca~e Opsil_IS haYing various porositles can be obtained by - varying pressure applied in shaping procedures Furthermore, Opsil-IIS is prepared from a shaped body of calcium silicate crystals ~Iherein the above-mentioned ~lobular secondary particles of cry talline ~e] i 111.~
~227~
sillcate are integrally interl~cl;eù :~iih Ol!e anothe~ with voids interspersed therebetween.
The shaped body composed of the g]obular secondary particles of c~lcium silicate cryst~ls and having a porosity of - 5 about 55/~ or more, ~preferably at least about 60%, is used to obtain Opsil_ ; IIS ha~ing a porosity of about 80% or more. Opsil-- IIS can also be pre~ared from ~psil-II by dewaterin~ and shaping the aqueous slurr~ of Opsil-II with pressure and drying the shaped mass. In this case Opsil-IIS having a ~orosity of about 50~ or more is obtain~ble by varying the pressure for shaping.
- The calcium silicate crystals in the versatile forms described and useful for the production of Opsils of this invention are known and can be prepared by known methods. For example, globular secondary particles of crystalline calcium silicate can be obtained by a method de~eloped by the present applican~ and de.scribed in ; Japanese Patent Publication No. 25771/1970. According to this method, an aqueous slurry of globular secondary particles is prepared by dispersing a siliceous material and a lime material in water, along with a desired rein-forcing material or like additivè~ if desired, to obtain a starting slurry and subjecting the slurry to hydrothermal reaction ~1ith stirring to effect crystallization. The shaped body of calcium silicate crystals composed of the globular secondary particles is prepared by a further method described in the Japanese Patent Publication No. 25771/1970.
~2 l~ZZ77~
With this method, a reinforcing material or like additive is added, when desired, to the aqueous siurry of the globular secondary particles obtained as above, and the resulting - slurry is shaped with dewaterin~ and dried, ~Jhereby a shaped body of calcium silicate crystals is obtained in ~lhich the secondary particles are compressed in at le~st one direction and interlocked YJith one another into the integral body. The shaped body composed of numerou5 primary particles of crystalline calcium silicate randomly three-dimensionally interlocked together for the production of Opsil-IS can be prepared by the method disclosed in Japanese patent . Publication No. 4040/1955, Japanese Patent Publication ;; , No, 1953/1966, U.S.P. No. 2665996 and U.S.P. No. 2699097, namely by gelling a starting slurry containing a siliceous material and a lime material dispersed in water, placing the gel in a mold or shaping by de~atering, and subjecting the shaped mass to hydrothermal reaction for crystalli-zation and hardening. The primary particle3 of crystalline calcium silicate can be readily prepared also by finely ZO dividing the globular secondary particles or the shaped body of calcium silicate crystal.
Useful siliceous materials for the preparation of the calcium sllicate crystals are natural amorphous siliceous materials, siliceous sand, synthetic siliceou5 materials~ diatomaceous earth, clay, ~lag, terra alba, 1~2Z77~
fly ash, pearlite, ~vhite carbon, sllicon clust and the like which predominantly comprises SiO2. These can be used singly, or two or more of them are usable in - admixture. Examples of lime materials are quick lime, slaked lime, carbide residue, cement, etc. which predominantly - comprises CaO. These materials are al~o usable singly, or two or more of them are usable in admixture. Generally, the materials may be used in a CaO to SiO2 mole ratio approximately of 0.5-3.5:1.
When desired, the starting materials may be used conjointly ~vith glass fibers, ceramic5 fiber5, asbestos, rock wool, synthetic fibers, natural fibers, pulp, stainless steel fibers, carbon fibers or like ~ibrous reinforcing material, and coloring agent or like additive which may be added to the materials~
The amount of water to be used, which is variable over a ~de range, may generally be about 3,5 to about 30 times the total weight of the solids. The reaction is ~ preferably conducted in an autoclave at a saturation temperature under particular ~vater vapor pressure. The reaction temperature is usually higher than 100 C, preferably higher than 150 C, and the reaction pressure is the saturated vapor pressure corresponding to the temperature applied. The reaction is usually completed in about 0.5 to about 20 hours. The calcium silicate crystals are ~4 ~2Z7~79 obtained with varying degrees of crystallization depending on the CaO to SiO2 mole ratio, reaction pressure, temperature and time referred to above. The calcium silicate crystals include~ for example, xonotlite, tobermorite~ foshagite, gyrolite, a-dicalcium silicate hydrate, CSH and like - cry~tals. The xonotlite crystals, when further baked at about 1,000 C, can be converted to wollastonite crystals without resulting in any change in the shape of the crystals ~Japanese Patent Publication No. 29493/1975).
According to this invention, the calcium silicate crystals in the form of primary particles, globular secondary particles and shaped bodies are contacted with carbon dloxide in the presence of water for forced carbonation.
The carbonation is effected by contacting the calcium silicate crystals ~ith the carbon dioxide in the presence of water. Preferably, the carbonation is effected, for example~ by placin6 the calcium silicate crystals of the aforesaid form in à suitable closed container and introducing ~ carbon dioxide gas into the container at a high humidity or under wet atmosphere, or by introducing carbon dioxide gas into ~later or carbonated water in which such calcium silicate cry~tals have been imrnersed. When the calcium silicate crystals are prepared in the form o an aqueous Slurry of secondary particles~ carbon dioxide gas may of - 25 course be introduced directly into the slurry. Insofar c ~= ~ -~22~7~
as carbo~ dioxide gas is introduced into the reaction system, the carbonation will proceed satisfactorily at room temperature under atmospheric pressure. However, it is preferable to effect the carbonation at increased pressure 'of up to 10 kg/cm2 gage, whereby the reaction can be completed within a shorter time at an accelerated velocity.
The carbon dioxide is used in a stoichiometric amount or in excess. When the calcium silicate cry~tals are carbonated as immersed in water, the carbonation velocity can be increased by 6tirring the reaction fiystem. The preferable ratio of water to calcium silicate crystals is in the range of 1-50 : 1, most preferably 1-25 to 1, by weight. The velocity of carbonation varies to some extent with the degree of crystallization of the calcium 6ilicate used as the starting material. However, when carbonating xonotlite crystals the carbonation of which proceed6 at the lowest velocity~ the reaction will be completed in about 4 to 10 hours by using water in an ;~ amount of about 2 to about 6 times the dry wei~ht of the crystal6. Further when the amount of water is 5 times ; as much~ the reaction will be completed usually in about one hour at reaction pressure of 2 kg/cm2 gauge~ or in as short a period of time as about 30 minutes at reaction pressure of 3 kg/cm2 gauge.
Depending on the particular type of calcium 77~
silicate crystals used and the degree of crystallization there-of, the carbonation proceeds as represented by the following equations.
xCaO SiO mH O + CO ~ CaC03 + SiO2 nH20 wherein x is a number of 0.5 to 3.5 In the step of carbonation calcium silicate crystals are converted into composite particles of amorphous silicate and calcium carbonate without any substantial change of the con-figuration of calcium silicate crystals. The resulting calcium carbonate particles are in the form of extremely fine particles having a particle size of less than about 2~ and found to be attached to amorphous silica particles through a chemical or physical action. For example, when t~le composite primary particles of amorphous silica and calcium carbonate resulting from the carbonation are dispersed in water to a concentration of 5 wt. %, stirred for 20 minutes and thereafter allowed to stand in an attempt to separate the particles into the two components by settling utilizing the difference in specific gravity, they are in no way separable and found to be firmly joined together through a chemical or physical action.
Since the step of carbonation produces no change in the configuration of calcium silicate crystals, the primary particles, secondary particles and shaped bodies of amorphous silica-calcium carbonate composite materials can respectively be obtained by the carbonation from primary particles, secondary particles and shaped bodies of ~L2Z'77~
calcium sil~cate crystals wlthout any change in configu-rations thereof.
The composite material of amorphous silica and calcium carbonate in the form of a primary particle compriseS
an amorphous silica particle and an extremely fine particle of calcium carbonate attached to the amorphous silica particle~ the amorphous silica particle having a crystalline appearance, at ~east two surfaces in symmetric relation, a length of about 1 to about 500~ and a thickness of about 50 A to about 1~ ~ the length being at least about 10 times the thickness. The composite meterial of amorphous silica and calcium carbonate in the form of a substantially globular secondary particle has a diameter of about 10 to about 150 ~ and ls composed of numerous amorphous silica-calcium carbonate composite primary particles and voids inter6per~ed therebetween, each of the conStituènt composite particles comprlsing an - amorphous silica particle in the form of a primary ;~ particle ~hd an extremely fine particle of calcium carbonate attached to the amorphous silica particle, the amorphous silica particle having a crystalline appearance, at least two surfaces in symmetric relation, a length of about 1 to about 500 ~ and a thickness of about 50 A to about 1~ ~ the length being at least about 10 times the thickness.
The composite materials of amorphous silica and calcium carbonate in the form of shaped body include a shaped '8 '~
1~%Z~
body composed of numerous composite primary particles and one composed of numerous composite secondary particles.
The former shaped body comprises amorphous silica-calcium carbonate composite primary partlcle~ randomly three-dimensionally interlocked with one another integrally into the bodyjwith voids inter.sper6ed therebetween, . each of the primary particles comprising an amorphous silica partilce in the form of a primary particle and ah extremely fine particle of calcium carbonate attached to the amorphous silica particle, the amorphous silica particle having a crystalline appearance, at least two surfaces in Syn~netric relation, a length of about 1 to about 500~ and a thickness of about 50 A to about 1~ , the length being at least about lO times the thlckness.
The latter shaped body comprises numerous amorphous 6ilica-calcium carbonate composite secondary particles be~ng compressed to at least one direction and lnter-rocked with one another and voids interspersed therebetween, each of the composite ~econdary part~cle6 having originally a substantially glob~lar form of a diameter of about lO to about 150 ~ and comprising an amorphous 6ilica particle in the form of a primary particle and extremely fine part~cle.of ca~cium carbonate attached to the arnorphous silica particle, the amorphous silica particle having a crystalline appearance, at least two surfaces in symmetric relation~ a length of about l to about 500~ and a thickness of about 50 A to about l~
~ZZ779 the length being at least about 10 times the thicknesS.
The composite material~ composed of the amorphous silica and ex~remely fine particle~ of calcium carbonate chemically or physically attached thereto find versatile applications for which Opsils are useful, because of their characteristics attributable to the Opsil contained therein.
Further 6ince the extremely fine particles of calcium carbonate are contained in the composite particles as attached to the Opsil, the composite particles are useful also as a filler. Moreover, the composite materials are useful as intermediate products for producing Opsil in various forms.
According to thls invention, the composite material of amorphous silica and calcium carbonate resulting from carbonation is thereafter treated with an acid to remove the calcium carbonate from the amorphous silica. The aclds to be used for this purpose include those having no reactivity with silica but being capab?e of decomposing ~ calcium carbonate to produce carbon dioxide and a water-soluble 6alt. Examples thereof are hydrochlorlc acid, - nitric acid, acetic acid, perchloric acid or the like.
The acid treat~ent i~ carried out usually by immersing the composite material in a solution of the acid, or by introducing an acid gas such as hydrochloric acid gas into water in which the composite particles are immersed c l~Z~79 or dispersed. The acid is used in a stoichiometric amount or in excess. ~his treatment is preferably conducted at room temperatures9 though elevated temperatures up to boiling points of the acid used are applicable. The reaction pressure is usually atmospher1c pressure, but increased pressure is also applicable. Through the treatment, the calcium carbo~ate attached to the amorphous silica is decomposed with the acid to a water-soluble calcium salt, which ls thereafter completely removed for example by washing with water, followed by drying, whereby primary particles, secondary particles or shaped body made up of amorphous silica are prepared. In the case of preparing shaped body, it can be treated with warm or hot water before drying, whereby linear shrinkage thereof due to drying can be lowered~ The treatment can preferably be conducted by immersing the shaped body in hot water of higher than 60 C for 0.5 to 10 hours. When hot water of higher than 100 C is used, autoclave or the like closed vessel may be $~ employed. The step of removing calcium carbonate produces no change in the configuration of the primary particles of amorphous silica. Accordir~gly, composite globular secondary particles of the composite material give globular secondary particles of amorphous silica, i.e. Opsil-II, retaining the original structure of the former, while shaped bodies of the composite material give shaped bodies c ~~
'l~ZZ7~
of amorphous silica, i.e. Opsil-IS and Opsil-IIS, similarly retaining the original structure thereof. Further, the composite materlals of amorphous silica and calcium carbonate ln the form of primary particles and globular secondary particles have shapability similar to Opsil-I and Opsil-II.
More specificallyJ the composite particles ~re eas~ly dispersible in water and give shaped body having mechanical strength~ when the slurry is shaped and dried. Therefore, Opsil-IS and Opsil-IIS can be prepared by shaping and drying the aqueous slurry of the composite particles to prepare shaped body thereof and subjecting the shaped body to the acid treatment as above, followed by washing wlth water and drying.
For a better understanding of this invention, Reference Examples and Examples of the invention are gi~en below.
~he accompanylng drawings show x-ray diffraction patterns, electron micrographs~ scanning electron micrographs and a pore ~iZe di~tribution diagram of the substances prepared in Examples and Reference Examples.
Figs. l(A) to (C) show x-ray diffraction patterns of a starting material, i.e. xonotlite crystals, composite partiCles of amorphous silica and calcium carbonate prepared from the crystals by carbonation, and Opsil-I of this invention respecti~ely;
1~L2;~79 Figs. 2 and 3 are electron micrographs at a magnification of 20,000X, in which Figs. (A) show calciurn silicate crystals used as starting materials, Figs. (B) show composite materials of amorphous silica and calcium carbonate prepared by carbonating the crystals, and Figs. (C) show ~the particles of Opsils-I obtained by treating the materials;
Figs. 4 are electron micrographs at a magnification of 5,000X in which Fig. (A) shows ~-dicalcium silicate hydrate crystals used as a starting material, and Fig. (B) shows Opsil-I prepared from the crystals;
Figs. 5 and 6 are scanning electron microyraphs, in which Figs. (A) shuw globu]ar secondary particles composed of calcium silicate crystals used as starting materials, Figs. (B) show globular secondary particles composed of composite materials of amorphous silica and calcium carbonate prepared by carbonating the crystals, and Figs. (C) show Opsil-II of this invention;
Figs. 7 are scanning electron micrographs of fractured surfaces of shaped bodies at a magnification of 20 ~ 600X, in which~(A) shows a shaped body of globular secondary particles of calcium silicate crystals used as starting materials, (B) shows a shaped body of globular secondary part-icles of composite material of amorphous silica and calcium carbonate and (C) shows a shaped body of Opsil-IIS.
Fig. 8 is a scanning electron microyraph at a magnification of 1,000X showing Opsil-IS of this invention;
and ~zz~
Fig. 9 is a pore size distribution diagram in which the pore size (2) is plotted as abscissa and the pore volume (cc~.g x 103) as ordinate.
The x-ray diffraction patterns in Figs. 1 are pre-pared using an x-ray diffractometer, irradiating the sample with x-rays of wavelength of 1.5405 ~ emitted with a Cu target and measuring the diffraction angle and intensity. Three diffraction lines having the highest intensities are determined for the identification of the samples.
~ , 2 7~79 Reference Example 1 Quick lime is used as a lime material and minus 350 mesh siliceous sand powder ~Tyler scale) as a siliceous material.
The materials are dispersed in water in a CaO to SiO2 mole ratio of 0.98:1 to prepare a slurry having a water to solids ratio by weight of 12:1. The slurry is placed in an autoclave and subjected to hydrothermal reaction at a temperature of 191C and a saturated vapor pressure of 12 kg/cm with heating and stir-ring for 8 hours to obtain a slurry of xonotlite crystals.
The x-ray diffraction pattern of the xonotlite crystals in Fig. 1 ~A) shows diffraction peaks ~23) at 12.7, 27.6 and 29.0 peculiar to xonotlite crystals. The analysis by ignition of the crystals reveals the following composition.
SiO2 48.88%
15 CzO 45.60 A' O 0.26 Fe2 3 Ig. loss 4.51 Total 99.80 The slurry of xonotlite crystals is shown i? the scanning electron micrograph of Fig. 5~A), which revea's that numerous lath-like xonotlite crystals are formed as randomly three-dimensionally interlocked with one another into many, substantially globular, secondary particles of xonotlite ranging from about 10 to about 60~ in diameter and suspended .. 1~2Z~779 in water. The ~econdary particle ha~ a porosity of about 95.6%.
Sub~equently, the slurry containing the globular secondary particle6 of xonotlite i6 dried at 150 C and then divided into primary particle~.
Fig. 2(A) shows an electron micrograph of the primary particles. The micrograph indicates that the primary particles have at least two surface~ in symmetric relation, a length of about 1 to about 20 ~ , a thickne~s of about 0.02 to about 0.1 and a width of about 0.02 to about l.O ~ , the length being at least about lO times the thickness. The primary particle~ have a 6pecific surface area of about 50 m2/g.
The slurry of xonotlite crystals prepared above is placed in a mold, 40 mm x 120 mm x 150 mm, and deY~atered and ~haped by a pre~s and dried to obtain a shaped body. Fig. 7(A) is a ~canning electron micrograph ~howing a fractured surface of the 6haped body of xonotlite. ~he micrograph indicate~
that globular secondary particles of xonotlite are compressed and formed a~ interlocked with one another; The shaped body has a bulk density of 0.2 g~cm3, bending 6trength of abou~
(Literature: Encyclopedia of Cnemical Technology 18, (1969) p 61-67) 1~ .
llZZ~77~
The characteristic values in Table 2 are determined by the following methods.
Bulk density: A 10 g quantity of particles are placed in a cylinder 5 cm2 in cross sectional area and subjected to a load of 250 g by a 50 g/cm2 capacity piston-- cylinder device. The volume of the coMpressed mass is then measured. Bulk den~ity is given by Bulk density - 10 (~
Volume (cm ) True specific gravity: l~e~sured by air compariSsn pycnometer Model 930, Bec~nann Co., with air replaced by He gas.
Average pore diameter: By BET nitrogen adsorption method.
Specific surface area; Same as above.
; Pore volume: Same as above.
Particle size: Determined under optical and electron microscopes.
Oil adsorption: Dioctyl phthalate (C6H4(COOC8H17)2) is \ added dropwise to 100 g of particles to cause the particles to adsorb the phthalate, and the amount of the phthalate is measured when the mass of the particels starts to become markedly viscous.
Hygroscopicity: Particles are placed in a container at R.H. 100% and maintained at 25 C, allowing the partlcles to adsorb moisture until an equilibrium i5 established.
77~
Hygro6coplcity i~ expressed in terms of the weight by % of the moisture adsorbed based on the particles.
~ The values listed are obtained using Opsil_I having a bulk density of 0.1 g/cm3, and silica gels with a bulk density of 0.7 g/cm3 for RD type, a bulk den~ity of 0.4 g/cm3 for ID type and a bulk density of 0.15 g/cm3 for LD type.
Table 2 s~ows that Opsil-I has a small average pore diameter and a large specific .urface area despite its Small bulk density, does not collapse when immersed in water because of its good resistance to water and is highly oil-adsorbent, remarkably hygroscopic and extremely low in thermal conductivity. Further, Opsil has an approximately neutral pH of 6 to 7 and high resistance to chemicals and will not be decomposed with hydrochloric acid and like acid~, These properties are very advantageous over the propertie5 of calcium silicate crystals from which they are derived; the crystals have a high pH of 10 to ll~ are decomposable with an acid such as hydro-chloric acid and therefore find limited uses~
Moreover, Opsil_I is easily dispersible in water to form an aqueous ~lurry thereof and has a peculiar shapability that the slurry gives, when shaped and dried, a light weight shaped body composed of Opsil-I randomly three-z5 dimensionally ~nterlocked with one another integrally into ...
~ 2 1~277~
the body and having a high mechanical strength The aqueous slurry to be shaped may preferably have a water to solid ratio of 4 - 50 : 1 by weight. When desired, the slurry may in-corporate therein a fibrous reinforcing material such as as-bestos, glass fibers, rock wool, synthetic fibers, naturalfibers, pulp, carbon fibers, stainless steel fibers, alumina sol, colloidal silica sol, clay, cement, coloring agent, filler and various other additives. The shaped body is usable variously for example as a heat insulating material, filtration medium, catalyst carrier, etc.
Because of the unique particulate shape and proper-ties described above, Opsil-I is serviceable as a substitute for silica gel in uses for which s lica gel is usually employed and is also serviceable in other uses to which silica gel is not applicable. For example, Opsil-I is useful as a filler, drying agent, adsorbent, deodorant, filter medium, heat-resist-ant filter, additive for adhesives, heat-resistant agent, delustering agent for paper making, emulsifier for cosmetics, abrasion-resistant agent, heat insulator, viscosity imparting agent, pigment, tooth powder, carrier for agricultural chem-icals, carrier for pharmaceuticals, catalyst, catalyst carrier, material for heat-resistant glass, absorbent for gas chroma-tography, excipient, anticaking agent, fixing agent for volatile , 7~9 substances, molecular sieve, shaped body, etc.
Opsil-II is in the form of substantially globular secondary particles of the amorphous silica of this invention.
Each of the secondary particles is composed of numerous pri-mary particles of amorphous silica randomly three-dimensionally interlocked with one another and voids interspersed therebetween and has a diameter of about 10 to about 150~l, preferably about 10 to about 80~, the primary particle having a crystalline appearance, at least two surfaces in symmetric relation, a length of about 1 to about 500~, preferably about 1 to about 300~, and a thickness of about 50 to about 1~, preferably about 100 to about 1~, the length being at least about 10 times, preferably about 10 to about 5,000 times, the thickness. Opsil-II usually has the porosity of at least about 75% preferably about 80 to about 98%.
Since Opsil-II is composed of Opsil-I described above, it has the foregoing properties of Opsil-I and finds the same uses as Opsil-I.
Moreover, Opsil-II is readily dispersible in water to form an aqueous slurry and has the peculiar shapability that the slurry gives a light-weight shaped body having high mechanical strength, when shaped and dried. Generally, the shaped body obtained from Opsil-II has higher mechanical strength than that obtained from Opsil-I having the same bulk density therewith. More specifically, when the aqueous slurry of ~2~779 Ops~ I is subjected to pressure for shaping~ the particles are cornpressed in the direction of pressure applied in the ihapingstep Namely, the particles of Opsil-II in the present shaped body are compressed more or less in at least one direction due to the pressure applied in the shaping step.
The compre&sed particles are interlocked with one another and shaped to an integral body in this state when dried.
The bulk density of the shaped body, v~hich i5 controllable as desired by altering the shaping pressure, can vary over a wide range. Preferably, the bulk density is in the range of about 0.1 g/cm3 to about 1.0 g/cm3. The shaped body is usable variously for example as a heat insulating material~ filtration medium, catalyst carrier, etc.
Generally~ the aqueous slurry of Opsil-II to be shaped may preferably have a water to solids ratio of 8 - 50 : 1 by weight. When desired, the aqueou; slurry may incorporate therein a fibrous reinforcing mate~~ial such as asbestos, ~lass fibers, rock wool~ synthetic fibers, ~ natural fibers, pulp, carbon fibers or stainless steel fibers, alumina sol,colloidal silica sol, clay, cement, coloring agent, filler and various other additives.
These additives afford useful properties to the shaped body.
Table 3 glves the propertie~; of Opsil-II.
c`
~2Z~'79 ~able 3 Bulk den~ity (g/cm3) 0.03~0.5 Specific surface area (m2/g) 250-600 Specific surface area (m2/~) after heating at 400 C 200-550 Porosity (%) prefer~bly at least 75 Oil adsorption (cc/100 g) 5U0-1200 pH 6-7 Heat resistance Secondary particlesO
retain shape at 950 C
The properties listed above are determined by the same methods as in Table 2, ~Iherein the porosity is given by Apparent specific gravity of Opsil -II
True specific gravity of Opsil-II
- 5 . The heat resistance i5 determined with the unaided eyeS -This invention further provides novel sh~ped bodies of amorphous silica which include a ~haped body composed of Opsil-I (hereinafter referred to as "Opsil-IS") and a shaped body composed of Opsil-II (hereinafter referred to as "Opsil-IIS"). Opsil-IS i5 a ;h~ped body WhiCh i6 integrally formed from the particles of Opsil-I
randomly three-dimensionally interlocked with one another.
,6 ~`
~z~
That is to say, Opsil-IS compri~e~ primary particle.5 of amorphous silica randomly three-dimen ionally i.nterlocked with one another integrally inlo ihe bou~
and voids interspersed therebetween, each of the ;5 primary particles having a crystalline appearance~ at least two surfaces in symmetric relation, a length of about 1 to about ~00~ , preferably about 1 to about 30~ , and a thickness of about ~50 ~ to about 1~1, preferably about 100 ~ to about 1~ , the length being at least about lO tiMes, preferably about 10 to about ~,000 times, the thickness~
~he shaped body usuall~ h~s a Porosit~ of ~t le~st about 50%, ~refer~bly ~b~ut ~ to abollt 95 opsil-IIs is a ~haped body in ~hich the particle~
of Opsil-II are interlocked with one another into the integral . 15 body. Namely, Opsil-IIS comprises secondary particles of amorphous silica compressed in at least one direction and interlocked with one another integrally into the body and voids inters~ersed therebetweenl the secondar~ ~article : '~ being composed of numerous primary particles of amorphous 6ilica randomly three-dimensionally interlocked with one another, each of the primary particles having a crystalline . - 17 -~.
~' I
- ~227~9 appearance~ at least two surfaceS insymmetric rela'cion~ !
a length of about 1 to 500 ~ , prefelably about 1 to about 300~ , and a thickness of about 50 ~ to about 1~ , preferably about 100 R to about 1~ , the length being at least 10 times, preferably about lO to about 5,000 times, the thickness. O~sil-IIS ususll~ h~s a poresit~ of at least _ . . . .
- about 50~, preferably about 60/~ to ~bout 97/n.
-- . . .
Both OpsiI-IS and Opsil-IIS have a large porosity, are lightweight and have high mechanical strength. More specifically, they have a low bulk density of about 0.1 to about 0.4 g/cm3 and high bending strength of,about 3 to 30 kg/cm2. The bulk density can be increased. The mechanical strength of the shaped body increases ~lith ; increasir~ bulk density. ~or example, shaped bodies with a bulk density of 0.4 g/cm3 to 1.0 g/cm3 possess hiGh bending strength of 20 to 100 kg/cm3. The lightvJeight and mechanlcally strong characteristics of ~uch shaped bodies are at~ribut~ble to the fact'that t,he component \ particles of,Opsil_I and/or Ops-il_II are firmly jolned to one anoth~r and have a'large porosity. The porosity lncreases with decreasing bulk density.
These shaped bodies, i.e. Opsil-IS and Opsil-IIS, may be composed of Opsil_I and Opsil_II or may further contaln any of various fibrous reinforcin~ materials such as glass fibers~ ceramic fibers, asbesto~, rock wool, , synthetic fibers (polyamide fiber, poly~inylalchol fiber, etc.), natural fibers, pulp, stainless steel fibers, metal fibers and carbon fibers, clay, cement~ coloring agent~ filler and like additives. The shaped bodies may incorporate therein iron reinforcing rods, wire nets, fabrics, etc Because of the properties deGcribed above, Opsil-IS
and Opsil-IIS are useful as heat insulators, refractories, filter media, catalyst carriers, etc.
~ Opsils of~the present invention can be prepared from various natural or synthetic silicate crystals having - 10 the network or chain structure of SiO4 tetrahedrons. The method for preparing Opsils of the invention is not limitative and optional methods are applicable, as far as the present Opsils are obtained. According to one of the preferred methods~ Opsils are prepared from calcium silicate crystals -by contacting the crystals with carbon dioxide gas in the presence of water to convert the calcium silicate to ; amorphous sllica and extremely fine particles of calcium - carbonate~ treatlng the resulting product with an acid to ~ decompose the calcium carbonate into carbon dioxide and calcium salt and separating the amorphous ~ilica from the calcium salt.
The most distinct feature of this method is that calcium sllicate can be converted to amorphous silica without entailing a substantlal change in the configuration of the component crystals of calcium silicate. Consequently, ~.
! 9 l~Z2779 the amorphous silica thus obtained, namely opsil~ substantially retains the original configuration of calcium silicate crystals and therefore possesses the foregoing variou5 useful properties as distinct from the properties of conventional amorphous Silica.
The calcium silicate crystals usable a~ the starting cry~tals include crystals of wollastonite-type calcium silicates such as wollastonite, xonotlite, foshagite~ hillebrandite, rohsenhanite, etc., crystals of tobermorite-type calcium silicate~ such as tobermorite, crystals of gyrolite-type calcium si]icateS such as gyrolite~ truscottite, reyerite, etc.~ crystals of ~
dicalcium silicates hydrate such as calcio-condrodite, kilchoanite, afwillite~ etc., crystals of a-dicalcium fiilicate hydrate~ tricalcium silicate hydrate, CSHn, - CSH(I), CSH(II), etc.
These crystals are used as a starting material - in the form of primary particles, secondary particles or ~ a ~haped body. Since Opsils as~ume the original configuration of the crystals without any substant~al change~ the forms of the starting crystal5 are retained ln Opsils free of any substantlal change. Put in detail, primary particles of crystalline calcium silicate (having at least two surfaces in symmetric relation, a length of about 1 to about 500 ~ and a thicl~ness of about 50 A to ~ 0 - ~ZZ~79 about 1~ ~ the length being at least about 10 times the thickness) give Opsil-I in which the configuration of the - crystalline particles remain intact. Secondary pàrticles of crystalline calcium silicate, each composed of numerous primary particles of silicate randomly thrce-dimensionally interlocked together into a substantially globular form D~
about 10 to about 150~ in diarnete~l and voids interspersed therebetween, afford Opsil-II substantially retaining the same form or structure. Secondary particles of crystalline calcium silicate having a poro~ity of about 50% or more are preferably used to obtain Opsil-II
having a porosity of about 75% or more. In this case-the secondary particles of crystalline calcium silicate having a porosity of at least about 60,~ are most preferable.
Further Opsil-IS is obtained from a .haped body of calcium silicate crystals which is intergrally formed from primary particles of crystalline calcium silicate randomly three-dimensionally interlocked with one anothe-. ~, , ; ~ and has voids inter~per~ed therebetween. Op~ IS
7 ,.................... .
having a porosity of about 50% or more can be prepared from a shaped body of calcium silicate crystals having a porosity of about 40% or more, preferably at least about 50%~ Opsil-IS can also be prepared from aqueoui slurry of Opsil_I a disclosed before. In this ca~e Opsil_IS haYing various porositles can be obtained by - varying pressure applied in shaping procedures Furthermore, Opsil-IIS is prepared from a shaped body of calcium silicate crystals ~Iherein the above-mentioned ~lobular secondary particles of cry talline ~e] i 111.~
~227~
sillcate are integrally interl~cl;eù :~iih Ol!e anothe~ with voids interspersed therebetween.
The shaped body composed of the g]obular secondary particles of c~lcium silicate cryst~ls and having a porosity of - 5 about 55/~ or more, ~preferably at least about 60%, is used to obtain Opsil_ ; IIS ha~ing a porosity of about 80% or more. Opsil-- IIS can also be pre~ared from ~psil-II by dewaterin~ and shaping the aqueous slurr~ of Opsil-II with pressure and drying the shaped mass. In this case Opsil-IIS having a ~orosity of about 50~ or more is obtain~ble by varying the pressure for shaping.
- The calcium silicate crystals in the versatile forms described and useful for the production of Opsils of this invention are known and can be prepared by known methods. For example, globular secondary particles of crystalline calcium silicate can be obtained by a method de~eloped by the present applican~ and de.scribed in ; Japanese Patent Publication No. 25771/1970. According to this method, an aqueous slurry of globular secondary particles is prepared by dispersing a siliceous material and a lime material in water, along with a desired rein-forcing material or like additivè~ if desired, to obtain a starting slurry and subjecting the slurry to hydrothermal reaction ~1ith stirring to effect crystallization. The shaped body of calcium silicate crystals composed of the globular secondary particles is prepared by a further method described in the Japanese Patent Publication No. 25771/1970.
~2 l~ZZ77~
With this method, a reinforcing material or like additive is added, when desired, to the aqueous siurry of the globular secondary particles obtained as above, and the resulting - slurry is shaped with dewaterin~ and dried, ~Jhereby a shaped body of calcium silicate crystals is obtained in ~lhich the secondary particles are compressed in at le~st one direction and interlocked YJith one another into the integral body. The shaped body composed of numerou5 primary particles of crystalline calcium silicate randomly three-dimensionally interlocked together for the production of Opsil-IS can be prepared by the method disclosed in Japanese patent . Publication No. 4040/1955, Japanese Patent Publication ;; , No, 1953/1966, U.S.P. No. 2665996 and U.S.P. No. 2699097, namely by gelling a starting slurry containing a siliceous material and a lime material dispersed in water, placing the gel in a mold or shaping by de~atering, and subjecting the shaped mass to hydrothermal reaction for crystalli-zation and hardening. The primary particle3 of crystalline calcium silicate can be readily prepared also by finely ZO dividing the globular secondary particles or the shaped body of calcium silicate crystal.
Useful siliceous materials for the preparation of the calcium sllicate crystals are natural amorphous siliceous materials, siliceous sand, synthetic siliceou5 materials~ diatomaceous earth, clay, ~lag, terra alba, 1~2Z77~
fly ash, pearlite, ~vhite carbon, sllicon clust and the like which predominantly comprises SiO2. These can be used singly, or two or more of them are usable in - admixture. Examples of lime materials are quick lime, slaked lime, carbide residue, cement, etc. which predominantly - comprises CaO. These materials are al~o usable singly, or two or more of them are usable in admixture. Generally, the materials may be used in a CaO to SiO2 mole ratio approximately of 0.5-3.5:1.
When desired, the starting materials may be used conjointly ~vith glass fibers, ceramic5 fiber5, asbestos, rock wool, synthetic fibers, natural fibers, pulp, stainless steel fibers, carbon fibers or like ~ibrous reinforcing material, and coloring agent or like additive which may be added to the materials~
The amount of water to be used, which is variable over a ~de range, may generally be about 3,5 to about 30 times the total weight of the solids. The reaction is ~ preferably conducted in an autoclave at a saturation temperature under particular ~vater vapor pressure. The reaction temperature is usually higher than 100 C, preferably higher than 150 C, and the reaction pressure is the saturated vapor pressure corresponding to the temperature applied. The reaction is usually completed in about 0.5 to about 20 hours. The calcium silicate crystals are ~4 ~2Z7~79 obtained with varying degrees of crystallization depending on the CaO to SiO2 mole ratio, reaction pressure, temperature and time referred to above. The calcium silicate crystals include~ for example, xonotlite, tobermorite~ foshagite, gyrolite, a-dicalcium silicate hydrate, CSH and like - cry~tals. The xonotlite crystals, when further baked at about 1,000 C, can be converted to wollastonite crystals without resulting in any change in the shape of the crystals ~Japanese Patent Publication No. 29493/1975).
According to this invention, the calcium silicate crystals in the form of primary particles, globular secondary particles and shaped bodies are contacted with carbon dloxide in the presence of water for forced carbonation.
The carbonation is effected by contacting the calcium silicate crystals ~ith the carbon dioxide in the presence of water. Preferably, the carbonation is effected, for example~ by placin6 the calcium silicate crystals of the aforesaid form in à suitable closed container and introducing ~ carbon dioxide gas into the container at a high humidity or under wet atmosphere, or by introducing carbon dioxide gas into ~later or carbonated water in which such calcium silicate cry~tals have been imrnersed. When the calcium silicate crystals are prepared in the form o an aqueous Slurry of secondary particles~ carbon dioxide gas may of - 25 course be introduced directly into the slurry. Insofar c ~= ~ -~22~7~
as carbo~ dioxide gas is introduced into the reaction system, the carbonation will proceed satisfactorily at room temperature under atmospheric pressure. However, it is preferable to effect the carbonation at increased pressure 'of up to 10 kg/cm2 gage, whereby the reaction can be completed within a shorter time at an accelerated velocity.
The carbon dioxide is used in a stoichiometric amount or in excess. When the calcium silicate cry~tals are carbonated as immersed in water, the carbonation velocity can be increased by 6tirring the reaction fiystem. The preferable ratio of water to calcium silicate crystals is in the range of 1-50 : 1, most preferably 1-25 to 1, by weight. The velocity of carbonation varies to some extent with the degree of crystallization of the calcium 6ilicate used as the starting material. However, when carbonating xonotlite crystals the carbonation of which proceed6 at the lowest velocity~ the reaction will be completed in about 4 to 10 hours by using water in an ;~ amount of about 2 to about 6 times the dry wei~ht of the crystal6. Further when the amount of water is 5 times ; as much~ the reaction will be completed usually in about one hour at reaction pressure of 2 kg/cm2 gauge~ or in as short a period of time as about 30 minutes at reaction pressure of 3 kg/cm2 gauge.
Depending on the particular type of calcium 77~
silicate crystals used and the degree of crystallization there-of, the carbonation proceeds as represented by the following equations.
xCaO SiO mH O + CO ~ CaC03 + SiO2 nH20 wherein x is a number of 0.5 to 3.5 In the step of carbonation calcium silicate crystals are converted into composite particles of amorphous silicate and calcium carbonate without any substantial change of the con-figuration of calcium silicate crystals. The resulting calcium carbonate particles are in the form of extremely fine particles having a particle size of less than about 2~ and found to be attached to amorphous silica particles through a chemical or physical action. For example, when t~le composite primary particles of amorphous silica and calcium carbonate resulting from the carbonation are dispersed in water to a concentration of 5 wt. %, stirred for 20 minutes and thereafter allowed to stand in an attempt to separate the particles into the two components by settling utilizing the difference in specific gravity, they are in no way separable and found to be firmly joined together through a chemical or physical action.
Since the step of carbonation produces no change in the configuration of calcium silicate crystals, the primary particles, secondary particles and shaped bodies of amorphous silica-calcium carbonate composite materials can respectively be obtained by the carbonation from primary particles, secondary particles and shaped bodies of ~L2Z'77~
calcium sil~cate crystals wlthout any change in configu-rations thereof.
The composite material of amorphous silica and calcium carbonate in the form of a primary particle compriseS
an amorphous silica particle and an extremely fine particle of calcium carbonate attached to the amorphous silica particle~ the amorphous silica particle having a crystalline appearance, at ~east two surfaces in symmetric relation, a length of about 1 to about 500~ and a thickness of about 50 A to about 1~ ~ the length being at least about 10 times the thickness. The composite meterial of amorphous silica and calcium carbonate in the form of a substantially globular secondary particle has a diameter of about 10 to about 150 ~ and ls composed of numerous amorphous silica-calcium carbonate composite primary particles and voids inter6per~ed therebetween, each of the conStituènt composite particles comprlsing an - amorphous silica particle in the form of a primary ;~ particle ~hd an extremely fine particle of calcium carbonate attached to the amorphous silica particle, the amorphous silica particle having a crystalline appearance, at least two surfaces in symmetric relation, a length of about 1 to about 500 ~ and a thickness of about 50 A to about 1~ ~ the length being at least about 10 times the thickness.
The composite materials of amorphous silica and calcium carbonate in the form of shaped body include a shaped '8 '~
1~%Z~
body composed of numerous composite primary particles and one composed of numerous composite secondary particles.
The former shaped body comprises amorphous silica-calcium carbonate composite primary partlcle~ randomly three-dimensionally interlocked with one another integrally into the bodyjwith voids inter.sper6ed therebetween, . each of the primary particles comprising an amorphous silica partilce in the form of a primary particle and ah extremely fine particle of calcium carbonate attached to the amorphous silica particle, the amorphous silica particle having a crystalline appearance, at least two surfaces in Syn~netric relation, a length of about 1 to about 500~ and a thickness of about 50 A to about 1~ , the length being at least about lO times the thlckness.
The latter shaped body comprises numerous amorphous 6ilica-calcium carbonate composite secondary particles be~ng compressed to at least one direction and lnter-rocked with one another and voids interspersed therebetween, each of the composite ~econdary part~cle6 having originally a substantially glob~lar form of a diameter of about lO to about 150 ~ and comprising an amorphous 6ilica particle in the form of a primary particle and extremely fine part~cle.of ca~cium carbonate attached to the arnorphous silica particle, the amorphous silica particle having a crystalline appearance, at least two surfaces in symmetric relation~ a length of about l to about 500~ and a thickness of about 50 A to about l~
~ZZ779 the length being at least about 10 times the thicknesS.
The composite material~ composed of the amorphous silica and ex~remely fine particle~ of calcium carbonate chemically or physically attached thereto find versatile applications for which Opsils are useful, because of their characteristics attributable to the Opsil contained therein.
Further 6ince the extremely fine particles of calcium carbonate are contained in the composite particles as attached to the Opsil, the composite particles are useful also as a filler. Moreover, the composite materials are useful as intermediate products for producing Opsil in various forms.
According to thls invention, the composite material of amorphous silica and calcium carbonate resulting from carbonation is thereafter treated with an acid to remove the calcium carbonate from the amorphous silica. The aclds to be used for this purpose include those having no reactivity with silica but being capab?e of decomposing ~ calcium carbonate to produce carbon dioxide and a water-soluble 6alt. Examples thereof are hydrochlorlc acid, - nitric acid, acetic acid, perchloric acid or the like.
The acid treat~ent i~ carried out usually by immersing the composite material in a solution of the acid, or by introducing an acid gas such as hydrochloric acid gas into water in which the composite particles are immersed c l~Z~79 or dispersed. The acid is used in a stoichiometric amount or in excess. ~his treatment is preferably conducted at room temperatures9 though elevated temperatures up to boiling points of the acid used are applicable. The reaction pressure is usually atmospher1c pressure, but increased pressure is also applicable. Through the treatment, the calcium carbo~ate attached to the amorphous silica is decomposed with the acid to a water-soluble calcium salt, which ls thereafter completely removed for example by washing with water, followed by drying, whereby primary particles, secondary particles or shaped body made up of amorphous silica are prepared. In the case of preparing shaped body, it can be treated with warm or hot water before drying, whereby linear shrinkage thereof due to drying can be lowered~ The treatment can preferably be conducted by immersing the shaped body in hot water of higher than 60 C for 0.5 to 10 hours. When hot water of higher than 100 C is used, autoclave or the like closed vessel may be $~ employed. The step of removing calcium carbonate produces no change in the configuration of the primary particles of amorphous silica. Accordir~gly, composite globular secondary particles of the composite material give globular secondary particles of amorphous silica, i.e. Opsil-II, retaining the original structure of the former, while shaped bodies of the composite material give shaped bodies c ~~
'l~ZZ7~
of amorphous silica, i.e. Opsil-IS and Opsil-IIS, similarly retaining the original structure thereof. Further, the composite materlals of amorphous silica and calcium carbonate ln the form of primary particles and globular secondary particles have shapability similar to Opsil-I and Opsil-II.
More specificallyJ the composite particles ~re eas~ly dispersible in water and give shaped body having mechanical strength~ when the slurry is shaped and dried. Therefore, Opsil-IS and Opsil-IIS can be prepared by shaping and drying the aqueous slurry of the composite particles to prepare shaped body thereof and subjecting the shaped body to the acid treatment as above, followed by washing wlth water and drying.
For a better understanding of this invention, Reference Examples and Examples of the invention are gi~en below.
~he accompanylng drawings show x-ray diffraction patterns, electron micrographs~ scanning electron micrographs and a pore ~iZe di~tribution diagram of the substances prepared in Examples and Reference Examples.
Figs. l(A) to (C) show x-ray diffraction patterns of a starting material, i.e. xonotlite crystals, composite partiCles of amorphous silica and calcium carbonate prepared from the crystals by carbonation, and Opsil-I of this invention respecti~ely;
1~L2;~79 Figs. 2 and 3 are electron micrographs at a magnification of 20,000X, in which Figs. (A) show calciurn silicate crystals used as starting materials, Figs. (B) show composite materials of amorphous silica and calcium carbonate prepared by carbonating the crystals, and Figs. (C) show ~the particles of Opsils-I obtained by treating the materials;
Figs. 4 are electron micrographs at a magnification of 5,000X in which Fig. (A) shows ~-dicalcium silicate hydrate crystals used as a starting material, and Fig. (B) shows Opsil-I prepared from the crystals;
Figs. 5 and 6 are scanning electron microyraphs, in which Figs. (A) shuw globu]ar secondary particles composed of calcium silicate crystals used as starting materials, Figs. (B) show globular secondary particles composed of composite materials of amorphous silica and calcium carbonate prepared by carbonating the crystals, and Figs. (C) show Opsil-II of this invention;
Figs. 7 are scanning electron micrographs of fractured surfaces of shaped bodies at a magnification of 20 ~ 600X, in which~(A) shows a shaped body of globular secondary particles of calcium silicate crystals used as starting materials, (B) shows a shaped body of globular secondary part-icles of composite material of amorphous silica and calcium carbonate and (C) shows a shaped body of Opsil-IIS.
Fig. 8 is a scanning electron microyraph at a magnification of 1,000X showing Opsil-IS of this invention;
and ~zz~
Fig. 9 is a pore size distribution diagram in which the pore size (2) is plotted as abscissa and the pore volume (cc~.g x 103) as ordinate.
The x-ray diffraction patterns in Figs. 1 are pre-pared using an x-ray diffractometer, irradiating the sample with x-rays of wavelength of 1.5405 ~ emitted with a Cu target and measuring the diffraction angle and intensity. Three diffraction lines having the highest intensities are determined for the identification of the samples.
~ , 2 7~79 Reference Example 1 Quick lime is used as a lime material and minus 350 mesh siliceous sand powder ~Tyler scale) as a siliceous material.
The materials are dispersed in water in a CaO to SiO2 mole ratio of 0.98:1 to prepare a slurry having a water to solids ratio by weight of 12:1. The slurry is placed in an autoclave and subjected to hydrothermal reaction at a temperature of 191C and a saturated vapor pressure of 12 kg/cm with heating and stir-ring for 8 hours to obtain a slurry of xonotlite crystals.
The x-ray diffraction pattern of the xonotlite crystals in Fig. 1 ~A) shows diffraction peaks ~23) at 12.7, 27.6 and 29.0 peculiar to xonotlite crystals. The analysis by ignition of the crystals reveals the following composition.
SiO2 48.88%
15 CzO 45.60 A' O 0.26 Fe2 3 Ig. loss 4.51 Total 99.80 The slurry of xonotlite crystals is shown i? the scanning electron micrograph of Fig. 5~A), which revea's that numerous lath-like xonotlite crystals are formed as randomly three-dimensionally interlocked with one another into many, substantially globular, secondary particles of xonotlite ranging from about 10 to about 60~ in diameter and suspended .. 1~2Z~779 in water. The ~econdary particle ha~ a porosity of about 95.6%.
Sub~equently, the slurry containing the globular secondary particle6 of xonotlite i6 dried at 150 C and then divided into primary particle~.
Fig. 2(A) shows an electron micrograph of the primary particles. The micrograph indicates that the primary particles have at least two surface~ in symmetric relation, a length of about 1 to about 20 ~ , a thickne~s of about 0.02 to about 0.1 and a width of about 0.02 to about l.O ~ , the length being at least about lO times the thickness. The primary particle~ have a 6pecific surface area of about 50 m2/g.
The slurry of xonotlite crystals prepared above is placed in a mold, 40 mm x 120 mm x 150 mm, and deY~atered and ~haped by a pre~s and dried to obtain a shaped body. Fig. 7(A) is a ~canning electron micrograph ~howing a fractured surface of the 6haped body of xonotlite. ~he micrograph indicate~
that globular secondary particles of xonotlite are compressed and formed a~ interlocked with one another; The shaped body has a bulk density of 0.2 g~cm3, bending 6trength of abou~
4 kg/cm2 and a poro6ity of about 92.7%.
Reference Example 2 Minus 325 mesh slaked lime (Tyler scale) is u6ed as a lime ~aterial and minus 325 me~h siliceou~ sand powder (Tyler 6cale) a6 a ~iliceous material. ~he materials are di~persed ln water ln a CaO to SiO2 mole ratio of 0.80:1 to prepare a 61urry having a water to ~olids ratio of l~Z779 12:1 by weight. The slurry is placed in an autoclave and sub-jects to hydrothermal reaction at a temperature of 191 C and a saturated vapor pressure of 12 kg/cm2 with heating and stir-ring for 5 hours to obtain a slurry of tobermorite crystals.
The x-ray diffraction of the tobermorite crystals shows diffraction peaks (2a) at 7.8, 29.0 and 30.0 peculiar to tobermorite crystals. The analysis by ignition of the cry-stals reveals the following composition.
SiO2 48.38%
CaO 38.55 A123 0.31 Ig. Loss 11.36 ^ Total 99.05 The slurry of tobermorite crystals is shown in the scanning electron micrograph of Fig. 6(A), which reveals that numerous plate-like tobermorite crystals are formed as randomly three-dimensionally interlocked with one another into many, sub-stantially globular, secondary particles of tobermorite ranging from about 10 to about 60~ in diameter and suspended in water.
The secondary particle has a porosity of about 94.0%.
Subsequently, the slurry containing the globular sec-ondary particles of tobermorite is dried and then divided into primary particles.
Fig. 3(A) shows an electron micrograph of the primary 277~
particle6. The mlcrograph indicates that the primary particle~ have at least two ~urfaces in sy~metric relation, a length of about 1 to a~out 20~ , a thicknesg of about 0.02 to about 0.1~ and a wiAth of about 0.2 to about 5.0~ , the length being at lea~t about 10 times the thi'ckness~ The primary particle~ have a specific surface area of about 61 m2/g.
The slurry of tobermorite crystal~ prepared above is placed in a mold, 40 mm x 120 mm x 150 mm, and dewatered and shaped by a press and dried to obtain a shaped body. The ~cannlng electron micrograph showing a fractured surface of the shaped body of tobermorite resembles that of Fig. 7(A) and , indicates that globular secondary particles of tobermorite are compressed and, formed as interlocked with one another.
The shaped body has a bulk density of 0.3 g/cm3, bending strength of about 12 kg/cm2 and a porosity of about 88~o%~
Reference Example ~
~ ick li~e is used as a lime material and commercial white carbon having a particle size of less than 100 ~ and containing abo~t 88 wt% of SiO2 (Ig. 10~8 about 12wt%) a~ a siliceous material. The materials are dispersed in water in a CaO to SiO2 mole ratio of 1.35:1 to prepare a slu~ry having a water to solids ratio of 12:1 by weight. The slurry is placed in an autoclave and subjected to hydrothermal reaction at a temperature of 191 C and a saturated vapor pressure of 14 kg/cm2 with heatlng and stirring for 3 hours to obtain a slurry of CSHn cry~tal6.
1~22-~7~
The x-ray diffraction of the C~hn crystals show6 diffraction peaks (2e) at 29.4, 31.8 and 49.8 peculiar to CSHn cry6tals. The analy6i~ by ignition of the crystals reveals the following compo~ition~
SiO2 38.19%
CaO 47.78 Fe20~ 0.41 Ig. loss 13.04 Total 99.05 The slurry o~ CSHn crystals is observed under a 6canning electron microscope with a similar result to those 6hown in ~igs. 5(A) and 6(A). It is found that numerou6 foil-like CSHn crystal~ are formed as randomly three-dimensionally interlocked with one another into many, substantially globular, secondary particles of CSHn ranging from about 10 to about 60~ in diameter and su~pended in water. The secondary particle has a porosity of about 94.1%.
~ SRbsequently, the 61urry containing the globular secondary particles i8 dried and then divided lnto primary particles, The electron micrograph of the primary particle~
indicates that the CSHn crystals are in the form of primary particles having a length of abovt 1 to aiout ~ , a thic~rlcs~
of about 0.01 to about 0.02~and a width of about 0.01 to about 5~ ~ the length being at least about 50 times the thickness. The prlmary particles have a specific surface area of about 150 m2/g.
_ ~9 _ c ~2~779 ~q ~
- The slurry of C~T1 crystals prepared above i6 placed in a mold, 40 mm x 120 mm x 150 mm , and dewatered and shaped by a press and dried to obtain a shaped body. The scanning electron micrograph showing a fractured surface of the shaped body of CSHn resembles that of Fig. 7(~) and indicates that globular secondary particles of CSHn are cor~pressed and formed as interlocked with one another. The shaped body has a bulk density of 0~3 g/c ~ , bending strength of about 8 kg/cm2 and a porosity of about 86.4%.
Reference Example 4 Quick lime is used as a lime material and commercial white carbon the same as in Reference Example 3 as a siliceous material. The materials are dispersed in water in a CaO to SiO2 mole ratio of 0.57:1 to prepare a slurry having a water to solids ratio of 12:1 by weight. The slurry is placed in an autoclave and subjected to hydrothermal reaction at a temperature of 200 C and a saturated vapor pressure of 15 kg/cm2 with heating and stirring for 8 hours to obtain a slurry of gyrolite crystals.
The x-ray diffraction of the gyrolite crystals shows diffraction peak~ at 4.0, 28~2 and 28.9 peculiar to gyrolite crystals. The analysis by ignition of the crystals reveals the follo~ing composition.
SiO2 56.88%
CaO 30.75 Fe23 0.29 Ig. Loss 11.39 Total 99.70 The slurry of gyrolite crystals is observed under a scanning electron microscope with a similar result to those shown in Figs. 5(A) and 6(A). It is found that numerous plate-like gyrolite crystals are formed as randomly three-dimensionally interlocked with one another into many, substantially globular, secondary particles of gyrolite ranging from about 10 to about 60~ in diameter and suspended in water. The secondary particle has a porosity of about 94.0%.
Subsequently, the slurry containing the globular secondary particles is dried and then divided into primary part-icles The electron micrograph of the primary particles in-dicates that the gyrolite crystals are in the form of primary particles having a length of about 1 to about 20~, a thickness of about 0.02 to about 0.1~ and a width of about 0.2 to about
Reference Example 2 Minus 325 mesh slaked lime (Tyler scale) is u6ed as a lime ~aterial and minus 325 me~h siliceou~ sand powder (Tyler 6cale) a6 a ~iliceous material. ~he materials are di~persed ln water ln a CaO to SiO2 mole ratio of 0.80:1 to prepare a 61urry having a water to ~olids ratio of l~Z779 12:1 by weight. The slurry is placed in an autoclave and sub-jects to hydrothermal reaction at a temperature of 191 C and a saturated vapor pressure of 12 kg/cm2 with heating and stir-ring for 5 hours to obtain a slurry of tobermorite crystals.
The x-ray diffraction of the tobermorite crystals shows diffraction peaks (2a) at 7.8, 29.0 and 30.0 peculiar to tobermorite crystals. The analysis by ignition of the cry-stals reveals the following composition.
SiO2 48.38%
CaO 38.55 A123 0.31 Ig. Loss 11.36 ^ Total 99.05 The slurry of tobermorite crystals is shown in the scanning electron micrograph of Fig. 6(A), which reveals that numerous plate-like tobermorite crystals are formed as randomly three-dimensionally interlocked with one another into many, sub-stantially globular, secondary particles of tobermorite ranging from about 10 to about 60~ in diameter and suspended in water.
The secondary particle has a porosity of about 94.0%.
Subsequently, the slurry containing the globular sec-ondary particles of tobermorite is dried and then divided into primary particles.
Fig. 3(A) shows an electron micrograph of the primary 277~
particle6. The mlcrograph indicates that the primary particle~ have at least two ~urfaces in sy~metric relation, a length of about 1 to a~out 20~ , a thicknesg of about 0.02 to about 0.1~ and a wiAth of about 0.2 to about 5.0~ , the length being at lea~t about 10 times the thi'ckness~ The primary particle~ have a specific surface area of about 61 m2/g.
The slurry of tobermorite crystal~ prepared above is placed in a mold, 40 mm x 120 mm x 150 mm, and dewatered and shaped by a press and dried to obtain a shaped body. The ~cannlng electron micrograph showing a fractured surface of the shaped body of tobermorite resembles that of Fig. 7(A) and , indicates that globular secondary particles of tobermorite are compressed and, formed as interlocked with one another.
The shaped body has a bulk density of 0.3 g/cm3, bending strength of about 12 kg/cm2 and a porosity of about 88~o%~
Reference Example ~
~ ick li~e is used as a lime material and commercial white carbon having a particle size of less than 100 ~ and containing abo~t 88 wt% of SiO2 (Ig. 10~8 about 12wt%) a~ a siliceous material. The materials are dispersed in water in a CaO to SiO2 mole ratio of 1.35:1 to prepare a slu~ry having a water to solids ratio of 12:1 by weight. The slurry is placed in an autoclave and subjected to hydrothermal reaction at a temperature of 191 C and a saturated vapor pressure of 14 kg/cm2 with heatlng and stirring for 3 hours to obtain a slurry of CSHn cry~tal6.
1~22-~7~
The x-ray diffraction of the C~hn crystals show6 diffraction peaks (2e) at 29.4, 31.8 and 49.8 peculiar to CSHn cry6tals. The analy6i~ by ignition of the crystals reveals the following compo~ition~
SiO2 38.19%
CaO 47.78 Fe20~ 0.41 Ig. loss 13.04 Total 99.05 The slurry o~ CSHn crystals is observed under a 6canning electron microscope with a similar result to those 6hown in ~igs. 5(A) and 6(A). It is found that numerou6 foil-like CSHn crystal~ are formed as randomly three-dimensionally interlocked with one another into many, substantially globular, secondary particles of CSHn ranging from about 10 to about 60~ in diameter and su~pended in water. The secondary particle has a porosity of about 94.1%.
~ SRbsequently, the 61urry containing the globular secondary particles i8 dried and then divided lnto primary particles, The electron micrograph of the primary particle~
indicates that the CSHn crystals are in the form of primary particles having a length of abovt 1 to aiout ~ , a thic~rlcs~
of about 0.01 to about 0.02~and a width of about 0.01 to about 5~ ~ the length being at least about 50 times the thickness. The prlmary particles have a specific surface area of about 150 m2/g.
_ ~9 _ c ~2~779 ~q ~
- The slurry of C~T1 crystals prepared above i6 placed in a mold, 40 mm x 120 mm x 150 mm , and dewatered and shaped by a press and dried to obtain a shaped body. The scanning electron micrograph showing a fractured surface of the shaped body of CSHn resembles that of Fig. 7(~) and indicates that globular secondary particles of CSHn are cor~pressed and formed as interlocked with one another. The shaped body has a bulk density of 0~3 g/c ~ , bending strength of about 8 kg/cm2 and a porosity of about 86.4%.
Reference Example 4 Quick lime is used as a lime material and commercial white carbon the same as in Reference Example 3 as a siliceous material. The materials are dispersed in water in a CaO to SiO2 mole ratio of 0.57:1 to prepare a slurry having a water to solids ratio of 12:1 by weight. The slurry is placed in an autoclave and subjected to hydrothermal reaction at a temperature of 200 C and a saturated vapor pressure of 15 kg/cm2 with heating and stirring for 8 hours to obtain a slurry of gyrolite crystals.
The x-ray diffraction of the gyrolite crystals shows diffraction peak~ at 4.0, 28~2 and 28.9 peculiar to gyrolite crystals. The analysis by ignition of the crystals reveals the follo~ing composition.
SiO2 56.88%
CaO 30.75 Fe23 0.29 Ig. Loss 11.39 Total 99.70 The slurry of gyrolite crystals is observed under a scanning electron microscope with a similar result to those shown in Figs. 5(A) and 6(A). It is found that numerous plate-like gyrolite crystals are formed as randomly three-dimensionally interlocked with one another into many, substantially globular, secondary particles of gyrolite ranging from about 10 to about 60~ in diameter and suspended in water. The secondary particle has a porosity of about 94.0%.
Subsequently, the slurry containing the globular secondary particles is dried and then divided into primary part-icles The electron micrograph of the primary particles in-dicates that the gyrolite crystals are in the form of primary particles having a length of about 1 to about 20~, a thickness of about 0.02 to about 0.1~ and a width of about 0.2 to about
5~, the length being at least about 10 times the thickness. The primary particles have a specific surface area of about 60 m2/g.
The slurry of gyrolite crystals prepared above is placed in a mold, 40 mm x 120 mm x 150 mm, and dewatered and shaped by a press and dried to obtain a shaped body. The scan-ning electron micrograph showing a fractured surface of ~l~2277~
the shaped body resembles that of Fig. 7(A) and indicate6 that secondary particles of gyrolite are compressed and for~ed a~ interlocked with one another. The shaped body has a bulk density of 0.3 ~cm3, bending strength of about 8 kg/cm2 and a porosity of about 88.0%.
Reference Example 5 Quick lime is used aS a lime material and minus 350 mesh siliceous san~ powder (Tyler scale) a6 a siliceou~
material. The materials are dispersed in water in a CaO to SiO2 mole ratio of 2.0:1 to prepare a slurry having a water to solids ratio fo 4:1 by weight. The slurry i~ ~laced in an autoclave and subjected to hydrothermal reaction at a temperature of 191 C and a saturated vapor pressure of 12 kg/cm2 with heating for 5 hours to obtain a slurry of~ -dicalcum 6ilicate hydrate cry~tals.
The x-ray diffraction of the crystals shows diffraction peak6 (2~) at 16.6, 27.3 and 37.2 peculiar ~o~ -dicalcium 6ilicate hydrate crystals. The analysis by ignition of the crystals ~e~eals.the following composition.
SiO2 30.81%
CaO 57.02 A120~ 0.45 Fe2 3 Ig. loss 10.05 Total 99.05 _ L? _ 77~
The slurry of ~-dicalcium silicate hydra-te crystals is dried to obtain a fine white powder. Fig. 4(A) shows an electron ~lcrograph of the powder at a magnificatlon of 5,000X. The micrograph indicates that the ~-dicalcium silicate hydrate crystals are in the iorm of plate-like primary particles having a length o about 1 to about 300~ , a thickness of about 0.1 to about 1 ~ and a width of 1 to 30~ , the length being at least about 10 tirnes the thickness~
The crystals have a specific surface area of about 6 m2/g.
: .
-~ZZ77~
Example 1 The primary particles of lath-like xonotlite crystals obtained in Reference Example 1 are used as a starting material. The particles are placed in a pressure-resistant container of the closed type along with water 5 times the weight of the particles. Carbon dioxide gas is forced into the container at room temperature, and the particles are carbonated for about 30 minutes while maintaining the internal pressure at 3 kg/cm2, whereby 10- composite particles of amorphous silica and calcium carbonate are obtained.
The analysis by ignition of the composite particles reveals the following composition.
SiO2 36.04%
CaO 33.54 A123 0,18 Fe203 o~38 Ig. loss 28.87 ~ Total 99.11 The x-ray diffraction of the particles sho~Js the result given in Fig. l(B), which indicates that all the peaks peculiar to calcium silicate crystals seen in Fig. l(A) have disappeared and that only diffractlon peaks (2~) indicative of calcium carbonate crystals have appeared at 23.0, 29.4 and 36Ø This evidences that the calcium _ I~L. -~L~22`779 sillcate has been converted to amorphous silica and calcium carbonate due to carbonation.
The composite particles are further observed under an electron microscope with the result given in Fig. 2(B). The microscopic observation reveals that the composite particles comprise amorphous silica particles and extremely fine particles, up to about 2 ~ in size, of calcium carbonate attached to the amorphous silica -particles and that the particles of arnorphous silica have at least two surfaces in symmetric relation, a length of about 1 to about 20~ , a thickness of about 0.02 to about and a width of about 0.02 to about 1.0~ , the length being at least about 10 times the thickness. The configuration of the amorphous silica particles is exactly the same as that of lath-like xonotlite crystals (Fig. 2(A)), Thi5 indicates that the amorphous silica particles retain the original lath-like configuration of xonotlite.
The composite particles are dispersed in water ~ to a conc~ntration of 5 wt. %, and the dispersion is allowed -to stand after stirring for 20 minutes so as to separate the particles into the constituent silica and calcium carbonate by~settling utilizing the difference in specific gravity. However, the two components are found to be entirely inseparable and proved to be firmly joined together chemically or phys~cally.
~%%7~'3 Subsequently, the cornposite particles of amorphous silica and calcium carbonate are immersed in a 6~ ~Cl solution for one minute. With the evolution of carbon dioxide gas, the calcium carbonate in the primary particles is converted to carbon dioxide gas and calcium chloride. The acid-treated particles are then thoroughly washed with water to cornpletely dissolve out the resulting calcium chloride. The particles are dried to obtain Opsil-I of this invention.
The Opsil-I thus prepared is subjected to ignition dehydration and thereafter to analysis~ The result is given below which indicates that the product is composed of silica of high purity.
SiO2 99.1%
CaO < 0.01 (Ig. loss 5.0 ) The x-ray diffraction pattern of Opsil-I iG
~ glven in ~ig. l(C) which displays no peaks indicating the lath-like xonotlite crystals, the starting mate~ al, nor the peaks indicating the calcium carbonate contained in the co~posite particles resulting from the carbonation.
It is therefore confirmed that the Opsil-I is amorphous silica.
The Opsil-I i5 shown in the electron micrograph ~ ~Z2~79 of Fig. 2(C) which, exactly like Fi~s. 2(A) and 2(B), reveàls that the Opsil-I has a crystal]ine appearance and at least two surfaces in symmetric relation. The particles of Opsil-I are about 1 to about 20 f~in length, about 0,02 to about 0.1 ~ in thickness and about 0.02 to about 1.0/~ in width, the length being at least about 10 times the thickness and are ~n the form of primary particles. The appearance resembling lath-like crystals remains-free of any change even when the particles are treated with acid.
The properties of the Opsil-I obtained above are as follows.
Bulk density 0.05 g/cm3 Specific surface area 335 m2/g Oil adsorption 800 cc/100 g pH 6.5 ~he reference numeral (1) in Fig. 9 shows the pore size distribution of the Opsil-I ~ith the peak at 27 A.
Example 2 ~ ~he primary particles of plate-like tobermorite crystals obtained in Reference Example 2 are used as a starting material~ The particels are placed in a pressure-resistant container of the closed type along with water 5 times the ~eight of the particlesO Carbon dioxide gas is forced into the container at room temperature, and the Z5 particles are carbonated for about 30 minutes while maintaining ~æz~79 the internal pressure at 3 kg/cm2, whereby composite particles of amorphous silica and calcium carbonate are obtained.
The analysis by iginition of the composite particles reveals the following composition.
SiO2 39.77%
CaO 31.43 A123 0.24 ~ 2 3 Ig. loss 27.42 Total 99.26 The x-ray difiraction of the particles shows the same result as given in Fig. l(B), which indicates that all the peaks peculiar to tobermorite crystals, the starting material, have disappeared and that only diffraction peaks (2~ indicative of calcium carbonate crystals have appeared at 23.0, 24~8, 27.0, 29.4, 32.8 and 36.o. This evidences that the calcium silicate has been converted to amorphous silica and calcium carbonate due to carbonation, ~ The composite particles are further observed ZO under an electron microscope with the result given in Fig. 3(B). The microscopic observation reveals that the composite particles comprise amorphous silica particles and extremely fine particles, up to about 2f~ in size~ of calcium carbonate attached to the amorphous silica particles and that the ~l~.;22779 particles of amorphous silica have at least -t~Jo ;urfaces in symmetric relation, a length of about 1 to about 20~ , a thickness of about 0.02 to about Ool~ and a ~idth of about 0.2 to about 5.0~ , the length being at least about 10 times the thickness. The configuration of the amorphous sllica particles is exactly the same as that of plate-like tobermorite crystals (Fig. 3(A)). This indicates that the amorphous silica particles retain the original plate-like configuration of tobermorite.
The composite particles are dispersed in ~Jater to a concentration of 5 wt. %, and the disper~ion is allowed to stand after stirring for 20 minutes so as to separate the particles into the constituent silica and calcium carbo~ate by settling utllizing the difference in specific gravity. However, the two components are found to be entirely inseparable a~d proved to be firmly joined to~ether chemically or physicallyO
Subsequently, the composite particles of amorphous ~ silica and calcium carbonate are immersed in a 6N HCl Eolution for one minute. ~ith the evolution of carbon dioxide gas, the calcium carbonate in the primary particles is converted to carbon dioxide gas and calcium chloride.
The acid_treated particles are then thoroughly washed with water to completely ~issolve out the re~ulting calcium chloride. The particles are dried to obtain Opsil-I of ~2Z~77~
this invention.
The Opsil-I thus prepared is subjected to iynition dehydration and thereafter to analysis. The result is given below which indicates that the product is composed of silica of high purity.
SiO2 99.3%
A123 0.23 CaO < 0.01 (Ig . loss4.7`) The x-ray diffraction pattern of Opsil-I is the same as in Fig. l(C) which displays no peaks indicating the plate-like tobermorite crystals, the starting material, nor the peaks indicating the calcium carbonate contained in the composite particles resulting from the carbonation. The Opsil-I is a-morphous silica.
The Opsil-I is shown in the electron microgragh of Fig. 3(C) which, exactly like Figs. 3(A) and 3(B), reveals that the Opsil-I has a crystalline appearance and at least two surfaces in symmetric relation. The particles of Opsil-I are about 1 to 20~ in length, about-0.02 to about 0.1~ in thickness and about 0.2 to about 5.0u in width, the length being at least about 10 times the thickness and are in the form of primary particles. The crystalline appearance remains free of any change even when the particles are treated with acid.
, .
~ZZ~79 The properties of the Opsil-I obtained above are as follows.
Bulk density 0.04 g/cm3 Specific surface area 277 m2/g Oil adsorption 750 cc/100 pH 6.7 The reference numeral (2) in Fig. 9 sho~s the pore size distribu~ion Or the Opsil-I v~ith the peal~ at 23 A.
Example 3 The primary particles OI calcium silicate (CSHn) in the form of foil-like crystals obtained in Reference Example 3 are used as a starting material. The particles are placed in a pressure-resi~tant container of the closed type along with water 5 times the weight of the particles.
Carbon dioxide gas is forced into the container at room temperature, and the particles are carbonated for about 30 minutes while maintaining the internal pressure at 3 kg/cm2~ whereby composite particles of amorphous 5ilica and calci~m carbonate are obtained.
Thé analysi~ by ignition of the composite particles reveals the following composition.
SiO2 ~9.98%
CaO 37-59 ~e23 0.27 Ig. loss 31,28 ~otal 99.51 ~;Z77g The x-ray diffraction of the particles shows the same result as given in Fig. l(B), ~.~hich indicates that all the peaks peculiar to CSHn crystals, the starting material, have disappeared and that only diffraction peaks (2~) indicative of calcium carbonate crystals have appeared at 23.0, 24.8, 27.0, 29.4, 32.8 and 36.o~ This evidences that the calcium ~ilicate has been converted to amorphous silica and calcium-carbonate due to carbonation.
The composite particles are further observed under an electron microscope with the result that the composite particles co~prise amorphous silica particles and extremely fine particles, up to about 2f1 in size, of calcium carbonate attached to the amorphous silica particles and that the particles of amorphous ~ilica have at least two surfaces in symmetric relation, a length of about 1 to about 5~ ~ a thickness of about 0.01 to about OAO2~ and a width of about 0.01 to about s.n~, the length being at least about 50 time~ the thickness. The configuration of the amorphous sllica particles i_ e~actly the same as that of Z0 foil-like CSHn crystals. This indicates that the amorphous silica particles retain the original foil-like configuration of CSHn.
The composite particles are dispersed in water to a concentration of 5 wt. %, and the di~per~,ion iG allowed to stand after stirring for Z0 minute~ 'JO a:; to separate 1~2~7~
the particles into the constituent silica and calcium carbonate by settling utilizing the difference in specific gravity.
However, the two components are found to be entirely inseparable and proved to be firmly joined together chemi-cally or physically.
Subsequently, the composite particles of amorphous silica and calcium carbonate are immersed in a 6N HCl solution for one minute. With the evolution of carbon dioxide gas, the calcium carbonate in the primary particles 0 i6 converted to carbon dioxide gas and calcium chloride.
The acid-treated particles are then throughly ~ashed ~ith water to completely di~solve out the re~ulting calcium chloride. The particles are dried to obtain Opsil-I of this invention.
The Opsil-I thus prepared is subjected to ignition dehydratlon and thereafter to analysis. The result i~ given beloY~ which indicatas that the product is ~omposed of sillca of high purity.
SiO2 99-7%
CaO ~ o.o~
(Ig. loss 5.1 ) The x-ray diffraction pattern of Op~ I i5 the same as ln Fig. 1 (C) ~hich displays no peak~. indicatin~
the foil-like CSHn crystal , the starting material, nor the peaks indicating the ealcium carbonate contained in _ 53 _ ~l~2Z779 the composite particles reGulting from the carbonation.
The Opsil-I is amorphous silica.
Observation of electron micrograph reveals t`nat the Opsil-I has a crystalline appearance and at least two surfaces in symmetric relation. The particles of Opsil-I
are about 1 to ~bout 5 ~in length3 about 0.01 to about 0.02yin thickness and about 0.01 to about ~.0 ~'in width, the length being at least about 50 times the thickness and are in the form of primary particles. The crystalline appearance remains free of any change even when the particles are treated with acid.
The properties of the Opsil-I obtained above are as follows~
Bulk density 0.07 g/cm3 Specific surface area 461 m2/g Oil adsorption 470 cc/100 g pH 6.5 The rcference numeral (3) in Fig. 9 shows the pore size distribution of the Opsil~ ith the peak at about 30 A and about 180 A~
Example L~
The primary particles of plate-like gyrolite crystal~ obtained in ~eference Example 4 are used as a starting material. The particle are placed in a pressure-resistant container of the clo ed type alonG with ~ater l~Z2~77~
5 times the weight of the particles. Carbon dioxide gas is forced into the container at room temperature, and the particles are carbonated for about 30 minutes while maintain-ing the internal pressure at 3 kg/cm2, whereby composite particles of amorphous silica and calcium carbonate are obtained.
The analysis by ignition of the composite particles reveals t`he following composition.
Si 2 4O . 22%
CaO 26.07 Fe23 0 . 25 Ig. loss 24. 33 Total 99.20 The x-ray diifraction of the particles shows the same result as given in Fig. l(B), which indic~tes that all the peaks peculiar to calcium silicate crystals~ the starting material, have disappeared and that only diffraction peaks (20) indicative of calcium carbonate crystals have ZO appeared at 23.0, 24.8, 27.0~ 29.4~ 32.8 and 36Ø
This evidences that the calcium silicate ha~ been converted to amorphou~ silica and calcium carbonate due to carbonation.
The composite particles are further observed under an electron mlcroscope with the result that the composite particles comprise amorphous ;ilica particles - ~22~7~
and extremely fine particles, up to about 2 ~ in size, of calcium carbonate attached to the amorphous silica particles and that the particles of amorphous silica have at least two surfaces in symmetric relation, a length of about 1 to about 20 ~, a thickness of about 0.02 to about 0.1 ~ and a width of about 0.2 to about 5/~ the length being at least about 10 ti~es the thickness. The configuration of the amorphous silica particles is exactly the same as that o~ plate-like gyrolite crystals. This indicates that the amorphous silica particles retain the original plate-like configuration of gyrolite.
The composite particles are dispersed in water to a concentration of 5 wt. %, and the dispersion is allowed to stand after stirring for 20 minutes so as to separate the particles into the con~tituent silica and calcium carbonate by settling utilizing the difference in specific grav~ty. However, the two components are found to be entirely inseparable and proved to be firmly joined together chemically or physically.
Subsequently, the composite particles of amorphous silica and calcium carbonate are immersed in a 6N HCl solution for one minute. ~ith the evolution of carbon dioxide ga, the calcium carbonate in the pr~mary particles is converted to carbon dioxide ~as and calcium chloride.
Z5 Th~ acid-treated particles are then thoroughly ~ashed v~ith ~ 2Z779 water to completely dissolve out the resulting calcium chloride. The particles are dried to obtain Opsil I of this invention.
The Opsil-I thus prepared is subjected to ignition dehydration and thereafter to analysis. The result is given below which indicates that the product is composed of silica of high purity.
SiO ` 99 4%
CaO C 0.01 (Ig. loss 5.8 ) The x-ray diffraction pattern of Opsil-I is the same as in Fig. l(C) which displays no peaks indicating the plate-like gyrolite crystals~ the starting material, nor the peaks indicating the calcium carbonate contained in the composite particles resulting from the carbonation.
The Opsil_I is amorphous silica.
Ob~ervation of electron micrograph reveals that the `~ Opsll_I has a crystalline appearance and at least two ~urfaces in symmetric relation. The particles of Opsil-I are about 1 to about 20 ~in length, about 0.02 to about 0.1~ in thickness and about 0.2 to about 5/~in width, the length being at least about 10 times the thickness and are in the form of prlmary particles. The crystalline appearance remains free of any change even when the particles are treated with acld.
` ~ The propeirtie6 of the Opsil-I obtained above are as follows.
Bulk dens~ty 0.065 g/cm3 ; Specific surface area 285 m2/g ; i Oil adsorption 530 cc/100 g - pH 6.3 The reference numeral ~4) in Fig. 9 shows the pore size distribution of pore diameters of the Opsil-I
10; with the peak at 28 ~.
Example 5 The primary particles of plate-like ~-dicalcium - silicate hydrate crystals obtained in Reference Example 5 are used as a starting material. The particles are placed in a pressure-resistant container of the closed type along with water 5 times the weight of the particles.
; Carbon dioxide gas is forced into the container at room temperature~ and the particles are carbonated for about 30 minutes while maintaining the internal pressure at 3 kg/cm2, ~hereby composite particles of amorphous silica and calcium carbonate are obtained, ' The analysiG by ignition of the composite particles reveal$ the following composition.
i, SiO2 22.8~
. CaO 42.24 A1203 0.31 Fe23 -33 . Ig. lofi~ 34.50 ?
'. A . ; _ i ' ; . Total 100. 24 . The x-ray diffraction of the particles shows the ~; . same result as given in Fig. l(B)~ which indicates that - - all the peaks peculiar to calcium silicate crystals, the - 10 - . starting material, have disappeared and that only diffraction . peaks (2e) indicative of calcium carbonate crys~als have ..
. appeared at 23.0, 24.8, 27.0, 29.4, 32.8 and 36Ø
This evidences that the calcium silicate has been converted .. .. ..
- ~ to amorphous silica and calcium carbonate due to carbonation.
:. 15 ; The composite particles are further observed ; under an electron microscope with the result that the i composite particles comprise amorphous silica particels .: and extremely fine particles, up to about 2~ in size~
t -~ ., j' of calcium carbonate attached to the amorphous silica Y
i; 20 particles and that the particles of amorphous silica ha~e at least two surfaces in ~ymmetric relation~ a length of about 1 to about 300~4~ a thickness of about 0~1 to about -;! ' 1 ~ and a width of about 1 to about 30~ ~ the length being at le~st abo~t 10 times the thickness. The configuration of the . 25 amorphous silica particles is exactly the s~me at that of :,, .
.; ~, ' ', .
. , , ~
, Z ~ 7 9 plate-like ~-dicalcium silicate hydrate crystals (Fig.
4~A)). This indicates that the amorphous silica particles retain the original plate-like configuration of the crystals.
The composite particles are dispersed in water ' 5 to a concentration of 5 wt. %, and the dispersion is .. . ..
allowed to stand after stirring for 20 minutes so as to separate the particles into the constituent silica and calcium carbonate by settling utilizing the difference in specific gravity. However, the two components are found ~ to be entirely inseparable and proved to be firmly joined together chemically or physically.
Subsequently, the composite particles of amorphous silica and calcium carbonate are immersed in a 6N HCl - solution for one minute. With the evolution of carbon dioxide gas, the câlcium carbonate in the primary particles i . . .
is converted to carbon dioxide gas and calcium chloride.
The acid-treated particles are then thoroughly washed with water to completely dissolve out the resulting calcium chloride. ~he particles are dried to obtain Opsil_I of thls invention.
The Opsil-I thus prepared is subjected to ignition dehydration and thereafter to analysis. The re~ult is given below which indicates that the product is composed of silica of high purity.
~Z77~
SiO2 99.6%
A123 0.12 CaO < 0.01 (Ig. loss 5.2 ) The x-ray diffraction pattern of Opsil-I is the same as in Fig. l(C) which displays no peaks indicating the plat2-like ~-dicalcium silicate crystals, the starting material, nor the peaks indicating the calcium carbonate contained in the com-posite particles resulting from the carbonation~ The Opsil-I is amorphous silica.
The Opsil-I is shown in the electron micrograph of Fig. 4(B) which reveals that the Opsil-I has a crystalline appearance and at least two surfaces in symmetric relation.
The particles of Opsil-I are about 1 to about 300~ in length, about 0.1 to about 1~ in thickness and about 1 to about 30~ in width, the length being at least about 10 times the thickness and are in the form of primary particles. The crystalline appearance remains free of any change even when the particles are treated with acid.
The properties of the Opsil-I obtained above are as follows.
Bulk density 0.15 g/cm3 Specific surface area 550 m2/g Oil adsorption 340 cc/100 g pEI 7.1 ~2'~`779 The reference numeral (5) in ~i~, 9 ~ho~ the pore size distribution Or t~le ~psil-I with the peak at 24 ~.
2~
Exam~le 6 The slurry of xonotlite crystals obtained in Reference Example 1 is dewatered to a water to solids (xonotlite crystals) ratio b~ weight of 5 : 1 and is then placed in a closed container. Carbon dioxide gas is forced into the container to maintain an internal pressure of 3 kg/cm , and the slurry is reacted for about 30 minutes.`
The reaction gives composite secondary particles of amorphous silica and calcium carbonate.
The analysis of the secondary particles reveals that they have the same composition as the primary particles constituting them.
. . .
; , The x-ra~ dilfraction of the particles further reveals the same result as given in ~ig. l(B), indicating that the peaks due to the calcium silicate crystals prior to the carbonation have all disappegred but showing - only the diffraction peaks (20) of calcium carbonate at -- :~ 23.0, 2~4 and ~6Ø This evidences that the - 20 composite secondary particles are composed of amorphous silica and calcium carbonate.
The composite secondary particles are lurther observed under a scanning electron microscope at a magnification of 600X with the result given in ~ig. 5(B), which shows that the composite secondary particles are .. . .
, - 63 - ~
1~22779 formed from numerous composite primary particle~
interlocked with one ano~ther substantially into globules ranging from about 10 to about 60 ~ in diameter. The electron microscope of the primary particles derived from the above secondary particles gives the same result as in Fig. 2(B).
~ his structure or form substantially conforms to that of second~r~ particles of xonotlite used as the starting material and shown in Fig. 5(A). This I~ indicates that the composite particles retain the original structure or nature of the secondary~particles of xonotlite despite the carbonation.
~he composite secondary particles are - dispersed in water to a concentration of 5 wt.%, and the disper~ion is allowed to stand after stirring for 20 minutes. However, the particles are found inqeparable by settling into their components, namely amorphoUS silica and calci~m carbonate.
; ~ Subsequently, the composite secondary particles are immersed in a 6N HCl solution for one minute.
~imultaneously with the immersion, carbon dioxide gas evolves due to the conversion of the calcium carbonate .
- iD the primary particles to calcium chloride. The p~rticles sre then thoroughly washed with water to completely dissolve out the resulting calcium chloride.
The particles are dried to give Opsil-II of this ~L~.2Z'77~
i nvention.
~ he x-ray diffraction of the Opsil-II thus prepared exhibits the same result as in Fig. l(C), showing that the peaks due to calcium ~ilicate crystals snd those due to calcium carbonate have 811 disappeared.
Thus the Opsil-II is found to be composed of amorphous silica.
~ he Opsil-II i8 observed under a scanning electron microscope at a magnification of 2,000X with the result given in Fig. 5(C), which indicates that the particles of Opsil-II have 6ubstantially the same shape as the secondary particles of xonotlite and also as the composite secondary particles of amorphous silica and calcium carbonate which retain the original structure of the former particles.
~ he Opsil-II prepared as sbsve is readil~
dispersible in water to give a slurry which in itself is shapable~ The Opsil~II hss the following properties.
; ~ulX densit~ 0.04 g/cm3 Specific surfsce area 400 m2/g Specific surface ares 2 after heating at 400 C 350 m /g Poro 8i ty 98 ~
Heat resistance No deformation at Oil adsorption 1,100 cc/100 g Chemical analysis:
SiO2 content 99.1 %
~2;~779 Example 7 The slurry of tobermorite cry~tals obtained in Reference ~xample 2 is dewatered to a water to qolids (kobermorite crystals) ratio by weight of 5 : 1 and i8 then placed in a closed container~ Carbon dioxide - gas is forced into the container to maintain an internal pressure of 3 kg/cm2, and the slurry is reacted for about ~0 minutes.
The reaction gives composite secondary - particles of amorphous silica and calcium carbonate.
The analysis of the secondary particlea reveals that they have the same composition as the primary particles constituting them.
The x-ray diffraction of the particles further 15 , reveals that the peaks due to the calcium silicate crystals prior to the carbonation have 811 disappeared but showing only the diffraction peaks (2~) of cslcium c8rbonate at 23.0~, 24.8, 27.0, 29.4~ 32.8 and ~6Ø
~ This evidences thst the composite secondary particles sre composed of amorphous silica and calcium carbonate.
The composite secondary particles sre further observed under a scanning electron microscope at a m~gnification of 600X with the result given in ~ig. 6(B), which ~ho~s that the composite secondary particles are - 25 formed from numerous composite primary particles ~ZZ779 interlocked with one another substantially into globules rsnging from about 10 to~about 60 ~ in diameter.
The electron micro~cope of the primary particles derived from the above secondary particles givea the same result as in Fig. 3(B).
This structure or form sub~tantially conforms to that of secondary particles of tobermorite used 8S the starting material and shown in Fig. 6(A). This indicates that the composite particles retain the original structure or nature of the secondary particles of xonotlite despite the carbonation.
The composite secondary particles are dispersed in water to a concentration of 5 wt.%, and the dispersion : i~ allowed to stand after stirring for 20 minutes.
However, the psrticles are found inseparable by aettling into their components, namely amorphous silica and cslcium carbonate.
Subsequently, the composite secondsry particles - ~ sre immersed in a 6N HCl solution for one minute.
Simultaneously with the immersion, carbon dioxide gas evolves due to the conversion of the calcium carbonate in the primsry particles to calcium chloride. The particles sre then thoroughly washed with water to completely dissolve out the resulting calciu~ chloride.
The pa~ticles sre dried to give Opsil-II of thi~
invention.
~22`779 The x-ray diffraction of the Opsil-II thus prepared shows that the peaks due to calcium silicate crystals and those due to calcium carbonate have all disappeared. Thus the Opsil-II is found to be composed of amorphous silica.
~ he Opsil-II is observed under a scanning electron microscope at a magnification of 600X with ~ the result given in Fig. 6(C), which indicates that the particles of Opsil-II have substantially the same shape as the secondary particles of tobermorite and also as the composite secondary p~rticles of amrophou$ silica and calcium carbonate which retain the original s~ructure of the former particles.
The Opsil-II prepared a~ above is readily dispersible in water to give a filurry which in itself i~ shapable. The Opsil-II has the following properties.
Bulk density 0.0~ gfcm3 Specific surface area430 m2/g Specific ~urface ares 2 2~ after heating at 400 C380 m ~g Porosity 98 %
Heat resistRnce~o deformation at Oil adsorption980 cc/100 g Ch~mic~l an~lysis:
~i2 content 99.3 %
~L22'77!~
Example 8 The slurry Or calcium silicate (cs~n) crystAls obtained in Reference Example 3 is dewatered to a water to solids (CS~n crystals) ratio by weight of 5 : 1 and is then placed in a closed container. Carbon dioxide gas is forced into the container to maintain an internal pre~sure of 3 kg/cm2, and the slurIy is reacted for about 30 minutes.
The reaction gives composite secondary particles of amorphous silica and calcium carbonate.
The analysis of the secondary particles reveals that they have the same composition as the primary particles constituting them.
The x-ray diffraction of the particles further reveals that the peaks due to the calcium silicate c~ystflls prior to the carbonation have all disappeared but showing only the diffraction peaks (2~) of calcium carbonate at 23.0~, 24.8, 27.0, 29.4~ 3~8 and -~ ; 36Ø This evidences that the composite secondary particles are composed of amorphou~ silica and - calcium carbonate.
The composite secondary particles are further observed under a scanning electron microscope with the same result 8S those given in Figs. 5(B) and 6(B), showing that the composite secondary particles are formed from numerous composite primary particle~ interlocked with .
~Z2 7~7~
one another substantially into globules ranging from about 10 to about 60 ~ in diameter. The electron microscope of the primary particles derived from the above secondary particles gives the same result as `- 5 obtained by that of composite primary particles prepared in Example ~.
This structure or form substantially conforms to that of secondary particles of CS~n used as the starting material. This indicates that the composite particles retain the original structure or nature of the secondary particles despite the carbonation.
The composite secondary particles are dispersed in water to a concentration of 5 wt.%, and the dispersion i9 allowed to stand after stirring for 20 minutes.
However, the particles are found inseparable by settiing into their components, namely ~morphous silica and calcium carbonate.
Subsequently, the composite secondary particles are immersed in a 6N HCl solution for one minute.
Simultsneously with the immersion, carbon dloxide gas e~olves due to the conversion of the calcium carbonate in the primary particles to calcium chloride. The particle~ are then thoroughl~ washed with water to completel~ dissolve out the resulting calcium chloride.
The particles are dried to give Opsil-II of this invention.
~2;2 ~7~
The x-ray diffraction of the Opsil-II thus prepared shows that the peaks due to calcium silicate crystals and those due to cslcium carbonate have all disappeAred. Thus the Opsil-II is found to be composed of amorphous silica.
The Opsil-II is observed under a scsnning electron microscope with the same result as those given in ~igs. 5(C) and`6(C), which indicates that the particles of Opsil-II have substantially the same shape as the secondary particles of CSHn and also as the composite secondary particles of amorphous silic8 and calcium carbonate which retsin the original structure of the former particles.
The Opsil II prepared as above is readily dispersible in water to give a slurry which in itself i8 shapable. The Opsil-II has the following properties.
Bulk density 0.08 g/cm3 Specific surface area 550 m2/g ~ Specific surrace area After 2 heating at 400 C 480 m /g Porosity 96 %
Heat resistsnce No deformstion at 950 C
Oil sdsorption 750 cc/100 g Chemic~l annlysis:
SiO2 content 99.7 %
77 9i Example 9 ~he secondary particles of xonotlite crystal6 obtalned in Reference Exa~ple 1 are baked at 1~000 C for one hour into ~-wollastoni'e crystals, and the crystals are - 5 placed, in a water to solids (~-wollastonite crystals) ratio by weight of 5 : 1, in a closed container.
Carbon dioxide gas is forced into the container to maintain an internsl press;ure of 3 kg/cm2, and the slurry is reacted for about 30 minutes.
The reaction gives composite secondary particles of amorphous silica and calcium carbonate.
The analysis of the secondary particles reveals the following composition.
SiO2 36.00 %
~aO 33.58 %
A123 0.15 %
Fe203 0.35 %
_ Ig. loss 28.9? %
Totsl 99.0 %
The x-ray diffraction of the particles further reveals that the peaks due to the calcium silicate crystals prior to the carbonation have all disappeared b~t showing only the diffraction peaks (20) of calcium carbonate st 23.0, 24.8, 27.0, 29.4, 32.8 and 36Ø
This evidences that the composite secondary particles l~Z`7`7~
are composed of amorphous silica and calcium carbonate.
The composite secondary particles are further observed under a scanning electron microscope with the same result as those given in Figs. 5(B) and 6(B), showing that the composite secondary particles are formed from numerous composite primary particles interlocked with one aDother substantially into globules ranging from sbout 10 to about 60~in diameter. By the electron microscope the primary particles derived from the above i0 secondary particles are found to be formed of amorphous silica particles having the original configuration of the starting ~-wollastonite crystals and extremely fine particles of calcium carbonate attached thereto.
This structure or form substantially conforms to that of secondary particles of ~-wollastonite used as the starting material. This indicates that the composite particles retain the original structure or nature of the secondary particles of ~-wollastonite dçspite the carbonation.
The composite secondary particles sre dispersed in water to a concentration of 5 wt.~/o~ and the dispersion is allowed to stand after stirring for 20 minutes.
However, the particles are found inseparable by settling into their components, namely amorphous silica and calcium carbonate.
- 73 ~
112ZY~7~
Subsequnetly, the composite seeondary particles are immersed in a 6N HCl~solution for one minute.
Simultaneously with the immersion, carbon dioxide gas evolves due to the conversion of the calcium carbonate in the primary particles to calcium chloride. The particles are then thoroughly washed with water to completely dissolve out the resulting calcium chloride.
The particles are dried to give Opsil-II of this invention.
~he x-ray diffraction of the Opsil-II thus prepared shows that the peaks due to calcium silicate crystals and those due to calcium carbonate have all disappeared. Thus the Opsil-II is found to be composed of amorphous silica.
The Opsil-II is observed under a scanning - electron mic~oscope with the 6ame result as those given in Figs. 5(C) and 6(C), which indicates that ~he particles - of Opsil-II have substantially the same.shape as the secondary particles of ~-wollastonite and also as the composite secondsry particles of amorphou~ silica and calcium carbonate which retain the original structure of the former pàrticles.
~he Opsil-II prepared as above is readily d~spersible in wster to give a slurry which in itselr is shapable.
~t ~2~779 The analysis reveals the Opsil-Il has revealed the following result which indicates that the product is composed of silica of high purity.
SiO 99.4 %
A1203 0.25 %
CaO <0.01 %
(Ig. los~ 5.0 /o) ~he prop;erties of the Opsil-II are as follows.
BulX density 0 04 g/cm3 Specific surface area 280 m2/g Specific surface area 2 ~fter heating at 400 C 2-~0 m /g ~orosity 98 %
Heat resistance No deformation at Oil ad~orption 780 cc/100 g Exam~le 10 ~he xonotlite shaped body (bulk density: 0.2 g/cm3) obtained in Reference Example 1 i~ placed with water, ln a water ~ solid6 ratio by weight of 2:1> in a closed container. Carbon dioxide gas i~ forced into the container to maintain an internal pressure of ~ kg/cm2 for about 30 minute~ for carbonation.
~he reaction, followed by drying, gives a composite shaped body of amorphous silica and calcium carbonate.
A fractured ~urface of the shaped body is observed under a scanning electron microscope with the result given i~ Fig. 7(B), which shows that the shaped body has exactly the ~ame 8trusture as the start~ng material, i.e. xonotlite ~ 2`779 shaped body (Fig. 7(A)). It is found that the shaped body is formed from globular secondary particles which are compressed and interlocked with one another and firmly into an integral mass, the composite body thus retaining the original structure of the starting material intact.
Furthermore, the primary particles forming the ~econdary particles are found to have the same form as shown in Fig.
2(B) by electron microscopic observation and have the same diffraction peaks as shown in Figo l(B) according to x-ray 10- diffraction. Thus the product is a composite shaped body made up of needle-like particles of amorphous silica and extremely fine particles of calcium carbonate attached thereto.
Subsequently, the composite shaped body is immersed in a 6N HCl solution for one minute. Simultaneously with the immersion, carbon dioxide gas evolves and the calcium carbonate in the shaped body is converted to calcium chloride. The shaped body is then thoroughly washed wlth water to completely dissolve out the resulting calcium chloride and is thereafter dried to give Opsil-IIS of this invention.
X-ray diffraction confirms that the Opsil-IIS, like Opsil-I and Opsil-II, is amorphous.
Observation under a scanning electron microscope gives the result ~hown in Fig~ 7(C), indicating that in ~tructure the Opsil IIS substantially resembles the starting ~aterial~ namely xonotlite ~haped body (Fig. 7(A))~ and ~Z2779 the composite ~haped body obtained by carbonating the material (Fig. 7(B)). The substantially globular particles of Opsil-II, ranging from about 10 to about 60 ~ in diameter, are compressed and interlocked with one another, forming the integral body of the Opsil-IIS.
The Opsil-lIS prepared as above has the following properties.
Bulk density 0.09 g/cmZ
Specific surface area 288 m2/g Compre~sion strength 6 kg/cm2 Porosity 95%
The Opsil-IIS prepared as above, when fired in an electric oven at 1000 C for 1 hour, gives a contraction:
of about 12%, but no changes are observed in the compressed globular form of Opsil-II constituting the shaped body.
The propertie6 of the fired product are as follows.
Bulk density 0.085 g/cm2 Compression Strength 10 kg/cm2 ; Porosity 95%
The fired product has a thermal expansion coefficient of 5.7 x 10-7~C and exhibits substantially no expansion and contraction in repeated heating tests conducted at 950 C.
Further, Opsil-IIS having a bulk density of 0.3 g/cm2 i~ prepared in thO same manner as above except that a shaped body of xonotlite crystals having a bulk density of 0.62g/cm3, which is prepared in the same manner as in Reference Example 1 with increased ~haping pressure, is employed as a starting material. The Opsil-IIS is cut along a plane vertical to ~Z2~79 the direction of the shaping pressure. The scanning electron micrograph of the cut 6urface indicates that the Opsil-II constituting the shaped body ha6 been compressed with the lath-like Opsil-I particle6 oriented in a direction vertical to the direction of the pressure applied. Thls ~tructure is the same as that~of the starting xonotlite shs~ed body. The properties of Opsil_IIS are as follows:
BuIk density ~ 0.3 g/c Specific surface area 290 m2/g Compression strength 15 kg/cm2 Porosity 85%
Example 11 The tobermorite shaped body (bulk density: 0.3 g/cm3) obtained in Reference Example 2 is placed with water, in a water to solids ratio by weight of ~:1, in a closed container.
Carbon dioxide gas i6 forced into the container to maintain an internal pres6ure of 3 kg/cm2 for about 30 minutes for carbonation.
~ The reaction, followed by drying, give6 a composite shaped body of amorphous silica and calcium carbonate.
A fractured surface of the shaped body i6 observed under a scanning electron microscope with the same result as given in Fig. 7(B), which shows that the shaped body has exactly the 6ame 6tructure a6 the starting materi~l, i,e. tobermorite shaped body. It is found that the shaped body is formed from globular secondary particles which are compre6sed and interlocked with one another and firmly into an integral mass, the composite body thus retaining the original structure of the starting material intact.
l~Z;27~
Furthermore, the primary particles forming the fiecondary particles are found to have the same form as shown in Fig.
3(B) by electron microscopic observation and have the ~ame diffraction peaks peculiar to calcium carbonate according to x-ray diffraction. Thus the product is a composite shaped body made up of plate-like particles of amorphous silica and extremely fine particles of calcium carbonate attached thereto.
Subsequently, the composite ~haped body is immer~ed in a 6N HCl solution for one minute. Simultaneously with the immersion, carbon dioxide gas evolves and the calcium carbonate in the shaped body is converted to calcium chloride.
The shaped body is then thoroughly washed with water to completely dissolve out the resulting calcium chloride and is thereafter dried to give Opsil-IIS of this invention X-ray diffraction confirms that the Opsll-IIS, like Opsil-I and Opsil-II, is amorphous.
Observation under a scanning electron microscope gives the ~ame result as shown in Fig~ 7(C), indicating that in structure the Opsil-IIS substantially resembles the ~tarting material, namely tobermorite ~haped body and the composite shaped body obtained by carbonatin~ the material. The substantially globular particles of Opsil-II, ranging from about 10 to about 60 ~uin diameter, are compressed and interlocked with onè another forrning the integral body of the Opsil-IIS.
l~ZZ77g The Opsil-IIS prepared as above ha6 the following propertie~.
Bulk density 0.13 g/cm2 Specific surface area 2~7 m~/g Compression strength 4 kg/cm Porosity 93%
Example 12 The shaped body (bulk density: 0.3 g/cm3) of calcium silicate (CSHn) obtained in Reference Example 3 is placed with water in a water to solids ratio by weight of 2:1, in a closed container. Carbon dioxide gas is forced into the container to maintain an internal pressure of 3 kg/cm2 for about 30 minutes for `carbonation.
The reaction, followed by drying, gives a composite shaped body of amorphous silica and calcium carbonateO
A fractured surface of the shaped body is obser~ed under a scanning electron microscope with the same result as given in Fig. 7(B), which shows that the composite shaped body has exactly the same structure as the starting material, 20 ~ l.e. CSHn shaped body. It is found that the shaped body is formed form globular secondary particles which are compressed and interlocked with one another and firmly into an integral mass, the composite body thus retaining the original structure of the ~tarting material intact. Furthermore, the primary particles forming the secondary particles are found to have the same form as foil-like particle peculiar to CSHn by ~-- ~
electron microscopic observation and have the same diffraction peaks peculiar to calcium carbonàte according to x-ray diffraction. Thus the product is a composite shaped body made up of foil-like particles of amophous silica and 5 extremely fine particles of calcium carbonate attached thereto.
Subsequently, the composite shaped body is immersed in a 6N HCl solution for one minute. Simultaneou61y with - the immersion, car~bon dioxide gas evolves and the calcium carbonate in the shaped body is converted to calcium chloride.
The shaped body is then thoroughly washed with water to completely dissolve out the resulting calcium chloride and is thereafter dried to give Opsil-IIS of this invention.
X-ray diffraction confirms that the Opsil-IIS, like Opsil-I and Opsil-II, is amorphous.
Observation under a scanning electron microscope gives the same result as shown in Fig. 7(C), indicating that in structure the Opsil-IIS substantially resembles the starting material, namely CSHn shaped body and the composlts shaped ~ body obtained by carbonating the material. The substantially globular particles of Opsil-II, ranging from about 10 to about 60~, are compressed and interlocked with one another, forming the integ~al body of the Opsil-IIS.
The Opsil-IIS prepared as above has the following propertie~.
- 81 _ ~2Z~79 Bulk den~ity 0.14 g/cm2 Specific ~urface area 461 m2/g Compres~ion ~trength 4 kg/cm Poro~ity 82%
- 82 _ Example 13 The powder of Opsil~II (100 wt. parts) obtained in Example 6 and 2 wt. parts of glass fibers are dispersed in water to a water to solids ratio by weight of 10:1, to prepare a slurry. The slurry is placed in a mol,d, 40 mm x 120 mm x 150 mm, and then dewatered by a press. The shaped mass is removed from the mold and dried at 105 C for 24 hours to obtain a shaped body of this invention, i.e. Opsil~ , having the following, properties.
10 Bulk density 0.11 g/cm3 Bending strength 6 kg/cm2 Compression strength 9 kg/cm2 Porosity 93gO
Example 14 The Opsil-II obtained in Example 7 is shaped in the same manner as in Rxample 13 to prepare a shaped body of this invention, i.e. Opsil-IIS, having the following properties.
Bulk density 0.15 g/cm Bending strength 4.5 kg/cm2 20 Compression strength 7 kg/cm2 Porosity 91o Example 15 The Opsil-II obtained in Example 8 is shaped in the same manner as in Example 13 to prepare an Opsil-IIS of this invention having the following properties.
~lZZ779 Bulk density 0.21 g/cm3 Bending strengt~ 2.3 kg/cm2 Co~pression strength 4 kg/cm2 Porosity 88 /0 ~xample 16 The composite secondary particles of amorphous silica and calcium carbonate obtained by the first step of Example 6`are dispersed in water,-to a water to solids ratio by weight of 10 : 1. The resulting slurry . is placed in a mold, 40 mm x 120 mm x 150 mm, and dewatered and shaped by a press to prepare a composite shaped body of amorphous silica and calcium carbonate. The shaped body has the same structure as the composite shaped body described in Example 10.
In the same manner as in Example 10, the shaped body is immersed in a 6N HCl solution for acid treatment, then washed with water to completely dissolve out the calcium chloride formed and thereafter dried to obtain an Opsil-IIS Or this invention.
~ The Opsil-IIS has substantially the same structùre and form as the Opsil-IIS obtained in Example 10.
The properties of the Opsil-IIS are ~s follows.
Bulk density 0.13 g/cm3 Bending strength 5 kg/cm Compression strength 10 kg/cm2 Porosity 92 %
1~2;~77~
Example 17 The Opsil-I obtgined in Exa~ple 1 is disper~ed in water in a water to solids ratio by weight of 5 : 1.
The mixture is placed in a mold, dewatered and shaped by a press with varying shaping pressures, followed by drying. The physical properties of the shaped body (Opsil-IS) thus obtained are as follows.
; Sample No.
. Bulk density (g/cm3) 0.15 0.38 0.95 Bending st2rength4.2 18 0 43.2 (kg/cm ) ~ompression strength 7,3 23.5 61.0 (kg/cm2 ) Porosity ~/0) 92.5 61.0 52.5 Speci(fi~/s)rface340 338 330 .
Example 18 ~ he Opsil-I obtained in Example 2 i~ dispersed in water in a water to solids rstio by weight of 5 : 1.
The mixture is placed in a mold, dewatered and shaped by a press with varying shaping pressures, followed by drying. The physical properties of the sh~ped body ~Opsil-IS) thus obtained are as follows.
- o5 -l~Z~ 9 Sample No.
Bulk densi.ty (g/cm3) 0.13 0.50 Bending strength (kg/cm2) 4.0 25 ~ompression strength (kg/cm,2) 5.2 ~5 ~orosity ~/0) 93.5 75.0 Specific surface area (m /g) Example 19 Quick lime and siliceous sand powder in a CaO to SiO2 mole ratio of 0.98 : 1 are dispersed in water to prepare a slurry having a water to solids ratio by weight . 10 of 5 : 1. The slurry is swollen with stirring at 100 C
for 5 hours, then press-molded and thereafter subjected in an autoclave to hydrothermal reaction at 15 kg/cm2 at 200 D C for 10 hours to obtain a shaped body with a bulk density of 0.35 g/cm3.
The x-rsy diffraction of the shaped body reveals the diffraction peaks (2~) peculiar to xonotlite crystals st 12.7, 27.6 snd 29Ø Elementary analysis also confirms that the shsped body is composed of xonotlite crystals. When 8 fractured surface of the shaped body iS obser~ed under sn electron microscope, it is ascertained that the body is formed from numerous needle-like xonotlite crystals randomly three-dimensionally interlocked with one 77~
snother to an integrsl mass.
In the same manner as in Example 10, the s~aped bod~ of xonotlite is placed, in a water to solids ratio by weight of 2 : 1, in a closed container. Carbon dioxide gas is froced into the container at an internal pressure of ~ kg/cm for about 30 minutes.
The x-ray diffraction of the resulting shaped body shows exactly the same result as given in Fig. l(B), revealing the diffraction peaks due to calcium carbonate.
Observation under an electron microscope further shows that the shaped body retains the original structure of xonotlite shaped body used as the starting material.
Thus the product is identified as a composite shaped body of amorphous silica and calcium carbonate which comprises amorphous silica having the original configurQtion of the xonotlite crystals and extremel~ fine particles of calcium carbonate attached thereto.
In the same manner as in Example 10, the ~ composite shaped body is immersed in a 6N HGl solution Z for one minute, then thoroughl~ washed with water to completel~ dissolve out the resulting calcium chloride and thereafter dried, whereby an Opsil-IS of this invention is obtained.
The x-ra~ diffraction of the Opsil-IS shows the same result as given in Fig. l(C), indicating no diffraction peaks. The analysis of the product further 112~779 reveals that the SiO2 content is not lower than 99%, indicating that the Opsil-IS is composed of amorphous silica of high purity. The scanning electron micrograph of Fig. 8, showing a fractured surface of the Opsil-IS
at a magnification of l,OOOX, indicates that in structure the Opsil-IS is substantially indentical to the starting material,i.e. xonotlite shaped body, and to the composite shaped body of amorphous silica and calcium carbonate obtained-by carbonating the material. More specifically, the product is formed from the particles of amorphous silica (Opsil-I) which are randomly three-dimensionally interlocked with one another into an integral mass and which have at least two surfaces in s~mmetric relation, a length of about 1 to about 20 ~, a thickness f about 0.02 to about 0.1 ~ and a width of about 0.02 to about 1.0 ~, the length being at least about 10 times the thickness .
The Opsil-IS has the following properties.
Bulk den~ity 0.20 g/cm3 Specific surface area251 m2/g Compression strength 5 kg/cm Porosity 9 %
Example 20 Commercial autoclave light-weight cohcrete containing about 80 wt.% of tobermorite and about 20 wt.%
of guartz and having a bulk density of 0.63 ~/cm3 i8 ;
- ~2;277~
immersed in water for 1 hour and placed in a closed vessel.
The concrete is subJected to carbonation and acid treatment in the same manner as in Example 10, followed by drying, to obtain shaped body of the invention. X-ray diffraction shows only the diffraction peaks (2~) of quartz at 26.7~ and 20.8 D, This evidences that the tobermerite is converted to amorphous silica. The analysis shows the product contains SiO2 in a purity of not lower t~an 98 ~/c. The shaped body is cut along planes vertical and parallel to the direction of the shaping pressure. The scanning electron micrographs of the cut surfaces indicate that the shaped body is formed of numerous plate-like amorphous silica particles randomly three-dimensionally interlocked with one another and substantially circular pores of a diameter of less than 1 mm. The properties of the shaped body are as follows.
Bulk density 0.30 g/cm3 Specific surface area 301 m2/g 20~ Compression strength 12 kg/cm2 Porosity 85 %
- 89 - ~
The slurry of gyrolite crystals prepared above is placed in a mold, 40 mm x 120 mm x 150 mm, and dewatered and shaped by a press and dried to obtain a shaped body. The scan-ning electron micrograph showing a fractured surface of ~l~2277~
the shaped body resembles that of Fig. 7(A) and indicate6 that secondary particles of gyrolite are compressed and for~ed a~ interlocked with one another. The shaped body has a bulk density of 0.3 ~cm3, bending strength of about 8 kg/cm2 and a porosity of about 88.0%.
Reference Example 5 Quick lime is used aS a lime material and minus 350 mesh siliceous san~ powder (Tyler scale) a6 a siliceou~
material. The materials are dispersed in water in a CaO to SiO2 mole ratio of 2.0:1 to prepare a slurry having a water to solids ratio fo 4:1 by weight. The slurry i~ ~laced in an autoclave and subjected to hydrothermal reaction at a temperature of 191 C and a saturated vapor pressure of 12 kg/cm2 with heating for 5 hours to obtain a slurry of~ -dicalcum 6ilicate hydrate cry~tals.
The x-ray diffraction of the crystals shows diffraction peak6 (2~) at 16.6, 27.3 and 37.2 peculiar ~o~ -dicalcium 6ilicate hydrate crystals. The analysis by ignition of the crystals ~e~eals.the following composition.
SiO2 30.81%
CaO 57.02 A120~ 0.45 Fe2 3 Ig. loss 10.05 Total 99.05 _ L? _ 77~
The slurry of ~-dicalcium silicate hydra-te crystals is dried to obtain a fine white powder. Fig. 4(A) shows an electron ~lcrograph of the powder at a magnificatlon of 5,000X. The micrograph indicates that the ~-dicalcium silicate hydrate crystals are in the iorm of plate-like primary particles having a length o about 1 to about 300~ , a thickness of about 0.1 to about 1 ~ and a width of 1 to 30~ , the length being at least about 10 tirnes the thickness~
The crystals have a specific surface area of about 6 m2/g.
: .
-~ZZ77~
Example 1 The primary particles of lath-like xonotlite crystals obtained in Reference Example 1 are used as a starting material. The particles are placed in a pressure-resistant container of the closed type along with water 5 times the weight of the particles. Carbon dioxide gas is forced into the container at room temperature, and the particles are carbonated for about 30 minutes while maintaining the internal pressure at 3 kg/cm2, whereby 10- composite particles of amorphous silica and calcium carbonate are obtained.
The analysis by ignition of the composite particles reveals the following composition.
SiO2 36.04%
CaO 33.54 A123 0,18 Fe203 o~38 Ig. loss 28.87 ~ Total 99.11 The x-ray diffraction of the particles sho~Js the result given in Fig. l(B), which indicates that all the peaks peculiar to calcium silicate crystals seen in Fig. l(A) have disappeared and that only diffractlon peaks (2~) indicative of calcium carbonate crystals have appeared at 23.0, 29.4 and 36Ø This evidences that the calcium _ I~L. -~L~22`779 sillcate has been converted to amorphous silica and calcium carbonate due to carbonation.
The composite particles are further observed under an electron microscope with the result given in Fig. 2(B). The microscopic observation reveals that the composite particles comprise amorphous silica particles and extremely fine particles, up to about 2 ~ in size, of calcium carbonate attached to the amorphous silica -particles and that the particles of arnorphous silica have at least two surfaces in symmetric relation, a length of about 1 to about 20~ , a thickness of about 0.02 to about and a width of about 0.02 to about 1.0~ , the length being at least about 10 times the thickness. The configuration of the amorphous silica particles is exactly the same as that of lath-like xonotlite crystals (Fig. 2(A)), Thi5 indicates that the amorphous silica particles retain the original lath-like configuration of xonotlite.
The composite particles are dispersed in water ~ to a conc~ntration of 5 wt. %, and the dispersion is allowed -to stand after stirring for 20 minutes so as to separate the particles into the constituent silica and calcium carbonate by~settling utilizing the difference in specific gravity. However, the two components are found to be entirely inseparable and proved to be firmly joined together chemically or phys~cally.
~%%7~'3 Subsequently, the cornposite particles of amorphous silica and calcium carbonate are immersed in a 6~ ~Cl solution for one minute. With the evolution of carbon dioxide gas, the calcium carbonate in the primary particles is converted to carbon dioxide gas and calcium chloride. The acid-treated particles are then thoroughly washed with water to cornpletely dissolve out the resulting calcium chloride. The particles are dried to obtain Opsil-I of this invention.
The Opsil-I thus prepared is subjected to ignition dehydration and thereafter to analysis~ The result is given below which indicates that the product is composed of silica of high purity.
SiO2 99.1%
CaO < 0.01 (Ig. loss 5.0 ) The x-ray diffraction pattern of Opsil-I iG
~ glven in ~ig. l(C) which displays no peaks indicating the lath-like xonotlite crystals, the starting mate~ al, nor the peaks indicating the calcium carbonate contained in the co~posite particles resulting from the carbonation.
It is therefore confirmed that the Opsil-I is amorphous silica.
The Opsil-I i5 shown in the electron micrograph ~ ~Z2~79 of Fig. 2(C) which, exactly like Fi~s. 2(A) and 2(B), reveàls that the Opsil-I has a crystal]ine appearance and at least two surfaces in symmetric relation. The particles of Opsil-I are about 1 to about 20 f~in length, about 0,02 to about 0.1 ~ in thickness and about 0.02 to about 1.0/~ in width, the length being at least about 10 times the thickness and are ~n the form of primary particles. The appearance resembling lath-like crystals remains-free of any change even when the particles are treated with acid.
The properties of the Opsil-I obtained above are as follows.
Bulk density 0.05 g/cm3 Specific surface area 335 m2/g Oil adsorption 800 cc/100 g pH 6.5 ~he reference numeral (1) in Fig. 9 shows the pore size distribution of the Opsil-I ~ith the peak at 27 A.
Example 2 ~ ~he primary particles of plate-like tobermorite crystals obtained in Reference Example 2 are used as a starting material~ The particels are placed in a pressure-resistant container of the closed type along with water 5 times the ~eight of the particlesO Carbon dioxide gas is forced into the container at room temperature, and the Z5 particles are carbonated for about 30 minutes while maintaining ~æz~79 the internal pressure at 3 kg/cm2, whereby composite particles of amorphous silica and calcium carbonate are obtained.
The analysis by iginition of the composite particles reveals the following composition.
SiO2 39.77%
CaO 31.43 A123 0.24 ~ 2 3 Ig. loss 27.42 Total 99.26 The x-ray difiraction of the particles shows the same result as given in Fig. l(B), which indicates that all the peaks peculiar to tobermorite crystals, the starting material, have disappeared and that only diffraction peaks (2~ indicative of calcium carbonate crystals have appeared at 23.0, 24~8, 27.0, 29.4, 32.8 and 36.o. This evidences that the calcium silicate has been converted to amorphous silica and calcium carbonate due to carbonation, ~ The composite particles are further observed ZO under an electron microscope with the result given in Fig. 3(B). The microscopic observation reveals that the composite particles comprise amorphous silica particles and extremely fine particles, up to about 2f~ in size~ of calcium carbonate attached to the amorphous silica particles and that the ~l~.;22779 particles of amorphous silica have at least -t~Jo ;urfaces in symmetric relation, a length of about 1 to about 20~ , a thickness of about 0.02 to about Ool~ and a ~idth of about 0.2 to about 5.0~ , the length being at least about 10 times the thickness. The configuration of the amorphous sllica particles is exactly the same as that of plate-like tobermorite crystals (Fig. 3(A)). This indicates that the amorphous silica particles retain the original plate-like configuration of tobermorite.
The composite particles are dispersed in ~Jater to a concentration of 5 wt. %, and the disper~ion is allowed to stand after stirring for 20 minutes so as to separate the particles into the constituent silica and calcium carbo~ate by settling utllizing the difference in specific gravity. However, the two components are found to be entirely inseparable a~d proved to be firmly joined to~ether chemically or physicallyO
Subsequently, the composite particles of amorphous ~ silica and calcium carbonate are immersed in a 6N HCl Eolution for one minute. ~ith the evolution of carbon dioxide gas, the calcium carbonate in the primary particles is converted to carbon dioxide gas and calcium chloride.
The acid_treated particles are then thoroughly washed with water to completely ~issolve out the re~ulting calcium chloride. The particles are dried to obtain Opsil-I of ~2Z~77~
this invention.
The Opsil-I thus prepared is subjected to iynition dehydration and thereafter to analysis. The result is given below which indicates that the product is composed of silica of high purity.
SiO2 99.3%
A123 0.23 CaO < 0.01 (Ig . loss4.7`) The x-ray diffraction pattern of Opsil-I is the same as in Fig. l(C) which displays no peaks indicating the plate-like tobermorite crystals, the starting material, nor the peaks indicating the calcium carbonate contained in the composite particles resulting from the carbonation. The Opsil-I is a-morphous silica.
The Opsil-I is shown in the electron microgragh of Fig. 3(C) which, exactly like Figs. 3(A) and 3(B), reveals that the Opsil-I has a crystalline appearance and at least two surfaces in symmetric relation. The particles of Opsil-I are about 1 to 20~ in length, about-0.02 to about 0.1~ in thickness and about 0.2 to about 5.0u in width, the length being at least about 10 times the thickness and are in the form of primary particles. The crystalline appearance remains free of any change even when the particles are treated with acid.
, .
~ZZ~79 The properties of the Opsil-I obtained above are as follows.
Bulk density 0.04 g/cm3 Specific surface area 277 m2/g Oil adsorption 750 cc/100 pH 6.7 The reference numeral (2) in Fig. 9 sho~s the pore size distribu~ion Or the Opsil-I v~ith the peal~ at 23 A.
Example 3 The primary particles OI calcium silicate (CSHn) in the form of foil-like crystals obtained in Reference Example 3 are used as a starting material. The particles are placed in a pressure-resi~tant container of the closed type along with water 5 times the weight of the particles.
Carbon dioxide gas is forced into the container at room temperature, and the particles are carbonated for about 30 minutes while maintaining the internal pressure at 3 kg/cm2~ whereby composite particles of amorphous 5ilica and calci~m carbonate are obtained.
Thé analysi~ by ignition of the composite particles reveals the following composition.
SiO2 ~9.98%
CaO 37-59 ~e23 0.27 Ig. loss 31,28 ~otal 99.51 ~;Z77g The x-ray diffraction of the particles shows the same result as given in Fig. l(B), ~.~hich indicates that all the peaks peculiar to CSHn crystals, the starting material, have disappeared and that only diffraction peaks (2~) indicative of calcium carbonate crystals have appeared at 23.0, 24.8, 27.0, 29.4, 32.8 and 36.o~ This evidences that the calcium ~ilicate has been converted to amorphous silica and calcium-carbonate due to carbonation.
The composite particles are further observed under an electron microscope with the result that the composite particles co~prise amorphous silica particles and extremely fine particles, up to about 2f1 in size, of calcium carbonate attached to the amorphous silica particles and that the particles of amorphous ~ilica have at least two surfaces in symmetric relation, a length of about 1 to about 5~ ~ a thickness of about 0.01 to about OAO2~ and a width of about 0.01 to about s.n~, the length being at least about 50 time~ the thickness. The configuration of the amorphous sllica particles i_ e~actly the same as that of Z0 foil-like CSHn crystals. This indicates that the amorphous silica particles retain the original foil-like configuration of CSHn.
The composite particles are dispersed in water to a concentration of 5 wt. %, and the di~per~,ion iG allowed to stand after stirring for Z0 minute~ 'JO a:; to separate 1~2~7~
the particles into the constituent silica and calcium carbonate by settling utilizing the difference in specific gravity.
However, the two components are found to be entirely inseparable and proved to be firmly joined together chemi-cally or physically.
Subsequently, the composite particles of amorphous silica and calcium carbonate are immersed in a 6N HCl solution for one minute. With the evolution of carbon dioxide gas, the calcium carbonate in the primary particles 0 i6 converted to carbon dioxide gas and calcium chloride.
The acid-treated particles are then throughly ~ashed ~ith water to completely di~solve out the re~ulting calcium chloride. The particles are dried to obtain Opsil-I of this invention.
The Opsil-I thus prepared is subjected to ignition dehydratlon and thereafter to analysis. The result i~ given beloY~ which indicatas that the product is ~omposed of sillca of high purity.
SiO2 99-7%
CaO ~ o.o~
(Ig. loss 5.1 ) The x-ray diffraction pattern of Op~ I i5 the same as ln Fig. 1 (C) ~hich displays no peak~. indicatin~
the foil-like CSHn crystal , the starting material, nor the peaks indicating the ealcium carbonate contained in _ 53 _ ~l~2Z779 the composite particles reGulting from the carbonation.
The Opsil-I is amorphous silica.
Observation of electron micrograph reveals t`nat the Opsil-I has a crystalline appearance and at least two surfaces in symmetric relation. The particles of Opsil-I
are about 1 to ~bout 5 ~in length3 about 0.01 to about 0.02yin thickness and about 0.01 to about ~.0 ~'in width, the length being at least about 50 times the thickness and are in the form of primary particles. The crystalline appearance remains free of any change even when the particles are treated with acid.
The properties of the Opsil-I obtained above are as follows~
Bulk density 0.07 g/cm3 Specific surface area 461 m2/g Oil adsorption 470 cc/100 g pH 6.5 The rcference numeral (3) in Fig. 9 shows the pore size distribution of the Opsil~ ith the peak at about 30 A and about 180 A~
Example L~
The primary particles of plate-like gyrolite crystal~ obtained in ~eference Example 4 are used as a starting material. The particle are placed in a pressure-resistant container of the clo ed type alonG with ~ater l~Z2~77~
5 times the weight of the particles. Carbon dioxide gas is forced into the container at room temperature, and the particles are carbonated for about 30 minutes while maintain-ing the internal pressure at 3 kg/cm2, whereby composite particles of amorphous silica and calcium carbonate are obtained.
The analysis by ignition of the composite particles reveals t`he following composition.
Si 2 4O . 22%
CaO 26.07 Fe23 0 . 25 Ig. loss 24. 33 Total 99.20 The x-ray diifraction of the particles shows the same result as given in Fig. l(B), which indic~tes that all the peaks peculiar to calcium silicate crystals~ the starting material, have disappeared and that only diffraction peaks (20) indicative of calcium carbonate crystals have ZO appeared at 23.0, 24.8, 27.0~ 29.4~ 32.8 and 36Ø
This evidences that the calcium silicate ha~ been converted to amorphou~ silica and calcium carbonate due to carbonation.
The composite particles are further observed under an electron mlcroscope with the result that the composite particles comprise amorphous ;ilica particles - ~22~7~
and extremely fine particles, up to about 2 ~ in size, of calcium carbonate attached to the amorphous silica particles and that the particles of amorphous silica have at least two surfaces in symmetric relation, a length of about 1 to about 20 ~, a thickness of about 0.02 to about 0.1 ~ and a width of about 0.2 to about 5/~ the length being at least about 10 ti~es the thickness. The configuration of the amorphous silica particles is exactly the same as that o~ plate-like gyrolite crystals. This indicates that the amorphous silica particles retain the original plate-like configuration of gyrolite.
The composite particles are dispersed in water to a concentration of 5 wt. %, and the dispersion is allowed to stand after stirring for 20 minutes so as to separate the particles into the con~tituent silica and calcium carbonate by settling utilizing the difference in specific grav~ty. However, the two components are found to be entirely inseparable and proved to be firmly joined together chemically or physically.
Subsequently, the composite particles of amorphous silica and calcium carbonate are immersed in a 6N HCl solution for one minute. ~ith the evolution of carbon dioxide ga, the calcium carbonate in the pr~mary particles is converted to carbon dioxide ~as and calcium chloride.
Z5 Th~ acid-treated particles are then thoroughly ~ashed v~ith ~ 2Z779 water to completely dissolve out the resulting calcium chloride. The particles are dried to obtain Opsil I of this invention.
The Opsil-I thus prepared is subjected to ignition dehydration and thereafter to analysis. The result is given below which indicates that the product is composed of silica of high purity.
SiO ` 99 4%
CaO C 0.01 (Ig. loss 5.8 ) The x-ray diffraction pattern of Opsil-I is the same as in Fig. l(C) which displays no peaks indicating the plate-like gyrolite crystals~ the starting material, nor the peaks indicating the calcium carbonate contained in the composite particles resulting from the carbonation.
The Opsil_I is amorphous silica.
Ob~ervation of electron micrograph reveals that the `~ Opsll_I has a crystalline appearance and at least two ~urfaces in symmetric relation. The particles of Opsil-I are about 1 to about 20 ~in length, about 0.02 to about 0.1~ in thickness and about 0.2 to about 5/~in width, the length being at least about 10 times the thickness and are in the form of prlmary particles. The crystalline appearance remains free of any change even when the particles are treated with acld.
` ~ The propeirtie6 of the Opsil-I obtained above are as follows.
Bulk dens~ty 0.065 g/cm3 ; Specific surface area 285 m2/g ; i Oil adsorption 530 cc/100 g - pH 6.3 The reference numeral ~4) in Fig. 9 shows the pore size distribution of pore diameters of the Opsil-I
10; with the peak at 28 ~.
Example 5 The primary particles of plate-like ~-dicalcium - silicate hydrate crystals obtained in Reference Example 5 are used as a starting material. The particles are placed in a pressure-resistant container of the closed type along with water 5 times the weight of the particles.
; Carbon dioxide gas is forced into the container at room temperature~ and the particles are carbonated for about 30 minutes while maintaining the internal pressure at 3 kg/cm2, ~hereby composite particles of amorphous silica and calcium carbonate are obtained, ' The analysiG by ignition of the composite particles reveal$ the following composition.
i, SiO2 22.8~
. CaO 42.24 A1203 0.31 Fe23 -33 . Ig. lofi~ 34.50 ?
'. A . ; _ i ' ; . Total 100. 24 . The x-ray diffraction of the particles shows the ~; . same result as given in Fig. l(B)~ which indicates that - - all the peaks peculiar to calcium silicate crystals, the - 10 - . starting material, have disappeared and that only diffraction . peaks (2e) indicative of calcium carbonate crys~als have ..
. appeared at 23.0, 24.8, 27.0, 29.4, 32.8 and 36Ø
This evidences that the calcium silicate has been converted .. .. ..
- ~ to amorphous silica and calcium carbonate due to carbonation.
:. 15 ; The composite particles are further observed ; under an electron microscope with the result that the i composite particles comprise amorphous silica particels .: and extremely fine particles, up to about 2~ in size~
t -~ ., j' of calcium carbonate attached to the amorphous silica Y
i; 20 particles and that the particles of amorphous silica ha~e at least two surfaces in ~ymmetric relation~ a length of about 1 to about 300~4~ a thickness of about 0~1 to about -;! ' 1 ~ and a width of about 1 to about 30~ ~ the length being at le~st abo~t 10 times the thickness. The configuration of the . 25 amorphous silica particles is exactly the s~me at that of :,, .
.; ~, ' ', .
. , , ~
, Z ~ 7 9 plate-like ~-dicalcium silicate hydrate crystals (Fig.
4~A)). This indicates that the amorphous silica particles retain the original plate-like configuration of the crystals.
The composite particles are dispersed in water ' 5 to a concentration of 5 wt. %, and the dispersion is .. . ..
allowed to stand after stirring for 20 minutes so as to separate the particles into the constituent silica and calcium carbonate by settling utilizing the difference in specific gravity. However, the two components are found ~ to be entirely inseparable and proved to be firmly joined together chemically or physically.
Subsequently, the composite particles of amorphous silica and calcium carbonate are immersed in a 6N HCl - solution for one minute. With the evolution of carbon dioxide gas, the câlcium carbonate in the primary particles i . . .
is converted to carbon dioxide gas and calcium chloride.
The acid-treated particles are then thoroughly washed with water to completely dissolve out the resulting calcium chloride. ~he particles are dried to obtain Opsil_I of thls invention.
The Opsil-I thus prepared is subjected to ignition dehydration and thereafter to analysis. The re~ult is given below which indicates that the product is composed of silica of high purity.
~Z77~
SiO2 99.6%
A123 0.12 CaO < 0.01 (Ig. loss 5.2 ) The x-ray diffraction pattern of Opsil-I is the same as in Fig. l(C) which displays no peaks indicating the plat2-like ~-dicalcium silicate crystals, the starting material, nor the peaks indicating the calcium carbonate contained in the com-posite particles resulting from the carbonation~ The Opsil-I is amorphous silica.
The Opsil-I is shown in the electron micrograph of Fig. 4(B) which reveals that the Opsil-I has a crystalline appearance and at least two surfaces in symmetric relation.
The particles of Opsil-I are about 1 to about 300~ in length, about 0.1 to about 1~ in thickness and about 1 to about 30~ in width, the length being at least about 10 times the thickness and are in the form of primary particles. The crystalline appearance remains free of any change even when the particles are treated with acid.
The properties of the Opsil-I obtained above are as follows.
Bulk density 0.15 g/cm3 Specific surface area 550 m2/g Oil adsorption 340 cc/100 g pEI 7.1 ~2'~`779 The reference numeral (5) in ~i~, 9 ~ho~ the pore size distribution Or t~le ~psil-I with the peak at 24 ~.
2~
Exam~le 6 The slurry of xonotlite crystals obtained in Reference Example 1 is dewatered to a water to solids (xonotlite crystals) ratio b~ weight of 5 : 1 and is then placed in a closed container. Carbon dioxide gas is forced into the container to maintain an internal pressure of 3 kg/cm , and the slurry is reacted for about 30 minutes.`
The reaction gives composite secondary particles of amorphous silica and calcium carbonate.
The analysis of the secondary particles reveals that they have the same composition as the primary particles constituting them.
. . .
; , The x-ra~ dilfraction of the particles further reveals the same result as given in ~ig. l(B), indicating that the peaks due to the calcium silicate crystals prior to the carbonation have all disappegred but showing - only the diffraction peaks (20) of calcium carbonate at -- :~ 23.0, 2~4 and ~6Ø This evidences that the - 20 composite secondary particles are composed of amorphous silica and calcium carbonate.
The composite secondary particles are lurther observed under a scanning electron microscope at a magnification of 600X with the result given in ~ig. 5(B), which shows that the composite secondary particles are .. . .
, - 63 - ~
1~22779 formed from numerous composite primary particle~
interlocked with one ano~ther substantially into globules ranging from about 10 to about 60 ~ in diameter. The electron microscope of the primary particles derived from the above secondary particles gives the same result as in Fig. 2(B).
~ his structure or form substantially conforms to that of second~r~ particles of xonotlite used as the starting material and shown in Fig. 5(A). This I~ indicates that the composite particles retain the original structure or nature of the secondary~particles of xonotlite despite the carbonation.
~he composite secondary particles are - dispersed in water to a concentration of 5 wt.%, and the disper~ion is allowed to stand after stirring for 20 minutes. However, the particles are found inqeparable by settling into their components, namely amorphoUS silica and calci~m carbonate.
; ~ Subsequently, the composite secondary particles are immersed in a 6N HCl solution for one minute.
~imultaneously with the immersion, carbon dioxide gas evolves due to the conversion of the calcium carbonate .
- iD the primary particles to calcium chloride. The p~rticles sre then thoroughly washed with water to completely dissolve out the resulting calcium chloride.
The particles are dried to give Opsil-II of this ~L~.2Z'77~
i nvention.
~ he x-ray diffraction of the Opsil-II thus prepared exhibits the same result as in Fig. l(C), showing that the peaks due to calcium ~ilicate crystals snd those due to calcium carbonate have 811 disappeared.
Thus the Opsil-II is found to be composed of amorphous silica.
~ he Opsil-II i8 observed under a scanning electron microscope at a magnification of 2,000X with the result given in Fig. 5(C), which indicates that the particles of Opsil-II have 6ubstantially the same shape as the secondary particles of xonotlite and also as the composite secondary particles of amorphous silica and calcium carbonate which retain the original structure of the former particles.
~ he Opsil-II prepared as sbsve is readil~
dispersible in water to give a slurry which in itself is shapable~ The Opsil~II hss the following properties.
; ~ulX densit~ 0.04 g/cm3 Specific surfsce area 400 m2/g Specific surface ares 2 after heating at 400 C 350 m /g Poro 8i ty 98 ~
Heat resistance No deformation at Oil adsorption 1,100 cc/100 g Chemical analysis:
SiO2 content 99.1 %
~2;~779 Example 7 The slurry of tobermorite cry~tals obtained in Reference ~xample 2 is dewatered to a water to qolids (kobermorite crystals) ratio by weight of 5 : 1 and i8 then placed in a closed container~ Carbon dioxide - gas is forced into the container to maintain an internal pressure of 3 kg/cm2, and the slurry is reacted for about ~0 minutes.
The reaction gives composite secondary - particles of amorphous silica and calcium carbonate.
The analysis of the secondary particlea reveals that they have the same composition as the primary particles constituting them.
The x-ray diffraction of the particles further 15 , reveals that the peaks due to the calcium silicate crystals prior to the carbonation have 811 disappeared but showing only the diffraction peaks (2~) of cslcium c8rbonate at 23.0~, 24.8, 27.0, 29.4~ 32.8 and ~6Ø
~ This evidences thst the composite secondary particles sre composed of amorphous silica and calcium carbonate.
The composite secondary particles sre further observed under a scanning electron microscope at a m~gnification of 600X with the result given in ~ig. 6(B), which ~ho~s that the composite secondary particles are - 25 formed from numerous composite primary particles ~ZZ779 interlocked with one another substantially into globules rsnging from about 10 to~about 60 ~ in diameter.
The electron micro~cope of the primary particles derived from the above secondary particles givea the same result as in Fig. 3(B).
This structure or form sub~tantially conforms to that of secondary particles of tobermorite used 8S the starting material and shown in Fig. 6(A). This indicates that the composite particles retain the original structure or nature of the secondary particles of xonotlite despite the carbonation.
The composite secondary particles are dispersed in water to a concentration of 5 wt.%, and the dispersion : i~ allowed to stand after stirring for 20 minutes.
However, the psrticles are found inseparable by aettling into their components, namely amorphous silica and cslcium carbonate.
Subsequently, the composite secondsry particles - ~ sre immersed in a 6N HCl solution for one minute.
Simultaneously with the immersion, carbon dioxide gas evolves due to the conversion of the calcium carbonate in the primsry particles to calcium chloride. The particles sre then thoroughly washed with water to completely dissolve out the resulting calciu~ chloride.
The pa~ticles sre dried to give Opsil-II of thi~
invention.
~22`779 The x-ray diffraction of the Opsil-II thus prepared shows that the peaks due to calcium silicate crystals and those due to calcium carbonate have all disappeared. Thus the Opsil-II is found to be composed of amorphous silica.
~ he Opsil-II is observed under a scanning electron microscope at a magnification of 600X with ~ the result given in Fig. 6(C), which indicates that the particles of Opsil-II have substantially the same shape as the secondary particles of tobermorite and also as the composite secondary p~rticles of amrophou$ silica and calcium carbonate which retain the original s~ructure of the former particles.
The Opsil-II prepared a~ above is readily dispersible in water to give a filurry which in itself i~ shapable. The Opsil-II has the following properties.
Bulk density 0.0~ gfcm3 Specific surface area430 m2/g Specific ~urface ares 2 2~ after heating at 400 C380 m ~g Porosity 98 %
Heat resistRnce~o deformation at Oil adsorption980 cc/100 g Ch~mic~l an~lysis:
~i2 content 99.3 %
~L22'77!~
Example 8 The slurry Or calcium silicate (cs~n) crystAls obtained in Reference Example 3 is dewatered to a water to solids (CS~n crystals) ratio by weight of 5 : 1 and is then placed in a closed container. Carbon dioxide gas is forced into the container to maintain an internal pre~sure of 3 kg/cm2, and the slurIy is reacted for about 30 minutes.
The reaction gives composite secondary particles of amorphous silica and calcium carbonate.
The analysis of the secondary particles reveals that they have the same composition as the primary particles constituting them.
The x-ray diffraction of the particles further reveals that the peaks due to the calcium silicate c~ystflls prior to the carbonation have all disappeared but showing only the diffraction peaks (2~) of calcium carbonate at 23.0~, 24.8, 27.0, 29.4~ 3~8 and -~ ; 36Ø This evidences that the composite secondary particles are composed of amorphou~ silica and - calcium carbonate.
The composite secondary particles are further observed under a scanning electron microscope with the same result 8S those given in Figs. 5(B) and 6(B), showing that the composite secondary particles are formed from numerous composite primary particle~ interlocked with .
~Z2 7~7~
one another substantially into globules ranging from about 10 to about 60 ~ in diameter. The electron microscope of the primary particles derived from the above secondary particles gives the same result as `- 5 obtained by that of composite primary particles prepared in Example ~.
This structure or form substantially conforms to that of secondary particles of CS~n used as the starting material. This indicates that the composite particles retain the original structure or nature of the secondary particles despite the carbonation.
The composite secondary particles are dispersed in water to a concentration of 5 wt.%, and the dispersion i9 allowed to stand after stirring for 20 minutes.
However, the particles are found inseparable by settiing into their components, namely ~morphous silica and calcium carbonate.
Subsequently, the composite secondary particles are immersed in a 6N HCl solution for one minute.
Simultsneously with the immersion, carbon dloxide gas e~olves due to the conversion of the calcium carbonate in the primary particles to calcium chloride. The particle~ are then thoroughl~ washed with water to completel~ dissolve out the resulting calcium chloride.
The particles are dried to give Opsil-II of this invention.
~2;2 ~7~
The x-ray diffraction of the Opsil-II thus prepared shows that the peaks due to calcium silicate crystals and those due to cslcium carbonate have all disappeAred. Thus the Opsil-II is found to be composed of amorphous silica.
The Opsil-II is observed under a scsnning electron microscope with the same result as those given in ~igs. 5(C) and`6(C), which indicates that the particles of Opsil-II have substantially the same shape as the secondary particles of CSHn and also as the composite secondary particles of amorphous silic8 and calcium carbonate which retsin the original structure of the former particles.
The Opsil II prepared as above is readily dispersible in water to give a slurry which in itself i8 shapable. The Opsil-II has the following properties.
Bulk density 0.08 g/cm3 Specific surface area 550 m2/g ~ Specific surrace area After 2 heating at 400 C 480 m /g Porosity 96 %
Heat resistsnce No deformstion at 950 C
Oil sdsorption 750 cc/100 g Chemic~l annlysis:
SiO2 content 99.7 %
77 9i Example 9 ~he secondary particles of xonotlite crystal6 obtalned in Reference Exa~ple 1 are baked at 1~000 C for one hour into ~-wollastoni'e crystals, and the crystals are - 5 placed, in a water to solids (~-wollastonite crystals) ratio by weight of 5 : 1, in a closed container.
Carbon dioxide gas is forced into the container to maintain an internsl press;ure of 3 kg/cm2, and the slurry is reacted for about 30 minutes.
The reaction gives composite secondary particles of amorphous silica and calcium carbonate.
The analysis of the secondary particles reveals the following composition.
SiO2 36.00 %
~aO 33.58 %
A123 0.15 %
Fe203 0.35 %
_ Ig. loss 28.9? %
Totsl 99.0 %
The x-ray diffraction of the particles further reveals that the peaks due to the calcium silicate crystals prior to the carbonation have all disappeared b~t showing only the diffraction peaks (20) of calcium carbonate st 23.0, 24.8, 27.0, 29.4, 32.8 and 36Ø
This evidences that the composite secondary particles l~Z`7`7~
are composed of amorphous silica and calcium carbonate.
The composite secondary particles are further observed under a scanning electron microscope with the same result as those given in Figs. 5(B) and 6(B), showing that the composite secondary particles are formed from numerous composite primary particles interlocked with one aDother substantially into globules ranging from sbout 10 to about 60~in diameter. By the electron microscope the primary particles derived from the above i0 secondary particles are found to be formed of amorphous silica particles having the original configuration of the starting ~-wollastonite crystals and extremely fine particles of calcium carbonate attached thereto.
This structure or form substantially conforms to that of secondary particles of ~-wollastonite used as the starting material. This indicates that the composite particles retain the original structure or nature of the secondary particles of ~-wollastonite dçspite the carbonation.
The composite secondary particles sre dispersed in water to a concentration of 5 wt.~/o~ and the dispersion is allowed to stand after stirring for 20 minutes.
However, the particles are found inseparable by settling into their components, namely amorphous silica and calcium carbonate.
- 73 ~
112ZY~7~
Subsequnetly, the composite seeondary particles are immersed in a 6N HCl~solution for one minute.
Simultaneously with the immersion, carbon dioxide gas evolves due to the conversion of the calcium carbonate in the primary particles to calcium chloride. The particles are then thoroughly washed with water to completely dissolve out the resulting calcium chloride.
The particles are dried to give Opsil-II of this invention.
~he x-ray diffraction of the Opsil-II thus prepared shows that the peaks due to calcium silicate crystals and those due to calcium carbonate have all disappeared. Thus the Opsil-II is found to be composed of amorphous silica.
The Opsil-II is observed under a scanning - electron mic~oscope with the 6ame result as those given in Figs. 5(C) and 6(C), which indicates that ~he particles - of Opsil-II have substantially the same.shape as the secondary particles of ~-wollastonite and also as the composite secondsry particles of amorphou~ silica and calcium carbonate which retain the original structure of the former pàrticles.
~he Opsil-II prepared as above is readily d~spersible in wster to give a slurry which in itselr is shapable.
~t ~2~779 The analysis reveals the Opsil-Il has revealed the following result which indicates that the product is composed of silica of high purity.
SiO 99.4 %
A1203 0.25 %
CaO <0.01 %
(Ig. los~ 5.0 /o) ~he prop;erties of the Opsil-II are as follows.
BulX density 0 04 g/cm3 Specific surface area 280 m2/g Specific surface area 2 ~fter heating at 400 C 2-~0 m /g ~orosity 98 %
Heat resistance No deformation at Oil ad~orption 780 cc/100 g Exam~le 10 ~he xonotlite shaped body (bulk density: 0.2 g/cm3) obtained in Reference Example 1 i~ placed with water, ln a water ~ solid6 ratio by weight of 2:1> in a closed container. Carbon dioxide gas i~ forced into the container to maintain an internal pressure of ~ kg/cm2 for about 30 minute~ for carbonation.
~he reaction, followed by drying, gives a composite shaped body of amorphous silica and calcium carbonate.
A fractured ~urface of the shaped body is observed under a scanning electron microscope with the result given i~ Fig. 7(B), which shows that the shaped body has exactly the ~ame 8trusture as the start~ng material, i.e. xonotlite ~ 2`779 shaped body (Fig. 7(A)). It is found that the shaped body is formed from globular secondary particles which are compressed and interlocked with one another and firmly into an integral mass, the composite body thus retaining the original structure of the starting material intact.
Furthermore, the primary particles forming the ~econdary particles are found to have the same form as shown in Fig.
2(B) by electron microscopic observation and have the same diffraction peaks as shown in Figo l(B) according to x-ray 10- diffraction. Thus the product is a composite shaped body made up of needle-like particles of amorphous silica and extremely fine particles of calcium carbonate attached thereto.
Subsequently, the composite shaped body is immersed in a 6N HCl solution for one minute. Simultaneously with the immersion, carbon dioxide gas evolves and the calcium carbonate in the shaped body is converted to calcium chloride. The shaped body is then thoroughly washed wlth water to completely dissolve out the resulting calcium chloride and is thereafter dried to give Opsil-IIS of this invention.
X-ray diffraction confirms that the Opsil-IIS, like Opsil-I and Opsil-II, is amorphous.
Observation under a scanning electron microscope gives the result ~hown in Fig~ 7(C), indicating that in ~tructure the Opsil IIS substantially resembles the starting ~aterial~ namely xonotlite ~haped body (Fig. 7(A))~ and ~Z2779 the composite ~haped body obtained by carbonating the material (Fig. 7(B)). The substantially globular particles of Opsil-II, ranging from about 10 to about 60 ~ in diameter, are compressed and interlocked with one another, forming the integral body of the Opsil-IIS.
The Opsil-lIS prepared as above has the following properties.
Bulk density 0.09 g/cmZ
Specific surface area 288 m2/g Compre~sion strength 6 kg/cm2 Porosity 95%
The Opsil-IIS prepared as above, when fired in an electric oven at 1000 C for 1 hour, gives a contraction:
of about 12%, but no changes are observed in the compressed globular form of Opsil-II constituting the shaped body.
The propertie6 of the fired product are as follows.
Bulk density 0.085 g/cm2 Compression Strength 10 kg/cm2 ; Porosity 95%
The fired product has a thermal expansion coefficient of 5.7 x 10-7~C and exhibits substantially no expansion and contraction in repeated heating tests conducted at 950 C.
Further, Opsil-IIS having a bulk density of 0.3 g/cm2 i~ prepared in thO same manner as above except that a shaped body of xonotlite crystals having a bulk density of 0.62g/cm3, which is prepared in the same manner as in Reference Example 1 with increased ~haping pressure, is employed as a starting material. The Opsil-IIS is cut along a plane vertical to ~Z2~79 the direction of the shaping pressure. The scanning electron micrograph of the cut 6urface indicates that the Opsil-II constituting the shaped body ha6 been compressed with the lath-like Opsil-I particle6 oriented in a direction vertical to the direction of the pressure applied. Thls ~tructure is the same as that~of the starting xonotlite shs~ed body. The properties of Opsil_IIS are as follows:
BuIk density ~ 0.3 g/c Specific surface area 290 m2/g Compression strength 15 kg/cm2 Porosity 85%
Example 11 The tobermorite shaped body (bulk density: 0.3 g/cm3) obtained in Reference Example 2 is placed with water, in a water to solids ratio by weight of ~:1, in a closed container.
Carbon dioxide gas i6 forced into the container to maintain an internal pres6ure of 3 kg/cm2 for about 30 minutes for carbonation.
~ The reaction, followed by drying, give6 a composite shaped body of amorphous silica and calcium carbonate.
A fractured surface of the shaped body i6 observed under a scanning electron microscope with the same result as given in Fig. 7(B), which shows that the shaped body has exactly the 6ame 6tructure a6 the starting materi~l, i,e. tobermorite shaped body. It is found that the shaped body is formed from globular secondary particles which are compre6sed and interlocked with one another and firmly into an integral mass, the composite body thus retaining the original structure of the starting material intact.
l~Z;27~
Furthermore, the primary particles forming the fiecondary particles are found to have the same form as shown in Fig.
3(B) by electron microscopic observation and have the ~ame diffraction peaks peculiar to calcium carbonate according to x-ray diffraction. Thus the product is a composite shaped body made up of plate-like particles of amorphous silica and extremely fine particles of calcium carbonate attached thereto.
Subsequently, the composite ~haped body is immer~ed in a 6N HCl solution for one minute. Simultaneously with the immersion, carbon dioxide gas evolves and the calcium carbonate in the shaped body is converted to calcium chloride.
The shaped body is then thoroughly washed with water to completely dissolve out the resulting calcium chloride and is thereafter dried to give Opsil-IIS of this invention X-ray diffraction confirms that the Opsll-IIS, like Opsil-I and Opsil-II, is amorphous.
Observation under a scanning electron microscope gives the ~ame result as shown in Fig~ 7(C), indicating that in structure the Opsil-IIS substantially resembles the ~tarting material, namely tobermorite ~haped body and the composite shaped body obtained by carbonatin~ the material. The substantially globular particles of Opsil-II, ranging from about 10 to about 60 ~uin diameter, are compressed and interlocked with onè another forrning the integral body of the Opsil-IIS.
l~ZZ77g The Opsil-IIS prepared as above ha6 the following propertie~.
Bulk density 0.13 g/cm2 Specific surface area 2~7 m~/g Compression strength 4 kg/cm Porosity 93%
Example 12 The shaped body (bulk density: 0.3 g/cm3) of calcium silicate (CSHn) obtained in Reference Example 3 is placed with water in a water to solids ratio by weight of 2:1, in a closed container. Carbon dioxide gas is forced into the container to maintain an internal pressure of 3 kg/cm2 for about 30 minutes for `carbonation.
The reaction, followed by drying, gives a composite shaped body of amorphous silica and calcium carbonateO
A fractured surface of the shaped body is obser~ed under a scanning electron microscope with the same result as given in Fig. 7(B), which shows that the composite shaped body has exactly the same structure as the starting material, 20 ~ l.e. CSHn shaped body. It is found that the shaped body is formed form globular secondary particles which are compressed and interlocked with one another and firmly into an integral mass, the composite body thus retaining the original structure of the ~tarting material intact. Furthermore, the primary particles forming the secondary particles are found to have the same form as foil-like particle peculiar to CSHn by ~-- ~
electron microscopic observation and have the same diffraction peaks peculiar to calcium carbonàte according to x-ray diffraction. Thus the product is a composite shaped body made up of foil-like particles of amophous silica and 5 extremely fine particles of calcium carbonate attached thereto.
Subsequently, the composite shaped body is immersed in a 6N HCl solution for one minute. Simultaneou61y with - the immersion, car~bon dioxide gas evolves and the calcium carbonate in the shaped body is converted to calcium chloride.
The shaped body is then thoroughly washed with water to completely dissolve out the resulting calcium chloride and is thereafter dried to give Opsil-IIS of this invention.
X-ray diffraction confirms that the Opsil-IIS, like Opsil-I and Opsil-II, is amorphous.
Observation under a scanning electron microscope gives the same result as shown in Fig. 7(C), indicating that in structure the Opsil-IIS substantially resembles the starting material, namely CSHn shaped body and the composlts shaped ~ body obtained by carbonating the material. The substantially globular particles of Opsil-II, ranging from about 10 to about 60~, are compressed and interlocked with one another, forming the integ~al body of the Opsil-IIS.
The Opsil-IIS prepared as above has the following propertie~.
- 81 _ ~2Z~79 Bulk den~ity 0.14 g/cm2 Specific ~urface area 461 m2/g Compres~ion ~trength 4 kg/cm Poro~ity 82%
- 82 _ Example 13 The powder of Opsil~II (100 wt. parts) obtained in Example 6 and 2 wt. parts of glass fibers are dispersed in water to a water to solids ratio by weight of 10:1, to prepare a slurry. The slurry is placed in a mol,d, 40 mm x 120 mm x 150 mm, and then dewatered by a press. The shaped mass is removed from the mold and dried at 105 C for 24 hours to obtain a shaped body of this invention, i.e. Opsil~ , having the following, properties.
10 Bulk density 0.11 g/cm3 Bending strength 6 kg/cm2 Compression strength 9 kg/cm2 Porosity 93gO
Example 14 The Opsil-II obtained in Example 7 is shaped in the same manner as in Rxample 13 to prepare a shaped body of this invention, i.e. Opsil-IIS, having the following properties.
Bulk density 0.15 g/cm Bending strength 4.5 kg/cm2 20 Compression strength 7 kg/cm2 Porosity 91o Example 15 The Opsil-II obtained in Example 8 is shaped in the same manner as in Example 13 to prepare an Opsil-IIS of this invention having the following properties.
~lZZ779 Bulk density 0.21 g/cm3 Bending strengt~ 2.3 kg/cm2 Co~pression strength 4 kg/cm2 Porosity 88 /0 ~xample 16 The composite secondary particles of amorphous silica and calcium carbonate obtained by the first step of Example 6`are dispersed in water,-to a water to solids ratio by weight of 10 : 1. The resulting slurry . is placed in a mold, 40 mm x 120 mm x 150 mm, and dewatered and shaped by a press to prepare a composite shaped body of amorphous silica and calcium carbonate. The shaped body has the same structure as the composite shaped body described in Example 10.
In the same manner as in Example 10, the shaped body is immersed in a 6N HCl solution for acid treatment, then washed with water to completely dissolve out the calcium chloride formed and thereafter dried to obtain an Opsil-IIS Or this invention.
~ The Opsil-IIS has substantially the same structùre and form as the Opsil-IIS obtained in Example 10.
The properties of the Opsil-IIS are ~s follows.
Bulk density 0.13 g/cm3 Bending strength 5 kg/cm Compression strength 10 kg/cm2 Porosity 92 %
1~2;~77~
Example 17 The Opsil-I obtgined in Exa~ple 1 is disper~ed in water in a water to solids ratio by weight of 5 : 1.
The mixture is placed in a mold, dewatered and shaped by a press with varying shaping pressures, followed by drying. The physical properties of the shaped body (Opsil-IS) thus obtained are as follows.
; Sample No.
. Bulk density (g/cm3) 0.15 0.38 0.95 Bending st2rength4.2 18 0 43.2 (kg/cm ) ~ompression strength 7,3 23.5 61.0 (kg/cm2 ) Porosity ~/0) 92.5 61.0 52.5 Speci(fi~/s)rface340 338 330 .
Example 18 ~ he Opsil-I obtained in Example 2 i~ dispersed in water in a water to solids rstio by weight of 5 : 1.
The mixture is placed in a mold, dewatered and shaped by a press with varying shaping pressures, followed by drying. The physical properties of the sh~ped body ~Opsil-IS) thus obtained are as follows.
- o5 -l~Z~ 9 Sample No.
Bulk densi.ty (g/cm3) 0.13 0.50 Bending strength (kg/cm2) 4.0 25 ~ompression strength (kg/cm,2) 5.2 ~5 ~orosity ~/0) 93.5 75.0 Specific surface area (m /g) Example 19 Quick lime and siliceous sand powder in a CaO to SiO2 mole ratio of 0.98 : 1 are dispersed in water to prepare a slurry having a water to solids ratio by weight . 10 of 5 : 1. The slurry is swollen with stirring at 100 C
for 5 hours, then press-molded and thereafter subjected in an autoclave to hydrothermal reaction at 15 kg/cm2 at 200 D C for 10 hours to obtain a shaped body with a bulk density of 0.35 g/cm3.
The x-rsy diffraction of the shaped body reveals the diffraction peaks (2~) peculiar to xonotlite crystals st 12.7, 27.6 snd 29Ø Elementary analysis also confirms that the shsped body is composed of xonotlite crystals. When 8 fractured surface of the shaped body iS obser~ed under sn electron microscope, it is ascertained that the body is formed from numerous needle-like xonotlite crystals randomly three-dimensionally interlocked with one 77~
snother to an integrsl mass.
In the same manner as in Example 10, the s~aped bod~ of xonotlite is placed, in a water to solids ratio by weight of 2 : 1, in a closed container. Carbon dioxide gas is froced into the container at an internal pressure of ~ kg/cm for about 30 minutes.
The x-ray diffraction of the resulting shaped body shows exactly the same result as given in Fig. l(B), revealing the diffraction peaks due to calcium carbonate.
Observation under an electron microscope further shows that the shaped body retains the original structure of xonotlite shaped body used as the starting material.
Thus the product is identified as a composite shaped body of amorphous silica and calcium carbonate which comprises amorphous silica having the original configurQtion of the xonotlite crystals and extremel~ fine particles of calcium carbonate attached thereto.
In the same manner as in Example 10, the ~ composite shaped body is immersed in a 6N HGl solution Z for one minute, then thoroughl~ washed with water to completel~ dissolve out the resulting calcium chloride and thereafter dried, whereby an Opsil-IS of this invention is obtained.
The x-ra~ diffraction of the Opsil-IS shows the same result as given in Fig. l(C), indicating no diffraction peaks. The analysis of the product further 112~779 reveals that the SiO2 content is not lower than 99%, indicating that the Opsil-IS is composed of amorphous silica of high purity. The scanning electron micrograph of Fig. 8, showing a fractured surface of the Opsil-IS
at a magnification of l,OOOX, indicates that in structure the Opsil-IS is substantially indentical to the starting material,i.e. xonotlite shaped body, and to the composite shaped body of amorphous silica and calcium carbonate obtained-by carbonating the material. More specifically, the product is formed from the particles of amorphous silica (Opsil-I) which are randomly three-dimensionally interlocked with one another into an integral mass and which have at least two surfaces in s~mmetric relation, a length of about 1 to about 20 ~, a thickness f about 0.02 to about 0.1 ~ and a width of about 0.02 to about 1.0 ~, the length being at least about 10 times the thickness .
The Opsil-IS has the following properties.
Bulk den~ity 0.20 g/cm3 Specific surface area251 m2/g Compression strength 5 kg/cm Porosity 9 %
Example 20 Commercial autoclave light-weight cohcrete containing about 80 wt.% of tobermorite and about 20 wt.%
of guartz and having a bulk density of 0.63 ~/cm3 i8 ;
- ~2;277~
immersed in water for 1 hour and placed in a closed vessel.
The concrete is subJected to carbonation and acid treatment in the same manner as in Example 10, followed by drying, to obtain shaped body of the invention. X-ray diffraction shows only the diffraction peaks (2~) of quartz at 26.7~ and 20.8 D, This evidences that the tobermerite is converted to amorphous silica. The analysis shows the product contains SiO2 in a purity of not lower t~an 98 ~/c. The shaped body is cut along planes vertical and parallel to the direction of the shaping pressure. The scanning electron micrographs of the cut surfaces indicate that the shaped body is formed of numerous plate-like amorphous silica particles randomly three-dimensionally interlocked with one another and substantially circular pores of a diameter of less than 1 mm. The properties of the shaped body are as follows.
Bulk density 0.30 g/cm3 Specific surface area 301 m2/g 20~ Compression strength 12 kg/cm2 Porosity 85 %
- 89 - ~
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A shaped body of amorphous silica comprising primary particles of amorphous silica randomly three-dimensionally inter-locked with one another integrally into the body and voids inter-spersed therebetween, each of the primary particles having a crystalline appearance, at least two surfaces in symmetric rela-tion, a length of about 1 to about 500µ and a thickness of about 50 .ANG. to about lµ,the length being at least about 10 times the thickness.
2. A shaped body as claimed in claim 1, wherein the porosity is at least about 50%.
3. A shaped body as claimed in claim 1, wherein the primary particles are about 1 to about 300µ in length and about 100 .ANG. to about 1µ in thickness, the length being about 10 to about 5,000 times the thickness.
4. A shaped body as claimed in claim 1, which contains a fibrous reinforcing material.
5. A shaped body as defined in claim 1, which contains clay.
6. A shaped body as defined in claim 1, which contains cement.
7. A method of preparing a shaped body of amorphous silica having a crystalline appearance comprising the steps of contacting calcium silicate crystals with carbon dioxide in the presence of water to convert the calcium silicate into amorphous silica having the configuration of the calcium silicate crystals and extremely fine particles of calcium carbonate, contacting the resulting product with an acid to decompose the calcium carbonate to carbon dioxide and calcium salt, and separating the amorphous silica from the calcium salt the calcium silicate crystals being in the form of a shaped body comprising numerous primary particles randomly three-dimensionally interlocked with one another inte-grally into the body and voids interspersed therebetween, each of the primary particles having a length of about 1 to about 500 µ and a thickness of about 50 .ANG. to about 1 µ, the length being at least about 10 times the thickness, the amorphous silica being in the form of a shaped body retaining the form of the shaped body and the configuration of the constituent primary particle of calcium silicate.
8. A method as claimed in claim 7 wherein the amount of the water is 1 to 50 times the weight of solids.
9. A method as claimed in claim 7 wherein the acid has no reactivity with silica and is capable of decomposing cal-cium carbonate into a water-soluble calcium salt and carbon dioxide.
10. A shaped body of amorphous silica and calcium carbonate comprising of amorphous silica-calcium carbonate composite primary particles randomly three-dimensionally interlocked with one another integrally into the body and voids interspersed therebetween, each of the primary particles comprising an amorphous silica-particle in the form of a primary particle and an extremely fine particle of calcium carbonate attached to the amorphous silica particle, the amorphous silica particle having a crystalline appearance, at least two surfaces in symmetric relation, a length of about 1 to about 500µ and a thickness of about 50 .ANG. to about 1 µ, the length being at least about 10 times the thickness.
11. A method of preparing a shaped body of amorphous silica having a crystalline appearance and calcium carbonate comprising the steps of contacting calcium silicate crystals with carbon dioxide in the presence of water to convert the calcium silicate into amorphous silica having the configur-ation of the calcium silicate crystals and extremely fine particles of calcium carbonate attached to the amorphous silica particles, the calcium silicate crystals being in the form of a shaped body comprising numerous primary particles randomly three-dimensionally interlocked with one another integrally into the body and voids interspersed therebetween, each of the primary particles having a length of about 1 to about 500 µ, and a thickness of about 50 .ANG. to about 1 µ, the length being at least about 10 times the thickness, the amorphous silica being in the form of a shaped body retaining the form of the shaped body and the configuration of the constituent primary particle of calcium silicate, the amorphous silica having calcium carbonate attached thereto.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA358,846A CA1122779A (en) | 1975-03-25 | 1980-08-22 | Amorphous silica, products thereof and methods of preparing the same |
Applications Claiming Priority (8)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3629975A JPS528023A (en) | 1975-03-25 | 1975-03-25 | Method of manufacturing high purity porous silica gel mouldings |
| JP3630075A JPS528024A (en) | 1975-03-25 | 1975-03-25 | Manufacturing of porous silica gel plastics |
| JP36298 | 1975-03-25 | ||
| JP36299 | 1975-03-25 | ||
| JP50036298A JPS51125699A (en) | 1975-03-25 | 1975-03-25 | The production of moldable high purity and porous silica gel secondary particles |
| JP36300 | 1975-03-25 | ||
| CA248,633A CA1097030A (en) | 1975-03-25 | 1976-03-24 | Amorphous silica, products thereof and methods of preparing the same |
| CA358,846A CA1122779A (en) | 1975-03-25 | 1980-08-22 | Amorphous silica, products thereof and methods of preparing the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1122779A true CA1122779A (en) | 1982-05-04 |
Family
ID=27508059
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA358,846A Expired CA1122779A (en) | 1975-03-25 | 1980-08-22 | Amorphous silica, products thereof and methods of preparing the same |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1122779A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2000046149A1 (en) * | 1999-02-03 | 2000-08-10 | Italcementi S.P.A. | Procedure for preparing silica from calcium silicate |
| EP1176124A1 (en) | 2000-07-25 | 2002-01-30 | Italcementi S.p.A. | Inorganic cohesion agent for self-compacting cement pastes |
| CN114014329A (en) * | 2021-12-10 | 2022-02-08 | 黑龙江省能源环境研究院 | Method for preparing white carbon black by using coal gangue ash low-temperature roasting hydrothermal combined activation method |
| CN114890816A (en) * | 2022-04-20 | 2022-08-12 | 广东欧文莱陶瓷有限公司 | Ceramic tile with tree leaf surface and preparation method thereof |
-
1980
- 1980-08-22 CA CA358,846A patent/CA1122779A/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2000046149A1 (en) * | 1999-02-03 | 2000-08-10 | Italcementi S.P.A. | Procedure for preparing silica from calcium silicate |
| EP1176124A1 (en) | 2000-07-25 | 2002-01-30 | Italcementi S.p.A. | Inorganic cohesion agent for self-compacting cement pastes |
| CN114014329A (en) * | 2021-12-10 | 2022-02-08 | 黑龙江省能源环境研究院 | Method for preparing white carbon black by using coal gangue ash low-temperature roasting hydrothermal combined activation method |
| CN114014329B (en) * | 2021-12-10 | 2023-08-29 | 黑龙江省能源环境研究院 | Method for preparing white carbon black by utilizing coal gangue ash low-temperature roasting hydrothermal combined activation method |
| CN114890816A (en) * | 2022-04-20 | 2022-08-12 | 广东欧文莱陶瓷有限公司 | Ceramic tile with tree leaf surface and preparation method thereof |
| CN114890816B (en) * | 2022-04-20 | 2023-04-25 | 广东欧文莱陶瓷有限公司 | Ceramic tile with tree leaf surface and preparation method thereof |
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