JPS59141415A - Aqueous slurry of amorphous silica - Google Patents

Abstract

PURPOSE:An aqueous slurry of amorphous silica that is obtained by dispersing amorphous silica primary particles which have crystal-like appearance and a specific form and size in water, thus giving a formed product with high strength only by forming and drying without any binder. CONSTITUTION:Carbon dioxide is made to act on a calcium silicate such as wollastonite to effect conversion into amorphous silica and fine particles of calcium carbonate and the product is treated with an acid to separate the amorphous silica from the calcium carbonate which is decomposed into carbon dioxide and a calcium salt. Thus, apparently crystal-like amorphous silica is obtained in the form of primary particles which have the crystalline habit of the calcium silicate, about 1-500mum length and 50Angstrom -1mum thickness where the length is more than 10 times the thickness. The resultant amorphous silica primary particles are dispersed in water to give the objective aqueous slurry of amorphous silica which is formable.

Description

[Detailed Description of the Invention] Akira Kosaki has developed an aqueous slurry of amorphous silica that can be molded into a molded product that has mechanical strength without using a binder or the like by simply molding and drying it. The present invention relates to a new aqueous slurry of amorphous silica with properties that can be imparted.

Silica gel is conventionally known as a typical amorphous silica. This is mainly produced by neutralizing an aqueous solution of sodium silica with an acid such as insectic acid or sulfuric acid, precipitating a precipitate, washing with water and drying, and if necessary, activating it by heating under reduced pressure. The silica gel can be obtained in an amorphous or spherical shape depending on the manufacturing method, but it itself has moldability, so it is essential to use a binder or the like when molding it.

However, the silica gel molded product obtained by this method is heavy and has low strength, and cannot be used for practical use as a heat insulating material, WR heating material, etc. for side soles.

Purpose of the invention +: The invention consists of dispersing amorphous silica primary particles having a specific shape (outer shape) and size different from the conventionally known silica gel in water, and dispersing them from the aqueous slurry. An invention to provide a new aqueous slurry of amorphous silica that has the characteristics of being able to give a lightweight molded product with practical mechanical strength by simply molding (dehydration molding) and drying. The composition, ie, the small invention, has a crystal habit of calcium silicate crystals, and has a crystal habit of about 1
Formable by dispersing in water crystal-like appearance amorphous silica primary particles having a length of ~500 μm and a thickness of about 50 A to about 1 μm, the length being at least 10 times the thickness. Pertains to amorphous silica aqueous slurry.

The biggest feature of the aqueous slurry of the present invention is that it can be molded without using any binder,
: It has a unique property that allows easy production of molded products with MLC and strength. However, the lever feature is due to the fact that the primary particles constituting the slurry have the above-mentioned specific external shape and size, and the external shape and size of the secondary particles are derived from silicate crystals and It is produced by converting silicate crystals into amorphous silica while leaving behind the crystalline remains. That is, as a result of xH diffraction analysis, it was confirmed that the secondary particles were amorphous, with no diffraction observed at all, and according to the chemical analysis results after ignited dehydration, the weight of the particles was 5102 and 98. Furthermore, as a result of electron microscopy observation, it is confirmed that although it is amorphous, it exhibits a crystal-like appearance that retains the crystal habit of the original crystal. This crystal-like appearance and size substantially corresponds to the appearance and size of the silicate crystal from which it originates. For example, amorphous silica primary particles derived from rectangular calcium silicate crystals such as wollastonite, seanotrite, and phoshadiseite have a rectangular outer shape.

It is derived from plate-shaped calcium silicate crystals such as Tobel Heptalite 1 Disei0lite, α-025H, etc., and has a plate-like external shape. Amorphous silica that exhibits a rectangular shape, plate shape, etc.
It has a length of about 1-500 μm and a thickness of about 5 OA-1 μm, and the length is at least 10 times the thickness. The strip-shaped amorphous silica derived from the seanotrite crystal retains the crystal habit of the crystal and is usually about 1 to 50 μm long and about 10 μm long.
0; ~0.5 μm thickness and approximately 100A ~ 2 μm 11
The length and thickness are about 10 to 5000 times longer. The plate-shaped one derived from the Tobel heptalite crystal retains the crystal habit of the crystal and has a thickness of approximately 1 to 50 μm and a thickness of approximately 100 A to O, up to 100 μm.
It has a thickness of about 0.2 to 20 pm, and a length of about 10 to 5000 times the thickness. The rectangular shape derived from wollastonite crystal retains the crystal habit of the crystal and has a crystal habit of about 1 to 5
00μm length, about 10OA-18m thickness and about 10
11] of 0 A to 5 μm, and the length is approximately 10 to 50 μm of the thickness.
It is oO times. A plate-shaped plate derived from a gyrolite crystal retains the crystal habit of the crystal and has a length of about 1 to 50 μm, a thickness of about 10'x to 0.5 μm, and a thickness of about 1 to 20 μm.
+lJ, and the length is 10 to 500p times the thickness.

The plate-shaped one derived from the α-tied calcium silicate hide L = -t crystal retains the crystal habit and approximately 1
The length is 10 to 5000 times the thickness, with a length of ~300 μm, a thickness of approximately 500Δ to 1 μm, and a width of approximately 1 to 50 μm.

The aqueous slurry of the invention is prepared by dispersing the amorphous silica primary particles described above in water.

The slurry usually has a water to solid content ratio (weight ratio) of 4 to 50;
It is better to set it to 1. In addition, the aqueous slurry of this 16th century may contain asbestos, glass fiber, rock wool, synthetic fiber,
Natural fiber, valve, carbon fiber/stainless steel Sfaino S-
It is possible to add various additives such as fibrous reinforcing agents such as aluminum silica, silica sol, clay), colorants, fillers, etc.

The amorphous silica secondary particles constituting the aqueous slurry of the present invention can be produced from various natural or synthetic silicon salt crystals having, for example, a 5i04 tetrahedral network or chain structure. The manufacturing method is not particularly limited and any method can be adopted, but the most advantageous method is to use calcium silicate crystals as a raw material.
When this is brought into contact with the acid power □ in the presence of water, amorphous silica and extremely fine corpse 1j! 'Conversion to calcium (carbonation), followed by treatment of the product with acid to decompose it into calcium carbonate carbon dioxide and calcium salts, and separation of the amorphous silica from the calcium salts (acid treatment). I can do it. The major feature of this method is that the calcium silicate constituting the calcium oxide crystals is converted into amorphous silica without substantially changing the external shape of the calcium acid crystals. Therefore, the amorphous silica secondary particles obtained in this manner have substantially the skeleton of calcium silicate crystals as they are. Calcium silicate crystals that can be used as source crystals include wollastonite-based calcium silicate crystals such as wollastonite, thonodolite, phossedisate 5゜plantite, 0-zenhanite, and tobel t-lite). Uite-based calcium silicate crystals, gyrj-lite, trasphtite, lierite, and other diseirolite ffl! Included are r-dicalcium silicate-based multi-calcium silicate crystals such as calcium crystals, cardiochondrosilicate, bovine lucoanite, and aphidillite, α-dicalcium silicate hydrates, and the like.

Any number of calcium silicate crystals for each of the above structures are known and can be produced by known methods. For example, the spherical shell-shaped secondary particles of calcium silicate crystals produced by the method described in Japanese Patent Publication No. 45-25771, which was previously published by the present applicant, and the molded bodies of calcium silicate crystals mainly composed of the secondary particles are suitably used. Should it be crushed or should it be crushed?Special Publication No. 30-4040, 7? Publication No. 41-1953, U.S. Patent No. 2
Jl: It is produced by crushing a molded body of calcium chloride crystals produced by the method described in U.S. Pat. No. 699,097, US Pat.

The silicic acid raw materials used as raw materials for obtaining the above-mentioned calcium silicate crystals include natural amorphous f4: [Greetings, Mu1゛ sand, hi+Mshi・Rishi, -, slag, white clay/fly ash, pearlite, white carbon, Various strains containing silicic acid as a main component, such as Silico and 7 Dust, can be used, and these can be used alone or in a mixture of two or more. Examples of lime raw materials include quicklime, slaked lime/carbide residue, cement, and other materials whose main component is lime, and these can be used alone or in a mixture of two or more. Each of these families usually contains CaO: 5i
It is best to mix so that the n2 ratio is in the range of about 0.5 to 3.51. Along with the above raw materials, if necessary, add glass fiber, St. laminated fiber, asbestos, rock wool, nylon, etc. Additives such as reinforcing agents such as carbon fiber (natural fiber, pulp, stenciled fiber) and coloring agents may be blended. Also, the amount of water used above can vary over a wide range. Generally, the amount is preferably about 3.5 to 30 times the combined weight of the solid content.

Carbonation of the calcium silicate crystals obtained as described above is carried out by introducing carbon dioxide scum into the reaction system and bringing the crystals into contact with carbon dioxide gas in the presence of moisture. The above-mentioned carbonation is preferably carried out by placing, for example, 6 to 4 m of calcium silicate crystals in a suitable airtight container and heating them with carbonic acid under high humidity or humidity. Alternatively, various forms of calcium silicate crystals may be immersed in water or carbonated water, and carbon dioxide gas may be introduced into the solution. This carbonation can be carried out satisfactorily even at room temperature and pressure as long as carbon dioxide gas is introduced into the system, but it is preferably carried out under a gauge pressure of approximately pressurized - FIOkti/Cd. The speed of reaction becomes even faster, and it becomes possible to complete the reaction in a short time. The amount of carbonate sludge used is a stoichiometric amount or more. Furthermore, when carbonating calcium silicate crystals by immersing them in water, the carbonization rate can also be increased by stirring the reaction system. The ratio of water to silica calcium crystal used is usually 1 to 50:l, preferably 1 to 25:l.
:I (weight ratio) is preferable.

The rate of carbonation differs slightly depending on the raw material and the crystallinity of the calcium silicate in the raw material. However, the amount of water added is 2 to 6
By approximately doubling the amount, the reaction is completed in 4 to 10 hours. In addition, the amount of water added was 5 times, and the reaction system was 2 kg /
If pressurized to d (gauge pressure), the reaction will normally be completed in around 1 hour, and if this pressurization condition is 3 kq/cyA (gauge pressure), the reaction will be completed in an extremely short time of 30 minutes. is recognized.

The above carbonation reaction depends on the type and crystallinity of the calcium silicate crystal used as the raw material, as shown in the reaction formula below.
go

xcao, SiO-FFJ O+CO222 → CaCO3+ 5I02, nH2O However, in the above formula, X is 0.5 to 3.5.

No matter which type of calcium silicate crystals are used, the #calcium oxide is a combination of amorphous silica and Ml calcium without substantially changing the outer shape of its secondary particles, and therefore without any morphological change. It is converted into ultrafine crystals. That is, the linked M structure of SiO4 tetrahedra that forms the skeleton structure of the calcium silicate-secondary crystal is maintained as it is, and the linked structure produces amorphous silica having a crystalline appearance and extremely fine calcium carbonate attached thereto.

The acid treatment of the silica-calcium carbonate complex obtained by the above carbonation is carried out to separate the charcoal calcium component from the amorphous silica constituting the above complex, and it is preferable that the silica is reactive with the silica. It is preferable to use an acid which does not contain calcium carbonate but can decompose calcium carbonate to produce carbon dioxide gas and Mizumachi bathing calcium salt. Examples of the nucleic acid include nitric acid-acetic acid and perchloric acid.

In addition, this acid treatment is usually carried out by immersing the above-mentioned conjugate in the melting process of each of the above-mentioned infarct acids, or by rapidly introducing acidic residue such as hydrogen chloride gas into which the above-mentioned temporary coalescence is immersed or dispersed in water. It can be implemented by In the above, the acid may be used in a chemically stoichiometric amount or more to react with the anthrax calcium. This acid treatment can preferably be carried out at room temperature, but heating to the θμ point of the acid used is also possible. The reaction pressure is usually normal pressure, but the reaction proceeds even under pressurized conditions. Reaction patents are generally very short. According to the acid treatment, the calcium carbonate present adhering to the amorphous silica constituting the composite is decomposed by the acid and becomes a soluble calcium salt. Therefore, by completely removing the calcium salt by, for example, washing with water and drying, primary particles made of amorphous silica can be obtained. There is no change in the external shape of the primary particles of amorphous silica even in this step of removing calcium.

The production of a molded article from the aqueous slurry of the present invention is carried out by dehydrating and molding the slurry and then drying it in accordance with a conventional method. The bulk density of the obtained molded product can be arbitrarily adjusted by changing the pressure during molding, and can be adjusted over a wide range. Preferably the bulk density is from about 0.19/d to about 1. It is better to set it to Of/d. The molded body thus obtained usually has a porosity expressed by the following formula of at least 50%, preferably 60%.
~95%, and has excellent mechanical strength despite being a light phosphor.

In particular, the obtained molded bodies all have a low electric density of about 0.1 to 0.4 f/d and a high bending strength of about 3 to 30 kQ/Cd. Also, the above bulk density is thicker ・/d
~1. For a molded product with a bulk density of Of/CrA, it is 20 to 100.
A large piece of music on the order of kQ/d has strength.

Therefore, the obtained molded product is useful for uses such as heat insulating materials, heat insulating materials, fireproof filter materials, catalyst carriers, and the like.

EXAMPLES Reference examples and examples will be given to further explain the present invention in detail.

X-ray diffraction diagrams and electron micrographs of the substances obtained in each reference example and example are shown in all drawings.

Figure 1 (4) to C) are the X-ray diffraction diagrams of the starting raw materials, thonodolite crystals, amorphous silica calcium carbonate bonded particles and amorphous silica secondary particles obtained by carbonating the crystals, respectively. be. This is an XH diffractometer (X-ray
diffrattomtttr) was used to generate an X-bowl with a wavelength of 1.5418.4 using a Cu target, and the sample was irradiated with this to determine the diffraction angle and diffraction intensity. 3 with the highest diffraction intensity
I read the book's diffraction guide and identified the sample.

FIGS. 2 and 3 are electron micrographs at a magnification of 20,000 times, and in each figure, the cap represents the calcium silicate crystal used as the starting material, and (5) represents the amorphous silica secondary particles.

Reference Example 1 Quicklime is used as a lime raw material and 350 mesh silica powder is used as a silicic acid raw material. A raw material slurry is prepared by dispersing these in water at a ratio of lime to silicic acid of 0.98:l, and setting the water to solids ratio (weight) to +2:l. The raw material slurry was charged into an autoclave and heated to 191°C.
A slurry of thonodolite crystals is obtained by heating the mixture to a temperature of +2#/- and carrying out a hydrothermal reaction with stirring for 8 hours under a saturated steam pressure of +2#/-.

The X-ray diffraction pattern of the obtained crystal is as shown in the ffjI diagram, and is +2.7. 9-noi at 27.6° and 29.0
It shows the diffraction shear (20) peculiar to light crystals. Its composition after ignition is as follows.

Sr 02 48.88% C'O45,60 Δ1203 00-2 6p OO-54 3 1g, 1oss Now, 5199.79 Next, the above slurry is dried at 150'C and then ground to separate the secondary particles into primary particles. A fine white powder is obtained. The electron micrograph is shown in Figure 2.

From the diagram, the above-mentioned secondary particle has a rectangular shape and has a length of about 1
~20μm 1 thickness approximately 0.02-1.0μm and width approximately 0.
02-1. It can be seen that the length is at least about 10 times the thickness.

The secondary particles have a specific surface area of about 50 i/f.

Reference Example 2 Slaked lime is used as a lime raw material and 350 mesh silica powder is used as a silicic acid raw material. A raw material slurry is prepared by dispersing these in water at a ratio of lime to silicic acid of 0.80:I and setting the water to solids ratio (weight) to 12:I. The raw material slurry was charged into an auto-cup, heated to 19 BiC, and subjected to a hydrothermal reaction under saturated steam pressure of 12 m/d while stirring for 5 hours to obtain a slurry of tobel heptalite crystals. is 7.8° as a result of X-ray diffraction analysis,
The composition after ignition is as follows.

Sr 02 4 & 38%cao38.5
5 yg22030.31 p't2o3 0.45 1g, 1oss 11.36 99.05 Next, the slurry was dried with the above slurry k I 50'C and ground to separate the secondary particles into primary particles to obtain white fine powder. The electron micrograph of 7 is shown in Figure 3.

From the diagram, the above-mentioned secondary particles have a plate-like outer shape and a length of about 1~
20 μm 1 thickness approximately 0.02~0. Iμm and rlj approximately 0
．． The particles have a size of 2 to 0.5 μm and are found to have a length at least about 10 times the thickness.
It has a specific surface area of nt'/9.

Reference Example 3 The mononotrite needle-shaped particles obtained in Reference Example 1 were used as a starting material. This was charged into a closed pressure vessel along with 5 times heavier water, and 1 charcoal gas was pressurized into the vessel at room temperature, and carbonation was carried out for about 30 minutes while maintaining the internal pressure at 3 kQ/d. , obtain amorphous silica-calcium carbonate composite particles. The X-ray diffraction results of the obtained primary particles are as shown in Figure 1 (5). 23.
Only diffraction peaks (20) of calcium carbonate crystals appeared at o-29, + and 36.0°, indicating that calcium silicate was converted into amorphous silica and calcium carbonate by charcoal chemical reaction. Recognize.

Next, the amorphous silica calcium carbonate gradient obtained above
Next, the particles are immersed in a 6N-tiC4 bath for 1 minute. Generation of carbonate scum is observed, and calcium carbonate in the secondary particles is converted to calcium chloride.

Next, the primary particles after the acid treatment are thoroughly washed with water to completely dissolve the produced calcium chloride. Thereafter, it is dried to obtain amorphous silica particles.

The results of elemental analysis of the primary particles thus obtained after ignited dehydration are as follows, and it can be seen that they are made of high-purity silica.

Chemical composition (1) SiO299,1''203 0-35 CaO < 0.01 (I, 1ass 5.0) The X-ray diffraction pattern of the above-mentioned -order particles is as shown in Figure 1, and the starting material and Both the calcium carbonate-based calcium carbonate contained in the composite particles obtained after carbonating the calcium carbonate, which is based on the needle-like crystals of suriichi notolite, have disappeared, and the secondary particles are composed of amorphous silica. It is confirmed that

An electron micrograph of the above-mentioned amorphous silica primary particles is shown in Fig. 2). Due to its origin, it is recognized that it exhibits a crystal-like appearance with a rectangular outer shape, exactly the same as that shown in Figure (2). Its size is about 1 to 20 ttms in length, about 0.02 to O0I ttm and 0.02 to 1 in riJ in thickness.
．． 0 μm, the length is more than 10 times the thickness, and it can be seen that the needle-like appearance is not impaired at all even by acid treatment. The starting material is crystalline particles. This was placed in a closed pressure vessel together with 5 times its weight of water, carbon dioxide gas was pressurized into the vessel at room temperature, and the internal pressure was maintained at 3 kQ/Cd to carry out carbonation for about 30 minutes to form an amorphous material. Obtain fine silica-calcium carbonate composite particles.

The X-ray diffraction analysis results are the same as in Figure 1 (B),
Carbonation causes the raw material calcium silicate to become amorphous.
It is confirmed that the carbon dioxide has been converted into energy and calcium carbonate.

Next, the amorphous silica obtained above - calcium carbonate composite -
The next particle is immersed in 6N-HC1 solution for 1 minute. Generation of carbonate scum is observed, and calcium carbonate in the secondary particles is converted to calcium chloride.

Next, the primary particles after the acid treatment are thoroughly washed with water to completely dissolve the produced calcium chloride. Thereafter, it is dried to obtain amorphous silica particles.

The results of elemental analysis of the primary particles obtained after ignited drying are as follows, and it can be seen that they are composed of highly pure particles.

Chemical composition (a) St O299.3 1ot2030.23 Coo <0.01 (7f, loss 4.7) Also, the X-ray diffraction diagram of the above-mentioned -order particles is the same as that shown in Figure 10, using Tobel as the starting material. The peaks based on the plate-like crystals of heptadite and the peaks based on calcium sulfate contained in the composite particles obtained after carbonation have all disappeared, indicating that the secondary particles are amorphous silica. It is confirmed that there is.

An electron micrograph of the above amorphous silica particles is shown in Figure 3 (
6). From the original drawing, it can be seen that this has a crystal-like appearance with a plate-like outer shape, just like that shown in Fig. 4 (4). Its size is approximately 1 to 20 μm in length and approximately 0 in thickness.
．． It can be seen that the crystal-like appearance is not impaired at all even by acid treatment.

EXAMPLE A slurry of the present invention was obtained by dispersing the amorphous silica secondary particles obtained in Reference Example 3 in water at a water to solid content weight ratio of 5/1.

This was placed in a mold, the molding pressure was changed, dehydration molded, and then dried to obtain three types of molded products. The physical properties of the obtained molded product are shown in Table 1 below.

Table 1 Example 2 The amorphous silica secondary particles obtained in Reference Example 4 were dispersed in water at a water to solid weight ratio of 5/1 to obtain an aqueous slurry of the present invention.

This was placed in a mold, the molding pressure was changed, dehydration molded, and then dried to obtain two types of molded products. The physical properties of the obtained molded product are shown in Table 2 below.

Table 2

[Brief explanation of drawings]

Figure 1 (4) to Ω are respectively a sonodorite crystal, an amorphous silica-calcium carbonate composite particle obtained by carbonating the crystal, and an amorphous silica carbonate obtained from the composite particle.
It is an X-ray diffraction diagram of the next particle.゛Figures 2 and 3 are electron micrographs at a magnification of 20,000 times. In each figure, the cap is the calcium silicate crystal used as the starting material, and (6) is the amorphous silica secondary particle from the crystal. represent (Above) Figure 1 → Mouth angle (20) Figure 2 and Figure 3,

Claims (1)

[Claims] It has a crystal habit of calcium urate crystals, and has a crystal habit of about 1 to 50
having a length of 0 μm and a thickness of about 50A to about 1 μm;
1. An aqueous slurry of amorphous silica having formability, comprising secondary particles of crystal-like amorphous silica having a length at least 10 times the thickness and dispersed in water.