CA1079480A - Process for the preparation of ettringite fibres - Google Patents
Process for the preparation of ettringite fibresInfo
- Publication number
- CA1079480A CA1079480A CA290,322A CA290322A CA1079480A CA 1079480 A CA1079480 A CA 1079480A CA 290322 A CA290322 A CA 290322A CA 1079480 A CA1079480 A CA 1079480A
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- Prior art keywords
- cao
- ettringite
- calcium
- caso4
- anyone
- Prior art date
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B14/00—Use of inorganic materials as fillers, e.g. pigments, for mortars, concrete or artificial stone; Treatment of inorganic materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone
- C04B14/38—Fibrous materials; Whiskers
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Civil Engineering (AREA)
- Materials Engineering (AREA)
- Structural Engineering (AREA)
- Organic Chemistry (AREA)
- Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The present invention relates to an improvement to the process of our earlier Canadian patent No. 1,000,470, making it possible to obtain ettringite in fibre form. According to the invention, the process is carried out in the same way as the earlier patent but using enough water to always have a suspension containing a maximum of 25% dry matter at the end of the reaction, and in subjecting said suspension to moderate stirring of 1 to 5 times the force necessary to maintain a homogeneous suspension. Application to the replacement of asbestos fibres, notably as a fire-proof product.
The present invention relates to an improvement to the process of our earlier Canadian patent No. 1,000,470, making it possible to obtain ettringite in fibre form. According to the invention, the process is carried out in the same way as the earlier patent but using enough water to always have a suspension containing a maximum of 25% dry matter at the end of the reaction, and in subjecting said suspension to moderate stirring of 1 to 5 times the force necessary to maintain a homogeneous suspension. Application to the replacement of asbestos fibres, notably as a fire-proof product.
Description
10'~94~0 ~ he present invention relates to an improvement to the process for the preparation of ettringite, or calcium trisulfoa-luminate described in the Canadian Patent no. 1,000,470.
The process of the Canadian Patent no. 1,000,470 comprises adding water to, and thereby hydrating, a substantially stoichiometric mixture of at least one calcium aluminate and at least one calcium sulphate at a temperature of from 20C to 100C
to give ettringite, the amount of water which is added comprising the stoichiometric amount for one of the reactions:
10 1) CaO, A12O3 + 2(CaO, H2O) + 3(CaSO4,2H2O) + 24 H2O
(CaO)3A12O3, 3~aS04,32H2O (ettringite),
The process of the Canadian Patent no. 1,000,470 comprises adding water to, and thereby hydrating, a substantially stoichiometric mixture of at least one calcium aluminate and at least one calcium sulphate at a temperature of from 20C to 100C
to give ettringite, the amount of water which is added comprising the stoichiometric amount for one of the reactions:
10 1) CaO, A12O3 + 2(CaO, H2O) + 3(CaSO4,2H2O) + 24 H2O
(CaO)3A12O3, 3~aS04,32H2O (ettringite),
2) (CaO)3A12O3 ~ 3(CaSO4, 2H2O) + 26 H2O > 1 ettringite
3) CaO (A12O3)2 + 5(CaO, H20) + 6(CaSO4,2H2O) ~ 47 H20 ~ 2 ettringite
4) 12CaO, 7A12O3 + 9 (CaO, H2O) + 21(CaSO4,2H2O) + 173 H2O )7 ettringite,
5) Cao, 6A12O3 + 17(CaO,H2O) + 18(CaSO4, 2H2O) + 139H2O >6 ettringite and at most an amount such as to obtain after the reaction a product containing 5% (dry) ettringite and 95% (by weight) water.
It is specified in the Canadian Patent no. 1,000,470 process permits the production of the mineral filler formed essentially of ettringite and known under the name of "satin white"
in all forms thereof (dry powder, solutions or suspensions of concentrations or variable amounts to all intents and purposes at will) and for various industrial compounds such as, for example, aluminous cements, calcium sulphates and hydraulic binders which do not exactly possess the properties of the cements they are normally intended to form.
- : ~
In example 7 of the same Canadian Patent no. 1,000,470 it is stated that sub-micron particles have been obtained by using a jar mill rotating at 70 rotations per minute.
The present invention, on the contrary, solves the problem of obtaining in a controlled and industrial manner ettringite in the form of fibres which,may, for example, have a length of from 1 to 350 microns, thus widening the field of applications of the process of the Canadian Patent no. 1,000,470.
Such fibres have already been observed by research workers in-the paste of special cements known as expansive cements (Journal of the American Ceramic Society 1973, vol. 56, no. 6, p. 318) or again in supersulphated cements in which 120 rods have been observed (Cement and Concrete Research, vol. 1, p.101;
1971.).
But those fibers were dispersed in the cement and it was impossible to separate them from it. Therefore, no industrial process for obtaining such fibers was suggested by those scienti-fical observations.
The process of the inventlon consists of an improvement to that of the invention of the Canadian Patent no. 1,000,470 said improvement consisting essentially in that water is added at least in a proportion such that at the end of the reaction a product is obtained containing at the most 25% solid matter, and in that the reaction is effected with continuous stirring at a - - force of from one to five times the force necessary to maintain the solid matter existing during the reaction in homogeneous suspension in water.
. . .
Therefore the invention provides a process for the preparation of ettringite fiber which comprises adding water to, and thereby hydrating a substantially stoichiometric mixture of at least one calcium aluminate and at least one calcium sulphate at a temperature of from 20C to 100C to give ettringite fiber, the amount of water which is added comprising the stoichiometric amclnt for one of the reactions:
)CasA123 + 2(CaO,H2O)+ 3 (CaSO4, 2H2O) + 24 H2O
(CaO)3A1203, 3CaS04,32H20(ettringite) ; 10 2)(CaO)3A12O3 + 3(CaSO4,2H2O)+ 26 H2O 1 ettringite 3)CaO(A12O3)2 + 5(CaO,H2O)+ 6(CaSO4,2H2O)+ 47 H2O -~>
2 ettrin~ite 4)12CaO,7A12O3 + 9(CaO,H2O)+ 21(CaSO4,2H2O)+ 173 H2O
7 ettringite 5)CaO,6A12O3+ 17(CaO,H2O)+ 18(Ca~04, 2H2O)+ 139 H2O
It is specified in the Canadian Patent no. 1,000,470 process permits the production of the mineral filler formed essentially of ettringite and known under the name of "satin white"
in all forms thereof (dry powder, solutions or suspensions of concentrations or variable amounts to all intents and purposes at will) and for various industrial compounds such as, for example, aluminous cements, calcium sulphates and hydraulic binders which do not exactly possess the properties of the cements they are normally intended to form.
- : ~
In example 7 of the same Canadian Patent no. 1,000,470 it is stated that sub-micron particles have been obtained by using a jar mill rotating at 70 rotations per minute.
The present invention, on the contrary, solves the problem of obtaining in a controlled and industrial manner ettringite in the form of fibres which,may, for example, have a length of from 1 to 350 microns, thus widening the field of applications of the process of the Canadian Patent no. 1,000,470.
Such fibres have already been observed by research workers in-the paste of special cements known as expansive cements (Journal of the American Ceramic Society 1973, vol. 56, no. 6, p. 318) or again in supersulphated cements in which 120 rods have been observed (Cement and Concrete Research, vol. 1, p.101;
1971.).
But those fibers were dispersed in the cement and it was impossible to separate them from it. Therefore, no industrial process for obtaining such fibers was suggested by those scienti-fical observations.
The process of the inventlon consists of an improvement to that of the invention of the Canadian Patent no. 1,000,470 said improvement consisting essentially in that water is added at least in a proportion such that at the end of the reaction a product is obtained containing at the most 25% solid matter, and in that the reaction is effected with continuous stirring at a - - force of from one to five times the force necessary to maintain the solid matter existing during the reaction in homogeneous suspension in water.
. . .
Therefore the invention provides a process for the preparation of ettringite fiber which comprises adding water to, and thereby hydrating a substantially stoichiometric mixture of at least one calcium aluminate and at least one calcium sulphate at a temperature of from 20C to 100C to give ettringite fiber, the amount of water which is added comprising the stoichiometric amclnt for one of the reactions:
)CasA123 + 2(CaO,H2O)+ 3 (CaSO4, 2H2O) + 24 H2O
(CaO)3A1203, 3CaS04,32H20(ettringite) ; 10 2)(CaO)3A12O3 + 3(CaSO4,2H2O)+ 26 H2O 1 ettringite 3)CaO(A12O3)2 + 5(CaO,H2O)+ 6(CaSO4,2H2O)+ 47 H2O -~>
2 ettrin~ite 4)12CaO,7A12O3 + 9(CaO,H2O)+ 21(CaSO4,2H2O)+ 173 H2O
7 ettringite 5)CaO,6A12O3+ 17(CaO,H2O)+ 18(Ca~04, 2H2O)+ 139 H2O
6 ettringite and a supplementary amount of water, to obtain after the reaction a product containing 25% by weight to 5~ by weight (dry) of ettringite, the remainder being water, the process further comprising stirring continuously the suspension, the force of agitation being at least equal to and at most five times the force necessary for maintaining said suspension in a homogeneous state.
In one embodiment of such process at least part of the calcium oxide is brought under the form of limestone and wherein the aluminous cement is first reacted with the limestone and lime which forms hydrated calcium monocarboaluminate of the formula:
3 CaO, A12O3, CaCO3, llH2O
~ 4 ~
:: 3 ; ' this product then being reacted on the calcium sulphate, resulting in the formation of ettringite and the release of very finl- particles of calcium carbonate.
The invention also provides such a process wherein anhydrous or hydrated lime is added to the mixture in an amount such that the resulting Ca++ ion stoichiometrically balances the ettringite formation reactions.
In certain aspects the calcium aluminate may comprise at least one of the aluminates 3 CaO, A12O3; 12 CaO, 7 A12O3;
CaO, A12O3; CaO, 2A12O3; and CaO, 6 A12O3. In another aspect the calcium sulphate in such a process may comprise at least one of gypsum (CaSO4, 2H2O), semihydrate (CaSO4 1/2 H2O), "soluble" anhydride (CaSO4), "overburnt" anhydrous CaSO4 and natural anhydrite.
In a certain embodiment the calcium sulphate comprises at least one of the synthetic compounds which are by-products of the phosphorous fertilizer, fluorine, or magnesium industries.
In another embodiment the present invention provides a product obtained by the above processes and consisting essentially in ettringite fibers having a length from 2 to 350 microns. The product may desirab]y further contain up to 20% by weight of calcium carbonate, principally in the form of calcite.
In a further embodiment the present invention provides a process of the above type wherein the hydration is carried out at a temperature of from 60 to 90C, and wherein at least part of the calcium oxide is brought under the form of limestone and wherein the aluminous cement is first reacted with the limestone and lime which forms hydrated calcium monocarbo-aluminate of the formula:
3 CaO, A12O3, CaO3, llH2O
~ - 4ta) -:`~''.:.' ' :
10794~0 this product then being reacted on the calcium sulphate, resulting in the formation of ettringite and the release of very fine particles of calcium carbonate.
Stirring may be carried out by various means:
stirrer rotating in a fixed vat, vat rotating on itself and containing solid bodies in suspension, vat subjected to alternating motion, liquid jets, etc. The force of stirring corresponds to that of the variations in time or space of the velocities or pressure in the suspension. It may be : 30 : - 4(b) -C
,, ~ .
1079~8~
considered that when the pouer used for stirring is multiplied by five,the stirring itself is also multiplied by five;
The intensity of stirring is, as a general rule, measured by the power used for this stirring. The rotation speed of a rotating stirrer or of a rotating vat, the number of alternate movements in a time unit with the same amplitude, the pressure of a liquid jet with a constant flow, for instance, may be considered proportional to said energy of stirring,and therefore to said intensity of stirring with a sufficient precision for the need of the present process.
- The force of stirring must obviously be regulated by preliminary trials in each case as a function of the starting conditions and the product desired. For the same suspension,and the other conditions of operation remaining unchanged, the weaker the stirring the longer are the fipres obtained, The temperature preferably lies in the range of `
from 60 to 90C to compensate by a higher temperature for the slowing down of the reaction resulting from weaker stirring.
EXA~IPLE 1 In the previously mentioned example 7 of the Cana-dian Patent N / there was reacted a suspension of an aluminous cement having the following composition:
A1203 = 72 parts by weight CaO z 27 parts by weight volatile matter = 0.24 part by weight ~ Fe203 = 0.07 part by weight ; SO with gypsum of the composition:
.
; -5 -~ B
~ _ _ . .. . .. . . . . .. ... . ..... . . . . . . .
CaO = 35-36 parts by wei~ht S03 = 39-40 parts by weight H20 = 18 parts by weight C2 = 6 parts by weight limc of the composition:
CaO 75%
C2 1-2%
H20 23-24%
and water9in the following proportions (by weight):
12.6 parts of aluminous cement,40.6 parts of gypsum, 13.3 parts of lime, 33.6 parts of water,to-obtain stoichiometry and the additional amount of water to obtain a paste containing 15% by weight of ettringite or 567 parts of water.
The who}e mass was treated in a jar mill rotating at a velocity of 70 rotations/minute.
In the present example the same aluminous cement as that described hereinabove was used, and was reacted with a calcium sulphate having a composition (by weight) of:
CaO 33.2 parts S03 43.4 parts C2 2.7 parts insolubles 12.5 parts and 89% commercial quicklime and water in the following proportions: 22 parts aluminous cement, 59 parts calcium sulphate, 19 parts lime, 1400 parts water, corresponding to . obtaining a suspension comprising 10% by weight ettringite.
i -6 .
~079480 The mixture was tre~ted in a jar mill identical to that used in thc above mentioned example, but maintained at - 70~C and regulatcd to rotate at 6 rotations per minute,or 50~ faster than the minimum velocity of rotation to maintain the solid mattex in suspension. After 24 hours stirring there was obtained a suspension of fibres having an average length of 60 microns, an average diameter of 1 to 2 microns (determlned by a microscope with a systematic exploration system).
1~ The ettringite fibres can be used to replace eithe~
completely or partially asbestos fibres when the carcinogenic properties of this material may constitute counter-indications to its use as, for example, in the preparation of "asbestos-cement" materials or coatings and binders for fireproofing.
The Canadian Patent n 1 000 470 mentions the possibility of preparing more or less thick suspensions of ettringite according to the amount o water added, and drying the thick suspensions,forming a paste to obtain them in powdery form.
In the case of fibrous ettringite,it was seen hereinabove that it is impossible to decrease the amount of water in the same proportions as it is necessary to have a suspension and not a paste. When it is desired to obtain ettringi~e in the dry form,or having a low--water content, water is removed from the suspension obtained which contains a maximum of 25% by weight solid matter until aggregates : containing 0 to 15% free water are obtained and which ` generally have a bulk density in the range of 0.5 to 1.3.
. ' ' _7~
. .. . .
` ' ' ' . . .
'' 10794~30 Amon~ t}le means w~lich may be used to remove water from the suspension the filter press is pre~erred.
~le aggregates obtained may provide, for example,catalyst substrates or be used in the manufacture of materials for thermal or phonic insulation.
An advantageous property of ettringite ~ibres is their good resistance to fire. They can be used for - this purpose elther in the form of fibres or aggregates prepared as explained hereinabove.
EXA~LE 2-A fire-resistance trial at 1100C using the IS0 standard method was conducted with 4 cm panels, certain of which were used as controls,these being made of plaster prepared from a semi-hydrate,the others being made of a mixture prepared from 70 parts of the same semi-hydrate and 30 parts of ettringite ~ibres obtained as ..
desc~ibed above. Fire-resistance was 2 hours for the plaster panels and 4 hours for the mixed paneis;
It is stated in the Canadian Patent n 1 000 470 that the raw materials may contain calcium carbonate,which is found at the end of the operation and does not hinder certain operations. It has been established that,in the case of fibres said calcium carbonate does not generally constitute a drawback especially if it is in fine particles.
According to a particular method of the invention in order for the carbonate to be in a very fine form in the final product,the aluminous cement is first reacted with the limestone and lime which forms hydrated calcium mono-carboaluminate of the formula:
3 Ca~, A1203 , CaC03 , 11 H20 .
107~480 this product then being reacted on the calcium sulphate, resulting in the formation of ettringite and the release of ver~ fine particles, in the range of 1 to 2 microns, of calcium carbonate in the form of calcite.
The resulting material can contain up to 20~ by weight of calcite.
A heated vat was used to hydrate a mixture containing the following components:
Aluminous cement : ;42.3 parts by weight Limestone : 22.8 parts by weight Lime : 34.9 parts by weight The aluminous cement and lime were of the same composition as in the previous example. The limestone was fine commercial calcium carbonate.
Ihe proportion by weight of water was 4 times the weight of the solid mixture of the starting components.
Hydration was conducted at 70C. Measurement of bonded water, differential thermal analysis and X-ray diffraction showed hydration to be complete after 4 hours stirring and that the product formed consisted entirely of hydrated calcium monocarboaluminate of the overall formula:
' 2 3' 3' 2 lhe following were then added:
-calcium sulphate in the form of the natural anhydrite of a mesh size of 100% passing at 200 microns in ; the proportion of :
69 parts by weight of primary hydrate 39.2 parts by weight calcium sulphate `~ 30 -water in an amount sufficient to obtain a final concentration of 15% hydrated dry matter and the operation was .
- B g . .
.
10794~30 conducted as in the preceding example.
An inert,white mineral powder was obtained consisting of:
1236 parts by weight of ettringite fibres 100 parts by weight of calcite.
Microscopic examination of the product obtained showed that the average length of fibres was 100 microns,with long fibres of up to 150 microns. The calcite was very fine,the grains observed being no greater than 1 to 2 microns in diameter.
The other methods and variants of the process described in the main patent are also applicable in the process of the present application with the exception of those relating to the presence of calcium silicates in the initial mixture resulting in the formation ~f ~ tobermorites.
. . .... .
,
In one embodiment of such process at least part of the calcium oxide is brought under the form of limestone and wherein the aluminous cement is first reacted with the limestone and lime which forms hydrated calcium monocarboaluminate of the formula:
3 CaO, A12O3, CaCO3, llH2O
~ 4 ~
:: 3 ; ' this product then being reacted on the calcium sulphate, resulting in the formation of ettringite and the release of very finl- particles of calcium carbonate.
The invention also provides such a process wherein anhydrous or hydrated lime is added to the mixture in an amount such that the resulting Ca++ ion stoichiometrically balances the ettringite formation reactions.
In certain aspects the calcium aluminate may comprise at least one of the aluminates 3 CaO, A12O3; 12 CaO, 7 A12O3;
CaO, A12O3; CaO, 2A12O3; and CaO, 6 A12O3. In another aspect the calcium sulphate in such a process may comprise at least one of gypsum (CaSO4, 2H2O), semihydrate (CaSO4 1/2 H2O), "soluble" anhydride (CaSO4), "overburnt" anhydrous CaSO4 and natural anhydrite.
In a certain embodiment the calcium sulphate comprises at least one of the synthetic compounds which are by-products of the phosphorous fertilizer, fluorine, or magnesium industries.
In another embodiment the present invention provides a product obtained by the above processes and consisting essentially in ettringite fibers having a length from 2 to 350 microns. The product may desirab]y further contain up to 20% by weight of calcium carbonate, principally in the form of calcite.
In a further embodiment the present invention provides a process of the above type wherein the hydration is carried out at a temperature of from 60 to 90C, and wherein at least part of the calcium oxide is brought under the form of limestone and wherein the aluminous cement is first reacted with the limestone and lime which forms hydrated calcium monocarbo-aluminate of the formula:
3 CaO, A12O3, CaO3, llH2O
~ - 4ta) -:`~''.:.' ' :
10794~0 this product then being reacted on the calcium sulphate, resulting in the formation of ettringite and the release of very fine particles of calcium carbonate.
Stirring may be carried out by various means:
stirrer rotating in a fixed vat, vat rotating on itself and containing solid bodies in suspension, vat subjected to alternating motion, liquid jets, etc. The force of stirring corresponds to that of the variations in time or space of the velocities or pressure in the suspension. It may be : 30 : - 4(b) -C
,, ~ .
1079~8~
considered that when the pouer used for stirring is multiplied by five,the stirring itself is also multiplied by five;
The intensity of stirring is, as a general rule, measured by the power used for this stirring. The rotation speed of a rotating stirrer or of a rotating vat, the number of alternate movements in a time unit with the same amplitude, the pressure of a liquid jet with a constant flow, for instance, may be considered proportional to said energy of stirring,and therefore to said intensity of stirring with a sufficient precision for the need of the present process.
- The force of stirring must obviously be regulated by preliminary trials in each case as a function of the starting conditions and the product desired. For the same suspension,and the other conditions of operation remaining unchanged, the weaker the stirring the longer are the fipres obtained, The temperature preferably lies in the range of `
from 60 to 90C to compensate by a higher temperature for the slowing down of the reaction resulting from weaker stirring.
EXA~IPLE 1 In the previously mentioned example 7 of the Cana-dian Patent N / there was reacted a suspension of an aluminous cement having the following composition:
A1203 = 72 parts by weight CaO z 27 parts by weight volatile matter = 0.24 part by weight ~ Fe203 = 0.07 part by weight ; SO with gypsum of the composition:
.
; -5 -~ B
~ _ _ . .. . .. . . . . .. ... . ..... . . . . . . .
CaO = 35-36 parts by wei~ht S03 = 39-40 parts by weight H20 = 18 parts by weight C2 = 6 parts by weight limc of the composition:
CaO 75%
C2 1-2%
H20 23-24%
and water9in the following proportions (by weight):
12.6 parts of aluminous cement,40.6 parts of gypsum, 13.3 parts of lime, 33.6 parts of water,to-obtain stoichiometry and the additional amount of water to obtain a paste containing 15% by weight of ettringite or 567 parts of water.
The who}e mass was treated in a jar mill rotating at a velocity of 70 rotations/minute.
In the present example the same aluminous cement as that described hereinabove was used, and was reacted with a calcium sulphate having a composition (by weight) of:
CaO 33.2 parts S03 43.4 parts C2 2.7 parts insolubles 12.5 parts and 89% commercial quicklime and water in the following proportions: 22 parts aluminous cement, 59 parts calcium sulphate, 19 parts lime, 1400 parts water, corresponding to . obtaining a suspension comprising 10% by weight ettringite.
i -6 .
~079480 The mixture was tre~ted in a jar mill identical to that used in thc above mentioned example, but maintained at - 70~C and regulatcd to rotate at 6 rotations per minute,or 50~ faster than the minimum velocity of rotation to maintain the solid mattex in suspension. After 24 hours stirring there was obtained a suspension of fibres having an average length of 60 microns, an average diameter of 1 to 2 microns (determlned by a microscope with a systematic exploration system).
1~ The ettringite fibres can be used to replace eithe~
completely or partially asbestos fibres when the carcinogenic properties of this material may constitute counter-indications to its use as, for example, in the preparation of "asbestos-cement" materials or coatings and binders for fireproofing.
The Canadian Patent n 1 000 470 mentions the possibility of preparing more or less thick suspensions of ettringite according to the amount o water added, and drying the thick suspensions,forming a paste to obtain them in powdery form.
In the case of fibrous ettringite,it was seen hereinabove that it is impossible to decrease the amount of water in the same proportions as it is necessary to have a suspension and not a paste. When it is desired to obtain ettringi~e in the dry form,or having a low--water content, water is removed from the suspension obtained which contains a maximum of 25% by weight solid matter until aggregates : containing 0 to 15% free water are obtained and which ` generally have a bulk density in the range of 0.5 to 1.3.
. ' ' _7~
. .. . .
` ' ' ' . . .
'' 10794~30 Amon~ t}le means w~lich may be used to remove water from the suspension the filter press is pre~erred.
~le aggregates obtained may provide, for example,catalyst substrates or be used in the manufacture of materials for thermal or phonic insulation.
An advantageous property of ettringite ~ibres is their good resistance to fire. They can be used for - this purpose elther in the form of fibres or aggregates prepared as explained hereinabove.
EXA~LE 2-A fire-resistance trial at 1100C using the IS0 standard method was conducted with 4 cm panels, certain of which were used as controls,these being made of plaster prepared from a semi-hydrate,the others being made of a mixture prepared from 70 parts of the same semi-hydrate and 30 parts of ettringite ~ibres obtained as ..
desc~ibed above. Fire-resistance was 2 hours for the plaster panels and 4 hours for the mixed paneis;
It is stated in the Canadian Patent n 1 000 470 that the raw materials may contain calcium carbonate,which is found at the end of the operation and does not hinder certain operations. It has been established that,in the case of fibres said calcium carbonate does not generally constitute a drawback especially if it is in fine particles.
According to a particular method of the invention in order for the carbonate to be in a very fine form in the final product,the aluminous cement is first reacted with the limestone and lime which forms hydrated calcium mono-carboaluminate of the formula:
3 Ca~, A1203 , CaC03 , 11 H20 .
107~480 this product then being reacted on the calcium sulphate, resulting in the formation of ettringite and the release of ver~ fine particles, in the range of 1 to 2 microns, of calcium carbonate in the form of calcite.
The resulting material can contain up to 20~ by weight of calcite.
A heated vat was used to hydrate a mixture containing the following components:
Aluminous cement : ;42.3 parts by weight Limestone : 22.8 parts by weight Lime : 34.9 parts by weight The aluminous cement and lime were of the same composition as in the previous example. The limestone was fine commercial calcium carbonate.
Ihe proportion by weight of water was 4 times the weight of the solid mixture of the starting components.
Hydration was conducted at 70C. Measurement of bonded water, differential thermal analysis and X-ray diffraction showed hydration to be complete after 4 hours stirring and that the product formed consisted entirely of hydrated calcium monocarboaluminate of the overall formula:
' 2 3' 3' 2 lhe following were then added:
-calcium sulphate in the form of the natural anhydrite of a mesh size of 100% passing at 200 microns in ; the proportion of :
69 parts by weight of primary hydrate 39.2 parts by weight calcium sulphate `~ 30 -water in an amount sufficient to obtain a final concentration of 15% hydrated dry matter and the operation was .
- B g . .
.
10794~30 conducted as in the preceding example.
An inert,white mineral powder was obtained consisting of:
1236 parts by weight of ettringite fibres 100 parts by weight of calcite.
Microscopic examination of the product obtained showed that the average length of fibres was 100 microns,with long fibres of up to 150 microns. The calcite was very fine,the grains observed being no greater than 1 to 2 microns in diameter.
The other methods and variants of the process described in the main patent are also applicable in the process of the present application with the exception of those relating to the presence of calcium silicates in the initial mixture resulting in the formation ~f ~ tobermorites.
. . .... .
,
Claims (15)
1. A process for the preparation of ettringite fiber which comprises adding water to, and thereby hydrating a substantially stoichiometric mixture of at least one calcium aluminate and at least one calcium sulphate at a temperature of from 20°C to 100°C to give ettringite fiber, the amount of water which is added comprising the stoichiometric amount for one of the reactions 1) CaO, Al2O3 + 2(CaO,H2O)+ 3(CaSO4,2H2O)+ 24 H2O ?
(CaO)3Al2O3, 3CaSO4,32H2O(ettringite) 2)(CaO)3Al2O3+ 3(CaSO4,2H2O)+ 26 H2O ? 1 ettringite 3)CaO(Al2O3)2 + 5(CaO,H2O)+ 6(CaSO4,2H2O)+ 47 H2O
? 2 ettringite 4)12CaO, 7Al2O3+ 9 (CaO,H2O)+ 21 (CaSO4,2H2O) +
173 H2O ? 7 ettringite 5)CaO, 6Al2O3 + 17 (CaO, H2O)+ 18 (CaSO4,2H2O) +
139H2O ? 6 ettringite and a supplementary amount of water, to obtain after the reaction a product containing 25% by weight to 5% by weight (dry) of ettringite,the remainder being water, the process further comprising stirring continuously the suspension,the force of agitation being at least equal to and at most five times the force necessary for maintaining said suspension in a homogeneous state.
(CaO)3Al2O3, 3CaSO4,32H2O(ettringite) 2)(CaO)3Al2O3+ 3(CaSO4,2H2O)+ 26 H2O ? 1 ettringite 3)CaO(Al2O3)2 + 5(CaO,H2O)+ 6(CaSO4,2H2O)+ 47 H2O
? 2 ettringite 4)12CaO, 7Al2O3+ 9 (CaO,H2O)+ 21 (CaSO4,2H2O) +
173 H2O ? 7 ettringite 5)CaO, 6Al2O3 + 17 (CaO, H2O)+ 18 (CaSO4,2H2O) +
139H2O ? 6 ettringite and a supplementary amount of water, to obtain after the reaction a product containing 25% by weight to 5% by weight (dry) of ettringite,the remainder being water, the process further comprising stirring continuously the suspension,the force of agitation being at least equal to and at most five times the force necessary for maintaining said suspension in a homogeneous state.
2.A process as claimed in claim 1,wherein the hydration is carried out at a temperature of from 60°C
to 90°C.
to 90°C.
3. A process as claimed in claim 1 wherein at least part of the calcium oxide is brought under the form of limestone and wherein the aluminous cement is first reacted with the limestone and lime which forms hydrated calcium monocarboaluminate of the formula:
3 CaO, Al2O3, CaCO3, 11H2O
this product then being reacted on the calcium sulphate, resulting in the formation of ettringite and the release of very fine particles of calcium carbonate.
3 CaO, Al2O3, CaCO3, 11H2O
this product then being reacted on the calcium sulphate, resulting in the formation of ettringite and the release of very fine particles of calcium carbonate.
4. A process as claimed in any one of claims 1 to 3 wherein water is removed from the suspension obtained and aggregates containing 0 to 15% free water are obtained.
5. A process as claimed in anyone of claims 1 to 3, wherein anhydrous or hydrated lime is added to the mixture in an amount such that the resulting Ca++ ion stoichiometrically balances the ettringite formation reactions.
6. A process as claimed in anyone of claims 1 to 3,wherein the calcium aluminate comprises at least one of the aluminates 3 CaO, Al2O3 ; 12 CaO, 7 Al2O3; CaO, Al2O3;
CaO, 2Al2O3;and CaO, 6 Al2O3.
CaO, 2Al2O3;and CaO, 6 Al2O3.
7. A process as claimed in anyone of claims 1 to 3,wherein the calcium sulphate comprises at least one of gypsum (CaSO4, 2H2O),semihydrate (CaSO4 1/2 H2O), "soluble" anhydride (CaSO4), "overburnt" anhydrous CaSO4 and natural anhydrite.
8. A process as claimed in anyone of claims 1 to 3,wherein the calcium sulphate comprises at least one of the synthetic compounds which are by-products of the phosphorous fertilizer, fluorine, or magnesium industries.
9. A process as claimed in anyone of claims 1 to 3,wherein the calcium sulphate is natural carbonated calcium sulphate containing at least 60% pure calcium sulphate.
10A process as claimed in anyone of claims 1 to 3 wherein the mixture additionnaly comprises carbonated hydrated lime containing less than 40% carbonate.
11.A process as claimed in anyone of claims 1 to 3 wherein the mixture comprises a refractory alumina cement, gypsum and lime.
12. A process as claimed in anyone of claims 1 to 3 wherein the calcium aluminate is finely ground.
13. A product obtained by a process as claimed in anyone of claims 1 to 3 and consisting essentially in ettringite fibers having a length from 2 to 350 microns.
14. A product obtained by a process as claimed in anyone of claims 1 to 3 and consisting essentially in ettringite fibers having a length from 2 to 350 microns, and further containing up to 20% by weight of calcium carbonate principally in the form of calcite.
15. A process as claimed in claim 2 wherein at least part of the calcium oxide is brought under the form of limestone and wherein the aluminous cement is first reacted with the limestone and lime which forms hydrated calcium monocarboaluminate of the formula:
3 CaO, Al2O3, CaCO3, 11H2O
this product then being reacted on the calcium sulphate, resulting in the formation of ettringite and the release of very fine particles of calcium carbonate.
3 CaO, Al2O3, CaCO3, 11H2O
this product then being reacted on the calcium sulphate, resulting in the formation of ettringite and the release of very fine particles of calcium carbonate.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA290,322A CA1079480A (en) | 1977-11-07 | 1977-11-07 | Process for the preparation of ettringite fibres |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA290,322A CA1079480A (en) | 1977-11-07 | 1977-11-07 | Process for the preparation of ettringite fibres |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1079480A true CA1079480A (en) | 1980-06-17 |
Family
ID=4109965
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA290,322A Expired CA1079480A (en) | 1977-11-07 | 1977-11-07 | Process for the preparation of ettringite fibres |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1079480A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113247933A (en) * | 2020-02-10 | 2021-08-13 | 河北工业大学 | Oversized ettringite fiber toughening material and preparation method and application thereof |
-
1977
- 1977-11-07 CA CA290,322A patent/CA1079480A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113247933A (en) * | 2020-02-10 | 2021-08-13 | 河北工业大学 | Oversized ettringite fiber toughening material and preparation method and application thereof |
| CN113247933B (en) * | 2020-02-10 | 2023-06-02 | 河北工业大学 | Oversized ettringite fiber toughening material and preparation method and application thereof |
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