Note: Descriptions are shown in the official language in which they were submitted.
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),
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.
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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.
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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
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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
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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
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: - 4(b) -
C
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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-
1 000 470
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
~ _ _ . .. . .. . . . . .. ... . ..... . . . . . . .
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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.
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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.
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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
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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.
EXAMPLE 3
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
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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.
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