Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BACKGROUND OF TH:~ INVENTION:
FIELD OF THE INVENTION:
.
The present invention relates to a process for preparing a
calcium silicate shaped product. More particularly, it relates to a
process ~or preparing a calcium silicate shaped product which has
low bulk density and excellent mechanical strength ancl is suitable
as a lagging product or a heat insulator.
DESCRIPTION OF THE YRIOR ARTS
~" It h~known to prepare calcium silicate products by
the following processes.
(1) A slurry is prepared by dispersing and mixing a
siliceous source ard a calcareous source and optionally inorganic
materials~,such as clay, asbestos with water~,and the slurry is poured
into a mold and cured in an autoclave (steam curing) and the cured
product is taken out from the mold and dried.
(2) The slurry prepared by the process (l) is heated at 80
to 100C to obtain a gel and the gel is poured into a mold and molded
by a press filter-molding and the product is taken out from the mold
and cured in an autoclave by directly feeding steam (steam curing)
and then, is dried.
(3~ The slurry prepared by the process (1) is heated under
higher pressure wi-th stirring -to crystallize and the resulting slurry
containing crystalline calcium silicate hydrate is poured into a rnold
and the product is molded by a press filter-molding and taken out
from the mold and dried.
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When a calcium silicate product is used as a lagging product
or a heat insulator, it is usually necessary to have high porosity
that is, low bulk density in,,order to obtain a product having low
thermal conductivity. However in the conventional processes, it
has been difficult to obtain a product having low bulk density and
high mechanical strength.
The inventors have found that the process for preparing a
calcium silicate shaped product by press filter molding an aqueous
slurry of a specific calcium silicate hydrate and steam-curing the
molded product to transform the calcium silicate hydrate crystal,
is effective to attain the desired process and have proposed in
Japanese Patent Application 63621/1977 and U. S.P. 4,193, 95~.
The inventors have further studied to improve this process
and have found that when the molded product obtained by press filter-
molding is cured in a closed tank by dry-heating without feeding
steam, uneven pressure and strain caused by the press filter molding
are gradually released without sudden expansion of the molded product
whereby a calcium silicate shaped product having excellent property
without any crack can be prepared in stable operation,
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The present inven-tion provides a process for pre-
paring a ealeium silieate shaped produet having low den-
sity and high meehanieal strength without any erack.
Aeeording to the present invention the process
comprises forming an aqueous slurry of calcium silicate
hydrate by reacting a calcereous souree with a silieeous
souree in wa-ter as a dispersion, under heating; and press
filter molding the aqueous slurry to form a molded produet
having a bulk density of less than 0.6 g/em3; euring the
molded produet in a elosed tank having a eapacity of 1.5
to 30 times of the volume oE the molded product at 140-300C
by dry-heating and -then drying the eured product.
In -the proeess of the present invention, an aqu-
eous slurry of ealeium silieate hydrate, prefereably tober-
morite group compounds having the below-mentioned wet vol-
ume of more than 15 cm /g is prepared by reacting a silic-
eous source with a ealeareous souree in water as an aqueous
dispersion under heating it.
Suitable silieeous sourees inelude natural sourees
sueh as diatomaeeous earth, quartzite and silieon dust;
silica obtained by reacting aluminum hydroxide with hexa-
fluorosilicic acid as a by-product in a wet process for
produeing phosphorie aeid (hereinafter referring to as a
wet proeess phosphorie acid by-product silica) and other in-
dustrial by-produet silica.
~r
llZ~7~
~ The siliceous sources can be arnorphous or crystalline
~`~
~r~, It is preferable to use an amorphous siliceous source s~lch as
diatomaceous earth, the wet process phosphoric acid by-product
silica and silicon dust because a slurry of calcium silicate hydrate
having the wet volume of more than 15 cm /g is easily obtained,
Suitable calcareous sources include quick lime, slaked
lime, carbide waste and other known sources.
The mole ratio of the calcareous source to the siliceous
source as CaO/SiO2 is usually in a range of 0, ~ to 1. 2 in the case
of xonotlite as the hydrated calcium silicate in the shaped product
and it is usually in a range of 0, 7 to 1. 0 ir. the case of tobe~morite
as the calcium silicate hydrate in the shaped product.
The amount of water used for dispersing the siliceous
source and the calcareous source is more than 15 times by weight
especially 17 to 40 times by weight to the solid content.
The aqueous slurry of calcium silicate hydrate can be
usually obtained by reacting both sources dispersed in wate~ at 80
to 230~C for 30 minutes to 10 hours under heating. Various calcium
silicate hydrates can be classiIied by the classification described in
The Chemistry of Cements (Edited by ~I. F. W. Taylor, Department
of Chemistry. University of Aberdeen, Scotlarlt) Volume I P, 182,
Table II.
In the process of the present invention, it is possible to
use anyone of tobermorite group compounds such as tobermorite
gel, C-S-H(II), C-S-H(I) and crystalline tobermorite and ~onotlite.
The calcium silicate hyclrate causes the transformation in the order
of tobermorite gel ~ C- S- E-I(II) ~ C- S- M(I) ~ 11. 3A tobermorite--
faJ
xonotlite whereby suitable crystallille type can be easily obtained by
controlling the reaction ternperature and the reaction time,
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The transformation of the crystalline type is caused to the arrow line
rcl,s j ~q
( j ) depending upon ~the reaction temperature or prolonging
the reaction time. The tobermorite group compound is usually
obtained by the reaction at the temperature for the first condition,
whereas xonotlite is obtained if the reaction temperature is remark-
ably high or the reaction time is remarkably long. In the latter case,
the reaction temperature is decreased or the reaction time is shorten-
ed. It is necessary to use tobermorite gel, C-S-H(I) or C-S-H(II)
as the calcium silicate hydrate in an aqueous slurry if the crystal7ine
tobermorite is desired as the crystal in the final shaped product.
In the process of the present invention, the calciurn silicate
hydrate in the aqueous slurry preferably has a wet volume of more
than 15 cm3/g,
The wet volume is calculated by the equation (I)
wet volume = W ..... (I)
wherein W represents a total weight of the calcareous source and
the siliceous source and V represents a volume of solid components
after 24 hours in a sedimentation of the aqueous slurry obtained by
the reaction,
The wet volume is measured as follows. Wl g of the
aqueous slurry obtained by the reaction (W0 g) is sampled and~,
in stand-still for 24 hours and the volume (V1 cm ) of the
solid cornponents is measured and the wet volume is calculated by the
equation (II);
V
wet volume = - lW (Il)
Wl ~ Wo
wherein W represents a total weight of the equation (I).
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In order to give the wet volume of more than 15 cm3/g, the
reaction is carried out at higher than 130C preferably 150 to 230C
especially 160 to 210C, under stirrillg. It is necessary to maintain
the reaction system in a liquid condition whereby the reaction is
carried out under higher pressure.
The resulting slurry is admixed with a reinforcing fibrous
material and the mixture is molded by press -filter-rnolding. The
reinforcing fibrous material can be incorporated before the prepara-
tion of the slurry, The temperature and pressure in the press filter-
molding are usually in ranges of 30 to 80~C and 1 to 200 kg/cm G
and the bulk density of the shaped product can be controlled by
adjustment of piston stroke of the pressing machine.
In the process of the present invention, the bulk density of the molded
product is usually controlled to be lower than 0. 6 g/cm preferably
in a range of 0. 05 to 0. 6 g/cm3,
Various reinforcing fibrous materials can be used.
Suitable reinforcing fibrous materials include asbestos, rockwool
and glass fiber. The reinforcing fibrous material is usually incorpo-
rated at a ratio of 0. 5 to 10 wt. %.
The resulting molded product is charged into a closed
tank having pressure resistance such as an autoclave which has a
capacity of 1. 3 to 30 times, preferably 2 to 20 times of the volume
of the molded product and is cured by dry-heating in the closed
condition. In the curing treatment, it is heated by a heater etc. to
provide the temperature of air in the tank of la~0 to 300C preferably
160 to 220C especially 1~0 to 210C and to maintain the molding
product in such atmosphere for about 2 to 20 hours.
In -the process of the present inventioll, the molded produc-t
obtained by the pres,s fil-ter-molding has a bulk density of less than
L2~
0. 6 g/cm . That is, the water content of the molded product is
more than 60 wt. %. Such molded product is heated to generate
steam from the molded product and the molded product is cured by
the self-generated steam.
In accordance with the dry heat curing, it is necessary
to attain the transformation from the molded product obtained by
the press filter-molding of the aqueous slurry of tobermorite gel,
C-S-H(I) or C-S-H(II) into crystalline tobermorite or xonotlite or
from the molded product obtained by the press filter molding of the
aqueous slurry of crystalline tobermorite into xonotlite.
When xonotlite is expected as the crystal of the Einal
shaped product, it is heated to provide the temperature OI air in the
tank of 170 to 250C. When tobermorite is expected as the crystal
of the final shaped product, it is heated to provide 140 to 230C.
As described above, in the process of the present invention,
steam is not directly fed into the closed tank whereby any condensed
water does not contact with the molded product before the growth of
the crystal or the transformation and accordingly any sudden expan-
sion of the molded product is not caused, and any crack is not caused.
The process of the present invention has been illustrated
in detail. In accordance with the present invention, it is possible
to obtain a calcium silicate shaped product having no cracks and having
high bending strength of 5 to 8 kg/cm at a bulk density of about
0.10 g/cm and having excellent dimension s-tability and thermal
insulating property and has high refractoriness at the temperature
of about 650 to 1000C. Accordingly, the calcium silicate shaped
product can be used in various fields such as a reEractory, heat
insulators and construc-tion suhstrates.
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The present invention will be illustrated by certain examples
which are provided for purpose of illustration only and are not intended
to be limiting unless otherwise specified.
EXAMPLE 1:
A slaking was carried out by adding hot water to 43. 2 wt,
parts of quick lime (98% of CaO)and 46. 8 wt. parts of ground quartzite
(97. 0% of SiO2; 1, 2% of A1203 arld 0, 09% of Fe203)(manufactured by
Tokai Kogyo Co., Ltd. ) was added to the slaked lime cmd water was
added to give 30 times by weight of water to the solid content. The
resulting suspension was stirred in an autoclave at 200C under the
pressure of 15 kg/cm2 G for 2, 5 hours to react them, whereby an
aqueous slurry of the C-S-H(I) having the wet volume of 23 cm3/g
was obtained. The aqueous slurry was admixed with 3 wt.parts of
an alkali resistan+ glass fiber and the mixture was heated at 70C
and shaped by a press filter-molding at 70C under a p~essure of
5 kg/crn in a size of 200 mm x 200 mm x 30 mm under controlling
- a feed of the slurry so as to give a bulk density of 0. 10, or 0. 25 g/cm3.
Each resulting molded product was charged in an autoclave
having a capacity of three times of the molded product and was cured
by heating in the autoclave at 200C by a heater for 7 hours. The
pressure resulted by steam generated from the molded product was
10 kg/cm G. The molded product was transformed from C-S-H(I)
into xonotli-te crystal by the curing. The molded product was further
dried at 150C for 6 hours.
The resulting shaped products had each bulk density of
0. 10 or 0, 25 g/cm3 and each bending strength of 6. 0 or 28 kg/cm2
and had the same size as the sizes of the molded products obtained
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by the molded product formed by the press filter molding and had
not any crack.
REFERENCE 1:
In accordance with the process of Example 1, the aqueous
slurry was controlled to give a bulk density of 0. 25 g/cm3 and press
filter-molded, and the resulting molded product was charged in the
autoclave having a capacity of three times of the molded product ancl
cured by directly feeding steam under the condition of 180C and
10 kg/cm for 7 hours to transform from C-S-H(I) into xonotlite
crystal. The molded product was further heated at 150aC for 8 hours.
The resulting shaped product had the same bending strength but had
cracks on the side surface.
EXAMP LE 2:
The aqueous slurry obtained by the process of Example 1
was controlled to give a bulk density of 0.10 g/cm and press filter-
molded to form a lagging product for pipe-cover having an inner
diameter of 90 mm, an outer diameter of 170 mm and a thickness
of 40 mm. The molded product was charged in an indirect heating
type autoclave equipped with a jacket and cured for 8 hours by main-
taining the inner temperature at 180C by a heat medium system.
The pressure resulted by steam generated from the molded product
was 8 kg/cm G. The molded product was transiormed from
C-S-H(I) into xonotlite crystal by the curing. The molded product
was further dried at 150C for 8 hours. The resulting shaped product
had a bulk density of 0, 1 g/cm2 an(l had the same size as the size
of thc molded product obtained by the press filter-molding and had
not ~my crack.
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REFERENCE 2:
The molded product obtained by the press filter molding
in Example 2 was heated in a dryer at 180C for 8 hours. The molded
product was highly shrinked.
