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 producing
a calcium silicate shaped product, More particularly, it relates to
S a process for produs~ing a calcium silicate shaped product which has
low bulk density and excellent refractoriness, heat resistance,
mechanical strength and dimensional stability and is suitable as a
refractory coat, a heat insulator and a lagging product,
~U
Calcium silicate shaped products especially products made of
xonotlite as a main component usually have heat resistance to a tem-
perature of at least 1, 000 C to be suitable as a lagging product, a heat
insulator and a refractory.
In usual, calcium silicate shaped products used for a lagging
product, a heat insulator and a refractory should have low thermal
conductivity and high mechanical strength. Such calcium silicate
shaped products have been produced by reacting a calcareous source
such as calcium oxide with a siliceous source such as a diatomaceous
earth in the presence of water under heating to obtain an aqueous slurry
and press filter-molding the aqueous slurry and drying the molded
product or steam-curing and drying the molded product. If the rnolded
product is steam-cured or dried just after the press filter-molding,
cracks may be formed in the shaped product by suddenly releasing
une~en pressure distribution and strain caused in the press filter-
molding.
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The inventors have studied the above-rnentioned problem and
have found that an excellent calcium silicate shaped product having no
crack can be prepared in s-table by a heat treatment under a specific
condition before -the steam-curing or drying of the molded product after
the press filter-molding of the aqueous slurry.
SUMMAR Y OF T~-TE INV ENI'ION:
It is an object of the present invention to provide a process
for preparing a calcium silicate ~haped product having low bulk density
and high mechanical strength without cracks.
The foregoing and other objects of the present invention have
been attained by producing a calcium silicate shaped product by forrning
an aqueous slurry of calcium silicate hydrate obtained by reacting
a calcareous source with a siliceous source dispered in water under
heating; molding said aqueous slurry; and heat-treating said molded
product under the condition pro-viding the equations (I) and (II):
100 5 0 T ...... (I)
50 ~ O ~ 300 ... .(II~
wherein ~3 represents a temperature cf the inner part of the molded
product (C) and T represents a time (hour) and providing a percent
water loss of the treated molded product of less than 25 wt.% before
drying or steam-curing and drying the molded product.
DETAILED DESCRIPTION OF THE PREFEI~RED EMBOD IENTS:
In the process of the present invention, an aqueous slurry o
calcium silicate hydrate preferably a tobermorite group compound
having the below-mentioned wet volume of more than 15 cm3/g is
prepared by reacting a siliceous source with a calcareous source in
j~ water as an aqueous dispersion under heating ~.
Suitable siliceous sources include natural sources such as
d;atomaceous earth, quartzite and silicon dust; silica obtained by
reacting aluminum hydroxide with hexafluorosilicic acid as a by-product
in a wet process for producing phosphoric acid (hereinafter referring to
as a wet proc~ess phosphoric acid by-product silica) and other industrial
by-product silica.
The æiliceous sources can be amorphous or crystalline f~rnr,
It is preferable to use an amorphous siliceous source such 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 cm3/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, 8 to 1. 2 in the case of
~onotlite as the hydrated calcium silicate in the shaped product and it is
usually in a range of 0. 7 to 1. O in the case of tobermorite as the
calcium silicate hydrate in the shaped product.
ZO 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, Various calcium silicate
hydrates can be calssified by the classification described in the
Chemistry of Cements (Edited by H.F.W. Taylor, Department of
2S Chernistry. University of Aberdeen, Scotland) Volume I P. 182,
Table II.
In the pr ocess 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 xonotlite.
The calcium silicate hydrate causes the transformation in the order of
tobermorite ~el~- )C-S-T-I(II) ~C-S-I~ ll.3A tobermorite~
xonotlite where~y a suitable crystalline type can be easily
obtained by controlling the reaction -temperature and the
reaction time in ranges of 80 to 230C and 30 minutes to 10
hours. The transforrnation of the crystalline type is caused
to the arrow line ( -~) depending upon raising the reaction
temperature or prolonging the reaction time. It is l~eces--
sary to use tobermorite gel, C--S-~I(I) or C-S-H(II) as the
calcium silicate hydrate in an aqueous slurry if the crys-
talline tobermorite is desired as -the crystal in the final
shaped produc-t.
In the process of the present invention, the cal-
cium silicate hydrate irl the aqueous slurry preferably has
a wet volume of more than 15 cm3/g.
The wet volume is calculated by the equation (III)
wet volume = W - .(III
wherein W represents a total weight of the calcareous
source and the siliceous source and V represen-ts a volume of
solid components after 24 hours sedimentation of the aqueous
slurry obtained by the reac-tion.
The wet volume is measured as follows. Wl g of the
aqueous slurry obtained by the reaction (WOg) is sampled and
and kept in stand-still for 24 hours and the volume (Vl cm )
of the sedimented solid components is measured and the wet
volume is calculated by the equation (IV):
V
wet volume = Wl x W ....(IV)
WO
wherein W represents a total weight of the equation (III).
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~,S~ I
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In order to give the wet volurne of more than
15 cm3 /g, the reaction is carried out at higher than 130C
preferably 150 to 230C especially 160 to 210C, under
stirring. It is ne~essary to maintain
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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 rnixture is molded by the pxess filter-molding, The
reinforcing fibrous material can be incorporated before the preparation
of the slurry, The temperature and pressur e in the press filter molding
are usual]y in ran~ges pf 30 to 80C and 1 to 200 kg. /cm2G and the bulk
density of the n~ product can be controlled by adjustment of piston
s-troke of the pressing machine.
Various reinforcing fibrous materials can be used. Suitable
reinforcing fibrous materials include asbestos, rockwool and glass
fiber. The reinforcing fibrous material is usually incorporated at a
ratio of 0.5to 10 wt.%,
The resulting molded product is hea-t-treated under the
condition providing the equations (I) and (II);
100< ~). T preferably 100 ~. T < 1,000, .... (I)
50 ~ <300 preferably 70 < (3 ~230, .... (II)
wherein ~ represents a temperature of the inner part of the molded
product (C) and T represents a time (hour) and providing a percent
water loss of the treated molded product of less than 25 wt.% preferably
less than 10 wt.% especially less than 5 wt.%.
When the temperature of the inner part of the molded product
used for the heat-treatment is lower than 50OC, the heat-treatment
under the above mentioned condition is carried out after pre-heating
the molded product by a suitable heating device. When the temperature
of the inner part of the molded~p,roduct is higher than 500C, it can be
directly heat-treated or also~'c~an be heat-treated after heating it to
a desired temperature of the inner part if necessary,
if excess of water is re(-luced from the nlolded
p~oduct, the molded product is highl,y shrinked. Therefore,
in the process of the present invention, it is preferahle
to use an apparatus havi,ng closing effect for presentlng
such adverse effect and having an outer jacket for in-
directly heating it or havi,ng an inner heater. in the
heat--treatment, a small amount of water can be added in the
apparatus so as to control the percent water loss o~ the
molded product.
In the process of the present Inven-tion, it is
preEerable to use an autoclave equipped with a heater, etc.
in the heat-treatment so that the steam-curing can be car-
ried out hy following to the heat-treatment without any
movement.
The molded produc-t is cured under higher pressure
by the steam curing, that is, the curing in an autoclave
(induration).
In accordance with the steam curing, it i,s neces-
sary to attain the transformation from tobermorite gel,
C-S-H(I) or C-S-H(II) to crystalline tobermorite or xonotlite
or from crystalline tobermorite to xonotlite. In accor-
dance with the transformation of the crystalline form byt,he steam curing, a shaped product having low bulk density
and excellent mechanical strength can be obtained.
The reaction time can be shortened by i,ncreasing
the steam pressure. The steam pressure is usually in a
range of 5 to 50 kg./cm G and it is especially in a range
of 12 to 40 kg./cm2G to obtain the shaped product of xonot-
lite and in a range of 6 to 30 kg./cm2G to obtain the shaped
product of tobermorite.
The transformation is easily attained under these
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z~
conditions. When a desirecl trallsForma-tion was not atta:ined,
for example, tobermorite is formed evell though xonotlile
is expected, the desired t~ansformation may be attained
by increasing the steam pressure or prolonging t'ne steam
curing time. When xonotlite is Eormed even though tobermor-
ite is expected, the desired transformation may be atta-Lned
by falling the steam pressure or shor-tening the stecim curing
time.
In the usage for requirinq high heat resistarlce,
it is preferable to transform into xonotlite. The product
is further treated by the dry--treatment to obtain a desired
calcium silicate shaped product.
lS In the case of the calcium silicate shaped pro~-
duct obtained by press-filter molding the aqueous slurry
containing xonotlite, the product can be treated by the dry-
treatment without any steam curing.
The process of the present invention has been
illustrated in detail. In accordance with the present in-
vention, it is possible to obtain a calcium silicate shaped
product having no cracks and having high bending strength
of more than 5 kg./cm2 at a bulk density of about 0.10 g./cm3
more than 30 kg./cm2 at a bulk density of about 0.30 g/cm3
and more than 100 kg~/cm2 at a bulk density of 0.55 g./cm3.
It can have various shapes as a lagging material, ect. with
excellent dimension stability. The resulting calcium sili-
cate shaped product has remarkably high therma] 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 re-
fractory heat insulator and construction substrate.
The present invention will be illustrated by cer-
tain examples which are provided for the purpose of illus-
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tration only and are not intencled to be limiting unless
otherwise specifiecl.
EXAMPIE_]
A slaking was carried out by addill~3 }-~ot water lo
43.2 wt. parts of quick lime (9~,% of CaO) and ~6.8 wt.
parts of ground quartzite (97.0~, of SLO2; 1.2" of AQ2O3 an(:l
0.09% of Fe2O3) (manufactured by
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~ ~32~19~11
Tokai Kogyo Co., Ltd. ) was added to the slaked lime and water was
added to give 30 times by weight of water to the solid content, The
resulting suspension was stirred in an autoclave at 2UO~C 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 resistant glass fiber and the mixture was heated at 700C and
shaped by a press filter-molding at 700C under a pressure of 5 kg, /cm2
in a size of Z00 mm x 200 mm x 30 mm under controlling a feed of the
slurry so as to give a bulk density of 0, 1OJ 0. 30 or 0, 55 g, /cm3,
Each resulting molded product was heat-treated in the atmosphere at
,~ 700C for 3 hours, ~ percent water loss caused by the heat treatment
was 5 wt . %,
Each resulting heat treated-molded product was cured with
steam in an autoclave at 180C under a pressure of 10 kg. /cm2 G,
for 7 hours and then, dried at 150C for 8 hours.
The resulting shaped products had not any crack and had
each bulk density of 0,10, 0, 30 or 0, 55 g, /cm3, The sizes of the
products were the same as the sizes of the molded product formed by
the press filter molding. The resulting shaped products had each
bending strength of 60 3, 38 or 100 kg, /cm2. The crystal was identified
to be xonotlite.
REFERENCE 1-
_
In accordance with the process of Example 1, the rrlolded
product obtained by the press filter molding was steam-cured in an
autoclave at ~ 80 C under a steam pressure of 10 kg, /cm2 G. for 7 hours
without the heat treatment, and the molded product was dried at 150C
for 8 hours, The resulting shaped product had the same bending
`
3~
strength as the product of Example 1, but had cracks on the side
surface of the shaped product. The crys-t was identifed to be xonotlite,
EXAMP'LE 2:
The aqueous slurry obtained by the process of Exarrlple 1
was used to control the amount so as to give a bulk density of 0.10 g. /
cm3 and was press filter molded to form a lagging product for pipe-
cover having an inner diarneter of 90 mm, an outer diameter of 170 mm
and a thickness of 40 mm at 70OC under a pressure of 5 kg, /cm2,
The molded product was heated in a heating apparatus to
raise a temperature of the inner part of the molded product from 70C
to 95 C and to maintain the temperature for 2 hours in the heat-
treatment, After the heat treatment, the molded product was charged
in an autoclave and steam-cured at 200C under a pressure of 15 kg. /
cm2 G for 4 hours and then, was dried at 150OC for 8 hours. The
resulting shaped product had a bulk density of 0, :L g, /cm3. The crystal
was identified to be xonotlite, The size was the same as the size of the
molded product obtained by the press filter-molding. The shaped
product had not any crack.
REFERENCE 2-
The molded product obtained by the press filter molding of
Example 2 was heated in a heating apparatus from 70OC to 80OC and
heat-treated at 80C for l hour.
After the heat treatment, the molded product was steam-
cured and dried in accordance with the process of Example 2.
2S The resulting shaped product had the increased thickness for
2 mm by increasing from 40 mm to 42 mm and had small cracks along
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.'1 ~ ~3,'~ffl~
-the edges, The phenomenon was the same as that of non-heat-treatment.
E MPIJE 3:
The aqueous slurry obtained by the process of Example 1 was
used to control the amount so as to give a bulk density of 0.10 g, /cm3
and was press filter-molded to form a lagging product for pipe-cover
having an inner diameter of 74 mm, an outer diameter of 204 mm and
a thicknes~ of 65 rnm at 70 C under a pressure of 5 kg. /cm,
The molded product was heated in a heating apparatu.s to
raise a temperature of the inner part of the molded product from 70OC
to 80~C and to maintain the temperature of 80C for 5 hours in the
heat-treatment. After the heat treatment, the molded product was
charged in an autoclave and steam-cured at 180C under a pressure of
10 kg. /cm2 G for 7. 5 hours and then, was dried at 130 C for 12 hours,
The r~ sulting shaped product had a bulk density of 0, 10 g. /cm3.
The crystal was identified to be xonotlite. The size was the same as
the size of the molded product obtained by the press filter molding,
The shaped product had not any crack.
EXAMPLE 4:
The aqueous slurry obtained by the process of Example 1
was used to control the amount so as to give a bulk density of 0.10 g. /
cm3 and was press filter~molded to form a lagging product for pipe-
cover having an inner diameter of 74 mm, an outer diameter of Z04 mm
and a thickness of 65 mrn at 60C under a pressure of 5 kg, /cm2.
The molded product was charged in an autoclave equipped with a fine
tube heater in the inner part and heated by the heater to carry out the
heat treatment at 75C for 8 hours and then, steam was fed to carry
Z~
out the steam~curing at 180 C under a pressure of 10 kg. /cm2 for
7, 5 hours and then, the product Wr'lS dried at 130C for 12 hours, The
resulting shaped product had a bulk density of 0. lû g, /cm3, 'I'he crystal
was identified to be xonotlite, The size was the same as the size of the
molded product obtained by the press filter-molding, The shaped
product had not any crack,
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