CA1182980A - Process for preparing calcium silicate shaped product - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE:

A process for producing a shaped calcium silicate product comprises (a) forming an aqueous slurry of calcium silicate hydrate obtained by heating and reacting a calcareous source with a siliceous source in water as a dispersion; (b) molding said aqueous slurry into a shaped object; (c) heat treating said molded product under the conditions specified by the following relationships (I) and (II):

100 ? .theta. ? T ......(I) 50 ? .theta. ? 300 ......(II) wherein 0 represents the temperature (°C) of the interior of said molded product and T represents the time (hrs), with the proviso that the amount of water loss during said heat treatment is less than 25 wt.%; (d) optionally steam curing said treated product; and (e) drying the cured product.

Description

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.

- 2 -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).

-~ - 5 -~,S~ I

~ z~

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 :l5 ';

5a -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 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-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 - 8a -~ ~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.

_ 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.

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 .'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,

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for producing a shaped calcium silicate product, comprising: (a) forming an aqueous slurry of calcium silicate hydrate obtained by heating and react-ing a calcareous source with a siliceous source in water as a dispersion; (b) molding said aqueous slurry into a shaped object; (c) heat treating said molded product under the conditions specified by the following relationships (I) and (II):

100 ? .theta. . T .......(I) 50 ? .theta. ? 300 .......(II) wherein .theta. repesents the temperature (°C) of the interior of said molded product and T represents the time (hrs), with the proviso that the amount of water loss during said heat treatment is less than 25 wt.%; and (d) drying the treated product with or without prior steam curing of the treated product.

2. The process of claim 1, wherein said aqueous slurry contains a calcium silicate of the tobermorite struc-ture having a wet volume of more than 15 cm3/g as defined by the equation:

wet volume = , wherein W represents the total weight of the calcareous source and the siliceous source and V represents the volume of the solid components after the aqueous slurry has set-tled for 24 hours.

3. The process of claim 1, wherein said aqeuous slurry of calcium silicate hydrate is admixed with a rein-forcing fibrous material and the resulting mixture is molded by press filter-molding and cured.

4) The process of Claim 1, wherein said aqueous slurry of calcium silicate hydrate is prepared by mixing the siliceous source and the calcareous source with a reinforcing fibrous material and heating the resulting mixture in water followed by completing the preparation of said molded product by press filter-molding said aqueous slurry and curing the molded product.

5) The process of Claim 1, wherein the reaction of the siliceous source and the calcareous source is conducted at a temperature of 150°C to 230°C.

6) The process of Claim 1, wherein the heat treating conditions of step (c) are defined by the relationships (I') and (II'):
100 ? .theta. ? T ? 1,000 ......(I') 70 ? .theta. ? 230 ...............(II')

7) The process of (Claim 1, wherein said heat treatment of step (c) is conducted under the provisions in which less than 10 wt.%
of the water is removed.

8) The process of Claim 1, wherein said heat treatment of step (c) is conducted under the provisions in which the amount of water removed is less than 5 wt.%.

9) The process of Claim 1, wherein the steam pressure during steam curing of the molded and heat treated product is conducted at a pressure ranging from 5 to 50 kg/cm2 G.

10) The process of Claim I, wherein the steam pressure during steam curing of the molded and heat treated product is conducted at a pressure ranging from 6 to 30 kg/cm2 G.