GB2405402A

GB2405402A - Calcium silicate hardened article

Info

Publication number: GB2405402A
Application number: GB0427475A
Authority: GB
Inventors: Akihiro Ogawa; Hiroyoshi Matsuyama
Original assignee: Asahi Kasei Corp; Asahi Chemical Industry Co Ltd
Current assignee: Asahi Kasei Corp; Asahi Chemical Industry Co Ltd
Priority date: 2002-07-03
Filing date: 2003-07-03
Publication date: 2005-03-02
Anticipated expiration: 2023-07-03
Also published as: WO2004005215A1; JPWO2004005215A1; JP4343108B2; DE10392839B4; GB0427475D0; CN1780800A; TW200402395A; DE10392839T5; AU2003246260A1; GB2405402B; CN100352786C; TWI227702B

Abstract

A calcium silicate hardened article which has a flexural strength of 0.05 MPa or more, a heat conductivity of 0.02 to 0.1 Wm<-1>K<-1>, and an air permeability of 5 X 10<-4> to 1 m<2>h<-1>Pa<-1> or less, and exhibits dynamic insulating property.

Description

LPATENT OFFICE C,ii'<5 Ivy GUPY 1 2405402

TITLE OF THE INVENTION

Cured form of calcium silicate

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a cured form of calcium silicate exhibiting a dynamic insulating prop erty. More particularly, the present invention is con cerned with a cured form of calcium silicate having a flexural strength of 0.05 MPa or more, and having a thermal conductivity of from 0.02 to 0.1 WmlKl and a gas permeability of from 5 x 10-4 to 1 m2hlPal, thereby exhibiting a dynamic insulating property. The cured form of calcium silicate of the present invention not only has a light weight and a high strength, but also is incombustible. Further, the cured form of calcium silicate of the present invention simultaneously exhib its high thermal insulating property and high gas per meability. Therefore, the cured form of calcium sili cate can be advantageously used as a wall material for buildings and the like, which is required to exhibit a dynamic insulating property. Herein, the "dynamic in sulating property" means a property wherein high perme ability and thermal insulating effect are simultane ously achieved. A building wall material which exhib its a dynamic insulating property can be advantageously used in the so-called "dynamic insulation technique" in which a planned ventilation (i.e., constant or inter mittent ventilation for keeping room air fresh) is per formed while reducing the heat energy loss. Further, the present invention is also concerned with a method for producing the above- mentioned cured form of calcium silicate.

Prior Art

Currently, there has been an increasing need for energy saving due to serious public problems, such as depletion of fossil fuel, air pollution caused by the massive use of fossil fuel, and global warming caused by carbon dioxide generated from fossil fuel. Espe cially in houses and buildings for commercial use, the amount of energy consumed has been increasing in accor dance with the growing tendency to desire a comfortable living space provided by the use of an air-conditioner.

Therefore, it has been attempted to save energy by ren dering the buildings highly heat-insulative and highly airtight. However, in an enclosed space which has been rendered highly heat-insulative and highly airtight, the room air quality is deteriorated by activities in the space. Therefore, for keeping the room air clean, a dehumidifier, a vaporizer, an air cleaner, etc. have been used, which, however, result in the lowering of the energy saving effect achieved by the above -mentioned enclosed space. Thus, in recent years, in buildings having an enclosed space which has been ren dered highly heat-insulative and highly airtight, a planned ventilation (i.e., constant or intermittent ventilation for keeping room air fresh) becomes neces sary and, hence, there have been demands for building designs and building materials which are effective for both heat insulation and ventilation.

However, it is known that the lowering of the heat transfer coefficient at walls and ceilings of a build ing is limited due to the structures thereof, and that, hence, the reduction in the loss of heat energy at walls and ceilings is also limited.

In this situation, the so-called "dynamic insula tion technique" in which the above-mentioned planned ventilation is performed while reducing the loss of heat energy have been studied mainly in northern Euro pean countries. Specifically, in the dynamic insula tion technique, outside air is introduced indoors through a heat insulation material used in walls and ceilings, to thereby prevent indoor heat from escaping outdoors through the walls and the ceilings. In this technique, the outside air introduced indoors through the heat insulation material is fresh, and the outside air is preheated in the wall material before being in troduced indoors. As a result, it becomes possible to perform the preheating of ventilation air (outside air which is introduced indoors) while lowering the appar ent heat transfer coefficient, thereby maintaining the room air quality at a high level.

For effectively practicing the dynamic insulation technique, it is necessary to use a material which has not only high thermal insulating property, but also high gas permeability. Further, such a material used for performing the dynamic insulation technique is de sired to exhibit excellent processability, excellent cost performance and high strength. Furthermore, from the viewpoint of a demand for fire resistance, such a material is desired to be incombustible.

Conventionally, as heat insulation materials, or ganic foam-type insulation materials have been used.

However, organic foam-type insulation materials have a high ratio of closed cells, thus exhibiting low gas permeability. Therefore, the organic foam-type insula tion materials are not suitable for use in the dynamic insulation technique. Further, organic foam-type insu ration materials have problems with respect to fire re sistance. On the other hand, as inorganic insulation materials, there can be mentioned a foamed glass which is obtained by foaming a glass. However, the foamed glass is expensive, and also has a high ratio of closed cells, thus exhibiting low gas permeability. Therefore, the inorganic insulation materials are also not suit able for use in the dynamic insulation technique. Fur ther, W002/06693 and Unexamined Japanese Patent Appli cation Laid-Open Specification No. 2001-122674 disclose techniques relating to a cured form of calcium silicate.

However, the cured form of calcium silicate obtained by the techniques described in the above-mentioned patent documents has low gas permeability and, thus, does not function as a dynamic insulation material.

In the conventional dynamic insulation technique, a wall material used is obtained by a method in which a frame having compartments having predetermined sizes is provided, and the compartments are filled with a heat insulation material, such as pulp pieces obtained from a recycled paper, and inorganic fibers (e.g., rock wool). However, such a frame itself has a thermal con ductivity higher than that of the heat insulation mate rial in the compartments, so that heat is conducted through the frame. For this reason, there is a problem in that the above- mentioned wall material cannot ex hibit a satisfactory dynamic insulation effect. Fur ther, in the conventional dynamic insulation technique, heat loss occurs at the gaps which are inevitably formed between the frame and the heat insulation mate rial blown into the compartments of the frame of the wall material. Thus, the conventional dynamic insula tion technique poses another problem in that, in prac tice, it is necessary to increase the thickness of a wall material so as to compensate for the above mentioned heat loss occurring at the gaps which are formed between the frame and the heat insulation mate rial.

Conventional building materials, such as a wood cement board and a concrete block, have an apparent specific gravity of 0.5 or more, thus exhibiting high thermal conductivity. Such high thermal conductivity inevitably causes great loss of heat energy. Therefore, conventional building materials pose a problem in that a satisfactory dynamic insulation effect cannot be ob tained. Further, Unexamined Japanese Patent Applica tion Laid-Open Specification No. 2001-348283 discloses a technique using a sound absorbing material. However, the sound absorbing material disclosed in the above -mentioned patent document has an apparent specific gravity around 0.35, thus exhibiting high thermal con ductivity. Therefore, the above- mentioned sound ab sorbing material is not suitable as a dynamic insula tion material.

Further, it has been attempted to use a rock wool board and a glass wool mat, each of which has a low thermal conductivity, as dynamic insulation materials.

However, the use of a rock wool board and a glass wool mat as dynamic insulating materials poses the following problems. The rock wool board and the glass wool mat are not actually hard materials, but are rather formed merely by entangling cotton fibers or thin fibers with each other and, hence, have a low flexural strength.

Therefore, each of the rock wool board and the glass wool mat needs to be reinforced by a beam or a frame so as to secure sufficient strength as a building material.

However, the beam and the frame conduct heat there through. Therefore, the use of the rock wool board or the glass wool mat poses a problem in that a satisfac tory dynamic insulation effect cannot be obtained.

Further, during the cutting of the rock wool board or the glass wool mat at a construction site, harmuful mi crofibers are generated and scattered, which damage the health of workers. Furthermore, each of the rock wool board and the glass wool mat has too high a gas perme ability and, thus, cannot be used independently as a dynamic insulation material. When it is intended to use the rock wool board or the glass wool mat as a dy namic insulation material, a plastic sheet having a large number of holes needs to be used to cover a sur face of each of the above-mentioned board and mat, which surface faces indoors. Therefore, problems arise in that the construction process becomes cumbersome and in that the fire resistance of the insulation material as a whole is lowered.

SUMMARY OF THE INVENTION

In this situation, the present inventors have made extensive and intensive studies with a view toward solving the above-mentioned problems accompanying the prior art. As a result, it has unexpectedly been found that a cured form of calcium silicate having specific properties, which is suitable as a dynamic insulation material, can be obtained by a method comprising: add ing a foaming agent to an aqueous slurry comprising a solid mixture which consists essentially of specific amounts of a siliceous material, a cementitious mate rial, at least one aluminum compound selected from the group consisting of aluminum sulfate and a hydrate thereof, and a sulfate compound other than aluminum sulfate and a hydrate thereof, and optionally a cal careous material; pouring the resultant aqueous slurry into a mold; and procuring the aqueous slurry, followed by autoclaving, with the proviso that the weight ratio of water to the solid mixture is controlled to 0.6 or less, or that, when the above-mentioned weight ratio is more than 0.6, at least two additives selected from the group consisting of a surfactant, a viscosity modifier and an anti-foaming agent are added to the aqueous slurry. Specifically, the above-mentioned cured form of calcium silicate has a flexural strength of from 0.05 MPa or more, and has a thermal conductivity of from 0.02 to 0.1 WmlKl and a gas permeability of from x 10-4 to 1 m2hlPal, thereby exhibiting a dynamic in sulating property. The above-mentioned cured form of calcium silicate not only has a light weight and a high strength, but also is incombustible. Further, the cured form of calcium silicate exhibits both high ther mal insulating property and high gas permeability.

Therefore, the cured form of calcium silicate can be advantageously used as a wall material for buildings and the like, which is required to exhibit a dynamic insulating property. Based on these findings, the pre sent invention has been completed.

Accordingly, it is an object of the present inven tion to provide a cured form of calcium silicate which not only has a light weight and high strength, but also is incombustible, and which exhibits both high thermal insulating property and high gas permeability, so that it can be advantageously used as a wall material for buildings and the like, which is required to exhibit a dynamic insulating property.

It is another object of the present invention to provide a method for efficiently producing the above -mentioned cured form of calcium silicate.

The foregoing and other objects, features and ad vantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings: Each of Figs. 1 and 2 is a graph showing a powder X-ray diffraction pattern obtained with respect to a cured form of calcium silicate produced in Example 13, wherein how to obtain the values of Ia and Ib is also indicated, and wherein "CPS" is an abbreviation for "counts per second"; Fig. 1 is a graph showing a powder X-ray diffrac tion pattern obtained with respect to the cured form of calcium silicate produced in Example 13, wherein the values of Ia (the minimum diffraction intensity ob served in the diffraction angle range between the two diffraction peaks respectively ascribed to the (220) plane and (222) plane of the tobermorite) and Ib (the diffraction peak intensity ascribed to the (220) plane of the tobermorite) are also indicated; Fig. 2 is a graph showing a powder X-ray diffrac tion pattern obtained with respect to the cured form of calcium silicate produced in Example 13, wherein the methods for determining the values of 1(220) [the dif fraction peak intensity ascribed to the (220) plane of the tobermorite] and 1(002) [the diffraction peak in tensity ascribed to the (002) plane of the tobermorite] are indicated; and Fig. 3 shows an explanatory diagrammatic view showing an example of an apparatus which is used for measuring the gas permeability as defined in the pre sent invention.

Description of Reference Numerals

l: Sample 2: Sample holder equipped with a rubber packing 3: Vacuum pump 4: Pressure regulating valve 5: Pressure regulating vessel 6: Differential pressure gauge 7: Flowmeter

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, there is pro vided a cured form of calcium silicate, having (1) a flexural strength of 0.05 MPa or more, and having (2) a thermal conductivity of from 0.02 to 0.1 WmlKl and (3) a gas permeability of from 5 x 10-4 to 1 m2hlPal, thereby exhibiting a dynamic insulating property.

For easy understanding of the present invention, the essential features and various preferred embodi ments of the present invention are enumerated below.

1. A cured form of calcium silicate, having (1) a flexural strength of 0. 05 MPa or more, and having (2) a thermal conductivity of from 0.02 to 0.1 WmlKl and (3) a gas permeability of from 5 x 10.-4 to l m2hlPal, thereby exhibiting a dynamic insulating property.

2. The cured form of calcium silicate according to item 1 above, which has a thermal conductivity of from 0.02 to 0.08 WmlK.

3. The cured form of calcium silicate according to item 1 above, which has a thermal conductivity of from 0.02 to 0.06 WmlKl.

4. The cured form of calcium silicate according to any one of items 1 to 3 above, which mainly comprises tobermorite and exhibits a powder X-ray diffraction pattern in which the diffraction peak intensity Ib as cribed to the (220) plane of the tobermorite and the minimum diffraction intensity Ia observed in the dif fraction angle range between the two diffraction peaks respectively ascribed to the (220) plane and (222) plane of the tobermorite satisfy the relationship Ib/Ia 2 3.

5. A method for producing a cured form of calcium silicate, which comprises: (1) providing an aqueous slurry comprising water and a solid mixture, the solid mixture consisting essentially of a si liceous material, a cementitious material, at least one aluminum compound selected from the group consisting of aluminum sulfate and a hydrate thereof, at least one sulfate compound selected from the group consisting of sulfates other than aluminum sulfate and hydrates thereof, and optionally a calcareous material, wherein the at least one aluminum compound is con tained in the aqueous slurry in an amount of from 0.09 to 10 % by weight in terms of the amount of Al203, based on the weight of the solid mixture, and the at least one sulfate compound is contained in the aqueous slurry in an amount of from 0.15 to 15 % by weight in terms of the amount of S03, based on the weight of the solid mixture, the amount of SO3 being the sum of the amount of the SO3 corresponding to the at least one aluminum compound and the amount of the SO3 correspond ing to the at least one sulfate compound, wherein the weight ratio of the water to the solid mixture is from 2.3 to 5.5, and wherein the weight ratio of the calcareous mate rial to the cementitious material is 0.6 or less: (2) adding a foaming agent to the aqueous slurry; (3) pouring the aqueous slurry into a mold; and (4) procuring the aqueous slurry, followed by auto claving.

6. The method according to item 5 above, wherein the foaming agent is at least one member selected from the group consisting of an aluminum powder and an aluminum containing aqueous slurry, and wherein the foaming agent is used in an amount of from 0.03 to 0.95 % by weight in terms of the weight percentage of the solids contained in the foaming agent, based on the weight of the solid mixture.

7. A method for producing a cured form of calcium silicate, which comprises: (1) providing an aqueous slurry comprising water and a solid mixture, the solid mixture consisting essentially of a si liceous material, a cementitious material, at least one aluminum compound selected from the group consisting of aluminum sulfate and a hydrate thereof, at least one sulfate compound selected from the group consisting of sulfates other than aluminum sulfate and hydrates.

thereof, and optionally a calcareous material, wherein the at least one aluminum compound is con tained in the aqueous slurry in an amount of from 0.09 to 10 by weight in terms of the.amount of Al203, based on the weight of the solid mixture, and the at least one sulfate compound is contained in the aqueous slurry in an amount of from 0.15 to 15 % by weight in terms of the amount of S03, based on the weight of the solid mixture, the amount of SO3 being the sum of the amount of the SO3 corresponding to the at least one aluminum compound and the amount of the SO3 correspond ing to the at least one sulfate compound, wherein the weight ratio of the water to the solid mixture is from 2.3 to 5.5, and wherein the weight ratio of the calcareous mate rial to the cementitious material is more than 0.6; (2) adding a foaming agent to the aqueous slurry; (3) pouring the aqueous slurry into a mold; and (4) precuring the aqueous slurry, followed by auto claving, wherein at least two additives selected from the group consisting of a surfactant, a viscosity modifier and an anti-foaming agent are added to the aqueous slurry, with the proviso that the addition of the vis cosity modifier and the addition of the anti-foaming agent are performed after the step (1) and before the step (2), and the addition of the surfactant is per formed simultaneously with the addition of the foaming agent in the step (2).

8. The method according to item 7 above, wherein the foaming agent is at least one member selected from the group consisting of an aluminum powder and an aluminum containing aqueous slurry, and wherein the foaming agent is used in an amount of from 0.03 to 0.95 by weight in terms of the weight percentage of the solids contained in the foaming agent, based on the weight of the solid mixture.

9. The method according to item 7 or 8 above, wherein the surfactant is at least one compound selected from the group consisting of a higher alcohol sulfate, a higher alcohol sodium sulfate and a polyoxyethylene al kyl ether, and wherein the surfactant is used in an amount of from 0.01 to 200 % by weight, based on the weight of the solids contained in the foaming agent.

10. The method according to any one of items 7 to 9 above, wherein the viscosity modifier is at least one compound selected from the group consisting of methyl cellulose and polyvinyl alcohol, and wherein the vis cosity modifier is used in an amount of from 0.01 to 1 % by weight, based on the weight of the solid mixture.

The method according to any one of items 7 to 10 above, wherein the antifoaming agent is at least one compound selected from the group consisting of a sili cone, an aliphatic acid, an aliphatic ester, an alcohol and a phosphoric ester, and wherein the anti-foaming agent is used in an amount of from 0.001 to 3 by weight, based on the weight of the solid mixture.

Hereinbelow, the present invention is described in detail.

In the present invention, the expression "cured form of calcium silicate" is a generic term for materi als of various forms, which are produced by curing a composition containing a calcium silicate compound. In general, examples of cured forms of calcium silicate include a concrete, a cured mortar, an autoclaved lightweight concrete (hereinafter, frequently referred to as "ALC") and a fiber reinforced calcium silicate board.

The cured form of calcium silicate of the present invention has (1) a flexural strength of 0.05 MPa or more, and has (2) a thermal conductivity of from 0.02 to 0.1 Wm1Kl and (3) a gas permeability of from 5 x 10-4 to 1 m2h1Pal, thereby exhibiting a dynamic insu lating property. Therefore, the cured form of calcium silicate of the present, invention can be advantageously used as a dynamic insulation material. Herein, the "dynamic insulation material" is a material usable in the so-called "dynamic insulation technique". With re spect to the dynamic insulation technique, reference can be made, for example, to B. J. Taylor et al., "Ana lytical Investigation of the Steady-State Behavior of Dynamic and Diffusive Building Envelopes" (Building and Environment, Vol. 31, No. 6, pp. 519-525, 1996) and "Takinogata Dannetsu Gijutu ni kansuru Kenkyu (Research on Multifunctional Insulation Technologies)" (Search report No. 53, Hokkaido Prefectural Cold Region Build ing Research Institute, Japan, 1993). In the dynamic insulation technique, a planned ventilation is per formed while reducing the heat energy loss. Specifi cally, in the dynamic insulation technique, outside air is introduced indoors through the heat insulation mate rial provided in the wall material and ceiling material.

Therefore, the dynamic insulation technique is advanta geous in that the outside air is preheated in the wall material and the ceiling material before being intro duced indoors, thereby preventing indoor heat fromes caping outdoors through the walls and ceilings. Fur ther, the dynamic insulation technique is advantageous also in that the air introduced indoors is fresh. As a result, it becomes possible to perform the preheating of ventilation air (outside air which is introduced in doors) while lowering the apparent heat transfer coef ficient, thereby maintaining the room air quality at a high level.

The cured form of calcium silicate of the present invention has a flexural strength of 0.05 MPa or more, preferably 0.07 MPa or more, more preferably 0.1 MPa or more. When the cured form of calcium silicate has a flexural strength of less than 0.05 MPa, it becomes difficult to maintain the cured form of calcium sili cate in the shape of a panel, which is a preferred shape of a dynamic insulation material, thereby lower ing the workability of the cured form of calcium sili cate.

The cured form of calcium silicate of the present invention has a thermal conductivity of from 0.02 to 0.1 WmlKl, preferably from 0.02 to 0.08 Wm lK-l, more preferably from 0. 02 to 0.06 WmlKl. When the cured form of calcium silicate has a thermal conductivity of more than 0.1 WmlKl, the thermal insulating property of the cured form of calcium silicate is lowered.

Therefore, when such a cured form of calcium silicate having a thermal conductivity of more than 0.1 WmlKl is used as a heat insulation material, for obtaining a satisfactory heat insulation effect, it becomes neces sary to increase the thickness of the wall (in which the heat insulation material is used), thereby lowering the workability of the cured form of calcium silicate.

On the other hand, from a practical point of view, the lower limit of the thermal conductivity of the cured form of calcium silicate is 0.02 WmlK.

The cured form of calcium silicate of the present invention has a gas permeability of from 5 x 10-4 to 1 m2hlPal, preferably from 1 x 10-3 to 0. 5 m2hlPal, more preferably from 5 x 10-3 to 0.1 m2h1Pal. When the cured form of calcium silicate has a gas permeability within the abovementioned range, it becomes possible to use the cured form of calcium silicate as a dynamic insulation material which can substantially reduce the heat transfer coefficient, while performing a ventila Lion. When the cured form of calcium silicate has a gas permeability of less than 5 x 104 m2hlPal, disad vantages are caused in that the cured form of calcium silicate cannot introduce the outside air indoors, so that it does not function as a dynamic insulation mate rial, and in that the ventilation ability is impaired.

For example, when the cured form of calcium silicate is produced by a method described in W002/06693 (mentioned above), the cured form of calcium silicate has a gas permeability of less than 5 x 10-4 m2hlPal and, hence, does not function as a dynamic insulation material. On the other hand, when the cured form of calcium silicate has a gas permeability of more than 1 m2hiPal, the flow rate of the outside air passing through the cured form of calcium silicate becomes too high, thus render ing it difficult to perform the preheating of ventila tion air (outside air which is introduced indoors). In addition, when the cured form of calcium silicate has too high a gas permeability, the differential pressure between both sides of the wall becomes too small, thereby rendering it impossible to cause a satisfactory air flow within the cured form of calcium silicate, which air flow is necessary for performing dynamic in sulation.

Specifically, in the present invention, the yes permeability of the cured form of calcium silicate can be determined as follows. A cylindrical sample of the cured form of calcium silicate (length: L; cross -sectional area: S) is prepared, and the surfaces of the cylindrical sample are sealed with an epoxy resin except for the surfaces at both ends thereof. Then, using a vacuum pump, the pressures at both ends (having unsealed surfaces) of the cylindrical sample are regu lated to cause an air flow to occur in the sample, and when the differential pressure between both ends of the sample becomes l kPa, the flow rate of air in the sam ple is measured. From the measured flow rate of air in the sample, the gas permeability is calculated by the following formula (1): Gas permeability (m2hlPal) = W x L / S / AP (1) wherein: W: flow rate of air (m3hl); L: sample length (m); S: sample cross-sectional area (m2); and AP: differential pressure (Pa).

Hereinbelow, explanations are given with respect to the method for measuring gas permeability, referring to Fig. 3.

Sample 1 is placed in sample holder 2 equipped with a rubber packing on the inner surface thereof, wherein the rubber packing can tightly seal the inside of sample holder 2 by air compression. Then, the pres sure in pressure regulating vessel 5 is regulated through pressure regulating valve 4 using vacuum pump 3.

When the differential pressure measured by differential pressure gauge 6 is 1 Pa, the flow rate of air in the sample is measured by flowmeter 7. From the measured flow rate of air in the sample, the gas permeability is calculated by formula (1) above.

The cured form of calcium silicate of the present invention mainly comprises tobermorite (5CaO 6SiO2 5H2O), and exhibits a powder X-ray diffrac tion pattern in which, with respect to the diffraction peak intensity Ib ascribed to the (220) plane of the tobermorite and the minimum diffraction intensity Ia observed in the diffraction angle range between the two diffraction peaks respectively ascribed to the (220) plane and (022) plane of the tobermorite, the value of Ib/Ia is preferably 3 or more, more preferably 4 or more. In the present invention, the expression "powder X-ray diffraction pattern" means a powder X-ray dif fraction pattern obtained by using Cu Ka radiation as X-ray. In the present invention, whether or not a cured form of calcium silicate

mainly comprises tobermorite is judged by observation of a cross-section of the cured form of calcium silicate by a scanning electron microscope and analysis of the cured form of calcium silicate by powder X-ray diffractometry. Specifically, the judgment is made as follows.

Firstly, in the powder X-ray diffraction pattern of the cured form of calcium silicate, when there is no diffraction peak having an intensity higher than the intensity of the diffraction peak ascribed to the (220) plane of the tobermorite (i.e., higher than the maximum intensity among the intensities of the diffraction peaks ascribed to the planes of the tobermorite), it is judged that the cured form of calcium silicate mainly comprises tobermorite. It should, however, be noted that, when the cured form of calcium silicate further comprises at least one coexisting highly crystalline substance selected from the group consisting of crys talline silica, calcium carbonate and gypsum, it is possible that the intensity of the diffraction peak as cribed to the coexisting substance (wherein, when the cured form of calcium silicate contains two or more of the coexisting substances, the intensity of the dif fraction peak ascribed to the coexisting substance means the maximum intensity among the intensities of the diffraction peaks ascribed to the coexisting sub stances) exceeds the intensity of the diffraction peak ascribed to the (220) plane of the tobermorite, even when the cured form of calcium silicate mainly com prises tobermorite. Therefore, secondly, a cross section of the cured form is observed by a scanning electron microscope at,magnification of x 2,500 as fol lows. 20 Portions (each having an area of 35.4 Am x 18.9 m) in the cross-section are randomly chosen, wherein each of 20 portions is in the matrix of the cured form, which matrix is other than coarse cell por tions formed by using a foaming agent (described below).

Then, the 20 portions are observed by a scanning elec tron microscope at a magnification of x 2,500. With respect to each of the 20 portions (each having an area of 35.4,um x 18.9 m), the ratio (I) of the area of the portion occupied by the board-shaped and strip-shaped particles of tobermorite is obtained, followed by cal culation of the average of the thus obtained 20 area ratios. When the average of the 20 area ratios is 50 or more, it is judged that the cured form mainly com prises tobermorite. It is preferred that the average of the 20 area ratios is 60 or more, more advanta geously 80 or more. Herein, the term "coarse cell portion" means a coarse cell itself plus a portion in the vicinity thereof within a distance of about 5 Em from the coarse cell. Since a coarse cell portion has a void space, tobermorite is likely to be formed in the coarse cell portion. Even in the case where the cured form of calcium silicate comprises the above-mentioned at least one coexisting highly crystalline substance as well as tobermorite and where the above- mentioned aver age of the 20 area ratios is 50 or more, it is pre ferred that the cured form of calcium silicate exhibits a powder X-ray diffraction pattern in which the dif fraction peak intensity Ib ascribed to the (220) plane of the tobermorite and the diffraction intensity Ic as cribed to the coexisting highly crystalline substance satisfy the relationship Ic/Ib s 3, more advantageously Ic/Ib s 2, wherein, when the cured form of calcium silicate contains two or more of the coexisting sub stances, the intensity Ic means the maximum intensity among the intensities of the diffraction peaks ascribed to the coexisting substances. In the above-mentioned observation by a scanning electron microscope at magni fication of x 2,500, the expression "board-shaped or strip-shaped particle" of tobermorite means a particle having the following characteristics. The tobermorite particle is further observed by the scanning electron microscope at magnification of x 5,000. The distance between two surfaces of the particle which are substan tially parallel to each other is equal to the minimum length of the particle (hereinafter, the minimum length of the particle is frequently referred to as the "thickness" of the particle). When the maximum length of the particle is 5 times or more the minimum length of the particle, the particle is defined as a board shaped or strip-shaped particle of tobermorite. Need less to say, each of the maximum length and thickness of the particle means a two-dimensionally projected length. With respect to the size of the tobermorite particle, there is no particular limitation. However, it is preferred that the maximum length of the tobermo rite particle is from several micrometers to 10 m.

In general, tobermorite coexists with a low crys talline calcium silicate hydrate (hereinafter, referred to as "CSH"). It is known that a CSH takes various particle forms. Since CSH is generally present in a particulate form, such as a fiber, a granule or a mass, a CSH can be clearly distinguished from tobermorite particles by observation under an electron microscope.

The cured form of calcium silicate of the present in vention may contain such a CSH so long as the skeleton of the tobermorite is not broken. However, the pres ence of a CSH in the cured form of calcium silicate may deteriorate various properties (such as strength, weatherability and durability) of the cured form which are required of a building material. When a CSH is contained in a large amount in the cured form of cal cium silicate, the dimensional stability of the cured form of calcium silicate is lowered after drying and moistening are repeated. Further, when the cured form of calcium silicate is allowed to stand in air for a long period of time, since the CSH is susceptible to a carbonation reaction with carbon dioxide in air, the CSH is likely to be decomposed into calcium carbonate and amorphous silicate. The carbonization reaction is accompanied by a volume shrinkage of the cured form of calcium silicate, so that the cured form of calcium silicate suffers cracking and structural deterioration.

Therefore, even when it is judged that a cured form of calcium silicate mainly comprises tobermorite by obser vation of a cross-section of the cured form of calcium silicate by a scanning electron microscope and analysis of the cured form of calcium silicate by powder X-ray diffractometry, it is preferred that the CSH content of the cured form of calcium silicate is as small as pos sible.

As mentioned above, CSH particles can be easily distinguished from tobermorite particles by observation under an electron microscope. However, since CSH takes various particle forms, it is sometimes difficult to clearly distinguish, by observation under an electron microscope, CSH particles from coexisting substances other than CSH, such as fibrous gypsum and particulate calcium carbonate, which are present in very small amounts. Therefore, it is difficult to determine the CSH content by observation under an electron microscope In the powder X-ray diffraction pattern of a cured form of calcium silicate in which a CSH coexists with tober morite, a broad diffraction peak ascribed to the CSH is observed in the diffraction angle range between the two diffraction peaks respectively ascribed to the (220) plane and (222) plane of the tobermorite. This dif fraction peak ascribed to the CSH generally appears at an angle in the range of from about 29.1 to 29.4 (26).

When the amount of the CSH is smaller than that of the tobermorite, the diffraction peak ascribed to the CSH is merged into a diffraction peak ascribed to the to bermorite, so that it is generally impossible to meas ure the intensity of the diffraction peak ascribed to the CSH.

On the other hand, however, when a large amount of CSH is contained in the cured form of calcium silicate, the intensities of the diffraction in the diffraction angle range between the two diffraction peaks respec tively ascribed to the (220) plane and (222) plane of the tobermorite are higher than that of the background, so that whether or not a large amount of CSH is con tained in the cured form of calcium silicate can be judged. When the cured form of calcium silicate con tains no CSH and is composed mainly of a highly crys talline tobermorite, the minimum diffraction intensity in the above-described angle range is equal to the in

tensity of the background.

Further, even in the case where no CSH is con tained in the cured form of calcium silicate, the ratio Ib/Ia becomes small when the crystallinity of the to bermorite is low. The reason for this is that the dif fraction peaks respectively ascribed to the (220) plane and (222) plane of the tobermorite are positioned close to each other, so that the two peaks overlap at the bases thereof. When the crystallinity of the tobermo rite is low, the strength and weatherability of the cured form of calcium silicate are lowered.

Therefore, when no CSH is contained in the cured form of calcium silicate, the larger the ratio Ib/Ia (i.e., the ratio of the diffraction peak intensity Ib ascribed to the (220) plane of the tobermorite to the minimum diffraction intensity Ia observed in the dif fraction angle range between the two diffraction peaks respectively ascribed to the (220) plane and (222) plane of the tobermorite), the higher the crystallinity of the tobermorite. When a CSH is contained in the cured form of calcium silicate, the larger the ratio Ib/Ia, the higher the crystallinity of the tobermorite and the smaller the CSH content in the cured form of calcium silicate. Each of the intensities Ia and Ib includes the intensity of the background. Examples of values of Ia and Ib are indicated in Fig. 1.

It is preferred that the cured form of calcium silicate of the present invention (which has a low spe cific gravity) exhibits a powder X-ray diffraction pat tern in which the ratio of the diffraction peak inten sity 1(002) ascribed to the (002) plane of the tobermo rite to the diffraction peak intensity 1(220) ascribed to the (220) plane of the tobermorite satisfies the re lationship I(002)/I(220) 0.25, more advantageously I(002)/I(220) 0.30. It is considered that, in a board- shaped or strip-shaped particle of the tobermo rite, the thicknesswise direction (i.e., direction per pendicular to the plane) of the particle is the C axis of the crystal. Therefore, when the relative intensity of 1(002) to 1(220) increases, the relative regularity with respect to the C axis of the crystal is improved, so that the thickness of the board- shaped or strip shaped crystal is increased. In the JCPDS (Joint Com mittee on Powder Diffraction Standard) Card No. 19-1364, it is described that the ratio I(002)/I(220) is 0.8 in an ideal tobermorite crystal. As the ratio I(002)/I(220) nears 0.8, the thickness of the tobermo rite increases, so that the strength of the crystal in creases, leading to an increase in the strength of the cured form of calcium silicate. The methods for calcu lating 1(002) and 1(220) are shown in Fig. 2. 1(002) is a true diffraction intensity obtained by linear ap proximation of the background around the diffraction angles of from 6 to 9 (20). Similarly, 1(220) is a true diffraction intensity obtained by linear approxi mation of the background around the diffraction angles of from 20 to 40 (20).

In the present invention, it is preferred that the cured form of calcium silicate has an apparent specific gravity of from 0.05 to 0.25, more advantageously from 0.05 to 0.2, still more advantageously from 0.05 to 0.18. In the present invention, the term "apparent specific gravity" means the apparent specific gravity as measured after drying the cured form of calcium silicate at 105 C for 24 hours, i.e., the absolute dry specific gravity.

The cured form of calcium silicate of the present invention may or may not contain a substantial amount of cells; however, it is preferred that the cured form of calcium silicate contains a substantial amount of cells. The term "cell" means a cell formed by using an aluminum powder as a foaming agent, which has conven tionally been used in the production of an autoclaved lightweight concrete, or a cell formed by using a sur factant which is used as a pre-foaming agent in a pre foaming method for producing an autoclaved lightweight concrete.

When the cured form of calcium silicate of the present invention contains a substantial amount of cells, it is preferred that the cured form of calcium silicate has pores in the portion other than the cells i.e., portion forming the skeleton (matrix) thereof.

Further, it is preferred that the thickness of the ma trix between the cells is small.

The cured form of calcium silicate of the present invention can be advantageously used as a wall material for buildings, such as the abovementioned dynamic in sulation material, an ordinary thermal insulating mate rial and a sound-absorbing material. When the cured form of calcium silicate is used as a wall material for buildings, it is preferred that the cured form of cal cium silicate is in the shape of a panel. With respect to the size and thickness of such a panel, there is no particular limitation so long as the shape of a panel can be maintained. When the cured form of calcium silicate is in the shape of a panel, it becomes easy to secure the airtightness required in dynamic insulation techniques and to simplify the working thereof.

Hereinbelow, an explanation is given with respect to the method for producing the cured form of calcium silicate of the present invention.

A cured form of calcium silicate can be produced by a method, which comprises the following steps (1) to (4): (l) providing an aqueous slurry comprising water and a solid mixture, the solid mixture consisting essentially of a si liceous material, a cementitious material, at least one aluminum compound selected from the group consisting of aluminum sulfate and a hydrate thereof, and at least one sulfate compound selected from the group consisting of sulfates other than aluminum sulfate and hydrates thereof, and optionally a calcareous material, wherein the at least one aluminum compound is con tained in the aqueous slurry in an amount of from 0.09 to 10 % by weight in terms of the amount of A12O3, based on the weight of the solid mixture, and the sul fate compound other than aluminum sulfate and a hydrate thereof is contained in the aqueous slurry in an amount of from 0.15 to 15 % by weight in terms of the amount of SO3, based on the weight of the solid mixture, the amount of SO3 being the sum of the amount of the SO3 corresponding to the at least one aluminum compound and the amount of the SO3 corresponding to the sulfate com pound other than aluminum sulfate and a hydrate thereof, wherein the weight ratio of the water to the solid mixture is from 2.3 to 5.5, and wherein the weight ratio of the calcareous mate rial to the cementitious material is 0.6 or less; (2) adding a foaming agent to the aqueous slurry; (3) pouring the aqueous slurry into a mold; and (4) procuring the aqueous slurry, followed by auto claving.

In the present invention, the term "siliceous ma serial" means a material containing 70 % by weight or more of SiO2 and metal oxides, such as aluminum oxide, as components other than SiO2. Examples of siliceous materials include a massive siliceous material; sili ceous sand; quartz; a rock having a high content of a massive siliceous material, siliceous sand or quartz; diatomaceous earth; silica fume; fly ash; natural clay mineral; and a calcination product of diatomaceous earth, silica fume, fly ash or natural clay mineral.

Among these, a massive siliceous material, siliceous sand, quartz, and a rock having a high content of a massive siliceous material, siliceous sand or quartz are crystalline siliceous materials. The term "crys talline siliceous material" means a siliceous material which exhibits a powder X-ray diffraction pattern wherein sharp diffraction peaks characteristic of a quartz, cristobalite and the like are observed. On the other hand, an "amorphous siliceous material" means a siliceous material which exhibits a powder X-ray dif fraction pattern wherein sharp diffraction peaks are not observed. Examples of amorphous siliceous materi als include diatomaceous earth, silica fume and fly ash.

In the present invention, the term "cementitious material" means a cement composed mainly of a silicate component and a calcium component. Examples of cemen titious materials include an ordinary Portland cement, a highearly-strength Portland cement and a belite ce ment. The term "calcareous material" means a calcium containing material which contains 50 % by weight or more of quick lime (CaO), and further contains calcare ous components other than quick lime (CaO), such as slaked lime (Ca(OH)2) and calcium carbonate (CaCO3).

Further, in the present invention, the term "alu minum sulfate" means a substance comprising a compound represented by the formula: Al2(SO4) 3. The term "hy crate of aluminum sulfate" means a hydration product of the aluminum sulfate. Examples of hydrates of aluminum sulfate include a substance comprising the aluminum sulfate and water of crystallization, such as a sub stance represented by the formula: Al2(SO4)3 17H2O.

Each of the aluminum sulfate and the hydrate thereof can be used in the form of a powder or a slurry. In the present invention, it is required that the amount of Al2(SO4) 3 in the hydrate of aluminum sulfate be 80 % by weight or more, based on the weight of the hydrate, wherein the weight of water of crystallization is ex eluded from the weight of the hydrate. The aluminum sulfate or a hydrate thereof is used in an amount of from 0. 09 to 10 % by weight, preferably from 0.2 to % by weight, more preferably from 0.5 to 8 % by weight, in terms of the amount of Al203, based on the total weight of the solid materials.

With respect to the above-mentioned sulfate com pound other than aluminum sulfate, there is no particu lar limitation so long as the sulfate compound contains SO3 or SO4. Examples of such sulfate compounds include sulfurous acid; sulfuric acid; gypsum anhydride (CaSO4), hydrates of gypsum, such as gypsum dibydrate (CaSO4 2H2O) and gypsum hemihydrate (CaSO4 1/2H2O); al kaline earth metal sulfates, such as magnesium sulfate; alkali metal sulfates, such as sodium sulfate; and metal sulfates other than alkaline earth metal sulfate and alkali metal sulfate, such as copper sulfate and silver sulfate. The above-mentioned sulfate compounds can be used individually or in combination. However, it is preferred to use gypsum dihydrate or a hydrate thereof. The amount of the at least one sulfate com pound in the aqueous slurry is from 0.15 to 15 % by weight, preferably from 0.2 to 10 % by weight, in terms of the amount of SO3, based on the total weight of the solid materials, wherein the amount of SO3 is the sum of the amount of the SO3 corresponding to the at least one aluminum compound and the amount of the SO3 corre sponding to the at least one sulfate compound.

Further, in the method of the present invention, the weight ratio of the above-mentioned calcareous ma terial to the cementitious material is 0.6 or less, preferably 0.4 or less, most preferably 0.3 or less, in terms of the amount of CaO. However, even when the weight ratio of the calcareous material to the cementi tious material is more than 0.6, the cured form of cal cium silicate of the present invention can be produced by adding at least two additives selected from the group consisting of a surfactant, a viscosity modifier and an anti-foaming agent to the above-mentioned aque ous slurry. With respect to the addition of the above -mentioned additives, the addition of the viscosity modifier and the addition of the anti-foaming agent are performed after step (1) and before step (2), and the addition of the surfactant is performed simultaneously with the addition of the foaming agent in step (2).

Further, in the present invention, even when the weight ratio of the calcareous material to the cementitious material is 0.6 or less, the addition of the above -mentioned additives may be performed in the same man ner as mentioned above in connection with the case where the weight ratio of the calcareous material to the cementitious material is more than 0.6.

Examples of surfactants include anionic surfactants, such as a higher alcohol sulfate and a higher alcohol sodium sulfate; and nonionic surfactants, such as a polyoxyethylenealkyl ether. The surfactant is used in an amount of from 0.01 to 200 % by weight, preferably from 0.1 to 100 % by weight, based on the weight of the solids contained in the foaming agent.

The above-mentioned viscosity modifier is at least one compound selected from the group consisting of methyl cellulose and polyvinyl alcohol. The viscosity modifier is used in an amount of from 0.01 to 1 % by weight, preferably from 0.02 to 0.5 % by weight, based on the weight of the solid mixture.

Examples of anti-foaming agents include silicones, such as a dimethyl silicone and an alkyl-modified silicone which is formed by replacing the methyl group(s) of a dimethyl silicone with a hydrocarbon having two or more carbon atoms; aliphatic acids, such as an aliphatic acid having a glycerol skeleton; ali phatic esters, such as glycerol aliphatic acid esters and sucrose aliphatic acid esters; higher alcohols, such as octyl alcohols; phosphoric esters, such as aro matic phosphoric esters and aliphatic phosphoric esters.

Of these anti-foaming agents, from the viewpoint of im parting water repellency to the cured form of calcium silicate, it is preferred to use silicones, especially, a dimethyl silicone and an alkyl-modified silicone.

The anti-foaming agent is used in an amount of from 0.001 to 3 % by weight, preferably from 0.005 to 2 % by weight, more preferably from 0.01 to 2 % by weight, based on the weight of the solid mixture.

In the method of the present invention, it is nec essary that the weight ratio of the water to the above -mentioned solid mixture (i.e., the water/solid ratio of the aqueous slurry) be in the range of from 2.3 to 5.5. When the aqueous slurry has a water/solid ratio of less than 2.3, it becomes impossible to obtain a molded article (i.e., cured form of calcium silicate) which has an apparent specific gravity within the range desired in the present invention, and the obtained molded article tends to have too high a thermal conduc tivity. On the other hand, when the aqueous slurry has a water/solid ratio of more than 5.5, there is a ten dency that the solid mixture and the water in the aque ous slurry get separated from each other, so that a molded article cannot be obtained.

In the present invention, the term "foaming agent" means an aluminum powder or the like which are gener ally used in the production of an autoclaved light weight concrete. With respect to the form of the alu minum powder, there is no particular limitation, and the aluminum powder may be used in any form which is employed in conventional methods for producing an auto claved lightweight concrete. Examples of conventional methods for producing an autoclaved lightweight con crete include a method in which an aluminum powder as such is added as a foaming agent; a method in which an aluminum powder is mixed, in advance, with water (a portion of water to be used for preparing an aqueous slurry containing raw materials of an autoclaved light weight concrete) to obtain an aluminum slurry, thereby improving dispersibility of the aluminum powder in the aqueous slurry containing raw materials; and a method in which an aluminum paste for production of an auto ' craved lightweight concrete is added as a foaming agent (see U.S. Patent No. 4,318,270). Herein, the term "aluminum slurry" means an aqueous dispersion of an aluminum powder. The above-mentioned aluminum slurry contains an aluminum powder in an amount of from 0.1 to % by weight, preferably from 1 to 30 % by weight, more preferably from 2 to 10 % by weight, based on the weight of water contained in the aluminum slurry. The foaming agent is used in an amount of from 0.03 to 0.95 % by weight, preferably from 0.05 to 0.7 % by weight, more preferably from 0.08 to 0.5 % by weight in terms of the weight percentage of the solids contained in the foaming agent, based on the weight of the solid mixture. The volume ratio of the foamed aqueous slurry to the aqueous slurry prior to foaming is preferably from 1.5 to 4.0, more preferably from 2.0 to 3.5, most preferably from 2.5 to 3.5.

In the aqueous slurry which is first provided in the method of the present invention, the molar ratio of CaO to SiO2(CaO/SiO2 ratio) is preferably from 0.5 to 1.1, more preferably from 0.6 to less than 1.0.

In the method for producing the cured form of cal cium silicate of the present invention, it is preferred that 50 % by weight or more of the siliceous material is a crystalline siliceous material. As a crystalline siliceous material, it is preferred to use a finely pulverized form of massive siliceous material, which has a specific surface area of 5,000 cm2/g or more, more advantageously 7,000 cm2/g or more, as measured by the Blaine permeation method. An extremely finely pul verized form of massive siliceous material is disadvan tageous in that such a form of massive siliceous mate rial is difficult to handle. Therefore, it is pre ferred that the specific surface area of the finely pulverized form of massive siliceous material is 300,000 cm2/g or less.

In the method for producing the cured form of cal cium silicate of the present invention, an aqueous slurry comprising a solid mixture is stirred, wherein the solid mixture consists essentially of a siliceous material, a cementitious material, at least one alumi num compound selected from the group consisting of alu minum sulfate and a hydrate thereof, a sulfate compound other than aluminum sulfate and a hydrate thereof, and optionally a calcareous material. The temperature of the aqueous slurry is preferably from 40 to 100 C, more preferably from 50 to 80 C. Further, the time for stirring the aqueous slurry is preferably 2 minutes or more, more preferably 10 minutes or more. The stir ring of the above-mentioned aqueous slurry comprising a solid mixture can be performed by a commercially avail able mixer. With respect to such a mixer, it is pre ferred to use a mixer equipped with a high speed rota Lion blade usable for a low viscosity mortar, such as a paddle mixer equipped with a baffle board.

In the method of the present invention, when the whole amount of the calcareous material (which is an optional raw material) is mixed at once with the sili ceous material and the cementitious material, there is a danger that the calcareous material lowers the rate of the initial hydration of the cementitious material.

Therefore, when it is intended to promote the procuring of the aqueous slurry after pouring thereof into the mold, it is preferred that the aqueous slurry to be provided in the method of the present invention is pre pared by a process comprising the steps of: (i) mixing water with the solid mixture exclusive of the calcare ous material or with the solid mixture containing a portion of the calcareous material to obtain a mixture in the form of a slurry, wherein the mixing is per formed at a temperature of from 40 to 100 C for from lO minutes to less than 5 hours; (ii) adding the whole of the calcareous material or the remainder of the cal careous material to the mixture obtained in the step (i), followed by mixing at a temperature of from 40 to lOO C for preferably 30 seconds to l hour, more pref erably l to 30 minutes. The resultant aqueous slurry is poured into the mold. Hereinafter, the charging of raw materials in step (i) is referred to as "primary charging", and the charging of raw materials in step (ii) is referred to as "secondary charging".

Further, it is preferred that the above-mentioned aluminum compound is mixed with water and the solid ma serials other than the aluminum compound in the above mentioned step (i) and the resultant mixture is stirred at a temperature of from 40 to 100 C for 10 minutes to less than 5 hours. With respect to the timing of performing the addi Lion of the viscosity

modifier and the anti-foaming agent, there is no particular limitation so long as the addition is performed prior to the addition of the foaming agent. However, it is preferred that the addi tion of the viscosity modifier and the anti-foaming agent is performed immediately after the charging of the solid mixture. Further, the addition of the sur factant to the aqueous slurry is performed simultane ously with the addition of the foaming agent.

It is preferred that the foaming agent is added after the charging of the solid mixture. The time for stirring the aqueous slurry after addition of the foam ing agent thereto is preferably from 10 seconds to 3 minutes, more preferably from 20 seconds to 1 minute.

When the stirring time is less than 10 seconds, there is a tendency that the foaming agent cannot be uni formly dispersed in the aqueous slurry, thereby causing unification of the cells into coarse cells. On the other hand, when the stirring time is more than 3 min utes, there is a tendency that unfavorable reaction of the foaming agent occurs, which reaction causes unifi cation of the cells and deforming.

Alternatively, the cured form of calcium silicate of the present invention can also be obtained by a pre -foaming method. Preferred examples of pre-foaming methods include a method in which air is introduced into a pre-foaming agent or an aqueous solution thereof to form a foam, followed by mixing the foam with the above-mentioned aqueous slurry (see Unexamined Japanese Patent Application Laid-Open Specification No. Sho 63 -295487), and a method in which a pre-foaming agent is mixed with the aqueous slurry, and the resultant slurry is caused to have a foam by a pre-foaming machine. In the pre-foaming method, a foaming agent is not used; however, it is necessary that a viscosity modifier and an anti- foaming agent be added. In the pre-foaming method, each of the viscosity modifier and the anti foaming agent may be used in the same amount as men tioned above in connection with the method using a foaming agent. The type of the pre-foaming agent is not specifically limited, and a conventional pre -foaming agent used in the art can be used. Examples of pre-foaming agents include a synthetic surfactant type pre-foaming agent, a resin soap type pre-foaming agent and a hydrolysis protein type pre-foaming agent.

In the present invention, it is preferred that the cured form of calcium silicate contains 0.1 to 3.0 by weight of a water repellent substance to thereby impart water repellency to the cured form of calcium silicate.

With respect to the method for imparting water repel lency to the cured form of calcium silicate by using a water repellent substance, there is no particular limi tation. For example, it is preferred to employ the so called "vapor deposition method" whereby a water con- tact angle as high as 100 or more can be achieved.

With respect to the types of water repellent sub stance, there is no particular limitation. Examples of water repellent substances include siloxane compounds, alkoxysilane compounds, fatty acids, salts of fatty ac ids, and resin emulsions comprising at least one resin selected from the group consisting of an epoxy resin, a urethane resin, a silicone resin, a vinyl acetate resin, an acrylic resin and a styrene/butadiene resin. These water repellent substances can be used individually or in combination. Of these water repellent substances, especially preferred are siloxane compounds, such as silicone oils (e.g., a polydimethylsiloxane wherein the methyl group may be replaced by a hydrogen atom, a phenyl group, a trifluoropropyl group or the like); and alkoxysilane compounds, such as an alkylalkoxysilane (e.g., methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane and isobutyltriethoxysilane).

The content of the water repellent substance in the cured form of calcium silicate is preferably from 0.1 to 3.0 by weight, more preferably from 0. 5 to 2 % by weight. When the content of the water repellent sub stance is less than 0.1 by weight, the desired water repellency cannot be exerted. On the other hand, when the content of the water repellent substance is more than 3.0 by weight, the strength of the cured form of calcium silicate gets lowered.

The cured form of calcium silicate of the present invention may also contain a small amount of a rein forcing fiber, a lightweight aggregate, a resin or the like so long as the properties of the cured form of calcium silicate are not impaired. The use of a rein forcing fiber is advantageous for improving the strength of the cured form of calcium silicate. Exam ples of reinforcing fibers include inorganic fibers, such as an alkali-proof glass fiber, a carbon fiber, a stainless steel fiber, a ceramic fiber and an asbestos fiber; and organic fibers, such as an aramid fiber, a vinylon fiber, a polypropylene fiber and a pulp fiber.

These reinforcing fibers can be used individually or in combination. Of these reinforcing fibers, from the viewpoint of obtaining the desired reinforcing ability, an aramid fiber, an alkali-proof glass fiber and a car bon fiber are preferred. Among the aramid fibers, paraaramid fibers are most preferred. Further, from the viewpoint of cost performance, a pulp fiber is also preferred. As a pulp fiber, a pulverized pulp is espe cially preferred. With respect to the fiber length of the reinforcing fiber, there is no particular limita tion. However, from the viewpoint of reinforcing abil ity and moldability, the fiber length of the reinforc ing fiber is preferably from 1 to 20 mm, more prefera bly from 3 to 10 mm, still more preferably from 5 to 8 mm. Further, with respect to the amount of the rein forcing fiber in the cured form of calcium silicate, there is no particular limitation. The amount of the reinforcing fiber in the cured form is preferably from 0.05 to 3 by volume, more preferably from 0.1 to 2 % by volume, based on the volume of the cured form of calcium silicate, wherein the volume of the cured form includes the volume of pores present therein. When the amount of the reinforcing fiber is less than 0.05 % by volume, the improvement in the strength of the cured form of calcium silicate by the use of the reinforcing fiber becomes unsatisfactory. On the other hand, when the amount of the reinforcing fiber is more than 3 by volume, fibers are likely to get entangled together to form fiber balls during mixing of raw materials (in cluding the reinforcing fiber) for producing the cured form of calcium silicate, rendering it difficult for the reinforcing fiber to be uniformly dispersed in the cured form. Further, as a lightweight aggregate, use can be made of any of those which are conventionally used for reducing the weight of concretes, such as a silastic balloon and pearlite. With respect to the amount of the lightweight aggregate used in the cured form of calcium silicate of the present invention, there is no particular limitation; however, the amount of the lightweight aggregate is preferably from 0.1 to % by weight, more preferably from 1 to 20 % by weight, based on the weight of the solid mixture. Fur thermore, as a resin, it is preferred to use a resin having heat resistance, such as a phenolic resin and a resole resin. With respect to the amount of the resin used in the cured form of calcium silicate of the pre sent invention, there is no particular limitation; how ever, the amount of the resin is from 0.1 to 30 % by weight, more preferably from 1 to 20 by weight, based on the weight of the solid mixture.

The aqueous slurry obtained by mixing the raw ma terials is poured into the mold and procured, followed by autoclaving. If desired, the abovementioned water repellent substance and/or the above-mentioned rein forcing fiber may be incorporated into the aqueous slurry prior to the pouring of the aqueous slurry into the mold. If desired, the mold may have a reinforcing iron rod or a reinforcing wire netting arranged therein.

In this case, it is preferred that the above-mentioned reinforcing iron rod or reinforcing wire netting has been subjected to a rust proof treatment. The aqueous slurry in the mold is precured either by heat self generated in the aqueous slurry or by heating of the aqueous slurry from the outside. It is preferred that the procuring of the aqueous slurry is conducted at 40 to 100 C for 1 to 48 hours or more. As the mold, an autoclaving chamber or the like can be used. It is preferred that the precuring of the aqueous slurry is performed while suppressing evaporation of water in the aqueous slurry. By procuring the aqueous slurry, a procured form is obtained. The obtained procured form is subjected to high temperature and high pressure autoclaving by an autoclave. If desired, prior to the autoclaving of the procured form, the procured form is cut into a desired shape. The cutting of the precured form can be performed by any conventional method which has generally been employed in the production of an autoclaved lightweight concrete. Examples of such con ventional methods include a method using a wire. It is preferred that the autoclaving of the procured form is performed at a temperature of from 160 C (gauge pres sure: approximately 5.3 kgf/cm2) to 220 C (gauge pres sure: approximately 22.6 kgf/cm2). The cured form ob tained by autoclaving of the procured form is dried, thereby obtaining the cured form of calcium silicate of the present invention.

The thus obtained cured form of calcium silicate of the present invention simultaneously exhibits high thermal insulating property and high gas permeability.

Therefore, the cured form of calcium silicate of the present invention can be advantageously used as a dy namic insulation material. Further, the cured form of calcium silicate of the present invention not only has excellent properties with respect to workability, cost performance and high strength, but also is incombusti ble. Therefore, the cured form of calcium silicate of the present invention is suitable for use as a dynamic insulation material.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinbelow, the present invention will be de scribed in more detail with reference to the following Examples and Comparative Examples, which should not be construed as limiting the scope of the present inven tion.

In the following Examples and Comparative Examples, various measurements and analyses were performed by the following methods.

(Thermal conductivity) The thermal conductivity was measured in accor dance with JIS A-1412 by a heat flow meter, wherein the cold plate temperature was 5 C and the hot plate temperature was 35 C. The test specimen used had a size of 200 x 200 mm x 25 mm (thickness), which had been kept at 20 C under a humidity of 60 until the weight of the test specimen became constant.

(Gas permeability) The gas permeability was measured using an appara tus as shown in Fig.3. Specifically, the gas perme ability was determined as follows. A cylindrical sam ple 1 (cross-sectional area (S) = 50 mml; length (L) = 50 mm) was prepared, and the surfaces of the sample were sealed with an epoxy resin except for the surfaces at both ends thereof. Then, sample 1 was placed in sample holder 2 having a rubber packing on the inner surface thereof, wherein the rubber packing can tightly seal the inside of sample holder 2 by air compression.

Then, the pressure in pressure regulating vessel 5 was regulated through pressure regulating valve 4 using vacuum pump 3. When the differential pressure measured by differential pressure gauge 6 was 1 kPa, the flow rate of air in the sample was measured by flow meter 7.

From the measured flow rate of air in the sample, the gas permeability was calculated by the following for mula (1): Gas permeability (m2hlPal) = W x L / S / LP (1) W: flow rate of air (m3hl) L: sample length (m) S: Sample cross-sectional area (m2) AP: differential pressure (Pa) Sample 1 used in the measurement had keen kept at C under a humidity of 60 until the weight thereof became constant.

(Flexural strength and compressive strength) A cured form of calcium silicate was kept in a thermo-hygrostat (in which the temperature and the relative humidity (RH) were maintained at 20 C and %, respectively) until the water content of the cured form became 10 + 2 %, based on the weight of the cured form in the absolutely dry state. The resultant was used as a sample for measuring the flexural strength and compressive strength. The sample had a size of 40 mm x 40 mm x 160 mm. Tests for measuring the flexural strength and compressive strength of the cured form of calcium silicate were performed in accor dance with JIS R 5201. Specifically, the sample was subjected to the flexural strength test, wherein the span was 100 mm. In the flexural strength test, a load was applied to the sample until it was broken in two.

Using one of the result,ant two broken pieces of the sample, the compressive strength was measured as fol lows. A load was applied to a 40 mm x 40 mm area of the sample to measure the maximum load, and the ob tained maximum load value was defined as the compres sive strength of the cured form of calcium silicate.

(Apparent specific gravity) From a cured form of calcium silicate which had been autoclaves, a sample having the same size as that used in the above-mentioned flexural strength test was taken. This sample was dried at 105 C for 24 hours and, then, the weight and size (volume) of the sample were measured. From the measured values of the weight and volume of the sample, the apparent specific gravity of the sample was calculated.

(Powder X-ray diffractometry: measurements of Ia and Ib) Substantially the same sample as used in the above-mentioned flexural strength test was pulverized using a mortar to obtain a sample for powder X-ray dif fractometry. The diffraction peak intensity Ib and the minimum diffraction intensity Ia were measured by an X-ray diffraction apparatus (trade name: RINT 2000; manufactured and sold by Rigaku Corporation, Japan) with respect to Ka radiation of Cu. The measurement was performed under conditions wherein the acceleration voltage was 40 kV, the acceleration current was 200 mA, the slit width of the light receiving slits was 0.15 mm, the scanning speed was 4 /min, and the sampling was 0.02 . The diffracted X-rays were counted after mono chromation thereof by a graphite monochromator.

Ia is defined as the minimum diffraction intensity observed in the diffraction angle range between the two diffraction peaks respectively ascribed to the (220) plane and (222) plane of tobermorite, wherein the in tensity includes that of the background. Ib is defined as the diffraction peak intensity ascribed to the (220) plane of tobermorite, wherein the intensity includes that of the background. The diffraction rays ascribed to the (220) plane and (222) plane of tobermorite are diffraction rays having diffraction angles of about 29.0 and about 30.0 (20), respectively. Fig. 1 indi cates how to obtain the values of Ia and Ib.

(Powder X-ray diffractometry: measurements of 1(002) and I(220)) The sample used and the measurement conditions were substantially the same as in the above-mentioned measurements of Ia and,Ib. 1(002) is a true diffrac tion intensity obtained by linear approximation of the background around the diffraction angles of from 6 to 9 (20). Similarly, 1(220) is a true diffraction in tensity obtained by linear approximation of the back ground around the diffraction angles of from 20 to 40 (20). The diffraction ray ascribed to the (002) plane of tobermorite is a diffraction ray having a diffrac tion angle of about 7.7 (26). The methods for deter- mining the values of 1(220) and 1(002) are indicated in Fig. 2.

(Sawability) A cured form of calcium silicate was cut using a woodworking saw for evaluating the sawability of the cured form of calcium silicate. Specifically, the sa wability of a cured form of calcium silicate was evalu ated, based on the ease in cutting the cured form of calcium silicate and the appearance of a cross-section obtained by the cutting.

Examples 1 to 13

In each of Examples 1 to 13, a cured form of cal cium silicate was produced using a solid mixture and water. The type and amount of each material of the solid mixture and the a,mount of water are indicated in Table 1. Specifically, in Examples 1 to 13, the solid mixtures were prepared using the following materials.

As siliceous material, a finely pulverized form of mas sive siliceous material (Blaine specific surface area: ll,OOO cm2/g) and silica fume (manufactured and sold by EFACO, Egypt) were used. As a cementitious material, a high-early-strength Portland cement was used in Exam pies 1 to 8, and an ordinary Portland cement was used in Example 9 to 13. As a calcareous material, quick lime (purity: 98 %) was used. As an aluminum compound, aluminum sulfate octadecahydrate was used. As a sul fate compound other than aluminum sulfate and hydrates thereof, gypsum dihydrate was used. As a surfactant, polyoxyethylene alkyl ether (nonionic surfactant) was used in Examples 1 to 5, and EMAL 20T (manufactured and sold by Kao Corporation, Japan) (anionic surfactant) was used in Examples 6 to 13. As a viscosity modifier, methyl cellulose was used. As an anti-foaming agent, an alkyl-modified silicone (manufactured and sold by Shin-Etsu Chemical Co., Ltd., Japan) was used. As an organic fiber, a finely pulverized form of pulp was used in Examples 10 and 13. With respect to each of aluminum sulfate octadecahydrate and gypsum dihydrate, the amount thereof is indicated in Table 1 in terms of parts by weight of the,anhydrous form thereof. Further, with respect to the surfactant, the amount thereof is indicated in Table 1 in terms of % by weight based on the weight of the solids contained in the foaming agent.

The water/solid ratio indicated in Table 1 is a weight ratio of the solid mixture to water.

In each of Examples 1 to 8, a cured form of cal cium silicate was produced using the above-mentioned solid mixture as follows. As a primary charging (de fined above) of raw materials, a finely pulverized form of massive siliceous material, silica fume, quick lime, high-early-strength Portland cement, aluminum sulfate octadecahydrate and gypsum dihydrate, a viscosity modi fier and an anti-foaming agent were charged into a stainless steel bath having a volume of 15 liters, which contained water having a temperature of 50 C.

The contents of the stainless steel bath were stirred by a stirrer (ultra stirrer DC-CHRM25; manufactured and sold by Iuchi Seieido Co., Ltd., Japan) at a revolution rate of 1,200 rpm under atmospheric pressure for two hours while heating the stainless steel bath at 50 C and suppressing evaporation of water in the stainless steel bath, to thereby obtain a mixture. Then, only in Examples 4 and 5, the obtained mixture was cooled to C and, then, quick lime was charged into the stainless steel bath as a secondary charging (defined above) of a raw material, followed by stirring of the contents in the stainless steel bath at 40 C for l minute. To the resultant mixture was added a foaming agent (an aluminum powder having added thereto a sur factant), followed by stirring for 20 seconds to thereby obtain an aqueous slurry. The obtained aqueous slurry was poured into a mold having a size of 30 cm x cm x 20 cm and allowed the aqueous slurry to foam in the mold. Immediately after the aqueous slurry was poured into the mold, the aqueous slurry was precured at 60 C while suppressing evaporation of water from the aqueous slurry, thereby obtaining a procured form of calcium silicate.

In each of Examples 9 to 13, a precured form of calcium silicate was produced in substantially the same manner as in Example 1, except that an ordinary port land cement was used as a cementitious material, that water having a temperature of 60 C was used, and that the stirring of the contents of the stainless steel bath after the primary charging was performed while heating the stainless steel bath at 60 C. Further, in Example 13, quick lime was charged into the stainless steel bath as a secondary charging of a raw material, followed by stirring at 60 C for 1 minute.

The precured form,of calcium silicate was released from the mold and subjected to a high temperature and high pressure autoclaving at 190 C in a saturated va por atmosphere for 4 hours, followed by drying, thereby obtaining a shaped article (cured form of calcium sili cate).

Various properties of the shaped article (cured form of calcium silicate) obtained in each of Examples 1 to 13 are shown in Table 3. The powder X-ray dif- fraction patterns of the cured form of calcium silicate obtained in Example 13 are shown in Figs. 1 and 2.

Example 14

In Example 14, a shaped article (cured form of calcium silicate) was produced in substantially the same manner as in Example 9, except that the raw mate rials were used in the amounts indicated in Table 1, and that a surfactant and an anti-foaming agent were not used. Various properties of the obtained shaped article are shown in Table 3.

Example 15

In Example 15, a shaped article (cured form of calcium silicate) was produced in substantially the same manner as in Example 11, except that the raw mate rials were used in the,amounts indicated in Table 1, and that a surfactant and an anti-foaming agent were not used. Various properties of the obtained shaped article are shown in Table 3.

Comparative Examples 1 and 2 In Comparative Examples 1 and 2, shaped articles (cured form of calcium silicate) were produced in sub stantially the same manner as in Examples 4 and 13, re spectively, except that a surfactant, a viscosity modi fier and an anti-foaming agent were not used. Various properties of the obtained shaped articles are shown in

Table 4.

Comparative Example 3 In Comparative Example 3, using the raw materials indicated in Table 2, a shaped article (cured form of lo calcium silicate) was produced in substantially the same manner as in Comparative Example 2. Various prop erties of the obtained shaped article are shown in Ta ble 4.

Comparative Examples 4 and 5 In each of Comparative Examples 4 and 5, a shaped article (cured form of calcium silicate) was produced in substantially the same manner as in Example 13, ex cept that a surfactant, an anti-foaming agent and a pulverized pulp were not used. Various properties of the obtained shaped article are shown in Table 4.

C parative Example 6

In Comparative Example 6, a shaped article (cured form of calcium silicate) was produced in substantially the same manner as in Example 13, except that a surfac- tant and an anti-foaming agent were not used. Various properties of the obtained shaped article are shown in

Table 4.

Comparative Example 7 In Comparative Example 7, a shaped article (cured form of calcium silicate) was produced in substantially the same manner as in Example 14, except that the raw materials are used in the amounts indicated in Table 4, and that a viscosity modifier and an aluminum powder were not used.

Comparative Example 8 In Comparative Example 8, a sample of a commer cially available heat insulation ALC (HEBEL DAMMPLATTE: manufactured and sold by Hebel, Germany) was prepared.

With respect to the sample, various properties thereof were measured. The results are shown in Table 4.

Comparative Example 9 78 Parts by weight of water having a temperature of 45 C, 0.5 part by weight of a surfactant (EMAL 20T; manufactured and sold by Kao Corporation, Japan), 0.8 part by weight of viscosity modifiers (0.4 part by weight of methyl cellulose and 0.4 part by weight of a melamine type viscosity reducer), 0.4 part by weight of an anti-foaming agent (alkyl- modified silicone oil) (manufactured and sold by Shin-Etsu Chemical Co., Ltd., Japan) and 0.12 part by weight of a foaming agent (alu minum powder) were added to a solid mixture containing 51 parts by weight of a silica powder having an average particle diameter of approximately 20 m, 42 parts by weight of a high-early-strength Portland cement, 5 parts by weight of quick lime and 2 parts by weight of gypsum dihydrate. The resultant mixture was stirred for 2 minutes to thereby obtain an aqueous slurry in which the components thereof were uniformly mixed. The obtained aqueous slurry was heated to 43 C and, then, poured into a mold and kept at 45 C until the aqueous slurry is semicured. The resultant (procured form of calcium silicate) was released from the mold and sub jected to a high temperature and high pressure auto claving at 180 C under 10 atm in a saturated vapor at mosphere for 4 hours, followed by drying, thereby ob taining a shaped article (cured form of calcium sili cate). With respect to the obtained shaped article, various properties thereof were measured. The results are shown in Table 4.

Comparative Example 10 A sample of a commercially available sound absorb ing ALC (Shizukalite; manufactured and sold by CLION Co., Ltd., Japan) was prepared. With respect to the sample, various properties thereof were measured. The results are shown in Table 4.

Comparative Example 11 A sample of a commercially available rock wool (Homemat; manufactured and sold by NICHIAS Corporation, Japan) was prepared. With respect to the sample, vari ous properties thereof were measured. The results are shown in Table 4. The measurements of the flexural strength and compressive strength of the sample were impossible because the shape of the sample was unable to be maintained. Further, the evaluation of the sa wability of the sample was also impossible because the fibers of the sample caught the teeth of the saw and, hence, the sample was unable to be cut.

Comparative Example 12 A sample of a commercially available glass wool (MAT-ACE; manufactured and sold by ASAHI FIBER GLASS Co., Japan) was prepared. With respect to the sample, various properties thereof were measured. The results are shown in Table 4. The measurements of the flexural strength and compressive strength of the sample were impossible because the shape of the sample was unable to be maintained. Further, the evaluation of the sa wability of the sample was also impossible because the fibers of the sample caught the teeth of the saw and, hence, the sample was unable to be cut.

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INDUSTRIAL APPLICABILITY

The cured form of calcium silicate of the present invention not only has a light weight and a high strength, but also is incombustible. Further, the cured form of calcium silicate of the present invention simultaneously exhibits high thermal insulating prop erty and high gas permeability. Therefore, the cured form of calcium silicate can be advantageously used as a wall material for buildings which is required to ex hibit a dynamic insulating property (i.e., dynamic in sulation material), and a sound absorbing material.

The conventional dynamic insulation materials were not completely incombustible. On the other hand, the cured form of calcium silicate of the present invention is completely incombustible and can be shaped into a panel which is a preferred shape of a dynamic insula tion material. Therefore, when the cured form of the present invention is in the form of a panel, it becomes easy to simplify the working thereof and to secure the airtightness required in dynamic insulation techniques.

Claims

1. A cured form of calcium silicate, having (1) a flexural strength of 0. 05 MPa or more, and having (2) a thermal conductivity of from 0.02 to 0.1 WmlKl and (3) a gas permeability of from 5 x 10-4 to 1 m2hlPal, thereby exhibiting a dynamic insulating property.

2. The cured form of calcium silicate according to claim 1, which has a thermal conductivity of from 0.02 to 0.08 WmlKl.

3. The cured form of calcium silicate according to claim 1, which has a thermal conductivity of from 0.02 to 0.06 WmlKl.

4. The cured form of calcium silicate according to any one of claims 1 to 3, which mainly comprises tober morite and exhibits a powder X-ray diffraction pattern in which the diffraction peak intensity Ib ascribed to the (220) plane of the tobermorite and the minimum dif fraction intensity Ia observed in the diffraction angle range between the two diffraction peaks respectively ascribed to the (220) plane and (222) plane of the to bermorite satisfy the relationship Ib/Ia 3.

5. A method for producing a cured form of calcium silicate, which comprises: (1) providing an aqueous slurry comprising water and a solid mixture, said solid mixture consisting essentially of a si liceous material, a cementitious material, at least one aluminum compound selected from the group consisting of aluminum sulfate and a hydrate thereof, at least one sulfate compound selected from the group consisting of sulfates other than aluminum sulfate and hydrates thereof, and optionally a calcareous material, wherein said at least one aluminum compound is contained in said aqueous slurry in an amount of from 0.09 to 10 % by weight in terms of the amount of Al2O3, based on the weight of said solid mixture, and said at least one sulfate compound is contained in said aqueous slurry in an amount of from 0.15 to 15 by weight in terms of the amount of SO3, based on the weight of said solid mixture, said amount of SO3 being the sum of the amount of the SO3 corresponding to said at least one aluminum compound and the amount of the SO3 correspond ing to said at least one sulfate compound, wherein the weight ratio of the water to the solid mixture is from 2.3 to 5.5, and wherein the weight ratio of the calcareous mate rial to the cementitious material is 0.6 or less; (2) adding a foaming agent to said aqueous slurry; (3) pouring said aqueous slurry into a mold; and (4) precuring said aqueous slurry, followed by auto claving.

6. The method according to claim 5, wherein said foaming agent is at least one member selected from the group consisting of an aluminum powder and an aluminum containing aqueous slurry, and wherein said foaming agent is used in an amount of from 0.03 to 0.95 % by weight in terms of the weight percentage of the solids contained in the foaming agent, based on the weight of said solid mixture.

7. A method for producing a cured form of calcium silicate, which comprises: (1) providing an aqueous slurry comprising water and a solid mixture, said solid mixture consisting essentially of a si liceous material, a cementitious material, at least one aluminum compound selected from the group consisting of aluminum sulfate and a hydrate thereof, at least one sulfate compound selected from the group consisting of sulfates other than aluminum sulfate and hydrates thereof, and optionally a calcareous material, wherein said at least one aluminum compound is contained in said aqueous slurry in an amount of from 0.09 to 10 % by weight in terms of the amount of A103, based on the weight of said solid mixture, and said at least one sulfate compound is contained in said aqueous slurry in an amount of from 0.15 to 15 % by weight in terms of the amount of SO3, based on the weight of said solid mixture, said amount of SO3 being the sum of the amount of the SO3 corresponding to said at least one aluminum compound and the amount of the SO3 correspond ing to said at least one sulfate compound, wherein the weight ratio of the water to the solid mixture is from 2.3 to 5.5, and wherein the weight ratio of the calcareous mate rial to the cementitious material is more than 0.6; (2) adding a foaming agent to said aqueous slurry; (3) pouring said aqueous slurry into a mold; and (4) procuring said aqueous slurry, followed by auto claving, wherein at least two additives selected from the group consisting of a surfactant, a viscosity modifier and an anti-foaming agent are added to said aqueous slurry, with the proviso that the addition of the vis cosity modifier and the addition of the anti-foaming agent are performed after said step (1) and before said step (2), and the addition of the surfactant is per formed simultaneously with the addition of said foaming agent in said step (2).

8. The method according to claim 7, wherein said foaming agent is at least one member selected from the group consisting of an aluminum powder and an aluminum containing aqueous slurry, and wherein said foaming agent is used in an amount of from 0.03 to 0.95 by weight in terms of the weight percentage of the solids contained in the foaming agent, based on the weight of said solid mixture.

9. The method according to claim 7 or 8, wherein said surfactant is at least one compound selected from the group consisting of a higher alcohol sulfate, a higher alcohol sodium sulfate and a polyoxyethylene alkyl ether, and wherein said surfactant is used in an amount of from 0.01 to 200 by weight, based on the weight of the solids contained in said foaming agent.

10. The method according to any one of claims 7 to 9, wherein said viscosity modifier is at least one com pound selected from the group consisting of methyl cel lulose and polyvinyl alcohol, and wherein said viscos ity modifier is used in an amount of from 0.01 to 1 by weight, based on the weight of said solid mixture.

11. The method according to any one of claims 7 to 10, wherein said antifoaming agent is at least one com pound selected from the group consisting of a silicone, an aliphatic acid, an aliphatic ester, an alcohol and a phosphoric ester, and wherein said anti-foaming agent is used in an amount of from 0.001 to 3 by weight, based on the weight of said solid mixture.