JPS6149272B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a novel method for producing an inorganic heat insulating material.More specifically, the present invention is an inorganic inorganic material with excellent heat insulating properties that foams and hardens simply by mixing raw materials into a paste form, and forms uniform bubbles in a short time without any heating operation. The present invention relates to a novel and useful method for stably obtaining a heat insulating material. Various methods have been proposed to obtain inorganic foams from aqueous alkali metal silicate solutions. For example, a method in which the above aqueous solution is directly heated to foam, a method in which a foaming agent that generates gas upon heating is mixed into the above aqueous solution, the mixture is solidified, and the solidified product is then heated and foamed; A method is known in which a curing agent such as a compound is mixed and heated to effect curing and foaming. However, in order to obtain a foam by these methods, a heating operation (usually at about 200 to 900°C) is necessary. That is, alkali metal silicates and foaming agents do not foam at all at room temperature, and heating is necessary for foaming. Moreover, the foams obtained by the various methods described above are composed of water-soluble alkaline components and are inherently inferior in water resistance, and the alkaline components are easily eluted upon contact with moisture, reducing the mechanical strength of the foams. It has the disadvantage of significantly lowering the temperature, and has almost no practical use as a heat insulating material. Furthermore, inorganic lightweight bodies (lightweight concrete, lightweight mortar, etc.) that are water resistant and have excellent mechanical strength have been known in the field of concrete and mortar, but most of these are simply pearlite and vermiculite. It is simply a mixture of lightweight aggregates such as Another known method is to add and knead metal aluminum and water to cement, heat and pressurize the mixture in an autoclave, and cause foaming and hydrothermal curing reactions due to the generation of hydrogen gas. It requires complicated operations and takes a long time for foaming and curing, and in particular, curing usually takes as long as one week. Furthermore, it is difficult to obtain lightweight foams using the various methods described above, and even the lightest foams have a bulk specific gravity of approximately 0.5 or more. The present invention solves all the difficulties in manufacturing operations of conventional inorganic foams and provides a new method for manufacturing inorganic foams useful as heat insulating materials. That is, the present invention provides (A) a water-soluble alkali metal silicate (hereinafter referred to as component A), (B) a cement material (hereinafter referred to as component B), (C) a metal foaming agent (hereinafter referred to as component C), (D) Foaming stabilizer (hereinafter referred to as component D), and (E)
Silica dust (hereinafter referred to as E) is a by-product of electric heating and metal
The present invention relates to a method for producing an inorganic heat insulating material, which comprises mixing ingredients (components) into a paste in the presence of water. One of the greatest features of the method of the present invention is that
By simply mixing the above components A to E to form a paste, the desired heat insulating material can be easily obtained at normal temperature and normal pressure without any subsequent heating operation. The foaming time of the above mixture is usually 5 minutes or more.
It can be adjusted as quickly as about 2 hours and over a wide range, and is almost constant depending on the composition of the mixture, and the curing process is usually completed within 24 hours. Furthermore, since the above-mentioned mixture is in the form of a paste, it is possible to use molds with complex shapes, and it is easy to mold into any desired shape. can also be molded. Therefore, there is no need for any specific molds or the like, and construction can be carried out by simply providing appropriate partitions at locations where insulation is required and pouring the material. In addition, the paste-like mixture of the present invention has excellent foaming stability that is not affected by climatic conditions, etc., and by appropriately adjusting the blending ratio of the components A to E, the foaming time can be increased as described above. It can be adjusted to a substantially constant value within a range, and the expansion ratio, that is, the bulk specific gravity of the product can be easily adjusted. In particular, this bulk specific gravity can be adjusted to an extremely low specific gravity of about 0.1 g/cm ² to 0.3 g/cm ² , which is impossible with lightweight aerated concrete (ALC), which is conventionally known as having excellent mechanical strength. Such a low specific gravity product also has sufficient mechanical strength to be practical as a heat insulating material. As a matter of fact, it is possible to easily manufacture a product having a bulk specific gravity similar to that of the above-mentioned ALC and a product having a similar high strength, and the product thus obtained can have thermal conductivity reduced to about 1/3 compared to ALC. The inorganic heat insulating material obtained by the method of the present invention is 0.5
It has substantially uniform cells within a range of about 5 mm, and its cell structure is extremely strong. Therefore, it has excellent heat insulation properties, nonflammability, heat resistance, and flame resistance. In particular, its heat resistance is extremely excellent, with no deformation observed at all even when the product sample is left in a 700°C furnace for 24 hours. Furthermore, the inorganic heat insulating material of the present invention has significantly superior waterproofness, water resistance, acid resistance, alkali resistance, and mechanical strength not found in conventional alkali silicate foams. The reason why an inorganic heat insulating material having the above characteristics can be produced by simply mixing the above components A to E according to the method of the present invention is not clear at present, but it is thought to be approximately as follows. That is, when most of the cement material as component B is mixed into a paste, it gradually solidifies through vapor hardening or hydration groove reaction due to the action of moisture, while the water-soluble alkali metal silicic acid as component A The salt and a part _of the above B component are hydrolyzed in the paste to form an alkali component such as alkali hydroxide and ^SiO2-3 , AlO ^- _O, etc., and the alkali component is a component of the metal blowing agent which is the C component. It promotes the foaming action and causes fine bubbles to be incorporated into the paste and the cured product of component B, _and SiO ^2-3 gradually gels in parallel with the foaming reaction and is densely filled in the cured product of component B. It is estimated that this improves the mechanical strength of the cured foam product. In addition, the foaming stabilizer used as component D enters into the system of component C, which tends to become localized gradually during the vaporization or hydration curing reaction of component B and the progress of the foaming reaction between components A to C. It seems to have the effect of maintaining a uniformly dispersed state, stabilizing the foaming reaction, accelerating the curing reaction, and further preventing the generated microbubbles from becoming unevenly distributed and continuous. Furthermore, it is presumed that the E component serves to strengthen each component while making the bubbles in the cured product smaller, thereby making a large contribution to improving mechanical strength and heat insulation. In any case, the present invention makes it possible to easily produce an inorganic heat insulating material that is stable at room temperature and pressure and has excellent properties simply by uniformly mixing the materials, and its industrial value is enormous. Its industrial value is enormous. In the present invention, it is essential to use a soluble alkali metal silicate as component A, and only then can the desired inorganic heat insulating material be obtained. The above-mentioned heat insulating material cannot be manufactured using insoluble or slightly water-soluble alkali metal silicates such as ordinary anhydrous glass cullet. Examples of the alkali metal constituting component A include lithium, sodium, potassium, and rubidium. In particular, sodium, potassium, etc. are preferable because they are inexpensive and easily available, and furthermore, they significantly promote the foaming effect. In addition, as long as the A component is water-soluble, its composition and alkali metal oxide (shown as R〓 ₂ O)
Although not limited to the molar ratio with SiO ₂ , the above
The molar ratio of SiO ₂ /R〓 ₂ O is preferably about 1.4 to 4.0, particularly about 1.8 to 3.0. When the molar ratio is 1.8 to 3.0, a heat insulating material with particularly excellent water resistance and high mechanical strength can be obtained. The above component A can be advantageously used alone or in combination of two or more in powder form or water-soluble form, but considering the ease of paste preparation, the solid content concentration should be adjusted. Ten
% or more, usually in the form of an aqueous solution of about 10 to 50%. That is, when component A is used in the form of an aqueous solution with a concentration within the above range, the paste can be easily prepared by simply mixing it with components B to E, and appropriate fluidity can be obtained while shrinkage during curing can be reduced. The rate is also relatively low. Next, in the present invention, the cement substance used as component B includes what is commonly called cement in the chemical industry, and includes air hard cement,
This includes hydraulic cement and special cement. Air-hardening cements include quicklime, slaked limestone, dolomite plaster, etc.
Examples include plain cements such as calcined gypsum, Keens cement, Parian cement, and martin cement, as well as magnesia cement.
In addition, hydraulic cements include single cements such as hydraulic lime, natural cement, Portland cement, and alumina cement, lime-mixed cement, blast furnace cement, silica cement, fly ash cement, masonry cement, and high sulfate cement. An example is mixed cement. Furthermore, special cements include fire-resistant cement, acid-resistant cement,
Examples include phosphate cement. Of these, hydraulic cement is particularly desirable, but it is not enough to use only one of the cement substances listed above; a combination of hydraulic cement and air-hard cement is also effective, or the same cement Even if it is a hard cement, two or more types can be used in a mixed manner. In the present invention, various metal elements and metals or intermetallic compounds can be used as the metallic foaming agent as component C. As metal elements, periodic table B,
A, B, A, B, A, B, A,
B, B, B, and those belonging to the groups can all be used, and among them, those belonging to the third to fifth periods are preferred. Examples of preferable metal elements include Mg,
Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga,
Examples include Sn, and metals such as Al, Mg, Fe, Ni, and Zn are particularly suitable because they are easy to obtain and have good reactivity. In the present invention, metalloid elements such as B and Si can also be used. In the present invention, alloys or intermetallic compounds (chemical combinations between metals or between metals and non-metals) of the above metals can also be used in the same manner as the above metals. Representative examples of the alloy or intermetallic compound include Al-Si, Al-Ti, Al-Mn,
Al−Cu−Si, Al−Cu, Zn−S, Zn−Sn, Sn−
Fe, Cu−Sn, Cu−Si, Cu−Pb, Cu−Ni, Fe−
Ni, Fe-Mn, Fe-Cr, Fe-Si, Mn-P, Si-
Examples include Ni, Co-Sb, Mn-Ag, etc. Above C
It is usually preferable to use one or more of the components in the form of fine powder, particularly preferably in a particle size of 150 μm or less. In addition, the foaming stabilizer used as component D in the present invention includes silica gel, zeolite, artificial zeolite, carbon black, activated carbon, alumina gel,
Inorganic substances selected from talc (talc) and mica (mica) and organic substances such as animal proteins and dimethylsilicon derivatives, which are conventionally known as cement-based foaming agents, can be used. These D components have the effect of uniformly dispersing the C component in the system, stabilizing the foaming reaction, and are effective in producing fine, uniform cells. When the D component is an inorganic substance, it is usually 200μ.
It is preferable to use it in powder form with the following particle size. Furthermore, in the present invention, the silica dust produced as a by-product of electric heating or gold as component E refers to the following. In the electric heating and metallurgical methods, high temperatures of 2000°C to 3000°C or higher are usually generated to heat-treat silica stone and/or single metal elements or their raw ores, and in order to avoid oxidizing atmosphere, coke or coke with high reducing performance is used. It allows hydrogen gas, carbon monoxide, etc. to pass through, and when it is used with any metal or gold, it removes oxides such as silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) in the metal ore, which is the crude raw material. Most of it becomes vapor and decomposes into highly reactive metal elements, but the vapor that combines with oxygen in the air or remains as silica or alumina undergoes rapid cooling in the air and becomes powdery. In this case, impurities such as sulfur, phosphorus, and carbon contained in the raw ore are often contained together, but their amounts are relatively small, so the fine powder that is produced as a by-product has a silica content. In particular, in the case of manufacturing silicon-based alloys, the purity of the silica content is extremely high, and these are collectively referred to as silica dust. Among these, the preferred silica dust used in the present invention has a particle size of approximately 0.1 to 1.0.
μ, specific surface area approximately 10 to 50 m ² /g and bulk specific gravity approximately 0.1
~0.3, and examples include those with a purity of about 80% by weight or more of silica. The blending ratio of the above components A to E should be determined based on the type of substance used as each component, especially when component A is used in the form of an aqueous solution, its concentration, bulk specific gravity of the desired product, strength, and molding to obtain the desired product. Although it varies depending on the conditions of the product, etc., it can usually be done as follows. That is, based on the solid content of component A,
For 100 parts by weight, component B may be about 10 to 100 parts by weight, preferably about 15 to 90 parts by weight, and component C may be about 2 to 30 parts by weight. In addition, if component D is an inorganic substance, the solid content is 5
-50 parts by weight, and if it is an organic substance, the solid content may be about 0.1 to 3 parts by weight, and furthermore, component E may be about 5 to 70 parts by weight. In general, if the A component is too much, the bubbles and bulk specific gravity will not be stable, the foaming state will be non-uniform, and the insulation product will tend to have poor water resistance. The viscosity of the liquid tends to become too high, and the workability of filling or spraying tends to deteriorate. Furthermore, if the C component is too small, foaming will be insufficient and the bulk specific gravity of the product will be heavy (approximately 1.0 or more), and if it is too large, the bubbles in the product will be large and excessive foaming will occur, making it difficult to obtain a product with the desired strength. When component D is inorganic, if it is too small, foaming will be uneven.
If it is too large, paste adjustment becomes difficult. Furthermore, when component D is an organic substance, if it is too large, open air bubbles will be generated and the insulation effect will be reduced. If the amount of component E increases, the shrinkage will increase during foam formation, which may cause cracks, and if it decreases, the heat insulation properties and mechanical strength will decrease. In the present invention, the above components A to E are mixed into a paste in the presence of water. The mixing method is not particularly limited, and for example, the above components A to E may be mixed together with an appropriate amount of water. It is operationally advantageous to add and mix it into component A. Furthermore, since component B and component C start curing and foaming reactions in a very short time after being mixed, it is preferable to mix these components into the paste at the same time as possible when preparing the paste. In addition, when preparing a paste by mixing ingredients A to E, the result is that the A ingredient in the paste is
Preferably, an amount of water is used such that the water is soluble in a concentration of 10 to 60% by weight, preferably 10 to 50% by weight;
Furthermore, it is preferable to carry out operations such as stirring to uniformly disperse the solid components in the paste. In any case, in the present invention, it is important to mix the above-mentioned components A to E into a paste form in the presence of water, and unless the mixture is formed into a paste form, a satisfactory foamed cured product cannot be obtained. Note that in the above description, paste refers to a soft and sticky solid dispersion, and the paste-like liquid of the present invention usually has a viscosity of about 0.5 to about 300 poise at 25°C. To the paste thus prepared, it is possible to further add, as necessary, a lightweight aggregate powder such as foamed silica, perlite, vermiculite, and shirasu balloons, which is usually fired at a temperature of 1000°C or higher, thereby reducing the bulk specific gravity of the product. Can be made smaller. Furthermore, for example, for the purpose of weight increase, reinforcement, etc., fused quartz, calcined cristobalite, silica powder, fly ash,
It is also possible to add various known fillers such as alumina powder, but care must be taken to ensure that the type and amount of these fillers does not interfere with the reaction form of the essential components A to E. There is a need. In the method of the present invention, hardening and foaming reactions occur immediately after a paste is prepared by mixing the components A to E and, if necessary, a lightweight aggregate powder. This curing and foaming reaction proceeds well at room temperature and under normal pressure without any external heating, and the foaming reaction is usually completed in about 5 minutes to 2 hours, and the curing reaction is also completely completed within 24 hours. As mentioned above, the present invention does not require any heating or pressurization, which is extremely advantageous from an industrial perspective. However, of course, the above-mentioned foaming and curing reactions proceed at about 1 to 90°C, and therefore these reactions are particularly promoted. If desired, it is also possible to heat up to about 90°C. For normal construction, room temperature to 50℃
It is preferable to set the temperature to about Thus, it usually has uniform air bubbles in the range of 0.5 to 5 mm, low specific gravity, high strength, and water absorption.
The inorganic heat insulating material of the present invention having excellent water resistance, chemical resistance, heat insulation properties, heat resistance, flame resistance, etc. can be obtained. As described above, the inorganic heat insulating material of the present invention is
Since they have various properties, they can bring out new advantages depending on their use. Next, we will discuss some special application examples.
Of course, the use is not limited to this. In recent years, central heating has been gaining attention as a heating method for general homes, hotels, hospitals, etc. The heat source is hot water, and the pipes that carry the hot water are buried in the floor, walls, and in some cases, the ceiling. In this case, conventionally, a heat equalizing plate such as aluminum foil was placed on the inside of the house of the hot water pipe, an exterior metal plate was placed on the outside of the house, and hard urethane foam was injected between them as a core material and insulation material. This method is widely used. However, since this urethane foam is organic, it is extremely brittle against overheating and high-temperature steam, and in addition, it has the fatal defect of igniting or emitting smoke if it comes into contact with flames in the event of a fire. In addition, internal adiabatic hardening strain occurs at the interface with the heat equalizing plate and the exterior metal plate,
It has the disadvantage of being prone to condensation. If the inorganic heat insulating material of the present invention is used instead of this conventional hard urethane foam, it will be effective in preventing fires even if they occur due to their high fire resistance, heat resistance, flame resistance, etc., and will have no heat insulation effect. The fruit itself is also larger than the hard urethane foam. Furthermore, it has good adhesion to heat-uniforming plates, metal plates, etc., so it has good impact resistance, and in addition, when it is injected in a paste form, workability is improved. As is clear from this application example, the same effect can be obtained not only when used for a heat insulating wall with central heating, but also when used for a general heat insulating wall without central heating. In general, the walls of buildings, with the exception of concrete construction, often have a hollow space inside the structure, and this is useful in reducing the burden on structural materials such as steel frames, prefabricated construction, and PC construction methods, and aiming for insulation. It is becoming common. A heat insulating wall is constructed by injecting a heat insulating paste according to the present invention into this hollow space. When the present inventors conducted various experiments in this regard, a completely unexpected fact was discovered. That is, when the inventive heat insulating material was injected into the hollow part of the wall surface through a hole of an arbitrary size using a pneumatic feeding method as a means of transporting it to the wall structure, it was found that the insulating material of the present invention was injected into the hollow part with a slit of only about 50 mm. Even when the base area is constant, a uniform foam system is formed, and "rise performance" (the property of the foam insulation material to increase its volume in the vertical direction through the foaming process, especially when the base area is constant, the foaming magnification It has been found that the rising performance is better when the paste according to the present invention is poured immediately after mixing. be. In general buildings, the width of the slit in the hollow part of the wall is about 30 mm if it is narrow, and 200 mm or 300 mm if it is wide, but it is generally about 50 to 100 mm, and the height (compartmentalized) Due to structural limitations, the maximum height of the building is 5 m or less, and the width is approximately 2 m.
It is as follows. Assuming an arbitrary wall hollow section, for example, if we take a hollow wall section with a slit width of 100 mm, a hollow section width of 1 m, and a height of 3 m, this is clearly equivalent to a hollow molded plate. Injecting conventional plastic foam into such a hollow part to ensure a 3-meter rise performance requires extremely difficult techniques, and the bubbles after foaming also lack uniformity, resulting in a reduced heat insulation effect. Regarding this point, when the paste of the present invention was injected by pneumatic feeding immediately after mixing, satisfactory results were obtained in terms of rising performance and bubble uniformity. Therefore, not only new buildings but also existing buildings can easily form walls with excellent insulation, impact resistance, water resistance, etc. by making small holes in the upper part and injecting the paste of the present invention. becomes possible. In addition, concrete, mortar, asbestos cement board, wood wool cement board, and various other base materials are used as the building materials that form the hollow part, but in particular, materials with poor adhesive properties such as metal plates and plastic boards are used. If the substrate is covered with paper in advance, there will be no problem in forming the heat insulating wall according to the present invention. As described above, it has various advantages over plastic foam conventionally used for insulation walls, but its excellent adhesive properties cannot be overlooked. By utilizing this adhesive effect, tiling construction can be performed simply and easily. That is, conventionally, in order to take advantage of the heat insulating effect of plastic foam, it has been common practice to attach tiles to the surface of plastic foam to form a heat insulating tile wall. However, since plastic foam does not have much adhesive properties, a large amount of adhesive is required. If the heat insulating material of the present invention is used in place of such plastic foam for tiling, it is possible to improve workability by eliminating the need for adhesives. Effects such as fire resistance and impact resistance can also be expected. Examples are given below to explain the present invention in more detail. The substances used as components A to E in each example are shown in Tables 1 to 5 below.

【table】

【table】

【table】

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[Table] In addition, various physical properties of the inorganic heat insulating material samples obtained in each example were tested by the following methods. The ambient air during the test was 20±2℃, 65±
It remained constant at 10RH%. (a) Bulk specific gravity: According to JIS A1161. (b) Water absorption rate: Shown in weight% according to JIS A 1161. (c) Compressive strength: According to JIS A 1161, expressed in Kg/cm ² . (d) Water resistance: After immersing each sample in water for 10 days, determine whether there are any abnormalities in the appearance, and mark no abnormalities as (-) and those with them as (+). (E) Acid resistance: After immersing in 1N HCl solution for 2 days, determine whether there are any abnormalities in appearance. No abnormalities are evaluated as (-), and those with abnormalities are evaluated as (+). (F) Alkali resistance: Determine whether there are any abnormalities in appearance after immersion in saturated Ca(OH) ₂ solution for 2 days. (g) Thermal conductivity: Kcal/m・h according to JIS R 2616
Shown in r°C. (h) Size of bubbles: Measure the bubbles on the fracture surface of each specimen, and indicate in mm diameter. (li) Heat resistance: Determine the presence or absence of deformation after leaving each specimen in a 650℃ furnace for 24 hours.
Absence is set as (-). (v) Flame resistance: Exposing to direct flame for 10 seconds, judge whether or not the sample is deformed. Example 1 100 g of aqueous solution No. A-1 as component A was collected in a polyethylene container (content 1.5). On the other hand, 10g of No.B-1 as B component, No.C- as C component
1, 7 g of No. D-1 as the D component, and 7 g of No. E-1 as the E component to prepare a mixed powder. Next, the mixed powder is added to the polyethylene container in which the component A was collected, and mixed and stirred at room temperature to form a uniform paste. If you continue to leave the above paste in the container,
Foaming occurs gradually and is completed 30 minutes after mixing and stirring. The foam phenomenon occurs beyond the rim of the polyethylene container. Thereafter, it was left for one day and night to completely cure, thereby obtaining inorganic heat insulating material No. 1 of the present invention. The time (minutes) required for foaming and the physical properties of the obtained heat insulating material were tested, and the results are shown in Table 6. Examples 2 and 3 No.A-1, which is the A component in Example 1, is used as No.
Inorganic heat insulating materials No. 2 and 3 were obtained in the same manner except that A-2 and A-3 were changed to 100 g each. Table 6 shows the foaming time and physical properties of each of the obtained heat insulating materials. Example 4 50g of No.A-4 powder as A component, 15g of No.B-1 as B component, 1g of No.C-1 as C component, 2g of No.D-1 as D component, E component Collect 4 g of No. E-2 into a polyethylene container and mix them to prepare a powder mixture.
Next, 40 g of water was added to the mixture, and the mixture was thoroughly stirred and mixed at room temperature to form a uniform paste. When the paste is subsequently left in the container, foaming gradually occurs, and foaming is completed in about 20 minutes after mixing and stirring water.
The foaming phenomenon occurs beyond the rim of the polyethylene container. Thereafter, it was left for one day and night to completely cure, thereby obtaining inorganic heat insulating material No. 4 of the present invention. Table 6 shows the foaming time and physical properties of the obtained heat insulating material.

[Table] Examples 5 to 8 No.B-1, which is the B component in Example 1, is
Inorganic heat insulating materials Nos. 5 and 6 were obtained in the same manner except that 10 g of each of -2 and B-3 was used. In addition, No.B-4 used as the B component in Example 1
Inorganic heat insulating materials Nos. 7 and 8 were obtained in the same manner except that 3 g and 6 g of Inorganic Heat Insulating Materials were added, respectively. The physical properties and foaming time of each of the obtained heat insulating materials are shown in Table 7 below.

【table】

[Table] Examples 9 to 12 Inorganic insulation materials No. 9 to 1 were prepared in the same manner as in Example 1 except that 2 g of each of No. C-2 to C-5 was used instead of No. C-1 as the C component. Get 12. The physical properties and foaming time of each of the obtained heat insulating materials are shown in Table 8 below.

[Table] Examples 13 to 16 Inorganic heat insulating agent No. 13 was prepared in the same manner as in Example 1 except that 2 g of each of Nos. D-2 to D-5 was used instead of No. D-1 as component D. The physical properties and foaming time of each of the heat insulating materials obtained were measured and the results are shown in Table 9 below.

[Table] Examples 17 to 19 2 g each of fused quartz, calcined cristobalite, and gypsum were added as fillers to the A to E components used in Example 1, and inorganic heat insulating materials No. 17 to 19 were obtained in the same manner. . The physical properties and foaming time of each of the obtained heat insulating materials were measured and the results are shown in Table 10 below.

【table】

Claims (1)

[Scope of Claims] 1 (A) water-soluble alkali metal silicate, (B) cement material, (C) metal foaming agent, (D) foaming stabilizer, and (E) by-produced by electric heating or gold. A method for producing an inorganic heat insulating material, comprising mixing silica dust into a paste in the presence of water. 2 Water-soluble alkali metal silicate SiO ₂ /R ^I ₂ O
(However, R ^I represents an alkali metal) molar ratio is
1.5 to 4.0. 3. The method of claim 1, wherein the mixture to be mixed into a paste contains an amount of water to form the water-soluble alkali metal silicate into an aqueous solution with a concentration of 10 to 60%. 4 Water-soluble alkali metal silicate at a concentration of 10 to 50
% in the form of an aqueous solution. 5 Silica dust produced by electric heating and metal
Claims characterized by having a particle size of about 0.1 to 1.0 μ, a specific surface area of about 10 to 50 m ² /g, a bulk specific gravity of about 0.1 to 0.3, and a purity of about 80% by weight or more of silica. The method described in paragraph 1. 6 For 100 parts by weight of water-soluble alkali metal silicate, 10 to 100 parts by weight of cement material, 2 to 30 parts by weight of metal foaming agent, 0.1 to 50 parts by weight of foaming stabilizer, and by-products from electric heating and gold The method according to claim 1, using 5 to 70 parts by weight of silica dust.