Inorganic foam

Abstract

To provide an inorganic foam having high heat insulating properties and strength, in which the decrease in strength and the occurrence of cracks due to the formation of cells are suppressed.SOLUTION: This invention relates to an inorganic foam which uses an inorganic polymer having a leucite crystal structure as a base material, and the inorganic foam is characterized in that the area of a peak derived from leucite crystals in the X-ray diffraction spectrum of the inorganic foam satisfying formula (1). D (geo) / D (pur)≥0.5 ... (1), (D(geo) is the area of the peak located at 2θ=27.3°, which is derived from leucite crystal in the X-ray diffraction spectrum of the inorganic foam. D(pur) is the area of the peak located at 2θ=27.3°, which is derived from leucite crystals in the X-ray diffraction spectrum of pure leucite.)SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to inorganic foams. [Background technology]

[0002] Geopolymer, a type of inorganic material, is an amorphous condensation polymer inorganic polymer produced by reacting aluminosilicate with alkali metal silicate. It is attracting attention as an environmentally friendly material because it emits little carbon dioxide from the production of raw materials to the manufacturing of the product.

[0003] Specifically, geopolymers are inorganic polymers that have a tetrahedral structure formed from SiO4 and AlO4, and that contain cations in the tetrahedral network that compensate for the negative charge of AlO4, and that have mesopores.

[0004] As such, geopolymer materials are lightweight yet have the same mechanical strength as cement, and can significantly reduce CO2 emissions compared to cement. Therefore, it has been proposed that they be used as building materials such as blocks and exterior wall materials to replace cement-based and ceramic-based materials (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2011-219281 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, materials made by forming bubbles in inorganic geopolymer materials to create foams have improved insulation properties due to the cellular structure, but the density of the material is lower, which can reduce compressive strength and make it more susceptible to cracking, leaving issues as an inorganic material.

[0007] The present invention has been made in consideration of the above circumstances, and has an object to provide an inorganic foam that has high thermal insulation properties and strength, in which the decrease in strength and the occurrence of cracks due to the formation of bubbles are suppressed. [Means for solving the problem]

[0008] According to the present invention, there is provided the following inorganic foam. [1] An inorganic foam based on an inorganic polymer having a leucite crystalline structure, The inorganic foam is characterized in that the area of ​​the peak derived from leucite crystals in the X-ray diffraction spectrum satisfies the following formula (1). D(geo) / D(pur)≧0.5 (1) (D(geo) is the area of ​​the peak at 2θ=27.3° due to leucite crystals in the X-ray diffraction spectrum of the inorganic foam, and D(pur) is the area of ​​the peak at 2θ=27.3° due to leucite crystals in the X-ray diffraction spectrum of pure leucite.) [2] The inorganic foam of the invention [1], wherein the inorganic polymer is a fired product of a reaction product of an aluminosilicate and an alkali metal silicate. [3] The inorganic foam of the invention [2] is characterized in that the alkali metal of the alkali metal silicate is potassium, and the molar ratio of potassium to the total of potassium, aluminum, and silicon in the inorganic foam (K / K+Al+Si) is 0.1 or more. [4] The inorganic foam according to the invention of [2] or [3], characterized in that the molar ratio of silicon to aluminum (Si / Al) in the inorganic foam is 1 or more. [5] In the inorganic foam of the inventions [1] to [4], the density of the inorganic foam is 150 to 1500 kg / m 3 It is characterized in that: [6] The inorganic foam according to any one of the above [1] to [5] inventions, characterized in that the inorganic foam has an average cell diameter of 0.1 to 5 mm. [7] A firebrick made of any of the inorganic foams described in [1] to [6]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an inorganic foam having excellent strength, in which the decrease in strength and the occurrence of cracks due to the formation of bubbles are suppressed. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a photograph of an actual block-shaped molded product (length 230 mm, width 115 mm, thickness 60 mm) showing one embodiment of the inorganic foam of the present invention. [Figure 2] 2 is an example of an enlarged photograph showing the cell structure of the inorganic foam of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present inventors have discovered that the strength of inorganic foam can be improved by using an inorganic polymer having a leucite crystal structure as a base material, and have completed the present invention.

[0012] Hereinafter, one embodiment of the inorganic foam of the present invention will be described. (Leucite) The inorganic foam of the present invention is based on an inorganic polymer having a leucite crystal structure. Leucite has the chemical formula KAlSiO or KO·AlO·4SiO. In the present invention, by using an inorganic polymer having a leucite crystal structure as a base material for the inorganic foam, the cell walls of the inorganic foam are formed by the inorganic polymer having a leucite crystal structure, which improves the strength of the cell walls and results in a foam with excellent heat resistance and strength. The base material refers to a component that, of all the components constituting the inorganic foam, preferably accounts for more than 50% by mass of the total mass of all the components, preferably 60% or more, and more preferably 70% or more.

[0013] The inorganic foam of the present invention is characterized in that the area of ​​the peak derived from leucite crystals in the X-ray diffraction spectrum of the inorganic foam satisfies the following formula (1). D(geo) / D(pur)≧0.5 (1) In formula (1), D(geo) is the area of ​​the peak at 2θ=27.3° due to leucite crystals in the X-ray diffraction spectrum of the inorganic foam, and D(pur) is the area of ​​the peak at 2θ=27.3° due to leucite crystals in the X-ray diffraction spectrum of pure leucite material.

[0014] From the viewpoint of obtaining an inorganic foam having superior strength, it is preferable that the following formula (2) is satisfied, and it is further preferable that the following formula (3) is satisfied.

[0015] D(geo) / D(pur)≧0.7 (2) D(geo) / D(pur)≧0.8 (3) In the present invention, the peak at 2θ=27.3° in the X-ray diffraction spectrum is used as the peak derived from leucite crystals, and the peak areas at 2θ=27.3° for the pure leucite material and the inorganic foam of the present invention are measured and calculated. The peak area ratio of the inorganic foam to the pure leucite material is calculated. Note that the peak does not necessarily have its top at 27.3° as long as it includes 27.3°. The peak area ratio can be calculated by X-ray diffraction using, for example, an X-ray diffractometer (Rigaku Corporation RINT2550H (Rotorflex type)).

[0016] (inorganic foam) The inorganic foam of the present invention has a foam density of 150 to 1500 kg / m 3 If the density of the inorganic foam is too low, the cell walls of the inorganic foam may become too thin, which may weaken the strength of the foam. On the other hand, if the density of the inorganic foam is too high, the heat insulating performance may decrease. From the above viewpoints, the lower limit of the density is 180 kg / m 3More preferably, it is 200 to 1000 kg / m 3 The upper limit of the density is more preferably 1200 kg / m 3 More preferably, it is 1000 kg / m 3 More preferably, it is 800 kg / m 3 More preferably, it is 500 kg / m 3 It is more preferable that:

[0017] The inorganic foam of the present invention also has a cellular structure. This cellular structure is formed by cellular walls having a thickness of approximately 0.5 to 2 mm, as shown in Figures 1 and 2, and is distinguished from the porous structure with pore diameters of 100 nm or less, known as mesopores, present in the cellular walls. The inorganic foam also preferably has an average cellular diameter of 0.1 to 5 mm. By setting the average cellular diameter within the above range, cellular walls with excellent strength are more likely to be formed. From this perspective, the average cellular diameter is more preferably 0.5 to 3 mm, and even more preferably 0.8 to 2 mm.

[0018] These cellular structures can be formed, for example, by using a foaming agent or by using spacers that have a particle diameter corresponding to the average cellular diameter and can be removed by heating or the like. The leucite of the present invention is preferably a fired product of a reaction product of an aluminosilicate and an alkali metal silicate.

[0019] The molar ratio of silicon to aluminum (Si / Al) in the inorganic foam is preferably 1 or more. When the molar ratio of silicon to aluminum (Si / Al) is within the above range, it becomes easier to form leucite in the inorganic foam. From the above viewpoint, the molar ratio (Si / Al) is preferably 1.2 or more, and more preferably 1.3 or more. The upper limit of the molar ratio is approximately 5, preferably 3. Note that the above molar ratio can be determined by elemental analysis of the inorganic foam, but since the blending ratio of aluminum and silicon in the raw materials is expected to be maintained during the manufacturing process, it can also be calculated from the blending ratio of the raw materials.

[0020] (aluminosilicate) When the aluminosilicate (xM2O·yAl2O3·zSiO2·nH2O, where M is an alkali metal) reacts with an alkali metal silicate in an aqueous solution (slurry), aluminum ions are dissolved into the solution and silicic acid monomers (silicic acid, Si(OH)4) are produced. The silicic acid monomers thus produced and cations undergo polycondensation to form a geopolymer with a polymer network consisting of a tetrahedral SiO4·AlO4 structure.

[0021] Examples of aluminosilicates include clay minerals such as beidellite, bentonite, kaolinite, halloysite, montmorillonite, pyrophyllite, vermiculite, mica, chlorite, saponite, sepiolite, and acid clay; industrial wastes such as fly ash, red mud, silica fume, and sewage sludge incineration ash; natural aluminosilicate minerals and their calcined products (e.g., metakaolin); volcanic ash; and other aluminum-containing silicate minerals. Among these, aluminosilicates primarily composed of metakaolin (chemical formula: Al2O3·2SiO2) are preferred. Furthermore, aluminosilicates of the desired composition can be prepared by appropriately pulverizing and classifying the above substances and using specific fractions.

[0022] (alkali metal silicates) When alkali metal silicates react with aluminosilicates, they form a highly alkaline aqueous solution when dissolved in water. By reacting this aqueous solution with aluminosilicates, cations such as Al can be eluted from the aluminosilicates and silicate monomers can be produced. The alkali metal silicates also serve as a source of silicate monomers for forming geopolymers through polycondensation.

[0023] Examples of alkali metal silicates include one or more of potassium silicate, sodium silicate (water glass), lithium silicate, etc. Among these, the alkali metal of the alkali metal silicate is preferably potassium. (Reaction product of aluminosilicate and alkali metal silicate) The reaction of aluminosilicate with alkali metal silicates produces a geopolymer with a tetrahedral polymer network, and calcination of this geopolymer produces an inorganic material with leucite crystals as the base polymer.

[0024] (aggregate) The inorganic foam of the present invention can also contain aggregate. Examples of aggregate include one or more of mica, wollastonite, chalk, talc, molokite, cordierite, basalt, feldspar, zircon, graphite, and borax, as well as crushed recycled materials such as scraps and scraps of the inorganic foam or geopolymer foam of the present invention. The aggregate is preferably a powder having an average particle size of 50 μm to 300 μm. The aggregate preferably contains mica, and in this case, the proportion of mica in the aggregate is preferably 50% by mass or more. It is more preferably 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more. Mica is a silicate mineral commonly called muscovite, and is generally KAl2(AlSiO 10)(F,OH)2. In the present invention, the term "mica" includes sheet silicate (phyllosilicate) minerals that are physically and chemically similar.

[0025] The aggregate content in the inorganic foam is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, relative to 100% by mass of the inorganic foam. When the aggregate content is within this range, the inorganic foam has further improved strength.

[0026] Furthermore, when the aggregate contains mica, it is preferable that the average particle size of the mica is 80 μm or more and 200 μm or less. When the average particle size of the mica contained in the aggregate is within this range, a good air bubble structure is formed in the expanded geopolymer produced as a precursor, and the air bubbles of the inorganic foam can be prevented from becoming finer. (Other additives) The inorganic foam may contain other materials such as a foam nucleating agent, a reactive material, or reinforcing fibers, as needed. Examples of reactive materials include one or more of clays such as bentonite, sepiolite, minugel, and attapulgite clay, cement binders, calcium aluminate cements, and organic polymer binders (e.g., cellulose binders). The addition of reactive materials can adjust the reaction (hardening) time of the foamable composition.

[0027] Reinforcing fibers can be added to improve the strength of inorganic foams and prevent cracking. Examples of reinforcing fibers include vinylon fibers, polypropylene fibers, aramid fibers, acrylic fibers, rayon fibers, carbon fibers, glass fibers, potassium titanate whiskers, alumina fibers, steel wool, and slag wool. Adding reinforcing fibers can increase the strength of the expanded geopolymer. The amount of other materials added is not particularly limited as long as the intended purpose of the present invention can be achieved. However, it is generally preferred that the amount be 20 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of inorganic foam.

[0028] The inorganic foam of the present invention having the above-mentioned properties has excellent heat resistance, heat insulation, and high strength, and is therefore particularly suitable for use as a heat-resistant brick. For example, by using the inorganic foam as the inner wall material of a melting furnace, a decrease in the furnace wall temperature can be prevented, and the heat retention of the furnace can be improved, making it possible to reduce the input heat itself, and significant energy savings can be expected. (Manufacturing method) The inorganic foam of the present invention can be produced by, for example, reacting and foaming a composition containing an aluminosilicate, an alkali metal silicate, aggregate, water, and a blowing agent to form a geopolymer foam in which a large number of bubbles are formed in the reaction composition of the aluminosilicate and the alkali metal silicate.The geopolymer foam can then be fired under specific conditions to further react the geopolymer foam, producing leucite crystals and resulting in an inorganic foam with a large number of bubbles and excellent thermal insulation properties and high strength.

[0029] (aluminosilicate) When the aluminosilicate (xM2O·yAl2O3·zSiO2·nH2O, where M is an alkali metal) reacts with an alkali metal silicate in an aqueous solution (slurry), aluminum ions are dissolved into the solution and silicic acid monomers (silicic acid, Si(OH)4) are produced. The silicic acid monomers thus produced and cations undergo polycondensation to form a geopolymer with a polymer network consisting of a tetrahedral SiO4·AlO4 structure.

[0030] The SiO2 (silicon dioxide) content in the aluminosilicate is preferably 20% by mass or more and 80% by mass or less. When the SiO2 content is in this range, the produced expanded geopolymer can easily form a good cell structure with a large number of bubbles. From this perspective, the SiO2 content is more preferably 30% by mass or less and 70% by mass or less. The SiO2 content and the Al2O3 content described below in the aluminosilicate can be determined by quantifying each element using an X-ray fluorescence analyzer (e.g., EA6000V manufactured by Hitachi High-Tech Science).

[0031] The aluminosilicate preferably has a crystallinity of 20% or less, more preferably 10% or less. When the aluminosilicate has a crystallinity within this range, when the aluminosilicate is reacted with an alkali metal silicate (described later) in an aqueous solution, the alkali component derived from the alkali metal silicate facilitates elution of aluminum ions from the aluminosilicate source, and silicate monomers are readily produced, stably carrying out polycondensation, and thus a favorable cell structure is readily formed.

[0032] The crystallinity can be determined by X-ray diffraction. For example, the crystallinity can be measured by performing X-ray diffraction on an aluminosilicate powder at room temperature using an X-ray analyzer equipped with a two-dimensional detector (e.g., Rint2550 manufactured by Rigaku Corporation) with the 2θ range set to 10 to 40°. The crystallinity can be determined by performing profile fitting on the diffraction pattern measured by X-ray diffraction measurement and calculating the ratio of the peak area of ​​the crystalline component to the total peak area ([peak area of ​​the crystalline component] + [halo pattern area of ​​the amorphous component]) from the obtained X-ray diffraction.

[0033] Examples of aluminosilicates include clay minerals such as beidellite, bentonite, kaolinite, halloysite, montmorillonite, pyrophyllite, vermiculite, mica, chlorite, saponite, sepiolite, and acid clay; industrial wastes such as fly ash, red mud, silica fume, and sewage sludge incineration ash; natural aluminosilicate minerals and their calcined products (e.g., metakaolin); volcanic ash; and other aluminum-containing silicate minerals. Among these, aluminosilicates primarily composed of metakaolin (chemical formula: Al2O3·2SiO2) are preferred. Furthermore, aluminosilicates of the desired composition can be prepared by appropriately pulverizing and classifying the above substances and using specific fractions.

[0034] The aluminosilicate is preferably a powder having an average particle size of 0.1 μm to 50 μm. When the average particle size is within this range, the produced expanded geopolymer has a good cellular structure and excellent heat insulating properties. From this perspective, the average particle size is more preferably 0.3 μm to 30 μm.

[0035] The average particle size of the aluminosilicate and aggregate can be measured by laser diffraction scattering. Specifically, the volume-based particle size distribution measured by laser diffraction scattering is converted to a number-based particle size distribution by assuming the particles to be spherical, thereby obtaining a number-based particle size distribution. The particle sizes based on this number-based particle size distribution are then arithmetically averaged to obtain the number-based arithmetic mean particle size, which is defined as the average particle size in the present invention. Note that the above-mentioned average particle size refers to the diameter of a hypothetical sphere having the same volume as the particle.

[0036] When an aluminosilicate containing metakaolin as a main component is used, the proportion of metakaolin in the aluminosilicate is preferably 50% by mass or more. When the proportion of metakaolin in the aluminosilicate is within the above range, a good cell structure with a large number of bubbles is easily formed. From this viewpoint, the proportion of metakaolin is more preferably 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0037] The Al2O3 content in the aluminosilicate is preferably 20 mass% or more, more preferably 30 mass% or more, based on the total mass of the aluminosilicate. It is also preferably 80 mass% or less, more preferably 70 mass% or less. When the Al2O3 content is within this range, the strength of the inorganic foam can be more easily increased.

[0038] (alkali metal silicates) Alkali metal silicates, when reacted with aluminosilicates and alkali metal silicates, form a highly alkaline aqueous solution when dissolved in water. By reacting this aqueous solution with aluminosilicates, cations such as Al can be eluted from the aluminosilicates and silicate monomers can be produced. Alkali metal silicates can also serve as a source of silicate monomers for forming geopolymers through polycondensation.

[0039] Examples of alkali metal silicates include one or more of potassium silicate, sodium silicate (water glass), lithium silicate, etc. The alkali metal silicate can be suitably used, for example, as an aqueous solution (alkali metal silicate aqueous solution) in which the alkali metal silicate is dissolved in water. Of these, potassium is preferred as the alkali metal in the alkali metal silicate. In order to adjust the hydrogen ion concentration of the aqueous solution and obtain an aqueous solution exhibiting the desired alkalinity, an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide can be added to the alkali metal silicate aqueous solution.

[0040] The molar ratio of silicon to alkali metal in the alkali metal silicate aqueous solution is preferably 0.1 to 5, more preferably 0.3 to 3. By setting the molar ratio within the above range, the strength of the expanded geopolymer can be further increased.

[0041] For example, the concentration of the alkali metal silicate in the alkali metal silicate aqueous solution is preferably 20% by mass to 80% by mass, more preferably 25% by mass to 70% by mass, and more preferably 30% by mass to 60% by mass. When the concentration of the alkali metal silicate is within this range, the fluidity of the slurry obtained by mixing the aluminosilicate and the alkali metal silicate aqueous solution is increased, improving the foamability of the foamable composition. In addition, a geopolymer foam with excellent strength and a good polymer network formed by a tetrahedral structure can be stably obtained.

[0042] Furthermore, when the alkali metal in the alkali metal silicate is potassium, the molar ratio of potassium to the sum of potassium, aluminum, and silicon in the inorganic foam (K / K+Al+Si) is preferably 0.1 or more, and more preferably 0.2 to 0.4. The above molar ratio can be determined by elemental analysis of the inorganic foam, but because the blending ratio of potassium, aluminum, and silicon in the raw materials is expected to be maintained in the geopolymer and inorganic foam due to the manufacturing process, it can also be calculated from the blending ratio of the raw materials.

[0043] Specifically, it is preferable to include the following steps 1 to 4.

[0044] A first step of mixing a mixture A containing an aluminosilicate and an aggregate with an aqueous alkali silicate solution to obtain a slurry; a second step of adding a foaming agent to the slurry to obtain a foamable composition; A third step is to foam the foamable composition while reacting the aluminosilicate with the alkali silicate, forming a large number of bubbles in the reaction mixture, and solidifying the reaction mixture to obtain a geopolymer foam having a large number of bubbles.

[0045] The fourth step is to calcinate the precursor as a geopolymer foam to obtain an inorganic foam containing leucite.

[0046] Each step will be described below. (1st step) In the first step, a mixture A containing an aluminosilicate and aggregate, an aqueous alkali metal silicate solution, and water for adjusting viscosity are mixed to obtain a slurry. The method for mixing the materials in the first step is not particularly limited, and they can usually be mixed at room temperature (25°C) using a known or conventional mixer or the like (e.g., a mortar mixer, a tilting mixer, a truck mixer, a twin-screw mixer, an omni mixer, a pan mixer, a planetary mixer, an Eirich mixer, etc.). The order in which the materials are added to the mixer or the like is also not particularly limited.

[0047] When mixing mixture A with an aqueous alkali silicate solution to form a slurry, it is preferable to add 30 to 300 parts by mass, and more preferably 50 to 200 parts by mass, of the aqueous alkali silicate solution to 100 parts by mass of mixture A. By adjusting the amount within this range, the components in the foamable composition can be uniformly dispersed.

[0048] The amount of water to be added to adjust the viscosity can be appropriately determined taking into consideration the viscosity of the slurry or the foamable composition, the compressive strength of the resulting molded article, etc., and is not particularly limited, but is usually preferably 20% by mass or more and 50% by mass or less, and more preferably 25% by mass or more and 45% by mass or less, relative to 100% by mass of the foamable composition in Step 2. Water may be added independently, or may be added as a solvent, for example, when water glass is used as the alkali metal silicate.

[0049] The viscosity of the slurry obtained by mixing mixture A with the alkali silicate aqueous solution is preferably 1 Pa s to 5 Pa s, and more preferably 2 Pa s to 4 Pa ​​s. By adjusting the viscosity to a relatively low level within the above range, the proportion of bubbles in the foam whose volume is equal to or greater than a specific value can be stably increased.

[0050] Furthermore, in the mixing of the aluminosilicate and alkali metal silicate in the first step, the molar ratio of Si to Al in the reaction slurry, Si / Al, is preferably 1 or greater. When the Si / Al molar ratio of the mixture is within this range, an appropriate amount of exchangeable cations can be present in the resulting geopolymer foam, and a good cellular structure can be formed. From this perspective, the molar ratio of Si to Al, Si / Al, is more preferably 1.1 or greater, and even more preferably 1.2 to 5.0. (2nd process) In the second step, a foaming agent is added to the slurry obtained in the first step to obtain a foamable composition. Examples of foaming agents include hydrogen peroxide, sodium peroxide, potassium peroxide, sodium perborate, and non-ferrous metal powder. Examples of non-ferrous metal powder include aluminum powder. Among these, it is preferable to use at least one of hydrogen peroxide water and non-ferrous metal powder, and hydrogen peroxide is more preferable. Furthermore, when hydrogen peroxide is used as a foaming agent, it is preferably used as hydrogen peroxide water. In this case, the concentration of hydrogen peroxide in the hydrogen peroxide water is preferably 10% by mass or more and 50% by mass or less. This range allows for stable foaming of the foamable composition and facilitates the production of an inorganic foam with a good cell structure. From this perspective, it is more preferable for the concentration of hydrogen peroxide in the hydrogen peroxide water to be 20% by mass or more and 40% by mass or less.

[0051] The amount of foaming agent added can be set appropriately depending on the design of the inorganic foam to be produced, and is not particularly limited. For example, when hydrogen peroxide is used, the amount is preferably 0.1% by mass to 5% by mass, more preferably 0.2% by mass to 3% by mass, and even more preferably 0.2% by mass to 2% by mass, based on 100% by mass of the foamable composition. This allows the foamable composition to foam sufficiently, and geopolymer foam with excellent thermal insulation properties can be stably obtained. (3rd step) In the third step, the foamable composition is foamed to form a large number of bubbles in the reactant composition of aluminosilicate and alkali silicate, thereby obtaining a geopolymer foam having a large number of bubbles.

[0052] In the third step, the foamable composition obtained in the second step can be molded into a desired shape suitable for a thermal insulating material by various molding methods. Specific molding methods that can be used include, for example, a casting method in which the foamable composition is poured into a mold and molded, a dehydration molding method in which the foamable composition is pressed in a mold or absorbed to dehydrate and mold it, and an extrusion molding method in which the foamable composition is extruded from a die provided downstream of an extruder or the like and shaped while being foamed.

[0053] The conditions for foaming the foamable composition are appropriately set depending on the desired physical properties of the geopolymer foam. For example, when foaming the foamable composition by the casting method, the foamable composition is reacted and foamed in a mold at a temperature of 20 to 100°C, preferably 50 to 80°C, for a holding time of 30 minutes to 24 hours, to obtain a geopolymer foam.

[0054] For example, when the casting method is used, the bubbles formed by the foaming of the foamable composition in the third step grow larger within 30 minutes to 1 hour after the addition of the blowing agent. Note that geopolymer foams typically have mesopores derived from the geopolymer structure, but these mesopores are distinct from the numerous bubbles formed by the blowing agent.

[0055] In the method for producing an inorganic foam according to the present invention, unlike physical foaming in which bubbles are formed by stirring or the like, bubbles are gradually grown by adding a foaming agent, and therefore, it is possible to obtain inorganic foam having a relatively uniform bubble structure in which bubbles are less likely to be miniaturized and there is little variation in bubble diameter. (4th step) In the fourth step, the geopolymer foam obtained in the third step is fired to obtain an inorganic foam containing an inorganic polymer having a leucite crystalline structure as a base material. The firing method is not particularly limited as long as it can be heated and fired at a predetermined temperature or higher, and can usually be performed by firing in a firing furnace or the like. Note that the cellular structure of the geopolymer foam is maintained during the firing process. Therefore, even after firing, the inorganic foam of the present invention has cell walls based on an inorganic polymer having a leucite crystalline structure.

[0056] It is important that the inorganic foam of the present invention contains leucite. Leucite can be produced by firing the geopolymer foam at a temperature of 1100°C or higher. It has been confirmed that the ratio of leucite produced tends to increase as the firing temperature increases. Furthermore, the strength of the inorganic foam improves depending on the ratio of leucite produced. From this perspective, the firing temperature is preferably 1200°C or higher, and more preferably 1300°C or higher. The firing time is preferably 1 to 24 hours.

[0057] The fourth step, firing, produces an inorganic foam having a leucite crystal structure, thereby improving the compressive strength of the resulting inorganic foam. It is believed that the compressive strength of an inorganic foam is determined by the strength of its thin cell walls. By firing the cell walls to an inorganic polymer having a leucite crystal structure, the strength of the cell membrane is improved, improving the compressive strength and suppressing cracking.

[0058] The inorganic foam thus obtained contains leucite and aggregate and has a density of 150 to 1500 kg / m 3 It is preferable that the foam of the present invention has a physical property of an average cell diameter of 0.1 to 5 mm, which allows the foam of the present invention to be suitably used as a fire-resistant insulating material having excellent heat insulating properties and strength. (Molding and in-mold compacts) In the inorganic foam of the present invention, a reaction slurry of aluminosilicate and alkali silicate is placed in a mold, the mold is heated, the aluminosilicate and alkali metal silicate are further reacted, and the blowing agent is expanded to form a geopolymer foam. The molded product is then fired to obtain an inorganic foam molded body having the shape of the mold. In particular, the above method can produce a block-shaped molded body that can be used as an insulating material such as a firebrick.

[0059] Furthermore, in the inorganic foam of the present invention, the strength is improved by the formation of leucite, so that when the foam is molded in a mold, cracking or chipping of the molded article due to shrinkage during firing is effectively prevented.

[0060] The molded article made of the inorganic foam of the present invention preferably has a thermal conductivity of 0.05 W / m·K or less at room temperature. When the thermal conductivity is within the above range, excellent heat insulating properties can be exhibited.

[0061] In the molded article made of the inorganic foam of the present invention, the strength of the cell walls forming the cell structure is particularly excellent, so that the reheat shrinkage rate when heated to 1200°C is preferably 4% or less, and more preferably 3% or less, and the molded article has excellent physical properties as a firebrick.

[0062] In the molded article made of the inorganic foam of the present invention, the strength of the cell walls forming the cell structure is particularly excellent, so that the compressive strength is preferably 0.3 to 3 MPa, more preferably 0.5 to 2 MPa, and the article has physical properties superior to those of a firebrick. [Example]

[0063] The inorganic foam of the present invention will be described below with reference to examples, but the inorganic foam of the present invention is not limited to the following examples in any way. (raw materials) The inorganic foam was produced using the following raw materials. Aluminosilicate: Metakaolin (Imerys: Argical M1200S, crystallinity 0%) Alkali metal silicate: Potassium silicate (Nippon Chemical Industry: 2K potassium silicate) Aggregate: Mica (Seishin Enterprises: C100M) Bubble nucleating agent: Talc (Matsumura Sangyo: Hi-filler 5000PJS) Foaming agent: Hydrogen peroxide solution (Fujifilm Wako Pure Chemical Industries, Ltd.: Hydrogen peroxide concentration 30% by mass) Potassium hydroxide (Fujifilm Wako Pure Chemical Industries, Ltd.: Special grade) (Method of manufacturing inorganic foam) First, aluminosilicate (metakaolin) and aggregate (mica) were mixed in the ratio shown in Table 1 to form mixture A. Potassium silicate, potassium hydroxide, and, if necessary, distilled water were mixed to prepare an aqueous alkali metal silicate solution (the concentration of the alkali metal silicate shown in the table; for example, when the concentration of the alkali metal silicate is 36.5 wt %, the molar ratio of silicic acid to potassium is 0.63).

[0064] Next, Mixture A and an aqueous alkali metal silicate solution were mixed in the proportions shown in Table 1 and stirred at a stirring speed of 60 rpm to prepare a slurry with a Si / Al ratio of 1.4 and a viscosity of approximately 3 Pa·s. Next, a foaming agent (hydrogen peroxide solution) was added to the slurry in the proportions shown in Table 1, and the mixture was stirred using a stirring spatula at a stirring speed of 60 rpm for 1 minute to prepare a foamable composition.

[0065] Next, the foamable composition was poured into a mold (molding die) with a molding space measuring 680mm long x 280mm wide x 100mm thick, and the mold was sealed. The mold was then placed in an oven at 60°C for one hour to allow the foamable composition to react and expand, resulting in a foamed geopolymer. The pressure inside the mold was atmospheric, and foaming was completed in about 30 minutes, and solidification was completed in about one hour. The mold was then opened, and the resulting geopolymer foam was removed and dried at 60°C for another day.

[0066] The resulting geopolymer foam was then heated in a firing furnace from room temperature to 1200°C at a heating rate of 5°C / min over a 4-hour heating period. The temperature was then held at 1200°C for 1 hour, followed by 5 hours of firing. After firing, the heating was discontinued and the foam was allowed to cool naturally (24 hours) from 1200°C to room temperature, yielding an inorganic foam. To produce a block-shaped molded product, the foam was cut into blocks measuring 253mm long x 125mm wide x 72mm thick before firing, and then fired to obtain a block-shaped molded product measuring 230mm long, 115mm wide, and 60mm thick. This 230mm long, 115mm wide, and 60mm thick sample was suitable for use as a firebrick (JIS R2101 Refractory Brick Shape and Dimensions).

[0067] The inorganic foams obtained were measured and observed for density before and after firing, Si / Al molar ratio, K / (Si+Al+K) molar ratio, leucite peak area ratio, cell diameter (average cell diameter, standard deviation of cell diameter), compressive strength, compressive strength improvement rate, thermal conductivity, reheat shrinkage rate, and crack occurrence using the following methods. The results are shown in Table 1. (Leucite peak area ratio) The leucite crystal peak area ratio was determined by measuring the peak area around 27.3°, where a peak derived from leucite crystals is observed, using an X-ray analyzer (Rigaku Corporation RINT2550H (Rotorflex type)). Pure leucite (100% crystalline component, Nichika Corporation) and the inorganic foam were analyzed by X-ray analysis, and the ratio was calculated. The pure leucite and inorganic foam were pulverized and measured as powders. The measurement conditions were in accordance with JIS K0131 (1996), with a CuKα tube, output of 40 kV, 30 mA, a measurement angle 2θ = 3.0° to 90.0°, a sampling interval of 0.02°, and a scan rate of 0.6 seconds / degree. (bubble diameter) Image data of the cross section of the test piece was obtained at a magnification of 20 times using a measuring device (Keyence Corporation, Digital Microscope VHX-7000). The area of ​​each bubble was measured using this image data and image processing software NS2K-pro manufactured by Nano Systems Co., Ltd. The area of ​​each bubble was converted into a circle, and the diameter of the circle was calculated. The arithmetic mean of these values ​​was calculated.

[0068] The bubbles present inside the cell walls were excluded from the measurement of the cell diameter. Also, bubbles whose cell walls were thought to have been broken off when the cross section of the test piece was prepared were excluded from the measurement of the cell diameter.

[0069] The detailed measurement conditions were as follows (monochrome conversion, smoothing filter (3x3, 8 neighbors, number of processes = 1), density unevenness correction (brighter than background, size = 5), NS method binarization (darker than background, clarity = 9, sensitivity = 1, noise removal, density range = 0 to 255), shrinkage (8 neighbors, number of processes = 1), image selection by feature (area) (only select 10000 to infinity μm2, 8 neighbors), expansion that is not connected to adjacent ones (8 neighbors, number of processes = 3), measurement of each circle equivalent diameter (calculated from area, 8 neighbors)). (Compression strength) Test pieces (size: compression surface 1 × 1 cm, height 3 cm) were cut out from each inorganic foam, and the compressive strength was measured at a loading rate of 0.5 mm / s in accordance with the test method of JIS R1608 (compressive strength of fine ceramics). (Compressive strength improvement rate) The percentage improvement in compressive strength of the inorganic foam after firing was reported based on the compressive strength of the unfired geopolymer foam. (thermal conductivity) The thermal conductivity of each test piece was measured at room temperature using a thermal conductivity measuring device (HC-074-200) in accordance with the measurement method of JIS A1412 (thermal resistance and thermal conductivity of thermal insulating materials). (reheat shrinkage rate) Each test piece of the inorganic foam was again fired in a firing furnace at 1200°C for 5 hours, and the reheat shrinkage rate was measured from the change in dimension before firing. (Crack occurrence) Each test piece was visually inspected for the occurrence of cracks.

[0070] [Table 1]

[0071] In Examples 1 to 7, geopolymer foam was calcined at a specific temperature using the above method to obtain inorganic foams based on inorganic polymers with a leucite crystal structure. It was confirmed that the compressive strength was improved compared to geopolymer foams.

[0072] Comparative Example 1 is an example of geopolymer foam fired at 1050°C, and the X-ray diffraction spectrum showed no peak at 2θ=27.3° due to leucite. However, the X-ray diffraction peak showed a peak due to caryophyllite. Therefore, it was confirmed that the compressive strength was unchanged compared to the precursor because the foam did not contain an inorganic polymer with a leucite crystal structure and contained caryophyllite, which has brittle properties.

[0073] Comparative Example 2 is an example of geopolymer foam fired at 1000°C, and the X-ray diffraction spectrum showed no peak at 2θ = 27.3° due to leucite. However, the X-ray diffraction peaks showed peaks due to caryophyllite. Therefore, it was confirmed that the compressive strength was lower than that of geopolymer foam because it did not contain an inorganic polymer with a leucite crystal structure and contained brittle caryophyllite.

[0074] Comparative Example 3 is a geopolymer foam and corresponds to Examples 1 to 3. This example does not contain an inorganic polymer having a leucite crystal structure. The X-ray diffraction spectrum did not show a peak at 2θ=27.3° due to leucite.

[0075] Comparative Examples 4 and 5 are geopolymer foams, and correspond to the densities of Examples 4 and 5, respectively. When compared at the same density, it was confirmed that the examples that did not contain an inorganic polymer having a leucite crystal structure had inferior strength.

[0076] Comparative Examples 6 and 7 are geopolymer foams, which correspond to Examples 6 and 7, respectively. It was confirmed that the examples that did not contain an inorganic polymer having a leucite crystal structure had poor strength.

Claims

1. An inorganic foam having a cellular structure, based on an inorganic polymer having a leucite crystal structure, An inorganic foam characterized in that the area of ​​the peak derived from leucite crystals in the X-ray diffraction spectrum of the inorganic foam satisfies the following formula (1): D(geo) / D(pur)≧0.5...(1) (D(geo) is the area of ​​the peak at 2θ=27.3°, which is attributable to leucite crystals, in the X-ray diffraction spectrum of the inorganic foam, and D(pur) is the area of ​​the peak at 2θ=27.3°, which is attributable to leucite crystals, in the X-ray diffraction spectrum of pure leucite.)

2. 2. The inorganic foam according to claim 1, wherein the inorganic polymer is a fired product of a reaction product of an aluminosilicate and an alkali metal silicate.

3. The inorganic foam according to claim 2, characterized in that the alkali metal of the alkali metal silicate is potassium, and the molar ratio of potassium to the total of potassium, aluminum, and silicon in the inorganic foam (K / K+Al+Si) is 0.1 or more.

4. 4. The inorganic foam according to claim 2, wherein the molar ratio of silicon to aluminum (Si / Al) in the inorganic foam is 1 or more.

5. The density of the inorganic foam is 150 to 1500 kg / m ３ 5. The inorganic foam according to claim 1, wherein

6. The inorganic foam according to any one of claims 1 to 5, characterized in that the inorganic foam has an average cell diameter of 0.1 to 5 mm.

7. A firebrick comprising the inorganic foam according to any one of claims 1 to 6.

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