Method for producing geopolymer foams

Abstract

To provide a method for producing a geopolymer foam having good appearance even when grain ash is used as a raw material.SOLUTION: The method for producing a geopolymer foam includes reacting a silicate of a metal having a valence of 2 or more with an alkali metal silicate to form a reaction slurry containing a geopolymer, and foaming the geopolymer in the reaction slurry with a foaming agent to form a geopolymer foam having a large number of cells, wherein as the alkali metal silicate, an alkali metal silicate solution obtained by adding a cereal ash containing 60% by mass or more of an amorphous silica component to an alkali metal ion-containing alkali solution is used. The total content of a carbon-containing substance and an insoluble metal oxide in the alkali metal silicate solution is controlled to ≤ 4 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to the technology of a method for producing geopolymer foam. [Background technology]

[0002] Geopolymer, a type of inorganic material, is an amorphous condensation polymer inorganic polymer produced by reacting silicates of divalent or higher metals with alkali metal silicates. Geopolymers are attracting attention as an environmentally friendly material because they emit little carbon dioxide from the production of raw materials to the manufacturing of products.

[0003] For example, geopolymers are inorganic polymers that have a tetrahedral structure formed from SiO4 and AlO4, and contain cations that compensate for the negative charge of AlO4 within the tetrahedral network. Geopolymers are also known to have mesopores.

[0004] Generally, geopolymers are obtained by reacting an active filler, a silicate of a divalent or higher metal, with an aqueous solution of an alkali metal silicate. The alkali metal silicate functions as an alkali source when forming the geopolymer, and also as a source of SiO2, which is in short supply during geopolymer formation. Potassium silicate, for example, is known as an alkali metal silicate used as a raw material for geopolymers (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-150335 Summary of the Invention [Problem to be solved by the invention]

[0006] Furthermore, from the viewpoint of obtaining environmentally friendly geopolymer foam, we considered using naturally derived ash such as grain husks (hereinafter referred to as "grain ash") to manufacture geopolymer foam instead of using silica sources such as potassium silicate. However, when using such raw materials, it was difficult to obtain geopolymer foam with a good appearance.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a method for producing a geopolymer foam that has a good appearance even when grain ash is used as a raw material. [Means for solving the problem]

[0008] [1] A method for producing geopolymer foam, which comprises reacting a silicate of a divalent or higher metal with an alkali metal silicate to form a reaction slurry containing a geopolymer, and foaming the geopolymer in the reaction slurry with a blowing agent to form a geopolymer foam having a large number of bubbles. The method comprises using an alkali metal silicate solution in which grain ash containing 60% by mass or more of amorphous silica components is added to an alkali metal ion-containing alkaline solution, and the total content of carbon-containing substances and insoluble metal oxides in the alkali metal silicate solution is 4% by mass or less. [2] The method for producing a geopolymer foam according to [1], wherein the average particle size of the grain ash is 20 μm or more and 200 μm or less. [3] A method for producing a geopolymer foam according to [1] or [2], wherein the total content of carbon-containing substances and insoluble metal oxides in the alkali metal silicate solution is 0.1% by mass or more and 3.5% by mass or less. [Effects of the Invention]

[0009] According to the method for producing geopolymer foam of the present invention, it is possible to obtain geopolymer foam with good appearance even when grain ash is used as a raw material. [Brief explanation of the drawings]

[0010] [Figure 1] 10 is a photograph of a cross section according to Example 2. [Figure 2] 1 is a photograph of a cross section according to Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Geopolymer foam manufacturing method> The inventors have discovered that when producing geopolymer foam using grain ash as a raw material, certain components contained in the grain ash excessively promote foaming by the blowing agent, resulting in the formation of excessive bubbles in the geopolymer foam. This excessive foaming not only results in a poor appearance of the geopolymer foam, but is also thought to cause deterioration of physical properties such as a decrease in compressive strength and an increase in thermal conductivity.

[0012] In the present invention, an excessively large bubble means a bubble that is significantly larger than other bubbles adjacent to it, and generally means a void portion that is three or more times the diameter of the bubble in contact with the excessively large bubble.

[0013] An example of a method for producing a geopolymer foam according to this embodiment is described below. In summary, this method involves reacting a silicate of a divalent or higher metal with an alkali metal silicate to form a reaction slurry containing a geopolymer, and then foaming the reaction slurry with a foaming agent to form a geopolymer foam with numerous bubbles. In this embodiment, an alkali metal silicate solution is used, in which grain ash is added to an alkali metal ion-containing alkaline solution. Details of the alkali metal silicate solution will be described later.

[0014] It is preferable that the silicate of a divalent or higher metal and the alkali metal silicate are reacted in the presence of aggregate. By using aggregate, a molded body in which the aggregate is dispersed in the expanded geopolymer is obtained. However, the use of aggregate is not essential in the present invention.

[0015] First, the characteristics of the silicate of a divalent or higher metal, the alkali metal silicate, and the aggregate used in the manufacturing method of this embodiment will be described.

[0016] The method for producing geopolymer foam of the present invention uses silicates of divalent or higher metals, such as aluminum, calcium, magnesium, titanium, and iron.

[0017] [Aluminosilicate] In the method for producing geopolymer foam of the present invention, it is preferable to use an aluminosilicate. An aluminosilicate is a compound having a structure in which some of the silicon atoms in a silicate are replaced with aluminum atoms. In the following description, the case where an aluminosilicate is used as a silicate of a divalent metal is described.

[0018] The SiO2 (silicon dioxide) content in the aluminosilicate is preferably 20% by mass to 80% by mass, more preferably 30% by mass to 70% by mass. When the SiO2 content in the aluminosilicate is within this range, the produced geopolymer foam is likely to have a good cell structure with a large number of bubbles.

[0019] The lower limit of the Al2O3 content in the aluminosilicate is preferably 20 mass% and more preferably 30 mass% based on the total mass of the aluminosilicate. The upper limit of the Al2O3 content in the aluminosilicate is preferably 70 mass% and more preferably 50 mass% based on the total mass of the aluminosilicate. An Al2O3 content in this range facilitates increasing the compressive strength of the geopolymer foam.

[0020] The SiO2 content and Al2O3 content in the aluminosilicate can be determined by quantifying each element using an X-ray fluorescence analyzer (for example, EA6000V manufactured by Hitachi High-Tech Science).

[0021] Specific examples of aluminosilicates include clay minerals such as beidellite, bentonite, metakaolin, kaolinite, halloysite, montmorillonite, pyrophyllite, vermiculite, mica, chlorite, saponite, sepiolite, and acid clay; industrial wastes such as fly ash, red mud, silica fume, blast furnace slag, and sewage sludge incineration ash; natural aluminosilicate minerals and their calcined products (e.g., metakaolin: Al2O3·2SiO2); volcanic ash; and other aluminum-containing silicate minerals. These may be used alone or in combination. When two or more aluminosilicates are used in combination, it is preferable to blend them so that the SiO2 and Al2O3 contents fall within the above-mentioned preferred ranges. Among these, metakaolin is preferred as the aluminosilicate. Aluminosilicates of the desired composition can be prepared by appropriately grinding and classifying these substances and using specific fractions.

[0022] When metakaolin is used as the aluminosilicate, 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 the above viewpoints, the proportion of metakaolin in the aluminosilicate is more preferably 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0023] The average particle size of the aluminosilicate is preferably 0.1 μm to 50 μm, more preferably 0.3 μm to 30 μm, and even more preferably 0.5 μm to 10 μm. When the average particle size of the aluminosilicate is within this range, the produced geopolymer foam will have a good cellular structure. The average particle size refers to the diameter of a hypothetical sphere having the same volume as the particle. The average particle size of the aluminosilicate refers to the arithmetic mean particle size on a number basis, determined by arithmetically averaging particle sizes based on particle size distribution determined by laser diffraction / scattering.

[0024] The crystallinity of the aluminosilicate is preferably 20% or less, more preferably 10% or less. When the crystallinity of the aluminosilicate is 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, which facilitates the formation of a good cell structure.

[0025] The crystallinity can be determined based on the method (absolute method) described in JIS K0131-1996. For example, the crystallinity can be measured by performing X-ray diffraction measurement on an aluminosilicate powder using an X-ray analyzer equipped with a two-dimensional detector (e.g., SmartLab manufactured by Rigaku Corporation) at room temperature 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.

[0026] [Alkali metal silicates] In this embodiment, as described above, an alkali metal silicate solution is used in which grain ash is added to an alkali metal ion-containing alkaline solution as the alkali metal silicate. When the grain ash is dissolved in the alkali metal ion-containing alkaline solution, aluminosilicate is eluted into the solution.

[0027] By reacting an alkali metal silicate solution with an aluminosilicate, cations such as Al are eluted from the aluminosilicate, and silicate monomers are produced. Meanwhile, the alkali metal silicate in the alkali metal silicate solution serves as an alkali source for polycondensation and also as a source of silicate monomers that form geopolymers through polycondensation. As a result, when the aluminosilicate reacts with the alkali metal silicate, a geopolymer is formed that has a good polymer network with a tetrahedral structure and is composed of the reaction product of the aluminosilicate and the alkali metal silicate.

[0028] Grain ash is ash obtained by burning grain husks, stems, leaves, etc. Among grain ash, those obtained by burning grain husks are preferred from the viewpoint of a high amorphous silica content, and grain ash obtained by burning rice husks is particularly preferred. The content of amorphous silica components in grain ash is generally 60% by mass or more from the viewpoint of ease of handling. When grain ash contains 60% or more of amorphous silica components, it can function sufficiently as a supply source of silicic acid monomers. From the above viewpoints, the content of amorphous silica components in grain ash is preferably 65% ​​by mass or more, more preferably 70% by mass or more, and even more preferably 75% by mass or more.

[0029] When burned grain husks are used as grain ash, the amorphous silicon dioxide content of the grain husks is, for example, 15% by mass or more, preferably 20% by mass or more. Examples of such grain husks include husks of rice, wheat, sugarcane, etc., and one or more of these may be used in combination. Among these, rice husks (rice husks) are particularly preferred because they are rich in amorphous silicon dioxide. In addition to amorphous silicon dioxide, grain husks also contain carbohydrates such as cellulose.

[0030] There are no particular limitations on the method for producing grain ash from grain husks, but for example, it is as follows. Grain ash can be obtained by drying grain husks in advance using hot air or sunlight, crushing them to a specified particle size in a crusher (mill), and then burning the crushed grains. The particle size of the crushed rice husks is preferably 1 mm or less, more preferably 500 μm or less, and even more preferably 300 μm or less.

[0031] The method for burning grain husks is not particularly limited, and can be performed by known methods using, for example, a rotary electric furnace, a fluidized bed combustion furnace, a muffle furnace, etc. When burning at a low temperature below 500°C, unnecessary components other than silica (silicon dioxide) may not be burned sufficiently, and these components may remain in a carbonized state. On the other hand, when burning at a high temperature above 800°C, impurities other than silica are almost completely burned, and although the purity of silica increases, crystallization of silica may be promoted. In consideration of the above, the burning temperature is preferably 500 to 800°C, more preferably 580 to 650°C, and particularly preferably about 600°C. The burning time of grain husks is adjusted appropriately depending on the moisture content and particle size of the grain husks, the burning apparatus, etc., but is expected to be, for example, about 30 minutes to 4 hours.

[0032] By calcining grain husks in this way, grain ash can be obtained in which components other than amorphous silicon dioxide are sufficiently reduced. The silicon dioxide in the grain ash not only maintains its amorphous nature similar to that at room temperature, but also has a mesoporous structure, which improves its alkali water solubility. Commercially available grain ash can be used, such as rice husk silica ash (Takeuchi Kikaku) and rice husk ash (RHA) (Sanyo Trading).

[0033] From the viewpoint of further suppressing the generation of excess bubbles, the average particle size of the grain ash is, for example, 200 μm or less, preferably 180 μm or less, more preferably 160 μm or less, and even more preferably 150 μm or less. From the viewpoint of handleability, it is preferably 10 μm or more, and more preferably 20 μm or more. The average particle size of the grain ash can be controlled, for example, by adjusting the grain crushing process before burning or the burning process conditions.

[0034] The average particle size of grain ash can be measured by a laser diffraction scattering method using a particle size distribution analyzer in accordance with JIS Z 8825. Specifically, the volume-based particle size distribution measured by the laser diffraction scattering method is converted to a number-based particle size distribution by assuming that the particles have a spherical shape, 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 a 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.

[0035] The alkali metal ion-containing alkaline solution is a solution in which an alkali metal compound is dissolved in a solvent. The alkali metal compound is, for example, an alkali metal hydroxide, such as potassium hydroxide or sodium hydroxide. The solvent is, for example, water.

[0036] In this embodiment, other alkali metal silicates may be used in addition to the alkali metal silicate solution in which grain ash is added to the alkali metal ion-containing alkaline solution.

[0037] The other alkali metal silicate is not particularly limited as long as it forms a highly alkaline aqueous solution when dissolved in water, and examples thereof include potassium silicate, sodium silicate (water glass), and lithium silicate, and one or more of these can be used. Among these, the alkali metal silicate is preferably potassium silicate.

[0038] Other alkali metal silicates are preferably used in the form of an aqueous solution. When the alkali metal silicate is used as an aqueous solution, the concentration of the alkali metal silicate in the alkali metal silicate aqueous solution is preferably 20% by mass or more and 60% by mass or less, more preferably 22% by mass or more and 50% by mass or less, and even more preferably 25% by mass or more and 45% by mass or less. When the concentration of the alkali metal silicate is within the above range, the foam moldability of the reaction slurry obtained by mixing the aluminosilicate and the alkali metal silicate aqueous solution can be improved.

[0039] In order to adjust the hydrogen ion concentration (pH) of the aqueous solution to obtain an aqueous solution exhibiting a desired alkalinity, an alkali metal hydroxide such as potassium hydroxide or sodium hydroxide may be added to the aqueous alkali metal silicate solution.

[0040] In particular, in order to adjust the pH of the reaction slurry and promote the reaction between the aluminosilicate and the alkali metal silicate, for example, 10 to 90 parts by mass of potassium hydroxide can be added per 100 parts by mass of the alkali metal silicate, and it is more preferable to add 50 to 80 parts by mass of potassium hydroxide.

[0041] [aggregate] Examples of aggregates used in the manufacturing method of this embodiment include one or more of mica, wollastonite, chalk, talc, molokite, cordierite, basalt, feldspar, zircon, graphite, and borax. Geopolymer powder may also be used as an aggregate. The geopolymer powder may be crushed scraps or scraps recovered during the manufacturing of geopolymer foam, or may be geopolymer foam that is originally in granular or powder form. The geopolymer powder may also be calcined.

[0042] Among these, mica is preferred as the aggregate. Mica is a silicate mineral commonly called muscovite, and is KAl2(AlSiO10 )(F,OH)2. In the present invention, the term "mica" encompasses sheet silicate (phyllosilicate) minerals that are physically and chemically similar. Mica has a structure in which crystal faces that grow in a planar direction are layered, and has the property of peeling off thinly in a planar manner. Therefore, the aspect ratio of mica generally exceeds 2. When mica is included in the aggregate, it is preferable that the average particle size of the mica be 50 μm or more and 200 μm or less from the viewpoint of forming a good cell structure.

[0043] The manufacturing method of this embodiment uses the above-described aluminosilicate, alkali metal silicate, and aggregate to manufacture a geopolymer foam. An example of the manufacturing method of the present invention will be described below. Specifically, the manufacturing method of the present invention includes, for example, steps 1 to 4.

[0044] First step: preparing an alkali metal silicate solution. Second step: A step of mixing the mixture containing the aluminosilicate and the aggregate with an alkali metal silicate solution to obtain a reaction slurry. Third step: A step of adding a foaming agent to the reaction slurry to obtain a foamable composition. Fourth step: obtaining geopolymer foam from the foamable composition.

[0045] Each step will be described in detail below.

[0046] <1> 1st step In the first step, an alkali metal silicate solution having a total content of carbon-containing substances and insoluble metal oxides of 4 mass % or less is prepared.

[0047] First, an alkali metal silicate solution is prepared by adding grain ash to an alkali metal ion-containing alkaline solution (a solution in which an alkali metal compound is dissolved in a solvent).

[0048] The concentration of the alkali metal hydroxide in the alkali metal silicate solution is, for example, 1% by mass to 50% by mass, preferably 5% by mass to 40% by mass, and more preferably 10% by mass to 30% by mass. By having the concentration of the alkali metal hydroxide in the alkali metal silicate solution within the above range, it can sufficiently react with the aluminosilicate and increase the strength of the geopolymer foam.

[0049] The concentration of the grain ash in the alkali metal silicate solution is, for example, 1% by mass to 50% by mass, preferably 5% by mass to 40% by mass, and more preferably 10% by mass to 30% by mass. When the concentration of the grain ash in the alkali metal silicate solution is within the above range, it functions as a source of SiO2.

[0050] In addition, in the alkali metal silicate solution, the mass ratio of alkali metal hydroxide to grain ash (rice husk ash / alkali metal hydroxide) is preferably 0.1 or more and 3.0 or less, and more preferably 0.3 or more and 1.5 or less.

[0051] Specifically, an alkali metal ion-containing alkaline solution is prepared so that the alkali metal hydroxide concentration in the alkali metal silicate solution falls within the above range, and then grain ash is added. After the grain ash is added to the alkali metal ion-containing alkaline solution, the mixture is stirred, for example, at 40 to 90°C for 0.5 to 8 hours to elute the silicate ions. The order in which the solvent (water), grain ash, and alkali metal compound are added is not particularly limited, as long as a solution containing the alkali metal silicate produced from the grain ash and the alkali metal compound is obtained.

[0052] Here, the alkali metal silicate solution contains carbon-containing substances and insoluble metal oxides as the residue (insoluble components) of the grain ash. Specific examples of carbon-containing substances include thermal decomposition products of organic substances. Examples of insoluble metal oxides include crystalline silicon dioxide (SiO), aluminum oxide (AlO), iron oxide (FeO), calcium oxide (CaO), titanium oxide (TiO), magnesium oxide (MgO), potassium oxide (KO), and diphosphorus pentoxide (PO). Here, "water-insoluble" refers to a substance whose solubility in water is less than 1 g / 100 g of water.

[0053] In the first step, the total content of carbon-containing materials and insoluble metal oxides in the alkali metal silicate solution is adjusted to 4% by mass or less. This allows for the production of geopolymer foams with good appearance and excellent physical properties, such as compressive strength and thermal conductivity, even when grain ash is used as the raw material. Previously, it was thought that the carbon-containing materials and insoluble metal oxides contained in the alkali metal silicate solution did not contribute to the geopolymer formation reaction, and therefore there was no need to adjust their content in the alkali metal silicate solution. However, the present inventors have discovered that the carbon-containing materials and insoluble metal oxides significantly affect the formation of bubbles when forming geopolymer foams.

[0054] The carbon-containing materials and insoluble metal oxides contained in the alkali metal silicate solution significantly affect the formation of bubbles in geopolymer foams. The porous nature of the carbon-containing materials contained in grain ash is believed to cause reactions with the foaming agent added during geopolymer foam formation, resulting in excessive foaming and the formation of excessively large bubbles. Furthermore, the insoluble metal oxides are thought to act as nuclei for bubble formation, promoting foaming. In the present invention, by limiting the carbon-containing materials and insoluble metal oxides contained in the alkali metal silicate solution to the above-mentioned specific ranges, it is possible to suppress the formation of excessively large bubbles in geopolymer foams.

[0055] Furthermore, the carbon-containing material and insoluble metal oxides contained in the alkali metal silicate solution can increase the viscosity of the reaction slurry. Adding water to the reaction slurry can reduce its viscosity, but this may result in a decrease in the compressive strength of the geopolymer foam. Therefore, in order to reduce the viscosity of the reaction slurry, it is preferable to limit the total content of the carbon-containing material and insoluble metal oxides in the alkali metal silicate solution to 4% by mass or less.

[0056] The "total content of carbon-containing substances and insoluble metal oxides" refers to the total content of carbon-containing substances and insoluble metal oxides when the alkali metal silicate solution contains both carbon-containing substances and insoluble metal oxides, and refers to the content of either the carbon-containing substance or the insoluble metal oxides when the alkali metal silicate solution contains only one of the carbon-containing substances and insoluble metal oxides.

[0057] As described above, the total content of carbon-containing substances and insoluble metal oxides in the alkali metal silicate solution causes excessive bubbles, but since trace amounts thereof improve compressive strength and thermal conductivity, the lower limit of the total content of carbon-containing substances and insoluble metal oxides in the alkali metal silicate solution is preferably 0.01% by mass or more, more preferably 0.1% by mass or more. The upper limit of the total content of carbon-containing substances and insoluble metal oxides in the alkali metal silicate solution is preferably 3.5% by mass or less, more preferably 3.0% by mass or less.

[0058] The total content of carbon-containing materials and insoluble metal oxides in the alkali metal silicate solution can be adjusted by removing insoluble components from the alkali metal silicate solution. The method for removing the insoluble components is not particularly limited, but solid-liquid separation such as filtration or centrifugation can be used, or a combination of these methods can be used. Specifically, the insoluble components can be removed using a filter press or a centrifugal dehydrator.

[0059] The total content of carbon-containing substances and insoluble metal oxides in the alkali metal silicate solution can be determined by filtering the alkali metal silicate solution, thoroughly washing the insoluble components obtained with pure water or the like, drying them, and measuring the mass.

[0060] The treatment to remove insoluble components is not essential. For example, if the amount of insoluble components contained in the grain ash is small and the carbon-containing substances and insoluble metal oxides are 4 mass% or less without removal, the treatment to remove insoluble components from the alkali metal silicate solution can be omitted. Alternatively, the alkali metal silicate solution can be a mixture of a solution obtained by adding potassium silicate and a solution derived from grain ash.

[0061] <2> 2nd process In the second step, a mixture containing an aluminosilicate and an aggregate (hereinafter referred to as the "powder mixture") is mixed with an alkali metal silicate solution to obtain a reaction slurry. In the reaction slurry, the aluminosilicate and the alkali metal silicate react to form a geopolymer.

[0062] The mixing method in the second step is not particularly limited, and for example, the materials are mixed at room temperature (25° C.) using a known mixer (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, etc. is not particularly limited.

[0063] The amount of aggregate added is 100 to 300 parts by mass relative to 100 parts by mass of the aluminosilicate. If the amount of aggregate added is too small, the geopolymer foam is more likely to crack. On the other hand, if the amount of aggregate added is too large, the compressive strength of the geopolymer foam decreases. If the amount of aggregate added is within the above range, the compressive strength of the geopolymer foam can be improved while suppressing cracking. From the above perspectives, the amount of aggregate added is preferably 120 to 270 parts by mass, more preferably 130 to 250 parts by mass, relative to 100 parts by mass of the aluminosilicate.

[0064] The amount of alkali metal silicate solution added is, for example, 5 to 100 parts by mass, preferably 10 to 80 parts by mass, per 100 parts by mass of the powder mixture, from the viewpoint of uniformly dispersing each component in the foamable composition in the third step. It is preferable to add the alkali metal silicate solution to the powder mixture so that the amount of alkali metal silicate added falls within the above range. When using an alkali metal silicate other than the alkali metal silicate solution using grain husks, the amount is, for example, 50 to 150 parts by mass per 100 parts by mass of the powder mixture.

[0065] In the second step, it is preferable to mix the aluminosilicate and alkali metal silicate so that the molar ratio (Si / Al) of Si to Al in the reaction slurry is 1 or greater. This range of Si / Al molar ratio allows for an adequate amount of exchangeable cations to be present in the geopolymer foam, and also allows for the formation of a good cell structure. From the above perspectives, the molar ratio (Si / Al) is more preferably 1.1 or greater, and even more preferably 1.2 or greater and 5.0 or less.

[0066] In this embodiment, by setting the total content of carbon-containing substances and insoluble metal oxides in the alkali metal silicate solution to 4 mass% or less in the first step, an increase in the viscosity of the reaction slurry can be suppressed in the second step.

[0067] When the alkali metal in the alkali metal silicate solution is potassium, the viscosity of the reaction slurry obtained in the second step is preferably from 10 to 60 Pa s, more preferably from 15 to 55 Pa s, when measured at a spindle rotation speed of 6 rpm, and is preferably from 1 to 20 Pa s, more preferably from 15 to 55 Pa s, when measured at a spindle rotation speed of 60 rpm. When the alkali metal in the alkali metal silicate solution is sodium, the viscosity is preferably 10 Pa s to 100 Pa s, more preferably 15 Pa s to 95 Pa s, when measured at a spindle rotation speed of 6 rpm, and is preferably 1 Pa s to 40 Pa s, more preferably 35 Pa s or less, when measured at a spindle rotation speed of 60 rpm. When the viscosity of the reaction slurry is within the above range, a sudden increase in viscosity due to the application of shear force to the reaction slurry in which the aggregate is dispersed does not occur, and the formation of bubbles becomes easy. Note that water may be added as needed to adjust the viscosity of the reaction slurry.

[0068] The viscosity of the reaction slurry is measured using a viscometer (for example, ATAGO VISCO manufactured by Atago, equipped with an A3 spindle) immediately after mixing the powder mixture containing the aluminosilicate and aggregate with the alkali metal silicate (before heating).

[0069] In the second step, various other additives may be added to the powder mixture of aluminosilicate and aggregate, such as a foam nucleating agent, reinforcing fibers, and cell-opening agents.

[0070] Examples of foam nucleating agents include talc, silica, metal soap, etc. Addition of a foam nucleating agent can improve the foaming properties due to the addition of a foaming agent.

[0071] Reinforcing fibers can be added to improve the strength of geopolymer foam and prevent cracking. Examples of reinforcing fibers include vinylon fiber, polypropylene fiber, aramid fiber, acrylic fiber, rayon fiber, carbon fiber, glass fiber, potassium titanate whisker, alumina fiber, steel wool, and slag wool.

[0072] The strength of the geopolymer foam can be increased by adding reinforcing fibers. Examples of cell-opening agents that can be used include microorganisms such as yeast and algae, proteins, and surfactants.

[0073] The amount of other additives added is not particularly limited as long as the object of the present invention can be achieved, and is preferably 20 parts by mass or less, and more preferably 10 parts by mass or less, relative to 100 parts by mass of the aluminosilicate. The amount of the foam nucleating agent added is preferably 2 parts by mass or more and 20 parts by mass or less, and more preferably 4 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the aluminosilicate.

[0074] The reaction slurry obtained in the second step refers to a fluid in which solid components are dispersed in water. The solid components include, for example, particles of the powder mixture, aggregate, and particles of geopolymers formed by the reaction of aluminosilicates and alkali metal silicates. It is not necessary for the aluminosilicates and alkali metal silicates to completely react to form the geopolymer in the reaction slurry; it is sufficient that the geopolymer formed from the aluminosilicates and alkali metal silicates exists as part of the reaction slurry. The solid content of the reaction slurry is preferably 30% to 80%, and more preferably 40% to 60%. The reaction slurry medium is primarily composed of water, but a water-soluble alcohol or other secondary component may be added.

[0075] <3> 3rd process In the third step, a foaming agent is added to the reaction slurry obtained in the second 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 it is more preferable to use hydrogen peroxide.

[0076] When hydrogen peroxide is used as a foaming agent, it is preferably used as a hydrogen peroxide solution. In this case, the concentration of hydrogen peroxide in the hydrogen peroxide solution is preferably 10% by mass or more and 50% by mass or less. When the concentration of hydrogen peroxide in the hydrogen peroxide solution is within the above range, the foamable composition can be stably foamed, making it easier to obtain an inorganic foam with a good cell structure. From the above perspectives, the concentration of hydrogen peroxide in the hydrogen peroxide solution is more preferably 20% by mass or more and 40% by mass or less.

[0077] The amount of foaming agent added can be appropriately set depending on the design of the geopolymer foam to be produced and is not particularly limited, but for example, when hydrogen peroxide is used as the foaming agent, the amount of foaming agent added is, for example, 0.1 to 30 parts by mass, preferably 0.3 to 25 parts by mass, per 100 parts by mass of aluminosilicate. By adding the amount of foaming agent within the above range, the foamable composition can be sufficiently foamed, and geopolymer foam with excellent thermal insulation properties can be stably obtained.

[0078] <4> 4th step In the fourth step, a geopolymer foam (molded body) having many bubbles is obtained from the foamable composition. Specifically, in the fourth step, the foamable composition is foamed to form many bubbles in the geopolymer, and then the foamable composition is solidified to obtain a geopolymer foam having many bubbles.

[0079] In the fourth step, the foamable composition obtained in the third step can be molded into a desired shape by various molding methods. Examples of molding methods that can be used in the fourth step include 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 and molded by absorbing water, and an extrusion molding method in which the foamable composition is extruded from a die provided downstream of an extruder using an extruder or the like, and is shaped while being foamed.

[0080] 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, thereby obtaining a geopolymer foam.

[0081] When the casting method is used, the bubbles formed by the foaming of the foamable composition in the fourth 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.

[0082] The method for producing geopolymer foam may include other steps in addition to steps 1 to 4. For example, the method may include a step of firing the geopolymer foam obtained in step 4. The fired geopolymer foam can be prevented from changing in dimension at high temperatures. Furthermore, each step may be performed partially simultaneously with the steps before and after it.

[0083] According to the manufacturing method exemplified above, it is possible to suppress the generation of excessive bubbles when using grain ash, which in turn leads to not only a good appearance but also good compressive strength and thermal conductivity.

[0084] <Geopolymer foam> The characteristics of the geopolymer foam produced by the above manufacturing method will be described.

[0085] [volume] The volume of the geopolymer foam is e.g. 300 cm 3 More than 500cm 3 More preferably, it is 1000 cm 3 That's all. If the volume of the geopolymer foam satisfies the above, it can be suitably used particularly as a fire-resistant insulating material.

[0086] [density] The density of geopolymer foam is e.g. 100 kg / m 3 More than 600kg / m 3 Below 150kg / m 3 More than 500kg / m 3 It is preferable that the saturation is 200 kg / m or less. 3 More than 400kg / m 3 More preferably, it is:

[0087] Density can be determined by dividing the weight of the geopolymer foam by the outer diameter of the geopolymer foam.

[0088] [Average bubble diameter] The average cell diameter of the geopolymer foam is preferably 0.1 mm or more and 4 mm or less. By setting the average cell diameter within the above range, it becomes easier to form cell walls with excellent strength. From the above viewpoint, the average cell diameter is more preferably 0.3 mm or more and 3 mm or less, and even more preferably 0.5 mm or more and 2 mm or less.

[0089] The method for determining the average bubble diameter of geopolymer is as follows. Specifically, image data of the cross section of the test piece is obtained at a magnification of 20x using a measuring device (Keyence Corporation Digital Microscope VHX-7000). The area of ​​each bubble in this image data is measured using image processing software NS2K-pro from Nano Systems Co., Ltd. The area of ​​each bubble obtained is converted into a circle, and the diameter when converted into that circle is calculated. The arithmetic mean of these values ​​is then calculated.

[0090] Note that bubbles present inside the cell walls are excluded from the measurement of the cell diameter. Also, bubbles whose cell walls are thought to have been broken off when the cross section of the test piece was prepared are also excluded from the measurement of the cell diameter.

[0091] The detailed setting conditions for acquiring image data are 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, sharpness = 9, sensitivity = 1, noise removal, density range = 0 to 255), shrinkage (8 neighbors, number of processes = 1), image selection by feature (area) (10000 to ∞μm 2 Select only (8 neighbors), expand without connection to neighbors (8 neighbors, number of processes = 3), measure each circle equivalent diameter (calculated from area, 8 neighbors)).

[0092] [Compression strength] The compressive strength of the geopolymer foam is 0.25 MPa or more, preferably 0.4 MPa or more, and more preferably 0.5 MPa or more. The upper limit of the compressive strength of the geopolymer foam is not particularly limited, but is, for example, 20 MPa.

[0093] The compressive strength of geopolymer foam can be measured using a Shimadzu Autograph AG-500B. A test specimen (size: 100 mm diameter, 15 mm height) without a skin (not a cut surface, but a molded surface) on the top surface is placed in the measuring device, and a compressive load is applied in the direction corresponding to the height of the sample at a loading rate of 0.5 mm / min to determine the maximum compressive stress, which is the compressive strength.

[0094] [Thermal Conductivity] The thermal conductivity of geopolymer foam is, for example, 1 W / (m·K) or less, preferably 0.6 W / (m·K) or less, and more preferably 0.2 W / (m·K) or less. When the thermal conductivity is within the above range, it can exhibit excellent thermal insulation properties.

[0095] The thermal conductivity of geopolymer foam can be measured using a thermal conductivity measuring device (HC-074-200) at room temperature in accordance with the measurement method of JIS A1412 (Thermal resistance and thermal conductivity of thermal insulation materials).

[0096] The geopolymer foam described above is suitable for use as a fire-resistant insulation material, although the use of the geopolymer foam is not limited to fire-resistant insulation materials. [Example]

[0097] The present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.

[0098] The examples and comparative examples were produced as follows: The composition of the raw materials is as shown in Table 1.

[0099] [Raw materials] Aluminosilicate: Metakaolin (Hyogo Clay: HC-K-1300W, crystallinity 0%) Alkali metal silicate solution Grain ash: Rice husk silica ash (manufactured by Takeuchi Kikaku Co., Ltd.) The rice husk silica ash can be classified using a sieve to obtain rice husk silica ash with a desired average particle size. The grain ash with an average particle size of 120 μm used in the examples was obtained by sieving the rice husk silica ash manufactured by Takeuchi Kikaku Co., Ltd. through a sieve with a mesh size of 53 μm, and using the ash remaining on the sieve. Potassium hydroxide: Potassium hydroxide (Fujifilm Wako Pure Chemical Industries, Ltd.) Aggregate: Mica (Seishin Enterprises: C100M, average particle size 78 μm, specific surface area 1 m 2 / g) Foaming 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)

[0100] The content of amorphous silicon dioxide in the grain ash was determined by measuring the silicon dioxide content in rice husk ash using a dispersive X-ray fluorescence analyzer, and also by separately measuring the Si concentration when the grain ash was dissolved in an alkaline solution containing alkali metal ions.The dissolved Si component was considered to be an amorphous component, and the content of amorphous silicon dioxide in the grain ash was calculated.

[0101] The average particle size of the grain ash was measured by laser diffraction scattering using a particle size distribution analyzer (HORIBA: Laser Scattering Particle Size Distribution Partica LA-960) in accordance with JIS Z 8825. Specifically, the volume-based particle size distribution measured by laser diffraction scattering was converted to a number-based particle size distribution by assuming the particle shape to be spherical, thereby obtaining the number-based particle size distribution. The particle sizes based on this number-based particle size distribution were then arithmetically averaged to obtain the number-based arithmetic mean particle size, and this value was 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.

[0102] An alkali metal silicate solution using grain ash was prepared as follows: Grain ash, potassium hydroxide, and water were mixed in the formulation shown in Table 1 and stirred at 50° C. or higher for 5 hours.

[0103] In the examples, insoluble components were removed by centrifugation. Specifically, a tabletop centrifuge (Kokusan, H-103N1) was used, and centrifugation was performed for 60 seconds per run for the number of times shown in Table 1. The total content of carbon-containing substances and insoluble metal oxides in the alkali metal silicate solution was calculated by filtering the resulting alkali metal silicate solution with a Kiriyama funnel filter paper (No. 5B) and measuring the weight of the insoluble components. X-ray fluorescence analysis confirmed that the insoluble components were carbon-containing substances and / or insoluble metal oxides.

[0104] Geopolymer foams were produced according to the formulations in Table 1 as follows:

[0105] First, metakaolin and mica as an aggregate were mixed to form a powder raw material mixture. The powder raw material mixture and an alkali metal silicate solution were mixed and stirred at a stirring speed of 60 rpm to produce a reaction slurry. A foaming agent (30% hydrogen peroxide solution) was then added to the reaction slurry, and the mixture was stirred at a stirring speed of 60 rpm for 1 minute using a mixing spatula to form a foamable composition. The foamable composition was then poured into a mold (molding mold) with a cylindrical molding space measuring 100 mm in diameter and 200 mm in height, and a mold (molding mold) with a prismatic molding space measuring 200 mm in diameter and 50 mm in height. The molds were then sealed and held at 60°C for 1 hour to obtain a geopolymer foam. The molds were then opened, and the formed geopolymer foam was removed and further dried at 60°C for approximately 1 day. In Reference Example 1, a potassium silicate aqueous solution (concentration: 30%) was used as the alkali metal silicate solution.

[0106] The viscosity of the reaction slurry before adding the blowing agent (viscosity measured at spindle rotation speeds of 6 rpm and 60 rpm) was also measured. The viscosity of the reaction slurry was measured using a viscometer (e.g., ATAGO VISCO manufactured by Atago, equipped with an A3 spindle). The viscosity was measured immediately after mixing the powder mixture containing the aluminosilicate and aggregate with the alkali metal silicate solution (before heating).

[0107] The resulting geopolymer foam was evaluated as follows, and the results are shown in Table 1.

[0108] <Occurrence of excessive bubbles> The number of excess bubbles was confirmed by visually counting them on a 100 mm × 100 mm cross section. Bubbles with a diameter three times or more the average diameter of adjacent bubbles were defined as excess bubbles.

[0109] <density> The density of the geopolymer foam was determined by dividing the weight of the geopolymer foam by the outer diameter dimension of the geopolymer foam.

[0110] <Average bubble diameter> The average bubble diameter was determined from image data of the cross section of the test piece acquired at a magnification of 20x using a measuring device (Keyence Corporation Digital Microscope VHX-7000). Specifically, the area of ​​each bubble was measured using this image data with image processing software NS2K-pro manufactured by NanoSystems 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. However, the excess bubble portion was excluded from the calculation of the average bubble diameter. Similarly, the excess bubble portion was separately measured for its bubble diameter.

[0111] 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.

[0112] The detailed setting conditions for acquiring image data are 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, sharpness = 9, sensitivity = 1, noise removal, density range = 0 to 255), shrinkage (8 neighbors, number of processes = 1), image selection by feature (area) (10000 to ∞μm 2 Select only (8 neighbors), expand without connection to neighbors (8 neighbors, number of processes = 3), measure each circle equivalent diameter (calculated from area, 8 neighbors)).

[0113] <Compression strength> The compressive strength of the geopolymer foam was measured using a Shimadzu Autograph AG-500B. A test specimen without a skin on the top surface (size: compression surface diameter 100 mm, height 15 mm) was placed in the measuring device, and a compressive load was applied in the direction corresponding to the height direction of the measurement sample at a loading rate of 0.5 mm / min to determine the maximum compressive stress, which was taken as the compressive strength.

[0114] <Thermal conductivity> The thermal conductivity of each test piece was measured using a thermal conductivity measuring device (HC-074-200) at room temperature in accordance with the measurement method of JIS A1412 (thermal resistance and thermal conductivity of thermal insulating materials).

[0115] [Table 1]

[0116] It was confirmed that in Example 1-4, the generation of excess bubbles was suppressed, the compressive strength was high, and the thermal conductivity was low compared to Comparative Example 1-3. Figure 1 shows a photograph of a cross section of Example 2, and Figure 2 shows a photograph of a cross section of Comparative Example 2.

[0117] Among Examples 1-4, Examples 2 and 3, in which the amount of insoluble components in the alkali metal silicate solution was 0.1% by mass or more and 3.5% by mass or less, exhibited significant effects of high compressive strength and low thermal conductivity. In Comparative Example 4, the alkali metal silicate solution contained a low amount of amorphous silica components and a high amount of insoluble components, resulting in a high viscosity of the reaction slurry, making it difficult to mix the foaming agent, and geopolymer foam could not be produced. In Reference Example 1, although the generation of excessive bubbles was suppressed, the thermal conductivity was higher and the compressive strength was lower than in Examples 1-4.

Claims

1. A silicate of a divalent or higher metal and an alkali metal silicate are reacted to form a reaction slurry containing a geopolymer; A method for producing a geopolymer foam by foaming the geopolymer in the reaction slurry with a foaming agent to form a geopolymer foam having a large number of bubbles, The alkali metal silicate may be An alkali metal silicate solution is used, in which grain ash containing 60% by mass or more of an amorphous silica component is added to an alkali metal ion-containing alkaline solution. A method for producing a geopolymer foam, characterized in that the total content of carbon-containing substances and insoluble metal oxides in the alkali metal silicate solution is 4% by mass or less.

2. 2. The method for producing a geopolymer foam according to claim 1, wherein the average particle size of the grain ash is 20 μm or more and 200 μm or less.

3. The method for producing a geopolymer foam according to claim 1 or 2, wherein the total content of carbon-containing materials and insoluble metal oxides in the alkali metal silicate solution is 0.1% by mass or more and 3.5% by mass or less.

Images