Dispersion for silicon carbide sintered body, green sheet for silicon carbide sintered body, prepreg material for silicon carbide sintered body, and silicon carbide sintered body

Abstract

The purpose of the present invention is to provide a dispersion for a silicon carbide sintered body which has low viscosity and excellent dispersibility. The present disclosure relates to a dispersion for a silicon carbide sintered body, which contains: silicon carbide particles that are charge-controlled such that the surface is positively charged; a water-soluble first metal compound that contains one or more first metals selected from the group consisting of rare earth elements, zirconium, and aluminum; a resin that has a hydroxyl group; and water.

Description

Dispersion for silicon carbide sintered bodies, green sheet for silicon carbide sintered bodies, prepreg material for silicon carbide sintered bodies, and silicon carbide sintered bodies

[0001] The present invention relates to a dispersion for silicon carbide sintered bodies, a green sheet for silicon carbide sintered bodies, a prepreg material for silicon carbide sintered bodies, and a silicon carbide sintered body.

[0002] Silicon carbide (SiC) is highly hard, possesses excellent high-temperature resistance, mechanical strength, impact resistance, wear resistance, oxidation resistance, and corrosion resistance, and has a low coefficient of thermal expansion. Therefore, it is expected to have various applications, including polishing compositions and high-temperature structural components.

[0003] In the application of silicon carbide, studies are being conducted to improve sintering temperatures and mechanical strength by mixing particulate silicon carbide (silicon carbide particles, SiC particles) with auxiliary agents. Known auxiliary agents include alumina, yttria, and yttria-alumina oxide particles. Furthermore, studies are being conducted to disperse silicon carbide particles in a dispersion medium or polymer material medium in order to form desired compositions and materials. To improve the functionality of dispersions containing silicon carbide particles, and molded or sintered bodies formed from these dispersions, dispersions in which silicon carbide particles have high dispersibility in the medium are particularly desired.

[0004] For example, Patent Document 1 discloses a technique for producing a dispersion by dispersing silicon carbide (SiC) particles together with boron nitride (BN) particles in a medium, and then sintering this dispersion to produce a sintered body. According to International Publication No. 2019 / 189254 (corresponding to U.S. Patent Application Publication No. 2021 / 139382), a dispersion for silicon carbide sintered bodies can be obtained in which silicon carbide particles and boron nitride particles are uniformly dispersed in the medium.

[0005] To efficiently manufacture silicon carbide sintered bodies using a dispersion containing silicon carbide particles and auxiliary agents, the dispersion needs to have a high concentration of silicon carbide while maintaining low viscosity, considering factors such as handling ease and sinterability (e.g., reduction in sintering temperature). However, current technologies have not been able to obtain dispersions with sufficiently low viscosity, and this remains an issue that needs improvement.

[0006] Therefore, the present invention has been made in view of the above problems, and aims to provide a dispersion for silicon carbide sintered bodies that has low viscosity and excellent dispersibility.

[0007] In order to solve the above problems, the inventors diligently conducted research. As a result, the inventors discovered that the above problems can be solved by a dispersion for silicon carbide sintered bodies containing a specific metal compound, and thus completed the present invention.

[0008] In other words, the above-mentioned problems of the present invention can be solved by the following means.

[0009] One embodiment of the present invention that can solve the above problems is a dispersion for a silicon carbide sintered body, comprising: silicon carbide particles whose surface is charge-controlled to have a positive charge; a water-soluble first metal compound containing one or more first metals selected from the group consisting of rare earth elements, zirconium, and aluminum; a resin having hydroxyl groups; and water.

[0010] Figure 1 is a graph showing the change in viscosity over time of the silicon carbide sintered body dispersions prepared in the examples and comparative examples. Figure 2 is a graph showing the change in pH over time of the silicon carbide sintered body dispersions prepared in the examples and comparative examples.

[0011] The embodiments for carrying out the present invention will be described in detail below. The embodiments shown herein are illustrative examples for embodying the technical idea of ​​the present invention and do not limit the present invention. Therefore, all other implementable forms, methods of use, and operating techniques that can be conceived by those skilled in the art without departing from the gist of the present invention are included in the scope and gist of the present invention, as well as in the scope of the invention described in the claims and its equivalents. The embodiments described herein can be combined in any way to form other embodiments. In this specification, "X to Y" indicating a range means "X or more and Y or less," and "weight" and "mass," "weight%" and "mass%," and "parts by weight" and "parts by mass" are treated as synonyms. In this specification, "A and / or B" includes forms A or B, and forms A and B. In this specification, unless otherwise specified, operations and measurements of physical properties, etc., are performed under conditions of room temperature (20°C or more and 25°C or less) / relative humidity 40% RH or more and 50% RH or less.

[0012] <Dispersion for Silicon Carbide (SiC) Sintered Body> One embodiment of the present invention is a dispersion for a silicon carbide sintered body comprising: silicon carbide particles whose surface is positively charged; a water-soluble first metal compound containing one or more first metals selected from the group consisting of rare earth elements, zirconium, and aluminum; a resin having hydroxyl groups; and water. A dispersion for a silicon carbide sintered body having such a configuration (the dispersion for a silicon carbide sintered body according to this embodiment) has low viscosity and excellent dispersibility.

[0013] The inventors hypothesize the following mechanism by which the above problems are solved by the present invention.

[0014] The silicon carbide sintered body dispersion according to this embodiment comprises silicon carbide particles whose charge is controlled so that their surface is positively charged, a water-soluble first metal compound (hereinafter referred to as "first metal compound") containing one or more first metals selected from the group consisting of rare earth elements, zirconium, and aluminum, and a resin having hydroxyl groups. Conventionally, the effect of rare earth oxides, zirconium oxides, aluminum oxides, etc., on lowering the sintering temperature of silicon carbide has been known. The inventors have discovered that in the silicon carbide sintered body dispersion, the first metal compound has the effect of lowering the sintering temperature when the silicon carbide sintered body dispersion is sintered. This is thought to be because the atoms (or ions) of the first metal constituting the first metal compound become oxides during sintering. Here, in the silicon carbide sintered body dispersion, since the atoms (or ions) of the first metal have a positive charge, it is presumed that they exist at an appropriate distance from the silicon carbide particles, which also have a positive charge. Furthermore, in the dispersion for silicon carbide sintered bodies, the resin acts as a binder, but since the atoms (or ions) of the first metal are smaller in size compared to the resin, it is thought that they do not inhibit the binder's action. As a result, it is speculated that by including the first metal compound, the interactions between silicon carbide particles, between resins, and / or between silicon carbide particles and resins are reduced in the dispersion for silicon carbide sintered bodies, and the distances between these components are well maintained. This suppresses aggregation of components, reduces viscosity, and results in a low-viscosity dispersion with excellent dispersibility.

[0015] It should be noted that the above mechanism is based on speculation, and its accuracy does not affect the technical scope of the present invention.

[0016] [Silicon Carbide (SiC) Particles] The dispersion for silicon carbide sintered bodies according to this embodiment contains silicon carbide (SiC) particles. The silicon carbide (SiC) particles used in the dispersion for silicon carbide sintered bodies according to this embodiment are charge-controlled so that their surface has a positive charge. Hereinafter, silicon carbide particles whose surface has a positive charge will also be referred to as "positively charge-controlled silicon carbide particles." The silicon carbide (SiC) particles constitute at least a part of the silicon carbide sintered body formed using the dispersion for silicon carbide sintered bodies. Because silicon carbide (SiC) particles have high hardness, excellent high-temperature heat resistance, mechanical strength, impact resistance, wear resistance, oxidation resistance and corrosion resistance, and a small coefficient of thermal expansion, they can be used in a variety of applications, including polishing compositions and high-temperature structural members.

[0017] The silicon carbide particles are not particularly limited as long as their charge is controlled so that their surface has a positive charge. For example, when the silicon carbide particles are charged by being coated with a coating layer containing a charge-controlling component, it is preferable to maintain a dispersed state in the dispersion medium from the time the particles are generated until they are coated with the coating layer. Maintaining a dispersed state in the dispersion medium from the time the silicon carbide particles are generated until they are coated with the coating layer prevents aggregation of the silicon carbide particles due to drying. As a result, the high dispersibility of the silicon carbide particles at the time of generation is maintained at an even higher level even when the silicon carbide particles are coated with the coating layer, thus achieving extremely high dispersibility of the silicon carbide particles coated with the coating layer.

[0018] [Charge Control of Silicon Carbide Particles] In the silicon carbide sintering dispersion according to this embodiment, silicon carbide particles are used that have their charge controlled so that their surface is positively charged. There are no particular limitations on the charge control of silicon carbide particles, but one method is to adjust the surface charge by forming a layer of other components (charge control components) on the surface of the silicon carbide particles to make them coated silicon carbide particles. Hereinafter, coated silicon carbide particles that have a layer of charge control components formed on their surface to control their positive charge (i.e., coated silicon carbide particles that have a coating layer containing charge control components on their surface) will be referred to as "charge control component coated silicon carbide particles". Also, to distinguish them from "charge control component coated silicon carbide particles", silicon carbide particles before the coating layer by the charge control component is formed will be referred to as "silicon carbide particles before coating by charge control component".

[0019] Examples of charge-controlling components include oxides such as silicon dioxide, aluminum oxide, titanium oxide, and zirconium oxide, or hydroxides such as aluminum hydroxide, magnesium hydroxide, yttrium hydroxide, and titanium hydroxide. In the silicon carbide sintering dispersion according to this embodiment, it is preferable to use silicon carbide particles coated with a layer containing aluminum hydroxide (aluminum hydroxide-coated silicon carbide particles) because this improves the dispersibility and dispersion stability of the silicon carbide particles. In other words, in the silicon carbide sintering dispersion according to this embodiment, it is preferable that the silicon carbide particles are charge-controlled by the aluminum hydroxide coating.

[0020] In this specification, aluminum hydroxide-coated silicon carbide particles are coated particles having silicon carbide particles and a coating layer containing aluminum hydroxide that coats the silicon carbide particles. Here, aluminum hydroxide-coated silicon carbide particles are particles in which at least a portion of the silicon carbide particles is coated with a coating layer containing aluminum hydroxide.

[0021] It is preferable that the aluminum hydroxide-coated silicon carbide particles can maintain their shape as aluminum hydroxide-coated silicon carbide particles even when washed with a solvent (preferably water) or when dispersed in water.

[0022] Furthermore, in the silicon carbide sintering dispersion according to this embodiment, for example, by adsorbing a functional polymer having the function of adjusting the positive charge onto the surface of silicon carbide particles, a coating layer of the functional polymer can be formed, thereby adjusting the surface charge. In other words, a functional polymer can be used as a charge control component. Cationic polymers are examples of functional polymers. According to one embodiment, in the silicon carbide sintering dispersion according to this embodiment, the silicon carbide particles are charge-controlled by a cationic polymer.

[0023] The cationic polymer is not particularly limited as long as it is positively charged in a predetermined dispersion medium, and conventionally known polymers can be used. For example, poly(diallyldimethylammonium chloride) (PDDA), poly(methacryloyloxyethyltrimethylammonium chloride), poly(acrylamide-co-diallyldimethylammonium chloride), poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine), polyethyleneimine, ethoxylated polyethyleneimine, poly(amideamine), poly(methacryloyloxyethyldimethylammonium chloride), poly(vinylpyrrolidone), poly(vinylimidazole), poly(vinylpyridine), poly(vinylamine), polyallylamine and its quaternaries, polyallylamine hydrochloride (PAH), polylysine, polyacrylamide, polypyrrole, polyaniline, and copolymers containing two or more of these or variations in the type of salt can be used.

[0024] The average secondary particle diameter of positively charged silicon carbide particles (for example, charge-controlled component coated silicon carbide particles such as aluminum hydroxide coated silicon carbide particles) is preferably 2 μm or less, more preferably 1.5 μm or less, even more preferably 1.0 μm or less, particularly preferably 0.5 μm or less, and most preferably 0.4 μm or less. When the average secondary particle diameter of positively charged silicon carbide particles is within the above range, the dispersibility can be further improved when the positively charged silicon carbide particles are dispersed in water, which is the dispersion medium. Furthermore, the average secondary particle diameter of positively charged silicon carbide particles is not particularly limited, but is preferably 0.03 μm or more, more preferably greater than 0.03 μm, even more preferably 0.05 μm or more, even more preferably greater than 0.05 μm, particularly preferably 0.1 μm or more, and most preferably greater than 0.1 μm. When the average secondary particle diameter of positively charged silicon carbide particles is within the above range, sufficient dispersibility can be achieved when the positively charged silicon carbide particles are dispersed in water, which is the dispersion medium. Although it is difficult to directly measure the average thickness of the coating layer, it is considered to be very thin, and therefore corresponds to the preferred average secondary particle diameter of the silicon carbide particles. According to one embodiment, the average secondary particle diameter of positively charged silicon carbide particles (for example, silicon carbide particles coated with charge-controlled components such as aluminum hydroxide-coated silicon carbide particles) is 0.03 μm or more and 2 μm or less, 0.05 μm or more and 1.5 μm or less, greater than 0.05 μm and 1.0 μm or less, 0.1 μm or more and 0.5 μm or less, or greater than 0.1 μm and 0.4 μm or less. Here, the average secondary particle diameter of positively charged silicon carbide particles (e.g., charge-controlled silicon carbide particles coated with aluminum oxide or other charge-controlled components) can be measured using a MICROTRAC MT3300 laser diffraction / scattering particle size distribution analyzer in a dispersion medium, where positively charged silicon carbide particles (e.g., aluminum hydroxide-coated silicon carbide particles) are dispersed to an appropriate concentration for measurement. Details of the measurement method are described in the examples.

[0025] Whether using aluminum hydroxide-coated silicon carbide particles, which are exemplified as positively charged silicon carbide particles, or using silicon carbide particles whose positive charge is controlled by a configuration other than aluminum hydroxide-coated silicon carbide particles (for example, coated particles in which a layer of charge-controlling components other than aluminum hydroxide is formed on the surface of the silicon carbide particles), it is preferable that the average secondary particle diameter is within the above range.

[0026] Here, the average secondary particle diameter of the silicon carbide particles constituting the positively charged silicon carbide particles (i.e., silicon carbide particles before coating with the charge-controlling component) is preferably less than 2 μm, more preferably 1.5 μm or less, even more preferably 1.0 μm or less, particularly preferably 0.5 μm or less, and most preferably 0.4 μm or less. When the average secondary particle diameter of the silicon carbide particles is within the above range, a dispersion with higher dispersibility can be obtained. Furthermore, the average secondary particle diameter of the silicon carbide particles is preferably 0.03 μm or more, more preferably greater than 0.03 μm, even more preferably 0.05 μm or more, even more preferably greater than 0.05 μm, particularly preferably 0.1 μm or more, and most preferably greater than 0.1 μm. When the average secondary particle diameter of the silicon carbide particles is within the above range, charge control by coating with the coating layer can be performed with high efficiency. Here, the average secondary particle size of silicon carbide particles can be measured using the MT3300 laser diffraction / scattering particle size distribution analyzer manufactured by MICROTRAC. Details of the measurement method are described in the examples.

[0027] [Ratio of the average secondary particle diameter of positively charged silicon carbide particles to the average secondary particle diameter of silicon carbide particles] The ratio of the average secondary particle diameter of positively charged silicon carbide particles (for example, silicon carbide particles coated with a charge-controlling component, such as aluminum hydroxide-coated silicon carbide particles) to the average secondary particle diameter of silicon carbide particles (silicon carbide particles before coating with a charge-controlling component) (hereinafter also referred to as the ratio of the average secondary particle diameter to silicon carbide particles) is not particularly limited, but is preferably 10 or less. Within this range, positively charged silicon carbide particles are produced while maintaining the high dispersibility of silicon carbide particles to a high degree. As a result, when positively charged silicon carbide particles are dispersed in water, a dispersion with higher dispersibility is obtained. From a similar viewpoint, the ratio of the average secondary particle diameter to silicon carbide particles is more preferably 5 or less, even more preferably 3 or less, even more preferably 2 or less, even more preferably 1.6 or less, and particularly preferably 1.2 or less. Furthermore, the ratio of the average secondary particle diameter to the silicon carbide particles is not particularly limited, but it is preferably greater than 1. For example, aluminum hydroxide-coated silicon carbide particles are formed by coating the surface of the silicon carbide particles with a coating layer containing aluminum hydroxide. Thus, in the production of aluminum hydroxide-coated silicon carbide particles, this range applies if no further operations are performed to break down the secondary particles of the silicon carbide particles. However, operations to break down the secondary particles of the silicon carbide particles may be performed, and regardless of whether or not such operations are performed, the ratio of the average secondary particle diameter to the silicon carbide particles may be 1 or less (lower limit greater than 0). Here, the average secondary particle diameter of aluminum hydroxide-coated silicon carbide particles and silicon carbide particles can be determined by the method described above.

[0028] Whether using aluminum hydroxide-coated silicon carbide particles, which are exemplified as positively charged silicon carbide particles, or using silicon carbide particles whose positive charge is controlled by a configuration other than aluminum hydroxide-coated silicon carbide particles (for example, coated particles in which a layer of charge-controlling components other than aluminum hydroxide is formed on the surface of the silicon carbide particles), it is preferable that the ratio of the average secondary particle diameter to the silicon carbide particles is within the above range.

[0029] [Method for producing charge control component-coated silicon carbide particles] In one embodiment, the method for producing charge control component-coated silicon carbide particles comprises adding a charge control component or a precursor of the charge control component and an acid to a raw material dispersion containing silicon carbide particles (preferably adjusting the pH to a range of 9.0 or more and 12.0 or less), thereby forming coated silicon carbide particles having a coating layer containing the charge control component on the surface of the silicon carbide particles, and preparing an aqueous dispersion containing silicon carbide particles. This method has a step of preparing an aqueous dispersion containing silicon carbide particles.

[0030] As the silicon carbide particles as the raw material, commercially available products or processed products may be used.

[0031] Further, the silicon carbide particles as the raw material may be used alone or in combination of two or more.

[0032] When the charge control component is aluminum hydroxide, examples of the precursor (raw material) of the charge control component include sodium aluminate. When the charge control component is a functional polymer (preferably a cationic polymer), the cationic polymer is used as it is.

[0033] As described above, in the dispersion for silicon carbide sintered body according to this embodiment, since the dispersibility and dispersion stability of silicon carbide particles are improved, it is preferable to use silicon carbide particles coated with a layer containing aluminum hydroxide (aluminum hydroxide-coated silicon carbide particles). Therefore, the method for producing aluminum hydroxide-coated silicon carbide particles will be described below.

[0034] The method for producing aluminum hydroxide-coated silicon carbide particles is not particularly limited. For example, a raw material dispersion (1) containing silicon carbide particles, an alkali, and water and having a pH of 9.0 or more and 12.0 or less, and a raw material solution (2) containing sodium aluminate (precursor of the charge control component) and water are each prepared in step (A). In step (B), the raw material solution (2) and an acid are added to the raw material dispersion (1) to maintain the pH in the range of 9.0 or more and 12.0 or less, and coated particles having a coating layer containing aluminum hydroxide (charge control component) on the surface of the silicon carbide particles are formed. A method having these steps is used.

[0035] Here, the aluminum hydroxide-coated silicon carbide particles to be produced may be produced in a state of being dispersed in a dispersion medium, or may be produced through a step of removing the dispersion medium thereafter. The aluminum hydroxide-coated silicon carbide particles produced in a state of being dispersed in water (dispersion medium) can be used as an aqueous dispersion containing silicon carbide particles in the mixing step described later.

[0036] (Step (A)) Step (A) is a step of preparing a raw material dispersion (1) containing silicon carbide particles, an alkali, and water and having a pH of 9.0 or more and 12.0 or less, and a raw material solution (2) containing sodium aluminate and water, respectively.

[0037] The method for preparing the raw material dispersion (1) is not particularly limited. For example, a method of adding an alkali to an aqueous dispersion of silicon carbide particles (a dispersion containing water as a dispersion medium, preferably an aqueous dispersion) can be mentioned.

[0038] The aqueous dispersion of silicon carbide particles may be a commercially available product or a processed product. When synthesizing (preparing) an aqueous dispersion of silicon carbide particles, there is no particular limitation, and known apparatuses and known methods can be used.

[0039] The content of silicon carbide particles in the aqueous dispersion of silicon carbide particles is not particularly limited. From the viewpoint of productivity, it is preferably 8% by mass or more, more preferably 10% by mass or more, based on the total mass of the aqueous dispersion. From the viewpoint of dispersibility, it is preferably 50% by mass or less, more preferably 30% by mass or less, based on the total mass of the aqueous dispersion.

[0040] In the method for preparing the raw material dispersion (1), the amount of the alkali used is not particularly limited, and the amount used may be adjusted so that the pH of the dispersion becomes a predetermined value of 9.0 or more and 12.0 or less.

[0041] Examples of alkalis that can be used include ammonia, potassium hydroxide, sodium hydroxide, ammonium bicarbonate, ammonium carbonate, potassium bicarbonate, potassium carbonate, sodium bicarbonate, sodium carbonate, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N-(β-aminoethyl)ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, anhydrous piperazine, piperazine hexahydrate, 1-(2-aminoethyl)piperazine, N-methylpiperazine, guanidine, imidazole, triazole, etc. These alkalis can be used individually or in combination of two or more.

[0042] Here, the silicon carbide particles are not particularly limited, but it is preferable to maintain the silicon carbide particles dispersed in the dispersion medium from their generation until the raw material dispersion (1) is prepared in step (A). Furthermore, it is even more preferable to maintain the silicon carbide particles dispersed in the dispersion medium from their generation until they are coated with a coating layer in step (B), which will be described later. By maintaining the silicon carbide particles dispersed in the dispersion from their generation until they are coated with a coating layer, the silicon carbide particles can avoid aggregation due to drying. As a result, the high level of dispersibility of the silicon carbide particles at the time of generation is maintained even in the state of aluminum hydroxide coated silicon carbide particles. Therefore, when the manufactured aluminum hydroxide coated silicon carbide particles are dispersed in water, a dispersion with extremely high dispersibility can be obtained.

[0043] The raw material dispersion (1) preferably contains water as a dispersion medium. The water is preferably water that contains as few impurities as possible. Here, the purity of the water can be increased by operations such as removing impurity ions using ion exchange resin, removing foreign matter by filtration, or distillation. Specifically, it is preferable to use, for example, deionized water (ion-exchanged water), pure water, ultrapure water, or distilled water.

[0044] The procedure and method for dispersing silicon carbide particles in water, and the procedure and method for adding alkali, are not particularly limited, and known procedures and methods can be used.

[0045] The raw material dispersion (1) may contain a dispersion medium other than water. The dispersion medium other than water may be a mixed solvent of water and an organic solvent for the dispersion or dissolution of each component. In this case, preferred organic solvents to be used are, for example, acetone, acetonitrile, ethanol, methanol, isopropanol, glycerin, ethylene glycol, propylene glycol, etc., which are organic solvents that are miscible with water. Alternatively, the organic solvent may be used without mixing it with water to disperse or dissolve each component, and then mixed with water. These organic solvents can be used individually or in combination of two or more.

[0046] Here, the water content in the raw material dispersion (1) is preferably 50% by mass or more, and more preferably 70% by mass or more, relative to the total mass of the raw material dispersion medium (1), from the viewpoint of promoting better coating of silicon carbide particles with aluminum hydroxide.

[0047] The raw material dispersion (1) obtained in this process preferably has a pH of 9.0 or higher and 12.0 or lower. If the pH is 9.0 or higher, localized aggregation at the acid drop site is less likely to occur. On the other hand, if the pH is 12.0 or lower, the generation of individual aluminum hydroxide particles is suppressed. From the viewpoint of improving the rate of coating layer formation and improving productivity, it is more preferable that the pH is greater than 9.0 and 12.0 or lower.

[0048] The method for preparing the raw material solution (2) is not particularly limited, but examples include adding sodium aluminate to water. The sodium aluminate content in the raw material solution (2) is not particularly limited, but it is preferably 10% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 40% by mass or less, based on the total mass of the raw material solution (2).

[0049] (Step (B)) Step (B) is a step in which the raw material solution (2) and an acid are added to the raw material dispersion (1) prepared in step (A) to maintain the pH in the range of 9.0 to 12.0, thereby forming coated particles having a coating layer containing aluminum hydroxide on the surface of the silicon carbide particles. In step (B), aluminum hydroxide coated silicon carbide particles are produced.

[0050] The method of adding the raw material solution (2) and the acid to the raw material dispersion (1) is not particularly limited as long as the pH can be maintained between 9.0 and 12.0 (i.e., the concentration of aluminate ions does not become excessive). For example, this could involve adding the raw material solution (2) and the acid simultaneously, or adding the raw material solution (2) and the acid little by little alternately.

[0051] The amount of raw material solution (2) added is not particularly limited, but it is preferable to add raw material solution (2) so that sodium aluminate is 1 part by mass or more per 100 parts by mass of silicon carbide particles, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more. When the amount of raw material solution (2) added is within this range, the silicon carbide particles are converted to aluminum hydroxide (Al(OH)) ３ This is because the material can be sufficiently coated with the aluminum-containing compound, allowing it to fully exhibit its functions. Furthermore, while there are no particular restrictions on the amount of raw material solution (2) added, it is preferable to add the raw material solution (2) so that the amount of sodium aluminate is 800 parts by mass or less per 100 parts by mass of silicon carbide particles, more preferably 400 parts by mass or less, and even more preferably 100 parts by mass or less. This is because, once the coating has progressed to a certain extent, the effect obtained by the coating becomes constant, and by keeping the amount of raw material solution (2) added below a predetermined amount, economic efficiency and production efficiency are improved. In one embodiment of the present invention, the amount of sodium aluminate used is 1 part by mass or more and 100 parts by mass or less per 100 parts by mass of silicon carbide particles.

[0052] The acid is not particularly limited, but examples include inorganic acids such as nitric acid, sulfuric acid, phosphoric acid, and hydrochloric acid (especially strong inorganic acids such as nitric acid, sulfuric acid, and hydrochloric acid), and organic acids such as acetic acid, citric acid, lactic acid, oxalic acid, and phthalic acid. Among these, strong inorganic acids are preferred, and nitric acid, sulfuric acid, or hydrochloric acid are more preferred, from the viewpoint that the objective can be achieved with a smaller amount added and that high-purity products with a low possibility of contamination by other elements are readily available.

[0053] Here, the acid is preferably added in the form of an aqueous solution, and the concentration of the acid in the aqueous solution is not particularly limited, but is preferably 1.0% by mass or more. This is because when the acid concentration is in this range, the amount that can be added is small, and productivity is high. From a similar viewpoint, the concentration of the acid in the aqueous solution is more preferably 1.5% by mass or more, and even more preferably 2.0% by mass or more. Furthermore, although the concentration of the acid in the aqueous solution is not particularly limited, it is preferably 30% by mass or less. This is because when the acid concentration in the aqueous solution is in this range, the corrosiveness is low and the load on the equipment is reduced. From a similar viewpoint, the concentration of the acid in the aqueous solution is more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0054] Furthermore, the rate at which the raw material solution (2) and the acid are added (addition rate) is not particularly limited, and should be within the range of pH 9.0 to 12.0, and should be adjusted as appropriate to facilitate the maintenance of the pH thereafter.

[0055] Furthermore, this process includes a step of forming coated particles having a coating layer containing aluminum hydroxide on the surface of silicon carbide particles by setting the pH in the range of 9.0 to 12.0.

[0056] In this stage, it is preferable that the maintenance time for the pH range of 9.0 to 12.0 is 1 minute or more. This is because a maintenance time within this range allows for more sufficient coating of silicon carbide particles with aluminum hydroxide, thereby improving the functionality derived from aluminum-containing compounds in the aluminum hydroxide-coated silicon carbide particles. Furthermore, in the production of dispersions for silicon carbide sintered bodies, when aluminum hydroxide-coated silicon carbide particles and boron nitride particles are dispersed in water, aggregation in the dispersion becomes less likely, making it possible to obtain a dispersion with high dispersibility. From a similar viewpoint, the maintenance time is preferably 30 minutes or more, more preferably 50 minutes or more, and even more preferably 60 minutes or more. Also, it is preferable that the maintenance time in this stage is 200 minutes or less. This is because once the coating has progressed to a certain extent, the effect obtained by the coating becomes constant, and a maintenance time within this range further improves economic efficiency and production efficiency. From a similar viewpoint, the maintenance time is preferably 150 minutes or less, and more preferably 120 minutes or less.

[0057] The pH at this stage is preferably between 9.0 and 12.0. If the pH is 9.0 or higher, aggregation of silicon carbide particles is less likely to occur, making it easier to maintain uniform dispersion. If the pH is 12.0 or lower, it is preferable because it can prevent the formation of a large amount of aluminum hydroxide particles.

[0058] By going through step (B), a dispersion containing aluminum hydroxide-coated silicon carbide particles and a dispersion medium can be obtained. That is, aluminum hydroxide-coated silicon carbide particles can be produced in a dispersed state in the dispersion medium.

[0059] (Other steps) The method for producing aluminum hydroxide-coated silicon carbide particles may further include steps other than steps (A) and (B), and steps (A) and (B) may further include steps relating to other operations.

[0060] While it may be difficult to directly measure the thickness of the coating layer due to changes in the particle's state caused by the coating, generally, the pH of the isoelectric point of the zeta potential tends to increase as the thickness of the coating layer increases. The fact that the coating layer is within a desirable thickness range can be determined by the fact that it falls within the pH range of the desirable isoelectric point for aluminum hydroxide-coated silicon carbide particles.

[0061] Furthermore, the presence of aluminum hydroxide in the coating layer can be confirmed by observing aluminum hydroxide-coated silicon carbide particles using SEM (Scanning Electron Microscope)-EDX (Energy Dispersive X-ray Spectroscopy) and EELS (Electron Energy Loss Spectroscopy).

[0062] [Isoelectric Point of Positively Charged Silicon Carbide Particles] The pH of the isoelectric point of positively charged silicon carbide particles is not particularly limited, but is preferably 4.5 or higher. When the pH of the isoelectric point of positively charged silicon carbide particles is within this range, aggregation in the dispersion medium is less likely to occur, and good dispersibility is maintained, even when positively charged silicon carbide particles and boron nitride particles (described later) are used together in a dispersion containing a dispersion medium. As a result, when positively charged silicon carbide particles and other particles are dispersed in a medium, a dispersion with higher dispersibility can be obtained. From a similar viewpoint, the pH of the isoelectric point of positively charged silicon carbide particles is more preferably 5 or higher, even more preferably 5.5 or higher, and particularly preferably 6 or higher. Also, although the pH of the isoelectric point of positively charged silicon carbide particles is not particularly limited, from a similar viewpoint, it is preferably 9 or lower. Based on these findings, in a preferred embodiment of the silicon carbide sintering dispersion according to this model, the pH of the isoelectric point of the positively charged silicon carbide particles is, for example, 4.5 or higher and 9 or lower.

[0063] The pH at the isoelectric point can be calculated by preparing zeta potential measurement solutions with pH values ​​in increments of 1.0, for example, in the range of pH 3.0 to 10.0 in increments of 1.0, measuring the data potential, and then using the pH values ​​before and after the change in the sign of the zeta potential, along with the zeta potential at those pH values, using the following formula.

[0064]

[0065] Here, pH can be measured using a pH meter (model number: F-71) manufactured by Horiba, Ltd. Zeta potential can be measured using a zeta potential measuring device (product name "Zetasizer nano ZSP") manufactured by Malvern Instruments. Details of the measurement methods are described in the examples.

[0066] [Zeta potential of positively charged silicon carbide particles in dispersion for silicon carbide sintered bodies] The zeta potential of positively charged silicon carbide particles in dispersion for silicon carbide sintered bodies is not particularly limited as long as they are positively charged, but from the viewpoint of improving dispersibility, it is preferably +5 mV or higher, and more preferably +10 mV or higher. The upper limit of the zeta potential of positively charged silicon carbide particles in dispersion for silicon carbide sintered bodies is not particularly limited, but is substantially +50 mV or lower, for example, +45 mV or lower.

[0067] [Content of silicon carbide particles in the dispersion for silicon carbide sintered body] The lower limit of the content of silicon carbide particles (i.e., silicon carbide particles before coating with charge control components) in the dispersion for silicon carbide sintered body according to this embodiment is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and most preferably 5% by mass or more, based on the total mass of the dispersion for silicon carbide sintered body. The upper limit of the content of silicon carbide particles (i.e., silicon carbide particles before coating with charge control components) in the dispersion for silicon carbide sintered body is preferably 55% by mass or less, more preferably 45% by mass or less, even more preferably 35% by mass or less, and most preferably 25% by mass or less, based on the total mass of the dispersion for silicon carbide sintered body. Within these ranges, the dispersion stability and handling properties of the dispersion are good. Furthermore, a high-quality silicon carbide sintered body can be obtained.

[0068] [Content of positively charged silicon carbide particles in dispersion for silicon carbide sintered body] The lower limit of the content of positively charged silicon carbide particles (e.g., charge-controlled component coated silicon carbide particles) in the dispersion for silicon carbide sintered body according to this embodiment is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and most preferably 5% by mass or more, based on the total mass of the dispersion for silicon carbide sintered body. The upper limit of the content of positively charged silicon carbide particles (e.g., charge-controlled component coated silicon carbide particles) in the dispersion for silicon carbide sintered body is preferably 55% by mass or less, more preferably 45% by mass or less, even more preferably 35% by mass or less, and most preferably 25% by mass or less, based on the total mass of the dispersion for silicon carbide sintered body. Within this range, the dispersion stability and handling properties of the dispersion are good. Furthermore, a high-quality silicon carbide sintered body can be obtained. Furthermore, the content of positively charged silicon carbide particles refers to, for example, the content of charge-controlled component-coated silicon carbide particles. In the case of aluminum hydroxide-coated silicon carbide particles, the coating layer is aluminum hydroxide (Al) ２ O ３This is the sum of the amount calculated as ( ) and the amount of silicon carbide particles.

[0069] [Content of charge control component in dispersion for silicon carbide sintered body] In the dispersion for silicon carbide sintered body according to this embodiment, the lower limit of the content of the charge control component included as a coating layer to control the positive charge of silicon carbide particles is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and most preferably 0.5% by mass or more, based on the total mass of the dispersion for silicon carbide sintered body. Furthermore, the upper limit of the content of the charge control component included as a coating layer to control the positive charge of silicon carbide particles in the dispersion for silicon carbide sintered body is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and most preferably 5% by mass or less, based on the total mass of the dispersion for silicon carbide sintered body. If the content of the charge control component is within the above range, the dispersion stability and handling properties of the dispersion will be good. When the charge control component is an oxide such as silicon dioxide, aluminum oxide, titanium oxide, or zirconium oxide, or a hydroxide such as aluminum hydroxide, magnesium hydroxide, yttrium hydroxide, or titanium hydroxide, the content of the charge control component is calculated in terms of oxide. For example, when the charge control component is aluminum hydroxide, the content of the above charge control component is calculated as aluminum oxide (Al ２ O ３ It is calculated as follows:

[0070] [Mass ratio of silicon carbide particles to charge control component in dispersion for silicon carbide sintered body] In the dispersion for silicon carbide sintered body according to this embodiment, the mass ratio of silicon carbide particles (i.e., silicon carbide particles before coating with the charge control component) to the charge control component included as a coating layer to control the positive charge of the silicon carbide particles (i.e., the mass ratio of silicon carbide to the charge control component) is preferably 99:1 to 50:50, more preferably 98.5:1.5 to 60:40, even more preferably 98:2 to 70:30, particularly preferably 97.5:2.5 to 80:20, and most preferably 97:3 to 85:15. When the mass ratio of silicon carbide to the charge control component is within the above range, the dispersion stability of the dispersion is further improved. When the charge control component is an oxide such as silicon dioxide, aluminum oxide, titanium oxide, or zirconium oxide, or a hydroxide such as aluminum hydroxide, magnesium hydroxide, yttrium hydroxide, or titanium hydroxide, the content of the charge control component is calculated in terms of oxide. For example, when the charge control component is aluminum hydroxide, the content of the above charge control component is calculated as aluminum oxide (Al ２ O ３ It is calculated as follows:

[0071] [First Metal Compound] The dispersion for silicon carbide sintered body according to this embodiment contains a water-soluble first metal compound containing one or more first metals selected from the group consisting of rare earth elements, zirconium, and aluminum. Here, since the first metal compound contains rare earth elements, zirconium, and / or aluminum, it is expected to have the effect of lowering the sintering temperature of the dispersion for silicon carbide sintered body. Furthermore, the pH of the dispersion for silicon carbide sintered body can be adjusted by the first metal compound; for example, the pH of the dispersion for silicon carbide sintered body can be lowered by containing the first metal compound.

[0072] Here, the first metal compound is a water-soluble metal compound, and in this specification, "water-soluble" means a substance that dissolves in water with a pH of 2.0 to 7.0 at room temperature (25°C) at a concentration of 1% by mass or more. The first metal compound (water-soluble metal compound) may be heated to accelerate dissolution, or it may be left to stand or stirred at room temperature for 48 hours to allow time for dissolution. The water used to dissolve the first metal compound (water-soluble metal compound) can be prepared by appropriately mixing an acidic compound such as hydrochloric acid, formic acid, acetic acid, or citric acid with water as needed, and adjusting the pH to 2.0 to 7.0 at room temperature (25°C).

[0073] The first metal in the first metal compound is selected from the group consisting of rare earth elements, zirconium, and aluminum. Examples of rare earth elements include scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Among these, from the viewpoint of lowering the sintering temperature, yttrium, aluminum, lanthanum, cerium, gadolinium, erbium, and ytterbium are preferred, yttrium, aluminum, ytterbium, gadolinium, and erbium are more preferred, and yttrium and aluminum are even more preferred. According to one embodiment, the first metal contained in the first metal compound is selected from the group consisting of yttrium, zirconium, and aluminum.

[0074] The type of the first metal compound is not particularly limited, but examples include salts of inorganic acids such as carbonic acid, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, and perchloric acid; fluorides, chlorides, bromides, iodides, hydroxides, sulfides; formic acid, acetic acid, trifluoroacetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, oleic acid, linoleic acid, linolenic acid, naphthenic acid, and Examples include carboxylic acids such as lacidonic acid, docosahexaenoic acid, eicosapentaenoic acid, lactic acid, malic acid, citric acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, gallic acid, melitic acid, cinnamic acid, oxalic acid, tartaric acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, maleic acid, aconitic acid, amino acids, anthranilic acid, and nitrocarboxylic acid; and salts of organic acids such as methanesulfonic acid and trifluoromethanesulfonic acid. The first metal compound may be in the form of an anhydride or a hydrate. Among these, it is preferably a salt of an inorganic acid, and more preferably a nitrate.

[0075] More specific examples of the first metal compound include, for example, metal compounds containing yttrium such as yttrium chloride, yttrium nitrate, yttrium acetate, yttrium bromide, yttrium perchlorate, yttrium trifluoromethanesulfonate, yttrium sulfide, yttrium iodide, yttrium oxalate, yttrium phosphate, yttrium trifluoroacetate, etc., and metal compounds containing aluminum such as aluminum chloride, aluminum nitrate, aluminum sulfate, aluminum lactate; or hydrates thereof. Among these, yttrium chloride or its hydrate, yttrium nitrate or its hydrate, yttrium acetate or its hydrate, yttrium sulfide, aluminum chloride or its hydrate, aluminum nitrate or its hydrate, aluminum sulfate or its hydrate, aluminum lactate, etc. are preferred, and yttrium chloride or its hydrate (for example, yttrium chloride hexahydrate), yttrium nitrate or its hydrate, aluminum nitrate or its hydrate (for example, aluminum nitrate hexahydrate), yttrium acetate or its hydrate (for example, yttrium acetate tetrahydrate) are more preferred, and yttrium nitrate or its hydrate (for example, yttrium nitrate hexahydrate) is even more preferred.

[0076] Here, when the first metal contained in the first metal compound is yttrium, the silicon carbide sintered body obtained by sintering the dispersion for the silicon carbide sintered body contains yttria (Y ２ O ３, yttrium oxide is included. For example, even if yttria is included in the dispersion for silicon carbide sintered bodies instead of the first metal compound, yttria will be included in the silicon carbide sintered body when the dispersion for silicon carbide sintered bodies is sintered. The inclusion of yttria makes it possible to lower the sintering temperature when sintering the dispersion for silicon carbide sintered bodies. As shown in the Examples section below, it was found that when the dispersion for silicon carbide sintered bodies contains yttria, the viscosity increases over time (Comparative Example 1). On the other hand, when water-soluble yttrium nitrate is used as the yttria source (yttrium source), it has been shown that the viscosity is low and there is little or no increase in viscosity over time. Therefore, according to the dispersion for silicon carbide sintered bodies of this embodiment, it is possible to lower the viscosity of the dispersion for silicon carbide sintered bodies by using the first metal compound, and furthermore, the stability of viscosity over time can also be improved. The mechanism by which these effects are achieved is not fully understood, but it is speculated to be as follows. For example, when oxides such as yttria are added, it is thought that the oxides decompose and undergo chemical changes due to hydration, and we believe that these chemical changes of the oxides may be reducing the time-dependent stability of the silicon carbide sintered body dispersion. By adding the first metal compound as an oxide source, it can be added to the silicon carbide sintered body dispersion in an aqueous solution state. As a result, we believe that time-dependent chemical changes are less likely to occur in the silicon carbide sintered body dispersion, and that the time-dependent stability of the viscosity of the silicon carbide sintered body dispersion can be improved.

[0077] The content of the first metal compound in the dispersion for silicon carbide sintered bodies (excluding the water of hydration in the case of a hydrate) is not particularly limited, but is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, particularly preferably 0.5% by mass or more, and most preferably 1.0% by mass or more, based on the total mass of the dispersion for silicon carbide sintered bodies. When the content of the first metal compound is within the above range, the effect of lowering the sintering temperature in the dispersion for silicon carbide sintered bodies is further improved. Furthermore, the content of the first metal compound in the dispersion for silicon carbide sintered bodies (excluding the water of hydration in the case of a hydrate) is not particularly limited, but is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, particularly preferably 5% by mass or less, and most preferably 3% by mass or less, based on the total mass of the dispersion for silicon carbide sintered bodies. When the content of the first metal compound is within the above range, the effect of lowering the sintering temperature is sufficiently exerted, and therefore, by limiting the amount of the first metal compound added to a predetermined amount or less, economic efficiency and production efficiency are further improved. Note that if the dispersion for silicon carbide sintered bodies contains two or more types of the first metal compound, the content of the first metal compound refers to the total amount of these compounds.

[0078] The content of the first metal (in terms of oxide) in the dispersion for silicon carbide sintered bodies is not particularly limited, but is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.15% by mass or more, particularly preferably 0.2% by mass or more, and most preferably 0.3% by mass or more, relative to the total mass of the dispersion for silicon carbide sintered bodies. When the content of the first metal is within the above range, the effect of lowering the sintering temperature in the dispersion for silicon carbide sintered bodies is further improved. Furthermore, although the content of the first metal (in terms of oxide) in the dispersion for silicon carbide sintered bodies is not particularly limited, is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, particularly preferably 5% by mass or less, and most preferably 3% by mass or less, relative to the total mass of the dispersion for silicon carbide sintered bodies. When the content of the first metal is within the above range, the effect of lowering the sintering temperature is sufficiently exhibited, and by limiting the amount of the first metal added to a predetermined amount or less, economic efficiency and production efficiency are further improved. According to one embodiment, the content of the first metal (in terms of oxides) in the dispersion for silicon carbide sintered body is 0.05% to 20% by mass, 0.1% to 10% by mass, 0.1% to 5% by mass, 0.1% to 3% by mass, 0.1% to 1% by mass, 0.1% to 0.8% by mass, 0.15% to 8% by mass, 0.2% to 5% by mass, 0.3% to 3% by mass, 0.3% to 2% by mass, 0.3% to 1% by mass, or 0.3% to 0.8% by mass, relative to the total mass of the dispersion for silicon carbide sintered body.

[0079] [Mass ratio of silicon carbide particles to the first metal in the dispersion for silicon carbide sintered body] In the dispersion for silicon carbide sintered body according to this embodiment, the mass ratio of silicon carbide particles (i.e., silicon carbide particles before coating with charge control components) to the first metal (i.e., the mass ratio of silicon carbide to the first metal) is preferably 99:1 to 50:50, more preferably 98.5:1.5 to 60:40, even more preferably 98:2 to 70:30, particularly preferably 97.5:2.5 to 80:20, and most preferably 97:3 to 85:15. When the mass ratio of silicon carbide to the first metal is within the above range, the dispersion stability of the dispersion is further improved. The content of the first metal is calculated in terms of oxide. As an example, when the first metal is yttrium nitrate, the content of the first metal is yttria (yttrium oxide; Y ２ O ３ It is calculated as follows:

[0080] The first metal compound is preferably added to the silicon carbide sintered body dispersion in a dissolved state in water.

[0081] [Second Metal Compound] The dispersion for silicon carbide sintered body according to this embodiment may also contain a second metal compound other than the first metal compound, which contains a second metal. In the second metal compound, it is preferable that the oxide of the second metal (oxide of the second metal) has a eutectic composition with the oxide of the first metal. In this case, the sintering temperature of silicon carbide can be lowered more effectively, and the first metal compound and the second metal compound (i.e., the oxide of the first metal and the oxide of the second metal) exert a significant effect in lowering the sintering temperature of silicon carbide.

[0082] Therefore, according to one embodiment of the present invention, a dispersion for a silicon carbide sintered body comprises charge-controlled silicon carbide particles whose surface has a positive charge, a water-soluble first metal compound containing one or more first metals selected from the group consisting of rare earth elements, zirconium, and aluminum, a second metal compound containing a second metal different from the first metal, a resin having hydroxyl groups, and water, wherein the oxide of the first metal has a eutectic composition with the oxide of the second metal.

[0083] The type of second metal in the second metal compound can be any metal whose oxide (oxide of the second metal) has a eutectic composition with the oxide of the first metal, and can be selected from the group consisting of zirconium, aluminum, titanium, magnesium, and silicon, for example. Among these, from the viewpoint of lowering the sintering temperature, the second metal is preferably zirconium, aluminum, or silicon, with zirconium and aluminum being more preferred.

[0084] According to one embodiment, the first metal in the first metal compound is selected from the group consisting of yttrium, lanthanum, cerium, gadolinium, erbium, and ytterbium, and the second metal in the second metal compound is selected from the group consisting of zirconium, aluminum, titanium, magnesium, and silicon.

[0085] Here, the second metal compound may coat the silicon carbide particles. That is, the silicon carbide particles may be controlled to have a positive charge by being coated with the second metal compound. In other words, the charge control component described above may be the second metal compound, in which case the silicon carbide has a coating layer containing the second metal compound. Examples of the second metal compound forming the coating layer include oxides such as silicon dioxide, aluminum oxide, titanium oxide, and zirconium oxide, or hydroxides such as aluminum hydroxide, magnesium hydroxide, yttrium hydroxide, and titanium hydroxide. For example, the second metal compound may be aluminum hydroxide (in this case, the second metal is aluminum).

[0086] Therefore, according to one embodiment of the present invention, a dispersion for a silicon carbide sintered body comprises silicon carbide particles, a water-soluble first metal compound containing one or more first metals selected from the group consisting of rare earth elements, zirconium, and aluminum, a second metal compound containing a second metal different from the first metal, a resin having hydroxyl groups, and water, wherein the oxide of the second metal has a eutectic composition with the oxide of the first metal.

[0087] The content of the second metal (in oxide terms) in the dispersion for silicon carbide sintered body is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and most preferably 0.5% by mass or more, based on the total mass of the dispersion for silicon carbide sintered body. Furthermore, the content of the second metal (in oxide terms) in the dispersion for silicon carbide sintered body is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and most preferably 5% by mass or less, based on the total mass of the dispersion for silicon carbide sintered body. According to one embodiment, the content of the second metal (in terms of oxide) in the dispersion for silicon carbide sintered body is 0.05% to 15% by mass, 0.1% to 10% by mass, 0.1% to 5% by mass, 0.1% to 3% by mass, 0.1% to 2% by mass, 0.1% to 1% by mass, 0.2% to 8% by mass, 0.2% to 5% by mass, 0.2% to 3% by mass, 0.5% to 5% by mass, 0.5% to 3% by mass, 0.5% to 2% by mass, or 0.5% to 1% by mass, based on the total mass of the dispersion for silicon carbide sintered body. If the content of the second metal is within the above range, the dispersion stability and handling properties of the dispersion will be good. As an example of the second metal, aluminum can be used, and the above content is aluminum oxide (Al ２ O ３ It is calculated as follows:

[0088] The mass ratio of the oxide of the first metal to the oxide of the second metal is preferably 1:99 to 99:1, more preferably 10:90 to 90:10, even more preferably 15:85 to 70:30, particularly preferably 20:80 to 60:40, and most preferably 25:75 to 50:50, in terms of oxides. When the mass ratio of the oxide of the first metal to the oxide of the second metal is within the above range, the effect of lowering the sintering temperature in the dispersion for silicon carbide sintered bodies is further improved. As an example, the oxide of the first metal is yttria (yttrium oxide; Y ２ O ３ ) and the second metal oxide is alumina (aluminum oxide; Al２ O ３ )

[0089] [Mass ratio of silicon carbide particles to the second metal compound in the dispersion for silicon carbide sintered body] In the dispersion for silicon carbide sintered body according to this embodiment, the mass ratio of silicon carbide particles (i.e., silicon carbide particles before coating with the second metal compound) to the second metal compound included as a coating layer to control the positive charge of the silicon carbide particles (i.e., the mass ratio of silicon carbide to the second metal compound) is preferably 99:1 to 50:50, more preferably 98.5:1.5 to 60:40, even more preferably 98:2 to 70:30, particularly preferably 97.5:2.5 to 80:20, and most preferably 97:3 to 85:15. When the mass ratio of silicon carbide to the second metal compound is within the above range, the dispersion stability of the dispersion is further improved. When the second metal compound is an oxide such as silicon dioxide, aluminum oxide, titanium oxide, or zirconium oxide, or a hydroxide such as aluminum hydroxide, magnesium hydroxide, yttrium hydroxide, or titanium hydroxide, the content of the second metal compound shall be calculated in terms of oxide. For example, when the second metal compound is aluminum hydroxide, the content of the second metal compound shall be calculated as aluminum oxide (Al ２ O ３ It is calculated as follows:

[0090] [Mass ratio of the first metal and the second metal to silicon carbide particles in the dispersion for silicon carbide sintered bodies] In the dispersion for silicon carbide sintered bodies according to this embodiment, the mass ratio of silicon carbide particles (i.e., silicon carbide particles before coating with the charge control component (second metal compound)) to the first metal and the second metal (i.e., the mass ratio of the first metal and the second metal to silicon carbide) is preferably 99:1 to 10:90, more preferably 98:2 to 20:80, even more preferably 97:3 to 50:50, particularly preferably 96:4 to 60:40, and most preferably 95:5 to 70:30. When the mass ratio of the first metal and the second metal to silicon carbide is within the above range, the dispersion stability of the dispersion is further improved. The content of the first metal and the second metal is calculated in terms of oxides.

[0091] The second metal compound can be used, for example, as a charge-controlling component that coats silicon carbide particles. Specifically, as in the method for producing charge-controlling component-coated silicon carbide particles described above, a dispersion for silicon carbide sintered bodies containing the second metal compound can be obtained by using a precursor of the charge-controlling component (second metal compound).

[0092] [Hydroxyl Group-Containing Resin] The dispersion for silicon carbide sintered body according to this embodiment includes a resin containing hydroxyl groups. The resin constitutes a binder (binder resin) for the green sheet formed using the dispersion for silicon carbide sintered body, thereby improving the moldability of the green sheet. The resin also constitutes a part of the prepreg material formed using the dispersion for silicon carbide sintered body, thereby improving the handling properties of the prepreg material. In the dispersion for silicon carbide sintered body according to this embodiment, excellent dispersibility can be obtained by using a resin containing hydroxyl groups.

[0093] Preferred examples of resins containing hydroxyl groups include, but are not limited to, polyvinyl alcohol (PVA) resin; hydroxyl group-containing polyvinyl acetal resins such as hydroxyl group-containing polyvinyl butyral (PVB), hydroxyl group-containing polyvinyl propylal, and hydroxyl group-containing polyvinyl formal; modified polyvinyl alcohol (modified PVA) resin, hydroxyl group-containing glyoxal resin, hydroxyl group-containing acrylic resin, phenol resin, hydroxyl group-containing polyvinylpyrrolidone (PVP), hydroxyl group-containing polyester resin, hydroxyl group-containing silicone resin, and hydroxyl group-containing polycarboxylic acid. According to one embodiment, the resin containing hydroxyl groups includes at least one resin selected from the group consisting of polyvinyl alcohol resin, hydroxyl group-containing polyvinyl acetal resin, hydroxyl group-containing glyoxal resin, hydroxyl group-containing acrylic resin, phenol resin, hydroxyl group-containing polyvinylpyrrolidone, hydroxyl group-containing polyester resin, hydroxyl group-containing silicone resin, and hydroxyl group-containing polycarboxylic acid. Among these, polyvinyl alcohol resin and hydroxyl group-containing polyvinyl acetal resin are more preferred from the viewpoint of ease of handling and ease of viscosity adjustment, and hydroxyl group-containing polyvinyl acetal resin is even more preferred.

[0094] The weight-average molecular weight of the resin having hydroxyl groups is not particularly limited, but is preferably 1,000 or more, more preferably 2,000 or more, and even more preferably 5,000 or more. Within these ranges, a dispersion with superior moldability for green sheets, prepreg materials, etc., can be obtained. The weight-average molecular weight of the resin having hydroxyl groups is not particularly limited, but is preferably 500,000 or less, more preferably 100,000 or less, and even more preferably 50,000 or less. Within these ranges, the possibility of excessive thickening of the dispersion is further reduced, and a dispersion more suitable for coating or impregnation can be obtained. The weight-average molecular weight of the resin can be measured by gel permeation chromatography (GPC), and specifically, it can be measured by the method described in the examples. From these, examples of weight-average molecular weight ranges for the resin having hydroxyl groups include, but are not limited to, 1,000 to 500,000, 2,000 to 100,000, 5,000 to 50,000, etc. In a preferred embodiment of the present invention, the resin having a hydroxyl group is a resin having a weight-average molecular weight within the above range.

[0095] The resin containing hydroxyl groups may be either a commercially available product or a processed product.

[0096] The resin having hydroxyl groups may be a single resin used alone, or a combination of two or more resins may be used.

[0097] The content of hydroxyl-containing resin in the dispersion for silicon carbide sintered bodies is not particularly limited, but is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.5% by mass or more, particularly preferably 1% by mass or more, and most preferably 3% by mass or more, based on the total mass of the dispersion for silicon carbide sintered bodies. When the content of hydroxyl-containing resin is within the above range, a dispersion with superior moldability for green sheets can be obtained. The content of hydroxyl-containing resin in the dispersion for silicon carbide sintered bodies is not particularly limited, but is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, particularly preferably 15% by mass or less, and most preferably 10% by mass or less, based on the total mass of the dispersion for silicon carbide sintered bodies. When the content of hydroxyl-containing resin is within the above range, the amount of other components removed during drying, degreasing, etc., is reduced, resulting in a dispersion with superior manufacturing cost. Based on the above, examples of the range of content of resins having hydroxyl groups in dispersions for silicon carbide sintered bodies include, but are not limited to, 0.01% to 50% by mass, 0.1% to 30% by mass, 0.5% to 20% by mass, 1% to 15% by mass, and 3% to 10% by mass, relative to the total mass of the dispersion for silicon carbide sintered bodies. Furthermore, if the dispersion for silicon carbide sintered bodies contains two or more resins having hydroxyl groups, the content of resins having hydroxyl groups refers to the total amount of these resins.

[0098] The content ratio of positively charged silicon carbide particles to the hydroxyl-containing resin is not particularly limited. The content of the hydroxyl-containing resin is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2.5 parts by mass or more, particularly preferably 5 parts by mass or more, and most preferably 10 parts by mass or more, per 100 parts by mass of positively charged silicon carbide particles. When the content of the hydroxyl-containing resin relative to the positively charged silicon carbide particles is within the above range, the dispersion stability of the dispersion is improved, and a dispersion with superior moldability for green sheets, prepreg materials, etc., can be obtained. The content of the hydroxyl-containing resin is preferably 1,000 parts by mass or less, more preferably 500 parts by mass or less, even more preferably 300 parts by mass or less, particularly preferably 150 parts by mass or less, and most preferably 100 parts by mass or less, per 100 parts by mass of positively charged silicon carbide particles. When the content of the resin having hydroxyl groups relative to the positively charged silicon carbide particles is within the above range, the amount of resin component removed during degreasing is reduced, resulting in a dispersion with superior manufacturing cost. Therefore, the content of the resin having hydroxyl groups can be, but is not limited to, 0.1 parts by mass to 1,000 parts by mass, 1 part by mass to 500 parts by mass, 2.5 parts by mass to 300 parts by mass, 5 parts by mass to 150 parts by mass, 10 parts by mass to 100 parts by mass, etc., per 100 parts by mass of positively charged silicon carbide particles.

[0099] In this specification, resins having hydroxyl groups are treated as distinct from cationic polymers used for charge control of silicon carbide particles and boron nitride particles.

[0100] [Aqueous solution containing a resin having hydroxyl groups] The method for producing an aqueous solution containing a resin having hydroxyl groups, that is, the procedure and method for dissolving the resin having hydroxyl groups in a solvent containing water, is not particularly limited, and conventionally known procedures and methods can be used.

[0101] The water used in the method for producing an aqueous solution containing a resin having hydroxyl groups is preferably water that contains as few impurities as possible. Here, the purity of the water can be increased by operations such as removing impurity ions using ion exchange resin, removing foreign substances by filtration, and distillation. Specifically, it is preferable to use, for example, deionized water (ion-exchanged water), pure water, ultrapure water, or distilled water.

[0102] [Water] The dispersion for silicon carbide sintered body according to this embodiment contains water. Water has the function of dispersing or dissolving each component as a dispersion medium or solvent. It is preferable to use water that contains as few impurities as possible. Here, the purity of the water can be increased by operations such as removing impurity ions using ion exchange resin, removing foreign matter by filtration, or distillation. Specifically, it is preferable to use, for example, deionized water (ion-exchanged water), pure water, ultrapure water, or distilled water.

[0103] The dispersion for silicon carbide sintered body according to this embodiment may further contain an organic solvent as a dispersion medium or solvent for the dispersion or dissolution of each component. In this case, preferred examples of organic solvents used are those that are miscible with water, such as acetone, acetonitrile, ethanol, methanol, isopropanol, glycerin, ethylene glycol, and propylene glycol. These organic solvents may also be mixtures with water. Alternatively, the organic solvent may be used without mixing with water, and the organic solvent may be mixed into a dispersion in which each component is dispersed or dissolved in water. These organic solvents can be used individually or in combination of two or more.

[0104] [Boron Nitride (BN) Particles] The dispersion for silicon carbide sintered bodies according to this embodiment may contain boron nitride (BN) particles. Since boron nitride (BN) is a hard material, combining boron nitride (BN) particles with silicon carbide particles is expected to improve the thermal shock resistance and machinability of the silicon carbide-containing sintered body.

[0105] The crystal structure of boron nitride is not particularly limited, and either hexagonal boron nitride or cubic boron nitride can be used. However, hexagonal boron nitride is preferred because it is easier to manufacture.

[0106] The average secondary particle diameter of the boron nitride particles is preferably less than 20 μm, more preferably 19 μm or less, even more preferably 18 μm or less, even more preferably less than 15 μm, particularly preferably less than 10 μm, and most preferably less than 5 μm. When the average secondary particle diameter of the boron nitride particles is within the above range, a dispersion with higher dispersibility can be obtained. Furthermore, the average secondary particle diameter of the boron nitride particles is preferably 0.3 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. When the average secondary particle diameter of the boron nitride particles is within the above range, charge control by coating in the coating layer can be performed with high efficiency. Here, the value of the average secondary particle diameter of the boron nitride particles can be measured using the MT3300 laser diffraction / scattering particle size distribution analyzer manufactured by MICROTRAC. Details of the measurement method are described in the examples.

[0107] Furthermore, the boron nitride particles may be commercially available or processed.

[0108] Boron nitride particles may be used individually, in combinations thereof, or in mixtures of two or more types.

[0109] [Aqueous dispersion containing boron nitride particles] The method for producing an aqueous dispersion containing boron nitride particles, that is, the procedure and method for dispersing boron nitride particles in a dispersion medium containing water, is not particularly limited, and conventionally known procedures and methods can be used.

[0110] The water used in the method for producing an aqueous dispersion containing boron nitride particles is preferably water that contains as few impurities as possible. Here, the purity of the water can be increased by operations such as removing impurity ions using ion exchange resin, removing foreign matter by filtration, and distillation. Specifically, it is preferable to use, for example, deionized water (ion-exchanged water), pure water, ultrapure water, or distilled water.

[0111] Furthermore, an aqueous dispersion containing coated boron nitride particles obtained by a method for producing boron nitride particles on which a functional polymer described later has been adsorbed can be used.

[0112] As described later, aqueous dispersions containing boron nitride particles may contain dispersion media other than water. From the viewpoint of minimizing environmental impact, the dispersion media is preferably water only.

[0113] [Charge Control of Boron Nitride Particles] Boron nitride particles are preferably those having the same sign of charge (zeta potential) as positively charged silicon carbide particles, and therefore, positively charged particles can be preferably used. This increases the repulsion between the boron nitride particles and the positively charged silicon carbide particles, improving the dispersibility of the dispersion. There are no particular limitations on the charge control of boron nitride particles, but one method is to adjust the surface charge by forming a layer of other components on the surface of the boron nitride particles.

[0114] Specifically, for example, the surface charge can be adjusted by adsorbing a functional polymer having the function of adjusting the surface charge onto the surface of boron nitride particles. In the dispersion for silicon carbide sintered bodies according to this embodiment, dispersibility and dispersion stability are improved by adjusting the zeta potential to be the same sign as the positively charged silicon carbide particles, so it is preferable to adsorb a cationic polymer as the functional polymer. In other words, in the dispersion for silicon carbide sintered bodies according to this embodiment, it is preferable that the boron nitride particles are charge-controlled by a cationic polymer.

[0115] The cationic polymer is not particularly limited as long as it is positively charged in a predetermined dispersion medium, and conventionally known polymers can be used. For example, poly(diallyldimethylammonium chloride) (PDDA), poly(methacryloyloxyethyltrimethylammonium chloride), poly(acrylamide-co-diallyldimethylammonium chloride), poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine), polyethyleneimine, ethoxylated polyethyleneimine, poly(amideamine), poly(methacryloyloxyethyldimethylammonium chloride), poly(vinylpyrrolidone), poly(vinylimidazole), poly(vinylpyridine), poly(vinylamine), polyallylamine and its quaternaries, polyallylamine hydrochloride (PAH), polylysine, polyacrylamide, polypyrrole, polyaniline, and copolymers containing two or more of these or variations in the type of salt can be used.

[0116] Preferably, the cationic polymer used is poly(diallyldimethylammonium chloride), poly(methacryloyloxyethyltrimethylammonium chloride), poly(acrylamido-co-diallyldimethylammonium chloride), poly(dimethylamine-co-epichlorohydrin-co-ethylenediamine), polyethyleneimine, ethoxylated polyethyleneimine, poly(amideamine), poly(methacryloyloxyethyldimethylammonium chloride), poly(vinylpyrrolidone), poly(vinylimidazole), poly(vinylpyridine), or poly(vinylamine).

[0117] The molecular weight of the cationic polymer is not particularly limited, but for example, a weight-average molecular weight of 20,000 to 200,000 is preferred. Within this range, the effects of the present invention can be particularly pronounced. In this specification, the value of "weight-average molecular weight" shall be the value measured by gel permeation chromatography (GPC).

[0118] [Cationic Polymer-Coated Boron Nitride Particles] In this specification, cationic polymer-coated boron nitride particles are coated particles having boron nitride particles and a coating layer containing a cationic polymer that coats the boron nitride particles. Here, cationic polymer-coated boron nitride particles are particles in which at least a portion of the boron nitride particles is coated by a coating layer containing a cationic polymer.

[0119] It is preferable that the cationic polymer-coated boron nitride particles can maintain their morphology as cationic polymer-coated boron nitride particles even when washed with a solvent (preferably water) or when dispersed in water.

[0120] [Average secondary particle diameter of cationic polymer-coated boron nitride particles] The average secondary particle diameter of cationic polymer-coated boron nitride particles is preferably 20 μm or less, more preferably 15 μm or less, even more preferably 10 μm or less, and particularly preferably 5 μm or less. When the average secondary particle diameter of cationic polymer-coated boron nitride particles is within the above range, the dispersibility can be further improved when the cationic polymer-coated boron nitride particles are dispersed in water, which is the dispersion medium. From a similar viewpoint, the average secondary particle diameter of cationic polymer-coated boron nitride particles is more preferably greater than 0.3 μm, even more preferably 0.5 μm or more, even more preferably greater than 0.5 μm, particularly preferably 1 μm or more, and most preferably greater than 1 μm. Here, the average secondary particle diameter of the cationic polymer-coated boron nitride particles can be measured using a MICROTRAC MT3300 laser diffraction / scattering particle size distribution analyzer in a dispersion medium prepared by dispersing the cationic polymer-coated boron nitride particles in a dispersion medium at an appropriate concentration for measurement. Details of the measurement method are described in the examples. Although it is difficult to directly measure the average thickness of the coating layer, it is considered to be very thin and therefore corresponds to the preferred average secondary particle diameter of the boron nitride particles.

[0121] Furthermore, even when using coated particles other than cationic polymer-coated boron nitride particles as charge-controlled boron nitride particles, in which a layer of other components is formed on the surface of the boron nitride particles, it is preferable that the average secondary particle diameter is within the above range.

[0122] [Ratio of average secondary particle diameter of cationic polymer-coated boron nitride particles to average secondary particle diameter of boron nitride particles] The ratio of the average secondary particle diameter of cationic polymer-coated boron nitride particles (coated particles) to the average secondary particle diameter of boron nitride particles (particles before coating) (hereinafter also referred to as the ratio of average secondary particle diameter to boron nitride particles) is not particularly limited, but is preferably 10 or less. Within this range, cationic polymer-coated boron nitride particles are produced while maintaining the high dispersibility of boron nitride particles to a high degree. As a result, when cationic polymer-coated boron nitride particles are dispersed in water, a dispersion with higher dispersibility is obtained. From a similar viewpoint, the ratio of average secondary particle diameter to boron nitride particles is more preferably 5 or less, even more preferably 3 or less, even more preferably 2 or less, even more preferably 1.6 or less, and particularly preferably 1.2 or less. In addition, the ratio of average secondary particle diameter to boron nitride particles is not particularly limited, but is preferably 0.9 or more.

[0123] Furthermore, even when using coated particles other than cationic polymer-coated boron nitride particles as charge-controlled boron nitride particles, in which a layer of other components is formed on the surface of the boron nitride particles, it is preferable that the ratio of the average secondary particle diameter to the boron nitride particles is within the above range.

[0124] [Method for producing cationic polymer-coated boron nitride particles] As described above, in the dispersion for silicon carbide sintered bodies according to this embodiment, the dispersibility and dispersion stability are improved because the positively charged silicon carbide particles and boron nitride particles have the same charge sign (zeta potential). Therefore, it is preferable to adsorb a cationic polymer onto the boron nitride particles. Accordingly, the method for producing boron nitride particles with an adsorbed cationic polymer will be described below.

[0125] The method for producing cationic polymer-coated boron nitride particles is not particularly limited, but for example, a method can be used that includes the steps of: (A) preparing a raw material dispersion (1) containing boron nitride particles and water, and a raw material solution (2) containing a cationic polymer and water; and (B) adding the raw material solution (2) to the raw material dispersion (1) and mixing to form coated particles having a coating layer containing a cationic polymer on the surface of the boron nitride particles.

[0126] The cationic polymer-coated boron nitride particles produced here may be manufactured in a dispersed state in water, or they may be manufactured after a step to remove the water. Cationic polymer-coated boron nitride particles manufactured in a dispersed state in water can be used as an aqueous dispersion containing boron nitride particles in the mixing step described later.

[0127] (Process (A)) Process (A) is a process of preparing a raw material dispersion (1) containing boron nitride particles and water, and a raw material solution (2) containing a cationic polymer and water.

[0128] The method for preparing the raw material dispersion (1) containing boron nitride particles and water is not particularly limited. Commercial products may be used, or processed products may be used. When synthesizing (preparing) the raw material dispersion (1) containing boron nitride particles and water, there are no particular limitations, and known apparatus and known methods may be used.

[0129] The content of boron nitride particles in the raw material dispersion (1) is not particularly limited, but from the viewpoint of productivity, it is preferably 8% by mass or more, and more preferably 10% by mass or more, relative to the total mass of the raw material dispersion (1). Furthermore, from the viewpoint of dispersibility, it is preferably 50% by mass or less, and more preferably 30% by mass or less, relative to the total mass of the raw material dispersion (1).

[0130] Here, the boron nitride particles are not particularly limited, but it is preferable to maintain a state in which positively charged silicon carbide particles are dispersed in the dispersion medium from their generation until the raw material dispersion (1) is prepared in step (A). Furthermore, it is more preferable to maintain the state in which the boron nitride particles are dispersed in the dispersion medium from their generation until they are coated with a coating layer in step (B) described later. By maintaining the state of dispersion in the dispersion from the generation of the boron nitride particles until they are coated with a coating layer, the boron nitride particles can avoid aggregation due to drying. As a result, the high level of dispersibility of the boron nitride particles at the time of generation is maintained even in the state of cationic polymer-coated boron nitride particles. Therefore, when the manufactured cationic polymer-coated boron nitride particles are dispersed in water, a dispersion with extremely high dispersibility can be obtained.

[0131] The raw material dispersion (1) preferably contains water as a dispersion medium. The water is preferably water that contains as few impurities as possible. Here, the purity of the water can be increased by operations such as removing impurity ions using ion exchange resin, removing foreign matter by filtration, or distillation. Specifically, it is preferable to use, for example, deionized water (ion-exchanged water), pure water, ultrapure water, or distilled water.

[0132] The procedure or method for dispersing boron nitride particles in water is not particularly limited, and known procedures or methods can be used.

[0133] The raw material dispersion (1) may contain a dispersion medium other than water. The dispersion medium other than water may be a mixed solvent of water and an organic solvent for the dispersion or dissolution of each component. In this case, preferred organic solvents to be used are, for example, acetone, acetonitrile, ethanol, methanol, isopropanol, glycerin, ethylene glycol, propylene glycol, etc., which are organic solvents that are miscible with water. Alternatively, the organic solvent may be used without mixing it with water to disperse or dissolve each component, and then mixed with water. These organic solvents can be used individually or in combination of two or more.

[0134] Here, the water content in the raw material dispersion (1) is preferably 50% by mass or more, and more preferably 70% by mass or more, with respect to the total mass of the raw material dispersion medium (1), from the viewpoint of promoting better coating of boron nitride particles by cationic polymers.

[0135] The raw material dispersion (1) obtained in this process is not particularly limited, but from the viewpoint of suppressing electrostatic aggregation, it is preferable that its pH be 5.0 or higher.

[0136] The method for preparing the raw material solution (2) is not particularly limited, but examples include adding a cationic polymer to water. The content of the cationic polymer in the raw material solution (2) is not particularly limited, but it is preferably 10% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 40% by mass or less, based on the total mass of the raw material solution (2).

[0137] (Step (B)) Step (B) is a step in which the raw material solution (2) and an acid are added to the raw material dispersion (1) prepared in step (A) to form coated particles having a coating layer containing a cationic polymer on the surface of the boron nitride particles. In step (B), cationic polymer coated boron nitride particles are produced in which the cationic polymer is adsorbed on the surface of the boron nitride particles.

[0138] The method of adding the raw material solution (2) to the raw material dispersion (1) is not particularly limited. For example, the raw material solution (2) may be added all at once, or it may be added little by little.

[0139] The amount of raw material solution (2) added is not particularly limited, but it is preferable to add raw material solution (2) so that the cationic polymer is 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, per 100 parts by mass of boron nitride particles. This is because when the amount of raw material solution (2) added is within this range, the boron nitride particles can be sufficiently coated with the cationic polymer, and the charge can be controlled so that the desired zeta potential can be obtained. Furthermore, although the amount of raw material solution (2) added is not particularly limited, it is preferable to add raw material solution (2) so that the cationic polymer is 80 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 10 parts by mass or less, per 100 parts by mass of boron nitride particles. This is because once the coating progresses to a certain extent, the effect obtained by the coating becomes constant, and by keeping the amount of raw material solution (2) added below a predetermined amount, economic efficiency and production efficiency can be improved.

[0140] In this stage, it is preferable to add the raw material solution (2) to the raw material dispersion (1) and stir to allow the reaction to proceed. The reaction time is not particularly limited, but it is preferable to be 1 minute or longer. This is because a reaction time within this range allows the boron nitride particles to be more sufficiently coated with the cationic polymer, and the charge can be controlled to obtain the desired zeta potential. Furthermore, in the production of a dispersion for silicon carbide sintered bodies, when positively charged silicon carbide particles and cationic polymer-coated boron nitride particles are dispersed in water, aggregation in the dispersion becomes less likely, making it possible to obtain a dispersion with high dispersibility. From a similar viewpoint, the reaction time is preferably 30 minutes or longer, more preferably 50 minutes or longer, and even more preferably 60 minutes or longer. Also, the reaction time in this stage is preferably 200 minutes or less. This is because once the coating has progressed to a certain extent, the effect obtained by the coating becomes constant, and if the reaction time is within this range, economic efficiency and production efficiency are further improved. From a similar viewpoint, the reaction time is preferably 150 minutes or less, more preferably 120 minutes or less, and even more preferably 90 minutes or less.

[0141] The pH at this stage is not particularly limited, but from the viewpoint of suppressing electrostatic repulsion with the functional polymer, a pH of 5.0 to 11.0 is preferred.

[0142] By going through step (B), a dispersion containing cationic polymer-coated boron nitride particles and a dispersion medium can be obtained. That is, cationic polymer-coated boron nitride particles can be produced in a dispersed state within the dispersion medium.

[0143] (Other steps) The method for producing cationic polymer-coated boron nitride particles may further include steps other than steps (A) and (B), and steps (A) and (B) may further include steps relating to other operations.

[0144] Furthermore, the fact that boron nitride particles are coated with a cationic polymer can be confirmed by measuring the zeta potential of the cationic polymer-coated boron nitride particles.

[0145] [Isoelectric Point of Boron Nitride Particles] Boron nitride particles (or charge-controlled boron nitride particles if charge-controlled) are not particularly limited as long as they have the same sign of charge as the positively charge-controlled silicon carbide particles, but it is preferable that their isoelectric point pH is 5 or higher. This makes it less likely for aggregation to occur in the dispersion for silicon carbide sintered bodies containing positively charge-controlled silicon carbide particles and boron nitride particles, and good dispersibility is maintained. This makes it possible to obtain a dispersion with high dispersibility. From a similar viewpoint, it is more preferable that the boron nitride particles have an isoelectric point pH of 5 or higher and 11 or lower.

[0146] Here, the absolute value of the difference between the pH of the isoelectric point of boron nitride particles and the pH of the isoelectric point of positively charged silicon carbide particles is preferably small, preferably 2 or less, more preferably 1.5 or less, and even more preferably 1 or less (lower limit 0). This is because particles with similar isoelectric point pH values ​​are less likely to aggregate.

[0147] [Zeta Potential of Boron Nitride Particles in Dispersion for Silicon Carbide Sintered Body] The zeta potential of boron nitride particles (or charge-controlled boron nitride particles if charge-controlled) in a dispersion for silicon carbide sintered body is not particularly limited as long as it has the same sign as positively charge-controlled silicon carbide particles. However, from the viewpoint of improving dispersibility, it is preferable that the absolute value be 10 mV or more, and more preferably +10 mV or more. The upper limit of the zeta potential of boron nitride particles in a dispersion for silicon carbide sintered body is not particularly limited, but substantially, the absolute value is 50 mV or less, for example, +50 mV or less.

[0148] [Content of Boron Nitride Particles in Dispersion for Silicon Carbide Sintered Body] The lower limit of the content of boron nitride particles (or charge-controlled boron nitride particles if charge-controlled) in the dispersion for silicon carbide sintered body according to this embodiment is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and most preferably 1% by mass or more, based on the total mass of the dispersion for silicon carbide sintered body. The upper limit of the content of boron nitride particles in the dispersion for silicon carbide sintered body is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and most preferably 20% by mass or less, based on the total mass of the dispersion for silicon carbide sintered body. Within these ranges, the dispersion stability and handling properties of the dispersion are good. Furthermore, a high-quality silicon carbide sintered body can be obtained. According to one embodiment, the content of boron nitride particles (or charge-controlled boron nitride particles if charge-controlled) in the dispersion for silicon carbide sintered body according to this embodiment is 0.1% to 50% by mass, 0.1% to 20% by mass, 0.1% to 10% by mass, 0.1% to 5% by mass, 0.1% to 3% by mass, 0.1% to 2% by mass, and 0% by mass, relative to the total mass of the dispersion for silicon carbide sintered body. The amounts are 3% to 40% by mass, 0.3% to 10% by mass, 0.3% to 5% by mass, 0.3% to 3% by mass, 0.3% to 2% by mass, 0.5% to 30% by mass, 0.5% to 10% by mass, 0.5% to 5% by mass, 0.5% to 3% by mass, 1% to 20% by mass, 1% to 10% by mass, or 1% to 5% by mass. Note that if the dispersion for silicon carbide sintered bodies contains two or more types of boron nitride particles, the boron nitride particle content refers to the total amount of these particles.

[0149] [Other Components] The silicon carbide sintered body dispersion according to this embodiment may contain other components as long as they do not impair the effects of the present invention. The other components are not particularly limited, but defoaming agents, plasticizers, etc., can be used.

[0150] [Plasticizers] There are no particular restrictions on the plasticizers used, but water-soluble plasticizers such as polyethylene glycol and glycerin, or water-insoluble plasticizers that migrate to an emulsion, such as phthalate ester plasticizers like dibutyl phthalate, may be used.

[0151] The content of plasticizer in the dispersion for silicon carbide sintered bodies is not particularly limited, but the lower limit of the plasticizer content is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, based on the total mass of the dispersion for silicon carbide sintered bodies. Furthermore, the upper limit of the plasticizer content in the dispersion for silicon carbide sintered bodies is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on the total mass of the dispersion for silicon carbide sintered bodies. Within these ranges, the dispersion stability and handling properties of the dispersion are good. In addition, a high-quality silicon carbide sintered body can be obtained. According to one embodiment, the content of the plasticizer in the dispersion for silicon carbide sintered body is 0.1% by mass or more and 30% by mass or less, 0.1% by mass or more and 20% by mass or less, 0.1% by mass or more and 10% by mass or less, 0.1% by mass or more and 5% by mass or less, 0.5% by mass or more and 20% by mass or less, 0.5% by mass or more and 10% by mass or less, or 1% by mass or more and 10% by mass or less, based on the total mass of the dispersion for silicon carbide sintered body.

[0152] [Antifoaming agent] There are no particular restrictions on the antifoaming agent, but silicone-based, acetylene glycol-based, fatty acids, higher alcohols, polyalkylene derivatives, polyether derivatives, etc. may be used.

[0153] The content of the defoaming agent in the dispersion for silicon carbide sintered bodies is not particularly limited, but the lower limit of the defoaming agent content is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.05% by mass or more. Furthermore, the upper limit of the defoaming agent content in the dispersion for silicon carbide sintered bodies is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. Within these ranges, the dispersion stability and handling properties of the dispersion are good. In addition, a high-quality silicon carbide sintered body can be obtained.

[0154] [pH] The dispersion for silicon carbide sintered body according to this embodiment preferably has a pH of 7.0 or less at 25°C, more preferably 6.8 or less, even more preferably 6.5 or less, particularly preferably 6.3 or less, and most preferably 6.0 or less. The dispersion for silicon carbide sintered body according to this embodiment preferably has a pH of 1.0 or more at 25°C, more preferably 1.2 or more, even more preferably 1.5 or more, particularly preferably 2.0 or more, and most preferably 2.5 or more. According to one embodiment, the dispersion for silicon carbide sintered body according to this embodiment has a pH of 5.8 or less, 5.6 or less, 5.5 or less, or 5.2 or less at 25°C. If the pH of the dispersion for silicon carbide sintered body is within the above range, it can exhibit an excellent effect of lowering the sintering temperature.

[0155] The pH adjusting agent used to achieve the above pH is not particularly limited, and any known pH adjusting agent capable of achieving the desired pH can be used as appropriate. For example, it is preferable to use known acids, bases, salts, amines, chelating agents, etc.

[0156] It is preferable that the pH of the dispersion for silicon carbide sintered bodies does not change over time. In the dispersion for silicon carbide sintered bodies according to this embodiment, it is preferable that the pH after storage at 25°C for 20 hours after the dispersion is prepared is 5.5 or less, 5.0 or less, 4.8 or less, or 4.6 or less.

[0157] [Viscosity] The dispersion for silicon carbide sintered bodies according to this embodiment has low viscosity. For example, the viscosity at 25°C immediately after preparation (within 5 minutes after preparation) is 2.0 Pa·s or less, or 1.5 Pa·s or less. The viscosity of the dispersion for silicon carbide sintered bodies according to this embodiment (immediately after preparation / 25°C) is preferably less than 1.5 Pa·s, more preferably 1.3 Pa·s or less, even more preferably 1.2 Pa·s or less, particularly preferably 1.0 Pa·s or less, and most preferably 0.9 Pa·s or less. The viscosity of the dispersion for silicon carbide sintered bodies according to this embodiment (immediately after preparation / 25°C) is not particularly limited, but in practical terms, it is 0.01 Pa·s or more, or 0.05 Pa·s or more. The viscosity of the dispersion for silicon carbide sintered bodies can be measured by the method described in the examples below.

[0158] It is preferable that the viscosity of the dispersion for silicon carbide sintered bodies does not change over time. In the dispersion for silicon carbide sintered bodies according to this embodiment, it is preferable that the viscosity after storage at 25°C for 20 hours after the dispersion is prepared is 2.0 Pa·s or less, or 1.5 Pa·s or less.

[0159] [Method for manufacturing a dispersion for silicon carbide sintered bodies] <Mixing step> The method for manufacturing a dispersion for silicon carbide sintered bodies according to this embodiment includes a mixing step of mixing an aqueous dispersion containing positively charged silicon carbide particles, an aqueous solution containing a water-soluble first metal compound containing one or more first metals selected from the group consisting of rare earth elements, zirconium, and aluminum, an aqueous solution containing a resin having hydroxyl groups, and, if necessary, an aqueous dispersion containing boron nitride particles.

[0160] In the method for producing a dispersion for a silicon carbide sintered body according to this embodiment, in a preferred embodiment, the method further includes a step for preparing an aqueous dispersion containing silicon carbide particles, in which, before the mixing step, a charge control component and an acid are added to the raw material dispersion containing silicon carbide particles to adjust the pH to a range of 9.0 to 12.0, thereby forming coated silicon carbide particles having a coating layer containing the charge control component on the surface of the silicon carbide particles, and preparing an aqueous dispersion containing silicon carbide particles. In addition, in the method for producing a dispersion for a silicon carbide sintered body according to this embodiment, according to one embodiment, the method further includes a step for preparing an aqueous dispersion containing boron nitride particles, in which, by adding a solution containing a functional polymer to the raw material dispersion containing boron nitride particles, the coated boron nitride particles having a coating layer containing the functional polymer on the surface of the boron nitride particles, and preparing an aqueous dispersion containing boron nitride particles.

[0161] Therefore, in the method for producing a silicon carbide sintered body dispersion according to this embodiment, a preferred embodiment further comprises at least one of the following steps: a step for preparing an aqueous dispersion containing positively charged silicon carbide particles, in which, before the mixing step, a charge control component and an acid are added to a raw material dispersion containing silicon carbide particles to adjust the pH to a range of 9.0 to 12.0, thereby forming coated silicon carbide particles having a coating layer containing the charge control component on the surface of the silicon carbide particles; and a step for preparing an aqueous dispersion containing boron nitride particles, in which, by adding a solution containing a functional polymer to a raw material dispersion containing boron nitride particles, a coated boron nitride particle having a coating layer containing the functional polymer on the surface of the boron nitride particles, thereby preparing an aqueous dispersion containing boron nitride particles.

[0162] The method for mixing an aqueous dispersion containing positively charged silicon carbide particles, an aqueous solution containing a first metal compound, and an aqueous solution containing a resin having hydroxyl groups is not particularly limited. Below, a mixing method for a silicon carbide sintered body dispersion according to this embodiment that contains boron nitride particles will be described.

[0163] For example, it is preferable to include the steps of: (1) preparing an aqueous dispersion containing positively charged silicon carbide particles (liquid 1), an aqueous solution of a resin having hydroxyl groups (liquid 2), an aqueous dispersion containing boron nitride particles (liquid 3), and an aqueous solution containing a first metal compound (liquid 4); (2) kneading liquid 1 and liquid 2; (3) adding liquid 3 to the mixture obtained in step (2) and kneading further; and (4) adding liquid 4 to the mixture obtained in step (3) and kneading further.

[0164] (Step (1)) In Step (1), an aqueous dispersion containing positively charged silicon carbide particles (liquid 1), an aqueous solution of a resin having hydroxyl groups (liquid 2), an aqueous dispersion containing boron nitride particles (liquid 3), and an aqueous solution containing a first metal compound (liquid 4) are prepared, respectively.

[0165] The method for preparing the aqueous dispersion (1 solution) containing positively charged silicon carbide particles is not particularly limited. The aqueous dispersion containing silicon carbide particles may be a commercially available product or a processed product. It may also be prepared using the method described above in [Method for Producing Charge-Controlled Component-Coated Silicon Carbide Particles]. In this case, it is preferable to adjust the pH of the aqueous dispersion (1 solution) so that the pH of the final dispersion reaches a desired value. For example, the pH of the aqueous dispersion after forming a coating layer on the silicon carbide particles by the above method can be adjusted to a desired pH using an acid or alkali. Furthermore, it is preferable to adjust the concentration of positively charged silicon carbide particles in 1 solution to 40 to 60% by mass by methods such as adding water or concentrating, as needed.

[0166] The method for preparing the aqueous solution of the resin having hydroxyl groups (2nd solution) is not particularly limited. In this case, it is preferable to adjust the pH of the aqueous solution of the resin having hydroxyl groups (2nd solution) so that the pH of the final dispersion is a desired value. The concentration of the resin having hydroxyl groups in the 3rd solution is not particularly limited, but it is preferable to adjust it to, for example, 5 to 40% by mass.

[0167] The method for preparing the aqueous dispersion (3 liquids) containing boron nitride particles is not particularly limited. Commercially available or processed products may be used for the aqueous dispersion containing boron nitride particles. It may also be prepared using the method described above in [Method for producing boron nitride particles with adsorbed functional polymers]. In this case, it is preferable to adjust the pH of the aqueous dispersion (3 liquids) containing boron nitride particles so that the pH of the final dispersion reaches a desired value. For example, the pH of the aqueous dispersion after adsorbing functional polymers onto boron nitride particles by the above method can be adjusted to a desired pH using an acid or alkali. Furthermore, it is preferable to adjust the concentration of boron nitride particles in the 3 liquids to 8 to 50% by mass by methods such as adding water or concentrating, as needed.

[0168] The method for preparing the aqueous solution (4th solution) containing the first metal compound is not particularly limited. In this case, it is preferable to adjust the pH of the aqueous solution (4th solution) containing the first metal compound so that the pH of the final dispersion is a desired value. The concentration of the first metal compound in the 4th solution is not particularly limited, but it is preferable to adjust it to, for example, 5 to 40% by mass.

[0169] The specific forms of water used as a dispersion medium / solvent in the preparation of solutions 1, 2, 3, and 4, and the acid used to adjust the pH, are the same as described above.

[0170] (Step (2)) In step (2), the two liquids prepared above are kneaded together. The method of kneading the two liquids is not particularly limited. At this time, other components such as plasticizers, defoamers, and pH adjusters (e.g., sodium hydroxide) may be added and mixed as needed.

[0171] The mixing method is not particularly limited, and conventionally known mixing and stirring machines such as a self-rotating agitator or a planetary mixer can be used. The mixing time is, for example, about 5 to 30 minutes. At this time, it is preferable to perform the mixing under vacuum from the viewpoint of suppressing the generation of bubbles during mixing.

[0172] (Step (3)) In step (3), the three liquids prepared above are added to the mixture obtained in step (2) and kneaded further.

[0173] The method of adding and mixing the three liquids is not particularly limited. Similarly, the method of kneading is not particularly limited; conventionally known kneading and stirring machines such as a self-rotating agitator or a planetary mixer can be used. The kneading time is, for example, about 5 to 60 minutes. At this time, from the viewpoint of suppressing the generation of bubbles during kneading, it is preferable to perform the kneading under vacuum.

[0174] (Step (4)) In step (4), the four liquids prepared above are added to the mixture obtained in step (3) and kneaded further.

[0175] The method of adding and mixing the four liquids is not particularly limited. Similarly, the method of kneading is not particularly limited; for example, conventionally known kneading and stirring machines such as a self-rotating agitator or a planetary mixer can be used. The kneading time is, for example, about 5 to 60 minutes. At this time, from the viewpoint of suppressing the generation of bubbles during kneading, it is preferable to perform the kneading under vacuum.

[0176] (Green Sheet for Silicon Carbide Sintered Body) One embodiment of the present invention relates to a green sheet for a silicon carbide sintered body formed using the above-described dispersion for silicon carbide sintered body. Another embodiment of the present invention relates to a method for manufacturing a green sheet for a silicon carbide sintered body, comprising the steps of obtaining a dispersion for a silicon carbide sintered body by the above-described method for manufacturing a dispersion for a silicon carbide sintered body, and applying the dispersion for a silicon carbide sintered body to a substrate. The dispersion for a silicon carbide sintered body according to this embodiment, and the dispersion for a silicon carbide sintered body obtained by the method for manufacturing the dispersion for a silicon carbide sintered body according to this embodiment, exhibit excellent dispersibility of positively charged silicon carbide particles and boron nitride particles, and have high dispersion stability. Therefore, a green sheet using this has a high density and uniform presence of positively charged silicon carbide particles and boron nitride particles, making resin separation less likely and resulting in fewer voids. Therefore, a high-strength silicon carbide sintered body can be manufactured.

[0177] The method for producing the green sheet is not particularly limited; for example, a method can be used in which the above-mentioned dispersion for silicon carbide sintered bodies is applied to a substrate to form a sheet.

[0178] While there are no particular limitations on the base material, resin films such as polyolefin films (polyethylene, polypropylene, etc.), polyester films (polyethylene terephthalate (PET), polyethylene naphthalate, etc.), and polyvinyl chloride are preferably used.

[0179] The thickness of the substrate is not particularly limited, but is, for example, 10 to 300 μm, and preferably 20 to 150 μm.

[0180] The method for coating the dispersion for silicon carbide sintered bodies is not particularly limited, and any known method can be used, such as bar coating, die coating, comma coating, gravure roll coating, blade coating, spray coating, air knife coating, dip coating, and transfer methods.

[0181] The thickness of the layer obtained by coating the silicon carbide sintered body dispersion is not particularly limited, but from the viewpoint of productivity and crack suppression, it is preferably 100 to 2000 μm.

[0182] (Prepreg material for silicon carbide sintered body and silicon carbide sintered body) One embodiment of the present invention is a prepreg material for a silicon carbide sintered body formed from the above-mentioned green sheet for silicon carbide sintered body. Another embodiment of the present invention relates to a method for manufacturing a prepreg material for a silicon carbide sintered body, comprising the steps of obtaining a green sheet for a silicon carbide sintered body by the above-mentioned method for manufacturing a green sheet for a silicon carbide sintered body, and laminating the green sheet for a silicon carbide sintered body onto a fibrous substrate.

[0183] Prepreg material refers to a semi-cured composite material produced by impregnating a fibrous base material such as glass cloth, silicon carbide fiber, or carbon fiber with a resin-containing dispersion and then drying it.

[0184] The general manufacturing method involves impregnating a fibrous substrate with a dispersion and then removing the solvent by evaporation during the drying process to produce prepreg material. Impregnation can be performed by dipping or coating, and can be repeated multiple times as needed.

[0185] Alternatively, prepreg materials can be manufactured by laminating sheet-like green sheets onto a fibrous substrate. Furthermore, prepreg materials can also be manufactured by combining this method with the method of impregnating the fibrous substrate with the dispersion described above.

[0186] The prepreg material of this embodiment can be sintered to form a silicon carbide sintered body and used as a silicon carbide fiber-reinforced silicon carbide composite material (silicon carbide / silicon carbide composite material). Therefore, one embodiment of the present invention relates to a silicon carbide sintered body formed from the above-mentioned prepreg material for silicon carbide sintered bodies. The above-mentioned silicon carbide / silicon carbide composite material has excellent physical properties such as light weight, high heat resistance, high hardness, and high fracture toughness, and can be used as a heat-resistant and environmentally resistant material.

[0187] The present invention encompasses the following embodiments and forms.

[0188] [1] A dispersion for a silicon carbide sintered body, comprising: silicon carbide particles whose surface is positively charged; a first water-soluble metal compound containing one or more metals selected from the group consisting of rare earth elements, zirconium, and aluminum; a resin having hydroxyl groups; and water; [2] The dispersion according to [1], wherein the pH is 6.0 or less; [3] The dispersion according to [1] or [2], wherein the silicon carbide particles are charge-controlled by aluminum hydroxide coating; [4] The dispersion according to any one of [1] to [3], wherein the first metal contained in the first metal compound is selected from the group consisting of yttrium, zirconium, and aluminum; [5] The dispersion according to any one of [1] to [4] above, wherein the resin having hydroxyl groups comprises at least one resin selected from the group consisting of polyvinyl alcohol resin, hydroxyl group-containing polyvinyl acetal resin, hydroxyl group-containing glyoxal resin, hydroxyl group-containing acrylic resin, phenol resin, hydroxyl group-containing polyvinylpyrrolidone, hydroxyl group-containing polyester resin, hydroxyl group-containing silicone resin, and hydroxyl group-containing polycarboxylic acid; [6] The dispersion according to any one of [1] to [5] above, further comprising boron nitride particles; [7] A green sheet for silicon carbide sintered body formed from the dispersion according to any one of [1] to [6] above; [8] A prepreg material for silicon carbide sintered body formed from the green sheet for silicon carbide sintered body according to [7] above; [9] A silicon carbide sintered body formed from the prepreg material for silicon carbide sintered body according to [8] above.

[0189] The present invention will be described in more detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples. Unless otherwise specified, "%" and "parts" mean "mass%" and "parts by mass," respectively. In addition, in the following examples and comparative examples, unless otherwise specified, the operations were carried out under conditions of room temperature (25°C) / relative humidity of 40-50% RH. Hereinafter, alumina, yttria, silicon carbide (SiC), and silicon nitride (BN) will be collectively referred to as "ceramics."

[0190] [Preparation of Ceramic Particle Aqueous Dispersion] <Alumina Particles> Using alumina particles (powder) with an average secondary particle diameter of 0.3 μm, a 20% by mass aqueous dispersion of alumina particles was prepared.

[0191] 《Yttria Particles》 Using yttria particles (powder) with an average secondary particle diameter of 0.4 μm, a 20% by mass yttria particle aqueous dispersion was prepared.

[0192] Preparation of Aqueous Dispersion of Boron Nitride (BN) Particles: A 22% by mass aqueous dispersion of boron nitride particles with an average secondary particle diameter of 3.07 μm was prepared by adding a 35% by mass aqueous solution of poly(diallyldimethylammonium chloride) (PDDA aqueous solution) so that the amount of PDDA was 10.0 parts by mass per 100 parts by mass of boron nitride particles. A dispersion containing PDDA-coated boron nitride particles was then prepared. Subsequently, 9.9% by mass hydrochloric acid was added to adjust the pH to 4.0 to obtain a 20% by mass PDDA-coated BN particle aqueous dispersion ("PDDA-BN particle aqueous dispersion").

[0193] Furthermore, by observing the change in the zeta potential of boron nitride particles due to PDDA addition, it was confirmed that the coating of boron nitride particles by PDDA was progressing.

[0194] A 25% by mass aqueous dispersion of silicon carbide (SiC) particles (average secondary particle diameter 0.28 μm, powder) was prepared.

[0195] 《Aluminum Hydroxide Coated Silicon Carbide (SiC) Particles》 A 20% by mass aqueous dispersion of silicon carbide (SiC) particles (average secondary particle size 0.28 μm, powder) was prepared, and a 1 M NaOH aqueous solution was added to adjust the pH to 10.0. Next, a 30% by mass aqueous dispersion of sodium aluminate was prepared, and a sodium aluminate aqueous dispersion in an amount of 29 parts by mass of sodium aluminate per 100 parts by mass of silicon carbide particles, along with 9.9% by mass hydrochloric acid, was added over 45 minutes while stirring to maintain a pH of 9.0 to 11.0. After stirring for another 45 minutes, 9.9% by mass hydrochloric acid was added to adjust the pH of the dispersion to 10.5, thereby preparing an aqueous dispersion containing aluminum hydroxide-coated silicon carbide (SiC) particles. Subsequently, 9.9% by mass hydrochloric acid was added to adjust the pH to 4.0, and the mixture was concentrated by suction filtration to obtain a 40% by mass aqueous dispersion of aluminum hydroxide-coated SiC particles ("Al-SiC particle aqueous dispersion"). The average secondary particle diameter of the aluminum hydroxide-coated SiC particles in the Al-SiC particle dispersion was 0.28 μm.

[0196] 《Composition and Structural Analysis of Particles in Aqueous Dispersion》 The particles in the dispersion obtained above were confirmed to be aluminum hydroxide-coated SiC particles by the following analysis.

[0197] Approximately 2 mL of the aqueous dispersion obtained above was collected and dropped onto a filter (pore size 5 μm). Next, suction filtration was performed, and then the powder was washed on the filter with 10 mL of pure water to dry the particles. The dried particles were then collected onto a Si wafer and observed using a scanning electron microscope SU-8000 manufactured by Hitachi High-Technologies Corporation using SEM (Scanning Electron Microscope)-EDX (Energy Dispersive X-ray Spectroscopy).

[0198] Furthermore, the dried particles were collected on carbon tape and subjected to EELS (Electron Energy Loss Spectroscopy) analysis using a TITAN 80-300 manufactured by FEI.

[0199] In SEM-EDX observation of the particles, C, Al, and O were selected as the elements to be observed. The EDX spectrum of Al was observed, and it was confirmed that the positions where the EDX spectra of C, Al, and O were observed corresponded clearly to the positions where the particles were observed in the SEM image. Therefore, it was determined that the SiC particles were coated with components containing Al and O.

[0200] Furthermore, in the EELS analysis of the particles, the observed EELS spectrum was aluminum hydroxide (Al(OH) ３ It was confirmed that the EELS standard spectrum of ) has a spectral shape unique to it (a different shape from the spectra of Al and other Al and O-containing compounds), therefore, the Al and O-containing component is Al(OH) ３ It was determined that it included [something].

[0201] [Preparation of the first metal compound (water-soluble metal compound)] <Yttrium ion-containing aqueous solution> Yttrium(III) nitrate hexahydrate was dissolved in an aqueous solvent to obtain a yttrium ion-containing aqueous solution, with a concentration of yttrium(III) nitrate of 35.9% by mass. Note that the yttrium-containing aqueous solution is shown in Table 1 as "50% by mass Y(NO ３ ) ３ 6H ２ It is written as "O".

[0202] <Example 1> <Preparation of Dispersion for SiC Sintered Body> 62.5 g of the 40% by mass aluminum hydroxide-coated SiC particle aqueous dispersion obtained above, 79.98 g of a 20% by mass hydroxyl group-containing polyvinyl acetal resin aqueous dispersion (a resin containing hydroxyl groups, degree of polymerization approximately 600, weight-average molecular weight 13,000), 8.00 g of polyethylene glycol (PEG200, number-average molecular weight: 200, weight-average molecular weight less than 1000) as a plasticizer, 2.15 g of an antifoaming agent (acetylene glycol EO adduct), and 36.36 g of pure water were stirred for 3 minutes at 500 rpm using a rotation-and-revolution type mixer (Hi-Rotor, HR003-02V, manufactured by Mitsuboshi Industrial Co., Ltd.) to obtain dispersion 1a. Next, the dispersion 1a obtained above and 19.50 g of an aqueous dispersion of 20% by mass PDDA-coated BN particles were stirred for 3 minutes at 500 rpm using a rotating-orbit mixer to obtain dispersion 1b. Next, the dispersion 1b obtained above and 8.68 g of an aqueous solution containing yttrium ions were stirred for 3 minutes at 500 rpm using a rotating-orbit mixer to obtain dispersion 1c.

[0203] The above dispersion 1c had a pH of 3.8 and was used as the dispersion for the SiC sintered body in Example 1.

[0204] 《Zeta Potential of Each Ceramic Particle》 The zeta potential of the aluminum hydroxide-coated SiC particles in the SiC sintered body dispersion of Example 1 was 47.7 mV.

[0205] <Example 2> An example of a SiC sintered body dispersion of Example 2 with a pH of 4.0 was obtained in the same manner as in Example 1, except that a predetermined amount of 4% by mass sodium hydroxide aqueous solution was added when preparing the dispersion 1a. The amount of pure water added when preparing dispersion 1a was reduced to compensate for the addition of the sodium hydroxide aqueous solution. The amounts of each raw material used in Example 2 are shown in Table 1. The zeta potential of the aluminum hydroxide-coated SiC particles in the SiC sintered body dispersion of Example 2 was 40.8 mV.

[0206] <Example 3> An example of a SiC sintered body dispersion of Example 3 was obtained in the same manner as in Example 1, except that a predetermined amount of 4% by mass sodium hydroxide aqueous solution was added when preparing the dispersion 1a. The amount of pure water added when preparing dispersion 1a was reduced to compensate for the addition of the sodium hydroxide aqueous solution. The amounts of each raw material used in Example 3 are shown in Table 1. The zeta potential of the aluminum hydroxide-coated SiC particles in the SiC sintered body dispersion of Example 3 was 32.7 mV.

[0207] <Comparative Example 1> <Preparation of Dispersion for SiC Sintered Body> 62.5 g of the 40% by mass aluminum hydroxide-coated SiC particle aqueous dispersion obtained above, 79.98 g of a 20% by mass hydroxyl group-containing polyvinyl acetal resin aqueous dispersion (a resin containing hydroxyl groups, degree of polymerization approximately 600, weight-average molecular weight 13,000), 8.00 g of polyethylene glycol (PEG200, number-average molecular weight: 200, weight-average molecular weight less than 1000) as a plasticizer, 2.15 g of an antifoaming agent (acetylene glycol EO adduct), and 37.87 g of pure water were stirred for 3 minutes at 500 rpm using a rotation-and-revolution type mixer (Hi-Rotor, HR003-02V, manufactured by Mitsuboshi Industrial Co., Ltd.) to obtain dispersion 2a. Next, the dispersion 2a obtained above and 19.50 g of an aqueous dispersion of 20% by mass PDDA-coated BN particles were stirred for 3 minutes at 500 rpm using a rotating / revolving mixer to obtain dispersion 2b. Next, the dispersion 2b obtained above and 6.40 g of an aqueous dispersion of 20% by mass yttria particles were stirred for 3 minutes at 500 rpm using a rotating / revolving mixer to obtain dispersion 2c.

[0208] The above dispersion 2c had a pH of 5.1 and was used as the dispersion for the SiC sintered body in Comparative Example 1.

[0209] The amounts of each raw material used in Comparative Example 1 are shown in Table 1. The zeta potential of the aluminum hydroxide-coated SiC particles in the SiC sintered body dispersion of Comparative Example 1 was 36.0 mV.

[0210] <Comparative Example 2> <Preparation of Dispersion for SiC Sintered Body> 88.24 g of the 25% by mass SiC particle aqueous dispersion obtained above, 9.60 g of the 20% by mass alumina particle aqueous dispersion, 79.98 g of a 20% by mass hydroxyl group-containing polyvinyl acetal resin (a resin containing hydroxyl groups, degree of polymerization approximately 600, weight-average molecular weight 13,000) aqueous dispersion, 8.00 g of polyethylene glycol (PEG200, number-average molecular weight: 200, weight-average molecular weight less than 1000) as a plasticizer, and 2.15 g of an antifoaming agent (acetylene glycol EO adduct) were stirred for 3 minutes at 500 rpm using a rotation-and-revolution type mixer (Hi-Rotor, HR003-02V, manufactured by Mitsuboshi Industrial Co., Ltd.) to obtain dispersion 3a. Next, the dispersion 3a obtained above and 19.50 g of an aqueous dispersion of 20% by mass PDDA-coated BN particles were stirred for 3 minutes at 500 rpm using a rotating-orbit mixer to obtain dispersion 3b. Next, the dispersion 3b obtained above and 8.68 g of an aqueous solution containing yttrium ions were stirred for 3 minutes at 500 rpm using a rotating-orbit mixer to obtain dispersion 3c.

[0211] The above dispersion 3c had a pH of 3.7 and was used as the dispersion for the SiC sintered body in Comparative Example 2.

[0212] The amounts of each raw material used in Comparative Example 2 are shown in Table 1. The zeta potential of the SiC particles in the SiC sintered body dispersion of Comparative Example 2 was 17.2 mV.

[0213] <Comparative Example 3> <Preparation of Dispersion for SiC Sintered Body> 88.24 g of the 25% by mass SiC particle aqueous dispersion obtained above, 9.60 g of the 20% by mass alumina particle aqueous dispersion, 79.98 g of a 20% by mass hydroxyl group-containing polyvinyl acetal resin (a resin containing hydroxyl groups, degree of polymerization approximately 600, weight-average molecular weight 13,000) aqueous dispersion, 8.00 g of polyethylene glycol (PEG200, number-average molecular weight: 200, weight-average molecular weight less than 1000) as a plasticizer, 2.15 g of an antifoaming agent (acetylene glycol EO adduct), and 1.51 g of pure water were stirred for 3 minutes at 500 rpm using a rotation-and-revolution type mixer (Hi-Rotor, HR003-02V, manufactured by Mitsuboshi Industrial Co., Ltd.) to obtain dispersion 4a. Next, the dispersion 4a obtained above and 19.50 g of an aqueous dispersion of 20% by mass PDDA-coated BN particles were stirred for 3 minutes at 500 rpm using a rotating / revolving mixer to obtain dispersion 4b. Next, the dispersion 4b obtained above and 6.40 g of an aqueous dispersion of 20% by mass yttria particles were stirred for 3 minutes at 500 rpm using a rotating / revolving mixer to obtain dispersion 4c.

[0214] The above dispersion 4c had a pH of 3.7 and was used as the dispersion for the SiC sintered body in Comparative Example 3.

[0215] The amounts of each raw material used in Comparative Example 3 are shown in Table 1. The zeta potential of the SiC particles in the SiC sintered body dispersion of Comparative Example 3 was 27.8 mV, and the zeta potential of the PDDA-coated BN particles was 34.7 mV.

[0216] [Average Secondary Particle Diameter of Ceramic Particles] The average secondary particle diameter of the ceramic particles was measured as the volume-averaged particle diameter using the dynamic light scattering method with the MT3300 laser diffraction / scattering particle size distribution analyzer manufactured by MICROTRAC. The average secondary particle diameter of each ceramic particle is shown in the section on the preparation of each ceramic particle dispersion.

[0217] [Zeta Potential Measurement of Ceramic Particles] In each example and comparative example, the aluminum hydroxide-coated SiC particle aqueous dispersion (Solution 1) or SiC particle aqueous dispersion (Solution 1), and BN particle aqueous dispersion (Solution 3) used were each diluted with pure water, and zeta potential measurement solutions of any desired pH were prepared using 0.01 to 0.1 M NaOH and HCl as pH adjusters. That is, in each example and comparative example, the pH of the zeta potential measurement solution was adjusted to match the pH of the dispersion finally obtained by mixing Solutions 1 to 4. Here, the pH was measured at 25°C using a pH meter (model number: F-71) manufactured by Horiba, Ltd.

[0218] The zeta potential of the ceramic particles was measured using a zeta potential measuring device (product name "Zetasizer nano ZSP") manufactured by Malvern Instruments. Here, the zeta potential was measured using typical particle conditions: a refractive index of 1.760 and an absorptive value of 0.300 for alumina, a refractive index of 2.170 and an absorptive value of 0.720 for BN, and a refractive index of 2.650 and an absorptive value of 0.900 for SiC. The zeta potential of each ceramic particle in the SiC sintered dispersion is shown in the section on preparation of the SiC sintered dispersion in Examples 1-3 and Comparative Examples 1-3.

[0219] [Measurement of Isoelectric Point of Ceramic Particles] The pH at which SiC particles and BN particles reach their isoelectric point (pH of the isoelectric point) was calculated by preparing zeta potential measurement solutions with pH samples ranging from 3.0 to 10.0 in increments of 1.0, measuring the pH of the zeta potential measurement solutions at the above pH range of 3.0 to 10.0 in increments of 1.0, and calculating the pH at the time the sign of the zeta potential changed, along with the zeta potential at the preceding and following pH values, using the formula described above.

[0220] The pH values ​​at which the isoelectric point of the SiC particles used in each example and comparative example were 4.5 for SiC particles without charge control and 8.7 for SiC particles coated with aluminum hydroxide. The pH at which the isoelectric point of the BN particles was 9.6 for BN particles coated with PDDA.

[0221] [Weight-average molecular weight measurement of resin] The weight-average molecular weight (Mw) of the resin (resin containing hydroxyl groups) contained in the SiC sintered body dispersion was measured by gel permeation chromatography (GPC) under the following measurement conditions, as a value converted to polyethylene oxide: <<GPC measurement conditions>> Sample concentration: 0.1% by mass Column: "TSKgel® GMPWXL" manufactured by Tosoh Corporation Detector: Differential refractometer Eluent: 100 mM sodium nitrate aqueous solution Flow rate: 1 mL / min Measurement temperature: 40°C Sample injection volume: 200 μL Measurement device: "HLC-8320GPC" manufactured by Tosoh Corporation.

[0222] Table 1 below shows the composition ratio (parts by mass) of each raw material in the SiC sintered body dispersions of Examples 1 to 3 and Comparative Examples 1 to 3, and Table 2 below shows the composition ratio (mass%) of each component. A blank space indicates that the component is not present.

[0223]

[0224]

[0225] The SiC sintered dispersions of Examples 1-3 and Comparative Examples 1-3 were left to stand at 25°C, and the pH and viscosity after a predetermined time were measured according to the method described below. The measurement results are shown in Table 3 below. Furthermore, the results of Examples 1-3 and Comparative Examples 1-3 from Table 3 are shown in Figure 1 as a graph of viscosity change over time (x axis: time, y axis: viscosity), and in Figure 2 as a graph of pH change over time (x axis: time, y axis: pH).

[0226] [pH Measurement] The pH of the SiC sintered dispersion was measured at 25°C using a pH meter (model number: F-71) manufactured by Horiba, Ltd.

[0227] [Viscosity Measurement] The viscosity of the SiC sintered dispersion was measured at 25°C using a Type B viscometer manufactured by Toki Sangyo Co., Ltd. (Model No.: TVB-10, Rotor No. 27, Rotor rotation speed: 6 rpm, Measurement time: 45 seconds).

[0228]

[0229] The dispersions prepared in Examples 1-3 and Comparative Examples 1-3 all exhibited good dispersibility. As shown in Table 3 and Figures 1 and 2, the dispersions prepared in Examples 1-3 had an initial viscosity of 1.5 Pa·s or less, yielding low-viscosity dispersions for SiC sintered bodies. Furthermore, the dispersions for SiC sintered bodies prepared in Examples 1-3 showed little change in pH and viscosity over time, indicating good stability of viscosity and pH over time. The dispersion prepared in Comparative Example 1 using yttria particles had an initial viscosity of 1.5 Pa·s or less, but the pH and viscosity increased significantly over time, resulting in insufficient stability of viscosity and pH over time. The dispersions prepared in Comparative Examples 2 and 3 had an initial viscosity exceeding 1.5 Pa·s.

[0230] [Preparation of Green Sheets and Prepreg Materials] <Example 4> <Preparation of Green Sheets> The dispersion obtained from Example 1 was kneaded under vacuum for 10 minutes using a rotary-orbit mixer (Hi-Rotor, HR003-02V, manufactured by Mitsuboshi Industrial Co., Ltd.) to obtain a coating liquid for green sheet formation (dispersion for green sheet formation). This coating liquid for green sheet formation was applied to a PET film (thickness: 100 μm) using an applicator with a 1000 μm gap to a wet film thickness of 1000 μm, and a green sheet was obtained by sheet molding. Two green sheets were produced in the same manner. The obtained green sheets had a uniform film thickness, and no aggregated particles were observed inside.

[0231] 《Manufacturing of Prepreg Material》 A prepreg material was obtained by laminating the single green sheet obtained above with SiC fiber woven fabric.

[0232] <<Sintering of Green Sheets and Prepreg Materials and Evaluation of Molded Products>> The green sheets and prepreg materials obtained above were sintered using a vacuum hot press (manufactured by Fuji Denpa Kogyo Co., Ltd.) under uniaxial pressure to sinter the SiC particle powders contained in them, thereby producing molded products containing sintered bodies of SiC particle powders. The sintering conditions were a sintering hold temperature of 1400°C or higher, a pressure of 5 MPa or higher, a sintering hold time of 60 minutes or more, and an argon atmosphere. During sintering, the temperature was measured at 2-second intervals using a thermocouple thermometer attached to the apparatus. Each of the resulting molded products was homogeneous with no aggregated particles inside.

[0233] This application is based on Japanese Patent Application No. 2024-170078, filed on 30 September 2024, the disclosures thereof being incorporated herein by reference in their entirety.

Claims

1. A dispersion for a silicon carbide sintered body, comprising: silicon carbide particles whose charge is controlled so that their surface is positively charged; a water-soluble first metal compound containing one or more first metals selected from the group consisting of rare earth elements, zirconium, and aluminum; a resin having hydroxyl groups; and water.

2. The dispersion according to claim 1, wherein the pH is 6.0 or less.

3. The dispersion according to claim 1 or 2, wherein the silicon carbide particles are charge-controlled by aluminum hydroxide coating.

4. The dispersion according to claim 1 or 2, wherein the first metal contained in the first metal compound is selected from the group consisting of yttrium, zirconium, and aluminum.

5. The dispersion according to claim 1 or 2, wherein the resin having hydroxyl groups comprises at least one resin selected from the group consisting of polyvinyl alcohol resin, hydroxyl group-containing polyvinyl acetal resin, hydroxyl group-containing glyoxal resin, hydroxyl group-containing acrylic resin, phenolic resin, hydroxyl group-containing polyvinylpyrrolidone, hydroxyl group-containing polyester resin, hydroxyl group-containing silicone resin, and hydroxyl group-containing polycarboxylic acid.

6. The dispersion according to claim 1 or 2, further comprising boron nitride particles.

7. A green sheet for a silicon carbide sintered body, formed from the dispersion described in claim 1.

8. A prepreg material for a silicon carbide sintered body, formed from the green sheet for silicon carbide sintered body described in claim 7.

9. A silicon carbide sintered body formed from the silicon carbide sintered body prepreg material described in claim 8.

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