Inorganic molded body

Abstract

To provide an inorganic molded body having good workability into a furnace and less shape change at high temperature.SOLUTION: An inorganic molded body comprises: 100 pts.mass in total of 30 to 100 pts.mass of alumina-based fiber having an alumina content ratio of 60 mass% or more and 0 to 70 pts.mass of mullite particles; and an inorganic binder. The bulk density is 130 kg / m3 or more and 1700 kg / m3 or less. It is preferable that the alumina-based fiber include two or more kinds of the alumina-based fibers having different average fiber lengths.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an inorganic molded body. More specifically, it relates to an inorganic molded body with good workability in a furnace and little shape change at high temperatures.

Background Art

[0002] Conventionally, heat treatment in the manufacture of electronic components and the like has been carried out by firing in an industrial furnace. In particular, as a heat insulating material to be installed inside an industrial furnace for high-temperature firing, those with good workability, low heat capacity and low thermal conductivity, and little shape change during heating are required. Here, an inorganic molded body containing alumina fibers with an alumina content of 60% by mass or more, alumina particles, and an inorganic binder has been proposed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide an inorganic molded body with good workability in a furnace and little shape change at high temperatures by a composition and method different from the conventional ones.

Means for Solving the Problems

[0005] The present invention is as follows. 1. A total of 100 parts by mass of 30 to 100 parts by mass of alumina fibers with an alumina content of 60% by mass or more and 0 to 70 parts by mass of mullite particles, and an inorganic binder, with a bulk density of 130 kg / m 3 or more and 1700 kg / m 3An inorganic molded body characterized by the following. 2. The inorganic molded body according to 1., wherein the alumina fiber contains two or more kinds of the alumina fibers having different average fiber lengths.

Effects of the Invention

[0006] The inorganic molded body of the present invention has good workability in a furnace and little shape change at high temperatures.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0008] Hereinafter, the present invention will be specifically described. The "inorganic molded body" of the present invention is not particularly limited as long as it is a molded body mainly composed of alumina fibers. For example, it can be a molded body such as a mat, board with a thickness of about 20 to 50 mm, a sheet with a thickness of about 2 to 3 mm, or a paper with a thickness of 0.4 mm or less.

[0009] The inorganic molded body of the present invention contains 30 to 100 parts by mass of alumina fibers having an alumina content of 60% by mass or more, 0 to 70 parts by mass of mullite particles, a total of 100 parts by mass, and an inorganic binder.

[0010] (1) Alumina fibers, mullite particles The inorganic molded body of the present embodiment contains 30 to 100 parts by mass of alumina fibers and 0 to 70 parts by mass of mullite particles, and the total thereof is 100 parts by mass. For example, a combination of 30 parts by mass of alumina fibers and 70 parts by mass of mullite particles may be used, or only 100 parts by mass of alumina fibers may be used.

[0011] (1-1) Alumina fibers The alumina fiber is a component that forms the skeleton of the inorganic molded body of the present invention. When the total amount of the alumina fiber is 100% by mass, the alumina content is 60% by mass or more. That is, there is no particular limitation as long as the alumina content is 60% by mass or more, and it may be 70% by mass or more, or may be 75% by mass or more. The components other than alumina are not particularly limited, and examples thereof include silica, zirconia, calcia, magnesia, etc. Among these, silica is preferable. The inorganic molded body of the present invention may contain only one kind of alumina fiber having the same alumina content as the alumina fiber, or may contain two or more kinds of alumina fibers having different alumina contents. Further, the inorganic molded body of the present invention may contain an alumina fiber that has been heat-treated at 1000 ° C or higher, preferably 1200 ° C or higher, as the alumina fiber. Furthermore, the inorganic molded body of the present invention may contain, as the alumina fiber, an alumina fiber from which shots have been removed by, for example, air classification, water sieving, etc., although there is no particular limitation. There is no particular limitation on the shot rate, but for example, it may contain 0.1% or less of shots of 45 μm or more remaining on a sieve with a nominal size of 45 μm according to JIS-Z-8801. The "alumina fiber" according to the present embodiment is composed of a pulverized product obtained by pulverizing a cotton-like or blanket-like alumina fiber by the method described below.

[0012] The average fiber length of the alumina fiber is not particularly limited, but it is preferably composed of two or more kinds of alumina fibers having different average fiber lengths. For example, it can be composed of two kinds of alumina fibers, a first alumina fiber having a long average fiber length and a second alumina fiber having a short average fiber length. The average fiber length of the first alumina fiber is not particularly limited, but is preferably 200 μm or more, and more preferably 200 to 1000 μm. The average fiber length of the second alumina fiber is also not particularly limited, but is preferably 30 to 200 μm, and more preferably 50 to 180 μm. The average fiber length can be, for example, the value obtained by randomly selecting a plurality of alumina fibers whose both ends can be confirmed in the monitor image of the alumina fibers observed by an optical microscope and calculating the arithmetic average of the lengths of the selected alumina fibers.

[0013] The ratio of the first alumina fiber to the second alumina fiber is not particularly limited, but it is preferably a total of 100 parts by mass of 30 to 90 parts by mass of the first alumina fiber and 10 to 70 parts by mass of the second alumina fiber.

[0014] The average fiber diameter of the alumina fiber is not particularly limited, but it is preferably 2 to 10 μm, and more preferably 3 to 7 μm.

[0015] The method for pulverizing the alumina fiber is not particularly limited, but it can be carried out by the following method. As a dry method, examples include cutters such as rotary cutters, pulverizing mills such as pin mills and hammer mills, presses such as roller presses, and pulverizing methods using picker rolls. As a method that can be used either dry or wet, pulverization by a ball mill is exemplified. As a wet method, pulverizing methods using a pulper and a high-speed disintegrator are exemplified. These methods may be used alone or in combination. For example, a hammer mill can be preferably used for the preparation of the first alumina fiber, and a roller press can be preferably used for the preparation of the second alumina fiber.

[0016] (1-2) Mullite particles The type of the mullite particles is not particularly limited, but it is a synthetic mullite with a mass ratio of Al2O3:SiO2 = 70 to 78:22 to 30, and the particle size is preferably 325 mesh or less (about 45 μm or less). With this particle size, the cohesiveness and moldability are good and preferable. The specific gravity (true specific gravity) of the mullite particles is not particularly limited, but it is preferably 3.00 to 3.20, and more preferably 3.10 to 3.15. Also, the coefficient of thermal expansion (×10-6) of mullite particles is preferably 5.0 to 6.0, more preferably 5.5 to 5.8, in the range of 20 to 800°C. Furthermore, it is preferably 6.0 to 7.0, more preferably 6.4 to 6.7, in the range of 20 to 1500°C.

[0017] (2) Inorganic binder The inorganic binder serves as a binder for bonding alumina fibers and mullite particles, or alumina fibers to each other. The type of the inorganic binder is not particularly limited as long as it can serve the above role, and examples thereof include colloidal silica, alumina sol, zirconia sol, and bentonite, with colloidal silica and alumina sol being particularly preferred. The inorganic binder may include one kind or two or more kinds. Colloidal silica includes alkali-type colloidal silica, acidic-type colloidal silica, cationic colloidal silica, anionic colloidal silica, etc. Also, commercially available alumina sols with different stabilizers, particle shapes, crystal forms, etc. can be used. Further, alumina sol can also act as a fixing agent for the organic binder described later. The inorganic molded body of the present invention may further contain an inorganic fixing agent. The inorganic fixing agent is not particularly limited, and for example, it may contain aluminum sulfate, ammonium sulfate. Colloidal silica, alumina sol, zirconia sol, bentonite, etc., which are inorganic binders, become dry solids when dried, and further, when heat-treated, they serve as inorganic binders through crystallization, chemical reactions, etc.

[0018] The proportion of the inorganic binder in the inorganic molded body of the present invention is not particularly limited, but it is preferably contained in an amount of 3 to 25 parts by mass based on a total of 100 parts by mass of 30 to 100 parts by mass of alumina fibers and 0 to 70 parts by mass of mullite particles. If it is less than 3 parts by mass, the strength of the inorganic molded body of the present invention becomes weak, and if it is contained in an amount of 25 parts by mass, the strength of the inorganic molded body of the present invention is usually sufficient.

[0019] (3) Other components The inorganic molded body of the present invention can contain the following other components. However, it may be a component that is contained in the molded body and partially or entirely disappears by heating, such as an organic binder or the like. (3-1) Organic binder The organic binder, like the inorganic binder, serves as a binder that binds alumina fibers and mullite particles, or alumina fibers to each other. It can also act as a fixing agent for the inorganic binder. Examples of the organic binder include starch, acrylic resin, latex emulsion, synthetic resin fiber, natural fiber, and thermosetting resin. There is no particular limitation on the starch, and examples include cationic starch, anionic starch, and amphoteric starch. There is no particular limitation on the acrylic resin, and examples include cationic, anionic, and amphoteric polyacrylamide-based paper strength agents. Further, it may contain aluminum sulfate as an inorganic fixing agent. There is no particular limitation on the latex emulsion, and examples include acrylate-based latex, acrylonitrile-butadiene-based latex, and styrene-butadiene-based latex. Further, it may contain aluminum sulfate as an inorganic fixing agent. There is no particular limitation on the synthetic resin fiber, and examples include polyethylene fiber, polypropylene fiber, core-sheath fiber of polyethylene / polypropylene, polyvinyl alcohol fiber, acrylic fiber, aramid fiber, and microfiber-like synthetic resin fiber. The synthetic resin fiber plays a role as a binder by entanglement due to heat melting or fibrillation. Examples of the natural fiber include pulp, hemp, paulownia, microfiber-like cellulose, and cellulose nanofiber. The natural fiber plays a role as a binder by entanglement due to fibrillation. Examples of the thermosetting resin include phenol resin, epoxy resin, melamine resin, and urea resin. It plays a role as a binder by thermosetting. The organic binder may contain one or more kinds.

[0020] As described above, the organic binder can also act as a fixing agent for the inorganic binder. For example, an anionic acrylic resin can be added as a fixing agent to alumina sol, which is an inorganic binder. Further, cationic starch can be added as a fixing agent to anionic colloidal silica, which is an inorganic binder.

[0021] The proportion of the organic binder in the inorganic molded body of the present invention is not particularly limited, but it is preferably contained in an amount of 3 to 15 parts by mass with respect to a total of 100 parts by mass of 30 to 100 parts by mass of alumina fibers and 0 to 70 parts by mass of mullite particles. If it is less than 3 parts by mass, the strength of the inorganic molded body of the present invention becomes weak, and if it is contained in an amount of 15 parts by mass, the strength of the inorganic molded body of the present invention is usually sufficient.

[0022] (3-2) Polymer flocculant The polymer flocculant is not particularly limited, and examples thereof include cationic, anionic, and nonionic flocculants of polyacrylamide-based polymers. It can further strengthen the aggregation of the slurry and serves as a yield improver for alumina fibers, mullite particles, inorganic binders, and organic binders.

[0023] (3-3) Surfactant When the inorganic molded body of the present invention contains a surfactant, it can be excellent in flexibility. Examples of the surfactant include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, and the like.

[0024] The bulk density of the inorganic molded body of the present invention can be increased by pressing. By increasing the bulk density, the strength of the molded body can be increased. The specific pressing method will be described in <Method for producing an inorganic molded body> below.

[0025] In addition, the inorganic molded body of the present invention can be heat-treated at 600°C or higher. By doing so, the organic components are removed, and the dimensional stability of the inorganic molded body at high temperatures can be improved. Inorganic binders such as colloidal silica, alumina sol, zirconia sol, and bentonite become dry solids when dried, and further heat treatment causes them to play the role of an inorganic binder through crystallization, chemical reactions, etc. The specific heat treatment method will be described in the <Method for manufacturing an inorganic molded body> below.

[0026] Furthermore, the inorganic molded body can be impregnated with colloidal silica and / or alumina sol. By doing so, the adhesion strength between the fibers of the inorganic molded body can be further increased.

[0027] The inorganic molded body has a bulk density of 130 kg / m 3 or more and 1700 kg / m 3 or less. There is no particular limitation within this range, but it is more preferably 150 kg / m 3 or more and 1300 kg / m 3 or less. If the bulk density is less than 130 kg / m 3 , the handling strength becomes weak, and if it is 1700 kg / m 3 or more, it is sufficient for normal use.

[0028] <Method for manufacturing an inorganic molded body> The method for manufacturing the inorganic molded body of the present invention is not particularly limited as long as the above-mentioned "inorganic molded body" can be manufactured, but it includes a slurry preparation step of dispersing a raw material containing 30 to 100 parts by mass of alumina fibers, 0 to 70 parts by mass of mullite particles, a total of 100 parts by mass, and an inorganic binder in water to prepare a slurry, and a dehydration molding step of dehydrating and molding the slurry by a papermaking machine or using a mold.

[0029] (1) Slurry preparation step The slurry preparation step can consist of a mixing step and a concentration adjustment step. (Mixing step) The mixing step is a process of dispersing and mixing a raw material containing 30 to 100 parts by mass of alumina fibers, 0 to 70 parts by mass of mullite particles, with a total of 100 parts by mass, and an inorganic binder (hereinafter, also simply referred to as "raw material") in water. The ratio of the inorganic binder is not particularly limited, but it can contain 3 to 15 parts by mass with respect to the total of 100 parts by mass. Also, the raw material is not particularly limited, but it can contain 3 to 15 parts by mass of an organic binder. Further, the raw material can contain the above-mentioned polymer flocculant, surfactant, etc.

[0030] Here, the alumina fibers can include two or more types of the alumina fibers having different average fiber lengths. For example, it can be composed of two types, namely, a first alumina fiber having an average fiber length of 400 μm and a second alumina fiber having an average fiber length of 70 μm. The ratio of the first alumina fiber and the second alumina fiber is not particularly limited, but the total of 100 parts by mass can be 30 to 90 parts by mass of the first alumina fiber and 10 to 70 parts by mass of the second alumina fiber.

[0031] Specifically, a predetermined amount of water is stored in a pulper (stirrer), and the above-mentioned raw material is charged and stirred and mixed. The water is not particularly limited, and examples thereof include distilled water, tap water, groundwater, industrial water, etc. The concentration of the raw material is not particularly limited, but when the total of the raw material solid content and water is 100% by mass, it is preferably 1 to 5% by mass of the raw material solid content, and more preferably 2 to 4% by mass.

[0032] (Concentration adjustment step) The concentration adjustment step is a process of further adding water to the mixed liquid obtained by mixing the raw materials, mixing to adjust the concentration, and obtaining a slurry having a predetermined concentration. Specifically, the raw material after being stirred in a pulper is pumped to a chest tank, and further water is also added, whereby a slurry having a predetermined concentration is obtained. The obtained slurry is fed to a slurry storage tank. In this case, in order to further lower the concentration, further water may be added and fed to the slurry storage tank. The water is not particularly limited, and the aforementioned water can be used. The concentration of the slurry is not particularly limited, but when the total slurry is 100% by mass, the solid content of the raw material is 0.1 to 5% by mass, more preferably 0.1 to 4% by mass, and particularly preferably 0.1 to 3% by mass. When the slurry concentration is less than 0.1% by mass, the amount of water to be removed in the dehydration forming process becomes too large, resulting in poor working efficiency. When it exceeds 5% by mass, it becomes difficult for the solid content to be uniformly dispersed in the slurry.

[0033] (2) Dehydration forming process The dehydration forming process is a process of dehydrating and forming the slurry obtained in the slurry preparation process by a papermaking machine or dehydration forming using a mold. To perform dehydration forming by a papermaking machine, for example, when the slurry is passed through a wire mesh in a slurry storage tank, most of the moisture passes through the wire mesh, and a formed body adheres and accumulates on the wire mesh. To perform dehydration forming using a mold, for example, in a slurry storage tank, the slurry is allowed to flow into a forming mold provided with a net, and moisture is sucked from the net surface by a vacuum pump or the like to form a dehydrated body on the forming mold. An inorganic formed body can be obtained by drying the formed body or dehydrated body obtained above. The drying temperature is not particularly limited, but is preferably 50 to 150 °C, more preferably 70 to 130 °C, and particularly preferably 80 to 120 °C.

[0034] (3) Other processes In the <method for manufacturing an inorganic formed body>, the following processes can be further provided. (3-1) Pressing process Before drying in the (2) dehydration forming process, a pressing process can be provided in which the obtained formed body or dehydrated body is pressed. By pressing, the bulk density of the inorganic formed body can be increased. The method and apparatus for pressing are not particularly limited, and examples include a flat press and a roller press. Also, if the bulk density can be increased, it can be performed by hand using a flat plate or a hand roller.

[0035] (3-2) Heat treatment process A heat treatment process can be provided in which heat treatment is performed at 600 °C or higher after drying in the (2) dehydration and forming process or after drying after the (3-1) pressing process. By performing the heat treatment, the organic components contained in the inorganic molded body can be evaporated and removed. In addition, the dimensional stability of the inorganic molded body at high temperatures can be improved. Colloidal silica, alumina sol, zirconia sol, bentonite, etc., which are inorganic binders, become dry solids when dried, and further, when heat-treated, they play a role as inorganic binders due to crystallization, chemical reactions, etc. The method and apparatus for heat treatment are not particularly limited, and for example, they can be performed by methods such as firing in an electric furnace or a gas furnace. Also, the firing temperature is not particularly limited, and for example, it can be 800 °C, 1200 °C, 1400 °C, 1600 °C. When alumina and silica, which are inorganic binders in the inorganic molded body, undergo a chemical reaction during firing at 1200 °C or higher, mullite is generated.

[0036] (3-3) Impregnation process An impregnation process of impregnating colloidal silica and / or alumina sol can be provided. By impregnating colloidal silica and / or alumina sol, the strength of the inorganic molded body can be further increased. The method and apparatus for impregnation are not particularly limited, and for example, they can be performed by methods such as immersing from the surface of the inorganic molded body by dipping, showering, etc., and attaching to the surface of the inorganic molded body by brushing coating, roller coating, etc. The impregnation process can be performed in the following stages. (a) In the (2) dehydration and forming process, (during dehydration before drying) and / or after drying (b) In the (3-1) (during dehydration before the pressing process) and / or (after drying after the pressing process) (c) Before and / or after the (3-2) heat treatment process In addition, in (a) to (c), when the impregnation process is the final one, further re-drying is performed. The temperature of the re-drying is not particularly limited, but is preferably 50 to 150 °C, more preferably 70 to 130 °C, and particularly preferably 80 to 120 °C.

[0037] The raw materials according to the method for producing the inorganic molded body of the present invention are the same as the alumina fibers, mullite particles, inorganic binders, and other components in the above-mentioned "inorganic molded body", as described above.

Examples

[0038] Hereinafter, the present invention will be described in more detail based on examples. The following examples are illustrative and do not limit the present invention. [Raw materials of test samples] Raw materials according to Examples (1-1) to (20) and Reference Examples (1-1) to (10) shown in Tables 1 to 10 were prepared to prepare slurries. Details of each component of the raw materials are as follows. The pulverized alumina fiber product was obtained by pulverizing alumina fibers (trade name: MAFTEC (registered trademark) Blanket: product number MLS (manufactured by Maftec Co., Ltd.)) having an average fiber diameter of 5 to 7 μm and an Al2O3:SiO2 = 72:28 (mass ratio) with a hammer mill to obtain a test product with an average fiber length of 393.3 μm as the first alumina fiber. Also, as the second alumina fiber, the same alumina fiber was pulverized with a roller press to obtain a test product with an average fiber length of 73.3 μm. Here, the average fiber length is a value obtained by randomly selecting 300 to 350 alumina fibers whose both ends can be confirmed in the monitor image of the alumina fibers observed by an optical microscope and calculating the arithmetic average of the lengths of the selected alumina fibers. Synthetic mullite with Al2O3:SiO2 = 71.26:27.44 (mass ratio): product number MMS (manufactured by Itochu Ceramics Co., Ltd.) was used as the mullite particles. Fine alumina with an average particle diameter of 4 μm: SA34 (manufactured by Nippon Light Metal Co., Ltd.) was used as the alumina particles. Colloidal silica as an inorganic binder used amorphous silica 30% by mass (trade name: Snowtex 30 (manufactured by Nissan Chemical Industries, Ltd.)). As the organic binder, starch, cationic starch: product number Ace-din HP-150 (manufactured by Daiwa Chemical Industry Co., Ltd.) was used.

[0039] Using the above raw materials, as examples, combinations of first alumina fibers and mullite particles, combinations of first alumina fibers and second alumina fibers, and as reference examples, combinations of first alumina fibers and alumina particles were each used to prepare inorganic molded body test pieces (hereinafter simply referred to as "test pieces"), and their physical properties were evaluated.

[0040] [1] Combination of first alumina fibers and mullite particles [Test pieces of Examples (1-1) and (1-2)] Test pieces were prepared for the raw materials of Examples (1-1) and (1-2) shown in Table 1 according to the following procedure respectively.

[0041] (A) Preparation of test pieces (A-1) Slurry preparation process 2.70 kg of first alumina fibers, 0.30 kg of mullite particles, 90 g (in terms of solid content) of colloidal silica, and 90 g (in terms of solid content) of starch were put into a plastic container filled with water and stirred. Further water was added to make the total volume 100 L, and then stirred again to obtain a slurry with a concentration of 3 mass% (in terms of the total solid content of the first alumina fibers and mullite particles). To 10 L of the obtained slurry, 20 L of water was further added to make it 30 L, and then stirred to obtain a test slurry with a concentration of 1 mass% (in terms of the total solid content of the first alumina fibers and mullite particles). (A-2) Dehydration molding process 30 L of the test slurry was poured into a molding die with a water storage tank equipped with a stainless steel mesh, and moisture was sucked by a vacuum pump in the direction of the mesh surface to form a flat dehydrated body on the mesh surface of the molding die. Next, the dehydrated body was transferred to a dryer and dried at 100 °C for 12 hours to obtain a test molded body. Then, the obtained test molded body was polished and cut to obtain two test pieces (thickness 25 mm × width 240 mm × length 240 mm) for measuring surface hardness and bulk density, which were used as the test pieces of Examples (1-1) and (1-2).

[0042] (B) Evaluation of test pieces The evaluation criteria were as follows. Regarding the surface hardness, the hardness of the upper and lower surfaces of the test piece was measured 4 times each using a durometer (manufactured by Teclock Corporation, model: GS-70IN), and the average value was taken. Regarding the bulk density, the bulk density of the test piece was calculated by dividing the mass of the test piece by the volume obtained from the outer dimensions. The criteria for this evaluation were the same in the following examples.

[0043] [Test pieces of Examples (2-1) and (2-2)] In the slurry preparation step (A-1), except that 1.65 kg of the first alumina fiber and 1.35 kg of mullite particles were used, and 15 L of water was further added to 15 L of the obtained slurry to make it 30 L, and the mixture was stirred to obtain a test slurry with a concentration of 1.5 mass% (in terms of the total solid content of the first alumina fiber and mullite particles), it was the same as the preparation of the test piece in (A). [Test pieces of Examples (3-1) and (3-2)] In the slurry preparation step (A-1), except that 0.9 kg of the first alumina fiber and 2.1 kg of mullite particles were used, and 40 L of the obtained slurry was used to obtain a test slurry with a concentration of 3 mass% (in terms of the total solid content of the first alumina fiber and mullite particles), it was the same as the preparation of the test piece in (A).

[0044]

Table 1

[0045] <Test results> It was found that from Examples (1-1) to (3-2) shown in Table 1, as the ratio of mullite particles to the first alumina fiber increased, both the surface hardness and the bulk density increased.

[0046] [Test specimens of Examples (4-1) and (4-2), test specimens of Examples (5-1) and (5-2), test specimens of Examples (6-1) and (6-2)] In the test specimens of Examples (1-1) and (1-2), the test specimens of Examples (2-1) and (2-2), and the test specimens of Examples (3-1) and (3-2), respectively, except that 7 parts by mass of colloidal silica and 7 parts by mass of starch were used, they were the same as the preparation of the test specimens of (A).

[0047]

Table 2

[0048] <Test results> It was found that from Examples (4-1) to (6-2) shown in Table 2, as the ratio of mullite particles to the first alumina-based fiber increases, both the surface hardness and the bulk density increase.

[0049] [Test specimens of Examples (7-1) and (7-2), test specimens of Examples (8-1) and (8-2), test specimens of Examples (9-1) and (9-2)] In the test specimens of Examples (1-1) and (1-2), the test specimens of Examples (2-1) and (2-2), and the test specimens of Examples (3-1) and (3-2), respectively, except that 15 parts by mass of colloidal silica and 15 parts by mass of starch were used, they were the same as the preparation of the test specimens of (A).

[0050]

Table 3

[0051] <Test results> It was found that from Examples (7-1) to (9-2) shown in Table 3, as the ratio of mullite particles to the first alumina-based fiber increases, both the surface hardness and the bulk density increase. Also, from Tables 1 to 3, when the ratio of the first alumina fiber to the mullite particles is the same, except for Examples (9-1) and (9-2), it was found that both the surface hardness and the bulk density increase as the ratio of colloidal silica and starch increases.

[0052] [2] Combination of the first alumina fiber and the second alumina fiber [Test specimens of Examples (10-1) to (12-2), test specimens of Examples (13-1) to (15-2), test specimens of Examples (16-1) to (18-2)] For the test specimens of Examples (10-1) to (12-2), in Examples (1-1) to (3-2), for the test specimens of Examples (13-1) to (15-2), in Examples (4-1) to (6-2), and for the test specimens of Examples (16-1) to (18-2), in Examples (7-1) to (9-2), the mullite particles were respectively replaced with the second alumina fiber, and the others are the same.

[0053]

Table 4

[0054]

Table 5

[0055]

Table 6

[0056] <Test Results> It was found that both the surface hardness and the bulk density increase as the ratio of the second alumina fiber to the first alumina fiber increases in Examples (10-1) to (18-2) shown in Tables 4 to 6. Furthermore, when the ratio of the first alumina fiber to the second alumina fiber is the same, except for Examples (16-1) and (16-2), it was found that both the surface hardness and the bulk density increase as the ratio of colloidal silica and starch increases.

[0057] [3]Combination of the first alumina fiber and alumina particles (reference example) [Test specimens of reference examples (1-1) to (3-2), test specimens of reference examples (4-1) to (6-2), test specimens of reference examples (7-1) to (9-2)] Regarding the test specimens of reference examples (1-1) to (3-2), in Examples (1-1) to (3-2), regarding the test specimens of reference examples (4-1) to (6-2), in Examples (4-1) to (6-2), regarding the test specimens of reference examples (7-1) to (9-2), in Examples (7-1) to (9-2), mullite particles were replaced with alumina particles, respectively, and the others are the same.

[0058] [Table 7]

[0059] [Table 8]

[0060] [Table 9]

[0061] [Test results] It was found that both the surface hardness and the bulk density increased as the ratio of alumina particles to the first alumina fiber increased in reference examples (1-1) to (9-2) shown in Tables 7 to 9. Also, in the case of 10 parts by mass of alumina particles, it was found that both the surface hardness and the bulk density increased as the proportions of colloidal silica and starch increased (Reference Examples (1-1), (1-2), (4-1), (4-2), (7-1), (7-2)). On the other hand, in the case of 45 parts by mass and 70 parts by mass of alumina particles, the bulk density was maximum when the proportion of colloidal silica and starch was 7 parts by mass, and the surface hardness was maximum when the proportion of colloidal silica and starch was 15 parts by mass (Reference Examples (2-1), (2-2), (5-1), (5-2), (8-1), (8-2) and Reference Examples (3-1), (3-2), (6-1), (6-2), (9-1), (9-2)).

[0062] [4] Comparison of pressed test pieces [Test piece of Example 19] The raw materials having the same formulation as in Examples (5-1) and (5-2) shown in Table 2 were put into a plastic container containing water and stirred, and further water was added to make the total volume 100 L, and further stirred to obtain a slurry having a concentration of 3% by mass (in terms of the total solid content of the first alumina-based fiber and mullite particles). To 30 L of the obtained slurry, 10 L of water was further added to make 40 L, and it was stirred to obtain a test slurry having a concentration of 2.25% by mass (in terms of the total solid content of the first alumina-based fiber and mullite particles). The obtained test slurry was dehydrated by the dehydration forming step (A-2) to obtain a dehydrated body. Furthermore, this dehydrated body was compressed in the thickness direction by a press to obtain a press-formed body. Next, the obtained press-formed body was transferred to a dryer and dried at 100 °C for 12 hours to obtain a test formed body. This test formed body was polished and cut to obtain one test piece (thickness 7 mm × width 240 mm × length 240 mm) for measuring surface hardness and bulk density, which was used as the test piece of Example 19.

[0063] [Test piece of Example 20] Test pieces were prepared using the raw materials having the same formulation as in Examples (14-1) and (14-2) shown in Table 5. Other than the formulation of the raw materials, all were the same as in Example 19. [Test piece of Reference Example 10] Test samples were prepared using the same raw materials as in Reference Examples (5-1) and (5-2) shown in Table 8. Except for the formulation of the raw materials, all other conditions were the same as in Example 19.

[0064]

Table 10

[0065] <Test Results> (a) Surface Hardness For Example 19 (mullite), compared with Example (5-1) without pressing, it was 1.32 - 1.34 times; for Example 20 (second alumina fiber), compared with Example (14-1) without pressing, it was 1.24 - 1.28 times; for Reference Example 10 (alumina particles), compared with Reference Example (5-1) without pressing, it was 1.25 - 1.26 times, resulting in higher surface hardness. (b) Bulk Density For Example 19 (mullite), compared with Example (5-1) without pressing, it was 5.58 times; for Example 20 (second alumina fiber), compared with Example (14-1) without pressing, it was 5.42 times; for Reference Example 10 (alumina particles), compared with Reference Example (5-1) without pressing, it was 4.52 times, resulting in a larger bulk density.

[0066] [5] Thermal Creep Amount For Examples (1-1), (5-1), (6-1), 19 related to mullite particles, Examples (10-1), (14-1), (15-1), 20 related to second alumina fibers, and Reference Examples (1-2), (5-2), (6-2), 10 related to alumina particles, tests on the thermal creep amount were conducted. Although they were the same test samples as the above examples and reference examples, the bulk density was measured again because the cut parts for measuring the thermal creep amount were different. For the examples and reference examples in Tables 11 - 13, to distinguish them from the test samples in [1] - [4] above, a "′" was attached. <Test Method> Measurement of the thermal creep amount: From each of the test pieces [1] to [3] (thickness: 25 mm × width: 240 mm × length: 240 mm) and the test piece [4] (thickness: 7 mm × width: 240 mm × length: 240 mm), one plate-shaped body with a thickness of 7 mm × width of 45 mm × length of 150 mm was cut out and used as a test piece for measuring the thermal creep amount (hereinafter referred to as "creep test piece"). The creep test piece was supported by a pair of support members at positions 15 mm from both ends in the longitudinal direction. Further, a 10 g weight in the shape of a rectangular parallelepiped with a width of 45 mm and a length of 30 mm was placed at the center in the longitudinal direction of the creep test piece. Next, with this weight placed, the creep test piece was heated at 1400 °C for 3 hours. Then, it was cooled to room temperature, and the amount of deflection at the center was measured, and this value was taken as the thermal creep amount (mm).

[0067]

Table 11

[0068]

Table 12

[0069]

Table 13

[0070] <Test Results> From Tables 11 to 13 and FIGS. 1 and 2, it was found that as the ratio of mullite particles, the ratio of the second alumina fiber, and the ratio of alumina particles to the first alumina fiber increase, the bulk density increases and the thermal creep amount decreases. Also, for Examples 19′, 20′, and Reference Example 10′, which are pressed products, it was found that in each case, compared with Examples 5-1′, 14-1′, and Reference Example 5-2′ having the same composition, the bulk density is significantly higher and the thermal creep amount is greatly reduced. Here, the amount of thermal creep in the examples related to mullite particles is generally approximately equivalent to that in the reference examples related to alumina particles. For Example 6-1′, the amount of thermal creep was smaller compared to Reference Example 6-2′ containing alumina particles at the same ratio as the mullite particles. Furthermore, the amount of thermal creep in the examples related to the second alumina fiber was clearly smaller compared to the amount of thermal creep in the reference examples related to alumina particles. That is, Examples 14-1′, 15-1′, and 20′ related to the second alumina fiber all had smaller amounts of thermal creep compared to Reference Examples 5-2′, 6-2′, and 10′ containing alumina particles at the same ratio, respectively. From the above results, it was found that the inorganic molded body containing mullite particles has less shape change at high temperatures than the inorganic molded body containing alumina particles. Also, it was found that the inorganic molded body containing the second alumina fiber clearly has less shape change at high temperatures than the inorganic molded body containing alumina particles.

Claims

1. 100 parts by mass in total of 30 to 100 parts by mass of alumina fibers having an alumina content of 60% by mass or more and 0 to 70 parts by mass of mullite particles, an inorganic binder, and an inorganic molded body containing the same, The bulk density is 130 kg / m ３ or more and 1700 kg / m ３ or less, and the inorganic molded body is characterized by this.

2. The inorganic molded body according to claim 1, wherein the alumina fibers include two or more types of the alumina fibers having different average fiber lengths.

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