Aluminalite porous material and heat treatment component made thereof

Abstract

The object of the present invention is to provide an aluminamlite porous body and a heat treatment component that are excellent in thermal shock resistance, durability, and corrosion resistance. [Solution] An alumina-mulite porous body that satisfies the following conditions (1), (2), (3), and (4). (1) The mass ratio of Al2O3 to SiO2 is 2.50 to 3.10. (2) The crystalline phase consists of two phases, a corundum phase and a mullite phase, and the mass ratio of the corundum phase to the mullite phase is 0.60 to 1.00. (3) The porosity is 25 to 32%. (4) The average pore size is 10 μm or less, and the ratio of the maximum pore size to the average pore size is 70 or less.

Description

Technical Field

[0001] The present invention relates to an alumina-mullite porous body, a heat treatment member made of the alumina-mullite porous body, and a method for producing the alumina-mullite porous body.

Background Art

[0002] In recent years, advanced materials such as electronic materials have been miniaturized and enhanced in performance, and the raw material powders used are required to be finer and of higher purity. In the heat treatment process of raw material powders, corrosion of the heat treatment member used occurs due to evaporation of the components of the powder to be treated during heat treatment, resulting in deterioration of the member, and reduction in stability during long-term use has become a problem. At the same time, in order to suppress fluctuations in the composition of the powder to be treated by heat treatment as much as possible, processes such as increasing the heating and cooling rates are being carried out. However, by increasing the heating and cooling rates, a large load such as thermal stress is applied to the heat treatment member, and the risk of cracks due to thermal shock and deterioration due to repeated heating and cooling increases. For these reasons, a heat treatment member excellent in thermal shock resistance, durability, and corrosion resistance is required.

[0003] For example, Patent Document 1 discloses that by setting a specific average pore size to prevent delamination of the SiC-containing ceramic substrate, the zirconia coating layer on the surface, and the mullite layer, the effectiveness of the kiln tool has been improved even under severe thermal cycles. However, this is a method for controlling the pore size to a specific value to prevent delamination of the zirconia and mullite coating layers, and does not disclose any technical ideas for improving thermal shock resistance or corrosion resistance. Patent Document 2 discloses a ceramic firing tool material made by blending and mixing specific amounts of electrofused alumina, electrofused mullite, and low-soda calcined alumina as aggregates of different particle sizes. However, the purpose of this invention is to create a firing tool material that causes little deformation in the fired object and hardly alters the alumina ceramic molded body during firing, and does not disclose any thermal shock resistance, which is considered more important than corrosion resistance for firing tool materials. Patent Document 3 discloses a lightweight, high-alumina tool using an alumina-based hollow body as the alumina raw material, which satisfies the requirements for a firing tool material in terms of strength and spall resistance. However, because the alumina-based hollow body itself has low strength, when used, for example, as a tube for a rotary kiln, the tube is subjected to high loads, posing a risk of cracking and other problems, making stable use impossible. Patent Document 4 discloses a rotary kiln furnace tube, a type of heat treatment component made of aluminum titanate or aluminum magnesium titanate, which has excellent heat resistance and corrosion resistance and high mechanical strength. However, because thermal decomposition of the crystalline phase occurs at high temperatures, there is a risk in using it as a stable heat treatment component. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-52657 [Patent Document 2] Japanese Patent Publication No. 2003-252677 [Patent Document 3] Japanese Patent Application Publication No. 11-189480 [Patent Document 4] Japanese Patent Publication No. 2005-314170 [Overview of the project] [Problems that the invention aims to solve]

[0005] The object of the present invention is to provide an aluminamlite porous body and a heat treatment component that are excellent in thermal shock resistance, durability, and corrosion resistance. [Means for solving the problem]

[0006] The inventors have diligently conducted research to obtain a heat treatment component made of an alumina-mullite porous material with excellent thermal shock resistance, durability, and corrosion resistance, for use as a heat treatment component for raw materials used in advanced technologies such as electronic materials. As a result, they have found that by setting the Al2O3 / SiO2 mass ratio, corundum phase / mullite phase ratio, porosity, pore size, and pore distribution of the alumina-mullite porous material within a specific range, it is possible to simultaneously improve not only thermal shock resistance but also durability and corrosion resistance compared to conventional porous materials, and furthermore, to increase strength and achieve superior mechanical properties compared to conventional porous materials. In this application, durability refers to resistance to cracking and fracture caused by repeated heating and cooling. The inventors have found that this alumina-mullite porous material can be manufactured by mixing high-purity alumina powder and mullite powder with suppressed particle size in a specific ratio. The present invention has thus been completed.

[0007] In other words, the present invention is defined by the following: [1] An alumina-mulite porous body satisfying the following conditions (1), (2), (3), and (4). (1) The mass ratio of Al2O3 to SiO2 is 2.50 to 3.10. (2) The crystalline phase consists of two phases, a corundum phase and a mullite phase, with the ratio of the corundum phase to the mullite phase being 0.60 to 1.00. (3) The porosity is 25-32%. (4) The average pore diameter is 10 μm or less, and the ratio of the maximum pore diameter to the average pore diameter is 70 or less. [2] A heat treatment member made of the aluminamlite porous material described in [1] above. [3] A method for producing the aluminamlite porous body according to [1], characterized by having the following steps. (a) A step of mixing coarse alumina powder having an alumina purity of 99.6% by mass or more and an average particle size of 200 to 850 μm with fine alumina powder having an alumina purity of 99.7% by mass or more and an average particle size of 5 to 20 μm, such that the mass ratio of the coarse alumina powder to the fine alumina powder (coarse alumina powder / fine alumina powder) is 0.45 to 0.75. (b) A step of mixing and dispersing chamotte powder and clay minerals having an Al2O3 / SiO2 mass ratio of 55 / 45 to 76 / 24, a total content of Al2O3 and SiO2 of 97% by mass or more, and an average particle size of 25 to 300 μm, in the mixture obtained in step (a) above, such that the Al2O3 / SiO2 mass ratio in the mixture, the chamotte powder and the clay minerals as a whole is 2.50 to 3.10. (c) A process in which the mixture obtained in step (b) above is molded and then fired at 1400 to 1650°C. [Effects of the Invention]

[0008] The alumina-mulite porous material of the present invention exhibits excellent thermal shock resistance, durability, and corrosion resistance. Furthermore, heat treatment components using the alumina-mulite porous material of the present invention can be used for heat treatment and firing of various raw material molded bodies and in various firing furnaces due to their excellent thermal shock resistance, durability, and corrosion resistance. The method for manufacturing the alumina-mulite porous material of the present invention can produce the alumina-mulite porous material of the present invention, which exhibits excellent thermal shock resistance, durability, and corrosion resistance. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows a microstructure observation image of the porous material obtained in Example 9. [Figure 2] Figure 2 shows a microstructure observation image of the porous material obtained in Comparative Example 6. [Figure 3] Figure 3 shows a cross-sectional view of Example 2 after the corrosion resistance evaluation. [Figure 4] Figure 4 shows a cross-sectional view of Comparative Example 6 after the corrosion resistance evaluation. [Figure 5] Figure 5 shows the X-ray diffraction pattern of the porous material obtained in Example 9. [Figure 6] Figure 6 shows the X-ray diffraction pattern of the porous material obtained in Comparative Example 9. [Modes for carrying out the invention]

[0010] The alumina-mulite porous material of the present invention is an alumina-mulite porous material that satisfies the following requirements (1), (2), (3), and (4). Each requirement is described below.

[0011] (1) The mass ratio of Al2O3 to SiO2 is 2.50 to 3.10. In the alumina-mullite porous body of the present invention, the mass ratio of Al2O3 to SiO2, i.e., the mass ratio of Al2O3 / SiO2, is 2.50 to 3.10. From the viewpoint of further improving corrosion resistance, the mass ratio of Al2O3 to SiO2 is preferably 2.70 to 3.00, and more preferably 2.80 to 3.00. If the mass ratio of Al2O3 to SiO2 is less than 2.50, the amount of SiO2 component contained in the porous body increases, and it reacts with impurities to form a glass phase or exists as a cristobalite phase, which is undesirable because it reduces corrosion resistance and durability. On the other hand, if the mass ratio of Al2O3 to SiO2 exceeds 3.10, corrosion resistance improves, but the amount of SiO2 component decreases, the amount of corundum phase contained in the porous body increases, and the amount of mullite phase decreases, which is undesirable because it reduces thermal shock resistance and durability. In this case, creep resistance also decreases, so it is undesirable because it becomes more prone to deformation when used at high temperatures for a long time. The content of each component is determined by quantitative analysis of the sample by crushing it into glass beads using X-ray fluorescence analysis. In this invention, impurities include CaO, MgO, Na2O, K2O, TiO2, Fe2O3, etc. The amount of impurities is preferably 2.50% by mass or less, more preferably 2.00% by mass or less, and even more preferably 1.80% by mass or less. If the amount of impurities exceeds 2.50% by mass, corrosion resistance and durability will decrease, which is undesirable.

[0012] (2) The crystalline phase consists of two phases, a corundum phase and a mullite phase, with the ratio of the corundum phase to the mullite phase being 0.60 to 1.00. In the alumina-mullite porous body of the present invention, the crystal phase needs to consist of two phases, the cordierite phase and the mullite phase. The presence of both phases in specific ratios enables it to have the essential properties as a heat treatment member, namely thermal shock resistance, durability, and corrosion resistance. The quantitative ratio of the cordierite phase to the mullite phase in the present invention is 0.60 to 1.00. When the quantitative ratio of the cordierite phase to the mullite phase is less than 0.60, the amount of the mullite phase increases, leading to a decrease in corrosion resistance, which is not preferable. On the other hand, when the quantitative ratio of the cordierite phase to the mullite phase exceeds 1.00, the cordierite phase increases and the mullite phase decreases, resulting in a decrease in thermal shock resistance and durability, which is not preferable. From the perspective of further improving thermal shock resistance, durability, and corrosion resistance, the quantitative ratio of the cordierite phase to the mullite phase is more preferably 0.65 to 0.95.

[0013] The qualitative and quantitative analysis of the crystal phase in the present invention is carried out by X-ray diffraction using the powder obtained by passing the porous body through a 325-mesh sieve as the measurement sample. The content ratio of the cordierite phase is determined by the following formula (i) from the diffraction intensity (IA(113)) of the crystal plane (113) of the cordierite phase (C) and the diffraction intensity (IM(210)) of the crystal plane (210) of the mullite phase (M). The content ratio of the mullite phase is determined by the following formula (ii) from IA(113) and IM(210). The quantitative ratio of the cordierite phase to the mullite phase in the present invention is determined by formula (iii) from the content ratio of the cordierite phase determined by formula (i) and the content ratio of the mullite phase determined by formula (ii). In the alumina-mullite sintered body of the present invention, it is necessary that no distinct crystal peaks indicating crystal phases other than the cordierite phase and the mullite phase are observed by X-ray diffraction measurement. In particular, the cristobalite phase is not preferable as it leads to a deterioration of properties.

[0014]

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[0015]

Number

[0016]

number

[0017] (3) The porosity is 25-32%. In the alumina-mulite porous material of the present invention, thermal shock resistance, durability, and corrosion resistance are required, so the porosity must be 25-32%, and preferably 27-31%. If the porosity is less than 25%, not only does the thermal shock resistance decrease, but repeated heating and cooling causes expansion and contraction, making it easy for strain to occur inside the porous material, resulting in deterioration, cracking, and poor durability, which is undesirable. On the other hand, if the porosity exceeds 30%, thermal shock resistance and other properties decrease, making it unsuitable for use in load-bearing applications, and corrosion and penetration of components into the pores become more likely, leading to a decrease in corrosion resistance, which is also undesirable. In the present invention, porosity refers to apparent porosity and is measured by the Archimedes method (in accordance with JIS R2205).

[0018] (4) The average pore diameter is 10 μm or less, and the ratio of the maximum pore diameter to the average pore diameter is 70 or less. In the alumina-mulite porous body of the present invention, the average pore diameter is the average pore diameter obtained by converting the pore area inherent in the cross-section of the sintered body into an equivalent circular diameter. Specifically, the average pore diameter and the maximum pore diameter in the present invention are measured as follows.

[0019] (Measurement of average pore size and maximum pore size) Alumina-mulite porous material is cut into 20mm x 20mm x 10mm test pieces. After embedding them in resin, they are processed using a surface grinding machine with diamond grinding wheels in the order of #140, #400, and #600 mesh. Surface observation is performed at 30x magnification using a digital microscope, scanning electron microscope, metallurgical microscope, etc., and images are obtained. From the obtained images, an 8mm x 10mm (80mm area) section is selected. 2The image is extracted from the field of view, processed using the analysis software WinROOF2023 (manufactured by Mitani Corporation), and the image is binarized to determine the pore area. The pore diameter is calculated by converting the obtained pore area to an equivalent circle diameter, and the average pore diameter is determined from the number of pores observed. The average of the average values ​​of three randomly observed fields is defined as the average pore diameter in this invention. Furthermore, the pore diameter representing the maximum value of pores in the three observed fields is defined as the maximum pore diameter, and the ratio of the maximum pore diameter to the average pore diameter in this invention is calculated as (maximum pore diameter / average pore diameter).

[0020] In the alumina-mulite porous body of the present invention, the average pore diameter must be 10 μm or less, and the ratio of the maximum pore diameter to the average pore diameter (maximum pore diameter / average pore diameter) must be 70 or less. An average pore diameter exceeding 10 μm is undesirable because it reduces the strength of the porous body. An average pore diameter of 7.5 μm or less is preferable. Furthermore, the lower limit of the average pore diameter in the present invention is preferably around 4.0 μm. The ratio of the maximum pore diameter to the average pore diameter allows for evaluation of the difference between the maximum pore diameter and the average pore diameter, and thus allows for evaluation of the pore diameter distribution. Even if the average pore diameter is within the range of the present invention, if the ratio of the maximum pore diameter to the average pore diameter exceeds 70, the difference between the average pore diameter and the maximum pore diameter becomes large, resulting in large defects in the maximum pore diameter. This is undesirable because it leads to a decrease in strength, resulting in reduced thermal shock resistance and durability, and increased susceptibility to corrosion from components of the treated powder or fired product, thus reducing corrosion resistance. The ratio of the maximum pore diameter to the average pore diameter (maximum pore diameter / average pore diameter) is preferably 60 or less. In the present invention, the lower limit of the ratio of the maximum pore diameter to the average pore diameter is approximately 40.

[0021] The alumina-mullite porous material of the present invention has a bending strength of 20 MPa or more, which is high strength for a porous material, by controlling the Al2O3 / SiO2 mass ratio, the amount ratio of corundum phase to mullite phase, porosity, pore size, and pore distribution within a specific range, that is, by satisfying all of the above requirements (1) to (4). Therefore, it has high thermal shock resistance, corrosion resistance, and durability, and can be used in various heat treatments as an excellent heat treatment component. The heat treatment component in the present invention is not particularly limited as long as it is a component used to heat treat the object to be heat treated, and examples include crucibles, tampans, setters, saggars, furnace tubes, and firing furnace components used in the heat treatment of electronic components, various ceramic materials and raw material powders, metal materials and metal powders, etc. Heat treatment in the present invention includes firing.

[0022] The method for producing the alumina-mullite porous body of the present invention is described below. The method for producing the porous body of the present invention is not particularly limited, but the porous body of the present invention can be produced by the following method. A mixed powder of coarse alumina powder having an alumina purity of 99.6% by mass or more and an average particle size of 200 to 850 μm and fine alumina powder having an alumina purity of 99.7% by mass or more and an average particle size of 5 to 20 μm is mixed with chamotte powder having an Al2O3 / SiO2 mass ratio of 55 / 45 to 76 / 24, a total Al2O3 and SiO2 content of 97% by mass or more, more preferably 98% by mass or more, and an average particle size of 25 to 300 μm. The coarse alumina powder and chamotte powder are important as aggregates for providing thermal shock resistance and durability. In the manufacturing method of the present invention, the coarse alumina powder is not particularly limited as long as it has an alumina purity of 99.6% by mass or more and an average particle size of 200 to 850 μm. Similarly, the fine alumina powder is not particularly limited as long as it has an alumina purity of 99.7% by mass or more and an average particle size of 5 to 20 μm. Examples include pulverized electrofused alumina and pulverized alumina (low soda alumina) produced by the Bayer process. To improve moldability and sinterability, clay mineral powders such as kibushi clay, kaolin clay, and kaolin are added to the alumina and chamotte mixture. The clay mineral components such as kibushi clay, kaolin clay, and kaolin preferably have a total Al2O3 and SiO2 content of 95% by mass or more, more preferably 96% by mass or more, and an average particle size of 10 μm or less, more preferably 5 μm or less. The average particle size of each powder represents the particle size at 50% of the cumulative value in the particle size distribution determined by laser diffraction / scattering (measured on a volume basis).

[0023] To the mixed powder obtained in this manner, predetermined amounts of paraffin-based particles, polyethylene resin particles, acrylic resin particles, polysaccharide particles, cellulose, etc., may be added to control the porosity, porosity, pore size, and distribution. Furthermore, it is preferable to give the mixed powder a moderate degree of wetting in order to uniformly mix these mixed powders, and it is preferable to add 5 to 20% by mass of water relative to the total amount of powder and 0.1 to 0.5% by mass of a surfactant (polycarboxylate, sulfate ester, sulfonate, etc.). The mixed powder obtained in this manner is mixed using a ball mill, blender, high-speed stirrer, etc., to uniformly mix and disperse each powder. Regarding the mixing conditions, the amount of each ingredient used and the mixing time should be adjusted appropriately according to the powder blending ratio to ensure that the structure of the porous material becomes uniform.

[0024] The obtained mixed powder is molded into a predetermined shape, and molding methods such as press molding, extrusion molding, and casting can be employed. In the case of press molding and extrusion molding, a predetermined amount of binder (PVA, methylcellulose, wax emulsion, etc.) is added to the obtained mixed powder. In the case of press molding, the powder with the binder added is used for molding, and in the case of extrusion molding, it is molded after kneading. In the case of casting molding, a predetermined amount of water is added to the mixed powder, stirred with a stirrer to form a slurry, and molded using a plaster mold or the like. After drying, the obtained molded body is fired to obtain the alumina-mulite porous body of the present invention. The firing temperature is preferably 1400 to 1650°C, more preferably 1450 to 1600°C, and even more preferably 1480 to 1580°C.

[0025] In the above manufacturing method, the mixing ratio of coarse alumina powder to fine alumina powder (coarse alumina powder / fine alumina powder) is preferably 0.45 to 0.75 by mass ratio, and more preferably 0.56 to 0.65. If the mixing ratio is less than 0.45, the amount of fine alumina powder increases, leading to a decrease in porosity and a smaller average pore size, which is undesirable as it reduces thermal shock resistance, corrosion resistance, and durability. On the other hand, if it exceeds 0.75, the filling of the powder during molding decreases, resulting in a decrease in sinterability, a decrease in the bonding force between crystal particles, an increase in porosity, and a larger average pore size, which is undesirable as it results in a decrease in thermal shock resistance, durability, and corrosion resistance. Furthermore, the mixing of the mixed powder of coarse-grained alumina powder and fine-grained alumina powder, chamotte powder, and clay mineral powder is carried out by selecting the mixing amounts of the mixed powder, chamotte powder, and clay mineral powder so that the overall Al2O3 / SiO2 mass ratio of the mixed powder, chamotte powder, and clay mineral powder is 2.50 to 3.10. For example, if the total of the mixed powder, chamotte powder, and clay mineral powder is taken as 100, it is preferable that the mixed powder of coarse-grained alumina powder and fine-grained alumina powder is 40 to 50% by mass, the chamotte powder is 5 to 25% by mass, and the clay mineral powder is 25 to 50% by mass. If the mixed powder of coarse-grained alumina powder and fine-grained alumina powder is less than 40% by mass, the amount of silica contained in the porous body increases, leading to an increase in the mullite phase and a decrease in corrosion resistance. In contrast, if the mixed powder of coarse-grained alumina powder and fine-grained alumina powder exceeds 50% by mass, the alumina content increases, leading to an increase in the corundum phase, which is undesirable as it reduces thermal shock resistance and durability. Furthermore, if the powders are not sufficiently uniformly mixed, segregation of each powder occurs, resulting in an uneven distribution of pores and an uneven presence of crystalline phases, which is undesirable as it impairs thermal shock resistance, durability, and corrosion resistance. When using the powder as a heat treatment component for heat treatment, the porous body in contact with the powder can achieve the desired surface roughness by appropriately adjusting the mixing ratio of coarse-grained alumina powder and the amount of chamotte powder added within the specified range to suppress powder adhesion.For example, the inner surface of a furnace tube for a rotary kiln, a typical heat treatment component, comes into contact with the powder being heat-treated. However, depending on the surface roughness of the furnace tube, the flow and movement of the powder may be impaired, or the furnace tube and powder may adhere to each other during heat treatment. Therefore, it is preferable that the surface roughness (Ra) be 10 μm or less, and more preferably 8 μm or less. [Examples]

[0026] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0027] [Examples 1-9 and Comparative Examples 1-9] In Examples 1-9 and Comparative Examples 1-9, alumina powder with an alumina purity of 99.6% by mass and an average particle size of 500 μm was used as the coarse-grained alumina powder, and alumina powder with an alumina purity of 99.7% by mass and an average particle size of 12.5 μm was used as the fine-grained alumina powder. The coarse-grained alumina powder and the fine-grained alumina powder were mixed, and chamotte powder with an average particle size of 163 μm and an Al2O3 / SiO2 mass ratio of 73 / 27 and kibushi clay with an average particle size of 4.5 μm were added to this mixed powder. Water and sodium polycarboxylate as a surfactant were added to this mixed powder according to the powder mixing ratio to provide appropriate wetting properties, and the mixture was mixed for 3 hours using a high-speed mixer. Carboxymethylcellulose was then added as a binder to enable extrusion molding, and a mixed powder was prepared. Using the obtained mixed powder, a ring with dimensions of φ120 mm × φ105 mm × 50 mm was extruded and fired for 3 hours to obtain a porous body. In Examples 1-9 and Comparative Examples 1-9, the ratio of coarse alumina powder to fine alumina powder (by mass), the respective mixing ratios to the total of the mixed powder of coarse and fine alumina powder, chamotte powder, and kibushi clay, and the firing temperature were as shown in Table 1. In Comparative Example 1, the mixing time using a high-speed mixer was 30 minutes. Figure 1 shows a microstructure observation image of the porous body (sintered body) obtained in Example 9. Figure 2 shows a microstructure observation image of the porous body (sintered body) obtained in Comparative Example 6.

[0028] The following properties were evaluated using the sintered bodies obtained in Examples 1-9 and Comparative Examples 1-9. The test pieces used for the property evaluation were prepared by cutting samples from the obtained alumina-mulite porous body and processing them in order with diamond grinding wheels #140, #400, and #600 mesh on a surface grinding machine to produce test pieces measuring 6 mm in length, 5 mm in width, and 50 mm in length. The 6 mm in length and 50 mm in length surface of the prepared test piece was chamfered with a #600 mesh.

[0029] (Measurement of the ratio of corundum phase to mullite phase) The sintered bodies obtained in Examples 1-9 and Comparative Examples 1-9 were pulverized to an average particle size of 50 μm or less. Measurements were performed using a powder X-ray diffractometer (Bruker Japan D8 ADVANCE) with Cu as the target, under the following conditions: step of 0.02°, step time of 0.4 s, voltage of 40 kV, current of 40 mA, incident divergent slit of 0.5°, incident solar slit of 4.1°, receiving divergent slit of 5.2 mm, and receiving solar slit open. The diffraction intensity of the corundum phase (C) on the (113) crystal plane (IA(113)) and the diffraction intensity of the mullite phase (M) on the (210) crystal plane (IM(210)) were used to determine the amount ratio of the corundum phase to the mullite phase from the above formulas (i), (ii), and (iii). Figure 5 shows the X-ray diffraction pattern of the sintered body obtained in Example 9. Figure 6 shows the X-ray diffraction pattern of the sintered body obtained in Comparative Example 9.

[0030] (Evaluation of thermal shock resistance and durability) Thermal shock resistance was evaluated by holding the test piece in an electric furnace at 530°C for 15 minutes, followed by dropping it into 5°C water. This thermal shock resistance test was performed using five test pieces. Durability was evaluated by holding the test piece in an electric furnace at 1130°C for 30 minutes, followed by a rapid cooling test five times at room temperature (20°C). Before and after the test, the test piece was measured using a precision universal testing machine (AGS-500NX, Shimadzu Corporation) with a 6mm x 5mm x 50mm #600 mesh finish, with the tensile surface facing 6mm x 50mm. The bending strength was measured using a three-point bending test with a lower support distance of 30mm and a crosshead speed of 0.5mm / min. Thermal shock resistance was evaluated using the ratio of "average bending strength after thermal shock test / average bending strength before thermal shock test," which is the ratio of the average bending strength of five test pieces after the thermal shock test (average bending strength after thermal shock test) to the average bending strength of five test pieces before the thermal shock test (average bending strength before thermal shock test). Similarly, durability was evaluated using the ratio of "average bending strength after durability test / average bending strength before durability test," which is the ratio of the average bending strength of five test pieces before the durability test (average bending strength before durability test). The thermal shock resistance and durability values ​​would show a value of 1 if no decrease in strength was observed due to the test. However, due to variations in test pieces, the value may exceed 1, in which case it was assumed that there was no decrease and the value was set to 1.

[0031] (Bending strength evaluation) The tensile surface of the 6mm x 50mm surface of the test piece, which was finished with #600 mesh and measured using a precision universal testing machine (AGS-500NX, Shimadzu Corporation), was tensile. Measurements were taken using a three-point bending test with a lower support distance of 30mm and a crosshead speed of 0.5mm / min.

[0032] (Corrosion resistance evaluation) The porous materials obtained in Examples 1-9 and Comparative Examples 1-9 were cut into 20mm x 20mm x 10mm sections, and the 20mm x 20mm surface was finished in the same way as the bending strength. Corrosion resistance evaluation was performed using PbO (lead oxide) as the material to be fired. The PbO (lead oxide) material to be fired was formed to a diameter of 10mm and a thickness of 1mm using a die press molding process with commercially available powder (Kishida Chemical Co., Ltd. product, Grade I lead(II) oxide, content 99.5% by mass) as the material to be fired. The molded PbO body was placed on the finished surface of the test piece and fired in an electric furnace at 870°C for 10 hours. The cut surface of the fired test piece, which had been eroded by the material to be fired, was processed using a surface grinding machine with diamond grinding wheels in the order of #140, #400, and #600 mesh. The degree of erosion (depth) from the inner surface to the outer surface was measured using a microscope (Keyence Digital Microscope VHX-6000) at a magnification of 20x. The evaluation results for the various evaluations described above are shown in Tables 1 and 2. Figure 3 shows a cross-sectional view of the sintered body obtained in Example 2 after the corrosion resistance evaluation. Figure 4 shows a cross-sectional view of the sintered body obtained in Comparative Example 6 after the corrosion resistance evaluation.

[0033] [Table 1]

[0034] [Table 2]

[0035] The alumina-mulite porous materials obtained in Examples 1-9 showed no significant strength degradation in thermal shock resistance evaluation and durability evaluation, and corrosion resistance tests also showed minimal erosion due to the reaction between the treated powder and the fired material.

[0036] In Comparative Example 1, the short mixing time resulted in poor mixing and uneven particle dispersion, leading to a large ratio of maximum pore size to average pore size. This failed to satisfy the requirements of the present invention, resulting in a large maximum pore size and wide pore distribution, which reduced thermal shock resistance, durability, and corrosion resistance. In Comparative Example 2, the firing temperature was 1300°C, lower than the firing temperature specified in the manufacturing method of the present invention. As a result, sintering did not progress, and the porosity was 36%, failing to satisfy the requirements of the present invention, resulting in reduced corrosion resistance. In Comparative Example 3, the firing temperature was 1700°C, higher than the firing temperature specified in the manufacturing method of the present invention. As a result, sintering progressed, the porosity decreased, and a reduction in thermal shock resistance and durability was observed. In Comparative Example 4, the Al2O3 / SiO2 (mass ratio) did not satisfy the requirements of the present invention. The high amount of alumina resulted in a reduction in thermal shock resistance and durability. In Comparative Example 5, the coarse alumina powder / fine alumina powder (mass ratio) was small, resulting in a porous material with a large amount of fine alumina as a raw material. Consequently, the maximum pore diameter / average pore diameter did not satisfy the requirements of the present invention and exceeded the upper limit. The large difference between the average pore diameter and the maximum pore diameter resulted in large pores becoming defects, and in thermal shock resistance and durability tests, the material deteriorated to the point of breaking the sample during handling. In Comparative Example 6, the mixing ratio of coarse alumina powder / fine alumina powder was 0.77, resulting in a porous material with a large amount of coarse alumina powder as a raw material. The pore diameter was large, reducing the bonding between particles and lowering thermal shock resistance, durability, and corrosion resistance. In Comparative Example 7, the ratio of corundum phase / mullite phase exceeded 1.00, and the corundum phase did not satisfy the requirements of the present invention, resulting in reduced durability. In Comparative Example 8, the ratio of corundum phase / mullite phase was less than 0.60, and the mullite phase did not satisfy the requirements of the present invention, resulting in reduced corrosion resistance. In Comparative Example 9, the Al2O3 / SiO2 (mass ratio) was less than 2.5, which did not satisfy the requirements of the present invention. As a result, the Christoballast phase formed in a porous body, and a decrease in corrosion resistance and durability was observed. From the results of Examples 1 to 9 and Comparative Examples 1 to 9, it is clear that if even one requirement of the present invention is not met, the thermal shock resistance, durability, and corrosion resistance will decrease, and the aluminalite porous body of the present invention, which has excellent thermal shock resistance, durability, and corrosion resistance, cannot be obtained. [Industrial applicability]

[0037] The alumina-lite porous material of the present invention is suitable for use as a component in heat treatment due to its excellent thermal shock resistance, durability, and corrosion resistance. The heat treatment component made of the alumina-lite porous material of the present invention can be used for heat treatment of various material powders such as electronic materials and secondary battery materials, and for firing of the object to be fired, and is also effective as a component for various firing furnaces.

Claims

1. An aluminallite porous body that satisfies the following conditions (1), (2), (3), and (4). (1) SiO ２ Al ２ O ３ The mass ratio is between 2.50 and 3.

10. (2) The crystalline phase consists of two phases, a corundum phase and a mullite phase, with the ratio of the corundum phase to the mullite phase being 0.60 to 1.

00. (3) The porosity is 25-32%. (4) The average pore size is 10 μm or less, and the ratio of the maximum pore size to the average pore size is 70 or less.

2. A heat treatment member made of an aluminalite porous body as described in claim 1.

3. A method for producing an aluminalite porous body according to claim 1, characterized by having the following steps. (a) A step of mixing coarse alumina powder having an alumina purity of 99.6% by mass or more and an average particle size of 200 to 850 μm with fine alumina powder having an alumina purity of 99.7% by mass or more and an average particle size of 5 to 20 μm, such that the mass ratio of the coarse alumina powder to the fine alumina powder (coarse alumina powder / fine alumina powder) is 0.45 to 0.

75. (b) To the mixture obtained in the above step (a), Al ２ O ３ / SiO ２ having a mass ratio of 55 / 45 to 76 / 24, and the total content of Al ２ O ３ and SiO ２ being 97% by mass or more and having an average particle diameter of 25 to 300 μm, and a clay mineral are mixed and dispersed in the whole of the mixture, the chamotte powder, and the clay mineral so that the mass ratio of Al ２ O ３ / SiO ２ becomes 2.50 to 3.

10. (c) A step of molding the mixture obtained in step (b) above and then firing it at 1400 to 1650°C.

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