JP2011088759A - Alumina refractory and method of producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alumina refractory excellent in corrosion resistance, heat shock resistance and endurance. <P>SOLUTION: The alumina refractory is characterized in that (a) it comprises a corundum single phase having no second phase as crystalline phase, (b) an alumina content is 94 wt.% or more, (c) a silica content is 0.5 to 5 wt.%, (d) a porosity is 20 to 40%, (e) an average crystal particle size (D<SB>1</SB>) of crystal particles of which the crystal particle size is 10 μm or less is 1 to 8 μm, an average crystal particle size (D<SB>2</SB>) of crystal particles of which the crystal particle size is more than 10 μm is 60 to 500 μm and the ratio D<SB>2</SB>/D<SB>1</SB>is 10 or more, and (f) a volume ratio V<SB>2</SB>/V<SB>1</SB>of the content V<SB>2</SB>(vol.%) of crystal particles of which the crystal particle size is more than 10 μm to the content V<SB>1</SB>(vol.%) of crystal particles of which the crystal particle size is 10 μm or less is 0.6 to 4.0. A method of producing the alumina refractory is also provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an alumina refractory excellent in corrosion resistance, thermal shock resistance and durability, and a method for producing the same.

  Since highly functional materials such as electronic materials and phosphor materials such as recent positive electrode materials for lithium secondary batteries are indispensable for precise composition control, contamination of impurities in the manufacturing process is suppressed. Therefore, rapid heat-up and temperature-fall treatments are performed in the heat treatment process to minimize the composition variation. Under such severe use conditions, the heat treatment member used has high corrosion resistance, thermal shock resistance and durability. It is requested.

  Although conventional dense heat-treating members are excellent in corrosion resistance and durability, they are easily cracked due to their low thermal shock resistance, and may be cracked by explosion. However, there are many cases where the adoption of refractory is considered because there is a problem that the continuous furnace and the like are suspended because not only the inside of the furnace is scattered and the inside of the furnace is contaminated.

  However, although the refractory is excellent in thermal shock resistance, it has not only the disadvantage of low corrosion resistance and durability, but also the particles that make up the refractory are separated by repeated use and mixed into the material to be fired. There is a problem that the refractory is deformed and mechanical properties are deteriorated. For example, commonly used refractories are composed of cordierite, corundum and mullite crystals, but each crystal shows different thermal expansion behavior with increasing temperature, so there is a difference in thermal expansion within the sintered body. Problems that are inferior in durability, such as deformation and strength deterioration of refractories due to generation of microcracks, have been pointed out. In addition, since the object to be fired is deformed in accordance with the deformation of the refractory, there is a problem in that the yield after firing is significantly reduced in the case of an object to be fired that requires precise shape control such as an electronic component.

  As described above, when used in the heat treatment process of a high-functional material, each of the conventional heat treatment members has a problem, and particularly the problem of being explode and breaking is fatal. Therefore, there is a demand for a heat treatment member that is excellent in corrosion resistance, thermal shock resistance and durability, and that does not explode and break, and various studies have been made so far.

For example, Patent Document 1 discloses a composite refractory composed of fused alumina and fused mullite having a particle size of 10 to 300 μm and low soda calcined alumina having a particle size of less than 10 μm. The invention product has excellent corrosion resistance of alumina by mixing fused mullite of the second aggregate in a predetermined ratio with the fused alumina which is the first aggregate, and using low-soda calcined alumina as the binder. Not only that, the properties of mullite are sufficiently exhibited, and the heat resistance and durability are excellent. However, although the material of the aggregate and the binder and the raw material particle size of the invention are adjusted, no consideration is given to the dispersion state of the aggregate particles and the binder particles in the sintered body. Since the particles are easily segregated and a uniform microstructure is difficult to form, the thermal shock resistance is poor. In addition, if the particle diameters of the aggregate particles and the binder particles are close to each other, the effect as an aggregate cannot be sufficiently obtained, and a large number of microcracks are generated in the sintered body by repeated use, and durability is also improved. There was an inferior problem. Moreover, since it is a composite refractory composed of two phases of corundum and mullite, a difference in thermal expansion occurs in the sintered body, and microcracks occur in the sintered body due to repeated use, resulting in poor durability. .
Patent Document 2 discloses a refractory that controls the particle size distribution of the raw material powder and is excellent in high strength and spall resistance. The product of the present invention has low corrosion resistance due to its low alumina content, and cannot be used at all for high-functional material applications that require precise composition control. Furthermore, the product of the present invention has high strength and excellent spall resistance by controlling the particle size distribution of the raw material and arranging the particles continuously at a constant ratio. However, the product of the invention has a low bending strength because the particle size of the aggregate is too coarse, and the thermal shock resistance is not sufficiently satisfactory under the severe heat treatment conditions of the high-performance material.
As described above, various studies have been made in order to improve the disadvantages of inferior durability, which was a problem of conventional refractories, but as a heat treatment member used for firing high-performance materials. There was nothing that could be used enough.

Japanese Patent Laid-Open No. 2003-252677 JP-A-11-189480

  An object of the present invention is to provide an alumina refractory excellent in corrosion resistance, thermal shock resistance and durability, and a method for producing the same.

  The present inventors have been satisfied with the refractories proposed so far as heat treatment members used for heat treatment in high-functional materials typified by lithium secondary battery positive electrode materials, phosphors and electronic components. Since it was not a thing, we have intensively studied to obtain an alumina refractory having excellent corrosion resistance, thermal shock resistance and durability. As a result, the alumina crystal is a corundum single phase, and the alumina content, silica content, and porosity are controlled within a specific range, and at the same time, the ratio of the average crystal particle size of each of two types of alumina crystals having different average crystal particle sizes By controlling the content to a specific range, it becomes a sintered microstructure with two distributions of bimodal peaks and a fine structure of sintered body, which is not possible with conventional refractories. It has been found that high corrosion resistance and durability equivalent to denseness can be obtained while having high thermal shock resistance, and the present invention has been completed. That is, in the case of only controlling the particle size and content of the alumina raw material used for production as in the case of conventional refractories, the distribution of alumina crystal particles in the sintered body becomes a microstructure having a broad distribution. Therefore, since excellent corrosion resistance, thermal shock resistance and durability could not be realized at the same time, in the present invention, precise microstructure control within a specific range of crystal phase, composition, porosity, crystal particles, etc. solved the problem. He focused on being an effective means. The corrosion resistance as used in the present invention means that there is little reaction with the object to be fired, and the durability means that there is no cracking due to heating / cooling and that the life is long.

That is, the first of the present invention comprises (a) a corundum single phase having no second phase as a crystal phase, (b) an alumina content of 94% by weight or more, and (c) a silica content of 0.5. in 5wt%, (d) porosity of 20~40%, (e) an average crystal grain size of the crystal grains of the crystal grain size of 10μm or less _{(D 1)} is 1 to 8 .mu.m, crystal grain size The average crystal particle diameter (D ₂ ) of crystal grains having a diameter of more than 10 μm is 60 to 500 μm, the ratio D ₂ / D ₁ is 10 or more, and (f) the content of crystal grains having a crystal grain diameter of 10 μm or less Alumina characterized in that the volume ratio V ₂ / V ₁ between V ₁ (volume%) and the content V ₂ (volume%) of crystal grains having a crystal grain diameter exceeding 10 μm is 0.6 to 4.0. Regarding refractories.
The second of the present invention is a coarse alumina raw material powder having an alumina content of 99.5% by weight or more and an average particle size of 60 to 500 μm, an alumina content of 99.5% by weight or more and an average particle size of 0.00. The weight ratio of 5-8 μm fine alumina raw material powder is in the range of coarse alumina: fine alumina = 80: 20-40: 60, and the silica content of the sintered body is a silicon compound having a specific surface area of 3 m ² / g or more. The alumina-based refractory according to claim 1, wherein the two kinds of alumina raw material powders are mixed, molded, and fired at 1400 ° C to 1700 ° C in the air so that the amount of N is 0.5 to 5% by weight. The present invention relates to a method for manufacturing a product. The alumina-based refractory referred to in the present invention is effectively used as a heat treatment member for sintering of electronic components such as a lithium secondary battery positive electrode material, a phosphor material, a ceramic capacitor, a piezoelectric body and a dielectric. Can do.

  The alumina-based refractory of the present invention is excellent in corrosion resistance, thermal shock resistance and durability as described above. Utilizing such excellent properties, the material to be used for heat treatment of various materials is used. It can be used inside or around a container for storing objects or various firing furnaces or melting furnaces. Specifically, it can be used in, for example, synthesis of lithium ion secondary battery materials, ceramic powder calcined synthesis containers, setters, metal melting containers, single crystal growth containers, and phosphor material heat treatment containers.

It is a figure which shows an example of the fine structure of this invention goods. Sample No. within the scope of the present invention (Example). 1 is an optical micrograph of 1. Sample No. within the scope of the present invention (Example). 1 is a scanning electron micrograph of 1. Sample No. which is outside the scope of the present invention (comparative example). 1 is an optical micrograph of 1.

  Hereinafter, each requirement to be satisfied by the alumina refractory excellent in corrosion resistance, thermal shock resistance and durability of the present invention will be described in detail.

(A) Consisting of a corundum single phase having no second phase as a crystal phase In the present invention, the crystal phase is a corundum having the most excellent mechanical properties and chemical stability among the crystal phases of alumina. Must be present and there should be no second phase other than corundum. When a second phase other than corundum is present, it is not preferable if it is used repeatedly because microcracks are generated in the sintered body due to the difference in thermal expansion between the corundum and the second phase, resulting in deformation and strength deterioration, and the durability is reduced. . Note that the absence of the second phase in the present invention means that X-ray diffraction (powder X-ray diffraction) cannot be qualitatively analyzed, and X-ray diffraction indicates that the sintered body has an average particle size of 5 μm or less. Then, Cu and a monochromator were used as targets, the slit was set to 0.15 mm, the diver slit was set to 1 °, and the scanning speed was set to 3 ° / min.
Thus, since the crystalline phase of the present invention consists of a corundum single phase, the occurrence of a difference in thermal expansion in the sintered body is extremely small compared to the conventional refractory, and the residual indicates the degree of deformation of the refractory by repeated use. The line change rate is 0 to 0.2%. If the residual line change rate exceeds 0.2%, a large amount of microcracks are generated inside the sintered body due to repeated heating and cooling, which is not preferable because durability is lowered. When the residual line change rate is less than 0%, since the refractory is contracted, not only the amount of the fired material that can be filled into the refractory is decreased, but also the porosity is lowered and the durability is poor, which is preferable. Absent. The residual line change rate referred to in the present invention is based on JIS R2208. The heat treatment of a 20 × 20 × 50 mm sintered body at 10 ° C./min, held at 1300 ° C. for 2 hours, and lowered to room temperature 5 times. Repeatedly, the length in the 50 mm direction was then measured and determined by the following formula.

[Equation 1]
Residual line change rate (%) = (L′−L) / L × 100
[L: 50 (mm), L ′: length in the 50 mm direction after raising and lowering the temperature (mm)]

(B) Alumina content is 94% by weight or more In the present invention, the alumina content contributes to corrosion resistance, so it needs to be 94% by weight or more, preferably 96% by weight or more. When the alumina content is less than 94% by weight, there are many impurities, which is not preferable because the corrosion resistance is lowered. The impurities referred to in the present invention are CaO, MgO, Na ₂ O, K ₂ O, ZrO _{2 and the} like, and the amount of impurities is preferably 1.0% by weight or less. When the amount of impurities exceeds 1.0% by weight, corrosion resistance is lowered, which is not preferable.

(C) About silica content of 0.5 to 5% by weight In the present invention, silica contributes to the formation of an appropriate glass phase at the alumina crystal grain boundary and has a function of increasing the bond strength of the crystal grain boundary. It is necessary as a sintering aid. The silica content needs to be 0.5 to 5% by weight, preferably 2 to 4% by weight. When the silica content exceeds 5% by weight, not only does the glass phase increase at the alumina crystal grain boundary and the corrosion resistance decreases, but the glass phase is preferentially corroded, so the alumina particles are deagglomerated and mixed into the material to be fired. This is not preferable because of the risk of When the silica content is less than 0.5% by weight, the effect of the sintering aid is insufficient, and the bonding strength of the grain boundaries is reduced, so that the bending strength is reduced and the thermal shock resistance is inferior, which is preferable. Absent.

(D) Porosity is 20 to 40% In the present invention, the pores are necessary to suppress the crack growth rate and contribute to the improvement of durability, and further to obtain the effect of making it difficult to explode. . The porosity is required to be 20 to 40%, and preferably 20 to 30%. When the porosity is less than 20%, since the amount of pores is small, the effect of dispersing cracks due to the pores is reduced and the cracks are likely to progress rapidly, and the durability is lowered. When the porosity exceeds 40%, there are many pores in the sintered body, the bending strength is lowered, and the thermal shock resistance is inferior. In addition, corrosion tends to proceed from the pores, causing a decrease in corrosion resistance. The pore diameter is preferably less than 10 μm, more preferably less than 7 μm, still more preferably less than 5 μm. When the pore diameter is 10 μm or more, the fired material easily impregnates the refractory material, and thus the reaction between the fired material and the refractory material is promoted, and the corrosion resistance is lowered, which is not preferable. The lower limit is about 4 μm. In addition, the porosity as used in the field of this invention refers to the apparent porosity, and was measured by the Archimedes method (based on JIS R2205). The pore diameter was measured by a mercury intrusion method (porosimeter) and calculated from the following formula.

[Equation 2]
Pore diameter (μm) = − 4γcos θ / P
[P = pressure (MPa), γ: surface tension of mercury 480 dyne · cm ⁻¹ ,
θ: mercury contact angle 140 °]

(E) The average crystal particle diameter (D ₁ ) of crystal particles having a crystal particle diameter of 10 μm or less is ₁ to 8 μm, and the average crystal particle diameter (D ₂ ) of crystal particles having a crystal particle diameter exceeding 10 μm is 60 to 500 μm. The ratio D ₂ / D ₁ is 10 or more. The alumina refractory according to the present invention is composed of two types of alumina crystal particles having different average crystal particle sizes with a crystal particle size of 10 μm as a boundary. The crystal particle distribution needs to be a bimodal distribution with two peaks, and the average crystal particle diameter and the ratio of the average crystal particle diameters must be controlled. In the present invention, the bending strength can be controlled by the size of the crystal particles having a crystal particle diameter of 10 μm or less. The average crystal particle diameter (D ₁ ) needs to be _{1 to 8} μm, preferably 2 to 6 μm. When D1 is less than ₁ μm, the bending strength is improved, but the corrosion resistance is remarkably lowered. If D ₁ is greater than 8 [mu] m, and bending strength is lowered, unfavorably inferior in thermal shock resistance.
In the present invention, the corrosion resistance can be controlled by the size of crystal grains having a crystal grain diameter exceeding 10 μm. The average crystal particle diameter (D ₂ ) needs to be 60 to 500 μm, preferably 70 to 300 μm, and more preferably 80 to 200 μm. If D ₂ is less than 60 [mu] m, undesirably corrosion resistance decreases. If D ₂ is greater than 500 [mu] m, although the corrosion resistance is improved, the bending strength is lowered, unfavorably inferior in thermal shock resistance.
On the other hand, in the present invention, the durability can be controlled by setting D ₂ / D ₁ in a specific range, and the value needs to be 10 or more, preferably 15 or more. When the crystal particle diameter is less 10 [mu] m in average less than the ratio of crystal grain diameter D ₂ of 10 crystal grains mean crystal grain size and the crystal grain diameter D ₁ of the crystal grains exceeds 10 [mu] m, the crystal grains the crystal grain size of less 10 [mu] m Since the difference in crystal grain size between crystal grains exceeding 10 μm and the crystal grain diameter is small, the particle cross-linking effect that suppresses the crack growth rate of crystal grains exceeding 10 μm in crystal grain diameter cannot be sufficiently obtained, and cracks occur rapidly. It is not preferable because it progresses to a lowering of durability. _The upper limit of D 2 / _{D 1} is 500 from the range of _{D 1} and _{D 2} of the present invention. The crystal particle diameter D referred to in the present invention was calculated by the following equation by observing the mirror-polished sintered body cross section with a scanning electron microscope and an optical microscope, measuring the major axis and minor axis of the alumina crystal particle. Further, the measurement of the average crystal particle diameter requires 100 or more measurements, preferably 500 or more, more preferably 1000 or more.

[Equation 3]
D = (a + b) / 2
[D: Crystal particle diameter (μm), a: Crystal particle major diameter (μm),
b: minor diameter of crystal particle (μm)]

(F) volume ratio _V 2 / _{V 1} of the content _{V 2} of crystal grains the crystal grain size crystal grain size content _{V 1} of the following crystal grains 10 [mu] m and (vol%) is more than 10 [mu] m (volume percent) 0 in the present invention about a .6～4.0, content _{V 1} (vol%) of the crystal grain size is 10μm or less crystal grains and the content _{V 2} (vol% of crystal grains having a particle diameter of more than 10μm ) Volume ratio V ₂ / V ₁ of 0.6 to 4.0, preferably 0.7 to 3.0. When V ₂ / V ₁ is less than 0.6, the content of crystal particles having a crystal particle diameter exceeding 10 μm is small, which is not preferable because corrosion resistance is lowered. When V ₂ / V ₁ exceeds 4.0, the bending strength is lowered and the thermal shock resistance is inferior. The volume ratio V _{2 /} V content of the crystal grain size of 10 [mu] m or less of crystal grains in the present invention V ₁ content V _{2 (volume%)} and the crystal grains the crystal grain size exceeds 10 [mu] m _{(volume%) 1} corresponds to the area ratio S1 / S2 of the total area S1 of crystal grains having a crystal grain diameter of 10 μm or less per unit area of the sintered body and the total area S2 of crystal grains having a crystal grain diameter of more than 10 μm. is there. The areas of S1 and S2 are measured by image analysis or the like, and the measurement area needs to be 4 mm ² or more, preferably 9 mm ² or more.
In the present invention, the bending strength is preferably 30 MPa or more, more preferably 35 MPa or more. When the bending strength is less than 30 MPa, the thermal shock resistance is inferior, which is not preferable. The bending strength referred to in the present invention was determined based on JIS R2208 such that the test piece size was 20 × 20 × 50 mm and a tensile stress was generated on the molding surface of the sintered body. In addition, the bending strength of refractories that are generally available on the market is 10 to 20 MPa, and this level of bending strength is not sufficiently satisfactory under severe heat treatment conditions such as highly functional materials. The invention product has a bending strength of 30 MPa or more, and can be sufficiently used even under severe heat treatment conditions.

  The method for producing an alumina refractory having excellent corrosion resistance, thermal shock resistance and durability according to the present invention will be described.

Coarse alumina raw material powder having an alumina content of 99.5% by weight or more and an average particle size of 60 to 500 μm, and a fine alumina raw material powder having an alumina content of 99.5% by weight or more and an average particle size of 0.5 to 8 μm It is necessary to mix the body at a weight ratio of coarse alumina raw material powder: fine alumina raw material powder = 40: 60 to 80:20, preferably 50:50 to 75-25. A silicon compound having a specific surface area of 3 m ² / g or more needs to be mixed with the mixed alumina raw material powder so that the sintered body has a silica content of 0.5 to 5% by weight. When the purity of the coarse alumina raw material powder and the fine alumina raw material powder is less than 99.5% by weight, the amount of impurities increases and the corrosion resistance decreases, which is not preferable. When the average particle diameter of the coarse alumina raw material powder is less than 60 μm, the corrosion resistance is lowered, which is not preferable. When the average particle diameter of the coarse alumina raw material powder exceeds 500 μm, the corrosion resistance is improved, but the bending strength is lowered and the thermal shock resistance is inferior. If the average particle size of the fine alumina raw material powder is less than 0.5 μm, the powder is likely to agglomerate, and the mixing / dispersibility with the coarse alumina raw material powder is reduced. Since the raw materials are likely to be separated during filling, the sintered body becomes inhomogeneous, the bending strength is lowered, and the thermal shock resistance is inferior. When the average particle diameter of the fine alumina raw material powder exceeds 8 μm, the bending strength is lowered and the thermal shock resistance is inferior. As the silicon compound, artificial raw materials such as silica and natural raw materials such as feldspar can be used, and one of them can be used alone or two or more of them can be used in combination. The silica content of the silicon compound is preferably 60% by weight or more. Further, when the specific surface area is less than 3 m ² / g, the mixing and dispersibility with the alumina raw material is lowered, so that the second phase is likely to be precipitated at the alumina crystal grain boundary and the durability is inferior. The upper limit of the specific surface area is about 30 m ² / g.
Each component is blended in a predetermined amount, and a known molding aid (for example, CMC, acrylic resin, etc.) is added in a predetermined amount, and mixed and dispersed with a universal mixing stirrer, a mill, or the like. The particle size distribution of the mixed raw material powder is a bimodal distribution measured by a laser diffraction particle size distribution measuring device (Nikkiso: MT-3300EX) in order to disperse fine alumina and coarse alumina uniformly. It is necessary to make adjustments according to the selection and processing conditions of the mixing / dispersing device. As a molding method, a normal refractory molding method can be employed, and press molding, cold isostatic pressing, or the like is employed. The obtained molded body is fired in the atmosphere at 1400 to 1700 ° C, preferably 1450 to 1650 ° C. When the firing temperature is less than 1400 ° C., not only the porosity is increased, but also the sintering is insufficient and the bonding strength of the grain boundaries is insufficient, so the bending strength is lowered and the thermal shock resistance is inferior. It is not preferable. When the firing temperature exceeds 1700 ° C., the sinterability is improved, but the pores are reduced, and when the cracks progress, the effect of dispersing the cracks due to the pores becomes insufficient, and the cracks rapidly progress and the durability is lowered. Therefore, it is not preferable.

  Hereinafter, although an example and a comparative example explain concretely, the present invention is not limited at all by these examples.

Example (sample No. 1-5), comparative example (sample No. 1-14)
The alumina raw material powder to be used is as follows. In the example (sample No. 1), the alumina content is 99.8% by weight, the coarse alumina raw material powder has an average particle size of 125 μm, the alumina content is 99.5% by weight, and the average particle size is 4. Using fine alumina raw material powder of 6 μm, the example (sample No. 2) has a coarse alumina raw material powder having an alumina content of 99.7% by weight and an average particle diameter of 214 μm, and an alumina content of 99. Example 7 (Sample No. 3) is a coarse alumina raw material powder having an alumina content of 99.8% by weight and an average particle diameter of 71 μm, using a fine alumina raw material powder having an average particle size of 7.1 μm. And an alumina content of 99.5% by weight and a fine alumina raw material powder having an average particle diameter of 4.6 μm, the examples (sample Nos. 4 and 5) have an alumina content of 99.8% by weight and an average From particle size 453μm Coarse alumina raw material powder and fine alumina raw material powder having an alumina content of 99.8% by weight and an average particle diameter of 0.8 μm, and the comparative example (sample No. 1) has an alumina content of 99.8. Using a coarse alumina raw material powder having a weight percent of 453 μm and an average particle size of 453 μm, and a fine alumina raw material powder having an alumina content of 99.5% by weight and an average particle size of 4.6 μm, a comparative example (sample No. 2, 6) A coarse alumina raw material powder having an alumina content of 99.7% by weight and an average particle diameter of 214 μm, and a fine alumina raw material powder having a purity of 99.5% by weight and an average particle diameter of 4.6 μm. In Comparative Example (Sample No. 3), an alumina content of 99.8% by weight, an average particle diameter of 533 μm, a coarse alumina raw material powder, an alumina content of 99.9% by weight, and an average particle diameter of 1 .2μm micro-al Comparative Example (Sample No. 4) was prepared using a raw material powder of 99.5% by weight with an alumina content and an average particle diameter of 317 μm, an average content of 99.5% by weight and an alumina content of 99.5% by weight. Using a fine alumina raw material powder having a particle diameter of 4.6 μm, the comparative example (sample No. 5) is a coarse alumina raw material powder having an alumina content of 99.2% by weight and an average particle diameter of 317 μm, and an alumina-containing powder. Using a fine alumina raw material powder having an amount of 99.1% by weight and an average particle size of 7.1 μm, the comparative example (Sample No. 7) has an alumina content of 99.7% by weight and an average particle size of 317 μm. A coarse alumina raw material powder and a fine alumina raw material powder having an alumina content of 99.7% by weight and an average particle diameter of 7.1 μm were used. The comparative example (sample Nos. 8 and 10) had an alumina content of 99. .8 layers %, Mean a coarse alumina raw material powder consisting of particles size 453Myuemu, alumina content 99.7 wt%, using a micro alumina raw material powder having an average particle size of from 7.1 [mu] m, comparative example (Sample No. 9) a coarse alumina raw material powder having an alumina content of 99.8% by weight and an average particle diameter of 57 μm, and a fine alumina raw material powder having an alumina content of 99.7% by weight and an average particle diameter of 3.1 μm. In Comparative Example (Sample No. 11), a coarse alumina raw material powder having an alumina content of 99.7% by weight and an average particle size of 214 μm, an alumina content of 99.7% by weight, and an average particle size of 0 In the comparative example (sample No. 12), a coarse alumina raw material powder having an alumina content of 99.8% by weight and an average particle diameter of 67 μm and an alumina content of 99.99 μm were used. Using a fine alumina raw material powder having 7% by weight and an average particle size of 7.1 μm, a comparative example (Sample No. 13) is a coarse Al material having an alumina content of 99.7% by weight and an average particle size of 214 μm. The raw material powder and the fine alumina raw material powder having an alumina content of 99.8% by weight and an average particle diameter of 0.8 μm were used, and the comparative example (sample No. 14) had an alumina content of 99.7% by weight. %, A coarse alumina raw material powder having an average particle diameter of 214 μm, and a fine alumina raw material powder having an alumina content of 99.7% by weight and an average particle diameter of 13.3 μm.
Moreover, the silicon compound to be used is as follows. Examples (Sample Nos. 1 to 4) and Comparative Examples (Sample Nos. 1, 3, 4, 7, 8, 10, 11, 13, 14) were conducted using Indian feldspar with a specific surface area of 4 m ² / g. Example (Sample No. 5) and Comparative Example (Sample No. ^2, 12) use silica sol with a specific surface area of 25 m ² / g, and Comparative Example (Sample No. 9) has Indian feldspar with a specific surface area of 2 m ² / g. In Comparative Example (Sample No. 5), Indian feldspar with a specific surface area of 8 m ² / g was used. In Comparative Example (Sample No. 6), mullite with a specific surface area of 6 m ² / g was used.
As shown in Table 1, the alumina raw material powder and the silicon compound are blended so that a predetermined amount is obtained, the CMC amount is adjusted and added as appropriate, mixed and dispersed using a universal mixing stirrer, and formed by press molding. And firing at 1350 to 1730 ° C. to obtain 20 × 20 × 50 mm alumina refractories. The properties of the obtained alumina refractory are shown in Table 2. Examples (Sample Nos. 1 to 5) are alumina refractories within the scope of the present invention (Examples), and Comparative Examples (Sample Nos. 1 to 14) satisfy at least one of the requirements of the present invention. (Comparative example) Alumina refractory.

In the corrosion resistance test, a lithium cobalt oxide (LiCoO ₂ ) compact is placed on each sintered compact, and after heat treatment at 900 ° C. for 5 hours in an electric furnace, the erosion depth of Li as a component of the lithium cobalt oxide compact is measured. did. The erosion depth was determined by mirror-polishing the sintered body cross section and analyzing it by energy dispersive X-ray analysis (EDX). The results are shown in Table 2.
In the thermal shock test, a sample was put in an electric furnace, heated at 500 ° C. for 30 minutes, and dropped into water at 20 ° C., and the sample after the test was visually evaluated for the presence of cracks. Further, in the durability test, when no crack was generated in the above thermal shock test, the sample was repeated 30 times under the same conditions as in the thermal shock test, and the presence or absence of the crack was visually evaluated. The results are shown in Table 2.
Residual line change rate is based on JIS R2208, 20x20x50mm sintered body is heated at 10 ° C / min, kept at 1300 ° C for 2h, and lowered to room temperature 5 times, then 50mm direction The length of was measured and determined by the following formula.

[Equation 4]
Residual line change rate (%) = (L′−L) / L × 100
[L: 50 (mm), L ′: length in the 50 mm direction after raising / lowering temperature (mm)]

The bending strength was determined based on JIS R2208 so that the test piece size was 20 × 20 × 50 mm and a tensile stress was generated on the molding surface of the sintered body.
As is clear from Table 2, the sintered body of the present invention has a high corrosion resistance equivalent to that of a dense heat-treating member with a corrosive depth of less than 1 mm of Li having high corrosiveness, and is further 30 times or more and 500 ° C. It has high thermal shock resistance and durability that does not generate cracks even when cooled rapidly. However, a sintered body that does not satisfy at least one of the requirements of the present invention is inferior in any one or more of corrosion resistance, thermal shock resistance and durability, and is not satisfactory as a heat treatment member. In Table 2, the durability test was not performed for those in which cracks occurred in the thermal shock test.
For example, in the comparative example (sample No. 1), the volume ratio of the content of crystal particles having a crystal particle diameter of 10 μm or less and the content of crystal particles having a crystal particle diameter of more than 10 μm is out of the scope of the present invention. It was inferior to that. The comparative example (Sample No. 2) was inferior in corrosion resistance because the silica content was outside the scope of the present invention. In Comparative Example (Sample No.3) has an average crystal grain size D ₂ were outside the scope of the present invention, it was inferior in thermal shock resistance. Comparative Example (Sample No. 4) was inferior in thermal shock resistance because the volume ratio of coarse alumina crystal particles to fine alumina crystal particles was outside the range of the present invention. The comparative example (sample No. 5) had an alumina content outside the scope of the present invention and was inferior in corrosion resistance. In Comparative Example (Sample No. 6), the crystal phase was a composite of corundum and mullite, so the residual line change rate was high and the durability was inferior. Comparative Example (Sample No. 7) was inferior in thermal shock resistance because the silica content was outside the scope of the present invention. Since the porosity of the comparative example (Sample No. 8) was outside the range of the present invention, the thermal shock resistance was inferior. Comparative Example (Sample No. 9) was inferior in corrosion resistance because the average crystal particle size of alumina crystal particles having a crystal particle size exceeding 10 μm was outside the range of the present invention. Since the porosity of the comparative example (sample No. 10) was outside the range of the present invention, the thermal shock resistance was inferior. Comparative Example (Sample No. 11) was inferior in corrosion resistance because the average crystal particle size of crystal particles having a particle size of 10 μm or less was outside the range of the present invention. Since the comparative example (sample No. 12) used a coarse alumina raw material powder and a fine alumina raw material powder having similar average particle sizes, the average crystal particle size and crystal particle size of crystal particles having a crystal particle size of 10 μm or less were used. Since the ratio of the average crystal particle diameter of crystal grains exceeding 10 μm was out of the range of the present invention, the durability was inferior. The comparative example (Sample No. 13) was inferior in durability because the porosity was outside the range of the present invention. Comparative Example (Sample No. 14) was inferior in thermal shock resistance because the average crystal particle size of crystal particles having a particle size of 10 μm or less was outside the range of the present invention.

Claims (2)

(A) a corundum single phase having no second phase as a crystal phase, (b) alumina content is 94% by weight or more, (c) silica content is 0.5 to 5% by weight, (d) The average crystal of crystal grains having a porosity of 20 to 40%, (e) crystal grains having a crystal grain diameter of 10 μm or less, an average crystal grain diameter (D ₁ ) of ₁ to 8 μm, and a crystal grain diameter exceeding 10 μm The particle diameter (D ₂ ) is 60 to 500 μm, the ratio D ₂ / D ₁ is 10 or more, and (f) the content V ₁ (volume%) of crystal particles having a crystal particle diameter of 10 μm or less and the crystal particles Alumina refractory, wherein the volume ratio V ₂ / V ₁ of the content V ₂ (volume%) of crystal particles having a diameter exceeding 10 μm is 0.6 to 4.0. Coarse alumina raw material powder having an alumina content of 99.5% by weight or more and an average particle size of 60 to 500 μm, and a fine alumina raw material having an alumina content of 99.5% by weight or more and an average particle size of 0.5 to 8 μm The weight ratio of the powder is coarse alumina: fine alumina = 80: 20 to 40:60, and a silicon compound having a specific surface area of 3 m ² / g or more has a silica content of 0.5 to 5 weight. 2. The method for producing an alumina refractory according to claim 1, wherein the two kinds of alumina raw material powders are mixed so as to be%, molded, and fired at 1400 ° C. to 1700 ° C. in the atmosphere.