JP2010083729A - Alumina-based sintered compact excellent in corrosion resistance, heat shock resistance, and durability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alumina-based sintered compact excellent in corrosion resistance, heat shock resistance, and durability, to provide a production method thereof, and to provide a heat treatment member comprising the alumina-based sintered compact. <P>SOLUTION: The alumina-based sintered compact excellent in corrosion resistance, heat shock resistance, and durability is characterized in that (a) it is an alumina-based sintered compact having an alumina content of 99.5 wt.% or higher, (b) it has a bulk density of 3.7 g/cm<SP>3</SP>or higher, (c) it has an average crystal particle diameter of 20-70 μm, (d) the major diameter/minor diameter of crystal particles on each of one surface of the sintered compact and the surface vertical thereto is 2.0 or higher, and (e) the ratio R1/R2 (wherein R1 is the major diameter/minor diameter on a larger one of the major diameter/minor diameter ratios on the one surface and the surface vertical thereto and the R2 is smaller one of them) is 1.0-2.0. A production method thereof, and a heat treatment member comprising the alumina-based sintered compact are also provided. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an alumina sintered body excellent in corrosion resistance, thermal shock resistance and durability, and a heat treatment member comprising the same.

  The crystal structure of alumina is a hexagonal system having a plate shape, and the crystal axis is composed of an a-axis and a c-axis. When the crystal grain size is small, the crystal grain shape is granular, but when the crystal grain becomes large, the crystal grain shape has a feature that the plate shape becomes clear.

  Alumina is excellent in corrosion resistance, heat resistance, etc., and is cheaper and easier to handle than other ceramic materials, so it is used in a wide range of fields such as high temperature members and heat treatment members. In particular, electronic materials such as recent positive electrode materials for lithium secondary batteries and phosphor materials are indispensable for precise composition control, and therefore, contamination of impurities in the manufacturing process is suppressed. In these heat treatments, rapid temperature increase / decrease processes are performed in order to minimize the variation of the composition and increase the production efficiency. Under such use conditions, an alumina heat treatment member having high thermal shock resistance and durability in addition to corrosion resistance is required.

  In order to solve these problems, orientation of alumina crystals has been studied. For example, Patent Document 1 discloses an oriented alumina sintered body having a high degree of orientation as a member for heat treatment made of an alumina sintered body having excellent corrosion resistance, by growing alumina crystal particles greatly to form plate-like particles. It is disclosed. However, although this alumina sintered body is excellent in corrosion resistance, since the crystal grains are large, a difference in thermal expansion between the a-axis and the c-axis of the alumina crystal appears remarkably. Even in the conventional alumina sintered body, the crystal grain shape is almost granular, but as the crystal grain becomes larger, the difference in thermal expansion between the a-axis and the c-axis increases, contributing to the improvement of fracture toughness, and the thermal shock resistance It is effective in improving the sex. However, in the present invention, the crystal grain size is increased, and at the same time, the crystals are oriented in one direction, so that distortion caused by the difference in thermal expansion appears greatly. For this reason, the mechanical properties are deteriorated, and problems such as generation of cracks and cracks due to rapid temperature increase / decrease processing due to the decrease in thermal shock resistance are caused. In addition, the generation and growth of microcracks occur due to repeated heating and cooling, and there is a problem that leads to the occurrence of cracks as seen in the decrease in thermal shock resistance. Further, the oriented alumina sintered body needs to combine the plate-like alumina particles and the granular alumina particle powder at a specific ratio in order to promote grain growth and orient the crystal. In addition to the high cost due to the need for a body, there is a problem in that the dispersion state of the slurry is unstable and difficult to mold, and the yield is low.

  On the other hand, Patent Document 2 discloses an alumina-based sintered body having high thermal shock resistance and corrosion resistance by adding a small amount of zirconia to alumina so as to granulate crystal grains and make the crystal grain size uniform. . However, although it is excellent in thermal fatigue due to heating / cooling, the thermal shock resistance may not be able to cope with recent severe rapid heating / cooling and cannot be used stably. Moreover, further improvement is requested | required also about corrosion resistance.

JP 7-315915 A JP 2001-114555 A

  An object of the present invention is to provide an alumina sintered body excellent in corrosion resistance, thermal shock resistance and durability, and a heat treatment member comprising the same.

  The inventors of the present invention have made extensive studies to obtain an alumina sintered body having excellent corrosion resistance, thermal shock resistance and durability. As a result, it was found that an alumina sintered body excellent in corrosion resistance, thermal shock resistance and durability can be obtained by controlling the crystal grain size, crystal grain shape and crystal orientation of alumina crystals. By making the alumina crystal particles in a certain size, plate-like, and random without being oriented, not only corrosion resistance but also strength and fracture toughness can be improved at the same time, thermal shock resistance And found to be excellent in durability and durability. In addition, the durability as used in the field of this invention means that it is long-life, without the crack by heating / cooling etc. being seen. In the present invention, the alumina content and the bulk density are within a certain range, and the alumina crystal particles have a shape close to a plate shape having a certain size, but there is almost no crystal orientation (that is, R1 / R2 is less than It is 1.0 to 2.0), and is characterized by being randomly distributed.

That is, the first of the present invention is (a) an alumina sintered body having an alumina content of 99.5% by weight or more, (b) a bulk density of 3.7 g / cm ³ or more, ( c) The average crystal grain size is 20 to 70 μm, (d) the major axis / minor axis of the crystal grain of one surface of the sintered body and the surface perpendicular to the surface are both 2.0 or more, and (e) one The major axis / minor axis of the surface having the larger major axis / minor axis of the crystal grain in the plane perpendicular to that plane and the major axis / minor axis of the smaller surface: ratio of the major axis / minor axis: R2 of the smaller one: R1 / R2 is 1. The present invention relates to alumina-based sintering excellent in corrosion resistance, thermal shock resistance and durability characterized by being 0 to 2.0.
A second aspect of the present invention relates to a heat treatment member comprising an alumina sintered body having excellent corrosion resistance, thermal shock resistance and durability according to claim 1.
According to the third aspect of the present invention, an alumina raw material powder having an alumina content of 99.7% by weight or more and an average particle size of 0.5 to 3 μm is added with a fluorine compound having an average particle size of 25 μm or less from 0.03 to 0.5. 2% by weight addition, pulverized and mixed with an average particle size of 2 μm or less, molded, and fired at 1600 to 1800 ° C. in the atmosphere, excellent in corrosion resistance, thermal shock resistance and durability The present invention relates to a method for producing an alumina sintered body.

  In addition, the member for heat processing as used in the field of this invention means the various members used in the inside or peripheral part of the container which stores the to-be-fired material used at the time of heat processing of various materials, or various baking furnaces, melting furnaces. Specifically, for example, ceramic powder calcining synthesis vessel, glass melting vessel, setter, metal melting vessel, single crystal growth vessel, phosphor material heat treatment vessel, tubular furnace core tube, radiant tube , Heater support tube, temperature measuring protection tube, gas blowing tube, gas sampling tube, lining furnace material, etc.

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

(A) Alumina content is 99.5% by weight or more In the present invention, the alumina content is required to be 99.5% by weight or more, and preferably 99.7% by weight or more. When the alumina content is less than 99.5% by weight, a large amount of glass phase or second phase is generated at the alumina crystal grain boundary, which not only deteriorates corrosion resistance but also undesirably decreases creep resistance. Furthermore, when the alumina content is less than 99.5% by weight, a large amount of impurities are contained, which makes it difficult to control the microstructure such as the crystal grain size and grain shape. Industrially, the upper limit is about 99.8% by weight.

(B) a bulk density in the present invention will be at 3.7 g / cm ³ or more, is possible bulk density must be at 3.7 g / cm ³ or more and 3.8 g / cm ³ or more More preferred. If the bulk density is less than 3.7 g / cm ³ , there will be many pores inside the sintered body, resulting in a decrease in mechanical properties, thermal shock resistance and durability, as well as at high temperatures. This is not preferable because it causes deformation, and corrosion is likely to proceed from the pores, causing a decrease in corrosion resistance.

(C) About an average crystal grain size of 20 to 70 μm In the present invention, the average crystal grain size needs to be 20 to 70 μm, preferably 30 to 70 μm, more preferably 30 to 60 μm. An average crystal grain size of less than 20 μm is not preferable because it tends to be deformed at a high temperature, resulting in a decrease in heat resistance and a decrease in corrosion resistance. When it exceeds 70 μm, the distortion of the sintered body increases due to the difference in thermal expansion coefficient between the crystal faces of the alumina crystals, and not only the mechanical properties deteriorate, but also the thermal shock resistance and durability deteriorate, Since it is inferior in practicality as a member for use, it is not preferable. However, even if the average crystal grain size is within the range of the present invention, if the crystal grain shape is extremely uneven, the corrosion resistance, heat resistance, thermal shock resistance and durability may be low. In addition, the average crystal grain size is one surface of the alumina sintered body and a surface perpendicular to the surface is mirror-polished, subjected to thermal etching, observed with a scanning electron microscope, and from an average of 10 points by the intercept method, The values of one surface and a surface perpendicular to the surface were obtained from the following formula, and the average value of the values was used.
D = 1.5 × L / n
[D: average crystal grain size (μm), L: measurement distance (μm), n: number of crystals per length L]

(D) Both the major axis / minor axis of the crystal grains of one surface of the sintered body and the surface perpendicular to the surface are 2.0 or more In the present invention, one surface of the sintered body and its surface Both the major axis / minor axis of the crystal grains in the vertical plane are required to be 2.0 or more, more preferably 2.5 or more. When the major axis / minor axis is less than 2.0, it means that the crystal grain shape is close to a sphere, so that it does not contribute to the improvement of fracture toughness, and the thermal shock resistance and durability are lowered. The upper limit of the major axis / minor axis is about 5. The major axis / minor axis is measured by observing the crystal particles with a scanning electron microscope in the same manner as the above-described method for measuring the crystal grain size, measuring 50 major and minor axes of the crystal particles, and calculating the average of the major axis / minor axis. The value was determined.

(E) The major axis / minor axis of the surface having the larger major axis / minor axis of the crystal grain on one surface of the sintered body and the surface perpendicular to the surface: R1 and the major axis / minor axis of the smaller surface: R2 Ratio: About the point where R1 / R2 is 1.0 to 2.0 In the present invention, the major axis / minor axis of the larger one of the major axis / minor axis of the crystal grain in one plane and a plane perpendicular to the plane: The ratio of the major axis / minor axis: R2 of R1 and the smaller surface: R1 / R2 needs to be 1.0 to 2.0, preferably 1.0 to 1.5. In the present invention, the ratio of major axis / minor axis indicates the orientation of crystal grains, and the larger the ratio, the more remarkable the orientation. Further, a ratio of major axis / minor axis of 1.0 indicates that the major axis / minor axis of the crystal grain size is the same on any plane. When the ratio of major axis / minor axis exceeds 2.0, it indicates that there is orientation of crystal grains, and as a result, the distortion of the sintered body increases and the mechanical properties deteriorate, resulting in a thermal shock resistance. This is not preferable because it shows a decrease in durability and durability.
“Oriented” or “orientated” means that the shape of crystal grains of “one surface of the sintered body” and “surface perpendicular to the surface of the sintered body” are greatly different. . For example, as shown in FIG. 5, in the case of being oriented, one surface has a lot of elongated particles, and the surface perpendicular to the surface has a lot of round particles. This is a case where there are crystal grains having the same shape on both the surface and the surface perpendicular to the surface.
The numerical value of the orientation is obtained by measuring 50 major / minor axis diameters of “one surface of the sintered body” and “a plane perpendicular to the surface of the sintered body” to obtain an average value. The larger one is R1, and the smaller one is R2, and is represented by R1 / R2. In the case of orientation, the difference between R1 and R2 becomes large, and R1 / R2 becomes larger than 2.0. Moreover, when it is not oriented, the difference between R1 and R2 is almost eliminated, so that it is in the range of 1.0 to 2.0.

The method for producing an alumina sintered body having excellent corrosion resistance, thermal shock resistance and durability according to the present invention will be described.
The alumina raw material powder to be used preferably has an alumina content of 99.7% by weight or more, more preferably 99.9% by weight or more, and an average particle diameter of 0.5 to 3 μm, preferably 0.5 to 2 μm. It is necessary to be. In addition, it is preferable that the fluorine content of the alumina raw material powder is 100 ppm or less. Further, the fluorine compound used preferably has a purity of 99.7% by weight or more, more preferably 99.9% by weight or more, and the average particle diameter is preferably 25 μm or less, more preferably 15 μm or less. Since the fluorine compound has fine primary particles and easily aggregates, the average particle diameter here is a value obtained by measuring an aggregate of the fluorine compound by a laser diffraction method. The raw material for refractories, such as alumina raw material powder, is used to promote the growth of alumina crystal particles by adding a fluorine compound when aluminum hydroxide is baked into alumina. It is necessary to react the raw material powder and the fluorine compound by firing, and when using the alumina raw material powder prepared by adding the fluorine compound to the aluminum hydroxide raw material powder in advance, only the disadvantage of low sinterability In addition, an alumina sintered body having the microstructure of the present invention cannot be obtained.
When the purity of the alumina raw material powder and the fluorine compound is less than 99.7% by weight, the amount of impurities contained in the alumina sintered body excellent in corrosion resistance, thermal shock resistance and durability is increased, and the alumina grain boundary Since the glass phase or the second phase is formed on the surface, not only the corrosion resistance but also deformation due to load loading is likely to occur at high temperatures. When the average particle diameter of the alumina raw material powder is less than 0.5 μm, the powder is likely to agglomerate and the moldability and the like are lowered, which is not preferable. On the other hand, when the alumina raw material powder exceeds 3 μm, the predetermined pulverization / dispersion time becomes long, and as a result, the amount of impurities increases due to the mixing of wear powder from the pulverizer, such being undesirable. When the average particle size of the fluorine compound exceeds 25 μm, the dispersion is inferior due to strong aggregation, and as a result, the uniform mixing and dispersibility of the alumina raw material powder and the fluorine compound is inferior, and the alumina crystal does not react sufficiently during firing. This is not preferable because the shape of the particles becomes uneven and the corrosion resistance, thermal shock resistance and durability are poor.

  The above raw materials are used, and the fluorine compound is added so as to be 0.03 to 0.5% by weight, preferably 0.05 to 0.3% by weight, and blended so that the composition of the raw materials becomes a predetermined ratio. Then, it is pulverized and dispersed using a wet ball mill or an attrition mill. When the fluorine compound is less than 0.03% by weight, the microstructure cannot be controlled by adding the fluorine compound, and when it exceeds 0.5% by weight, not only the sinterability is lowered but also the glass phase or the second phase is crystallized. It is not preferable because it forms a lot at the grain boundary and deteriorates the corrosion resistance and mechanical properties.

  In the present invention, examples of the fluorine compound used include magnesium fluoride and calcium fluoride.

Furthermore, the addition of zirconia powder is effective as a sintering aid, but the addition amount is preferably less than 0.1% by weight, and if it exceeds 0.1% by weight, the crystal particles are likely to be granular. Therefore, it is not preferable. In addition, the zirconia sintered body has lower corrosion resistance than the alumina sintered body, and therefore, when used as a heat treatment member, it is corroded by the object to be processed, and the zirconia component is mixed into the object to be processed. Is not preferable.
The average particle size after pulverization / dispersion is controlled by adjusting the powder concentration during pulverization / dispersion, the diameter of the balls used and the processing time. The average particle size after pulverization / dispersion is preferably 2 μm or less, more preferably 1.5 μm or less. When the average particle diameter exceeds 2 μm, the density of the compact does not increase, the sinterability decreases, and the porosity increases, which is not preferable because the corrosion resistance decreases. The lower limit is about 0.3 μm.

As a forming method, an ordinary ceramic forming method can be employed, and press forming, rubber press forming, cold isostatic pressing (CIP), or the like is employed. If necessary, a known molding aid (for example, wax emulsion, PVA, acrylic resin, etc.) is added to the obtained pulverized / dispersed slurry, and dried by a known method such as a spray dryer to produce a molded powder. Use to mold.
The obtained molded body is fired in the atmosphere at 1600 to 1800 ° C., preferably 1650 to 1750 ° C. When the firing temperature is less than 1600 ° C., the sintering is insufficient and the pores are increased, and the corrosion resistance is lowered. This is not preferable, and when it exceeds 1800 ° C., the sinterability is improved, but abnormal grain growth and grain Since pores are easily generated in the boundary, it is not preferable.

The alumina sintered body excellent in corrosion resistance, thermal shock resistance and durability of the present invention has the following excellent properties.
(1) Since the corrosion resistance is excellent, it is possible to prevent the object to be heat-treated from being contaminated.
(2) Since the high temperature characteristics are excellent, there is little deformation at high temperatures.
(3) Since it has excellent thermal shock resistance, it can sufficiently withstand repeated heating and cooling.
(4) The alumina sintered body excellent in corrosion resistance, thermal shock resistance and durability of the present invention has excellent heat resistance and corrosion resistance as described above, and utilizes such excellent properties. Thus, it can be effectively used as a member for heat treatment of electronic parts such as synthesis of positive electrode materials for lithium secondary batteries, synthesis of phosphor materials, ceramic capacitors, piezoelectric bodies and dielectrics. Furthermore, it is also effective as a crucible for melting metals and alloys. In addition, since it has excellent thermal shock resistance, it is effective for various heat treatment core tubes, high-temperature transfer rollers, support tubes, radiant tubes, gas blowing tubes, and gas sampling tubes. It is particularly effective for use in reducing, vacuum and inert atmospheres.

  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. 1-6)
Example No. 1 to 3 and Comparative Example No. 1 In Examples 5 and 6, alumina raw material powder having a purity of 99.8% by weight and an average particle diameter of 0.8 μm was used as the raw material. 4, 5 and Comparative Examples 2 and 3 use alumina raw material powder having a purity of 99.8% by weight and an average particle size of 1.5 μm as a raw material. 1 is an alumina raw material powder composed of plate-like particles having a purity of 99.88% by weight and an average particle diameter of 3 μm, and an alumina raw material powder composed of granular particles having a purity of 99.89% by weight and an average particle diameter of 0.5 μm. It was used by mixing at a weight ratio of 8: 2. No. 4 used alumina raw material powder having a purity of 99.85% by weight and an average particle size of 3.5 μm and a fluorine content of 170 ppm. In addition, Example No. 1-5 and Comparative Example No. Nos. 2 to 5 use calcium fluoride having a purity of 99.9% by weight and an average particle size of 15 μm. 6 used calcium fluoride having a purity of 99.9% by weight and an average particle diameter of 45 μm.
As shown in Table 1, the alumina raw material powder and calcium fluoride powder are blended so as to be a predetermined amount, and are pulverized, dispersed, and mixed using water as a solvent using an alumina ball and pot mill to produce a slurry. did. Table 1 shows the average particle size of the pulverized powder of the obtained slurry. The obtained slurry was cast by a plaster mold and fired at 1550 ° C. to 1800 ° C. to obtain an alumina sintered body having a diameter of 6 × 45 mm. Table 2 shows the characteristics of the obtained alumina sintered body. Example Sample No. Nos. 1 to 5 are alumina sintered bodies within the scope of the present invention (Examples). Nos. 1 to 6 are alumina sintered bodies that do not satisfy at least one of the requirements of the present invention (Comparative Example).
The “pulverized powder” in Table 1 is “alumina raw material powder and calcium fluoride powder (fluorine compound) mixed in a predetermined amount, pulverized / dispersed / mixed, and pulverized. It refers to the average particle size of “powder”.

  Example Sample No. which falls within the scope of the present invention. A scanning electron micrograph of 4 is shown in FIG. Further, for a scanning electron micrograph outside the scope of the present invention, the comparative sample No. 1 is shown in FIG. 3 is shown in FIG. 6 is shown in FIG.

  In the corrosion resistance test, a lead zirconate titanate (PZT) molded body was placed on each sintered body, and after heat treatment at 1250 ° C. for 5 hours in an electric furnace, the erosion depth of PbO as a component of the PZT molded body was measured. . The erosion depth was determined by analyzing the cross section of the sintered body by energy dispersive X-ray analysis (EDX). The results are shown in Table 2.

  In the thermal shock test, a sample was placed in an electric furnace, heated at 180 ° C. for 30 minutes, and dropped into water at 20 ° C., and the sample after the test was evaluated by the presence or absence of cracks due to fluorescent flaw detection. In the durability test, the same sample as above was heated at 150 ° C. for 30 minutes and dropped into water at 20 ° C., and the test was repeated 10 times. The results are shown in Table 2.

The left and right drawings of FIGS. 1 to 3 arrange “one surface of the sintered body” and “a surface perpendicular to the surface” as shown in FIG. That is, it is an SEM photograph of one surface (left) of each sintered body and a surface perpendicular to the surface (right).
As is clear from Table 2 above, the sintered body of the present invention has high thermal shock resistance and durability while having high corrosion resistance. For example, in the sintered body of Example (Sample No. 4), the average value of the major axis / minor axis of one surface as shown in Photo 1 in FIG. As shown in FIG. 1, both are 2.0 or more and are within the scope of the present invention. In addition, the major axis / minor axis: R1 of one surface and the surface having a larger major axis / minor axis of the crystal particle (Photo 1) and a surface having a smaller major axis / minor axis (Photo 2). The ratio of major axis / minor axis :) of R2: R1 / R2 is shown in Table 1 and is 1.04, which is within the scope of the present invention. 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. .
For example, in the comparative example (sample No. 1), as shown in FIG. 2, the major axis / minor axis: R1 of one surface and the surface with the larger major axis / minor axis of the surface perpendicular to the surface (Photo 3): R1 Is within the scope of the present invention as shown in Table 1, but the major axis / minor axis of the smaller major axis / minor axis (Photo 4): R2 and R1 / R2 are out of the scope of the present invention and It became inferior. The comparative example (sample No. 2) was out of the range of the present invention in terms of the average crystal grain size, and was inferior in corrosion resistance and thermal shock resistance. As shown in photographs 5 and 6 in FIG. 3, the comparative example (sample No. 3) is the main point in that the major axis / minor axis of the crystal grains on one plane and the plane perpendicular to the plane are both 2.0 or more. It was outside the scope of the invention, and was inferior in thermal shock resistance. The comparative example (sample No. 4) was out of the range of the present invention in terms of bulk density, and was inferior in corrosion resistance, thermal shock resistance and durability. In the comparative example (sample No. 5), the major axis / minor axis of the larger diameter / minor axis of the crystal grain of one surface and the surface perpendicular to the surface: R1 is within the scope of the present invention. The average crystal grain size, the major axis / minor axis of the smaller one of the major axis / minor axis of the crystal grain of one plane and the plane perpendicular to the plane: out of the scope of the present invention in terms of R2 and R1 / R2. The durability was inferior. In Comparative Example (Sample No. 6), as shown in Photo 7 of FIG. 4, the major axis / minor axis of the larger one of the major axis / minor axis of the crystal grain of one surface and the surface perpendicular to the surface: R1 Is within the scope of the present invention, but the major axis / minor axis of the smaller major axis / minor axis shown in Photo 8 is outside the scope of the present invention, and the shape of the crystal grains is extremely uneven. Therefore, it was inferior in corrosion resistance, thermal shock resistance and durability.
The sintered body made of plate-like crystal particles as in the present invention has two ways of arranging the crystal particles. As shown in FIG. 5A, when oriented, the plate-like crystal particles are regularly arranged in a certain direction. On the other hand, as shown in FIG. 5B, when not oriented, the plate-like crystal particles are irregular and face in various directions. That is, when the microstructures of both sintered bodies are observed on “one surface” and “a surface perpendicular to the surface”, the result is as shown in FIG.

Sample No. within the scope of the present invention (Example). 4 is a scanning electron micrograph of No. 4; Sample No. which is outside the scope of the present invention (comparative example). 1 is a scanning electron micrograph of 1. Sample No. which is outside the scope of the present invention (comparative example). 3 is a scanning electron micrograph of 3. Sample No. which is outside the scope of the present invention (comparative example). 6 is a scanning electron micrograph of 6. (A) is a figure which shows an example when the crystal grain is orientated, (B) is a figure which shows an example when the crystal grain is not oriented.

Claims (3)

(A) An alumina sintered body having an alumina content of 99.5% by weight or more, (b) a bulk density of 3.7 g / cm ³ or more, and (c) an average crystal grain size of 20 to 70 μm, (d) the major axis / minor axis of the crystal grain of one surface of the sintered body and the surface perpendicular to the surface are both 2.0 or more, and (e) one surface and the surface perpendicular to the surface The major axis / minor axis of the surface having the larger major axis / minor axis of the crystal particle: R1 and the major axis / minor axis of the smaller surface: R2 ratio: R1 / R2 is 1.0 to 2.0. Alumina sintered body with excellent corrosion resistance, thermal shock resistance and durability.   A member for heat treatment comprising an alumina sintered body having excellent corrosion resistance, thermal shock resistance and durability according to claim 1.   0.03 to 0.5% by weight of a fluorine compound having an average particle size of 25 μm or less is added to an alumina raw material powder having an alumina content of 99.7% by weight or more and an average particle size of 0.5 to 3 μm. The alumina sintered body excellent in corrosion resistance, thermal shock resistance and durability according to claim 1, wherein the diameter is pulverized and mixed to 2 µm or less, molded, and fired at 1600 to 1800 ° C in the air. Production method.