JP2013010668A - Alumina ceramics, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide alumina ceramics having high processing efficiency, while having high purity, and generating few breaks or chippings during processing, and to provide a method for producing the same.SOLUTION: The alumina ceramics having alumina purity of ≥99.5 wt.% contain ≥60% anisotropic crystal particles 10 of alumina having a major axis length of ≥10 μm and an aspect ratio of ≥2. Since the larger particle size of alumina particles has lower resistance of a grain boundary, processing efficiency becomes high because the major axis length of the alumina particles is ≥10 μm. Since the aspect ratio of alumina particles is ≥2, when being hit by a grindstone in some fixed direction G, a tendency of being easily broken appears remarkably. Resultantly, the alumina ceramics can be obtained, having high processing efficiency, while having high purity, and generating few breaks or chippings during processing.

Description

  The present invention relates to an alumina ceramic having an alumina purity of 99.5% by weight or more and a method for producing the same.

Conventionally, an alumina member excellent in strength has been applied to various fields and uses. For example, the alumina sintered body described in Patent Document 1 has an isotropic Al ₂ O ₃ crystal grain having a major axis of 3 μm or less and an aspect ratio of 1.5 or less in a total amount of 15 to 80% by volume, and a major axis of 10 μm or more. Anisotropic Al ₂ O ₃ crystal grains having an arpect ratio of 3 or more are contained at a ratio of 20 to 85% by volume in the total amount. And it is trying to improve intensity | strength and fracture toughness with such a composition.

On the other hand, research and development focusing on workability is also being conducted. Aluminum-based composite material described in Patent Document 2, by including particles of aluminum borate represented by the chemical formula _{9Al 2 O 3 · 2B 2 O} 3 50~75 vol%, high Young's modulus, specific gravity small and machining We are trying to provide a material that is easy and has a high fracture toughness value.

  On the other hand, alumina members are used as members of semiconductor and liquid crystal manufacturing apparatuses because of their high corrosion resistance and mechanical strength in corrosive environments such as fluorine plasma. A higher-purity alumina member is desired for use in such an environment.

Japanese Patent Application Laid-Open No. 09-87008 JP 2004-353049 A

  However, since high-purity alumina has high mechanical strength, when trying to manufacture a large-sized and complex part required in recent years, the processing time increases and the cost increases. Furthermore, chipping and the like during processing are likely to occur. On the other hand, the aluminum-based composite material described in Patent Document 2 is excellent in cutting workability, but the purity of alumina is too low to be used for a member of a semiconductor or liquid crystal manufacturing apparatus, and contamination is easily caused by boron.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an alumina ceramic and a method for producing the same, which have high processing efficiency and low chipping and chipping during processing despite high purity. And

  (1) In order to achieve the above object, the alumina ceramic of the present invention is an alumina ceramic having an alumina purity of 99.5% by weight or more, a major axis length of 10 μm or more, and an aspect ratio of 2 or more. It is characterized by containing 60% or more of anisotropic crystal grains of alumina.

  As the particle diameter of the alumina particles increases, the resistance of the grain boundary decreases, so that the length of the major axis of the alumina particles is 10 μm or more, thereby increasing the processing efficiency. In addition, since the aspect ratio of the alumina particles is 2 or more, the tendency to break easily appears when the grindstone hits in a certain direction. As a result, it is possible to obtain an alumina ceramic that has high processing efficiency and little chipping or chipping during processing despite its high purity.

  (2) Further, the alumina ceramic of the present invention is characterized in that the anisotropic crystal particles of the alumina contain an average of two or more pores per particle. As described above, since two or more pores per particle are included on average, breakage within the particles is likely to occur, and alumina ceramics has high processing efficiency and can reduce chipping and chipping during processing.

  (3) The method for producing an alumina ceramic of the present invention is a method for producing an alumina ceramic having an alumina purity of 99.5% by weight or more, wherein the average particle size is 0.5 μm or more and 1 μm or less, and the major axis direction A step of forming an alumina particle comprising particles having a length of 0.5 μm or more and an aspect ratio of 2 or more, and a step of firing the formed alumina particle at 1400 ° C. or more for 3 hours or more. It is characterized by that.

  Thus, since the alumina granule which consists of particle | grains with an average particle diameter of 0.5 micrometer or more is used, a pore tends to remain in particle | grains. On the other hand, since the alumina particle | grains which consist of particle | grains with an average particle diameter of 1 micrometer or less are used, it can prevent that a pore generate | occur | produces in a grain boundary. In addition, since the alumina granule contains particles having an aspect ratio of 2 or more and a length in the major axis direction of 0.5 μm or more, the anisotropic crystalline particles of alumina having an aspect ratio of 2 or more in the obtained alumina ceramics. Generated.

  (4) Moreover, the manufacturing method of the alumina ceramics of this invention is characterized by the temperature increase rate of the said baking process being 300 degrees C / h or less. Thereby, the alumina ceramics whose thickness after sintering is 10 mm or more can be easily fired. In particular, if the rate of temperature rise is too high, a temperature difference is likely to occur between the surface and the inside, and a difference in workability due to the site occurs.

  (5) Moreover, the manufacturing method of the alumina ceramics of this invention is characterized by using the alumina granule which added Ti oxide as an additive in the said formation process. Thereby, alumina particles having a major axis length of 10 μm or more can be easily generated.

  According to the present invention, it is possible to increase processing efficiency and reduce chipping and chipping during processing despite being a high-purity alumina ceramic.

(A) (b) It is a conceptual diagram which shows the relationship between arrangement | positioning of the alumina particle of each surface, and the direction which a grindstone hits. It is the image figure which imitated the SEM photograph of the surface of the alumina ceramics of this invention.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description, “processing” refers to grinding using a diamond grindstone.

(Configuration of alumina ceramics)
The alumina ceramic of the present invention (hereinafter referred to as “alumina ceramic”) has an alumina purity of 99.5% by weight or more, and is used, for example, as a member of a semiconductor or liquid crystal manufacturing apparatus. The length of the long axis of the alumina particles contained in the alumina ceramic is 10 μm or more, and the larger the particle size of the alumina particles, the lower the resistance of the grain boundary, so that the processing efficiency of the member increases. In particular, alumina ceramics are suitable for members having a thickness of 10 mm or more because there is no difference in workability between the surfaces.

  The alumina ceramic contains 60% or more of anisotropic crystal grains of alumina having a major axis length of 10 μm or more and an aspect ratio of 2 or more. Preferably, the content of anisotropic crystal particles is 70% or more. The aspect ratio of the anisotropic crystal particles is 2 or more, and such particles tend to be easily broken when a grindstone hits in a certain direction. Grinding is processed by hitting the workpiece with a grindstone when viewed microscopically. The micro mechanism during processing will be described below.

  FIGS. 1A and 1B are conceptual diagrams showing the relationship between the arrangement of alumina particles on the surface and the direction in which the grindstone strikes, respectively. FIGS. 1A and 1B show the cross section of particles near the grinding surface of alumina ceramics and the direction in which the grinding wheel of the grinding grinder hits. In the example shown in FIG. 1A, the direction G in which the grindstone strikes is perpendicular to the major axis direction of the anisotropic crystal particles 10. Further, in the example shown in FIG. 1B, the direction G in which the grindstone strikes is parallel to the major axis direction of the anisotropic crystal particle 10. Compared to the arrangement shown in FIG. 1B, the arrangement shown in FIG.

  The direction of the major axis of the anisotropic crystal grains of alumina may have some orientation, but is preferably random. When the structure has orientation, chipping and chipping are likely to occur on a specific surface unless the grinding conditions are changed depending on the processed surface. However, in the case of complicated machining using a machining center, it is difficult to change the machining conditions for only a specific surface. When the alumina particles have an aspect ratio, the c-axis becomes long. In the case of an alumina sintered body, the resulting alumina ceramic structure may have orientation depending on the forming method or firing method.

  It is preferable that the number of pores contained in one anisotropic crystal particle of alumina in the alumina ceramic is two or more on average. The more pores, the more likely to break in the particles during processing. However, if there are too many pores, it leads to a decrease in density. Therefore, the number of pores per anisotropic crystal grain is preferably 15 or less. Also, if the average number of pores per particle of anisotropic crystal particles exceeds 15, it becomes a source of contamination when used in semiconductor manufacturing equipment, and especially dust from outside and fine pores can be washed. This is not preferable because it is difficult to remove.

(Production method)
A method for producing alumina ceramics configured as described above will be described. Alumina particles having an average particle diameter of 0.5 μm or more and 1 μm or less are used for alumina particles as a raw material for the alumina ceramics. When particles having an average particle size of less than 0.5 μm are used, pores hardly remain in the particles. On the other hand, if it exceeds 1 μm, pores are likely to be generated at the grain boundaries. The raw material alumina particles include particles having an aspect ratio of 2 or more and a length in the major axis direction of 0.5 μm or more. By including such particles, anisotropic crystal particles having an aspect ratio of 2 or more in the alumina ceramics are generated. Particles having an aspect ratio of 2 or more and a length in the major axis direction of 0.5 μm or more are preferably 5% by volume or more.

  Next, the raw material alumina granules prepared in this way are formed. As a molding method, CIP or casting can be used. Moreover, you may carry out by a hot press or HIP. Since the molding method is related to the control of the orientation, it is preferable to select a molding method in which the orientation is less likely to occur.

  The formed alumina particles, that is, the formed body, are fired in the atmosphere at 1400 ° C. or higher for 3 hours or longer. Baking at 1500 ° C. or higher for 3 hours or longer is preferable, and baking at 1500 ° C. or higher for 5 hours or longer is more preferable. Moreover, it is preferable that this temperature increase rate is 300 degrees C / h or less. This is because if the rate of temperature rise is too high, a temperature difference is likely to occur between the surface and the inside, the microstructure is different, and a workability difference depending on the site occurs. In particular, in order to fire a sintered material having a thickness of 10 mm or more, it is preferable to fire under the above-mentioned raw material conditions and firing conditions.

  It is preferable to add Ti oxide as an additive to the alumina particles. By adding the Ti oxide, particles of 10 μm or more are easily generated in the alumina ceramic. The amount of Ti oxide added is preferably 0.05% by weight or more and 0.5% by weight or less in terms of oxide. More preferably, it is 0.10 weight% or less. When added in an amount of less than 0.05% by weight in terms of oxide, pores are unlikely to remain and grain growth is difficult to proceed. On the other hand, if it exceeds 0.5% by weight in terms of oxide, the purity of alumina cannot be maintained. In addition, an experimental result has been obtained that if the raw material contains a large amount of Ti, it becomes a sintering inhibiting substance and grain growth is less likely to occur.

Further, a group 1A, 2A, 3B or 4B element may be added to the alumina particles. These addition amounts are effective even with a slight amount of impurity level. Such addition further promotes the generation of alumina particles of 10 μm or more in the alumina ceramic. This is due to the lower eutectic point of the alumina and additive elements. As the additive element, Mg, Si, and Ca are particularly preferable. Even when MgO, SiO ₂ , and CaO are present at 50 ppm or less, sufficient effects are obtained.

(Examples and comparative examples)
With respect to the alumina ceramics, examples and comparative examples were prepared, and the presence of processing load, chipping, and chipping was evaluated. As a raw material, alumina particles having a purity of 99.5 wt% and titania having a purity of 99.9 wt% or more and a particle size of 0.4 μm or less and a rutile ratio of 80% or more were used. A solvent, an organic binder, and a dispersing agent were added to such alumina particles in an appropriate formulation, and mill mixed. The mixture thus obtained was granulated with a spray dryer. And the granule was CIP-molded and the plate-shaped molded object of 150x150x20 mm was produced. Furthermore, this was baked at 1400 degreeC or more for 3 hours.

Thus, the workability of the alumina ceramics obtained as a sintered body was evaluated. A diamond grindstone was ground using a wheel fixed with a resin bond. A diamond grindstone having a roughness of # 100 and a wheel diameter of 200 mm was used for grinding at a rotation speed of 2000 rpm. At this time, the load (current display) applied to the shaft of the processing machine was measured. Moreover, the presence or absence of kogation as a chipping or chipping after processing or an alumina surface state was visually observed. “Koge” here means that the resin of the grindstone burns and attaches to the workpiece, and is considered to be caused by the workpiece being hard and having low workability. The contents other than alumina were measured by ICP analysis. Table 1 shows the characteristics of the compositions of Examples and Comparative Examples and the evaluation of processability.

(Particle size and pore in Example)
About said Example 1, the processed surface was grind | polished and SEM observation was carried out. FIG. 2 is an image simulating an SEM photograph of the surface of alumina ceramics. As shown in FIG. 2, the particle size of the alumina particles A was measured by converting the measurement length from the SEM photograph. Further, particles having a major axis of 10 μm or more, a particle size of 2 μm or more, and a pore P of 2 μm or less present in the particles were counted in a 200 × 200 μm area. As shown in Table 2, the number of measured particles was 26, and it was found that 21 particles had an aspect ratio of 2 or more. Therefore, it was found that the ratio of the anisotropic crystal particles to the number of particles was 21/26, which was 80.8%.

In addition, the surface of the alumina ceramic of Example 1 was Ra 0.1 μm or less by lapping, and was etched by thermal. And about 500 times SEM observation was performed about arbitrary places, and the number of pores in a particle was measured in an area of 200 × 200 μm. Since the pores can be observed as bright spots from the surroundings by the lapping and etching described above, the measurement was performed on objects that can be confirmed at a magnification of 500 times. As a guide, a pore of 0.5 μm or more was measured. As a result, it was proved that the anisotropic crystal particles of alumina had an average of two or more pores.

  As described above, despite the high purity, it was possible to obtain an alumina ceramic with high processing efficiency and little chipping or chipping during processing. In particular, it has been demonstrated that even higher effects can be obtained when an average of two or more pores per anisotropic crystal grain of alumina is included.

10 Anisotropic crystal grain G Direction in which the grinding wheel strikes A Alumina particle P Pore

Claims (5)

An alumina ceramic having an alumina purity of 99.5% by weight or more,
Aluminous ceramics comprising 60% or more of anisotropic crystal grains of alumina having a major axis length of 10 μm or more and an aspect ratio of 2 or more.   2. The alumina ceramics according to claim 1, wherein the anisotropic crystal grains of alumina contain an average of two or more pores per particle. A method for producing an alumina ceramic having an alumina purity of 99.5% by weight or more,
A step of molding alumina particles comprising particles having an average particle size of 0.5 μm or more and 1 μm or less, a length in the major axis direction of 0.5 μm or more, and an aspect ratio of 2 or more;
And firing the shaped alumina particles at 1400 ° C. or more for 3 hours or more.   The method for producing an alumina ceramic according to claim 3, wherein a temperature rising rate in the firing step is 300 ° C / h or less.   The method for producing an alumina ceramic according to claim 3 or 4, wherein alumina particles to which Ti oxide is added as an additive are used in the forming step.

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