TWI586461B - An alumina sintered body and a method for producing the same - Google Patents

Description

Alumina sintered body and method of producing the same

The present invention relates to the field of precision ceramics, and more particularly to an alumina sintered body and a method of producing the same.

Precision ceramics are used in various fields such as information communication, precision machinery, and medical treatment. Among them, the representative is an alumina sintered body. Alumina is relatively inexpensive, has high versatility, and is excellent in mechanical strength, heat resistance, corrosion resistance, and the like, and thus is often used as a structural member. However, the alumina sintered body has poor workability, and requires a large amount of processing when a structural member having a large or complicated shape is produced, which tends to increase the processing cost ratio in the manufacturing cost. Therefore, if the workability can be improved, it can be expected to significantly reduce the manufacturing cost.

Products made of titanium oxide and aluminum oxide are those having electrical characteristics of electrostatic chucks. For example, an electrostatic chuck chassis obtained by calcining a titanium oxide as a main component and adding titanium oxide in a reducing atmosphere is proposed (refer to Japanese Laid-Open Patent Publication No. Hei 06-97675).

In order to improve strength and damage toughness, there are also materials with characteristic tissue structure. It is proposed that anisotropic alumina crystal particles having a long diameter of 3 [μm] or less and an aspect ratio of 1.5 or less are mixed with anisotropic alumina crystal particles having a long diameter of 10 [μm] or more and an aspect ratio of 3 or more. The alumina sintered body (refer to Japanese Laid-Open Patent Publication No. Hei 09-87008).

There are also those who pursue easy processing. Proposal: Aluminum-based composites containing aluminum borate A material-processable composite material obtained by injecting a molten aluminum alloy into an aluminum borate powder and casting it (refer to Japanese Laid-Open Patent Publication No. 2004-353049).

However, in the electrostatic chuck chassis described in the prior art document, when aluminum oxide is added in an amount of 0.5 to 2.0% by weight and calcined in a reducing atmosphere, aluminum titanate should be formed, and titanium oxide may be deficient in oxygen. Therefore, when aluminum titanate is formed and microparticles are formed, there is a possibility that the workability is lowered due to the unevenness of the particles, or the original milky white appearance of the alumina is impaired.

In the alumina sintered body described in the prior art, the isotropic alumina crystal particles are mixed with the anisotropic alumina crystal particles, so that the sintered body structure is uneven, and processing may become difficult. The easy-to-process composite material described in the prior art document 3 is troublesome because it is produced by casting.

The present invention has been made in view of such circumstances, and an object of the invention is to provide an alumina sintered body having a uniform sintered structure and excellent workability, and a method for producing the same.

(1) In order to achieve the above object, the alumina-based sintering system of the present invention comprises crystal particles and a grain boundary phase; wherein, in the crystal particles, titanium or a titanium compound is dissolved in a titanium oxide ratio of 0.08 [% by weight] Above and 0.30 [% by weight] or less.

According to the alumina sintered system of the present invention, titanium or a titanium compound is solid-dissolved in the crystal lattice to promote grain growth, so that the sintered body structure is uniform and the workability is improved. Moreover, the formation of aluminum titanate and the oxygen deficiency of titanium oxide are hard to occur.

(2) The alumina-based sintered system of the present invention has an average major axis length of the crystal particles of 20 [μm] or more. By having such a particle shape, the processing resistance can be reduced.

(3) A method for producing an alumina sintered body of the present invention, which is a method for producing an alumina-based sintered body in which titanium oxide is solid-solved in crystal particles, and comprises: a ratio of alumina powder to titanium oxide powder by mass ratio of 99.95 a step of mixing in a range of 0.050 to 99.5:0.50; and after molding the mixed powder, the obtained molded body is heated from a room temperature to a calcination temperature at a temperature increase rate of 80 [° C./hr] or less to be calcined. Calcination step.

Since calcination is carried out by raising the temperature to a calcination temperature at a temperature increase rate of 80 [° C./hr] or less from room temperature, titanium or a titanium compound is solid-solubilized in the alumina to promote grain growth. Thereby, an alumina sintered body having a uniform sintered body structure and good workability can be produced. Further, since calcination is carried out in an atmospheric environment, generation of aluminum titanate and oxygen deficiency of titanium oxide can be prevented.

According to the present invention, since titanium or a titanium compound enters in the crystal lattice to promote grain growth, the sintered body structure is uniform and the workability is good. Moreover, the formation of aluminum titanate and the oxygen deficiency of titanium oxide are less likely to occur.

(Composition of alumina sintered body)

The alumina-based sintering system of the present invention is composed of crystal particles of alumina and a grain boundary phase. In the crystal particles, titanium or a titanium compound is solid-solved in an amount of 0.08 [weight%] or more and 0.30 [% by weight] or less in terms of titanium oxide. By solid-dissolving titanium or a titanium compound in the crystal lattice to promote grain growth, the sintered body structure can be made uniform and the workability can be improved. Further, the formation of aluminum titanate and the oxygen deficiency of titanium oxide are less likely to occur, and the original coloration of the alumina sintered body can be maintained.

The average major axis length of the alumina sintered body is preferably 10 [μm] or more. Accordingly, since the grain growth is sufficiently performed, the workability is high. However, if the crystal grains are excessively grown, pores are likely to be formed and the density may be impaired. Therefore, the average major axis length is preferably 50 [μm] or less.

Further, the average long axis length of the alumina crystal particles is preferably 20 [μm] or more. By having such a particle shape, the processing resistance can be reduced.

(Manufacturing method of alumina sintered body)

Next, a method of producing an alumina sintered body will be described. First, the high-purity alumina powder and the high-purity titanium oxide powder are mixed in a mass ratio of 99.95:0.050 to 99.5:0.50 to form an alumina powder, preferably having a purity of 99% or more, more preferably 99.9% or more. By. Further, the particle diameter of the alumina powder to be used is preferably 1.0 [μm] or less. Further, it is more preferably 0.1 [μm] or more and 0.5 [μm] or less.

The purity of the added titanium oxide powder is preferably 99% or more, and more preferably More than 99.9%. Further, the particle diameter of the titanium oxide powder is preferably 0.5 [μm] or less. It is more preferably 0.03 [μm] or less. Further, although it is preferable to add the titanium oxide powder, it is not limited thereto, and may be added in various forms such as a chloride which forms an oxide after sintering in the atmosphere, and an organic titanium compound. By using titanium oxide powder, an alumina sintered body excellent in workability can be obtained.

The slurry of the alumina powder and the titanium oxide powder can be mixed using a ball mill. For example, it is mixed and slurried using a resin container filled with alumina balls. A raw material powder is prepared by appropriately adding a dispersing agent, a binder, or the like and mixing them.

The obtained raw material powder was dried and subjected to molding. For example, uniaxial press forming by a mold and molding by CIP. The raw material powder can be formed in various forms such as uniaxial compression molding, CIP molding, wet molding, pressure casting, and sludge casting. Among them, casting molding such as pressure casting and sludge casting is preferred. The slurry used in this case is preferably produced by thorough mixing. For example, the mixing time is set to 18 hours or more. By thoroughly mixing, a uniformly dispersed slurry can be obtained.

The obtained molding system is heated from room temperature to a calcination temperature at a temperature increase rate of 80 [° C./hr] or less, and calcined at 1500 [° C.] or more and 1700 [° C.] or less. The calcination temperature is set to a temperature at which the average major axis length of the alumina sintered body is 20 [μm] or more and can be sufficiently densified.

The calcination is preferably carried out under normal pressure in various environments such as atmosphere, vacuum or inert gas. Among them, the atmospheric environment of atmospheric pressure is better. When calcined in a reducing environment containing a reducing substance such as carbon or CO, there is a blue of the sintered body. The color spots tend to be obvious, but this can be prevented if it is carried out in an atmospheric atmosphere.

The temperature increase rate from room temperature to the calcination temperature is preferably 80 [° C./hr] or less. It is more preferably 50 [°C/hr] or less. By lowering the rate of temperature rise, the titanium or titanium compound is easily dissolved in alumina and the crystal grain size is uniformized. When the temperature increase rate is more than 80 [° C./hr], it is difficult to form a solid solution, and as a result, coloring occurs in the material, and cracking, cracking, and the like are likely to occur during firing.

(experimental results)

The experimental results are as follows. Table 1 shows the manufacturing conditions and evaluation of the samples 1 to 18.

(sample 1~10)

An alumina powder having an average particle diameter of 0.5 [μm] and a purity of 99.5%, and a titanium oxide powder having an average particle diameter of 0.02 [μm] and a purity of 99.9% were mixed into a mixed powder according to the mixing ratio shown in Table 1. The mixing of the respective powders was carried out by using a resin container containing an arbitrary amount of Φ10 alumina balls, mixing for 18 hours, and slurrying. After the slurry is dried, it is molded by uniaxial pressure molding by a mold and CIP, and the molded body is fired.

In the alumina powder, titanium oxide is charged and mixed in a mass ratio of 99.95:0.050 to 99.5:0.50, and the molded body of the mixed powder is heated to 1500 to 1700 at a temperature rising rate of 10 to 80 [° C./hr]. °C], after maintaining for 3 hours, natural cooling was used to obtain a sintered body. The production conditions and results of the obtained sintered body are shown in Table 1 in Samples 1 to 10. All of the aluminum oxide particle diameters have an average major axis length of 20 [μm] or more, and are excellent in workability.

(sample 11~18)

In the alumina powder, titanium oxide is charged and mixed in a mass ratio of 99.90:0.1 to 99.0:1.0, and heated to a temperature of 1400 to 1700 [° C.] at a temperature increase rate of 25 to 100 [° C./hr] for 3 hours. Thereafter, the sintered body was obtained by natural cooling. The production conditions and results of the obtained sintered body are shown in Table 1 in Samples 11 to 18. Compared with the sample 1 to 10, the sample containing more titanium oxide showed blue spots on the sintered body. Further, among the samples having a low calcination temperature, the average major axis length of the alumina particle diameter is 4 [μm] or less, and the workability is low.

(evaluation method)

The evaluation methods performed in the above examples and comparative examples will be described. First, the obtained alumina-based sintered body was measured for the sintered body density, the solid solution amount of titanium or titanium compound in terms of titanium oxide, and the average particle diameter. The sintered body density was measured by the Archimedes method. The amount of solid solution in terms of titanium oxide of titanium or titanium compound is determined by inductively coupled plasma luminescence spectrometry (SPS-3500 manufactured by SII NanoTechnology Inc.) using inductively coupled plasma luminescence spectrometry. The method was determined by quantitative analysis.

The total amount of titanium contained in the alumina sintered body is obtained by dissolving a sample in a pressurized container using sulfuric acid and performing quantitative analysis of titanium contained in the solution. The total amount of titanium contained in the alumina sintered body is a total amount of titanium dissolved in the alumina crystal particles and titanium which is not dissolved in the crystal grain boundary.

In the alumina sintered body, the amount of titanium contained in the crystal grain boundary is further heated by hydrofluoric acid-aqua regia mixed with a sample for 30 minutes under normal pressure, and the titanium contained in the filtrate is applied after filtering the insoluble matter. The quantitative analysis can be obtained. Then, the amount of titanium contained in the crystal grain boundary is subtracted from the total titanium amount, and the amount of titanium dissolved in the alumina crystal particles is determined and compared in terms of oxide. The average particle diameter was subjected to mirror polishing on the surface of the sintered body, and the polished surface on which the crystal grain boundary was precipitated by thermal etching was observed by SEM. Each particle was approximated as a rectangle, and the long side was set to the long axis, and the length was measured, and the average value was calculated. In addition, the average value was obtained by taking the number of samples of 15.

Claims (3)

An alumina-based sintered body is composed of a crystal particle and a grain boundary phase. Among the crystal particles, titanium or a titanium compound is dissolved in a solid oxide ratio of 0.08 [% by weight] or more and 0.30 [% by weight]. the following. The alumina sintered body according to the first aspect of the invention, wherein the crystallites have an average major axis length of 20 [μm] or more. A method for producing an alumina sintered body, which is a method for producing an alumina sintered body in which titanium oxide is solid-solved in crystal particles; and comprises: a ratio of alumina powder to titanium oxide powder by mass ratio of 99.95: 0.050 to 99.5: A step of mixing in a range of 0.50; and a calcination step in which the obtained molded body is heated from a room temperature to a calcination temperature at a temperature increase rate of 80 [° C./hr] or less to form a calcination.