JPH10324519A - Production of easily sinterable high purity alumina powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce easily sinterable high purity alumina powder in large quantities at a low cost by pulverizing alumina powder having a specified purity to a specified average particle diameter and a specified specific surface area with iron media having a specified diameter and carrying out washing with hydrochloric acid or nitric acid and further washing with sulfuric acid having a specified concn. SOLUTION: A solvent such as water or alcohol is added to commercially available high purity alumina powder having >=99.99% purity to prepare a slurry having about 20-40 wt.% concn. of the alumina powder, the slurry is charged into a crusher such as an attrition mill, a ball mill, an attriter or a bead mill and the powder is pulverized to <=0.2 μm average particle diameter and >=15×10<3> m<2> /kg specific surface area with iron media having <=2 mm diameter. The slurry is then washed with 10-50 times (mol) as much acid soln. as the theoretical amt. expressed by formula I or II and it is filtered. These processes repeated several times. When the acid is hydrochloric acid, dilute hydrochloric acid is preferably used. The slurry is further washed with >=10N sulfuric acid under heating, freed of the acid by washing with pure water, filtered with a filter press, etc., and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing high-purity alumina powder, and more particularly to a method for producing high-purity alumina powder having easy sinterability.

[0002]

2. Description of the Related Art Due to the high integration and miniaturization of semiconductors, ceramics having not only excellent chemical resistance and plasma resistance but also extremely few pores are required for parts and members used in semiconductor manufacturing equipment. In particular, the demand for alumina ceramics which are inexpensive and easy to use is increasing.

[0003] In order to respond to this demand, conventionally, high-purity alumina powder has been subjected to normal pressure sintering and then HIP treatment (hot isostatic pressure treatment) to obtain a sintered body remaining in normal pressure sintering. The number was reduced by crushing the inside pore. However, since this method requires a high temperature of 1500 ° C. or more for normal pressure sintering, grain growth occurs, and a sufficient pore reduction effect is not exhibited even by HIP treatment, and many pores are formed in the sintered body. There is a problem that remains.

[0004] In addition, since a high temperature of 1500 ° C or more is required for normal pressure sintering, a HIP processing temperature of 1400 ° C or more is required. Therefore, a heat source (heater) and a heat insulating material of the HIP processing apparatus are made of carbon material. Needed to be formed. As a result, problems arise in the structure and durability of the HIP processing apparatus,
There is no large-scale HIP device capable of performing the HIP process at a temperature of 00 ° C. or higher, and there is a problem that the size of a manufactured product is limited.

In order to solve this problem, as a method for producing high-purity alumina powder which can be sintered at a temperature of 1400 ° C. or less, aluminum carbonate hydroxide ammonium (NH ₄ AlCO ₃ (OH)) is used. After the decomposition, a method of manufacturing by roasting at a temperature of 1200 to 1400 ° C. is described in “Kirakukyo, 84, 255 to 258 (199).
6) ". In addition, a method of hydrolyzing an aluminum alkoxide and calcining the obtained hydrate to produce the hydrate is also described in “Chemical Review, 48, 173-178 (198).
5) ". These methods are high-purity and extremely fine powders of the produced alumina powder, so that the powder can be sintered under normal pressure even at a low temperature of 1400 ° C. or less.

[0006]

However, the former method has a problem that a large amount of alumina powder cannot be produced due to the complicated production steps. Also, in the latter method, since the aluminum alkoxide to be used is expensive, the produced alumina powder becomes very expensive, and there is a problem that the alumina powder cannot be produced at low cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the method for producing an easily sinterable high-purity alumina powder which can be sintered at a low temperature. An object of the present invention is to provide a method for producing a high-purity alumina powder that can be easily sintered.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, obtained by pulverizing a commercially available high-purity alumina powder with a small diameter medium made of iron having a large specific gravity, and then mixing Fe powder mixed from the medium. It has been found that removal of acid by acid washing can provide a large amount of high-purity alumina powder having easy sintering properties at low cost and completed the present invention.

That is, according to the present invention, an alumina powder having a purity of 99.99% or more is prepared by using an iron medium having a diameter of 2 mm or less with an average particle size of 0.2 μm or less and a specific surface area of 15 × 10 ³ m ² / k.
g, and then the alumina powder is washed with hydrochloric acid or nitric acid, and further washed with sulfuric acid having a concentration of 10 N or more. I do. The details will be described below.

[0010] This production method is a production method in which a commercially available high-purity alumina powder which can be purchased at a low cost is finely pulverized to obtain a high-purity alumina fine powder having an easy sintering property at a low cost and in a large amount. The starting material has a purity of 9
A high-purity alumina powder of 9.99% or more was obtained. If the purity is lower than 99.99%, it is not preferable because sintering can be performed at a temperature lower than 1400 ° C., but grain growth occurs, and it becomes difficult to obtain a sintered body having few pores.

The high-purity alumina powder is pulverized into fine particles. It is well known that the activity of the powder is improved by pulverizing the raw material powder by a pulverizing operation, so that an easily sinterable powder can be obtained.However, abrasion of the medium cannot be avoided by the pulverization. Contamination occurs, and although the sinterability is improved due to the contamination, grain growth occurs on the contrary, and it becomes difficult to reduce pores.

For this reason, as a medium to be used, contamination is generated, but an iron medium having a large specific gravity is used as a medium that can remove the contamination and can further advance the miniaturization. Although a ZrO ₂ medium having a large specific gravity is conceivable, it is difficult to remove contaminants from the ZrO ₂ medium, and high purity cannot be achieved. It is also conceivable to use high-purity alumina which has no problem for contamination as a medium.However, since the specific gravity of the medium is small, the grinding efficiency is poor, and long-term grinding is required to achieve the desired fineness. ,
Not realistic.

The size of the iron medium used is 2 m in diameter.
m or less. If it is larger than 2 mm, miniaturization becomes difficult, which is not preferable. The fineness of the pulverization is 0.2 μm or less in average particle size and 15 × 10 ³ m ^{2 in} specific surface area.
/ Kg or more. If the average particle size is coarser than 0.2 μm, sinterability cannot be expected, and if the specific surface area is less than 15 × 10 ³ m ² / kg, sinterability cannot be expected.

In order to remove Fe mixed in by abrasion in pulverization, alumina powder is first washed with hydrochloric acid or nitric acid,
Further, it was decided to wash with sulfuric acid. Several% of F by grinding
Most of them are first washed with hydrochloric acid or nitric acid because e is mixed. Some 50-50 still exist in the washed powder.
Since it contains 0 ppm of Fe, it is further washed with sulfuric acid having a strong detergency. The sulfuric acid concentration needs to be 10 N or more. If the concentration is lower than 10 N, the cleaning effect is weak, and the remaining Fe and the like (Fe, Fe ₂ O _3, etc.) cannot be sufficiently removed. The acid is finally washed away from the de-ironed powder, followed by drying, so that a fine and high-purity alumina powder that is easily sintered can be obtained.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The production method of the present invention will be described in more detail. First, a commercially available high-purity alumina powder having a purity of 99.99% or more is prepared. A solvent such as water or alcohol is added to the powder, which is then put into a pulverizer such as an attrition mill, a ball mill, an attritor, a bead mill, and pulverized to a desired fineness with an iron medium having a diameter of 2 mm or less. I do. The crushing time may be determined according to each crusher. The concentration of alumina in the slurry varies depending on the desired average particle size and the type of the pulverizer, but when the average particle size is aimed at 0.2 to 0.1 μm, the concentration is 20 to 40 wt%. Degree is fine.

Next, the pulverized alumina slurry is washed with hydrochloric acid or nitric acid. In this washing, washing and filtration are repeated several times with an acid solution of 10 to 50 times the theoretical amount shown in the following formula.
When hydrochloric acid is used, dilute hydrochloric acid is preferably used in order to further exhibit the cleaning effect. After the washing, the substrate is further heated and washed with sulfuric acid having a concentration of 10 N or more, and then washed with pure water and filtered to remove the acid. The slurry is filtered by a filter press or the like and dried, or dried by a spray dryer or the like. 2Fe + 6HCl → 2FeCl ₃ + 3H ₂ 2Fe + 6HNO ₃ → 2Fe (NO ₃ ) ₃ + 3H ₂

If alumina powder is produced by the above method,
Fine, high-purity alumina powder excellent in sinterability can be obtained.

[0018]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples of the present invention and Comparative Examples.

(Examples 1 and 2) (1) Pulverization of alumina powder Ion-exchanged water was added to alumina powder (KP-20, manufactured by Showa Denko KK) having a purity of 99.99% and an average particle size of 0.5 μm. In addition, a slurry having a solid content of 25% was obtained. This slurry was pulverized by an attrition mill for 20 minutes using the media shown in Table 1.

(2) Washing of alumina powder The obtained slurry was analyzed by chemical analysis to find that 5 wt.
% Fe, so 3N with 2N hydrochloric acid or nitric acid
Washing and suction filtration were performed twice. Add 10 more to the slurry
N sulfuric acid was added in an amount of 2 parts by weight based on 100 parts by weight of the alumina powder, washed with heating at 60 ° C., and filtered. 3 parts by weight of pure water was added to the alumina powder, and washing and filtration were repeated twice, and then dried to obtain an alumina powder.

(3) Evaluation The average particle size of the obtained powder was measured by a sedimentation method, and the specific surface area was measured by a nitrogen adsorption method. In addition, impurities in the obtained powder were analyzed by chemical analysis. Further, the densities of the atmospheric pressure sintered body and the HIP-treated sintered body prepared as described below using the obtained powder are determined by the Archimedes method, and the HIP-treated sintered body is ground and mirror-finished. Was observed under a microscope to determine the number of pores of 5 μm or more. Table 1 shows the results.
Shown in The sintered body was formed by molding a die of alumina powder and then pressing the powder at a pressure of 1400 Kg / cm ² at φ50 × t5.
A 0 mm compact was subjected to CIP molding, and the compact was sintered at 1350 ° C. in the atmosphere under normal pressure for 2 hours, and then 1400 ° C.
HIP treatment at a temperature of 1800 Kg / cm ² .

(Comparative Examples 1 to 5) For comparison, Comparative Example 1
Then, pulverize for 60 minutes using a 5 mm diameter Fe medium,
In Comparative Example 2, the Al ₂ O ₃ medium was used instead of the Fe medium.
The alumina powder was ground and washed in the same manner as in Example 1 except that ZrO ₂ medium was used in Comparative Example 3 except that the alumina powder was ground.
evaluated. In Comparative Example 4, the alumina powder was pulverized, washed and evaluated in the same manner as in Example 1 except that 5N sulfuric acid was used. Further, in Comparative Example 5, for reference, a sintered body produced in the same manner as in Example 1 using an alumina powder obtained by thermal decomposition of aluminum carbonate, hydroxide and ammonium was evaluated. Table 1 shows the results.

[0023]

[Table 1]

As is clear from Table 1, in Examples 1 and 2, the fineness of the alumina powder is within the range of the present invention. The impurities in the powder are 10%.
It is significantly lower than 0 ppm. The number of pores of the sintered body produced by performing HIP treatment using this powder was 4 or less. This indicates that the obtained alumina powder is a fine and high-purity powder equivalent to the alumina powder obtained by pyrolysis of aluminum carbonate, hydroxide and ammonium, and the fine and high-purity powder This indicates that sintering can be performed at a low temperature and that pores in the sintered body can be extremely reduced.

On the other hand, in Comparative Example 1, the size of the medium was too large, so that the fineness of the alumina powder did not become the fineness of the present invention, and the powder was not densified at the temperature of Example 1.
Further, in Comparative Example 2, although the medium was alumina, although the amount of impurities was small, the fineness of the powder was also coarse as in Comparative Example 1, and the powder was not densified. Further, in Comparative Example 3,
Since the medium was zirconia, fineness was satisfied, but as much as 3% of impurities (ZrO ₂ ) remained, the pores in the sintered body could not be reduced sufficiently, and the number of pores was much larger than in the examples. Furthermore, in Comparative Example 4, since the concentration of sulfuric acid was too low, impurities could not be completely removed and remained considerably, and this also had a large number of pores.

[0026]

By producing alumina powder by the method of the present invention, commercially available high-purity alumina is crushed,
Fine, high-purity alumina powder can now be obtained. As a result, it has become possible to provide a production method capable of obtaining a large amount of alumina powder that is equivalent to the easily sinterable and high-purity alumina powder obtained by the conventional production method at low cost.

Claims (1)

[Claims] 1. An alumina powder having a purity of 99.99% or more is pulverized with an iron medium having a diameter of 2 mm or less to an average particle diameter of 0.2 μm or less and a specific surface area of 15 × 10 ³ m ² / kg or more. After that, the alumina powder is washed with hydrochloric acid or nitric acid,
A method for producing an easily sinterable high-purity alumina powder, further comprising washing with sulfuric acid having a concentration of 10 N or more.