JPS5997527A - Manufacture of high purity alumina particle - Google Patents

Abstract

PURPOSE:To manufacture high purity alumina particles with superior flowability without causing contamination by charging high purity alumina powder into a high temp. flame in the presence of an excess of oxygen to melt the surface of the powder. CONSTITUTION:Alumina powder having >=about 99.8%, preferably >=99.9% purity and about 0.1-50mum average particle size is used. It is preferable to add 0.1-1pt.wt. of hydrochloric acid to 100 parts of the high purity alumina. The high purity alumina powder as a starting material is fed into a flame generator using hydrogen, etc. as starting materials in the presence of an excess of oxygen, and the surface of the powder is melted or half-melted with a high temp. flame.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-purity alumina particles, and more particularly to a method for producing high-purity alumina particles with excellent fluidity.

Conventionally, many methods for producing high-purity alumina powder are known, such as the pyrolysis method of ammonium alum, the underwater discharge method of aluminum, and the pyrolysis method of aluminum alkoxide. The powder had extremely poor fluidity and was considered difficult to use in the field of producing single crystals such as sapphire.

For this reason, the powder may be press-molded, then melted, and then pulverized into granules for use, or the powder may be granulated by a spray drying method and then sintered to form a granular raw material. Measures have been taken.

However, these granulation methods have the drawback that not only are the processes complicated, but also impurities such as iron, silicon, and soda are likely to be mixed in during operations such as molding, firing, and pulverization.

In view of these circumstances, the inventors of the present invention conducted intensive studies to obtain high-purity alumina grains with excellent fluidity without contaminating the high-purity alumina powder used as a raw material. The inventors discovered that when high-purity alumina powder is processed, not only the fluidity but also the purity of the resulting high-purity alumina grains is improved compared to the starting material alumina, leading to the completion of the present invention. .

That is, the present invention provides a method for producing high-purity alumina particles, which is characterized by introducing alumina powder of the same purity into a high-temperature flame with excess oxygen, and melting or semi-melting the powder surface. High-purity alumina particles are obtained by melting or semi-melting the surface of the powder using the method described above, using a raw material powder containing 100 parts by weight of high-purity alumina and 0.1 to 1 part by weight of hydrochloric acid as the raw material powder to be introduced. There is a flea company that provides a manufacturing method.

The method of the present invention will be explained in more detail below.

The alumina powder used in Method 1 of the present invention usually has a purity of about 99.
8% or more, preferably 99.9% or more, average particle size 0.1-
It is a high-purity alumina with a diameter of about 50 μm, and its manufacturing methods include ammonium alum thermal decomposition method, aluminum underwater discharge method, aluminum alkoxide thermal decomposition method,
A known method such as the Bayer method may be used.

Next, when carrying out the method of the present invention, a high-purity alumina powder raw material is supplied into a flame generator using a flammable gas such as hydrogen, propane, acetylene, etc., and the surface of the raw material powder is melted or heated in the flame. Half-melted cape: However, in this case, the treatment must be carried out under conditions of excess oxygen.

If the oxygen concentration in the flame generator is not higher than that which can completely burn the flammable gas, the carbon generated by the thermal decomposition of the combustible gas will be incorporated into the alumina particles, and the purity of the raw material alumina will be reduced. This results in a low f value or a frequent occurrence of crystal defects in alumina, resulting in significant formation of transitional alumina, making it impossible to use it as a raw material in the above-mentioned single-crystal manufacturing field where α-alumina is primarily desired. Therefore, it is not suitable.

The raw material-based purity alumina powder to be treated in a high-temperature flame with excess oxygen may be a single high-purity alumina powder having the required purity; When raw material powder to which 100% hydrochloric acid has been added in advance is thrown into a flame, the impurities in the raw material powder are reduced compared to before the treatment, and the purity is further increased (this is due to the formation of transition alumina). The amount of hydrochloric acid added to the alumina powder is 0.1, which is a preferred embodiment because the ratio also decreases.
% not 7.7 In this case, the effect of the addition is not significant; on the other hand, if it exceeds 1%, the corresponding addition effect will not appear (in fact, the equipment material will be corroded by one chlorine gas generated). So I don't like it.

Although it is not clear why the production of transition alumina is lower due to the addition of hydrochloric acid to the raw material high purity alumina powder in the method of the present invention,
Iron, silica, nose, etc. contained in this coexist with hydrochloric acid,
It is assumed that volatile chlorides are formed and removed by evaporation due to high temperature heating at a temperature of 2000° C. or higher.

The method of the present invention as described above is (・Hame r11
This method makes it possible to obtain high-purity alumina with excellent fluidity by reducing the transition to transitional alumina crystals without reducing the purity, and its industrial value is enormous. .

The method of the present invention will be explained in more detail below with reference to Examples.

Example Sieve purity α-almite powder synthesized by alum method V (average particle size 1oμill, purity 99, 95-6)
was introduced into a propane-oxygen flame via a powder feed means. Thermal spraying conditions are propane l On? / 11. ?
+f element 60yy//h, alumina powder input M 10
kQ/ll.

(Powder carrier gas, oxygen 1 m”/b) The melted alumina powder was placed in a hollow stainless steel pipe (100 m”/b).
yw×1000**e) was collected in water after washing.

The obtained alumina particles have an X-ray I of more than 90% or α-
Formation of γ-alumina was observed in some of the alumina particles.

The average particle size was 8 μm and approximately spherical. The heavy density of this particle is 2.80 r/y, the light density is 2.12 r/ea, and the angle of repose of this particle is 30 degrees,
The angle of repose of the powder before thermal spraying was 35°, indicating improved flowability.

Example 2 High purity alumina powder was thermally sprayed in the same manner as in Example 1 under the conditions shown in Table 1.

Table 1 shows the processing conditions and characteristics of the obtained pure alumina particles.

Table 1

Claims (1)

[Claims] l) A method for producing high-purity alumina particles, which comprises: introducing high-purity alumina powder into a sieve flame with excess oxygen, and melting or semi-melting the powder surface. 2) High-purity alumina powder added to a high-temperature flame with excess oxygen contains 0.1 to 1 part of hydrochloric acid per 100 parts by weight of high-purity alumina.
The method according to claim 1, characterized in that part by weight is added.