KR20010046015A - Manufacturig method of alumina powder - Google Patents

Abstract

PURPOSE: A preparation method of alpha-alumina powder from aluminum hydroxide by Bayer method, which is characterized by adding a grinding step to a conventional method before thermal-treating, Accordingly, the resultant alumina powder used as an abrasive has a homogeneous particle distribution and very fine particle size(0.05- 0.5micrometer). CONSTITUTION: The method comprises the steps of: grinding Al(OH)3 from Bayer method or intermediate Al2O3 obtained by presintering Al(OH)3 at 400-1100deg.C to 0.3-3micrometer; soaking intermediate Al2O3 in HCl, filtering and washing to gain an alumina cake that Na is removed; mixing it with (NH4)OH, HCl or AlCl3 to remove Na effectively, in a form of NaCl; sintering at 1150-1350deg.C to get alpha-Al2O3; filtering and washing to remove Na again, which results in low Na-grade alumina powder.

Description

Manufacturing method of alumina powder {Manufacturig method of alumina powder}

The present invention relates to a method for producing fine and uniform alumina powder for abrasives and ceramics from Bayer method aluminum hydroxide, which is more uniform than a product made by using the α-alumina powder manufacturing method from conventional Bayer method aluminum hydroxide. Alumina powder having a size can be prepared and small particles having an average particle size of 0.05 µm to 0.5 µm can be obtained.

In the process of making α-alumina using conventional Bayer method aluminum hydroxide to make fine alumina powders such as abrasives and ceramics, grain growth occurs during stabilization of alumina to α-alumina through heat treatment, resulting in α-alumina macroparticles. It is easy to occur. In order to prevent this, generally, by adding a particle growth inhibitor such as Mg component and performing heat treatment, agglomerates composed of fine primary particles of α-alumina are synthesized and pulverized to primary particle sizes to prepare fine α-alumina particles. However, it is difficult to produce α-alumina particles having an average particle size of about 0.3 μm or less, and it is difficult to completely control uneven particle growth during the process. Accordingly, the present invention relates to a method for preparing ultrafine α-alumina powder having an average particle size of 0.05 μm to 0.5 μm, which is difficult to make by conventional methods, so that non-uniform particle growth does not occur. It's about how you can make it.

Details of the present invention are as follows. The key point of the present invention is that before the final heat treatment for stabilizing the Bayer method aluminum hydroxide to α-alumina state, the particle state is ground to some extent according to the desired size of the final particles, and the final heat treatment is performed. Alumina must be prepared. The reason for this is that when the final heat treatment is performed without using a conventional Bayer aluminum hydroxide in the middle stage without undergoing grinding, the Bayer aluminum hydroxide, which is about 50 to 100 µm, is hydrated at high temperatures during the transition to α-alumina. Impurities and internal stress in aluminum cause excessive grain growth, non-uniform grain formation and growth. In more detail, in order to minimize the influence of impurities and internal stress in aluminum hydroxide during stabilization of the α-alumina phase, Bayer method aluminum hydroxide, which is a raw material, may be pulverized or crushed in an intermediate stage before the α-alumina phase is stabilized. Stabilization of α-alumina phase through heat treatment prevents excessive growth of impurities, internal stress, etc. in the large particles of raw material 50㎛ ~ 100㎛ Bayer's aluminum hydroxide. can do. When the α-alumina is produced by this method, it is possible to obtain a product having a fine particle size and uniform particle size distribution with an average particle size of 0.05 μm to 0.5 μm. Improved polishing force and uniform particle size do not exist due to the uniform particle size has almost no scratch. Therefore, the α-alumina produced by the present invention can exhibit very excellent properties when used as an abrasive for semiconductor wafer processing (CMP process), videotape and compact discs.

Depending on the field of use and purpose of the α-alumina product, a low soda (Low Na) product having a low content of impurities, especially sodium, is required. In order to obtain the product of the present invention as a low soda product, a simple process is added. You can easily obtain low soda grade products with Na ₂ O content of 0.05% or less.

In other words, when performing heat treatment to stabilize α-alumina, the final heat treatment is performed by grinding Bayer method aluminum hydroxide or alumina intermediate, which is a raw material, to prevent particle growth, abnormal particle generation and growth. In the second method, the raw material aluminum hydroxide or alumina intermediate in the pulverized state is mixed with a material containing Cl component which is easy to react with Na component to make α-alumina through the final heat treatment step, and the produced NaCl component is leached and filtered. Na component can be removed. In this case, as a material containing Cl, hydrochloric acid, ammonium chloride, aluminum chloride, basic aluminum chloride, and mixtures thereof may be used. In this way, a low soda product having a Na ₂ O component content of up to about 0.03% can be obtained. In the second method, the Bayer method aluminum hydroxide or alumina intermediate after pulverization is reacted with dilute hydrochloric acid to dissolve the Na component, and then subjected to final heat treatment to prepare α-alumina. Can be removed to form a low soda α-alumina. This method usually produces low soda grade α-alumina up to 0.05%. In the third method, the Bayer method aluminum hydroxide or alumina intermediate after pulverization is reacted with dilute hydrochloric acid to elute the Na component, and then the Na component is simply removed. Then, the additives are mixed again as in the first method, followed by leaching, filtration, Na component is removed by washing. In this way, low soda-grade alumina with Na ₂ O content of up to about 0.01% can be produced.

Example 1

Table 1 below shows the contents of the alumina powder prepared by the present invention and the alumina prepared by the conventional method.

In the manufacturing method, the Bayer method aluminum hydroxide was pre-fired and then pulverized. Examples # 1 to # 4 were used to pulverize the Bayer method aluminum hydroxide, Example # 5, and the results are shown in the table.

The comparative example shows that the existing Bayer method aluminum hydroxide was calcined as it is.

As shown in Table 1, the method of the present invention was able to obtain α-alumina powder even at a lower temperature than the conventional method, and to obtain a small particle size.

Example 2

To prepare a low soda-grade alumina powder, Bayer method aluminum hydroxide having an average particle size of 75 μm and a Na ₂ O content of 0.25% was prebaked at 700 ° C., and then ground to an average particle size of 1 μm, and diluted to 0.2 normal concentration. It is added to hydrochloric acid so that solid content concentration is 30% and stirred well for 1 hour to leach the sodium component in alumina. This is filtered through a filter press and washed to remove sodium. The obtained filter cake and the aluminum chloride solution were mixed well so as to have a weight ratio of 0.5% by weight of AlCl ₃ to alumina in the filter cake, and calcined at 1200 ° C for 3 hours. After cooling to room temperature, the remaining sodium component is further removed by filtration and washing. Finally, α-alumina powder having an average particle size of 0.10 μm and a maximum particle size of 0.7 μm was obtained through wet grinding, and the Na ₂ O content was 0.008%.

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Claims (4)

In the production of fine α-alumina powder from Bayer's aluminum hydroxide, intermediate alumina made by grinding or preliminary firing of aluminum hydroxide as a raw material to prevent excessive concentration of impurities during firing or influence of internal stress. After pulverizing the method of producing an α-alumina powder, characterized in that the final firing to make a-alumina again. The method for producing α-alumina powder according to claim 1, wherein the average particle size is in the range of 0.3 µm to 3 µm when the Bayer method aluminum hydroxide as a raw material or an intermediate state of alumina pre-fired is pulverized. The method of claim 1, wherein the preliminary firing temperature is in the range of 400 ° C to 1100 ° C and the final firing temperature is in the range of 1150 ° C to 1350 ° C. The intermediate alumina obtained by pre-firing with hydrochloric acid, filtered and washed to remove sodium components first, and the intermediate alumina cake obtained with ammonium chloride, hydrochloric acid, aluminum chloride or basic aluminum chloride. A method of producing α-alumina powder, characterized in that the low-sodium α-alumina is prepared by additionally removing the sodium component by mixing and final firing and filtering and washing the obtained α-alumina again.