An improved method for preparing alumina using an alcohol aluminum process as a filler

Abstract

The invention discloses an improved method for preparing alumina by an alcohol aluminum method for fillers, and belongs to the technical field of chemical production processes. The method first uses high-purity aluminum, anhydrous isopropanol and high-purity water as raw materials, and adopts alcohol salt hydrolysis method to prepare high-purity aluminum hydroxide powder; the aluminum hydroxide powder is calcined according to two calcination processes to obtain aluminum oxide powder A and aluminum oxide powder B respectively, and mixed according to the weight ratio of (10-15): (90-85) to obtain mixed aluminum oxide powder; the mixed aluminum oxide powder is subjected to air flow milling to obtain aluminum oxide fine powder; high-purity water is added thereto for full stirring to obtain aluminum oxide slurry; and finally aluminum oxide powder is obtained by spray drying. The present invention drives out the air-propylene mixed gas and organic byproducts coated with the powder by a simple stirring process, reduces the viscosity of the powder, and arranges the powder closely by spray drying, effectively improving the filling amount and stacking ratio.

Description

Technical Field

[0001] The invention relates to the technical field of chemical production technology, and in particular to an improved method for preparing aluminum oxide using an alcohol aluminum method as a filler. Background Art

[0002] At present, alumina powder is prepared by the alkoxide hydrolysis method using isopropyl alcohol as raw material. The entire production process of preparing alumina by the alkoxide hydrolysis method is purified, and the impurity content of the produced alumina is extremely low. It is currently recognized at home and abroad as the production method of alumina with the highest purity, and is very suitable as an insulating packaging material in the electrical and electronic fields.

[0003] When high-purity aluminum, anhydrous isopropanol and high-purity water are used as raw materials to prepare high-purity aluminum hydroxide powder, although the industry uses a multi-step hydrolysis process to recover isopropanol, which will reduce the content of isopropanol in the product, the dried aluminum hydroxide will still contain residual isopropanol. After high-temperature calcination, isopropanol generates propylene, accompanied by some by-products (Ma Huixia et al., Thermodynamic Analysis of the Dehydration of Isopropanol to Prepare Propylene [J], Modern Chemical Industry, 2020, 40 (6): 196-198, 203). There are pores between the grains of the calcined alumina powder, and the texture is relatively loose. After calcination, some propylene and organic by-products are still coated by the powder and cannot escape, resulting in the filler filling not being tight enough and the shrinkage ratio of the cast product not being ideal.

[0004] At the same time, the alumina powder prepared by the alcohol salt hydrolysis method has coarse particles, small bulk density, and limited filling capacity, which is not conducive to its application as a filler.

[0005] Generally speaking, the larger the original crystal size, the fewer crystal defects, and the smaller and narrower the particle size distribution, the higher the packing ratio (packing density) of the alumina powder. However, gaps will appear between larger grains. By filling the gaps with alumina powder with a small original crystal size and smaller particle size, the filling amount and packing ratio of the filler can be further increased.

[0006] In order to further improve product quality, it is necessary to improve the alcohol salt hydrolysis method and develop a preparation technology for high-purity and high-bulk ratio alumina powder for filler. Summary of the invention

[0007] The purpose of the present invention is to provide an improved method for preparing alumina by the alcohol aluminum method for fillers. The method adopts alumina powder with different original crystal sizes, eliminates the gas between the powders through powder refinement processing, and achieves the purpose of improving the stacking ratio and filler filling rate.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] An improved method for preparing aluminum oxide using an aluminum alcohol process for fillers comprises the following steps:

[0010] (1) Using high-purity aluminum, anhydrous isopropyl alcohol and high-purity water as raw materials, and using alcohol salt hydrolysis method to prepare high-purity aluminum hydroxide powder;

[0011] (2) calcining the aluminum hydroxide powder prepared in step (1) according to two calcination processes to obtain aluminum oxide powder A and aluminum oxide powder B respectively, and mixing the aluminum oxide powder A and the aluminum oxide powder B in a mass ratio of (10-15):(90-85) to obtain a mixed aluminum oxide powder;

[0012] (3) jet milling the mixed alumina powder to obtain alumina fine powder;

[0013] (4) adding high-purity water to the alumina fine powder and stirring the mixture to obtain an alumina slurry;

[0014] (5) The alumina slurry is spray-dried to obtain alumina powder.

[0015] In step (2), the purity of the alumina powder A and the alumina powder B is not less than 99.999%. Thus, the impurity element content of the alumina powder A and the alumina powder B, especially the content of sodium, iron and silicon, is within the index of the alumina powder for filler.

[0016] In step (2), the calcination process for obtaining alumina powder A is calcination temperature of 1100-1300°C, calcination time of 2-5 hours, and the grain size of the alumina powder A is 0.1-0.3 microns. The calcination process for obtaining alumina powder B is calcination temperature of 1350-1500°C, calcination time of 5-10 hours, and the grain size of the alumina powder A is 1-3 microns.

[0017] In this way, two kinds of alumina powder A and alumina powder B with different original crystal sizes are obtained, and the mixed powder can be prepared according to the mass ratio of alumina powder A to alumina powder B of (10-15):(90-85).

[0018] The total amount of impurities introduced by the jet milling process in step (3) is 5 to 10 ppm. The particle size index of the obtained alumina fine powder is D 50 In this way, the mixed powder can be ground to a certain fineness by air jet mill, wherein the powder size of the alumina powder A, which accounts for (90-85)%, is greater than 1 micron, the original crystal size is 1-3 microns, and the crystal defects are few, which increases the overall filling amount and bulk ratio of the powder. The powder of the alumina powder B, which accounts for (10-15)%, fills the gaps of the alumina powder A, further increasing the filling amount and bulk ratio.

[0019] In step (4), the mass ratio of the alumina fine powder to the high-purity water is 1:(1-10). The stirring time is 0.5-2 hours, and the end point is when no new bubbles are generated on the liquid surface. In this way, the mixed gas of air and propylene encapsulated in the alumina powder will be released during stirring. Furthermore, the residual organic by-products will diffuse to the top of the high-purity water and naturally stratify with the water-based suspension of the alumina powder. The water-based suspension is transported to the spray drying equipment through a peristaltic pump, and the organic by-products will remain in the stirring barrel and will not affect the spray drying process.

[0020] The total amount of impurities introduced by the spray drying process in step (5) is 10-30 ppm, the sodium content of the alumina powder is not more than 2 ppm, the iron content is not more than 2 ppm, and the silicon content is not more than 30 ppm. The particle size index of the alumina powder in step (5) is D 50 No larger than 3 microns, and the particle size distribution width is 0.1 to 35 microns.

[0021] In this way, the final purity index of alumina powder can meet the filler requirements, the purity of aluminum hydroxide produced by the alcohol salt hydrolysis process is not less than 99.999%, the calcination, air flow milling and spray drying processes will not introduce metal impurities, and the overall content of introduced silicon impurities does not exceed 30ppm.

[0022] Furthermore, the particle size index D of the alumina powder after spray drying 50 No more than 3 microns, maintaining the D 50 The powder has good fluidity.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) Alumina powder with a purity of not less than 99.999% is produced by hydrolysis of alcohol salts. The amount of impurities introduced in the subsequent processing process is small, and no metal ions such as sodium and iron are introduced. It is suitable for the electronic and electrical fields.

[0025] (2) Two types of alumina powders of original crystal sizes are obtained through two calcination processes. After being mixed in a certain proportion, the powder particle size is reduced through a jet milling process, effectively improving the filling amount and bulk ratio.

[0026] (3) The air-propylene mixed gas and organic by-products encapsulating the powder are driven out through a simple stirring process, the powder viscosity is reduced, and the powder is densely arranged through spray drying, effectively increasing the filling amount and bulk ratio. DETAILED DESCRIPTION

[0027] In order to further understand the present invention, the present invention is described below in conjunction with examples, but the examples are only for further elaboration of the features and advantages of the present invention, rather than for limiting the claims of the present invention.

[0028] The invention firstly adopts an alcohol aluminum hydrolysis method using isopropanol as a raw material to prepare aluminum hydroxide (this step is a conventional process), then adopts different calcination processes to obtain aluminum oxide powder A and aluminum oxide powder B, mixes the aluminum oxide powder A and the aluminum oxide powder B according to a certain proportion, grinds them to a certain fineness through a jet mill, adds high-purity water to the fine powder and fully stirs it, releases the gas wrapped between the powders, and the organic intermediate product diffuses to the upper part of the high-purity water and naturally separates from the aluminum oxide powder water-based suspension, and sprays and dries the aluminum oxide powder water-based suspension to obtain high-purity and high-bulk ratio aluminum oxide powder for filler.

[0029] Embodiment 1:

[0030] 99.992% high-purity aluminum chips and 99.9% isopropanol were used as raw materials, and aluminum hydroxide was prepared by alcohol salt hydrolysis method. The purity of aluminum hydroxide was 99.9993% (the purity here refers to the purity content obtained by removing the remaining impurities after aluminum hydroxide was tested by GDMS). The aluminum hydroxide powder was calcined at 1150° C. for 4 hours to obtain aluminum oxide powder A, with a primary crystal size of 0.2 μm and a bulk ratio of 0.63 g / cm 3 At the same time, the aluminum hydroxide powder was calcined at 1380℃ for 7 hours to obtain aluminum oxide powder B, with a crystal size of 1.4 microns and a bulk ratio of 0.71g / cm 3 Alumina powder A and alumina powder B were mixed in a mass ratio of 12:88 to obtain a mixed alumina powder, and the mixed alumina powder was ground by a jet mill to obtain alumina fine powder with a purity of 99.9987%, D 50 2.173 μm, D 90 It is 6.139 microns.

[0031] The above-mentioned alumina fine powder was added into high-purity water, the mass ratio of alumina to high-purity water was 1:5, and stirred with a non-metallic rod for 1 hour. The slurry was spray-dried to obtain alumina powder with a purity of 99.9968%. 50 2.292 μm, D 90 The particle size is 25.168 microns, and the bulk ratio is 0.82 g / cm 3 .

[0032] Embodiment 2:

[0033] 99.994% high-purity aluminum aluminum chips and 99.9% isopropanol were used as raw materials, and aluminum hydroxide was prepared by alcohol salt hydrolysis method. The purity of aluminum hydroxide was 99.992% (the purity here refers to the purity content obtained by removing the remaining impurities after aluminum hydroxide was tested by GDMS). The aluminum hydroxide powder was calcined at 1200° C. for 4 hours to obtain aluminum oxide powder A, with a primary crystal size of 0.25 μm and a bulk ratio of 0.60 g / cm 3At the same time, the aluminum hydroxide powder was calcined at 1400℃ for 6 hours to obtain aluminum oxide powder B, with a crystal size of 1.7 microns and a bulk ratio of 0.75g / cm 3 Alumina powder A and alumina powder B were mixed in a mass ratio of 11:89 to obtain mixed alumina powder, and the mixed alumina powder was ground by a jet mill to obtain alumina fine powder with a purity of 99.9985%. 50 1.772 μm, D 90 It is 6.489 microns.

[0034] The above-mentioned alumina fine powder was added into high-purity water, the mass ratio of alumina to high-purity water was 1:7, and stirred with a non-metallic rod for 1.5 hours. The slurry was spray-dried to obtain alumina powder with a purity of 99.9963%. 50 1.940 μm, D 90 The particle size is 32.005 microns, and the bulk ratio is 0.87 g / cm 3 .

Claims

1. An improved method for preparing alumina by using an alcohol aluminum process as a filler, characterized in that: The method comprises the following steps: (1) Using high-purity aluminum, anhydrous isopropyl alcohol and high-purity water as raw materials, high-purity aluminum hydroxide powder is prepared by alcohol salt hydrolysis method; (2) calcining the aluminum hydroxide powder obtained in step (1) according to two calcination processes to obtain aluminum oxide powder A and aluminum oxide powder B respectively, and mixing the aluminum oxide powder A and the aluminum oxide powder B in a weight ratio of (10-15): (90-85) to obtain mixed aluminum oxide powder; (3) subjecting the mixed alumina powder to a jet mill to obtain alumina fine powder; (4) adding high-purity water to the alumina fine powder and stirring the mixture to obtain an alumina slurry; (5) spray drying the alumina slurry to obtain alumina powder; In step (2), the calcination process of calcining aluminum hydroxide powder to aluminum oxide powder A is: calcination temperature 1100~1300℃, calcination time 2~5 hours; the grain size of the aluminum oxide powder A is 0.1~0.3 microns; the calcination process of calcining aluminum hydroxide powder to aluminum oxide powder B is: calcination temperature 1350~1500℃, calcination time 5~10 hours; the grain size of the aluminum oxide powder B is 1~3 microns.

2. The improved method for preparing alumina by using an alcohol aluminum process as a filler according to claim 1, characterized in that: In step (2), the purity of the alumina powder A and the alumina powder B is not less than 99.999%.

3. The improved method for preparing alumina by using an alcohol aluminum process as a filler according to claim 1, characterized in that: In step (3), the total amount of impurities introduced into the alumina fine powder is 5-10 ppm by the air flow milling process, and the particle size index D of the alumina fine powder is 50 No larger than 3 microns.

4. The improved method for preparing alumina by using an alcohol aluminum process as filler according to claim 1, characterized in that: In step (4), the mass ratio of the alumina fine powder to high-purity water is 1:(1-10).

5. The improved method for preparing alumina by using an alcoholate method for fillers according to claim 1, characterized in that: In step (4), the stirring time is 0.5 to 2 hours, and the stirring end point is when no new bubbles are obviously generated on the liquid surface.

6. The improved method for preparing alumina by using an alcoholate method for fillers according to claim 1, characterized in that: In step (5), the total amount of impurities introduced by the spray drying process is 10-30 ppm; the sodium content of the prepared alumina powder is not more than 2 ppm, the iron content is not more than 2 ppm, and the silicon content is not more than 30 ppm.

7. The improved method for preparing alumina by using an alcohol aluminum process as a filler according to claim 1, characterized in that: The particle size index D of the alumina powder prepared in step (5) 50 No larger than 3 microns, the particle size distribution range is 0.1~35 microns.