A process for the preparation of spherical alumina by hydrothermal spray pyrolysis

Abstract

The application discloses a process for preparing spherical alumina by a hydrothermal spray method, and specifically comprises the following steps: adding aluminum sulfate octadecahydrate, aluminum nitrate nonahydrate and deionized water in a certain molar ratio into an A beaker and stirring uniformly at room temperature; adding a certain amount of urea and deionized water into a B beaker, stirring uniformly, and then pouring the solutions in the A beaker and the B beaker into a 100ml polytetrafluoroethylene liner according to a certain molar ratio; placing the reaction kettle into an oven and drying for 2h at a certain temperature; after the reaction kettle is naturally cooled to room temperature, filtering the suspension, and then performing suction filtration, washing, spray drying and high-temperature calcination on the filter residue obtained by filtration, so as to obtain the spherical alumina; the alumina obtained by the process has uniform particle size distribution and regular morphology, and the process is simple, low in cost and small in pollution.

Description

Technical Field

[0001] This invention relates to a process for preparing spherical alumina by hydrothermal spraying, belonging to the field of alumina preparation technology. Background Technology

[0002] With the rapid development of fields such as electronics and information technology and catalytic chemistry, high-end spherical alumina, due to its excellent thermal conductivity, dispersibility, and interfacial bonding properties, has become a core functional material in the production of electronic packaging materials, high-efficiency catalyst carriers, and precision ceramic matrices. In the preparation of high-end spherical alumina, precise control of the precipitation and crystallization processes is necessary to achieve synergistic optimization of particle sphericity, particle size distribution, and purity to meet the stringent requirements of high-end applications. The hydrothermal method, using aluminum sulfate octadecahydrate and aluminum nitrate nonahydrate as raw materials and urea as a precipitant, is a highly efficient preparation route suitable for this need. Currently, the main methods for producing high-end spherical alumina are direct precipitation and sol-gel methods. Direct precipitation is difficult to control in terms of reaction rate, easily leading to particle agglomeration and irregular morphology due to excessively high local concentrations, and the product has a wide particle size distribution, making subsequent purification difficult. In the sol-gel method, the gel formation rate is easily affected by environmental factors such as humidity and temperature, resulting in poor system stability. Furthermore, cracking and shrinkage are prone to occur during drying and calcination, leading to impaired sphericity and making large-scale production difficult. These factors all constrain the industrial upgrading and high-value application of high-end spherical alumina in my country. A method using aluminum sulfate octadechydrate and aluminum nitrate nonahydrate as composite raw materials, urea as a precipitant, and aluminum hydroxide precursor prepared via a hydrothermal process, followed by high-temperature calcination to produce high-end spherical alumina, offers advantages such as high product sphericity, uniform particle size distribution, high purity, excellent dispersibility, controllable process flow, and low pollution, making it more suitable for the actual production needs of high-end fields.

[0003] This invention provides a process for preparing high-purity, high-end spherical alumina from aluminum sulfate octadechydrate and aluminum nitrate nonahydrate. Aluminum sulfate octadechydrate and aluminum nitrate nonahydrate, as aluminum source chemical raw materials, are characterized by abundant resources, easy access, high purity, and excellent solubility. Their combined use allows for flexible control of the aluminum ion concentration in the system, adapting to the preparation needs of products with different particle sizes, which is beneficial for large-scale production. Urea, as a homogenizing precipitant, slowly hydrolyzes and releases hydroxyl groups under hydrothermal conditions, avoiding particle agglomeration caused by localized overconcentration and achieving uniform nucleation and growth of the precursor. The hydrothermal method promotes directional crystal growth and morphology optimization through a high-temperature and high-pressure environment, significantly improving the crystallinity, sphericity, and dispersibility of the aluminum hydroxide precursor. Furthermore, the reaction system is closed and controllable, with minimal impurity introduction, convenient subsequent filtration and washing, and easy removal of impurity ions such as sulfate and nitrate. The production process is green and environmentally friendly, causing no pollution. Summary of the Invention

[0004] The present invention aims to provide a process for preparing spherical alumina by hydrothermal spraying. The process includes the following steps: At room temperature, aluminum sulfate octahydrate, aluminum nitrate nonahydrate, and deionized water are added to beaker A in a specific molar ratio and stirred until homogeneous. A certain amount of urea and deionized water are added to beaker B and stirred until homogeneous. The solutions from beakers A and B are then poured into a 100ml polytetrafluoroethylene (PTFE) liner at a specific molar ratio. The reaction vessel is placed in an oven at 120-140°C and dried for 2 hours. After the reaction vessel cools naturally to room temperature, the suspension is filtered. The resulting filter residue is washed by vacuum filtration, spray-dried, and then calcined at high temperature to obtain spherical alumina.

[0005] The advantages of this invention in preparing spherical alumina are as follows: (1) Aluminum sulfate octadeca and aluminum nitrate ...

[0006] The following description of the invention with reference to embodiments is not intended to limit its scope of protection.

[0007] At room temperature, aluminum sulfate octahydrate, aluminum nitrate nonahydrate, and deionized water in a molar ratio of 1:3 were added to beaker A and stirred until homogeneous. A certain amount of urea and deionized water were added to beaker B to prepare a 1 mol / L urea solution, and the mixture was stirred continuously until homogeneous. The solutions from beakers A and B were poured into a polytetrafluoroethylene (PTFE) liner at a molar ratio of 1:10, filling the liner to 60%. The liner was dried at 120°C for 2 hours. After the reactor cooled to room temperature, the suspension was filtered and washed. The resulting aluminum hydroxide was washed three times and then spray-dried at 240°C to obtain a white aluminum hydroxide powder precursor. The precursor was calcined at 1100°C for 2 hours to obtain spherical alumina. Attached Figure Description

[0008] Appendix Figure 1 This is a particle size distribution diagram of the alumina product. It can be seen that the alumina prepared by this method has a uniform particle size distribution, with a median diameter of 3.386 μm. Among them, particles smaller than 4 μm account for 68.36%, which meets the requirements for alumina.

Claims

1. A process for preparing spherical alumina by hydrothermal spraying, characterized in that... The following steps are performed: At room temperature, add aluminum sulfate octahydrate, aluminum nitrate nonahydrate, and deionized water in a certain molar ratio to beaker A and stir until homogeneous; add a certain amount of urea and deionized water to beaker B and stir until homogeneous. Pour the solutions from beakers A and B into a 100ml polytetrafluoroethylene liner in a certain molar ratio. Place the reactor in an oven and dry it at a certain temperature for 2 hours. After the reactor has cooled naturally to room temperature, filter the suspension. The filter residue obtained is washed by vacuum filtration, spray-dried, and then calcined at high temperature to obtain spherical alumina.

2. The process for preparing spherical alumina by hydrothermal spraying as described in claim 1, characterized in that, The ratio of aluminum sulfate octadechydrate to aluminum nitrate nonahydrate is 1:3 to 1:

4.

3. The process for preparing spherical alumina by hydrothermal spraying as described in claim 1, characterized in that, The concentration ratio of urea to aluminum salt is 1:5 to 1:

10.

4. The process for preparing spherical alumina by hydrothermal spraying as described in claim 1, characterized in that, The polytetrafluoroethylene (PTFE) liner has a filling degree of 40% to 70%.

5. The process for preparing spherical alumina by hydrothermal spraying as described in claim 1, characterized in that, The oven is set to a temperature of 100℃~140℃.

6. The process for preparing spherical alumina by hydrothermal spraying as described in claim 1, characterized in that, The specified proportion of magnesium chloride is 4% to 12% of the emulsion.

7. The process for preparing spherical alumina by hydrothermal spraying as described in claim 1, characterized in that, The spray drying temperature is 230~240℃.

8. The process for preparing spherical alumina by hydrothermal spraying as described in claim 1, characterized in that, The high-temperature calcination temperature is 1100℃~1200℃.

9. The process for preparing spherical alumina by hydrothermal spraying as described in claim 1, characterized in that, The high-temperature calcination time is 1~2 hours.

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