Preparation Of Ultrafine Spherical Alumina And Control Of Its Particle Size And Crystal Form

Ultrafine spherical alumina with wide applications belongs to fine chemical products of the family of alumina, the spheroidization of ultrafine alumina particles can greatly improve the application performance of alumina products, so the preparation of ultrafine spherical alumina has practical significance. At present, the methods for preparing spherical alumina is mainly included homogeneous precipitation, sol-emulsion-gel, oil-drop, template, aerosol decomposition and spray method. By employing the characterization methods of SEM, XRD, laser particle size analyzer and TG, this paper conducts a research on morphology, particle size and crystal structure of ultrafine alumina particles. The research contents include the following aspects:(1)The preparation of ultrafine alumina powder with industrial alumina as raw material by using ball milling method were investigated. The ratio of corundum balls with different size was determined by controlling variables. The effects of milling time, ball material ratio and milling speed on the particle size of products were researched by means of the orthogonal experiment method. Under the optimum conditions, the effect of grinding aids was investigated.(2)Ultrafine spherical alumina was prepared by hydrothermal method using aluminum sulfate as raw material and urea as precipitator. The effect of temperature and time of the hydrothermal reaction on the particle size distribution, particle size, specific surface area and morphology of the products were discussed. Under the optimum factors, ultrafine spherical alumina powder with larger specific surface area was obtained, as the temperature elevating and the time increasing, the morphology of the solid sphere can be transformed into a hollow sphere with hole which is covered by a sheet structure. During calcination at high temperature, alumina particles keep the same morphology with the spherical precursor. Ultrafine spherical alumina with different crystalline forms was obtained through choosing the optimum evaporation and calcination method in the different temperature.(3)Using aluminum nitrate as raw materials, ammonia as precipitant, with the method of spray drying, ultrafine spherical alumina with larger specific surface area was prepared. The effect of nozzle size on particle size distribution, particle size, specific surface area and morphology of alumina was studied. With the increase of nozzle diameter particle size distribution and median diameter of powder gradually increased, and specific surface area decreased. Ultrafine spherical alumina particles with different crystalline forms were obtained through calcination in the different temperature. The gravity sedimentation classification of ultrafine alumina powder was carried out, the narrow particle size distribution of ultrafine alumina powders can be obtained by subsidence.