The change in particle size of the spherical alumina in the system. These methods use a large amount of organic solvents and surfactants, and the sol-emulsion-gel sol-emulsion-gel method is developed on the basis of the sol-gel method. In the early stage, the sol-gel method was used. To prepare alumina sol, it is more to study the structure of the obtained colloid. Gradually, this method is a common method for preparing ultrafine powder. In order to obtain spherical powder particles, people use the interfacial tension between oil phase and water phase. The formation of minute spherical droplets causes the formation and gelation of the sol particles to be limited to minute droplets, and finally spherical precipitated particles are obtained. TakashiOgihara et al. used the aluminolysis of alcohol to prepare spherical alumina powder through sol-gel process. The whole hydrolysis system is complicated. The octanol which dissolves aluminum alkoxide accounts for 50%, the acetonitrile solvent accounts for 40%, and the octanol and butanol of dispersed water respectively. 9% and 1%, and using hydroxypropylcellulose as a dispersing agent, spherical γ-alumina powder having a very good sphericity was obtained, as shown in Fig. 3(a). The author believes that in the whole hydrolysis system, the main role of the formation of spherical particles is the hydrophilic reagent acetonitrile and the lipophilic reagent octanol. In order to confirm this point, the author simplified the hydrolysis system of TakashiOgihara, dissolved aluminum octanol, The water was dispersed in acetonitrile, and spherical hydrated alumina was obtained without using any dispersant. The TEM image is shown in Fig. 3(b), and the influence of solvent polarity on the morphology of the particles was investigated. Okorn et al.  pyrolyzed aluminum isopropoxide in mineral oil to obtain spherical alumina. Chatterjee et al. studied the critical micelle concentration and hydrophilic-lipophilic balance in an emulsion system consisting of organic solvents such as n-hexane, cyclohexane, carbon tetrachloride and n-butanol with surfactants such as Tween and Siban. The effect of the formation of spherical alumina. Tannenbaum et al. studied the control of the morphology and size of alumina products by the lipophilic reagent sodium di(2-ethylhexyl) sulfonate in the milling process of aluminum isopropoxide hydrolysis, peptization, aging and calcination. It was found that the addition of sodium bis(2-ethylhexyl) sulfonate in the aging stage makes it easier to form spherical particles. Lee et al.  studied the addition of some of the reagents composed of paraffin oil and Siban 80 in the early stage of forming gel particles, which caused troubles in the separation and drying of the powder. 1.3 Drop ball method The drop ball method is to drop the alumina sol into the oil layer (usually using paraffin, mineral oil, etc.), and form spherical sol particles by the action of surface tension, and then the sol particles are gelled in the ammonia solution. Finally, the gel particles are dried and calcined to form a spherical alumina. This method is a further improvement of the sol-emulsion-gel process in the aging phase of the sol, and the oil phase is maintained, eliminating the separation of the powder and the oily agent. Lin [23-25] continued the process and established the experimental setup as shown in FIG. However, this method is generally used to prepare spherical alumina having a large particle size, and is mainly applied to an adsorbent or a catalyst carrier. Liu Pengcheng used a drop ball technique to prepare a 2 mm spherical alumina catalyst support. A similar apparatus was also established by Ismagilov et al. to prepare a spherical alumina support for use in a fluidized bed reactor.
The features of aluminum oxide Al2O3