Сверхкритические флюиды. Теория и практика
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2018, N1, pp. 04-15

Yu.D. Ivakin, M.N. Danchevskaya

Analysis of a Fine-Crystalline Corundum Recrystallization in Supercritical Water Medium Using the Lognormal Particle Size Distribution Function

A mechanism of the fine-crystalline corundum synthesis from aluminum hydroxide in the conditions of induced nucleation in the supercritical water fluid at 400°C, an initial pressure of 26.4 MPa, and subsequent exposure in a synthesis medium is considered. The size distribution of the crystals was based on the analysis of electron microscopic images. The use of the lognormal function to describe the crystal size distribution of the synthesized corundum particles is substantiated. The possibility of using the lognormal particle size distribution function and the time dependence of its parameters to reveal the formation routes of the product crystals is analyzed. It is found that the dimensional spectrum of microcrystals has four components, the appearance of which is associated with different routes of the product formation. The number of distribution components remains unchanged during the prolonged exposure, but their average characteristics have different time dependences. The redistribution of the mass during recrystallization, which leads, on the whole, to a decrease in the average crystal size, is explained by differences in the mobility of the crystal structure of different components. It is concluded that the states of corundum in the newly formed crystals and in the buildup layer on the particles of the inducing additive are different.

Key words: fine-crystalline corundum, sub- and supercritical water, solid phase mobility, crystal formation, microcrystal size distribution, lognormal function, coalescence, surface spreading, recrystallization

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