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