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Ivakin Yu. D., Zuy A. I., Muravieva G. P., Danchevskaya M. N.
Nucleation
and Growth of Microcrystals of Corundum at Heat Treatment of Hydrargillite in
an Atmosphere of Water Vapour
Abstract
The
process of corundum microcrystals formation is investigated during
termovaporous treatment of hydrargillite (PH2O = 24 MPa, T = 400°C). The
formation of fine-crystalline corundum proceeds in a solid phase at sequential
transmutation of hydrargillite {Al (OH)3} into boehmite {AlOOH} and
then into corundum {a-Al2O3}. The long induction
period precedes a stage of corundum occurrence. The kinetics of corundum
formation is featured by the equation of Erofeev for a case of a ramified chain
nucleation. The occurrence of corundum starts with formation of thin hexagonal
plates. The growth of the corundum crystals happens on two mechanisms: spread
over surface and oriented the build-up. With a rise of the distortion of
hydrargillite structure during mechanical treatment, the rate of a nucleation
of corundum is increased. Thus the diminution of the most probable size of
corundum crystals from 42,5 microns up to 18 microns is observed. The
amorphization of hydrargillite at mechanical action results in diminution of
rate of the corundum nucleation.
Copyright (C) Chemistry Dept., Moscow State University, 2002
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