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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.
Moscow University Chemistry Bulletin.
2001, Vol. 42, No. 4, P. 258
   

Copyright (C) Chemistry Dept., Moscow State University, 2002
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