Key words: hydrargillite, boehmite, transformation in an aqueous medium, solid-phase mobility of the structure, quasi-equilibrium, nucleation, self-adsorbed layer, self-organization
The kinetics of the isothermal transformation of hydrargyllite with a 3.5 microns average particle size into boehmite in the course of autoclave treatment at 160—180 °C has been studied in a liquid water and steam media. Samples of hydrargillite were used with and without the addition of boehmite previously obtained at 200 °C. It was found that when boehmite is added to hydrargillite, the induction period decreases, and the rate of boehmite formation does not change. In a water vapor medium, the induction period is sharply reduced and the rate of boehmite formation increases compared to the process in liquid water. A study of the morphology of the transformation products has shown that the formation and growth of boehmite crystals occurs on the surface of hydrargillite particles. The values of the activation energy 89.3±11.2 kJ/mol and 147.6±11.4 kJ/mol were determined by the temperature dependence of the constants of the isothermal rate of boehmite formation in liquid water and steam, respectively. The mechanism of transformation of hydrargillite into boehmite is discussed.