Kinetics of phase transitions of gibbsite during heat treatment in air and in water vapor

Results are provided for a study of the kinetics and mechanism of phase transitions (PT) of gibbsite during heat treatment in air and in water vapor (in the range 170–550°C) by iso-and non-isothermal thermogravimetry, x-ray-phase analysis (XPA), transmission electron microscopy (TEM), nuclear magnetic resonance in 27Al nuclei (NMR 27Al), and chemical analysis. It is shown that PT of gibbsite in air there are two interconnected transitions that occur in parallel: gibbsite → boehmite (γ-AlOOH) and gibbsite → x-ray amorphous Al2O3 that are realized by a topochemical mechanism. In water vapor gibbsite only experiences transition to boehmite (PT-3) that occurs by a dissolution — precipitation mechanism. Apparent activation energies for the PT that occur are determined.