ON THE THERMAL DECOMPOSITION MECHANISM FOR DEHYDROXYLATION OF ALKALINE-EARTH HYDROXIDES

The activation energy for thermal dehydroxylati0n i vacuum of alkaline-earth hydroxides has been calculated from thermogravimetric data. The experimental results of Mg(OH)2 Ca(OH) 2 and Sr(OH)2 are in agreement with an unimolecular decay law and their activation energies are similar to the values of enthalpies of decomposition. In contrast, as the dehydroxylation process of Ba(OH)2 takes place in liquid phase and the BaO does not dissolve into the molten Ba(OH)2, a kinetic of zero order describes the reaction rate and the activation energy is lower than the enthalpy of decomposition. The kinetic mechanism of thermal decomposition f both synthetic Mg(OH)z and natural brucite has received extensive attention [1-4]. However, though thermal decomposition f the other alkaline-earth hydroxides has been studied [5-8], these studies have been fundamentally guided to determine the stability and identification of the new phases formed during the dehydration processes, while nobody seems to have treated the kinetics aspects of these processes, per-forming calculations about the kinetic parameters. The kinetic of thermal dehydroxylation f alkaline-earth hydroxides has bee