Kinetics of thermal dehydration and decomposition of hydrated chlorides of some 3d transition metals (Mn-Co series). Part-III. Dehydration and decomposition of COCl2 hydrates

Abstract

An attempt has been made to study the thermal dehydration behavior of CoCl, with different states of hydration in static air as well as in flowing nitrogen atmosphere by TG/DTA method. It is observed that the salt containing more than two [notes or water of hydration dehydrates in three steps and only the dihydrate salt dehydrates in two steps losing one mole of H2O in each step. Because of the variable nature of the loss of H2O moles in the first step of dehydration, kinetics of this have not been studied. However, the kinetics of the dehydration of the last two moles of H2O in air as well as in flowing N-2 atmosphere have been studied by using the isoconversion method. While nucleation and/or growth is found to be the best fit model for dehydration in static air, in N-2 atmosphere progress of reactant/product interphase appears to be the most appropriate model. The anhydrous salt is stable up to about 400(n) above which CoCl, decomposes with the formation of spinel oxide (Co3O4). The kinetics of decomposition also tends to follow the progress of phase boundary model.