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

Regional Research Laboratory, Bhubaneswar-751 013, India

Manuscript received 4 July 2003, revised 19 March 2004, accepted 13 April 2004

An attempt has been made to study the thermal dehydration behavior of CoCI₂ with different states of hydration in static air as well as in !"lowing nitrogen atmosphere by TG/DTA method. It is observed that the salt containing more than two moles of 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 N₂ atmosphere have been studied by using the isoconversion method. While nucleation and/or growth is found to he the best fit model for dehydration in static air, in N₂ atmosphere progress of reactant/product interphase appears to be the most appropriate model. The anhydrous salt is stable up to about 400° above which CoCI₂ decomposes with the formation of spinel oxide (Co₃O₄) The kinetics of decomposition also tends to follow the progress of phase boundary model.