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

The kinetics of dehydration of NiCl 2 .2H 2 O have been studied by isothermal method in air and by non-isothermal method in air as well as in flowing nitrogen atmosphere. While in air (or self-generated atmosphere) the dehydration apparently takes place in single step, in nitrogen atmosphere two steps, corresponding to the losses of about 1.46 and 0.48 moles of H 2 O, can be identified in the TG curves. Whereas in static air three-dimensional diffusion (D3 or D4 model) appears to be the best fit mechanistic model, in nitrogen atmosphere the three-dimensional progress of the reaction phase boundary (R3) followed by the first order decay of partially dehydrated porous particles (Fl ) appear to be the best fit models for the two steps of dehydration. When the hydrated salt is calcined at temperature above 450, rapid dehydration renders the material porous and therefore, subsequent dechlorination also follows first order decay law (Fl). Generally, there is a broad agreement in mechanistic model as well as in Arrhenius parameters between isothermal and non-isothermal methods of dehydration.