Kinetics of thermal dehydration and decomposition of hydrated chlorides of some 3d transition metals (Mn-Cu series). Part-IV. Dehydration and decomposition of NiCI2.2H2O

Regional Research Laboratory, Bhubaneswar-751 013, India Manuscript received 4 July 2003, revised 19 March 2004, accepted 13 April 2004 The kinetics of dehydration of NiCI2.2H2O 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 H2O, 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 (FI) appear to be the best fit models for the two steps of dehydration. When the hydrated salt is calcined at temperature above 450º, rapid dehydration renders the material porous and therefore, subsequent dechlorination also follows first order decay law (FI). Generally, there is a broad agreement in mechanistic model as well as in Arrhenius parameters between isothermal and non-isothermal methods of dehydration