Kinetics of thermal dehydration and decomposition of hydrated chlorides of some 3d transition metals (Mn-Cu series). Part-I. Dehydration of MnCl2.4H2O

Regional Research Laboratory, Bhubaneswar-751 013, India
Manuscript received 4 July 2003. revised 9 March 2004, accepted 10 March 2004 The thermal dehydration of MnCl₂ hydrate has been studied by using simultaneous TG/DTA under the static air (or self-generated atmosphere) and also under the flowing nitrogen condition at different heating rates. In either of the above condition the salt dehydrates in three steps, with the losses of about 1.0, 1.2 and 1.1 moles of water in static air and 0.9, 2.1 and 1.1 moles of water in flowing nitrogen atmosphere. The heats of the three steps of dehydration in air have been estirnate 2d from area under the corresponding DTA peaks at the heating rate of 10°/min. The first step of dehydration is accompanied with the melting of the salt and therefore does not follow any kinetic model of solid state decomposition. For the other two steps of dehydration changes in the mechanism an observed and attempts have been made to identify these changes. All these have been possible by converting non-isothermal time into isothermal time which is more appropriate in the kinetic analysis. It is observed that either nucleation and growth or progress of the reactant/product interface is generally the most suitable kinetic model for the dehydration of manganese chloride hydrate.