A MECHANISM FOR THE THERMAL-DECOMPOSITION OF POTASSIUM-PERMANGANATE CRYSTALS BASED ON NUCLEATION AND GROWTH

The mechanism of the thermal decomposition of potassium permanganate c rystals is critically reappraised through new microscopic and kinetic observations which are discussed with due consideration of the many an d extensive literature reports that relate to this solid state reactio n. We identify, from electron micrographs, a crystalline product of un usual texture that is formed early in the reaction. The topography of the residual products of the completely decomposed salt was, however, irregular and no significant textural features were identified. From c onsideration of the published reports relating to reaction stoichiomet ry and the chemistry of related reactions, we conclude that the solid products contain material that is inhomogeneous, poorly crystallized a nd possibly non-stoichiometric. The decomposition kinetics are shown t o be satisfactorily described by the Avrami-Erofe'ev equation (n = 2) based on a nucleation-and-growth reaction model. We conclude that perm anganate ions decompose in the poorly crystallized zone at the advanci ng KMnO4/product interface by an electron transfer process, in agreeme nt with a previously published mechanism.