A KINETIC AND MECHANISTIC STUDY OF THE THERMAL-DECOMPOSITION OF NICKEL PERMANGANATE

The isothermal anion decomposition reaction of nickel permanganate ((Ni(MnO4)2 --> [NiMn2O5]+1.5O2) has been studied in the range 356-400 K and the phases present in the [residue] have not been fully characterized. Fractional reaction alpha-time plots are sigmoid shaped, indicative of solid state nucleation and growth reactions, but the possible participation of local and temporary melt formation has not been excluded. Data obey the Avrami-Erofe'ev equation (n = 2) and the activation energy for salt breakdown is 100 +/- 5 kJ mol-1. The first half of the reaction (alpha < 0.5) proceeds relatively more rapidly (x 2) under dry conditions compared with the rate in the presence of 4-5 Torr water vapour. Decomposition of nickel permanganate is more rapid than the breakdown of MnO4- in aqueous solution, which is not influenced by the presence of dissolved nickel ions. This is an example of an autocatalytic reaction proceeding more rapidly in the solid state than the comparable homogeneous reaction in solution.