Kinetics of the thermal decomposition of cobaltic acid, CoO(OH)

Abstract

The isothermal decomposition of cobaltic acid, CoO(OH), has been examined. Two mechanisms are found to operate : above 300 °C, phase-boundary control in two dimensions dominates with an activation energy of 101 kJ mol^–1; below 290 °C, a nucleation and growth mechanism is appropriate, the activation energy being 214 kJ mol^–1. Kinetic data have been analysed by a wide variety of methods all leading to essentially the same conclusions. At all temperatures the product of decomposition is the microcrystalline spinel Co₃O₄. A preliminary study of a sample of the mineral heterogenite has also been undertaken, the activation energy obtained for its decomposition being 109 ± 20 kJ mol^–1. A small amount of occluded water made this work difficult.