Thermal behaviour of γ-MnO2 and some reduced forms in oxygen

Abstract

The products obtained by partial chemical reduction of an electrodeposited γ-manganese dioxide have been studied by thermal analysis in an oxygen environment between room temperature and 725 K. Weight loss in the temperature range 430–520 K was independent of sample composition when up to 35 % of Mn^IV was replaced by Mn^III. Substitution of > 50 % Mn^IV led to a dependence of weight loss on degree of reduction. With the aid of X-ray diffractometry and magnetic susceptibility measurements, these results could be explained by the formation of a single phase solid solution below ∼50 % reduction and a two-phase system when greater amounts of Mn^III were incorporated into the solid. Weight loss in the neighbourhood of 630 K could be resolved into two entities. The low temperature component was associated with the phase transition from γ-MnO₂ to β-MnO₂ accompanied by some loss of oxygen. The high temperature component was attributed to the loss of water resulting from the decomposition of Mn(OH)₄.