Thermal Behaviour of y-MnO2 and Some Reduced Forms in Oxygen

Abstract

The products obtained by partial chemical reduction of an electrodeposited y-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 MnIV was replaced by Mn’H Substitution of >50 % MnIV 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’n 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 y-MnO2 to /3-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.