Thermal decomposition characteristics in air and their relationship with electrochemical activity of different polymorphic forms of MnO2

Abstract

Thermal decomposition characteristics of various synthetic MnO2 samples were studied with the help of DTA and TG in air. Each crystalline modification group produced its own characteristic thermogram which could be distinguished from the thermogram of other modifications. However, there were a few instances of overlapping, because some samples were not truly homogeneous and contained one or more polymorphic forms as impurities. The results indicate that relationships exist between electrochemical activity and DTA peak temperature for the loss of initial molecular water on the one hand, and DTA peak temperature for the decomposition of MnO2 to Mn2O3, on the other hand. The amount of combined water determined by the difference in weight loss at 400 and 200°C was found to be related to the electrochemical activity or depolarizing capacity of the samples.