THERMAL-BEHAVIOR OF PARTIALLY REDUCED GAMMA-MNO2 IN ARGON ATMOSPHERE

Thermal behaviour of partially reduced γ-MnO2 having the general formula (1 ∼ n) MnO2·nMnOOH with values of n = 0.075 to 0.825 were investigated by simultaneous TG, DTG and EGA in an argon atmoshphere. Water evolution showing a peak rate at 260°C and increasing in total amount with increasing n was observed in agreement with previous work. However, subsequent oxygen evolution up to 900°C was found to occur at three clearly resolved stages, not two as previously reported for a similar range of compounds. By applying XRD after successive decompositions it was shown that the oxide Mn5O8 was formed during the water evolution stage according to the equation {A figure is presented}. Residual MnO2 decomposed into Mn2O3 with a peak rate of 540°C but the Mn5O8 was still present after the sample had reached 570°C. A separate oxygen evolution peak rate at 600°C was found to correspond to the decomposition of Mn5O8. © 1979.