Pyrolysis of r MnOOH prepared by the reaction of manganese sulfate and ammonia aqueous solution in the presence of hydrogen peroxide was studied by means of TGA, DTA, X-ray diffraction, IR spectroscopy and chemical analysis. Results obtained are as follows;
(1) In air, r-MnOOH was decomposed to B-MnO2 at 220 C which changed to a-Mn2O3 at 550 C. At the transformation from r-MnOOH to B-MnO2, an increase in weight and two exothermic peaks were observed.
(2) In nitrogen, only one endothermic peak was observed at 275 C owing to dehydration of r-MnOOH, and then dehydration product (MnO1.63) changed to ev-Mn203 at 640 C. The dehydration process was confirmed by the decrease in absorption, strength of OH band in IR spectra.
(3) It was recognized that the dehydration of r-MnOOH also occured at the exothermic region in air from the measurements of endothermic peak and IR spectra in nitrogen atmosphere for the specimens which had been heated up to various temperatures in air.
(4) Activation energy for dehydration obtained by Freeman-Carrol's method was 26, 0 and 13.2kcal in nitrogen and air, respectively. (5)From the above results, it may be considered that the formation of B MnO2 proceeds by the following two successive reactions;
2MnOOH -- Mn2O3 H2O (1)
Mn2O3 + 1/2 O2 --- 2MnO2 (2)