CHARACTERIZATION OF THE THERMAL GENESIS COURSE OF MANGANESE OXIDES FROM INORGANIC PRECURSORS

NH4MnO4, Mn3O4 and Mn(NO3)2.6H2O were used as precursor compounds for the thermal genesis (at 150-600-degrees-C) of manganese oxides. Thermal events occurring during the genesis course were monitored by means of thermogravimetry and differential thermal analysis, in oxidizing and non-oxidizing atmospheres. Intermediate and final solid-phase products were characterized using X-ray diffractometry and infrared spectroscopy. Model manganese oxides were subjected to similar examinations for reference purposes. The results indicated that NH4MnO4 is almost completely decomposed near 120-degrees-C, giving rise to predominantly alpha-Mn2O3. The presence of K+ contaminant supports an oxidative conversion of alpha-Mn2O3 into KMn8O16 at greater-than-or-equal-to 300-degrees-C. In contrast, the genesis of pure alpha-Mn2O3 from Mn(NO3)2 . 6H2O is not achieved unless the calcination temperature exceeds 500-degrees-C; beta-MnO2 was the only detectable intermediate. Mn3O4, obtained at room temperature by the addition of aqueous Mn2+ to ammonia solution, was converted into alpha-Mn2O3 via the formation and subsequent decomposition of Mn5O8 at greater-than-or-equal-to 300-degrees-C.