THERMAL AND CHEMICAL EVENTS IN THE DECOMPOSITION COURSE OF MANGANESE COMPOUNDS

Thermogravimetry and differential thermal analysis, infrared spectroscopy (solid phase and gas phase), and X-ray diffraction were used to characterize the pathways of the decomposition of the hydrated acetate, oxalate and nitrate of manganese in air. The non-isothermal activation energy (Delta E, kJ mol(-1)) was determined for the thermal processes monitored throughout the decomposition course. The results showed that Mn(CH3COO)(2) . 4H(2)O dehydrates in three steps up to 130 degrees C, and then decomposes to a mixture of manganese oxides Mn3O4 (major) and Mn2O3 (minor) through the intermediates Mn(OH)CH3COO and/or MnOCH3COO and MnCO3. MnC2O4 . 2H(2)O dehydrates in one step at 150 degrees C, and then decomposes via MnCO3 into Mn3O4 (hausmannite structure) at 350 degrees C. Mn(NO3)(2) . 4H(2)O undergoes stepwise dehydration up to 175 degrees C, and decomposes above 200 degrees C via an unstable oxynitrate intermediate yielding MnO2; this decomposes at about 550 degrees C to the alpha-Mn2O(3) phase.