Thermal and chemical events in the decomposition course of manganese compounds

Abstract

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 ( ΔE, kJ mol −1) was determined for the thermal processes monitored throughout the decomposition course. The results showed that Mn( CH 3 COO) 2·4 H 2 O dehydrates in three steps up to 130 °C, and then decomposes to a mixture of manganese oxides Mn 3O 4 (major) and Mn 2O 3 (minor) through the intermediates Mn(OH)CH 3COO and/or MnOCH 3COO and MnCO 3. MnC 2 O 4·2 H 2 O dehydrates in one step at 150 °C, and then decomposes via MnCO 3 into Mn 3O 4 (hausmannite structure) at 350 °C. Mn( NO 3) 2·4 H 2 O undergoes stepwise dehydration up to 175 °C, and decomposes above 200 °C via an unstable oxynitrate intermediate yielding MnO 2; this decomposes at about 550 °C to the α-Mn 2O 3 phase.