Effects of lithium doping on the thermal decomposition of manganese carbonate

Abstract

The influence of lithium oxide doping on the thermal decomposition of manganese carbonate was studied using DTA, TG, DTG and X-ray diffraction techniques. Pure MnCO 3 was found to undergo thermal decomposition at 450°C losing 31% of its weight to yield Mn 2O 3. The pure solids heated at 900 and 1100°C consisted of well-crystalline Mn 3O 4 with a trace amount of undecomposed Mn 2O 3, the amount of which decreased with increasing calcination temperature from 900 to 1100°C. The DTA, TG and DTG analyses revealed that lithium doping of MnCO 3 effected a slight decrease in the percentage of its decomposition proportional to the amount of doping agent. Manganese carbonate treated with different proportions of Li 2CO 3 underwent thermal decomposition at about 315°C yielding MnO 2 which decomposed readily at about 400°C giving Mn 2O 3. The presence of Li 2CO 3 was found to enhance the decomposition of both MnO 2 and Mn 2O 3 producing Mn 2O 3 and Mn 3O 4, respectively. X-ray diffraction showed that pure MnCO 3 calcined at 500°C consisted entirely of well-crystalline Mn 2O 3, and the lithium-treated solids heated at the same temperature were composed of γ-Mn 2O 3, Mn 2O 3 and Li 2MnO 3. The diffraction lines of Li 2MnO 3 persisted in the case of doped solids heated at 900°C, together with those of Mn 3O 4, and disappeared on heating at 1100°C with the subsequent appearance of Mn 2O 3 which remained stable at such high temperatures due to the formation of a Li 2OMn 2O 3 solid solution.