Thermal Transformations of Graphite and Anthracite in the Presence of Lithium Carbonate

The mixtures of graphite and anthracite with lithium carbonate in atmospheres of argon and air were studied using differential scanning calorimetry (DSC). It was found that, in a temperature range of 100–500°C, the weight loss in argon was stronger than that in air. This phenomenon was caused by the removal of oxygen compounds with carbon. Competing processes of the formation of oxygen compounds with carbon and coal and the desorption of oxygen-containing substances occurred in air. The thermal effects for graphite–lithium carbonate systems in argon and in air were compared using DSC and gravimetry curves. It was found that the molar ratio between carbon(IV) and carbon(II) oxides in the reaction products up to 700°C can be estimated at 10 : 1. Endothermic effects of lithium carbonate melting in an argon atmosphere for the mixtures of graphite and anthracite with lithium carbonate were observed at 732 and 727°C, respectively. The peaks of endothermic effects in air did not correspond to the heat absorption curves in argon. The most probable explanations of the observed effects were given: the presence of lithium carbonate and lithium oxide phases and the manifestation of the stretched nature of the pre-transition region of lithium carbonate. Using powder X-ray diffractometry, it was found that the burnout of a carbon phase at 500°C in graphite and anthracite did not lead to a significant change in the interplanar distances in lithium carbonate.