Pyrolysis Mechanism of Basic Calcium Carbonate

Pyrolysis of basic calcium carbonate (BCC) in inert gas flow was studied.Three endothermic peaks in the DTA curve and three weight losses corresponding to the TA peaks in the TG curve were observed.The evolved gas was analyzed and the thermal decomposi tion process was investigated by high temperature Xray diifractometry.The first endothermic process was found to correspond to the formation of BCC anhy dride y dehydration of BCC crystals.The second one corresponded to the formation of calcite and Ca(OH)2 by decomposition of BCC anhydride, and dehydration of the resulting Ca(OH)2 into CaO.The third one was related to decarbonation of the calcite into CaO.In frared absorption spectra of intermediate products sup port these results.Electron microscopic studies showed that, after the decomposition of plate-like BCC anhydride, calcite particles were produced inside the plate-like condensates.After decarbonation, single crystals of CaO were formed by disintegration of the condensates.