Transformation of vaterite into calcite in the absence and the presence of copper(II) species. Thermal analysis, IR and EPR study

The transformation of vaterite into calcite may be performed by heating in the presence and the absence of oxygen. Vaterite remains thermally stable until a calcination temperature of 450°C. It transforms progressively to calcite up to 500°C giving two exothermic peaks: 1) at 481°C due to the transformation of vaterite surface which is in contact with a small amount of calcite phase already formed with the time on the solid surface from the humidity atmosphere; 2) at 491°C due to the transformation of pure vaterite bulk. The calcite phase remains stable until 700°C. Above this temperature the formation of CaO is observed.