The crystal structure of ultra-fine CaCO3 and its thermal decomposition

The thermal decomposition of three ultra-fine CaCO3 having different partic le sizes and agglomeration states was investigated. The kinetic parameters obtained by using the contracting volume mechanism R-3 and Coats and Redfer n's equation were in good agreement with those using Kissinger non-mechanis m equation. Furthermore, the result showed that a considerable diminution o f the activation energy E-a up to 60 similar to 80 kJ . mol(-1) is observed in the case of ultra-fine calcite. The Voigt analysis of the X-ray diffrac tion data for the samples showed that abnormally large strain existed in th e lattice of these samples. We suggest that this may be the reason of their abnormal decomposition behavior. At the same timet we observed that the co nglomeration states revealed by TEM and SEM images result in the minute dif ference between those ultra-fine CaCO3.