THE EFFECT OF SAMPLE PREPARATION ON THE THERMAL-DECOMPOSITION OF CACO3

It is pointed out that many of the thermal analysis techniques commonl y utilized to measure the rates of thermal decomposition reactions are plagued with problems of mass and energy transport limitations. Becau se the technique employed here, dynamic X-ray diffraction (DXRD), allo ws for in situ observations of the solid reactants, intermediates, and products, and for better control of the heat and mass transfer resist ance, most of these problems are obviated. Results are presented which not only compare the dramatic differences in global reaction rates be tween TGA and DXRD experiments, but also demonstrate the effects of sa mple preparation on calcite decomposition. Specifically, it is shown t hat sample cleaning, which tends to remove nucleation sites, as well a s sample de-gassing, which probably removes water vapor, can lead to v ery different calcite decomposition rates.