Kinetics of the hexacelsian to celsian transformation in barium aluminosilicates doped with CaO

摘要

Pre-synthesized hexacelsian powders doped with CaO were held isothermally at different temperatures between 1200 and 1275 ℃ to study, using X-ray diffraction, the kinetics of the hexacelsian-to-celsian transformation in barium aluminosilicate. Semi-quantitative analysis was used to determine the extent of the transformation. Values of rate constant, k, and Avrami exponent, n, for the transformation at various temperatures were evaluated using the Johnson-Mehl-Avrami equation. The average Avrami exponent of 1.0 and the lower activation energy of 45.4 kJ/mol for the CaO-enhanced transformation might suggest that the presence of mineralizer like CaO could promote the formation of celsian nuclei with a plate-like shape on basal planes in the hexacelsian structure.