Abstract
The effect of temperature and crystallinity on the kinetics of the vaterite-calcite thermal transformation has been examined by analysis of isothermal data evaluated by X-ray diffraction techniques and differential scanning calorimetry. These results were compared with dynamic differential scanning calorimetry results and complemented by X-ray line profile analysis and scanning electron microscopy studies. In the 445 to 485°C temperature range, the kinetic data can be fitted reasonably well to a phase-boundary equation. At higher temperatures (510 to 530°C) by using differential scanning calorimetry techniques, an Avrami equation describes more accurately the conversion curves and a decrease in activation energy is observed. This change in the formal mechanism is supoported by the external morphology of the particles, revealed by scanning electron microscopy. Prior mechanical treatment of vaterite causes an increase in activation energy, due to the recrystallization process that accompanies the reaction.
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Barriga, C., Morales, J. & Tirado, J.L. Changes in the kinetics of the vaterite-calcite transformation with temperature and sample crystallinity. J Mater Sci 21, 947–952 (1986). https://doi.org/10.1007/BF01117377
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DOI: https://doi.org/10.1007/BF01117377