Abstract
THE differential thermograms of calcium sulphate dihydrates (gypsums) show two relatively large endothermic effects in close sequence below 250° C. There is general agreement1,2 that these two effects represent the two-step decomposition of the dihydrate to hemihydrate and to soluble anhydrite. A third small endothermic effect, which is always associated with the second endothermic effect, was observed recently in differential thermograms of dihydrate and β-hemihydrate and is considered due to the removal of the last traces of water of crystallization from the β-hemihydrate lattice2. A relatively small exothermic effect above 250° C. is attributed to the conversion of soluble to insoluble anhydrite3. The temperatures at which these effects appear depend on a number of experimental conditions such as rate of heating and size of sample.
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References
Schedling, J. A., and Wein, J., Österr. Akd. Wiss., 164, 175 (1955).
Fleck, W. E. P., et al., Canad. J. Chem., 38, 936 (1960).
Powell, D. A., Nature, 182, 792 (1958).
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KUNTZE, R. Differential Thermal Analysis of Calcium Sulphate Dihydrate. Nature 193, 772–773 (1962). https://doi.org/10.1038/193772a0
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DOI: https://doi.org/10.1038/193772a0
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