Letter | Published:

Differential Thermal Analysis of Calcium Sulphate Dihydrate

Naturevolume 193pages772773 (1962) | Download Citation



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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  1. 1

    Schedling, J. A., and Wein, J., Österr. Akd. Wiss., 164, 175 (1955).

  2. 2

    Fleck, W. E. P., et al., Canad. J. Chem., 38, 936 (1960).

  3. 3

    Powell, D. A., Nature, 182, 792 (1958).

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  1. Department of Chemistry, Ontario Research Foundation, Toronto, Ontario

    • R. A. KUNTZE


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