The transformation of finely divided soluble anhydrite into orthorhombic anhydrite

Abstract

The transformation of finely divided soluble anhydrite into orthorhombic anhydrite was carried out both in vacuo and catalysed by water vapour, and its progress studied by X-ray diffractometry and measurement of apparent density. A few measurements were made by differential thermal techniques. The soluble anhydrite studied was prepared from calcium sulphate hemihydrate made from gypsum by (a), dry calcination, and (b), autoclaving.

The results indicate that the transformation can proceed by two mechanisms. Surface diffusion probably contributes to a high temperature mechanism, whereas a low temperature mechanism appears to be diffusionless.