Studies in the system calcium sulphate/water. Part 5.—Surface area and porosity changes in the dehydration of calcium sulphate dihydrate

Abstract

Changes in surface area and porosity caused by heating calcium sulphate dihydrate have been studied by nitrogen sorption at 77 K, with limited oxygen and argon studies at the same temperature. Hysteresis is observed, mainly in hexagonal CaSO₄, but the observed increases in surface area are not accompanied by marked increases in porosity. Sintering, with a consequent reduction in surface area is only observed in orthorhombic CaSO₄. The oxygen and argon sorption results are interpreted in the light of previous work.