Studies on alkaline-earth metal sulphites. Part 9. Solid solutions of Ca3(SO4)2SO3·12H2O in Ca3(SO3)2SO4·12H2O: structure, stability, and dehydration products

Abstract

Results of chemical and thermal analyses and of X-ray powder diffraction measurements show the instability of the expected compound, Ca₃(SO₄)₂SO₃·12H₂O (3), homologous to CaSO₃·4H₂O (1) and Ca₃(SO₃)₂SO₄·12H₂O (2). A solid solution of (2) and (3) containing up to ca. 0.25 mole fraction of (3) is stable and structurally similar to (2) and (1). A crystallographic structure is proposed for this solid solution. The factors contributing to the stability of the highly hydrated compounds (1)–(3), and their solid solutions, are presented and discussed.