Le polymorphisme du sulfate de sodium anhydre et les phases intermédiaires, glasérite et aphtitalite, dans le binaire Na2SO4-K2SO4

Abstract During studies on the evaluation of the by-products, the phase diagram of the binary system Na 2 SO 4 -K 2 SO 4 was reinvestigated. While the dimorphism of the potassium salt is obvious, the polymorphism of Na 2 SO 4 is subject to discussion: the compound NaK 3 (SO 4 ) 2 , glaserite, forms a large solid solution, and the mineral NaKSO 4 , aphtitalite, does not appear in the equilibrium diagram. In this study, these two compounds appear with stoichiometric compositions. Glaserite gives a peritectoic reaction at 444°C; aphtitalite has a congruent transformation at 470°C. At high temperatures, the hexagonal modifications of Na 2 SO 4 (form I) and K 2 SO 4 (α-form) show total miscibility.