KLa(SO4)2-CaSO4 System

Solid-state reactions have been used to study phase relations between KLa(SO4)(2) and CaSO4 at temperatures in the range 600-800 degrees C. The phase diagram of the KLa(SO4)(2)-CaSO4 system has been constructed using thermogravimetry and X-ray diffraction results. The system has been shown to contain neither intermediate compounds nor solid solutions. The KLa(SO4)(2) double sulfate decomposes at a temperature of 970 degrees C. An endothermic peak at a temperature of 900 degrees C is observed over the entire composition range and corresponds to a eutectic line. Differential thermal analysis curves of the constituent sulfates KLa(SO4)(2) and CaSO4 do not show this peak. The largest magnitude of the 900 degrees C endotherm corresponds to a eutectic containing 70 mol % CaSO4.