Phase Transformations in the KNd(SO4)2∙H2O–SrSO4∙0.5H2O System under Heating to 1000°С

X-ray powder diffraction and thermogravimetric analyses revealed the existence of three KNd(SO4)2∙H2O crystal hydrate phases, and their unit cell parameters were determined. The dehydration of KNd(SO4)2∙H2O upon heating at 250°C yields a partially dehydrated phase of approximate composition KNd(SO4)2∙0.2H2O. Further heating to 400°C ends with complete dehydration to yield anhydrous monoclinic KNd(SO4)2. The high-temperature triclinic KNd(SO4)2 phase exists in the range 635–900°С and decomposes when heated above 900°С. The trigonal KNd(SO4)2 phase forms solid solutions with the SrSO4·0.5H2O crystalline matrix. The anhydrous KNd(SO4)2 phase does not form solid solutions with anhydrous orthorhombic SrSO4.