Phase diagram of the Li2SO4–Na2SO4 system

The thermal analysis and X‐ray powder diffraction studies of the Li2SO4–Na2SO4 system, including the high‐temperature X‐ray diffraction technique, have elucidated four phases of variable composition: three solid solutions based on the α‐Li2SO4, α‐Na2SO4, and α‐LiNaSO4 high‐temperature polymorphs, and a low‐temperature β‐LiNaSO4 phase. α‐Na2SO4‐Base solid solution disintegrates into two phases via a monotectoid phase transformation. It is quite probable that the monotectoid process is related to the conversion of the second‐order phase transition to the first‐order phase transition.