Phase equilibria in the Tl–TlI–Se system and thermodynamic properties of the ternary phases

Abstract

By using differential thermal analysis (DTA), X-ray analysis and electromotive force (EMF) methods the Tl–Se–I system was investigated in the Tl–TlI–Se composition range. Several polythermal sections, the isothermal section at 300K and the projection of the liquidus surface of the system were constructed. The fields of primary crystallization of phases as well as types and coordinates of non- and monovariant equilibria were determined. Formation of two congruently melting ternary compounds (Tl5Se2I at 720K, and Tl6SeI4 at 705K) was observed. The system is characterized by the existence of wide areas of solid solutions on the base of Tl2Se (α-phase) and Tl5Se2I (δ-phase). The partial molar thermodynamic functions (ΔG‾,ΔH‾,ΔS‾) of thallium as well as the standard integral thermodynamic functions of Tl6SeI4 and Tl5Se2I compounds and Tl5Se3−xIx solid solution (for x=0.2, 0.4, 0.5, and 0.8) were calculated based on the EMF data.