Research On The Phase Equilibria Of The Binary Systems Involving Rare Earth Halides (PrCl₃, SmCl₃, YbCl₃, LaI₃) With The Alkali Halides And Alkali Earth Halides

Phase Diagram Study is an important branch in Physical Chemistry and in Applied Materials Science. The main study of the phase diagram is the relationships among the components, the phases of matter system and the outside conditions around the system in equilibria state or quasi - equilibria state. Once the phase diagram is obtained, the relationships among the matter's components, structure and properties can be easily got, which is just the place where Phase Diagram Study shows very important meaning. With the development of science, CALPHAD (Computer Coupling of Phase Diagrams and Thermochemistry) approach is becoming a very important theory and technology for Phase Diagram Study.The optimization and calculation of the binary systems (SmCl3-MCl (M= Na, K, Rb, Cs); LaI3-MI (M=Na, K, Cs); YbCl3-AECl2 (AE= Mg, Ca, Sr, Ba); PrCl3-CaCl2) were carried out by using the CALPHAD technique. According to the characters of stronger interactivities of the rare earth halide systems, the modified quasichemical model in the pair-approximation for short-range ordering was properly used as a basic theory to optimize and calculate this kind of phase diagrams by rational analysis. A set of self-consistent thermodynamic parameters was obtained. The calculated phase diagrams and experimental phase diagrams agree with each other very well. Due to the calculation, the enthalpies of mixing in these systems (SmCl3-MCl (M= Na, K, Rb, Cs), LaI3-MI (M=Na, K, Cs)) were predicted in this work. Further discussion about the calculated and experimental enthalpy of mixing in the systems was undertaken: the enthalpy of mixing decreases with the increasing of the radius of alkali metal ion from Na+ to Cs+; moreover, the broad minimum values of the interactive coefficients were found at the 25% mole fraction of rare earths halides, which...