Study On The Molten Salt Phase Diagrams Of Alkali Halide And Molybdate Systems

Molten salt phase diagrams are of central importance in metallurgy and materials science. They contribute to our knowledge of the behavior of materials in many applications and provide information relation to ionic interactions in solution.In this thesis, the regularities of the formation of solid solution in the binary alkali halide systems having common ions have been investigated using the support vector machine -atomic parameter pattern recognition method. A few sets of binary phase diagrams for the systems MF-MCl(M=K, Rb, Cs), RbF-RbO CsF-RbF, Li₂MoO₄-Na₂MoO₄, Na₂MoO₄- K₂MoO₄ have been experimentally determined by X-ray diffraction and differential thermal analysis. The results are mainly as following:1. The phase diagrams for the binary systems MF-MCl(M=K, Rb, Cs) have been determined using the differential thermal analysis. Both DTA and the limiting liquidus slope at the MCl(M=K, Rb, Cs) extreme indicate that these systems are eutectic with little solid solubility at the MCl extreme. There is a eutectic at 602℃and 46 mol% KF in the KF-KCl system. And at the KCl extreme, a solid solution of as 7±0.5 mol% KF in KCl at the eutectic temperature. There is a eutectic at 541℃and 48 mol% RbF in the RbF-RbCl system. And at the RbCl extreme, a solid solution of as 10±0.5 mol% RbF in RbCl at the eutectic temperature. There are two eutectic at 444℃,50 mol% CsF and 412℃, 2 mol% CsF in the CsF-CsCl system. And at the CsCl extreme, a solid solution of as 8±0.5 mol% CsF in CsCl at 444℃. Hereby, we modified the expression of the excess enthalpy of the liquid for the system KF-KCl that was calculated by Sangster and Pelton.2. Using the support vector machine -atomic parameter pattern recognition method, the formability of solid solution in some phase diagrams for binary molten salt systems have been investigated, including the alkali halide systems having common cation and the monovalent metal halide systems having common anion. The mathematical model obtained in the paper can predict that the CsF-RbF system should form solid solution, and the RbF-RbI system is a simple eutectic with zero solid solubility.3. The phase diagrams for the binary systems RbF-RbI and RbF-CsF have been determined using differential thermal analysis. Experimental data indicated that there is a eutectic at 495℃and 35mol% RbF for the RbF-RbI system, and there is no temperature minimum either in the solidus or in the liquidus for the RbF-CsF system. The phase diagram of the RbF-CsF system is belonged to the continuous solid solubility system. It is in agreement with the computerized results.4. The phase diagrams for the binary systems Li₂MoO₄-Na₂MoO₄ and Na₂MoO₄-K₂MoO₄ have been reassessed using differential thermal analysis and X-ray diffraction analysis. For the Li₂MoO₄-Na₂MoO₄ system, there is no solid solution at Na₂MoO₄ extreme. In this system an intermediate compound is formed: Li₂MoO₄·3Na₂MoO₄, melting incongruently at 484℃.The eutectic point is 460℃, 51mol% Li₂MoO₄. For the Na₂MoO₄-K₂MoO₄ system, there is an orderly extended solid solution based on 1:1(Na₂MoO₄:K₂MoO₄) compound under the solidus curve, and the extended solid solution approximately ranged from 1:1(Na₂MoO₄:K₂MoO₄) to 1:2(Na₂MoO₄:K₂MoO₄). In order to stabilizeα-structure, it maintained high temperatureα- K₂MoO₄ structure, namelyα-K₂SO₄ structure. At the same time, there is a continuous solid solution between liquidus curve and solidus curve in this binary system. The structure of the continuous solid solution is of (X-K2SO4 type too, but it is unorderly.