Research On The Correlation Between Alloy Mixing Enthalpy And Vacuum Distillation Gas-liquid Equilibrium

Thermodynamic properties are fundamental data for many areas,such as metallurgy,materials,chemicals,and so on.As one of the important thermodynamic properties,enthalpy has been widely used in material preparation and metallurgical engineering.The correlation between enthalpy and phase equilibrium has traditionally been an important research topic in the thermodynamics field.Establishing of the relationship between enthalpy and vapor-liquid equilibrium is helpful for calculation of phase equilibrium of actual industrial separation process in vacuum metallurgy.It is significant to find a way to calculate vapor-liquid equilibrium for the theoretical research and experimental design of vacuum distillation of crude metals without knowing activity data in the field of vacuum metallurgy.The main researches of this paper are as follows:According to the Wilson equation,expressions of partial molar enthalpies and enthalpies of mixing of binary system are deduced.The partial molar enthalpies and mixing enthalpies of Sn-based binary alloys are calculated based on the Wilson equation’s interaction parameters of Sn-X(X=Al,Bi,Cd,Ga,Ge,In,Pb,Ti and Zr)systems obtained by method of nonlinear least-squares.Calculated values are compared with experimental data reported in the literature.The average relative deviations of the partial molar enthalpies are within 9.8%,and the average relative deviations of the mixing enthalpies are within 2.5%.The results indicate that the method proposed in this work is reliable for predicting thermodynamic properties for Sn-based binary alloys.Expressions of mixing enthalpies of multicomponent systems are derived.The mixing enthalpies of Al-Ga-In,Cd-Ga-Sn,In-Sn-Zn and Bi-Cd-Ga-Zn alloys are calculated based on the Wilson equation’s interaction parameters which obtained by method of nonlinear least-squares and enthalpies of mixing of binary system.The maximum deviation of the mixing enthalpy is 9.42%.The results indicate that calculated values are statistically in agreement with experimental data reported in the literature.The above method is extended to ternary alloy system.The isoenthalpy diagrams of ternary alloys are drawn and the effect of correlation between the mixing enthalpy and the interaction between components on calculation of vapor-liquid equilibrium is analyzed.By means of molar volumes and infinite-dilution excess enthalpy of components,interaction parameters of the Wilson equation have been obtained.VLE(vapor-liquid equilibrium)phase diagrams of Sn-X(X=Bi,Cd,Fe,Ga,Ge,In and Pb)systems at 5pa are modeled successfully based on the Wilson equation.The average relative deviations of Cd-Sn and Fe-Sn systems are about 30% and 10%,respectively.There is slightly larger deviation for Cd-Sn system.Except for Cd-Sn and Fe-Sn systems,the deviations of the other systems are within 7.70%.The results indicate that the existing systems’ predicted values agree well with the experimental data within a reasonable error range.The VLE deviations calculated by infinite-dilution excess enthalpy are analyzed based on the influence of the symmetry of the mixing enthalpy data on calculation of vapor-liquid equilibrium.It shows that the method could provide effective prediction for the process of vacuum distillation of alloys and theoretical guides for separating and purifying crude metals.