Thermodynamics of the Formation and Vaporization of Melts in an Aluminum Telluride–Tellurium System

Abstract—The partial vapor pressure of tellurium over melts of an Al₂Te₃–Te system is calculated by multiplying the total pressures determined from the boiling points (isothermal variant) at 700–1200°C (973–1473 K) by the fraction of tellurium in the vapor phase. The partial pressure of the saturated vapor of aluminum telluride over melts of it with tellurium, and the partial and integral thermodynamic functions of the vaporization of aluminum telluride–tellurium melts, are calculated via numerical integration of the Gibbs–Duhem equation. It is found that the saturated vapor pressure of molten aluminum telluride corresponds to the dependence $\ln \,p_{{{\text{A}}{{{\text{l}}}_{2}}{\text{T}}{{{\text{e}}}_{3}}}}^{^\circ }[{\text{Pа}}] = 18.828 - 11\,865{{T}^{{ - 1}}}$. The thermodynamic functions of the formation of the Al₂Te₃–Te melts are calculated on the basis of the partial saturated vapor pressures of the components. The formation of alloys is accompanied by an increase in the degree of system disordering in the range of hypoeutectic Te concentrations with a maximum of 5.8 J/(mol K) around 74 at % Te, and by slight ordering in hypereutectic alloys (−1.3 J/(mol K)). The formation of alloys based on Al₂Te₃ is accompanied by heat absorption with a maximum of +4.22 kJ/mol around 70 at % Te, and by an exothermic effect of −6.35 kJ/mol for tellurium-based melts around ~94 at % Te. The location of the boundaries of the regions of vapor–liquid equilibrium indicates the distillation separation of the Al₂Te₃–Te system into tellurium and aluminum telluride is impossible with only one operation of vacuum distillation, since rarefaction lowers the coefficient of separation of Al₂Te₃ and Te.