| Summary: | The boundaries of liquid and vapor coexistence fields at pressures of 101.3 and 0.133 kPa were calculated based on the partial vapor pressure values of the components in the Al-Al<sub>2</sub>Se<sub>3</sub> and Al<sub>2</sub>Se<sub>3</sub>-Se partial systems. The vapor pressures of the more volatile aluminum selenide and selenium in the above systems were determined by the isothermal version of the boiling-point method. The partial pressures of the fewer volatile components were determined by numerical integration of the Gibbs–Duhem equation. The partial and integral values of the thermodynamic functions of the formation and evaporation of solutions were calculated based on the values of the partial vapor pressure of the system components. Based on the analysis of the complete phase diagram, it was found that the purification of aluminum by vacuum distillation in a single operation can remove aluminum selenide and selenium at an appropriate rate. The distillation of selenium from melts in vacuum in the whole concentration range of the Al<sub>2</sub>Se<sub>3</sub>-Se system will proceed from the mixture of the solution with Al<sub>2</sub>Se<sub>3 cryst</sub>., with accumulation of the latter in the distillation residue.
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