As a result of research using the boiling point method, the partial pressure of magnesium above Mg-Sn alloys was determined, represented by the temperature-concentration dependence. The decomposition of dimagnesium stannide into its constituent metals has been preliminarily established. The pressure of magnesium above the intermetallic compound (pD) corresponds to the equation: ln pD Pa = 26.695-21,250 × T-1. The decomposition temperature of Mg2Sn at atmospheric pressure corresponds to the value (1401 ± 131 K), which, within the limits of determination errors, coincides with the boiling point of the melt (1494 ± 105 K). The thermodynamic activities of magnesium and tin were determined, based on which the partial and integral mixing functions-entropy and enthalpy-were calculated and presented in tabular form. Based on the partial values of the vapor pressure of magnesium and tin, the boundaries of the vapor-liquid equilibrium fields at atmospheric pressure (101.3 kPa) and in a vacuum (0.7 kPa) were calculated. A complete phase diagram was constructed, including the boundaries of the liquid-vapor phase transition at the specified pressures. A pressure drop in the system below 0.7 kPa may be accompanied by the crystallization of dimagnesium stannide from the melt. The boiling point of magnesium at atmospheric pressure is 1100 °C, in a vacuum - 695 °C, tin -2609 °C and 1791 °C, respectively. The areas of coexistence of liquid and vapor are large in terms of temperature. The boiling point of the melt in a vacuum (821 °C), corresponding to dimagnesium stannide, exceeds the melting point of the compound (770.5 °C) by ⁓50 °C. The composition of the equilibrium vapor phase is represented by magnesium in virtually the entire range of component concentrations. Thus, at a content of 0.1 wt. % Mg (1 × 10-3 at. %) in the melt, the vapor phase will contain 99.73-99.76 wt. % magnesium, with the remainder being tin. That is, the separation of magnesium by distillation in a vacuum does not present any technological difficulties.
Володин et al. (Fri,) studied this question.