From Sb-Pb-Ag liquid alloy in vacuum distillation

Most of today's research is mostly concentrated on the thermodynamics of the separation of polymetallic alloys by vacuum distillation, as it allows you to determine whether the direction and limitation of the flow of the metallurgical reactions. While studying the kinetics of evaporation of metals it is possible to identify the effective process conditions, such as temperature, vacuum grade and duration of distillation required in the design process for the separation of the components of the alloys. The goal of the work was to determine the rate of evaporation of the metals from the Sb-Pb-Ag alloys of different composition depending on temperature and pressure, and identify the limiting stage of the process. In the making prototype models, sample source metal was welded in an induction furnace in argon atmosphere of high purity, to obtain the alloy composition, mol. %: 16-77 Sb; 75-20 Pb; Ag 9-3. It this work the kinetics of evaporation of metals from Sb-Pb-Ag alloy in temperature range 823-1073 K and a pressure of 1.33-133 Pа is defined, as described by the first order equation. Values of the apparent rate of the first order constants with the sublimation of metals from the melt depends on temperature, pressure and chemical composition of the alloy. The total mass transfer coefficients of lead, antimony, silver (kMe, m·s-1) evaporation of Sb-Pb-Ag (0,55-0,40-0,05) of the alloy is (3.718-7.852)·10-7, (1.194-2.436)·10-7, (1.859-3.790)·10-10 at T = 823-1073 K, P = 13.3 Pa, respectively. The calculated apparent activation energy of evaporation of the metals from the Sb-Pb-Ag alloy: E = 20,93-46,41 kJ/mol. The apparent activation energy of evaporation of the metals, calculated by the Arrhenius equation leads to the conclusion of an easier evaporation of components from the composition of the Sb-Pb-Ag alloy compared to pure metal: E = 150-280 kJ/mol. It is shown that quantitative transport of lead and antimony in the gas phase does not limit the speed in vacuum distillation. The evaporation of the metals from the Sb-Pb-Ag alloy is controlled jointly by mass transfer, mainly in the liquid phase, as well as through the surface layer at the phase interface liquid-gas in the studied experimental conditions. Increasing temperatures above 823 K increases the rate constants of the evaporation kMe components Sb-Pb-Ag alloy. Reducing system pressure less than 133 Pa contributes to the sublimation of antimony, lead and silver.