Separation Factors and Peclet Numbers in Evaporation Refining of Elemental Substances near Their Melting Point

• Published in: Inorganic materials 2022-08, Vol.58 (8), p.860-865
• Main Authors: Kravchenko, A. I., Zhukov, A. I.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Crystallization; Diffusion coefficient; Diffusion rate; Distillation; Impurities; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Materials Science; Melting points; Peclet number; Process parameters; Separation; Sublimation; Vaporization
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1134/S0020168522080076

— Using the Burton–Prim–Slichter equation, we demonstrate that distillation or sublimation refining of some elemental substances (as exemplified by Sm, Yb, Mg, Eu, Te, Zn, Cd, Be, and Tb) at T = (0.9–1.2) T m (where T m is the melting point) can degrade with increasing temperature as a consequence of the increase in the effective separation factor, β < 1, and/or the increase in the diffusional Peclet number Pe = wX /ρ D (where w is the substance vaporization rate per unit area, D is the impurity diffusion coefficient, ρ is the density of the substance, and X is a size factor of the material being evaporated), the particular effect of β or Pe being dependent on the nature of the host and impurities. In addition, we demonstrate that Pe is small in crystallization refining processes, so the main process parameter is the separation factor.