Zone refining segregation

Selenium purification by zone refining is not feasible. At practical zone-refining speeds, crystallization does not occur and impurities do not segregate. However, a controlled differential thermal treatment of selenium in a long vertical glass tube has been described (45). The treatment time is several weeks to several months. 

The "Filtration Model" as proposed in this study represents the overall rate of the solute transfer (macro-segregation) in zone refining very well for a wide range of experimental conditions. 

A graphical representation of Eqs. (7) and (8) can be seen in Figs. 56 and 57. As the interface migration speed is reduced, the wider the clean or purified area becomes. The above discussion provides the theoretical basis for zone refining, a method used to remove impurities through controlled solidification and segregation. 

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