Purification by Zone Refinement

Aeeording to the Clausius-Clapeyron equation the transition temperature at the solid — liquid phase boundary of a binary mixture shifts by (5Z) upon a relative eoneentration ehange (dc) between the two eonstituents  

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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. 

Purification by zone refining relies on the same principles of crystal formation as the solvent and melt methods of crystallization. Zone refining was developed as crystallization from the melt with the restriction that only a portion of the material is molten... 

The primary application for floating-zone melting is crystal growth rather than purification. Semiconductor-grade siUcon is not purified by zone refining siUcon chlorides are distilled and then reduced with hydrogen. 

Crystallization from the liquid metal has been assessed theoretically and experimentally as a purification method for both Sr and Ba After five recrystallizations, metals of 99.9999% purity can be produced. The purification of Ba by zone refining is inefficient, many passes being required for the removal of the other alkaline-earth metals. The application of combined methods (i.e., vacuum distillation plus crystal growthor vacuum distillation plus zone refining ) to the purification of both metals has also been described. 

Pyrene and naphthalene were purified by zone refinement for more than 130 passes (Bridgmen method). After such purification the central part of the glass ampoule was extracted and used in the sample preparation. Drop coating of the pyrene (naphthalene) with SWNT suspension in toluene on a quartz substrate was used to form a thin film for Raman measurements. The film was deposited onto the quartz substrate from nanotube suspension in toluene (0.1 mg/mL) and from suspension of nanotube with pyrene (or naphthalene) after short sonication (20 minutes 44 kHz). The weight ratio was 1 1 and 1 4 for mixture with pyrene (samples PI and P2, respectively) and 1 1 with naphthalene (sample N). 

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