Metals electrotransport solid state

Electrotransport In this process too a super-clean atmosphere is necessary. In electrotransport (a kind of solid-state electrolysis) a large dc current (typically 200 A cm-2) is passed through a rod of the metal at a temperature 100-200°C below its melting point. In the rare earth metals the interstitial impurities slowly move towards the anode, while several metallic impurities move towards the cathode. In this case too, as in zone melting, the purest portion of the bar is its central part. 

Ultrapure Th metal has been processed at the Ames Laboratory by solid-state electrotransport under very low pressures (on the order of 0.3 nPa), which has produced the purest Th metal known, that with a resistivity ratio of 4200 for doubly refined metal (99-101). This resistivity ratio of 4200 translates into probably <50 ppm total impurities in the metal (see footnote 1) (87-90, 104). Single crystals measuring 0.25 cm in diameter by 1.1 cm in length with resistivity ratios of 1700-1800 have also been grown (55). 

Secondary refining processes such as zone melting and solid-state electrotransport (Section III,D) should yield ultrahigh-purity Pa metal. 

If the actinide metal is available in sufficient quantity to form a rod or an electrode, very efficient methods become applicable eiectrorefining, zone melting, solid state electrotransport. Thorium, uranium and plutonium have been refined by electrolysis in molten salts An electrode of impure metal is dissolved anodically in a molten salt bath, e.g. in LiCl-KCl eutectic the purified metal is deposited on the cathode as a solid or a liquid. 

For further purification of the rare earth metals electrotransport [or solid-state electrolysis (SSE) as it is sometimes called] has been the most successful technique. But it has only been demonstrated on the low vapor pressure rare earth metals (Sc,... 

The method of solid state electrotransport has produced rare earth metals of higher purity than any other method. The principle of purifying metals by... 

The passage of a narrow molten zone along a solid rod has been successfully used to purify semiconductor materials and less reactive metals for over 25 years. Just as for the electrotransport purification method, zoning was unsuccessful until vacua of 10 Torr or better became standard practice in the laboratory. In this technique a molten zone is repeatedly passed in one direction, usually 20 passes are required to reach steady-state conditions. Impurities which raise the melting point of the solvent are left behind during solidification as the liquid zone moves forward. Thus with continued passes these impurities are moved to the beginning end of the rod. Those impurities which lower the melting point tend to remain in the molten zone... 

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