Solid state electrotransport (SSE) is one of the most promising methods for the removal of interstitial gaseous impurities from metallic materials. In this review, from the viewpoint of the purification, the trends of the SSE processing are reviewed after the 1960's since when the SSE processing has been mainly used as one of the purification techniques. Firsts of all, a history of the SSE studies and the characteristics and the general concept in the SSE treatment are described. Various

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... ng methods of the SSE properties, such as the effective valence, non-dimensional number 8, are explicated and the features in the individual methods are pointed out. By using many results in the literature, the attainable purification degree by the SSE treatment is discussed not only under the steady state but also under the unsteady state conditions. At last, by exemplifying the discrepancies between the theoretical results and the experimental results, the causes of the discrepancies are explained.