Anodic Electrocrystallization in Low-Temperature Alkaline Melts Norton Method

3 Anodic Electrocrystallization in Low-Temperature Alkaline Melts Norton Method 

Attempts has been made to extend the Norton method to cuprate systems. La2- Naj Cu04 was obtained by anodically polarizing a NaOH melt with addition of 

La203 and CuO [384,385]. In this case, the charge consumed per molecule a fortiori amounts to less than one electron and corresponds formally to partial oxidation of the copper. This process is extremely sensitive to the melt composition and leads to the desired product only in the complete absence of water. The kinetics of the process is determined, according to the authors, by the diffusion of lanthanum hydroxo complexes. In acid (moist) melts, the oxygen evolution is apparently accelerated on the anode, and this enhances the acidity locally in the near-electrode layer and causes the precipitation of CuO. 

Electrochemical studies in alkaline melts are complicated by the absence ol detailed information on the chemistry of corresponding systems, and in particular or solvation processes. Moist melts generally represent the limiting case of strong base solutions. It would undoubtedly useful to study the changes in the kinetics and the composition of the products of anodic electrocrystallization in a model system upor the gradual transition from common alkaline solutions to concentrated bases, anc then to alkaline melts with different water contents. 

A certain similarity to the Norton method can be recognized in the combinec technique for growing YBCO crystals from a high-temperature melt [386], where electrolysis is used for locally increasing the oxygen concentration and thus foi promoting nucleation in melts saturated with respect to CuO. 

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