Kinetics of electroreduction of zirconates on tungsten in fluoride melts

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Abstract

Aluminum alloys with zirconium additives are increasingly used in the aerospace industry, instrument making and power engineering, due to the combination of increased corrosion and thermal resistance without compromising density and electrical conductivity. A promising method for producing such alloys is synthesis in molten fluorides of alkali and alkaline earth metals, using oxides as a consumable metal-containing component. According to existing scientific and technical data, the use of electrolysis can contribute to an increase in the efficiency of reducing zirconium oxide to metallic oxide, in connection with which, the study of the electrochemical behavior of zirconium ions in fluoride melts is relevant. The method of cyclic chronovoltammetry was used to study the main regularities of cathodic electroreduction of zirconium and aluminum ions from melts based on KF–AlF3 with additives of zirconium and aluminum oxides at a temperature of 750°C on a tungsten cathode. A series of polarization curves were obtained both in a pure melt and with additives of zirconium and aluminum oxides at potential scan rates from 0.1 to 2 V. It was shown that the discharge of aluminum ions is observed more negative than the potential of –1.6 V, and at a potential of –1.8 to –1.9 V, the Al peak corresponding to the reduction of aluminum ions is formed. In the region of potentials more positive than –1.6 V, the cathodic process AlxWy is also observed, presumably associated with the reduction of aluminum ions and the formation of its intermetallic compounds with tungsten. When ZrO2 is added to the melt under study, the voltammograms additionally show a Zr platform and an Al+Zr peak at potentials of –1.3 and –1.6 V, associated with the discharge of zirconium ions and the combined discharge of zirconium and aluminum ions, respectively. When scanning the potential to the anodic region, the Al’ peak is observed at a potential of about –1.6 V and the Al’ and Zr’ waves, associated with the oxidation of metallic aluminum and aluminum with zirconium from the intermetallic compound, respectively. For the tungsten electrode, an increase in the current densities of the Al+Zr peak and a potential shift with an increase in the potential scanning rate are expectedly observed, which indicates the electrochemical irreversibility of the process under study.

About the authors

A. A. Filatov

Institute of High-Temperature Electrochemistry, Ural Branch of the Russian Academy of Sciences

Author for correspondence.
Email: Aleksander.F.A@yandex.ru
Russian Federation, Yekaterinburg

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