ON THE MECHANISM OF INTERMETALLIC FORMATION DURING CATHODIC CO-REDUCTION OF IONS IN MOLTEN SALTS

Abstract

Two mechanisms of electrolytic synthesis of intermetallic (IMs) during the simultaneous reduction (co-reduction) of their ions at the cathode in salt melts are known. And both are wrong. One of them is in contradiction with the experimental data. He violates also the thermodynamics law. Another does not represent a co-reduction process, since the ions of both metals must be simultaneously reduced at the cathode and not just one some of them. The present work does not contain new experimental data, she is purely theoretical. The mechanism of the co-reduction process is proposed and thermodynamically substantiated. It is shown for the first time that the first IM crystals appear not on the surface of an electropositive metal. They appear on the surface of a binary homogeneous solid solution consisting of IM components and which is formed at the initial moment of electrolysis. It has been shown and reconfirmed thermodynamically that electronegative metal ions are reduced with depolarization For the first time, the electrochemical equations for the crystallization of a phase of constant composition during long-term electrolysis, as well electrochemical equations as for crystallization of other intermetallic phases on the surface of the previous ones are presented. The presence of several IM phases in the cathode deposits obtained during long-term electrolysis under galvanostatic conditions is explained for the first time. The IMs electrocrystallization mechanism is examined for the cases of galvanostatic and potentiostatic electrolysis modes, as well as for cyclic and square wave voltammetry. It is also applicable to the co-reduction process of crystallization of metal compounds with non-metals.