Electrochemical study of the mechanism of formation of the surface alloy of aluminum-niobium in LiCl-KCl eutectic melt

This work aims to describe the reduction mechanism by which niobium-aluminum alloys are formed in LiCl-KCl eutectic melt. The electrochemical reduction of AlCl₃ at an inert electrode such as tungsten and at a niobium electrode, and the electroreduction of AlCl₃ and Nb₃Cl₈ simultaneously were investigated by cyclic voltammetry, convolution voltammetry and chronoamperometry. At a tungsten electrode, AlCl₃ was reduced to metallic aluminum via a quasi-reversible process involving a three-electron process. At a niobium electrode, AlCl₃ showed very complex behaviour: underpotential deposition of aluminum followed by formation of a surface alloy of aluminum-niobium occurring at 540 and 180 mV above the pure aluminum deposition potential, respectively. The electroreduction of AlCl₃ and Nb₃Cl₈, both present in the LiCl-KCl, confirmed these observations. From chronoamperometric measurements it was suggested that the niobium electroactive species is not reduced to the metallic form until the co-deposition of aluminum begins.