Electrochemical preparation of aluminium–nickel alloys by under-potential deposition in molten fluorides

The electrochemical behaviour of AlF3 was investigated in LiF–CaF2 medium first with inert tungsten and then with reactive nickel electrodes. Cyclic voltammetry, square-wave voltammetry and chronopotentiometry indicated that the reduction of Al(III) in Al(0) is a single-step process exchanging three electrons:Al(III) + 3e− = AlThe electrochemical reduction is controlled by the diffusion of AlF3 in the solution. On a nickel electrode, a depolarisation effect for Al(III) reduction was observed in cyclic voltammetry due to the formation of Al–Ni alloys when aluminium ions react with the nickel substrate. Galvanostatic and potentiostatic electrolyses on a nickel electrode led to the formation of four nickel aluminides characterised by SEM: AlNi3, AlNi, Al3Ni2 and Al3Ni. Layers with a uniform composition of AlNi3, AlNi and Al3Ni2 were prepared by varying the electrolysis potential, the current density and duration of intermetallic diffusion.