THE ELECTRODEPOSITION OF AL3TI FROM CHLOROALUMINATE ELECTROLYTES

The electrochemistry of Ti(II) in 2:1 AlCl3:NaCl and the electrodeposi tion of metastable aluminum-titanium alloys containing up to 28 atom p ercent Ti are reported. Ti(II)/Ti(III) was studied by chronoamperometr y, chronopotentiometry, cyclic voltammetry, and convolution voltammetr y during the electrochemical dissolution of titanium. It was concluded that Ti(II)/Ti(III) behaves reversibly in this electrolyte and that, at low current densities, titanium dissolves to form Ti(II). The disso lution follows Faraday's law for Ti(II) concentrations approaching 75 mmol/liter, though concentrations up to 325 mmol/liter can be obtained at dissolution current efficiencies less than 100%. Single-phase Al3T i with the ordered face-centered cubic L1(2) structure is deposited un der conditions where the Ti partial current is not diffusion limited. Current transients and microscopic analysis of the early stages of pot entiostatic deposition suggest that Al3Ti forms by instantaneous three -dimensional nucleation at potentials where the growth process is unde r mixed kinetic and diffusion control.