THE ELECTRODEPOSITION OF AL3TI FROM CHLOROALUMINATE ELECTROLYTES

The electrochemistry of Ti(II) in 2:1 AlCl3:NaCl and the electrodeposition of metastable aluminum-titanium alloys containing up to 28 atom percent Ti are reported. Ti(II)/Ti(III) was studied by chronoamperometry, chronopotentiometry, cyclic voltammetry, and convolution voltammetry 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 dissolution 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 Al3Ti with the ordered face-centered cubic L1(2) structure is deposited under conditions where the Ti partial current is not diffusion limited. Current transients and microscopic analysis of the early stages of potentiostatic deposition suggest that Al3Ti forms by instantaneous three-dimensional nucleation at potentials where the growth process is under mixed kinetic and diffusion control.