Electrochemistry of Titanium and the Electrodeposition of Al-Ti Alloys in the Lewis Acidic Aluminum Chloride–1-Ethyl-3-methylimidazolium Chloride Melt

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Abstract
The chemical and electrochemical behavior of titanium was examined in the Lewis acidic aluminum chloride-1-ethyl-3-methylimidazolium chloride (AlCl3­EtMeImCl)(AlCl3­EtMeImCl) molten salt at 353.2 K. Dissolved Ti(II), as TiCl2,TiCl2, was stable in the 66.7-33.3% mole fraction (m/o) composition of this melt, but slowly disproportionated in the 60.0-40.0 m/o melt. At low current densities, the anodic oxidation of Ti(0) did not lead to dissolved Ti(II), but to an insoluble passivating film of TiCl3.TiCl3. At high current densities or very positive potentials, Ti(0) was oxidized directly to Ti(IV); however, the electrogenerated Ti(IV) vaporized from the melt as TiCl4(g).TiCl4(g). As found by other researchers working in Lewis acidic AlCl3­NaCl,AlCl3­NaCl, Ti(II) tended to form polymers as its concentration in the AlCl3­EtMeImClAlCl3­EtMeImCl melt was increased. The electrodeposition of Al-Ti alloys was investigated at Cu rotating disk and wire electrodes. Al-Ti alloys containing up to ∼19% atomic fraction (a/o) titanium could be electrodeposited from saturated solutions of Ti(II) in the 66.7-33.3 m/o melt at low current densities, but the titanium content of these alloys decreased as the reduction current density was increased. The pitting potentials of these electrodeposited Al-Ti alloys exhibited a positive shift with increasing titanium content comparable to that observed for alloys prepared by sputter deposition. © 2003 The Electrochemical Society. All rights reserved.