Electrodeposition of Aluminum-Transition Metal Alloys from Chloroaluminate Ionic Liquids
Gery R. Stafford, Hussey Charles
Neither aluminum nor its alloys can be electrodeposited from aqueous solutions because hydrogen is evolved before aluminum is plated. Thus, it is necessary to employ nonaqueous solvents (both molecular and ionic) for this purpose. Among the solvents that have been used successfully to electrodeposit aluminum and its transition metal alloys are the chloroaluminate molten salts, which consist of inorganic or organic chloride salts combined with anhydrous aluminum chloride. One of the attributes of the chloroaluminates is the adjustable Lewis acidity, which can be altered by varying the ratio of AlCl_(3) and the halide salt. This adjustable Lewis acidity is largely responsible for the high solubility of electroactive transition metals, either in the form of discrete anionic chloride complexes (basic melt) or metal ions that are weakly solvated by anionic species such as AlCl_(4)- and Al2Cl_(7)- (acidic melt). This makes the chloroaluminates particularly well suited for the electrodeposition of a wide variety of aluminum alloys such as AlMn, AlTi and AlCu. This talk will review aluminum alloy deposition from both AlCl_(3)-NaCl and AlCl_(3)EMImCl (1-ethyl-3-methylimidazolium chloride) at temperatures ranging from 25 to 425 °C. Many of these alloys may be of technological importance, particularly in thin-film form, because they show improved resistance to chloride-induced pitting corrosion relative to aluminum.