Electrodeposition of copper and copper-aluminum alloys from a room-temperature chloroaluminate molten salt

• Published in: Journal of the Electrochemical Society 1998-09, Vol.145 (9), p.3110-3116
• Main Authors: TIERNEY, B. J, PITNER, W. R, MITCHELL, J. A, HUSSEY, C. L, STAFFORD, G. R
• Format: Article
• Language: English
• Subjects: Applied sciences; Chemistry; Electrochemistry; Exact sciences and technology; General and physical chemistry; High temperature electrochemistry (including molten salts); Metallic coatings; Metals. Metallurgy; Production techniques; Surface treatment
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.1838772

The electrodeposition of copper and copper-aluminum alloys was investigated in the Lewis acidic aluminum chloride-1-methyl-3-ethylimidazolium chloride (60.0-40.0 mol %) molten salt containing electrogenerated Cu(I) at 40plus/minus1 deg C. Sampled current and rotating ring-disk electrode voltammetry experiments indicated that it was possible to produce Cu-Al alloy deposits at potentials positive of that corresponding to the electrodeposition of bulk aluminum (approx = 0 V). For a 5.0mult 10 exp -2 mol L exp -1 solution of Cu(I), the onset of the aluminum codeposition process was found to occur at around 0.30 V vs. The Al(III)/Al couple; however, a limiting current for the reduction of Cu(I) to pure copper metal can be observed in the 0.60-0.30 V potential interval in this solution. The Cu-Al alloy composition was found to be independent of the Cu(I) concentration, reaching a maximum value of 43% atomic fraction aluminum at 0 V. The surface morphology of bulk Cu-Al alloy electrodeposits was highly dependent on the aluminum content; pure copper deposits had a dense, nodular appearance, whereas deposits containing appreciable amounts of aluminum consisted of fragile dendrites. X-ray diffraction studies indicated that Cu-Al deposits containing about 7.2% atomic fraction Al retained the face-centered cubic (fcc) copper structure; however, deposits containing 12.8% atomic fraction Al were two-phase with the second phase tentatively identified as martensitic beta '-Cu sub 3 Al. This phase appears to form before fcc copper becomes saturated with aluminum.