Electrodeposition of Copper and Copper‐Aluminum Alloys from a Room‐Temperature Chloroaluminate Molten Salt

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Abstract
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 40 ± 1°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 (∼0 V). For a 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 percent 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 percenter atomic fraction Al retained the face‐centered cubic (fcc) copper structure; however, deposits containing 12.8 percent atomic fraction Al were two‐phase with the second phase tentatively identified as martensitic . This phase appears to form before fcc copper becomes saturated with aluminum.

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