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

The electrodeposition of copper and copper-aluminum alloys was investigated in the Lewis acidic aluminum chloricle-1-methyl-3-ethylimidazolium chloride (60.0-40.0 mol %) molten salt containing electrogenerated Cu(I) at 40 +/- 1 degrees 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 (similar to 0 V). For a 5.0 x 10(-3) mol L-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 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 beta'-Cu3Al. This phase appears to form before fee copper becomes saturated with aluminum.