Electrodeposition of cobalt-aluminum alloys from room temperature chloroaluminate molten salt

The electrochemical reduction of cobalt(II) in the 1.5:1.0 AlCl sub 3 :EMIC (EMIC=1-ethyl-3-methylimidazolium chloride) room temperature molten salt leads to cobalt metal at potentials positive of +0.4 V and to CoAl sub x alloys when the deposition potential is negative of +0.4 V. The value of x in CoAl sub x gradually increases up to a value of 2 as the electrodeposition potential (E sub deposition ) decreases; however, plots of x vs. E sub deposition exhibit sloping plateaus and indicate preferential formation of alloys having integral compositions of CoAl sub 1 and CoAl sub 2 . The formation of these alloys can be interpreted as an under-potential deposition-based process or as a free energy of alloy formation. Evaluation of the chronoamperometric transient behavior during electrodeposition shows that pure Co deposition proceeds via 3D progressive nucleation with diffusion-controlled growth. However, as E sub deposition crosses from Co metal into the alloy-forming range, the nucleation process exhibits characteristics indicative of kinetic control.