ELECTRODEPOSITION OF COBALT-ALUMINUM ALLOYS FROM ROOM-TEMPERATURE CHLOROALUMINATE MOLTEN-SALT

The electrochemical reduction of cobalt(II) in the 1.5:1.0 AlCl3:EMIC (EMIC = 1-ethyl-3-methylimidazolium chloride) room temperature molten salt leads to cobalt metal at potentials positive of +0.4 V and to CoA lx alloys when the deposition potential is negative of +0.4 V. The val ue of x in CoAlx gradually increases up to a value of 2 as the electro deposition potential (E(deposition)) decreases, however, plots of x vs . E(deposition) exhibit sloping plateaus and indicate preferential for mation of alloys having integral compositions of CoAl1 and CoAl2. The formation of these alloys can be interpreted as an under-potential dep osition-based process or as a free energy of alloy formation. Evaluati on of the chronoamperometric transient behavior during electrodepositi on shows that pure Co deposition proceeds via 3D progressive nucleatio n with diffusion-controlled growth. However, as E(deposition) crosses from Co metal into the alloy-forming range, th nucleation process exhi bits characteristics indicative of kinetic control.