Electrochemical characterization of Co-Cu mechanical alloys

The equilibrium Co-Cu phase diagram presents a very low solubility of either copper in cobalt or cobalt in copper in the solid state; however, the mechanical alloying process has shown that it is possible to obtain supersaturated solid solutions in the whole composition range by ball milling of elemental powder mixtures. The mechanically alloyed Co-Cu powders are chemically homogeneous and exhibit crystallite sizes of a nanometer order. In the present work, the linear voltammetry technique has been used to characterize Co-Cu mechanically alloyed powders. That is, the anodic dissolution characteristics of linear sweep voltammograms are analyzed to study the electrochemical behavior of such mechanical alloys in 0.5 M NaOH and 0.15 M Na2BO3 aqueous solutions, and to relate those characteristics to the enhanced solubility found in Co-Cu mechanical alloys. In order to systematically study this system, the voltammograms of pure Cu, pure Co, Co-Cu original powder mixtures and Co-Cu alloys, obtained by melting and casting, were also analyzed for comparison. The results showed that the voltammograms of mechanically alloyed Co-Cu powders presented peaks of dissolution at potentials intermediate between those exhibited in pure Cu and Co samples. Moreover, a third dissolution peak occurred at more noble potentials in mechanical alloys, but not in as-cast alloys. This peak is associated with the formation of the solid solution, in mechanical alloys. This suggests that both elements are dissolved simultaneously, which confirms that Co-Cu mechanical alloys are true supersaturated solid solutions.