Interaction of chromium atoms with other metals (Zn, Mn, Tl, Pb and Cu) in the mercury phase

Abstract Oxidation of a homogeneous chromium amalgam and homogeneous Cr–Zn, Cr–Mn, Cr–Tl, Cr–Pb, and Cr–Cu amalgams were investigated by the double potential-step chronocoulometric method. Experiments conducted with various concentrations of chromium in mercury confirm our earlier results, showing de-activation of the chromium amalgam. In the presence of Zn and Tl, no change in oxidation of the chromium amalgam was observed. In the presence of other metals (Mn, Pb and Cu), oxidation of the chromium amalgam was less efficient than in the absence of these metals. We interpret our experimental data in terms of high-spin Cr atom formation (with electronic configuration 3d 5 4s 1 ), and fast Cr–Cr molecule formation. Since the dissociation energy of Cr 2 is 142±5 kJ mol −1 , it is electrochemically inactive in the potential range investigated. In the case of the Cu–Cr amalgam, de-activation of the chromium amalgam was higher than in the cases of Pb–Cr and Mn–Cr. We interpret this as a result of a higher interaction energy of the Cu–Cr compound, than that of the Cr 2 . From literature data it follows that the dissociation energy of the Cu–Cr compound is, indeed, higher, being ca. 150 kJ mol −1 .