On the formation and oxidation of a heterogeneous amalgam of iron

Electrode processes involving the formation of a heterogeneous amalgam of iron during the electroreduction of Fe(II) ions on mercury and the oxidation of the iron amalgam were investigated by cyclic voltammetry, chronoamperometry and cyclic chronopotentiometry. The hanging mercury drop electrode and an iron plate placed on a mercury pool electrode were used in the experiments as working electrodes. It was established that particles of the electrodeposited iron are wetted by mercury and penetrate into the bulk of mercury electrodes forming a suspension. However, during electroreduction of Fe(II) ions from concentrated CaCl2 and Ca(ClO4)2 solutions a small amount of metallic iron remains on the surface of mercury. Oxidation of the heterogeneous amalgam of iron occurs at potentials about 100–150 mV less positive than the onset potential of mercury oxidation in the solutions studied. At these potentials oxidation of mercury may become significant enough to uncover some parts of the iron microcrystals. These iron particles become partially passivated and their surface energy at the Fe/solution interface decreases; consequently, the spreading coefficient of mercury on iron decreases, microcrystals of iron are expelled from mercury and finally oxidized.