The Corrosion of Bivalent Transition Metals in Acid Media Under Polarization

The initial and the steady-state expressions of the current density and of the degrees of coverage with adsorbed atomic and molecular hydrogen under potentiostatlc conditions have been studied, assuming a one-step dissolution of a bivalent metal and an electrochemical desorption mechanism or hydrogen evolution. At 25°C, the anodic slope Δη/Δ log i for metal dissolution ranges between 19.5 and 59 mV for the steady state and between 59 and 118 for the initial moment of polarization, depending on the ratios between the chemical rate constants of the reaction concerned. As a function of these ratios, of the pH and the anodic overvoltage, the initial current can be higher than, equal to, or smaller than the steady-state current.