Conditions for the onset of current oscillations at the limiting current of the iron electrodissolution in sulfuric acid solutions

The experimental conditions and parameters that control the transition from a steady to an non-steady limiting current and vice versa in the anodic Fe dissolution are studied in sulfuric acid solutions by using a downward-fac ing Fe electrode. Periodic and chaotic current oscillations are observed at the beginning of the limiting current region within a fixed potential regi on by decreasing the sulfuric acid concentration, by increasing the Fe-disk rotation rate and by increasing a series external resistance. It is found that current oscillations emerge when the IR drop exceeds a critical value (IR)(crit). The latter depends on the hydrodynamic conditions pertaining to the system. This is realized by the differences appeared in the value of ( IR)(crit) on using a stationary or a rotating Fe electrode. The effect of h ydrodynamic conditions is shown by additional experimental results obtained by using an upward-facing Fe electrode, by increasing the density and visc osity of the solution on addition of glycerol, and by altering the solution properties near the Fe surface on addition of halide ions.