Abstract
The anodic behavior of pure iron in 1 mol/dm3 sulfuric acid solution was studied with special reference to the oscillation of current and potential in a range between the active and passive states of the metal. A method using two Luggin capillaries, one for potentiostatic polarization and the other for local potential measurements, were used to study the oscillatory behavior, and the factors determining reproducibility of polarization curves were investigated. The results are summarized as follows:
(1) Periodic oscillations of current and potential are observed when the electrode process is controlled by diffusion. This phenomenon is related to the formation of a poorly conductive layer of ferrous sulfate.
(2) Although the potential is controlled at a constant value by a potentiostat, a sudden change in current occurs at the potentials corresponding to the pre-passive state. In this case, the potential distribution on the metal surface is not uniform, which indicates that the formation and destruction of the passive film are repeated irregularly with respect to location and time.
(3) Modified Degn-Franck mechanism is proposed in order to explain the oscillatory behavior.
