Current and potential oscillations occur during corrosion or passivation of metals and alloys, particularly at the activepassive transition. We present a kinetic model which describes the current oscillations of iron in sulfuric acid. The model is based on the modified chemical system of iron dissolution near the active-passive transition range proposed by Schweickert, Lorentz, and Friedburg, [This Journal, 127, 1693 (1980)] but has introduced energetic interaction among the absorbed intermediates, (FeOH)ad,, [Fe(OH)2]ads, and {Fe[Fe(OH)2]}aas. The calculated results from the mathematical model indicate stable periodic current oscillations similar to the experiments.Over the past century, the current or potential oscillations of metals and alloys have been investigated experimentally and various models to interpret these oscillations have been hypothesized (1-12).Thirty years ago, Frank and FitzHugh (1) studied the oscillations at a potentiostated iron electrode. They formulated a full mathematical model for iron polarized at a constant potential and found oscillatory solutions for surface coverage and overpotential. The basic feature of this model is the assumption of a discontinuous change in reaction kinetics at the Flade potential. The discontinuity in kinetics, however, is somewhat artificial and probably not realistic, since the chemical system is considered to be continuous at the microscopic level where oscillatory phenomena originate. Therefore, their model is not sufficiently detailed to give a complete description of the oscillatory behavior of the iron/sulfuric acid system.The kinetic discontinuity remains in the work of Pearlstein and Johnson (2) in which they studied the FrankFitzHuge model carefully and analytically. The situation is more or less the same in the modified model in which Wang et al. (3) introduce a smoothed Heaviside function instead of the Heaviside step function.Degn developed an oscillation model (4) based on the ohmic resistance, the passivation reaction, and the concentration overpotential of the electrode reaction. This model does not consider the more complex chemical reactions involved in the passivation process. The microscopic origin of the current oscillation is rather uncertain in this model.Recently, Talbot and Oriani (5) studied, using simple models of passive film formation, steady-state multiplicity and oscillations in passive film formation. They assumed non-Langmuirian isotherms for adsorption kinetics and introduced adsorbate-adsorbate interactions taking the form of exp (-I~O) for adsorption and desorption rates. The results are significant in that oscillatory behaviors were obtained by this assumption. Since their models are generalized, it is considered that more specific models are necessary to describe the oscillatory behavior of iron in sulfuric acid.These works indicate that the oscillation phenomena associated with iron in sulfuric acid may involve a higher level of complexity than was included in earlier models. In spite of this complication, the developme...