Non-Equilibrium Fluctuations

Unified Understanding of Pitting Corrosion

Abstract

A new concept “non-equilibrium fluctuation” has been introduced to describe electrochemical reactions with intense non-uniformity along the electrode surface, such as pitting corrosion and nucleation. This concept comes from the fact that the reactions locally proceed through the breakdown of electrostatic equilibrium formed by electrical double layer owing to thermal motion of solution particles. We call this kind of breakdown non-equilibrium fluctuation because it occurs at the electrode potential not equal to the equilibrium potential. Therefore, the reaction rate is controlled by the fluctuation, i. e., the development of the electrolytic current with time is equivalent to the unstable growth of the fluctuation. After determining the intrinsic spectrum of the fluctuation in experiments, we can calculate the current density, overpotentials, surface morphology, and so on. Consequently, microscopic surface morphology of nickel pitting corrosion has been theoretically related to macroscopic total pitting current we can measure.