Prediction of the Temperature Effect on Pit Stability using Stochastical Modeling of the Pit Localized Dissolution Kinetics.

摘要

The localized dissolution kinetics of the reactions taking place within an active pit are used to explain the stability of the pit propagation. Modeling the chemical kinetics of these reactions as a Markov Stochastical process, an algorithm was developed that provides the transient evolution with time of the metal dissolution current density within the pit in relation to the initial bulk environment conditions and the applied external potential. The predicted temperatures for spontaneous stable pitting using this stochastical algorithm for a 316L stainless steel under several reducing and oxidizing environments are compared with the results from corresponding experiments. The transition between meta-stable and stable pit propagation is assessed using Electrochemical Noise, potentio-static and potentio-dynamic measurements under controlled temperatures. The results from the stochastical model developed and the analysis of the experiments performed, indicate that the necessary conditions for stable pit propagation are: The formation of saturated metal chloride environment within the pit's cavity and reaching a limiting value for the product of the pit radius to the propagating current density (pit stability constant) at the given temperature. Spontaneous stable propagating pitting then occurs when these condition are satisfied at open circuit conditions.