Session: RIP: Predictive Modeling and Characterization of Corrosion Processes in Complex Environments (In Honor of Professor Digby Macdonald) (Part I of IV)
In 1979, Digby Macdonald developed the Point Defect Model (PDM). This more advanced theory describes Oxide Film growth by considering the creation and annihilation of point defects (vacancies and interstitials) within the film. PDM-I, developed in the early 1980s, assumed that the passive film was a single defective oxide layer containing cation and oxygen vacancies, which were generated and annihilated at the metal/film and film/solution interfaces. PDM-II was developed to address these issues. It incorporated the film's bi-layer structure, introduced metal interstitials, recognized barrier-layer dissolution, and recognized the need to classify reactions as lattice-conservative or nonconservative, but assumed that control of the passive current resided solely in the barrier layer. PDM-III has been developed to extend the theory to cases where the outer layer is so resistive that it controls the interface impedance and, hence, the corrosion rate. PDM- IV generation remains an open challenge for the new generation of scientists. We will discuss several areas for future work include bridging the gap between macroscopic electrochemical data and nanoscale films, extending the model to complex alloys, semiconductors, and non-aqueous environments, addressing mathematical challenges, and improving optimization techniques for the multi-variable model (adding AI techniques will benefit greatly).
