Tafel-Piontelli model for the prediction of uniform corrosion rate of active metals in strongly acidic environments

Corrosion represents a threatening and expensive problem for every industrial sector. To address this issue, several predictive models were developed and categorized in empirical, semiempirical and mechanistic, ac-cording to their underlying hypotheses, their representation of major physicochemical phenomena, and their applicability limits. In this work, a mechanistic model strongly based on the theory of kinetics of electrochemical corrosion is presented and validated. The model, called Tafel-Piontelli, was firstly proposed in 2017 as a tool for the calculation of the corrosion rate of active metals in acidic environments, characterized by hydrogen evolution as the dominant cathodic process. Starting from its initial version, the base-equation of the model has been revised and the theoretical architecture improved. The model was validated according to the experimental data collected for a variety of strong acids in a wide range of temperature and pH sets. The kinetic parameters of the equation, such as the cathodic Tafel slope and the hydrogen evolution exchange current density, were deter-mined via cathodic potentiodynamic polarization tests (Tafel extrapolation method), while the iron ion activity and the corrosion rate were determined from mass loss tests and application of the Faraday law. The results show a remarkable improvement in the representation of the iron ion activity and of its exponential dependence on pH and temperature with respect to the original formulation. Additionally, the estimated corrosion rates accurately capture the dynamics observed in the empirical data, thus confirming the validity of the model.