(Corrosion Division Rusty Award for Mid-Career Excellence) Rust At a Glance: Electrochemical Thermodynamics and Kinetics of Porous Corroding Interfaces

Abstract

The development of a rust layer is governed by physico-chemical processes at the electrode/electrolyte porous interface, including electrochemical thermodynamics and kinetics, as well as transport and reaction processes. While rust can be protective under passive and inert regions found on the Pourbaix diagram, it becomes interesting to see whether its stability is compromised under harsh conditions that lead to active dissolution of this porous interface.Thermodynamics calculations can predict phase transformation, which nucleation and growth is governed by the chemical activity of the porous interfaces as well as by the saturation of the electrolyte solution. Understanding the electrochemical interface is a major challenge to unravel the corrosion mechanism of porous systems. The heterogeneous nature of the oxide structure as well as the development of amorphous gel regions influences the formation of active sites and point defects with a high lability for reacting with gas phases dissolved, entrapped, or occluded within interfacial substructures.The stabilization and corrosion protection of the rust interface requires to understand the adsorption of corrosion inhibitors on the surface of the active site on the electrode ‒ creating a stable protective passive film. Enthalpy and entropy of the dissolution process can explain the spontaneous formation of a rust layer as well as the displacement of water molecules, which ultimately will result in the effective physico-chemical adsorption of the inhibitor molecules.In summary, this communication is aimed to present the role of rust at a glance, and its implications on the electrochemical corrosion mechanisms on porous interfaces. The application of electrochemical fundamentals and first principles combined with state of the art electrochemical, chemical and surface characterization techniques provides a comprehensive vision and mission on current trends in corrosion and protection of steel in porous media.