The CIMNAS project is structured in three tasks, each implementing a new vision of corrosion science :
Task #1. Understanding the stability of surface oxide films
A surface oxide film (called « passive film ») is necessary to protect metals and alloys against corrosion. However, the oxidation process preceding passivation may cause by itself the appearance of structural/chemical heterogeneities/defects that may later trigger the initiation of localized corrosion. This is investigated in details using a surface science approach of corrosion initiation combining scanning tunelling microscopy and electron spectroscopy. Important new insight into the nature and the mechanisms of formation of surface oxides and their impact on the initiation of localized corrosion is expected and should provide the basis for new opportunities to design treatments to preclude passivity breakdown by acting on pre-passivation.
Task #2. Understanding corrosion initiation and passivation at the surface terminations of grain boundaries
Progress is needed to better understand the intrinsic reactivity of grain boundaries in aggressive environments. This task adresses the mechanisms of dissolution and passivation of grain boundary terminations, for simple boundaries (twin boundaries) as well as for a variety of more complex boundaries. A novel methodology combining ex situ microstructural and in situ nanostructural and electrochemical characterisation is being developed. The success in elucidating the mechanisms of dissolution/passivation of grain boundaries could be the basis for developing ways of controlling the orientation of grain boundaries at the surface, and/or curing the surface defects associated with the grain boundary termination by a passivation process of the grain boundary emergence sites.
Task #3. Understanding the corrosion inhibition of surfaces not uniformly passivated
This task interrogates the adsorption of organic inhibitors on surfaces exposing both oxide and metallic areas in order to elucidate the long lasting issues of the metal chemical state involved in the activity of the inhibitor and the key factors for inhibiting corrosion of both metallic and oxide areas co-existing on the surface. The expected impact is to find the knowledge-based guidelines for predicting effective inhibitors working on partially oxidised surfaces (i.e. inhibiting the metal, the oxide and the periphery of the oxide patches, thought to be critical for corrosion initiation).