Multiscale Modelling of Atmospheric Corrosion . Linking a electrochemical model of porous oxides with a multi-scale microclimate model

Multiscale Modelling of Atmospheric Corrosion . Linking a electrochemical model of porous oxides with a multi-scale microclimate model  

 Ivan Cole,  Murali Venkatraman, Bosco Emmanuel

CSIRO Materials Science and Engineering, Clayton, Victoria, Australia

Ivan.cole@csiro.au

A multi-scale  model of the atmospheric corrosion of metals is being developed and can be classified into two parts. Part 1  is based on integrating modules that define such processes as marine aerosol production by oceans and breaking surf, transport of marine aerosols across landscapes, deposition of aerosols onto structures, cleaning of surfaces by wind and rain, and the wetting and drying of surfaces throughout surface temperature and relative humidity cycles. The integration of these modules into a software framework enables the user to extract accurate estimates of surface conditions for structures located at any geographical location in Australia.  Part 2 is aimed at developing a more fundamental approach to estimating corrosion based on the response of a metal to its environment .At present the focus is on developing a model of a porous oxide.

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The oxide that develops on the surface of the metals like zinc is usually porous.  Any further oxidation of the metal can happen only if the electrolyte percolates through the oxide and comes in contact with the metal and also only if there is a provision for the cathodic reaction to happen elsewhere.  In most systems like zinc, this cathodic reaction is usually oxygen reduction reaction.  This reaction, depending on the conditions could take place either on the metal surface or on the porous oxide surface.  That is, the porous oxide matrix could also conduct electrons which, at contact with the electrolyte in the pores, may lead to oxygen reduction locally.  However the anodic reaction namely the metal dissolution would occur only on the metal surface since free metal is not available for corrosion anywhere else.  The present one-dimensional model investigates the role of various parameters like work function of the metal and metal oxide, metal oxide conductivity, exchange current densities of anodic and cathodic reactions, porosity and tortuosity on the extent and location of the cathodic reaction.  Also conditions leading to passivation are identified.

An overall framework is being develop to integrate Part 1 of the model development with the components of Part 2. Relevance of the model to global variations in atmospheric corrosion and the design of metals and oxides to reduce corrosion is discussed