Investigating the electrochemistry of organic coated metal surfaces at defect sites

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The project forms part of a larger partnership involving BASF Coatings, in collaboration with Swansea University and Imperial College London, where the main theme will involve furthering the understanding of corrosion-induced failure of protective organic coatings when applied to metal surfaces. The principal focus of the project will be directed towards a fundamental understanding of the processes which occur within the confined space of a penetrative organic coating defect, down to the underlying metal. A detailed knowledge in this area is key in designing improved coating technologies which provide "self-healing" capability under situations where damage is induced, and a small area of metal becomes exposed (e.g., a stone chip in painted car bodywork). The research will concentrate on three specific areas of interest: (i) the development of appropriate electrochemical techniques and experimental methodologies which allow the study of dynamic changes in the corrosion behaviour of exposed metal surfaces at a penetrative organic coating effect.(ii) the influence of the defect topography and composition of the protective organic coating, with particular emphasis on the primer layer, on the corrosion processes and kinetics of corrosion occurring on the exposed metal surface. The metal substrates to be studied will comprise cold rolled, galvanized and zinc-aluminium-magnesium alloy coated steel, while organic coatings will concentrate on simple model paint systems.(iii) correlation of dynamic changes in the electrochemistry of the exposed metal at the defect with release of inhibitive agents stored within the protective coating, initially focusing on industry standard corrosion inhibitive pigment technologies, but extending to novel, intelligent release additives.The investigation will be carried out using comprehensive in-situ and ex-situ electrochemical characterization by means of scanning Kelvin Probe (SKP), Scanning Vibrating electrode technique (SVET), alongside potentiodynamic and electrochemical impedance spectroscopy methods in the laboratories of the Swansea University corrosion research group. Surface chemical and structural characterization will be carried using a suite of instrumentation including X-ray-photoelectron spectroscopy (XPS), glancing angle X-ray diffraction (XRD), and field emission gun scanning electron microscopy (FEG-SEM).Project Tasks:- Develop experimental methodologies to investigate the electrochemistry of exposed metal substrates at a penetrative coating defect, initially concentrating on the application of SKP to monitor changes in corrosion potential and SVET to determine time-dependent changes in anodic and cathodic currents. It is anticipated that the use of microprobe electrode technology can also be adapted to characterise metal substrate electrochemistry at a defect under external polarisation.- A systematic study the effect of defect size, organic coating thickness and composition on dynamic changes in the corrosion behaviour of the exposed metal.- Carry out chemical characterisation of the post-corrosion metal surface at the defect site to elucidate the phenomena responsible for the observed dynamic changes in corrosion behaviour.