Engineering: Fully Funded M2A EngD Scholarship: The Influence of Oxygen Reduction on Corrosion Protective Organic Coating Failure
Start date: October 2022
Expected interview date: Late June-July 2022
Academic supervisors: Professor Geraint Williams (primary) and Professor James Sullivan (secondary)
Industrial supervisors: Dr Patrick Keil
Sponsoring company: BASF Coatings
It is well known that localized corrosion causes paint films to delaminate from metal surfaces, through a mechanism involving anodic metal dissolution at a penetrative coating defect, coupled to cathodic oxygen reduction occurring on the adjacent organic-coated metal. This cathode-driven disbondment of the organic coating is thought to proceed through the formation of an under-film alkaline environment, which promotes loss of adhesion through hydrolysis of interfacial bonds, polymer degradation, and dissolution of amphoteric oxide layers. However, it is also thought that the presence of highly reactive intermediate species in the oxygen reduction reaction, such as peroxides and free radicals may also play an important role in de-adhesion on certain metal surfaces. This project forms part of a larger partnership involving BASF Coatings Ltd, in collaboration with Swansea University and Imperial College London, where the main theme will involve furthering knowledge of corrosion-induced failure of protective organic coatings when applied to metal surfaces. The principal focus of this project will be directed towards a fundamental understanding of the role of oxygen reduction in organic coating degradation via a cathodic delamination mechanism.
This project aims to fundamentally understand the role of the oxygen reduction reaction on the corrosion-driven failure of protective organic coatings applied to steel and galvanized steel surfaces. The principal objectives will comprise the following:
- A correlation of oxygen reduction rate, determined electrochemically on bare metal surfaces with organic coating failure rate under atmospheric conditions when the same surfaces are coated with a protective organic layer.
- An understanding of the influence of surface oxide composition and the presence of thin film pretreatments on oxygen reduction rate and the associated tendency to undergo organic coating disbondment.
- A mechanistic understanding of the interfacial processes associated with oxygen reduction which cause de-adhesion at the metal-polymer interface, along with a knowledge of any chemical changes produced within the polymer film.
The research will concentrate on three specific areas of interest:
(i) Developing methodologies which enable the oxygen reduction reaction to be characterized in situations where metal surfaces such as cold-rolled steel and galvanized steel are coated with an organic layer.
(ii) Gaining mechanistic information of the cathodic disbondment process by identifying chemical and physical changes in the de-adhered polymer film caused by interfacial oxygen reduction
(iii) A comparison of electrochemical measurements of oxygen reduction rates on various metal substrates with empirically gathered organic coating cathodic delamination rates to identify controlling factors such as surface composition/chemistry; understand the means to mitigate against cathode-driven coating failure.
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 world class suite of instrumentation including X-ray-photoelectron spectroscopy (XPS), glancing angle X-ray diffraction (XRD), and field emission gun scanning electron microscopy (FEG-SEM), available in the Materials Research Centre at the Faculty of Science & Engineering.