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Direct to metal anti-corrosion coatings / GWYNFOR CALLAGHAN

Swansea University Author: GWYNFOR, CALLAGHAN

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Abstract

The primary objective of this work was to evaluate the corrosion driven coating failure mechanisms affecting a commercial polyurethane coating (RAPTOR), traditionally applied as a topcoat, when instead directly applied to iron. This was done by evaluating its susceptibility to corrosion driven catho...

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Published: Swansea 2021
Institution: Swansea University
Degree level: Master of Research
Degree name: MSc by Research
Supervisor: Wint Natalie ; Williams Geraint
URI: https://cronfa.swan.ac.uk/Record/cronfa58762
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Abstract: The primary objective of this work was to evaluate the corrosion driven coating failure mechanisms affecting a commercial polyurethane coating (RAPTOR), traditionally applied as a topcoat, when instead directly applied to iron. This was done by evaluating its susceptibility to corrosion driven cathodic disbondment and Filiform corrosion. The effect of cure time on the completion of the polymerization reaction was characterised using ATR-FTIR. It showed a direct correlation between cure time and resistance to cathodic disbondment. The kinetics for cathodic disbondment was investigated using adapted Stratmann delamination cells as well as the scanning Kelvin probe. Free corrosion potential profiles were generated and allowed for the rate of delamination of RAPTOR from iron to be deduced. The rate limiting mechanism for the cathodic disbondment of RAPTOR was shown to be migration of electroactive species under the coating . Filiform corrosion was initiated via addition of an aqueous iron chloride solution to penetrative RAPTOR coating scribes. Samples were maintained at a relative humidity of 94 % . Image analysis software was used to evaluate the geometry of filaments formed and the results were compared to those obtained in the case of polyvinyl butyral coatings (PVB) Aluminium polyphosphate and glass flake pigments were evaluated as potential corrosion inhibitors. The inhibitive properties of Aluminium polyphosphate have been shown to reduce the rate of coating delamination via cathodic disbondment. This is proposed to be linked to the production of partially/insoluble precipitates that limit the migration of electroactive species. Aluminium polyphosphate has also shown to increase the initiation time required to form filaments during the filiform corrosion process. Glass flake had little influence on the rate of cathodic disbondment but was shown to limit both the initiation and propagation of filaments during filiform corrosion.
Item Description: A selection of third party content is redacted or is partially redacted from this thesis due to copyright restrictions.
Keywords: Corrosion, coating, cathodic disbondment, Filiform corrosion
College: College of Engineering