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Title: Corrosion mechanisms and inhibition on organic coated packaging steel
Author: Watson, T. M.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2006
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Initial work was undertaken to identify the electrochemical and mechanical properties behind filiform propagation and its influence on coating disbondment. A specially constructed dual compartment gas cell is used to allow the head and tail of a filiform to be exposed to different atmospheres. This experiment revealed that filiform corrosion on iron propagates in a saltatory fashion when both filament head and tail are in contact with air. Under these conditions a dark ring of corrosion products can be observed at the periphery of the filiform head. Furthermore, experiments revealed that the cathodic formation of these corrosion products is not rate limiting and thus cathodic disbondment of the organic coating is not a rate-limiting step. A modified version of the dual-compartment cell was then able to show that the rate – determining step for the propagation of an individual filiform on iron is the flow of ions. This was achieved by incrementally increasing the pressure over the head of the filiform and measuring the change in rate of propagation. This indicates that the achievable pressures within a filiform head are significant and suggests that delamination of coating via mechanical disbondment is feasible. Once vital information had been uncovered on the nature of coating disbondment and filiform propagation a specific non-toxic corrosion inhibitor system was developed, using the anion exchange clay hydrotalcite, to prevent its occurrence. This work showed that hydrotalcite wholly inhibits cathodic disbondment for NaCl induced corrosion (Phase 1) and partially inhibits subsequent filiform growth (Phase 2). The next phase of development saw the use of this vital information on the effectiveness of hydrotalcite to show that its ion exchange mechanism could be used effectively to reduce through coating permeation of aggressive species found in foodstuffs e.g. acetic acid. Testing showed that a polyethylene terepthalate (PET) based coating containing hydrotalcite (Ø = 0.2) on electrolytic chromium coated steel (ECCS) showed no corrosion when exposed to 5% acetic acid at sterilisation conditions (120°C).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Eng.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available