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Title: Conducting network anti-corrosion coatings
Author: Holness, R. J.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2004
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This Thesis describes the development and electrochemical testing of novel Zinc-Rich Paints (ZRPs) and coatings loaded with conducting polymers (specifically polyaniline) for use in the corrosion protection of steel, zinc and aluminium. Initial work concentrated on the development of model ZRPs using spherical and flake zinc powders dispersed in polyvinyl butyral (PVB). Both morphologies displayed a dramatic increase in through-film electrical conductance when the zinc volume fraction (Φ) reached the critical level (0.28) for long-range charge percolation. At the same level, these coatings sacrificially protect coated steel samples incorporating a defect. The duration of the protection increased with increased Zn volume fraction. The next phase of development saw carbon and a conducting polymer, Polyaniline Emeraldine-Salt (PAni-ES) used as "extenders" within a model ZRP organic coating. It was found that these systems fail to provide protection, despite "extending" charge percolation. This reflects the high level of cathodic activity on carbon itself and a chemical interaction between zinc and PAni-ES which rendered the coatings poor galvanic protectors. Only in instances with a high external cathode area (cut-edges) did the carbon "extended" coatings show acceptable performance. PAni-ES can protect iron and zinc surfaces in its own right. PAni-ES dispersions present in a PVB coating and solution-cast onto iron or zinc were shown to reduce rates of corrosion-driven cathodic disbondment. The presence of an adequate PAni-ES concentration also reduces the level of filiform corrosion on coated aluminium (AA2024-T3) substrates. The PAni-ES works on metal substrates by a combination of (a) raising the surface potential, (b) forming an oxide layer and (c) buffering under-film pH. The ZRPs have been developed into a system close to commercial applicability for the production of domestic appliances and from the data obtained to-date PAni-ES seems appropriate for the protection of a range of metals, as a replacement for the toxic and carcinogenic chromate systems currently in use.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Eng.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available