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Title: Mechanistic corrosion studies in organically coated galvanised steels
Author: Williams, D. I.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2003
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In this thesis Scanning Electrochemical Techniques are used to study the mechanism of cut edge corrosion and coating delamination on organically coated galvanised steel and to evaluate environmentally friendly alternatives to strontium chromate as anti-corrosion pigments in the primer layer. Possible artefacts induced by the scanning vibrating electrode technique (SVET) whilst scanning over the surface of a sample are reported. In particular the effect of large amplitudes of vibration inducing flow into the electrolyte above the sample. When the amplitude of vibration is <25µm there is no perturbation but when increased to values up to 250µm the values of the cathodic currents reported from corroding cut edges are found to exceed andic current by an order o magnetude. Having evaluated and diagnosed an appropriate amplitude of vibration for SVET analysis (25µm), the SVET is used to study the effect of coating symmetry and in particular porosity on the mechanism of corrosion at the cut edge. The coating porosity was varied by altering the conditions of cure. Results from the SVET illustrate that asymmetry in the cure of the coating can induce differential aeration corrosion at the cut edge, with anodic activity focused on beneath the coating with the greater barrier properties. Montmorillonite ion exchange clay pigments were incorporated into the primer layer of fully formulated organically coated galvanised steel samples and evaluated using the SVET. These samples were compared to identical systems containing strontium chromate, sheildex and TiO2 pigmented primers on several different chemically pre-treated surfaces. These clay samples were found to perform very promisingly in comparison with the existing technologies especially on systems containing a chromate pre-treatment with similar levels of anti-corrosion action.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Eng.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available