Environmental Integrity of Coating/Metal Interface
Final rept. 1 Mar 1987-31 Jan 1990
ROCKWELL INTERNATIONAL CORP THOUSAND OAKS CA SCIENCE CENTER
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The role of chemical electrochemical reactions at the coatingmetal interface in the region of a cathodic disbond in degrading adhesion of organic coatings to steel has been studied using scanning acoustic microscopy, wetting analysis and x-ray photo-electron spectroscopy XPS. The results show that cathodic polarization accelerates adhesion loss by the combined effects of a shift in the zeta potential of the steel substrate and build-up of an alkaline sodium hydroxide electrolyte that chemically degrades the polymer. Cathodic formation of sodium hydroxide not only degrades the polymer, but also lowers the surface tension of the electrolyte so as to favor displacement of the polymer. A mechanism of interfacial bond rupture made irreversible by polymer degradation is proposed.
- Coatings, Colorants and Finishes