Cathodic delamination was investigated for polyethylene-coated steel pipe of which surface had been previously treated with silane coupling agents. The steel surface was treated by dipping in various concentrations of epoxy-silane or amino-silane aqueous solutions. The cathodic delamination length for polyethylene-coated steel sample treated with epoxy-silane was almost the same as for one treated with amino-silane. For the least coating delamination, the concentration of silane coupling agent was 0.02-0.05 M.
The adsorption isotherm of silane coupling agent was obtained from the observation of the steel surface dipped in the various concentrations of silane coupling agent aqueous solution by XPS. These adsorption isotherms of silane coupling agent had the first peak at its concentration of around 0.02-0.05 M and the amount of adsorbed silane coupling agent monotonously increased at 0.1 M or higher. The concentration of silane coupling agent for the least coating delamination was the same as that for the first peak of the adsorption isotherm. At a high concentration of silane coupling agent aqueous solution, the polymerization of silane coupling agent was assumed, which resulted in adsorption prevention on the steel surface.
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