FT-IR and temperature-programmed desorption (TPD) study of the adsorption of probe molecules used to model epoxy resin adhesion to chromium, iron andstainless steel substrates

In this study, we investigated the reactivity of chromium, iron, and surfac e-treated 304L stainless steels (SS) toward molecules representing model ep oxy resins. These molecules were ammonia (a basic probe molecule also repre sentative of the hardener amine group), 1,2-epoxybutane (for epoxy groups) and 2(methylamino)ethanol (for the beta-amino alcohol resulting from the re action of epoxy with amine). These molecules were analyzed in the adsorbed state by either FT-IR or temperature-programmed desorption (TPD). Surface analysis showed that the top surface of the treated 304L samples on ly contains chromium and iron as metallic elements. The chromium/iron ratio can be varied within a wide range according to the SS surface treatment us ed. When increasing the SS surface chromium enrichment, we show a simultane ous increase of (i) both density and strength of surface acid sites, (ii) t he amount of beta-amino alcohol adsorbed. In addition, there is a marked im provement of the epoxy resin/304L bond strength when the SS surface is more chomium-enriched.