Interface analysis of epoxy varnishes on different metal oxides by cryo-ULAM and XPS
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Bonding of metal surfaces with adhesives is dependent on base-acid interactions. Consequently, the chemical
structure of the metal oxide has a significant impact in adhesion. For that reason, we analysed the surfaces of pure
Zn, Sn and Al sheets by X-ray photoelectron spectroscopy (XPS). The metals were coated with epoxy model
varnishes obtaining a coating thickness of 5 µm. The components of the water-based varnish and the cross-linked
coating were also characterized by XPS.
To model a possible reaction of the hardener based on dicyandiamide (DICY) and the metal oxide, the metal
substrates were immersed in a solution of DICY in distilled water. The XPS investigations confirmed the
hypothesized reactions of amine groups from DICY with the metal oxides. By means of cryo ultra-low-angle
microtomy (cryo-ULAM), a preparation technique which has proven to be successful for depth profiling of
polymeric samples without destroying the chemistry , a similar reaction was ascertained between the more
complex model epoxy coatings and the metal oxide passivation layers. A pronounced enrichment of the hardener
at the exposed metal/polymer interface in case of Zn and Sn was deduced.