Interaction of diethanolamine with non-rinse chromate treated steel surfaces

Abstract

The interactions between diethanolamine (DEA), which is used as a model of an amine cured epoxy resin, and non-rinse chromate treated steel substrates have been investigated by X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). The saturation coverages of DEA, as determined by XPS adsorption isotherms, were as follows: chromate surface>chromate+colloidal SiO ₂ surface>silica surface. The chromate+SiO ₂ surface has less capacity for DEA, because its surface is rich in silica and strongly affected by the adsorption characteristics of this material. Three specific interactions between both chromate treated steel surfaces and DEA are proposed on the basis of the XPS and ToF-SIMS data: (i) Brönsted acid-base interaction between the amine of DEA and the hydroxyl functionality of the chromate surface by proton transfer from the OH to the amine, (ii) Lewis acid-base interaction between the amine of DEA and CrO ₄ ^– and/or silanol groups, (iii) dehydration reaction between the alcohol group of DEA and the hydroxyl functionality of the chromate surface.