The application of X-ray photoelectron spectroscopy to the study of polymer-to-metal adhesion

Abstract

The delamination of a commercial epoxy coating applied to cathodically protected mild steel has been investigated from both a mechanistic and a kinetic standpoint. X-ray photoelectron spectroscopy shows the locus of failure to be invariant with surface profile, and essentially adhesive in nature. The substrate pretreatment does, however, determine the kinetics of disbondment. A three-stage process for such failure is identified, the rate-controlling step passing from oxide reduction at a defect to the cathodic area exposed, and finally to interfacial path length. A simple relationship is presented to describe the disbondment rate in terms of this interfacial path length. The concept of a critical disbondment velocity for the epoxy mild steel system is proposed. It is shown that oxide reduction is an important precursor to cathodic disbondment for this system.