Aging Process of Metal/Epoxy Laminates Investigated with X-ray Photoelectron Microscopy and Spectroscopy

In this article we describe the application of X-ray photoelectron spectroscopy to epoxy/dicyandiamide laminates on zinc galvanized steel which were aged under different environmental conditions involving high humidity and temperatures.

X-ray photoelectron microscopy allows us to identify the distribution of chemical elements with a lateral resolution of 10μm. Areas selected in the microscopy mode were then analyzed in the spectroscopy mode in order to get information on the local chemical composition.

We compared the spectroscopic features of the aged but freshly delaminated surfaces of samples stored under ambient conditions at room temperature with samples exposed to the “Kataplasmann” and the “KWT” test, respectively. Furthermore, a comparison was made with a model sample which was prepared in vacuum and on which the curing process was investigated.

Though there is no substantial loss in the lap-shear strength of the samples, we find drastic spectroscopic changes in the Kataplasma and KWT treated samples compared with the sample kept at room temperature. We conclude that the chemical changes induced by these tests cause an internal interphase boundary between the epoxy/metal interface and the bulk adhesive along which delamination occurs. Comparison with the behavior of the water-vapor-treated model sample gives evidence that hydrolysis is the main reaction in these tests.

The results described here complement our former study.¹