Electron microscopic studies on the diffusion of metal ions in epoxy–metal interphases

Cross sections of epoxy adhesive joints (DGEBA and DETA) of Al or Cu PVD substrates were prepared by ultra-microtomy and studied with STEM, EELS and EDX to reveal the metal concentration profile after curing and after ageing in moist–warm air for 300 days. After curing, ca. 0.3 at% of aluminium is detected in a thin interphase of less than 50 nm thickness. Up to 0.5 at% of copper is found within 20–75 nm from the interface and it is still detected at 1000 nm distance to the substrate. In aged samples, no further diffusion of Al species into the polymer took place whereas the Cu substrate shows a higher roughness and varying thickness after ageing. Accordingly, up to 0.9 at% of Cu is detected within the first 20–120 nm from the substrate. Thus, corrosive dissolution of the surface oxide layer and the metallic copper substrate and diffusion of Cu species into the polymer proceed under moist–warm conditions.