Effect of nano-Al2O3 on adhesion strength of epoxy adhesive and steel

Nanosized Al2O3 particles were introduced into an epoxy adhesive to improve the adhesion strength of bonded steel utilizing both modified and unmodified epoxy adhesive. The adhesion strength was measured by pull-off adhesion test as a function of nano-Al2O3 amount and interface roughness. The results indicated that the adhesion strength was increased dramatically by addition of nano-Al2O3 into the epoxy adhesive compared with that of pure epoxy adhesive. The highest adhesion strength was obtained with 2 wt% nano-Al2O3 in epoxy adhesive, being almost four times higher than that of the unmodified. As the adhesion strength increased, the locus of failure changed from interfacial to the mixture of interfacial and cohesive.Scanning electron microscopy (SEM), transmission electron microscope (TEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS) were used to investigate the interface morphology and chemical composition of steel and epoxy adhesive. TEM proved that nano-Al2O3 was finely dispersed in the epoxy adhesive. The results of SEM and EDX showed little difference between unmodified and modified samples. The XPS results showed that a new chemical group, identified as a carboxyl group, was formed at the interface between the steel and epoxy adhesive after modification by nano-Al2O3. Thus, the enhancement in adhesion strength was correlated with the introduction of this new polar group.