ABSTRACT
In the above discussions relating the presence of water and the thermodynamic relationships at the interface, it had to be presumed first that water could reach the interface via the adhesive and/or travel successfully along the interface from the edge areas. Brockmann (373) has pointed out that the polymer adsorbed on anodized aluminum oxide was still separable in water, indicating that chemical bonding alone between polymers and metal oxides cannot account for the stable adhesion in water demonstrated by many investigators using anodized aluminum adherends [Minford (533,534, 773, 774)]. Brockmann et a!. (523) have demonstrated that very small differences in the parameters of the aluminum surface pretreatment leading, in turn, to relatively small differences in surface morphology can still significantly change the water stability of the boundary layer in the joint. The transition zone between the oxides and various primers also was investigated by using a wet-peel testing procedure. Ultrathin cross sections from this boundary zone before and after delamination of the joints were studied by TEM, whereas the actual failed adhesive surfaces were analyzed by ESCA. As a result of the water exposure, a zone was found very near to the oxide layer whose properties were quite different from those of the bulk adhesive. In many cases, relatively large amounts of the adhesive remained on the oxide after failure, but no metal oxide was detectable on the failed adhesive layers. It was concluded that, at least partly, the adhesional failure is actually cohesional failure in very weak boundaries of the adhesive. The properties in this area have undoubtedly been influenced by the state of the anodized aluminum oxide surface. Other Brockmann papers relating to the effects of surface morphology on aluminum joint strength and durability have been co-authored by Kollek (3012) and Hennemann (523,1046), whereas investigations by Bijlmer (3014) and Ahearn et al. (3015) would have related value.
