Titanium metal was subjected to two surface treatments (alkaline peroxide etch and chromic acid anodization) and resulting oxide morphology examined by high-resolution scanning electron microscopy in a Jeol 100-CX STEM. The effects of treatment time in alkaline peroxide upon oxide morphology were followed and parallel mechanical measurements made on the strengths of adhesive bonds between the metal and an epoxy resin. These strengths were measured after a standard environmental exposure, namely 120 h in water at 80 ~ C. As time-of-treatment increases, a micro-porous oxide layer is developed and adhesive strength rises to a maximum. Prolonged treatment with alkaline peroxide produces a drastic fall in adhesive strength accompanied by gross etching of the metal surface without changes in the oxide morphology. The loss of adhesive durability in this case is therefore attributable to surface chemistry effects rather than morphological changes.

No abstract

A recently developed fracture mechanics test, which involves pressurization of an internal circular flaw, has been used to investigate the adhesion of an epoxy resin to Pyrex glass. Specimens were tested after various times of immersion in water at 80 °C, and the adhesive failure energy 6 determined as a function of crack velocity. The effects of adding silane coupling agents to the epoxy resin, and the influence of water pH, were particularly studied. The theory of generalized fracture mechanics is used to derive, from 6, an intrinsic adhesive failure energy d0 which is the energy required to break interatomic bonds across unit area of the interface. The decrease of 60 with time follows first-order reaction kinetics with a rate constant controlled by the type and concentration of coupling agent as well as by the pH of the aqueous environment. At zero immersion time the data all extrapolate to a ‘dry ’ 0o-value of 7.25 J m-2, some 24 times the expected van der Waals interaction energy. The results are interpreted in terms of the chemical hydrolysis of interfacial bonds.