The Effect of Silane Incorporation on a Metal Adhesive Interface: A Study by Electron Energy Loss Spectroscopy

A silane-based adhesive formulation, used in the aerospace industry, was studied using sub-nanometre spatially-resolved energy loss spectroscopy, as a function of the concentration of silane used in the adhesive. The changes in the relative oxygen concentration and the occupancy of p-type states in the oxygen density of states reveal the existence of a composite layer between the aluminium and the epoxy resin. This composite layer is prevalent in the 1% (w/w) organosilane sample, whilst it is smaller or absent for the 0.5% (w/w) and 2% (w/w) silane concentration. These observations correlate well with the observed macroscopic durabilities observed when these adhesives are used for the structural adhesive bonding of aluminium aerospace alloys.