The pre-treatment of aluminium surfaces prior to adhesive bonding and coating processes is of major technological significance. However, the two major commercial pre-treatments, chromic acid and phosphoric acid anodising, both make use of Cr(VI) containing solutions with the attendant problems of waste disposal. The disposal of this harmful solution poses severe environmental problems. Therefore, other environmentally friendly alternatives are being investigated, one of the most popular candidates is the use of one-step pretreatment processes based on organosilane adhesion promoters.
This study examines a model system made from polished aluminium sheet treated with an organosilane; γ-glcidoxypropyltrimethoxysilane (GPS). The interface was characterised by TEM carried out on microtomed sections. The information gained from imaging and Electron Energy Loss Spectroscopy (EELS) analysis revealed a layer of oxide, approximately 70 nm thick. Silicon was found to have been incorporated within this oxide layer. Thus it is suggested that during the curing of the GPS, at elevated temperature, growth of aluminium oxide takes place which gives rise to an Al/O/Si phase.