Abstract
Adhesion promoters play an important role in the future of adhesives for structural adhesive bonding of steels. At present this is limited by the poor performance in the presence of water. The work described in this thesis examines the adsorption of two very different systems; an inorganic and an organic adhesion promoter, onto a technologically important substrate. Yttrium hydroxide is seen to deposit as a thin film as a result of thermodynamic considerations predicted by the relevant Pourbaix diagram. The deposit formed is heterogeneous in nature and is not disrupted by prolonged immersion in water. Organosilane adsorption has been studied using XPS and ToF-SIMS and the silane layer deposited from a methanolic solution of glycidoxypropyltrimethoxysilane (GPS) appears to be disordered. Despite this, there is evidence of the formation of primary bonds between the silane and the iron substrate. The failure surfaces of adhesive bonds, prepared using these adhesion promoters and a commercial adhesive system, have been studied with a variety of surface analytical techniques. Careful investigation of failed lap shear joints has enabled the exact locus of failure to be determined. Interfacial failure occurs as a result of electrochemically driven cathodic delamination, as such, the yttrium pretreatment is seen to have no effect upon the durability for the systems studied and the environmental exposure conditions employed. There is evidence that the efficacy of the inorganic pretreatment is critically dependent on both the adhesive and exposure conditions chosen for the tests. Molecular modelling techniques have also been evaluated for their potential usefulness to the adhesion community. The orientation of three organosilanes on iron has been studied and the results, although different for each molecule, are in agreement with the models proposed on the basis of surface analysis results. These initial studies confirm the benefit of the approach, although it is recommended that it continues to be used in conjunction with the well established surface analytical techniques.