Novel Vanadium Oxide Anti-Wear Additives for Boundary Lubricated Contacts

The work in this thesis aims to develop novel antiwear additives for lubricants in metal-metal contacts. Current additives contain sulphur and phosphorus, both of which are becoming increasingly regulated by current legislature. This work discusses the use of ligated transition metal compounds as precursor materials for metal oxide-based tribofilms. These have been developed through tribological testing in a number of oils in multiple tribometers, namely the TE77 pin-on-plate reciprocating tribometer, the Mini Traction Machine with Space Layer Interferometry attachment (MTM-SLIM) and a ball on disk tribometer. Results from this thesis show than vanadium-based additives show exceptional antiwear abilities (up to 88 % reduction in base oil) and can reduce friction under certain tribological conditions. Physical methods (AFM, TEM) have shown that the reason for the tribological performance of the additives is due to the formation of a tribofilm on the metal surface. Chemical characterisation of this film (EDX, XPS, XANES) has shown this film to be a nano-composite, multi-oxidation state film. Vanadium oxides possess different mechanical properties and the mixture of oxides within the tribofilm rationalise the exceptional tribological performance of the additives. This work has provided the basis for a vast array of work - most broadly would be to test ligated systems of a multitude of other metals. Only three metals were tested in this thesis (V, Zr, Ti), so there is a large amount of potential work to be done on alternative metals. Additionally, further wok could be conducted on the effect of the ligands used on the metals and whether they can be further developed to become functional within the additive. Overall, this work provides the basis for the understanding and development of a novel alternative for ZDDP as an antiwear additive.