Abstract
Zinc dialkyldithiophosphates (ZDDPs) are used ubiquitously as anti-wear agents in automotive lubricants. The phosphate glasses formed by the in-situ decomposition of ZDDPs drastically reduces mechanical wear; however, P and S containing by-products are known to poison the catalytic converter, rendering it ineffective. The research outlined within this thesis is directed towards the development of new anti-wear agents that afford equal or greater anti-wear protection, but with reduced S and/or P content, thus reducing the potential environmental impact by limiting catalytic converter degradation.Initially, this work looked at the development of precursors to metal oxide species appropriate for use as anti-wear agents (Chapters 2, 3 and 4), and from this a vanadium oxide precursor was identified as the leading candidate. Other precursors to vanadium were then explored in an effort to identify further prospective anti-wear agents. Further work looked at S-free zinc dialkyl phosphate species (Chapter 5) and metal boroxide compounds (Chapter 6).
Chapter 1: Introduction: An introduction to the field of tribology and lubrication is provided alongside a description of prior efforts to replace ZDDPs.
Chapter 2: Metal Acetylacetonate Precursors: Here, the synthesis, characterisation and tribological testing of a series of metal acetylacetonate complexes (Ti, Zr, V) is described. Tribofilms formed from the most effective V based anti-wear agent are characterised, and the presence of multiple vanadium oxide species identified, alluding to a mode of action postulated to arise from the presence of a mixed valence pseudo composite material.
Chapter 3: Vanadium Alkoxide and Phenoxide Complexes: Having identified a V-based compound as an effective anti-wear agent, this chapter details the synthesis and characterisation of a series of V(IV) and V(V) alkoxide and phenoxide species. The most promising V(V) compounds are subject to tribological testing, and the resulting tribofilms characterised. Strong wear protection was observed in all cases and characterisation of the resulting tribofilms indicated the formation of a chemically similar tribofilm regardless of the precursor used.
Chapter 4: Vanadium Schiff Base Complexes: In this chapter, mono- and di- protic chelating Schiff-base ligands are used to synthesise a series of V(IV) and V(V) complexes. In both chapters two and three, the compounds tested caused high levels of oxidation and corrosion in industrially relevant tests. Electrochemical characterisation of the compounds studied was conducted in an effort to further understand potential causes of this and identify potential solutions.
Chapter 5: Zinc Dialkyl Phosphates: Presented in the alternative format, this work details the synthesis and characterisation of a series of S-free zinc dialkylphosphate compounds featuring different donor base ligands. The solid-state structures are detailed, and the species found in solution upon dissociation of the compounds identified using DOSY-NMR.
Chapter 6: Metal Amino-Boryloxy Complexes: This chapter, also presented in the alternative format, details the synthesis and characterisation of a series of phenol stabilised metal boroxide compounds derived from borate pro-ligands. The structures found both in solution and in the solid state are presented and discussed, with interesting $\mu^3$ (Li) and $\mu^2$ (Sn, Zn) boroxide ligand binding modes observed. The application of these systems as prospective anti-wear agents is discussed.
Chapter 7: Conclusions: Final concluding remarks are made and potential areas for future work outlined.
Chapter 8: General Experimental: Details of the synthetic and analytical techniques employed within this thesis are described. The synthesis of general reagents used are also detailed. Note that the synthetic methods used to make the compounds discussed within this work are detailed within the relevant chapter.
| Date of Award | 29 Mar 2023 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Sponsors | Infineum International Ltd |
| Supervisor | Andrew Johnson (Supervisor) & Michael Hill (Supervisor) |
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