Abstract
The research presented in this thesis aims to identify and investigate the synthesis and detailed characterisation of novel metal oxide precursors that could be utilised as anti-friction and anti-wear additives in automotive lubricants. Initially, this investigation was focused on designing precursors that offer comparable or superior tribological properties to commonly used additives such as MoDTC or ZDDP. These additives function by reducing friction and wear by facilitating the formation of lamellar sulfide materials and phosphate glasses respectively.However, it is well-documented that the presence of byproducts containing both P and S have been known to impede the efficacy of catalytic converters. Therefore, the primary focus of this research is centred on alleviating the reliance on P and S-based precursor formulations. In response to these challenges, efforts are made to transition towards alternative precursors that mitigate the environmental impact on the catalytic converters and the surrounding ecosystem, with a particular focus on metal oxide-based precursors.
By addressing these concerns, this research contributes to the development of more environmentally friendly and novel precursors, potentially leading to enhanced engine performance and reduced environmental pollution.
Chapter 1: Introduction
This chapter serves as an introduction to the field of tribology and the principles which underpin friction and wear from a general perspective. This discussion progressively narrows its focus to the world of tribology as it pertains specifically to the internal combustion engine and what measures are employed to reduce friction and wear within a highly intricate system. Furthermore, a detailed description of the mechanisms which promote the anti-friction and anti-wear phenomena are discussed alongside an introduction to alternative tribologically active species and the criteria required for refining novel precursors for use within the engine.
Chapter 2: Group IV and Group VI Schiff Base Metal Oxide Precursors
This results chapter describes the synthesis and characterisation of Schiff base ligand frameworks capable of encapsulating MIV (Ti, Zr, Hf) and MVI (Mo, W) systems and acting as oil-soluble molecules for depositing metal oxides in situ. The three principal Schiff base frameworks investigated were salicylimine, salen and benzylidene hydrazone ligand systems containing imino and hydroxy functionalised groups allowing for coordination to the aforementioned metals. Beyond the synthesis and characterisation, the resulting complexes were subjected to thermal and solubility testing to ensure their suitability for use within automotive lubricants. Several systems were identified as suitable candidates for further tribological and surface analyses.
Chapter 3: Group VI Aminobisphenolate Precursors
This results chapter describes how the focus of research shifted towards Mo and W aminobisphenolate as metal oxide precursors. The group VI aminobisphenolate systems were honed to maximise the desirable properties of the ligand systems discussed in Chapter 2 whilst also further developing framework design. These systems demonstrate a range of interesting properties displaying conformational changes upon introducing solvents of differing polarity. This led to the discovery of a class of novel oligomeric metal-oxo systems bound in a cyclic conformation. The long-chain derivatives displayed promising thermal and oil-solubility properties and consequently, these systems were identified as viable candidates for further tribological and surface analyses.
Chapter 4: Tribological Testing and Surface Analysis
The final results and discussion chapter of this thesis focuses exclusively on the tribological properties of selected precursors from Chapter 2 and Chapter 3 and the subsequent surface analysis to determine the tribological performance of the materials to deduce the triboactive nature of the precursors. The precursors were subjected to analysis in multiple oil formulations with differing additive concentrations to investigate the effect each additive has on the formation of potential new tribofilms. Initial results revealed the presence of synergistic and antagonistic interactions between the precursors with the latter primarily influencing the anti-wear capabilities of the newly-formed tribofilms. Surface analyses of the formed tribofilms indicate the presence of metal oxide or metal sulfide species within the wear track for all precursors. This investigation provided a preliminary outlook on the effects of additive concentration on the formation of tribofilms and the constituent elements determined from surface analysis. This provides an interesting platform for further investigation into the interactions which arise between molecules in situ and how this impacts the tribological performance.
| Date of Award | 2024 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Infineum UK Ltd |
| Supervisor | Andrew Johnson (Supervisor) & Matthew Jones (Supervisor) |