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Title: Novel anion-bound borates as lubricant additives
Author: Shaw, Katherine
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2016
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Effective anti-wear lubricant additives are highly desirable in order to improve the performance and lifetime of automotive engines and transmission systems, whilst keeping in line with environmental standards. Although there has been recent research interest into the use of additives containing both boron and phosphorus, the field is rather underdeveloped and there is much scope for further exploration of this area. To this end, this thesis describes the synthesis and anti-wear testing of a series of novel phosphate-bound borate potential lubricant additives. An investigation into pyroborate compounds, a key building block of these additives, is presented. The synthesis of a range of known and novel pyroborates is reported, and (3-MeOcatB)2O is crystallographically characterised. Analysis of the Lewis acidity of these species via the Gutmann-Beckett method is discussed, revealing loss of acidity when alkyl substituents and nitrogen donor atoms are introduced. A preliminary DFT study of (catB)2O, (3-MeOcatB)2O, (Naph-1,2-O2B)2O, (Ph{NH}2B)2O and (pinB)2O indicates that Lewis acidity depends on both the size and energy of the empty pz orbitals on the boron centres only in the case of alkoxy-donor species. The synthesis of a range of novel four-coordinate bis-borate species via a largely solvent-free methodology is reported and the crystallographic analysis of a selection of these compounds is presented. A preliminary study indicates very weak conductivity of these species, due to lack of solubility and large ionic radii. This presents a starting point for the further variation of such species for electrochemical applications. The use of short-chain anion-bound pyroborate species as models for longer-chain additive compounds is discussed. The synthesis of a range of model species is reported, and a study of their solution-phase behaviour carried out by NMR spectroscopy. The anion-binding behaviour of a selection of these species is discussed and the binding strength of (catB)2O and (3-MeOcatB2O) with several anions compared. The extension of this methodology to long-chain analogues is presented, highlighting the hydrolytic stability and scalability offered by such species. The screening of the lubricant suitability of a range of long-chain phosphate-bound borate species is discussed, with attention paid to hydrolytic stability and oil-solubility. The testing of the suitable additives under engine oil and driveline conditions is presented, and the resulting wear scar diameters, coefficients of friction and contact potentials discussed. This offers insight into the structure-performance relationship at play in these systems, indicating structural motifs to be avoided in the design of these additives. The comparison of the performance of these compounds with existing anti-wear additives is presented, with many of these novel phosphate-bound species offering superior anti-wear activity, particular those of lower molecular weight. Further testing of the high-performing additive {HNnBu3}{[(4-PIB1000catB)2O][HnBuPO4]} in both engine oils and driveline tests indicates the strong promise of these compounds as a new family of lubricant additives.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD146 Inorganic chemistry ; TJ Mechanical engineering and machinery