Ionic liquids as additive for lubricants

Abstract

This thesis explores the use of ionic liquids (ILs) as lubricant additives, focusing on their potential for commercial applications and environmental benefits compared to conventional additives.Chapter 1 introduces the critical role of lubrication in reducing friction and wear in machinery, thus lowering energy costs and emissions. The chapter also covers the fundamentals of lubricants and the use of ILs as emerging additives in tribology, setting the stage for further exploration. In Chapter 2, the miscibility and tribological performance of four commercially available tetraalkylphosphonium ILs in Group III+ base oils are evaluated. The findings from this chapter provide a foundation for subsequent chapters, offering insights into molecular designs and a more focused approach for evaluating new additive compounds.Chapter 3 investigates neutral boron compounds as additives. Boron’s ability to form hard metal boride films enhances wear resistance, and compounds containing nitrogen show improved friction reduction. This research offers a pathway to more functionalised, environmentally friendly boron-based IL additives. Chapter 4 focuses on new boronium ILs as lubricant additives, revealing how IL speciation relates to their oil solubility and tribological behaviour.Finally, Chapter 5 details the development of novel ILs combining ester and carboxylate functionalities. These new ILs have shown remarkable reductions in friction and wear, outperforming conventional additives like zinc alkyl dithiophosphate (ZDDP) and glycerol monooleate (GMO). This work is regarded as the author’s main contribution, with its novelty protected by a patent.

Thesis embargoed until 31 Dec 2034.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Petronas Research
Supervisor	Gosia Swadzba-Kwasny (Supervisor) & John Holbrey (Supervisor)