Development of New Precursors for Lubricious Coatings

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Antiwear and reduced friction agents are a class of engine oil additives used to both reduce self-inflicted damage from metal-metal contact inside internal combustion engines, as well as acting as friction modifiers, which serves to improve engine efficiency. Zinc dialkyl dithiophosphates are one of the leading materials used as such agents. However, despite their effectiveness, they are known to contaminate catalytic converters - a problematic issue which has led to significant research into finding replacements. Although the electrification of the transport industry has already started, tribology and the design and formulation of antiwear and antifriction additives play an important role in the optimisation of efficiency of every mechanical device. Extensive use of zinc dialkyldithiophosphates and other materials such as molybdenum disulphide (MoS2) as antiwear and lubricious materials are present across many applications that involve devices with moving mechanical components. This PhD proposes to expand upon this area of research starting from a new perspective on the topic of wear and tribochemistry by investigating new inorganic materials as protective coatings. The aim of this project is to synthesise a range of precursor complexes and to assess their potential application in the formation of either friction-reduction thin films. Objectives: modern ICEs contain a plethora of working parts coated with protective anti-wear or friction reducing coatings ranging from SiO2, TiO2, CrN and diamond. Our initial focus in this project will be directed toward the targeting and formulation of specific materials identified by their know application such as MoS2 or WS2, which have been known for some time to display lubricious behaviour at high temperatures. These materials and their derivatives exhibit intrinsic defects which in turn results in the formation of Shear planes. It is these Shear planes which under stress, can facilitate sliding and contribute to the lubricious nature of these materials. Addition of soft cations, such as silver and potassium, as dopants has also been shown to affect the formation of materials with desirable friction coefficients. Following a series of pre-established design criteria, i.e. precursors should be hydrolytically stable; soluble in higher hydrocarbon fractions (C8-C20), low toxicity; display a heat induced degradation in oil; as well as the final oxide material displaying a high thermal stability. Intrinsic to the development of any prospective precursor, studies will involve the following: assessment of the precursor and their properties with respect to thermal screening, composition of thin films formed and their characterisation; stability and solubility studies; as well as mechanical trials for example using pin-on-disc reciprocating rigs and ultra-shear viscometers, allowing for relevant information on the thin film formed to be fed back into precursor design. Targets within the first 3 months include development of ligand frameworks suitable for supporting homometallic systems containing which the desired elements for the final lubricious thin film. Initial Focus is directed towards the development of new precursors for molybdenum and tungsten sulphide systems. Supervisor Contributions: The primary supervisor (Dr Andrew Johnson) is to direct the project given his expertise in deposition of thin film materials and in precursor design. Primary supervisor contribution weighting: 80%. The secondary supervisor (Prof Matt Jones) is to advise the project given his expertise in ligand development and inorganic coordination chemistry Secondary supervisor contribution weighting: 20%.The vision of the EPSRC is to advance the knowledge and technology of scientists to tackle several key areas one of which is climate change. The development of novel lubricious materials aids in the reduction of carbon, not only lowering the effefcts of climate change but conserving the current environment.