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Title: The effect of specific additives on the lubrication efficiency of IF-WS2 nanoparticle suspensions
Author: Kratky, Ales
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2012
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Inorganic lamellar solid particles, for example molybdenum disulphide, have been used as solid additives in lubricants to improve their friction and wear properties. Recently, inorganic fullerene-like materials (IFLM) of metal dichalcogenides with a closed-cage structure have been synthesized. It has been shown that mechanical dispersion of IFLM nanoparticles in mineral and synthetic base oils gives benefits of low friction coefficient and wear and the benefits are superior to those of lamellar solids. The IFLMs positive effect on the oils performance was attributed to rolling mechanism and to their mechanical degradation. The aim of the thesis is to extend knowledge of inorganic tungsten disulphide (IFWS2) nanoparticles behaviour through study of their interactions with other additives in prepared oils. The investigation of the IF-WS2 lubrication efficiency had several major objectives. These were: to evaluate effect of various sliding-rolling ratios and temperatures, to classify the IF-WS2 from the point of view of additive groups and to evaluate the nature of interactions between specific additives and the nanoparticles. Lubrication efficiency of IF-WS2 nanoparticles dispersed in oils was evaluated on tribo-rigs with ball-on-disc configuration at a wide range of operating conditions. For the testing of oils with IF-WS2 Mini Traction Machine (MTM) and High-Frequency Reciprocating (HFRR) rigs were employed. Standard highly polished specimens made of AISI M52100 steel were used. In addition, Elastohydrodynamic (EHL) rig was utilised for film thickness measurements. One of the major outcomes of this work was establishing a positive effect of elevated temperature on IF-WS2 dispersion, friction and wear behaviour. Also, a certain sulphuric extreme pressure additive improved IF-WS2 dispersion properties, which was attributed to a synergistic reaction between these two additives. Moreover, the tribological performance of the nanosuspension was found to be improved by addition of stearic acid under moderate conditions, where nanoparticles show no contribution. Study of interactions between ZDDP and the nanoparticles has shown superior performance of the ZDDP solution compared to the nanosuspension under given conditions.
Supervisor: Sayles, Richard Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available