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The amphiphilic qualities of plant oils that emerge from their fatty acid makeup lead to improved lubricity. To produce diesel that is friendlier to the environment requires severe hydrotreating, unfortunately the same process also reduces the lubricity of the fuel. Adding petroleum based lubricity additives to the fuel may improve diesel lubricity but also present the challenge of being environmentally unfriendly or expensive. Plant oils such as castor oil, moringa oil and canola oil offer a green and relatively inexpensive approach to lubricating hydrotreated diesel fuels. This work reports on lubricity tests carried out on diesel fuel treated with castor oil, moringa oil and canola oil as lubricity enhancers to investigate lubricating abilities of the resulting mixtures. The high frequency reciprocating rig (HFRR) which is generally accepted as a universal test apparatus for determining the lubricity of diesel fuels was used. The diesel fuel was treated with these plant oils up to a concentration of 1 % (w/w). The friction coefficient (COF) and the amount of wear that occurred was measured and the wear scar surfaces were also evaluated. Factors that influence wear were also taken into consideration. The following findings were made from this study: • Castor oil, moringa oil and canola oil can function as diesel lubricity enhancers. Increase in plant oil concentration in diesel stimulated a stable film formation and improved the tribo-characteristics of the fuel. • A concentration of less than 1 % (w/w) of any of the three plant oils investigated in diesel (i.e. castor oil, moringa oil or canola oil) was enough to cause the wear scar diameter (WSD) of the fuel to reduce appreciably. As reference, the wear scar diameter (WSD) of the untreated diesel fuel after HFRR tests was 897 μm. However, at 1 % (w/w) of each plant oil in the diesel fuel, the observed reduction in WSD was 221.2 μm (castor oil), 339.06 μm (moringa oil), and 281.84 μm (canola oil). • Castor oil has comparatively better lubrication in diesel than moringa oil and canola oil owing to its hydroxyl functional group that increases both the viscosity and polarity of the oil. A concentration of less than 0.2 % (w/w) of castor oil in diesel was enough to bring the WSD of the fuel down to below the maximum allowable limit of 460 µm as specified in ISO 12156. • Viscosities of castor oil, moringa oil and canola oil have a significant effect on performance as a lubricity enhancers. • Friction coefficient for diesel treated with castor oil, moringa oil and canola oil increases with increasing temperature because at high temperatures, the lubricant film formed by fatty acids tends to be less stable and breaks down more easily. As expected, increase in temperature also causes an increase in wear, for all three mixtures. • Lubricating ability of moringa oil is much lower compared to castor oil and canola oil. Mild to severe abrasive wear was observed for diesel treated with moringa oil. • Moisture in the atmosphere affects the repeatability of the friction and wear tests. This occurs because of the formation of an oxide layer on the metal surface that involves water. Upon keeping a close humidity range of 50 % - 55 % in the test chamber an improvement in repeatability of the test results was observed. Keywords: plant oil, biodegradability, diesel fuel, lubricity enhancer. / Dissertation (MEng (Chemical Engineering))--University of Pretoria, 2021. / Chemical Engineering / MEng (Chemical Engineering) / Unrestricted

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In the present study, efforts have been made to produce protective surface layers in order to improve the tribological, electrochemical and tribo-electrochemical response of titanium. In order to achieve this, two different techniques were employed: 1) thermal oxidation (TO) and 2) pack carburisation with oxygen diffusion (PC). Thermal oxidation of commercially pure titanium (CP-Ti) was undertaken at a temperature of 625 °C for durations of 5, 20 and 72 h. This results in a multi-layered structure comprising a titanium dioxide layer (rutile) atop of an α-titanium oxygen diffusion zone (α-Ti(O)). Initial attempts have also been made to improve the frictional behaviour of the oxide layer, using a prior surface mechanical attrition treatment (SMAT) and controlled slow cooling after oxidation. The results demonstrate that these prior and post treatments have a positive effect on the tribological performance of the oxide layer. Electrochemical and tribo-electrochemical characterisation was also carried out in a 0.9% NaCl solution. Electrochemical tests provided evidence that oxygen content in the upper part of the oxygen diffusion zone (depths < 5 μm from the surface) helps to accelerate passive film formation and thus improve the corrosion resistance of CP-Ti. Tribo-electrochemical testing of TO-Ti was carried out against an alumina counter face under various anodic and cathodic potentials. It is shown that the rutile oxide layer offers low friction and improved wear resistance. An unusual anodic protection behaviour for the oxide film has also been observed. When the TO-Ti is polarised anodically during sliding, the durability of the oxide layer is prolonged, resulting in low friction and much reduced material loss. In the present work a new pack carburising surface treatment method has been developed, whereby oxygen diffusion and carburisation of CP-Ti were undertaken concurrently. Optimisation of the process showed that a temperature of 925 °C for 20 h resulted in a multilayer structure comprising of a titanium carbide (TiC) network layer atop of a relatively thick α-Ti(O) diffusion zone. Tribological testing demonstrated that the new surface treatment can significantly enhance the tribological properties of titanium, in terms of much reduced friction (μ ≈ 0.2), improved wear resistance and enhanced load bearing capacity. Electrochemical corrosion testing also showed the PC-Ti retained the favourable corrosion characteristics of CP-Ti. Tribocorrosive testing revealed an improved tribological response when compared with that of untreated CP-Ti.

Five tribochemically deposited coatings on honed cast iron cylinder liner segments has been studied with respect to surface properties, material composition, coating thickness, hardness and friction. Methods like Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), 3D topography using white light interferometry (VSI) and Electron Spectroscopy for Chemical Analysis (ESCA) were used to study the surface, coating thickness and material composition. Lubrication regimes (friction) were studied using a test set-up in a Lathe. An in-situ scratcher and nano indenter were used to study the hardness. It was found that the honing plateau surface is smoothened by the coating process while the honing scratches are kept more or less intact. The deposited coating thickness is approximately 10-100 nm. The coating is softer than the substrate and shows a butter-like behavior when scratched. Using only sulfur additive in the process fluid gives a smooth surface and an evenly distributed coating. Tungsten additive in the process fluid gives a thicker coating but a more irregular material distribution. Tungsten additive in the process fluid does not seem to stimulate the formation of WS2, but rather WO3 is formed.

The goal of this work is to investigate the physical mechanisms that distress thrust washer bearings through physical modeling and numerical techniques. The thrust washer bearing is subjected to non-axisymmetric loads within the planetary gear sets of automatic transmissions in automobiles. In practice the thrust washer bearing often distresses severely and unpredictably, causing transmission breakdown and liability issues. A specially designed thrust washer bearing test rig allows for controlled variation of the operational parameters (speed, load, lubrication flow rate, etc.) governing the tribological behavior of the washer. The test rig also records pertinent real-time data (frictional torque and temperature) from the bearing. In conjunction with the experimental model, a new comprehensive numerical simulation of thrust washer bearings is constructed. The numerical simulation incorporates the effects of macro-scale deformation, micro-scale surface asperity contact, heat generation, boundary and full film lubrication. To model surface asperity contact, the current work performs an extensive finite element study of elasto-plastic spherical contact. The numerical and experimental results show that significant sliding asperity contact can cause high temperatures, high friction, and severe wear.

Friction and wear have been observed m mechanical systems when there is a relative motion between two solid bodies Friction mainly results in loss of energy and wear results in matenal loss The proper understanding of friction and wear mechanisms provides practical solutions to tribological related problems Various models are available m tribology literature to calculate function coefficient and wear rate of matenals However, expenments suggest that these models are incomplete and fortuitous as the tnbological response is system dependent The objective of present investigation is to understand the tribological lesponse of commercially puie titanium and OFHC copper pins sliding on polyciystallme alumina discs Di\ shdm% tests were conducted in air, and vacuum (1 5 x 10~2Pa) at room tempeiatuie under different experimental conditions The normal load was vaned from 15 3 N to 76 0 N, sliding speed was vaned from 0 01 ms"1 to 1 4 ms"1, and tempeiatuie was varied from 293 K to 793 K It is found that the haidness of metals do not have any effect on their tribological response The experimental obseivations indicate that tribological response of metals mainly depends up on miciostructural evolution, oxygen activity and relative shear strength of metals and ceramics Chapter 1 starts with the background and concepts of tribology A brief literature survey is given with published work in relation with the present work In Chapter 2, the experimental proceduies of the dry sliding test and compression test are given Chapter 3 explains the tribological response of titanium during shdmg against alumina Different wear mechanisms such as oxidation, deformation and adhesion were identified Deformation wear mechanism is explained using strain rate response approach Chapter 4 explains the tribological response of copper during sliding against alumina The influence of environment and microstructural evolution on its tribological behavior are studied Chaptei 5 explains the dependence of tribological response of metals on micro structural evolution, oxygen activity and relative shear strength of metals and ceramics This thesis ends with the conclusions of the present investigation

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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