Tribological Characterization of Roles of Nanoparticles in Lubrication
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This research investigates the tribological performance and rheological properties of nanoparticles as lubricant additives. Experimental approach combined with analysis were used to study the chemical and physical interactions between nanoparticles and lubricating system. Three areas of investigation were carried out as summarized in the following. Tribological performance and rheological properties of α-ZrP (Zr(HPO₄)₂•H₂O) and V₂O₅ nanoparticles were investigated as lubricant additives. α-ZrP showed 50% reduction in friction and 30% in wear compared to the conventional additives ZDDP. Spectroscopic characterization indicated that the tribofilm consists of iron oxide, zirconium oxide, and zirconium phosphates. Through Raman spectrum and EDS analysis, it was found that V₂O₅ involved tribochemical reaction during rubbing. Vanadium intermetallic alloy (V-Fe-Cr) was found to enhance the antiwear performance. This research revealed that nanoparticles could be effective additives to improve tribological performance. Tribofilms play vital roles in protecting lubricated surfaces in mechanical systems in motion. Strategically-selected-illuminative nanoparticles of NaYF₄ were added to a base oil in order to enable their tracking. Electrical conductivity was monitored during sliding that was found to be linked to the state of the interface and the tribofilm. This work discovered three stages to form a tribofilm: running in, reactive, and growth. Interestingly, the formation of a tribofilm was more dominated by frictional force than applied load. This is significant because we can now use alternative strategies to generate quality tribofilms. For the lubricating dynamics, the physical interaction between the nanoparticles and lubricating systems were investigated. Mechanisms of interfacial interaction between the shark skin and water have yet to be fully understood. In the present research, diamond particles worked as tracking particles in fluid. The shark-skinned surface with 90 degree orientation scale showed a more uniform distribution of diamond particles, which indicated to a lower gradient of velocity. Less momentum transfer between adjacent layers of fluid leads to a lower drag. Eventually, a viscosity map of shark-skinned surface with different scale orientation was created. It will facilitate the design of shark-skinned surface with better performance. The understanding generated in this study could be used as guideline for future study in surface design and texturing.
Dai, Wei (2017). Tribological Characterization of Roles of Nanoparticles in Lubrication. Doctoral dissertation, Texas A&M University. Available electronically from