Abstract
There is a consensus that savings of 1.0-1.4% of a country's gross domestic product may be achieved through lubrication R&D. Recent studies have shown great potential for using surface-functionalized nanoparticles (NPs) as lubricant additives to enhance lubricating performance. NPs were reported with ability of producing a low-friction antiwear tribofilm, usually 20-200 nm in thickness, on the contact surface. In contrast, this study reports an unexpected 10 times thicker (2-3 μm) tribofilm formed by dodecanethiol-modified palladium NPs (core size: 2-4 nm) in boundary lubrication of a steel-cast iron contact. Adding 0.5-1.0 wt % such NPs to a lubricating oil resulted in significant reductions in friction and wear by up to 40 and 97%, respectively. Further investigation suggested that the PdNP core primarily was responsible for the improvement in both friction and wear, whereas the thiolate ligand only contributed to the wear protection but had little impact on the friction behavior. In addition, unlike most previously reported tribofilms that contain a substantial amount of metal oxides, this PdNP-induced tribofilm is clearly dominated by Pd/S compounds, as revealed by nanostructural examination and chemical analysis. Such a ultrathick tribofilm with unique composition is believed to be responsible for the superior lubricating behavior.
| Original language | English |
|---|---|
| Pages (from-to) | 31804-31812 |
| Number of pages | 9 |
| Journal | ACS Applied Materials and Interfaces |
| Volume | 10 |
| Issue number | 37 |
| DOIs | |
| State | Published - Sep 19 2018 |
Funding
The authors wish to thank A.G. Bro and C. Dubln from ExxonMobil for providing the PAO base oil and D. Coffey from ORNL for preparation of the STEM samples using FIB. The research was supported by the Vehicle Technologies Program (DE EE0006925), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE). Electron microscopy characterization was performed at ORNL’s Center for Nanophase Materials Sciences, sponsored by the Scientific User Facilities Division, Office of DOE-BES. The authors wish to thank A.G. Bro and C. Dubln from ExxonMobil for providing the PAO base oil and D. Coffey from ORNL for preparation of the STEM samples using FIB. The research was supported by the Vehicle Technologies Program (DE EE0006925), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE). Electron microscopy characterization was performed at ORNL's Center for Nanophase Materials Sciences, sponsored by the Scientific User Facilities Division, Office of DOE-BES. *E-mail: [email protected]. ORCID Jun Qu: 0000-0001-9466-3179 Notes The authors declare no competing financial interest. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/ doe-public-access-plan).
| Funders | Funder number |
|---|---|
| Office of DOE-BES | |
| Scientific User Facilities Division | |
| US Department of Energy | |
| U.S. Department of Energy | |
| Office of Energy Efficiency and Renewable Energy | |
| Oak Ridge National Laboratory | DE EE0006925 |
| ExxonMobil Foundation |
Keywords
- friction
- lubricants
- nanoparticles
- tribofilm
- wear