Abstract
Interactions among antiwear additives (AWs), friction modifiers (FMs), and dispersant in a lubricating oil are critical for tribological performance. This study investigates compatibilities of three oil-soluble ionic liquids (ILs, candidate AWs) with an FM, molybdenum dithiocarbamate (MoDTC), and a dispersant, polyisobutene succinimide (PIBSI) under boundary lubrication. Either synergistic or antagonistic effects were observed depending on the IL's chemistry. Adding an aprotic phosphonium-alkylphosphate or phosphonium-alkylphosphinate IL into the oil containing MoDTC and PIBSI had detrimental impact on the friction and wear behavior. PIBSI was found to preferably interact/react with the aprotic IL to lose its ability of suspending MoDTC and to partially consume or even deplete the IL. In contrast, a protic ammonium-alkylphosphate IL seemed to be able to coexist with PIBSI and work synergistically with MoDTC, yielding a sustainable, ultralow boundary friction. A three-stage tribochemical process is proposed to explain how this IL + MoDTC pair interacts with the contact surface to form a chemically reacted, wear-protective tribofilm supporting a physically adsorbed, friction-reducing film on top. This study provides fundamental insights of the compatibilities among three common lubricant components, antiwear, friction modifier, and dispersant, which can be used to guide future lubricant development.
| Original language | English |
|---|---|
| Pages (from-to) | 17077-17090 |
| Number of pages | 14 |
| Journal | ACS Applied Materials and Interfaces |
| Volume | 12 |
| Issue number | 14 |
| DOIs | |
| State | Published - Apr 8 2020 |
Funding
The authors thank J. Dyck and E. Conrad from Solvay for providing phosphonium cation feedstocks, A.G. Bro and C. Dubin from ExxonMobil for providing the PAO base oil, O. Farng from ExxonMobil for providing the MoDTC and PIBSI, E. Bardasz from Lubrizol for providing the ZDDP, and D. Coffey and R. Wang from ORNL for preparing the STEM sample and measuring the depth and roughness of wear scars, respectively. Research was sponsored by the Vehicle Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE). Electron microscopy characterization was in part performed at ORNL’s Center for Nanophase Materials Sciences, sponsored by the Scientific User Facilities Division, Office of DOE-BES. The support by the Chinese Academy of Sciences (CAS) during the visit of W.L. to ORNL is also appreciated.
| Funders | Funder number |
|---|---|
| Office of DOE-BES | |
| Scientific User Facilities Division | |
| U.S. Department of Energy | |
| Office of Energy Efficiency and Renewable Energy |
Keywords
- MoDTC
- ZDDP
- dispersant
- friction modifier
- ionic liquids
- synergistic effect