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Cooperativity Between Zirconium Dioxide Nanoparticles and Extreme Pressure Additives in Forming Protective Tribofilms: Toward Enabling Low Viscosity Lubricants

A Correction to this article was published on 23 September 2021

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Realizing the efficiency benefits of low viscosity lubricants requires novel strategies to avoid failures resulting from increased boundary contact. Zirconium dioxide (ZrO2) nanoparticles (NPs) form protective tribofilms through tribosintering at lubricated contacts in pure hydrocarbon base oils, suggesting they hold promise for reducing boundary contact-induced failures. However, their tribological behavior alongside co-additives found in fully formulated oils has not been examined in depth. Here, the macroscopic tribological performance of dispersed ZrO2 NPs (1 wt% loading; 5 nm diameter nearly spherical ZrO2 tetragonal phase NPs with organic capping ligands for oil solubility) with and without the presence of co-additives found in fully formulated commercial gear oils was studied using a mini-traction machine (MTM). The results show that ZrO2 NPs reproducibly develop surface-bound ~ 100 nm thick tribofilms on both contacting surfaces under a wide range of rolling-sliding contact conditions, from 0 to 100% slide-to-roll ratio. Steady-state traction coefficient values of ZrO2 tribofilms formed alongside co-additives (0.10–0.11) do not substantially differ from ZrO2 tribofilms formed in neat polyalphaolefin base oils (0.10–0.13). However, there is improvement in the tribological performance of the contact, with at least a twofold reduction of wear of the steel. This behavior is proposed to be a result of cooperating mechanisms, where the extreme pressure additives adsorbed on the steel surfaces protect them against early adhesive wear, during the time that a protective ZrO2 tribofilm incorporating the co-additives forms on the steel surfaces, preventing further wear.

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We gratefully acknowledge support from the U.S. Army Combat Capabilities Development Command Ground Vehicle Systems Center (CCDC GVSC) under Small Business Technology Transfer (STTR) Phase II Award Number DE-SC-0009222. This work was also performed in part at the University of Pennsylvania’s Singh Center for Nanotechnology, an NNCI member supported by NSF Grant ECCS-1542153. Elinski, M. B. acknowledges support from the University of Pennsylvania Provost Postdoctoral Fellowship program. We also thank Pixelligent Technologies, LLC for providing the oil formulations. The authors are appreciative of many useful discussions with N. G. Demas and B. J. Gould at Argonne National Laboratory, S. J. Thrush and A. S. Comfort at the U.S. Army CCDC GVSC, J. Lohuis and S. G. Williams (Pixelligent Technologies, LLC), Z. B. Milne (University of Pennsylvania), and H. S. Khare (formerly at the University of Pennsylvania, now at Gonzaga University).


U.S. Army Combat Capabilities Development Command Ground Vehicle Systems Center (CCDC GVSC) Small Business Technology Transfer (STTR) Phase II Award Number DE-SC-0009222. University of Pennsylvania’s Singh Center for Nanotechnology, an NNCI member supported by NSF Grant ECCS-1542153. Elinski, M. B. acknowledges support from the University of Pennsylvania Provost Postdoctoral Fellowship program.

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Correspondence to Robert W. Carpick.

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Lei Zheng, Andrew Jackson, Robert J. Wiacek are affiliated with the commercial vendor for the ZrO2 nanoparticles (Pixelligent Technologies, LLC). L. Z. and R. J. W. are employees of Pixelligent and have equity in the company. A. J. is a consultant to Pixelligent. No other coauthors declare competing financial interest.

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Description of Supporting InformationThe Supporting Information has five sections. Section A (Fig. S1) includes additional WLI analysis of MTM-SLIM tests run in 75W-80. Section B (Fig. S2-S3) show traction curves and Stribeck curves for all samples. Section C details the specific film thickness calculations. Section D (Fig. S4-S5) provides supporting tribofilm characterization, including the end-of-test SLIM images and representative characterization with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Section E (Fig. S6-S7) discusses the ZrO2 tribofilms formed on the disc specimens corresponding to the ball specimens discussed in Fig. 3 of the main text.

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Elinski, M.B., LaMascus, P., Zheng, L. et al. Cooperativity Between Zirconium Dioxide Nanoparticles and Extreme Pressure Additives in Forming Protective Tribofilms: Toward Enabling Low Viscosity Lubricants. Tribol Lett 68, 107 (2020).

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  • Nanoparticles
  • Tribofilm
  • Extreme pressure additives
  • Tribosintering
  • Low viscosity gear oil
  • Co-additives