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Title: Is more always better? Tribofilm evolution and tribological behavior impacted by the concentration of ZDDP, ionic liquid, and ZDDP-Ionic liquid combination

Abstract

Anti-wear additives (AWs), like zinc dialkyldithiophosphates (ZDDPs), have been used in lubricants for more than a half-century, and more effective candidate AWs, like oil-soluble ionic liquids (ILs), are emerging. However, there is a lack of fundamental understanding of how the AW concentration impacts the tribochemical activities at the contact interface. This study systematically investigated the friction and wear behavior in correlation to the tribofilm morphology and composition as a function of the concentration of a ZDDP, a phosphonium-alkylphosphate IL, and an IL+ZDDP combination. The ZDDP concentration rising from 0.4 to 6.4 wt% caused a proportionally increased friction coefficient, which was well correlated to a thicker, rougher, and more brittle tribofilm. This was further understood by the decreasing phosphates but increasing sulfur compounds in the ZDDP tribofilm. In contrast, the IL and IL+ZDDP maintained a low and stable friction coefficient at 0.5 wt% or above. There was no sulfur in the IL tribofilm, and the sulfur compounds were maintained at a low level in the tribofilm for IL+ZDDP even at high concentrations. Results suggested minimizing the sulfur content in the tribofilm would be an effective way to control the friction. An interesting V-shape relationship between the AW concentration and the wearmore » loss was observed for both the IL-containing AWs, with an optimum at 2 wt% for the IL alone and 0.46–0.92 wt% for the IL+ZDDP, respectively. A unique heat map was created using the phosphorus binding energy distribution to reveal the phosphate polymerization at different depths of the tribofilms, which provided additional insight for the tribofilm evolution.« less

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [1]
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  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. General Motors (GM) Technical Center, Pontiac, MI (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
1559704
Alternate Identifier(s):
OSTI ID: 1567982
Grant/Contract Number:  
AC05-00OR22725
Resource Type:
Accepted Manuscript
Journal Name:
Wear
Additional Journal Information:
Journal Volume: 432-433; Journal Issue: C; Journal ID: ISSN 0043-1648
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Lubricant; Anti-Wear additive concentration; Ionic liquid; ZDDP; Tribofilm

Citation Formats

Zhou, Yan, Weber, Joel, Viola, Michael B., and Qu, Jun. Is more always better? Tribofilm evolution and tribological behavior impacted by the concentration of ZDDP, ionic liquid, and ZDDP-Ionic liquid combination. United States: N. p., 2019. Web. doi:10.1016/j.wear.2019.202951.
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Zhou, Yan, Weber, Joel, Viola, Michael B., & Qu, Jun. Is more always better? Tribofilm evolution and tribological behavior impacted by the concentration of ZDDP, ionic liquid, and ZDDP-Ionic liquid combination. United States. https://doi.org/10.1016/j.wear.2019.202951
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Zhou, Yan, Weber, Joel, Viola, Michael B., and Qu, Jun. Sat . "Is more always better? Tribofilm evolution and tribological behavior impacted by the concentration of ZDDP, ionic liquid, and ZDDP-Ionic liquid combination". United States. https://doi.org/10.1016/j.wear.2019.202951. https://www.osti.gov/servlets/purl/1559704.
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@article{osti_1559704,
title = {Is more always better? Tribofilm evolution and tribological behavior impacted by the concentration of ZDDP, ionic liquid, and ZDDP-Ionic liquid combination},
author = {Zhou, Yan and Weber, Joel and Viola, Michael B. and Qu, Jun},
abstractNote = {Anti-wear additives (AWs), like zinc dialkyldithiophosphates (ZDDPs), have been used in lubricants for more than a half-century, and more effective candidate AWs, like oil-soluble ionic liquids (ILs), are emerging. However, there is a lack of fundamental understanding of how the AW concentration impacts the tribochemical activities at the contact interface. This study systematically investigated the friction and wear behavior in correlation to the tribofilm morphology and composition as a function of the concentration of a ZDDP, a phosphonium-alkylphosphate IL, and an IL+ZDDP combination. The ZDDP concentration rising from 0.4 to 6.4 wt% caused a proportionally increased friction coefficient, which was well correlated to a thicker, rougher, and more brittle tribofilm. This was further understood by the decreasing phosphates but increasing sulfur compounds in the ZDDP tribofilm. In contrast, the IL and IL+ZDDP maintained a low and stable friction coefficient at 0.5 wt% or above. There was no sulfur in the IL tribofilm, and the sulfur compounds were maintained at a low level in the tribofilm for IL+ZDDP even at high concentrations. Results suggested minimizing the sulfur content in the tribofilm would be an effective way to control the friction. An interesting V-shape relationship between the AW concentration and the wear loss was observed for both the IL-containing AWs, with an optimum at 2 wt% for the IL alone and 0.46–0.92 wt% for the IL+ZDDP, respectively. A unique heat map was created using the phosphorus binding energy distribution to reveal the phosphate polymerization at different depths of the tribofilms, which provided additional insight for the tribofilm evolution.},
doi = {10.1016/j.wear.2019.202951},
journal = {Wear},
number = C,
volume = 432-433,
place = {United States},
year = {Sat Jul 06 00:00:00 EDT 2019},
month = {Sat Jul 06 00:00:00 EDT 2019}
}
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Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1016/j.wear.2019.202951
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Cited by: 13 works
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Figures / Tables:

Table 1 Table 1: Correlations between the AW concentration and phosphorus content in oil
All figures and tables (12 total)
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Works referenced in this record:

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    Works referencing / citing this record:

    Material‐Dependent Antagonistic Effects between Soot and ZDDP
    journal, February 2020

    • Kumara, Chanaka; Meyer, Harry M.; Qu, Jun
    • Advanced Materials Interfaces, Vol. 7, Issue 6
    • DOI: 10.1002/admi.201901956
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      Figures / Tables found in this record:

      Table 1 (p. 4)table
      Figure 1 (p. 6)figure
      Figure 2 (p. 7)figure
      Figure 3 (p. 9)figure
      Figure 4 (p. 11)figure
      Figure 5 (p. 13)figure
      Figure 6 (p. 15)figure
      Figure 7 (p. 16)figure
      Figure 8 (p. 17)figure
      Table 2 (p. 18)table
      Figure 9 (p. 19)figure
      Figure 10 (p. 20)figure
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