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Ultralow Wear PTFE and Alumina Composites: It is All About Tribochemistry

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Abstract

Over the last decade, researchers have explored an intriguing polymer composite composed of granular polytetrafluoroethylene (PTFE) 7C and alumina particles. This material is extraordinary because a very small amount of alumina additive (<5 wt%) decreased the wear rate of the PTFE composite by over four orders of magnitude. Previous studies have shown that this wear resistance was initiated and maintained by the formation of a stable, robust, and uniform polymeric transfer film on the surface of the countersample. Although its importance to this tribological system is clear, the transfer film itself has not been well understood. Careful spectroscopic analysis throughout the stages of transfer film development revealed that tribochemistry plays a major role in the significant wear rate reductions achieved in PTFE and alumina composites. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy reveal that PTFE chains break due to the mechanical stresses at the wear surface and, in the presence of oxygen and water in the ambient environment, produce carboxylic acid end groups. These carboxylic acid end groups can chelate to the exposed metal on the steel surface and nucleate the formation of the transfer film. The resulting thin and robust fluoropolymer transfer film protects the surface of the steel and changes the sliding interface from polymer on steel to polymer on polymer transfer film. These effects keep friction coefficients and wear rates low and stable. Ultimately, the real mechanisms responsible for the exceptional wear performance of these materials are all about the tribochemistry.

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Acknowledgments

The authors would like to thank the many collaborators at DuPont for their thoughtful guidance and insight, specifically: Dan Kasprzak (IR), Ross Johnson, Lei Zhang and Lucas Amspacher (XPS), Heidi Burch, and Tim Krizan. We would also like to thank Prof. David L. Burris of University of Delaware for his insightful discussions.

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Authors and Affiliations

  1. Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, 32611, USA

    Angela A. Pitenis & W. Gregory Sawyer

  2. Department of Materials Science and Engineering, University of Florida, Gainesville, FL, 32611, USA

    Kathryn L. Harris & W. Gregory Sawyer

  3. DuPont Central Research and Development, 200 Powder Mill Road, PO Box 8352, Wilmington, DE, 19803, USA

    Christopher P. Junk & Gregory S. Blackman

  4. Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, PA, 18015, USA

    Brandon A. Krick

Authors
  1. Angela A. Pitenis
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  2. Kathryn L. Harris
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  3. Christopher P. Junk
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  4. Gregory S. Blackman
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  5. W. Gregory Sawyer
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  6. Brandon A. Krick
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Correspondence to Brandon A. Krick.

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Pitenis, A.A., Harris, K.L., Junk, C.P. et al. Ultralow Wear PTFE and Alumina Composites: It is All About Tribochemistry. Tribol Lett 57, 4 (2015). https://doi.org/10.1007/s11249-014-0445-6

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  • DOI: https://doi.org/10.1007/s11249-014-0445-6

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