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MSE Seminar - Professor Robert Carpick, Univ. of Pennsylvania
Monday, November 23, 2015 - 4:45pm
GTMI (MARC) Building Auditorium
Professor R. W. (Robert) Carpick
John Henry Towne Professor and Department Chair
Department of Mechanical Engineering and Applied Mechanics,
University of Pennsylvania
Monday, November 16, 2015
4:00 p.m. MARC (GTMI/Callaway Bldg.) Auditorium
Reception at 3:30 p.m. in the MARC Atrium
How Nanostructured Films Keep your Car Engine Running:
In situ Nanoscale Studies of Lubricant Tribofilms
Engine oils are far more than just oil: they include a multitude of highly engineered additives that endow the oil with the ability to enhance the resistance to wear, friction, oxidation, and thermal variations. One particularly important additive molecule found in engine oils and many other lubricants is zinc dialkyldithiophosphates (ZDDP). ZDDPs work by forming antiwear tribofilms at the contacting interfaces. However, the mechanisms governing this tribofilm growth are not well understood, and this limits the development of replacements that offer better performance and are less likely to degrade automobile catalytic converters over time. Using atomic force microscopy in ZDDP-containing lubricant base stock at elevated temperatures, we monitored the growth and properties of the tribofilms in situ in well-defined single-asperity sliding nanocontacts . Surface-based nucleation, growth, and thickness saturation of patchy nanoscale tribofilms were observed. The growth rate increased exponentially with either applied compressive stress or temperature, consistent with a thermally activated, stress-assisted reaction rate model. This can explain the known graded-structure of the films and its self-limiting growth. Although some models rely on the presence of iron to catalyze tribofilm growth, the films grew regardless of the presence of iron on either the tip or substrate, highlighting the critical role of stress and thermal activation. Using this novel approach, we have also explored the use of metal oxide nanoparticles as potential replacements for ZDDP. We also see the formation of dense tribofilms at the nanoscale, and from this, we determine that such nanoparticles have potential for functioning as protective anti-wear additives.
 Gosvami, N.N., Bares, J. A., Mangolini, F., Konicek, A.R., Yablon D.G., and R. W. Carpick. “Mechanisms of Antiwear Tribofilm Growth Revealed in situ by Single Asperity Sliding Contacts,” Science, 348, 102 (2015).
Robert Carpick is John Henry Towne Professor and Chair, Dept. of Mechanical Engineering and Applied Mechanics, University of Pennsylvania. Previously, he was a faculty member at the University of Wisconsin-Madison (2000-2007). He received his B.Sc. from the University of Toronto (1991), and his Ph.D. from the University of California at Berkeley (1997), both in Physics, and was a postdoc at Sandia National Laboratory (1998-1999). He studies nanotribology, nanomechanics, and scanning probes. He is the recipient of a NSF CAREER award (2001), the ASEE Outstanding New Mechanics Educator award (2003), the ASME Newkirk award (2009), an R&D 100 Award (2009), and is a Fellow of the American Physical Society and the American Vacuum Society. He holds 3 patents and has authored over 130 peer-reviewed journal publications.