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An in situ synchrotron XAS methodology for surface analysis under high temperature, pressure, and shear

DOI: 10.1063/1.4973354 DOI Help

Authors: Abdel Dorgham (University of Leeds) , A. Neville (University of Leeds) , K. Ignatyev (Diamond Light Source) , F. Mosselmans (Diamond Light Source) , A. Morina (University of Leeds)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Review Of Scientific Instruments , VOL 88

State: Published (Approved)
Published: January 2017
Diamond Proposal Number(s): 12907

Abstract: The complex tribochemical nature of lubricated tribological contacts is inaccessible in real time without altering their initial state. To overcome this issue, a new design of a pin-ondisc tribological apparatus was developed and combined with synchrotron X-ray absorption spectroscopy (XAS). Using the designed apparatus it is possible to study in-situ the transient decomposition reactions of various oil additives on different surfaces under a wide range of realistic operating conditions of contact pressure (1.0 - 3.0 GPa), temperature (25 - 120 oC) and sliding speed (30 - 3000 rpm or 0.15 - 15 m/s). To test the apparatus, several tribological tests were performed at different shearing times ranging from 2.5 to 60 minutes. These tests were carried out under Helium atmosphere at a temperature of 80 oC, contact pressure of 2.2 GPa and sliding speed of 50 rpm. The XAS experiments showed that the zinc dialkyldithiophosphate (ZDDP) antiwear additive decomposes in the oil to form a tribofilm on the iron surface at different reaction kinetics from the ones of the thermal film. This confirmed the findings of several previous studies that the formation of the tribofilm is a thermally activated mechanically assisted process, which is faster than the one involved the thermal film that is only thermally activated. Furthermore, the results indicated that the sulfur of the formed film, whether a tribofilm or a thermal film, appears initially in the form of sulfate, with some sulfide, which under heat or shear is reduced into mainly sulfide.

Journal Keywords: In-situ Synchrotron, Tribochemistry, Tribology, ZDDP tribofilm

Subject Areas: Technique Development, Materials, Chemistry

Instruments: I18-Microfocus Spectroscopy