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

Area of Science:

• Tribology
• Materials Science
• Spectroscopy

Background:

• Studying real-time tribochemical reactions in lubricated contacts is challenging due to state alteration.
• Understanding additive decomposition is crucial for lubricant performance and wear prevention.

Purpose of the Study:

• To develop a novel apparatus for in situ investigation of tribochemical processes.
• To analyze the real-time decomposition of oil additives under realistic tribological conditions.

Main Methods:

• Development of a pin-on-disc tribological apparatus integrated with synchrotron X-ray absorption spectroscopy (XAS).
• In situ analysis of oil additive decomposition under varying contact pressures (1.0–3.0 GPa), temperatures (25–120 °C), and sliding speeds (0.15–15 m/s).

Main Results:

• Zinc dialkyldithiophosphate antiwear additive forms a tribofilm on iron surfaces.
• Tribofilm formation is a shear-accelerated thermally activated process, distinct from thermal film formation.
• Sulfur in the film initially exists as sulfate and is reduced to sulfide under heat or shear.

Conclusions:

• The developed apparatus enables real-time monitoring of tribochemical reactions.
• Shear significantly influences the kinetics of tribofilm formation.
• Understanding the chemical evolution of protective films is vital for designing advanced lubricants.