Tribochemistry

Tribochemistry is a subfield of tribology that studies chemical reactions occurring at interfaces under mechanical action, such as sliding, rubbing, or impact in the presence of contact stresses. It examines how the energy dissipated during friction can drive bond breaking and formation, leading to chemical transformations that influence friction, wear, and material performance. The concept encompasses mechanochemistry, where mechanical energy lowers reaction barriers and enables reactions that may not occur thermally.

Chemical changes at contacting surfaces can produce tribofilms—thin surface layers formed in situ from lubricants, additives, or the substrate itself. Common processes include oxidation, sulfidation, polymerization, and fracture of soft materials under shear. Additives designed to respond to friction, such as zinc dialkyldithiophosphate, can decompose to form protective phosphate- or sulfide-containing films that reduce wear and modify friction. Tribochemical reactions can also generate radicals and reactive species that alter reaction pathways at the interface.

Methods to study tribochemistry combine tribology experiments with surface characterization and modeling. Experimental approaches include pin-on-disk or similar tribometers, coupled with in situ or ex situ spectroscopy (Raman, infrared, X-ray photoelectron spectroscopy) and microscopy (AFM, TEM). Theoretical work uses quantum chemistry and reactive molecular dynamics simulations to explore reaction mechanisms and energy barriers during sliding.

Applications span lubricant formulation, brake systems, and materials design, where understanding tribochemical processes helps optimize wear resistance and energy efficiency. The field continues to investigate non-equilibrium reaction pathways, the role of environment and temperature, and the design of additives that form protective tribofilms under real-world conditions.