Tribological properties of carbon nanotubes as lubricant additive in oil and water for a wheel–rail system

TLDR

Carbon nanotubes, discovered in 1991, possess exceptional mechanical, thermal, electrical, chemical, and optical properties that have spurred their investigation as lubricant additives in oil and water. This study examines the tribological performance of carboxyl‑functionalized single‑ and multi‑walled CNTs added at 0.01–0.05 % concentrations under rolling‑sliding conditions. Tests were performed on a twin‑disk machine at 5 % creepage with contact pressures of 0.8 and 1.1 GPa. The presence of CNTs lowered both the friction coefficient and wear rate in the oil and water systems.

Abstract

Since their discovery in 1991 carbon nanotubes (CNTs) have attracted much interest due to their remarkable mechanical, thermal, electrical, chemical and optical properties. In connection with their mechanical properties, CNTs have been studied in various forms for tribological applications including their use as lubricant additives for oil and water. In this work, the tribological properties of functionalized nanotubes (single and multi-walled) modified with carboxylic acid when used as lubricant additives at different concentrations (0.01, 0.05%) were studied under rolling-sliding conditions in a twin-disk testing machine. The tests were performed using 5% of creepage and pressures of 0.8 GPa and 1.1 GPa. The results indicated that the presence of carbon nanotubes leads to a decrease in both friction coefficient and wear rate for both systems studied (oil and water).