The efficiency of Co-based single-wall carbon nanotubes (SWNTs) as an AW/EP additive for mineral base oils

Abstract

This paper describes the tribological behavior of Co-based single-wall carbon nanotubes (SWNTs) and a commercial antiwear (AW) and extreme-pressure (EP) additive to a mineral base oil (SAE 20). Single-wall carbon nanotubes possess interesting tribological properties; therefore, in our investigation, they were used as an AW and EP additive to SAE 20 base oil. Friction and wear were tested using a Pin on Disk C.S.M tribometer, while a four-ball tester was used to evaluate the extreme pressure properties. After friction tests, the rubbed surface was investigated with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) to understand the mechanism of action on an atomic scale. The single-wall carbon nanotubes were produced by chemical carbon vapor deposition (CCVD) and were characterized suing transmission electron microscopy (TEM). Tube diameter was determined using RAMAN spectroscopy. Used as an additive to base oil, SWNTs are more efficient than a commercial additive (CA) control. In tests, the friction coefficient decreased to 0.087 using only 0.5wt% SWNTs added to SAE 20. A synergistic effect was found between SWNTs and the commercial additive, giving this combination the best tribological properties.