Study of tribological properties and applications of carbon nanostructures in lubricants

Restoring lubricant service life is of great importance, as this brings significant economic benefits to companies and helps reduce waste. Addition of nanomaterials to lubricants can improve their properties and prolong duration of their operation in mechanisms. In this study, multiwall carbon nanotubes (MWCNTs) containing O-containing functional groups and carbon nanotoroidal structures were used as additives in a water-based lubricant Sigralub M-40 that has lost its initial properties. The introduction of carbon nanostructures into the lubricant significantly reversed the significant decrease in load-bearing capacity. Storage of the lubricant for an extended period of more than 6 months at temperatures in the range of + 5÷ + 22°C resulted in a substantial loss of load-carrying capacity, decreasing it by 87%. MWCNTs functionalized with -OH and -COOH groups improved adhesion properties of the lubricant. Samples containing MWCNT-COOH nanostructures were found to demonstrate the highest load-bearing capacity values. An average nanostructure concentration of 0.1 wt% was superior to 0.3 wt%. The MWCNTs acted as microscopic rollers, reducing friction; the nanotoroids provided the rolling and sliding effect in the lubricants. Infrared spectroscopy images confirmed the presence of specific functional groups that enhance the dispersion of nanostructures in the lubricant.