Thermophysical and tribological behaviors of multiwalled carbon nanotubes used as nanolubricant additives

Abstract

This study investigates the thermophysical and tribological characteristics of engine oil (SAE 10W-40) using multiwalled carbon nanotubes (MWCNTs) as nanolubricant additives. The MWCNT additives based nanolubricant were formulated using an ultrasonic probe. The tribological performances of MWCNTs nanolubricant were evaluated by a reciprocating platform that simulated the piston ring and cylinder liner interface under various circumstances (i.e., contact loads and sliding velocity). The thermophysical performances of MWCNTs nanolubricant were evaluated using ultraviolet-visible spectrometry, Brookfield viscometers, a thermal conductivity meter, and thermogravimetric analysis. Furthermore, the wear mechanisms of the frictional surfaces were supported by field emission scanning electron microscopy and energy dispersive spectrometer. Critically, the flow characteristics of MWCNTs nanolubricant samples displayed non-Newtonian (shear-thinning) behavior, but the behavior of SAE 10W-40 oil was similar to Newtonian fluids. The friction coefficient decreased by 4%–34% and 26%–32% at different loads and speeds. Moreover, the specific wear rate of the ring and liner surfaces decreased by 29% and 40%, respectively, at 240 N load and 0.33 m s−1 velocity after a sliding distance of 22.57 km. These results suggest that MWCNT additives based nanolubricant effectively lubricated the mechanical applications.