MoS2 nanolayer coated carbon spheres as an oil additive for enhanced tribological performance

Submicrometer-sized carbon spheres coated with a MoS2 nanolayer (CS-MoS2) have been synthesized and investigated as a viable oil additive to enhance the tribological properties of conventional oil lubricants in both the boundary and mixed lubrication regimes. Submicrometer-sized carbon spheres (CS) are obtained by the rapid ultrasound-assisted polymerization of resorcinol and formaldehyde, and MoS2 is subsequently coated onto the CS particles via controlled heat treatment. The tribological performance of the proposed lubricant mixture was studied using a tribometer under the ball-on-disk and cylinder on-disk configurations. The hybrid lubricant is comprised of 1 wt % CS-MoS2 particles dispersed in a standard engine oil (SAE 5W30) and demonstrated a significant reduction in friction and wear (15-35%) relative to the pristine reference oil under various disk speeds. Raman spectroscopic investigation of the wear scars following the tribological tests suggest high chemical stability of the CS-MoS2 particles. The enhanced tribological performance of the CS-MoS2 and oil mixture lubricant is attributed to both the spherical carbon particles and the superior lubrication of the MoS2 nanolayer. The combination of these tribological properties demonstrated by the secondary particle could prevent direct contact between sliding surfaces and act as a particulate ball bearing at the nanoscale. (C) 2016 Elsevier Ltd. All rights reserved.