Tribological and microstructural enhancement of engine oil using reduced graphene oxide and nano-graphite additives

Abstract

This study investigated the tribological and microstructural properties of fully synthetic engine oil (SEO) Shell 5W-30, enhanced with 0.5% concentrations of reduced graphene oxide (RGO) and nano-graphite (NG). The tribological performance of the prepared samples was assessed using a pin-on-disc tribometer under the test conditions of 150 RPM speed and a 981N load. Microstructural analysis was conducted using scanning electron microscopy (SEM). Additionally, Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA) and UV-Vis spectroscopy were used to examine the functional group interactions, thermal stability and infrared absorption properties, respectively. The results demonstrated that adding 0.5 weight % RGO to Shell 5W-30 oil significantly improved the tribological performance compared to NG-based lubricants by effectively reducing both frictional forces and the coefficient of friction (approximately 50%). SEM analysis revealed that RGO produced a noticeably smoother worn surface  with smaller pits,  resulting in the lowest coefficient of friction and frictional forces among all tested samples including NG-based lubricants and unmodified shell 5W-30 oil. FTIR analysis revealed a significant reduction in hydroxyl and alkoxy groups following the addition of RGO to shell 5W-30 oil compared to nano-graphite-based lubricants. TGA analysis further indicated more substantial thermal degradation in RGO, attributed to the presence of oxygen-containing functional groups. These findings suggest that incorporating RGO to Shell 5W-30 oil could optimize the lubricant performance across a wider range of applications, particularly in automotive sector, where friction reduction is critical for improving engine efficiency.