The Tribological Properties of Mixed Zinc Sulfide and Reduced Graphene Oxide as Lubricant Nano-Additives

Abstract This research investigated using a mix of nanolayered reduced graphene oxide (rGO) and nanosized zinc sulfide (ZnS) as an oil additive. The aim was to leverage the advantages of both components to create a highly efficient lubricant that enhances oxidation resistance. The mixture was prepared in a 1:1 ratio with varying concentrations of 0.2%, 0.4%, 0.6%, 0.8%, and 1% by weight blended with paraffin oil. To ensure proper mixture dispersion in the oil for an extended period, it was sonicated for 15 min in the presence of carboxymethylcellulose Natriumsalz, 98 granular, which was also added at a 1:1 ratio. Tribological tests were conducted using a cross-pin machine at room temperature, applying different normal loads of 10 N, 15 N, and 20 N. During the lubrication process, the rotating pin was lubricated with the proposed mixture before the experiment and every 30 s throughout a total experimental duration of 5 min. The wear was measured by estimating the scar diameter on the worn surface using an optical microscope, and the worn surfaces of the specimens were analyzed using scanning electron microscopy (SEM). The research results demonstrated that mixed nano-additives of rGO and ZnS enhanced the tribological properties of the proposed lubricant. At weights of 20 N, 15 N, and 10 N, respectively, the greatest friction coefficient values of 0.280, 0.340, and 0.395 were noted in dry conditions (without lubricant). Conversely, under the same load conditions (20 N, 15 N, and 10 N), the lowest friction coefficient values of 0.164, 0.206, and 0.266 were observed at a mixed concentration of 0.4 wt%. The incorporation of mixed rGO nanoplates and ZnS nanoparticles as lubricant additives significantly enhances lubrication efficiency, promoting robust self-repairing tribofilms, a rolling bearing effect, and improved performance and longevity of mechanical systems. These advancements facilitate better lubrication techniques and system efficiency.