The microwave-synthesized reduced graphene oxide (MRG), boron-doped reduced graphene oxide (B-MRG), nitrogen-doped reduced graphene oxide (N-MRG), boron-nitrogen-co-doped reduced graphene oxide (B-N-MRG), and TiO2-reinforced B-N-MRG (TiO2-B-N-MRG) nanomaterials have been synthesized and characterized by various state-of-the-art techniques, like Raman spectroscopy, powder X-ray diffraction, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Furthermore, the tribological properties of prepared nanomaterials as antiwear additives in neutral paraffin oil have been evaluated using a four-ball machine at an optimized additive concentration (0.15% w/v). The tribological parameters, like mean wear scar diameter, coefficient of friction, and wear rates, revealed that these nanomaterials have potential to be developed as environmentally friendly sulfated-ash-, phosphorus-, and sulfur-free antiwear lubricant additives. The friction- and wear-reducing behavior of MRG increased upon successive doping of nitrogen, boron, and both nitrogen and boron. Among these additives, B-N-co-doped MRG shows superior tribological behavior in paraffin base oil. Besides this, the load-carrying properties of B-N-co-doped MRG have significantly improved after its reinforcement with TiO2 nanoparticles. A comparative study of the surface morphology of a lubricated track in the presence of various additives has been assessed by SEM and contact-mode atomic force microscopy. The X-ray photoelectron spectroscopy studies have proved that the excellent lubrication properties of TiO2-B-N-MRG are due to the in situ formation of a tribofilm composed of boron nitride, adsorbed graphene layers, and tribosintered TiO2 nanoparticles during the tribocontact. Being sulfur-, halogen-, and phosphorus-free, these graphene-based nanomaterials act as green antiwear additives, protecting interacting surfaces significantly from wear and tear.

No abstract

Tribological performance of sulfur, phosphorous and metal-free Schiff bases and their synergistic formulations with borate ester in paraffin oil has been evaluated using a four-ball tester at optimized concentrations (1% w/v).

Pure zinc oxide (ZnO) and magnesium-doped zinc oxide (ZMO) nanoparticles (NPs) with the composition of Zn0.88Mg0.12O have been prepared by an autocombustion method. The as-synthesized ZMO nanoparticles were calcined for 2 h at 800 and 1000 °C to yield different-sized ZMO nanoparticles abbreviated as ZMO-1 and ZMO-2, respectively. These nanoparticles have been characterized by powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) techniques. The average size of these nanoparticles is found to be 30, 27, 39, and 44 nm, respectively for ZnO, ZMO, ZMO-1, and ZMO-2. A stable dispersion of ZMOs (ZMO, ZMO-1, and ZMO-2) nanoparticles in paraffin oil has been achieved with an appropriate percentage of surfactant sodium dodecylsulfate (SDS), abbreviated as SZMOs (SZMO, SZMO-1, and SZMO-2). The effect of the particle size of these nanoparticles on the tribological behavior of the paraffin oil has been investigated at an optimized additive concentration (0.25% w/v with 0.10% SDS) using different ASTM D4172 and D5183 standards. In addition, a test has been conducted by varying the loads for a 30 min time duration and by varying the test durations at 392 N load. All tribological testing of SZMOs nanoparticles were conducted on a four-ball lubricant tester. These tribological tests revealed that the SZMOs nanoparticles act as excellent antiwear agents and friction modifiers and also enhance the load-bearing ability. Being the smaller particle size, SZMO nanoparticles (27 nm) exhibited better tribological behavior than SZMO-1 (39 nm) and SZMO-2 (44 nm). The morphology of the worn surfaces lubricated with nanoparticles and without SZMOs at a 392 N applied load for 60 min and at higher loads for a 30 min test duration has been examined by scanning electron microscopy (SEM) and contact mode atomic force microscopy (AFM) analyses. Energy-dispersive X-ray (EDX) analysis of the surface lubricated with SZMO nanoparticles shows the presence of zinc, magnesium, iron, carbon, and oxygen on the steel surface which confirmed the adsorption of the additive on the interacting/rubbing surface. These elements form tribochemical film on the interacting surfaces to prevent the metal–metal contact thereby reducing wear and friction.