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Carbon nanospheres, copper nanoparticles and their composite Cu@C having copper nanoparticles embedded in carbonaceous material were synthesized hydrothermally. The analytical techniques; powder X-ray diffraction(XRD), field emission scanning electron microscopy(FE-SEM) with energy-dispersive X-ray spectroscopy(EDX), transmission electron microscopy/high- resolution transmission electron microscopy(TEM/HR-TEM), Raman and X-ray photoelectron spectroscopy (XPS) have been employed for their characterization. Tribological behavior of blends of the synthesized additives with paraffin oil has been investigated on a four-ball lubricant tester using ASTM D4172 and ASTM D5183 at 0.1% w/v concentration. Comparative activity of the base oil and the blends has been adjudicated considering the experimental data for mean wear scar diameter (MWD), coefficient of friction (COF), load-carrying capacity and wear rates collected from the above standard tests. The admixture-containing nanohybrid, Cu@C appears to show the best activity followed by that of copper nanoparticles and then carbon spheres. The relative activity of different admixtures is verified by atomic force microscopy(AFM) and scanning electron microscopy(SEM) with EDX results of the wear pathway. The EDX spectrum of Cu@C shows the existence of copper together with carbon on the wear scar surface confirming their contribution in the formation of in situ tribofilm. Thus, these additives may be approved for enhancing lubrication. [ABSTRACT FROM AUTHOR]

Zirconia and 10%, 20%, and 30% cerium-doped zirconia nanoparticles (ZCO), ZCO-1, ZCO-2, and ZCO-3, respectively, were prepared using auto-combustion method. Binary nanohybrids, ZrO2@rGO and ZCO-2@rGO (rGO = reduced graphene oxide), and ternary nanohybrids, ZrO2@rGO@MoS2 and ZCO-2@rGO@MoS2, have been prepared with an anticipation of a fruitful synergic effect of rGO, MoS2, and cerium-doped zirconia on the tribo-activity. Tribo-activity of these additives in paraffin oil (PO) has been assessed by a four-ball lubricant tester at the optimized concentration, 0.125% w/v. The tribo-performance follows the order: ZCO-2@rGO@MoS2 > ZrO2@rGO@MoS2 > ZCO-2@rGO > ZrO2@rGO > MoS2 > ZrO2 > rGO > PO. The nanoparticles acting as spacers control restacking of the nanosheets provided structural augmentation while nanosheets, in turn, prevent agglomeration of the nanoparticles. Doped nanoparticles upgraded the activity by forming defects. Thus, the results acknowledge the synergic effect of cerium-doped zirconia and lamellar nanosheets of rGO and MoS2. There is noncovalent interaction among all the individuals. Analysis of the morphological features of wear-track carried out by scanning electron microscopy (SEM) and atomic force microscopy (AFM) in PO and its formulations with various additives is consistent with the above sequence. The energy dispersive X-ray (EDX) spectrum of ZCO-2@rGO@MoS2 indicates the existence of zirconium, cerium, molybdenum, and sulfur on the wear-track, confirming, thereby, the active role played by these elements during tribofilm formation. The X-ray photoelectron spectroscopy (XPS) studies of worn surface reveal that the tribofilm is made up of rGO, zirconia, ceria, and MoS2 along with Fe2O3, MoO3, and SO42− as the outcome of the tribo-chemical reaction. [ABSTRACT FROM AUTHOR]

Synthesis of carbon spheres and their composite Ag@C was accomplished by the hydrothermal method. The composite Ag@C was stabilized by the ionic liquid, 1-decyl 3-methyl imidazolium boron tetrafluoride (DMIM BF 4) to yield (IL-Ag@C). The Fourier Transform Infrared(FT-IR) spectra approved the formation of composites. The powder XRD patterns of the composites matched with JCPDS files. Examination of morphological characteristics of Ag@C by scanning electron microscopy/high-resolution scanning electron microscopy(SEM/HR-SEM), transmission electron microscopy/high-resolution transmission electron microscopy(TEM/HR-TEM) revealed spherical nanoparticles of about 30–40 nm size embedded on carbon spheres of 1.2–1.6 μm. Upon addition of ionic liquid, the composite appears to be wrapped in it. Energy-dispersive X-ray(EDX) analysis associated with SEM exhibited the presence of additional elements of ionic liquid, fluorine and nitrogen, besides silver and carbon in IL-Ag@C confirming its formation. The binding energy data obtained from X-ray photoelectron spectroscopy (XPS) corroborated the formation of IL-Ag@C. Triboactivity of the carbon nanospheres and the composites were assessed in base lube PEG-200 at 0.5% w / v concentration on a four-ball tester under ASTM D4172 and ASTM D5183 conditions. Based on tribological data namely coefficient of friction(COF), mean wear scar diameter(MWD), load-carrying capacity and loss of frictional power, the relative order of activity of different additives could be established as: IL − Ag @ C > Ag @ C > IL > C spheres > PEG − 200 The above order was authenticated by morphological studies of the wear scar by SEM and AFM(Atomic Force Microscopy) techniques. The EDX analysis of the wear scar surface lubricated with IL-Ag@C showed iron also in addition to the constituent elements of the composite. Thus, active participation of the adsorbed additive towards tribofilm formation is validated. The XPS studies of the same surface, further confirm the presence of boron nitride, boron carbide along with iron oxide. These boron compounds have, indeed, enriched the tribofilm for improved triboactivity. Unlabelled Image • Synthesis of carbon spheres, Ag@C and IL-Ag@C composite by hydrothermal method • Characterization of the synthesized additives by FT-IR, TGA, XRD, FE-SEM, TEM, Raman and XPS • Evaluation of triboactivity of the synthesized additives at the optimized concentration 0.5% w / v • Morphological studies of the worn surface by SEM/EDX and AFM • Characterization of tribofilm by XPS [ABSTRACT FROM AUTHOR]