Synthesis, Characterization, and Tribological Evaluation of SDS-Stabilized Magnesium-Doped Zinc Oxide (Zn0.88Mg0.12O) Nanoparticles as Efficient Antiwear Lubricant Additives

Abstract

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. © 2016 American Chemical Society.