A Tribological Study of γ-Fe2O3 Nanoparticles in Aqueous Suspension

Abstract

In this work, the nano- and macroscale tribological properties of maghemite (γ-Fe2O3) nanoparticles in aqueous solution are compared and contrasted for alumina contacts as a function of nanoparticle concentration. A quartz crystal microbalance (QCM) technique was used for nanotribology measurements and a ball-on-disk method was used to measure macroscale friction coefficients. Statistical methods were employed to identify significant associations between the QCM and ball-on-disk measurements, employing selected candidate performance factors for each system. In particular, the macroscale response was parameterized by % reduction in the friction coefficient while candidate QCM “bulk” and “surface” performance factors were selected from functions of the frequency f and resistance Rm shifts upon addition of nanoparticles to the water surrounding the QCM. Incremental increases in concentration were performed and reductions in friction and drag forces were observed for concentrations up to 0.6 wt%, after which further reductions were not observed. The factor δRfilm/δffilm exhibited a linear correlation with the reduction in macroscale friction coefficient, defined as the ratio of the shift in resistance to the shift in frequency attributable to interfacial effects and changes in the glide plane location. Atomic force microscopy was also utilized to both qualitatively and quantitatively determine surface roughness before and after particle uptake, leading to the observations that particles are easily removed from the surface and do not significantly alter surface morphology.