Tribologic behaviour and suspension stability of iron and copper nanoparticles in rapeseed and mineral oils

Abstract

Metal particles, suspended as wear debris or as additives, have a major influence on lubrication technology. They are known mostly for negative roles, but even iron nanoparticles, which are likely to pass through most filters, have not yet been quantitatively evaluated for their effects on friction and wear. In this study iron and copper nanoparticle suspensions were formulated in high sulphur paraffinic mineral oils and food grade rapeseed oil. The suspension stabilisation mechanism based on steric repulsion appeared more effective than ionic repulsion principle. Iron nanoparticle suspensions were investigated using four ball antiwear tribotester. Iron nanoparticles did not show statistically significant effects on wear or friction in mineral oil suspension. However, addition of surfactants improved the tribological performance. Wear, friction and sample temperature data along with microscopy evaluation suggested that formation of protective films in the friction zone was the most likely reason for reduction of wear, average friction and the duration of break-in regime.

Tribological effects of Cu, Fe and Zn nano-particles, suspended in mineral and bio-based oils

“…Other suspension samples were stored undisturbed and their stability monitored. Some data on long‐term suspension stability of nanoCu and nanoFe blends along with the surfactant influence on sedimentation rates had been reported in detail elsewhere, showing that at least an hour was necessary to see any trace of separation even in the least stable suspensions, which was clearly too slow to have any effect on four‐ball tests. One blend with Fe micro‐particles (as opposed to nanoFe) of less than 20 µm in size was prepared for comparison as well.…”

“…For given four‐ball conditions several different values of elastic indentation can be extrapolated from reports of other researchers: 0.22 mm, 0.21 mm and 0.20 mm . If liquid adsorption is negligible, Hertz elastic indentation D HZ can be calculated to produce 0.272 mm . However, at 150‐N load the interfacial pressures are relatively low, and their lateral distribution might be significantly affected by the adsorption of an additive layer .…”

“…Blending of samples without nanoparticles was carried out at final volumes of 100 g or higher, by weighing the components to ±0.05 g accuracy and mixing on conventional magnetic stirrer for 1 to 2 h, with heating at 40–45 °C. Preparation of nanoparticle suspensions had been described in detail . Briefly, the blends were prepared by making a concentrated 10% suspension in AO‐inhibited oil under argon atmosphere.…”

“…Preparation of nanoparticle suspensions had been described in detail. 14,17 Briefly, the blends were prepared by making a concentrated 10% suspension in AO-inhibited oil under argon atmosphere. Then the 10% suspension was diluted with respective oil (if necessary, containing AW additives) in order to obtain 0.01% to 1% wt.…”

“…24 If liquid adsorption is negligible, Hertz elastic indentation D HZ can be calculated to produce 0.272 mm. 14,17,25 However, at 150-N load the interfacial pressures are relatively low, and their lateral distribution might be significantly affected by the adsorption of an additive layer. 26 Therefore, 0.20 mm was used as a basis to compare wear rates in this study.…”