Improvement of the lubrication performance of an ester base oil with coated ferrite nanoadditives for different material pairs
María J.G. Guimarey, José M. Liñeira del Río, Josefa Fernández
Abstract
In the present work, lubrication properties (friction and wear) of a synthetic ester oil, tris(2-ethylhexyl) trimellitate (TOTM) containing ferrite nanoparticles coated with oleic acid (F3O4-OA) were investigated for two different material pairs: steel ball-steel disc and silicon nitride ball-steel disc. Thus, four TOTM nanolubricants were formulated: TOTM + 0.010 wt% Fe3O4-OA, TOTM + 0.015 wt% Fe3O4-OA, TOTM + 0.020 wt% Fe3O4-OA and TOTM + 0.025 wt% Fe3O4-OA showing all of them a moderate time stability due to the oleic acid coating. Wettability behaviour of the ferrite-based nanolubricants on steel surface was analysed, revealing that the addition of Fe3O4-OA nanoparticles in TOTM decreases the contact angle between the steel surface and TOTM lubricant surface. Friction sliding tests were performed with the neat TOTM and with the formulated nanolubricants under a 20 N of load. All nanolubricants showed lower coefficients of friction than those reached with TOTM base oil for both material pairs. Worn area was significantly reduced for all Fe3O4-OA concentrations in the steel-steel contact and for the highest concentrations in the silicon nitride-steel contact. Specifically, the largest achieved reductions were for the TOTM + 0.010 wt% F3O4-OA nanolubricant: 43% reduction in friction (silicon nitride-steel) and reductions of 17% in wear track width, 42% in wear track deep and 36% in area (steel-steel). In addition, roughness analysis and Raman microscopy of the tested discs showed that tribofilm formation and surface repairing mechanisms occur.