Synergy between boron nitride or graphene nanoplatelets and tri(butyl)ethylphosphonium diethylphosphate ionic liquid as lubricant additives of triisotridecyltrimellitate oil

Abstract

In this work, the synergy between an ionic liquid (IL) and nanoparticles as additives of lubricants was studied. For this purpose, four dispersions based on graphene nanoplatelets, GnPs, or nanoparticles of hexagonal boron nitride, h-BN, with or without the IL tri(butyl) ethylphosphonium diethylphosphate in an ester type base oil, triisotridecyltrimellitate (TTM), were prepared and tribologically analyzed as potential nanolubricants. The mass concentration of the nanoadditives is 0.1 wt%, whereas for the IL it is 2 wt%. The prepared blends were stable for three weeks. New density and viscosity values show that both properties slightly increase with the addition of IL and/or nanoparticles. Tribological tests were performed under a normal load of 20 N for TTM, the four dispersions and the TTM + 2 wt% IL mixture. With respect to base oil, a maximum friction reduction of 33% was achieved for TTM/IL/GnP nanodispersion. The best antiwear performance also corresponds to this same nanodispersion with a wear track width reduction of 44% and a strong decrease of the average cross sectional area of 65%, both respect to those obtained with the neat oil. In the case of wear scar depth, the maximum reduction is 32% for TTM/IL/h-BN nanodispersion. In addition, the values for roughness of worn surfaces tested with both TTM/IL/GnP and TTM/IL/h-BN nanodispersions are lower than those corresponding to the neat oil, to the TTM/IL mixture and to those of the corresponding binary dispersions. Hence, positive synergies between the IL and GnP or h-BN as additives of TTM were found. Confocal Raman microscopy demonstrates tribofilm formation and mending effect on worn surfaces.