Investigation of Tribofilm Growth and Removal of a Sinterable Antiwear Additive

Nanoparticles have the potential to become a new classification of lubricating oil additives. Metal oxide nanoparticles have demonstrated the ability to create antiwear films through a tribosintering type process. Commercially prepared, spherical zirconia (ZrO2) nanoparticles with an average particle size (APS) of 5 nm and functionalized with a hydrocarbon ligand were dispersed in a polyalphaolefin (PAO) base oil, producing a 10 nm stabilized ZrO2 nanofluid. The resulting nanofluid was characterized including thermal conductivity and viscosity as a function of nanoparticle concentration. Long-term stability was verified using dynamic light scattering (DLS) and APS was quantified as function of time. A 10 %wt ZrO2 nanofluid maintained a 10 nm APS over 25 months, with no signs of agglomeration or sedimentation, and redispersion was not necessary before testing. The tribological performance of several concentrations of ZrO2 nanofluids was characterized with a ball-on-disk tribometer. Tribofilm growth over time was collected via optical interference imaging.