Tribological analysis of surfactant modified nanolubricants containing CeO2 nanoparticles

Cerium oxide (CeO2) nanoparticles are added to different lubricating oils together with suitable surfactants to obtain modified nanolubricants. Lubricating properties of these surfactant modified nanolubricants have been investigated using a pin on disc tribotester under boundary lubrication conditions. Coconut oil, paraffin oil and a commercial engine oil (SAE15W40) have been used as base oils for the present study. Changes in frictional coefficient and specific wear rate have been studied as a function of nanoparticle concentration in the lubricant together with an estimation of the settling trend of nanoparticles with time. Results show that the frictional force and specific wear rate decrease with increase in concentration of nanoparticles, come to a minimum at a specific concentration level and then increase, showing the presence of an optimum concentration level at which both friction and wear are the least. At this concentration level, coconut oil shows the lowest frictional coefficient and specific wear rate among the three oils studied. The morphology of the pin surfaces after sliding has been studied using atomic force microscopy, optical interferometer and SEM. When CeO2 nanoparticles are added to the lubrication oil together with surfactant modification, settling trend and agglomeration of nanoparticles with time are reduced to a great extent compared to the case in which nanoparticles are added without surfactant modification.