Effect of Nanoparticle Additive Size on Friction and Wear Properties of Synthetic Nanolubricants

Oscar E. Montemayor, Angel G. Romero Cantú, Karen L. Nava Montemayor, Mónica Herrera Maldonado, Luisana Contreras Lizcano, Laura Peña-Parás

Abstract

Nanoparticles are being explored as lubricant additives due to the significant reduction of friction and wear mass loss of materials. It is important to determine the role that nanoparticle size plays for improving tribological performance of lubricants. In this study, different sizes of TiO2 nanoparticles: 5, 30, 165, 300, and 500 nm, with a concentration of 0.05 wt. % were dispersed by ultrasonication on a synthetic oil employed for metal-working processes. Tribological characterization of lubricants was performed on a T-05 block-on-ring tribotester. Coefficient of friction (COF), and wear mass loss were obtained. Surface roughness measurements were acquired with an optical 3D surface system. Results showed that the highest improvement in wear mass loss of 42% and 44%, compared with the base lubricant, were obtained at a nanoparticle size of 5 nm and 30 nm, respectively. Coefficient of friction was also lowered by 55%. These improvements are attributed to small nanoparticle size helping long-term suspension and to nanoparticles being able to fill surface valleys providing a mending effect. Results obtained in this study demonstrate that TiO2 nanoparticles are effective in reducing COF and wear mass loss, and that nanoparticle size determines the tribological performance that may be obtained for the synthetic lubricant.