Investigation of the Tribological Behavior of Mineral Lubricant Using Copper Oxide Nano Additives

Abstract

In this study, tribological properties of custom formulated and stabilized nano lubricant are investigated. Spherical CuO nanoparticles are suspended in 20W-50 mineral base lubricant using Oleic Acid (OA) as a surfactant. Three different nano lubricant concentrations with 0.2, 0.5, and 1 wt.% were analyzed through ASTM G-99 pin-on-disc tribometer standardized test under boundary/mixed lubrication regimes. The generated friction and wear analyses confirm a consolidation of tribological properties with a reduction in friction coefficient in the range of 14.59–42.92%, compared with the base lubricant. Analysis of worn surfaces (SEM/EDX) as well as (AFM) was conducted. Combined hypotheses were proposed from the analysis of worn surfaces; these hypotheses suggested that CuO nanoparticles exhibit an integrated effect of two phenomenal lubrication mechanisms. Additionally, dispersion stability evaluation of the suspended nanoparticles was performed through Zeta potential, (FTIR), and sedimentation analyses. Stability results showed that steric stabilization is the dominating effect of the repulsive forces between nanoparticles, surpassing the electrostatic repulsive forces.

Keywords

• oleic acid (OA)
• ASTM G-99
• anti-wear/friction additives
• zeta potential
• colloidal stability