Tribological Properties of Nano-Scale Al₂O₃ Particles with Different Shapes as Lubricating Oil Additives

Enhancing lubrication across various tribological systems in the maritime industry is essential for improving safety, efficiency, and environmental sustainability. Al₂O₃ nanoparticles, employed as additives in lubricating oils, demonstrate favorable tribological properties including anti-wear and anti-friction characteristics. In this work, nano-scale γ-Al₂O₃ particles with different shapes, i.e., nanosheet, nanorod, nanosphere, and irregular-shaped nanoparticles, were prepared and calcinated forming the same crystalline phase with nanoscale size, which dispersed well in lubricating oil. The tribological properties of Al₂O₃ nanoparticles as lubricating oil additives were examined using block-on-ring wear tests, and the effects of the particle shape and particle concentration were investigated. The results indicated that the frictional properties are largely influenced by the particle shape and the concentration of the Al₂O₃ additives, with the optimal concentration being around 0.1 wt% for each shape. The lubricating oil with nanosheet additives presented the best tribological performance, followed by those with nanorod, nanosphere, and irregular-shaped Al₂O₃ nanoparticle additives. Al₂O₃ nanosheets as the lubricating oil additives reduced the stress effect on the friction surface because of their larger bearing area and are inter-particle-sheared during sliding due to the movement of friction pairs, which can further improve the tribological properties compared to other shapes.