Enhancement of tribological properties of mineral oil by addition of sorbitan monostearate and borate

Abstract

The development of modern automobile and engine industries requires lubricants that can withstand high temperatures and pressures. Recent advances made in the chemistry provide the use of inorganic particles as lubricant additives. Therefore inorganic boron-based additives have been the focus of much attention, as they posses a good combination of properties, such as wear resistance, friction-reducing ability. In this study, the state of art in the field of inorganic particle, zinc borate synthesis and its employment in tribology were investigated. The synthesis of zinc borate was achieved not just by precipitation, but also production methods such as inverse emulsions. The products were characterized by SEM, FTIR, TGA, DSC, EDX. In lubrication part, the friction reducing and antiwear ability of the particles as an additive in the mineral oil was focused. Sorbitan monostearate was used to cover the surfaces of inorganic particles in order to provide better dispersion of additives in the oil. Friction and wear behavior of the lubricants were measured by four-ball wear test machine. The effects of dispersing agent, zinc borate type as well as surfactant concentration on the tribological properties of the lubricants were investigated. Sorbitan monostearate not only outperformed as a dispersing agent of inorganic particles, but also it proved to be an efficient antiwear agent. The lowest wear scar diameter was obtained by the lubricant containing zinc borate synthesized via coordination precipitation method. The addition of this sample with the surfactant in the oil reduced the wear scar diameter from 1.402 mm to 0.550 mm.