Influence of green synthesized aluminum oxide nanoparticle concentration on wear and coefficient of friction of vegetable oil-based lubricants

Abstract

Green manufacturing is increasingly becoming popular especially in lubricant manufacturing as more environmentally friendly substitutes for mineral base oil and synthetic additives are being found amongst plant extracts and progress in methodologies for extraction and synthesis is being made. It has been observed that some of the important performance characteristics need enhancement of which nanoparticle addition has been noted as one of the effective solutions. However, the concentration of the addictive that would optimised the performance characteristics of interest remains a contending area of research. The research was out to find how the concentration of green synthesized aluminum oxide nanoparticles in nano-lubricants formed from selected vegetable oil influence the friction and wear. A bottom-up green synthesis approach was adopted to synthesize aluminum oxide (Al2O3) from aluminum nitrate (Al(NO3)3) precursor in the presence of plant-based reducing agent—Ipomoea pes-caprae. The synthesized Al2O3 nanoparticles were characterized using TEM and XRD and found to be mostly of spherical shape of sizes 44.73 nm. Al2O3 nanoparticles at different concentrations—0.1 %wt, 0.3 %wt, 0.5 %wt, 0.7 %wt, and 1.0 %wt—were used as additives to castor, jatropha, and palm kernel oils to formulate nano lubricants and tested alternately on Ball-on-aluminum (SAE 332) and low-carbon steel Disc Tribometer. All the vegetable-based oil nano-lubricant showed a significant decrease in the Coefficient of Friction (CoF) and wear rate with Ball-on-(aluminum SAE 332) Disc Tribometer up to 0.5 %wt of the nanoparticle: the best performances (COF = 92.29; WR = 79.53) coming from Al2O3-castor oil nano lubricant and Al2O3-palm kernel oil, afterwards the started to increase. However, the performance indices displayed irregular behaviour for both COF and Wear Rate (WR) when tested on a ball-on-low-carbon steel Disc Tribometer