Tribological performance of fatty acid, acid/amine additive mixture and ionic liquid

Bio-based materials have attracted great attention from industry and academia in tribology because they are renewable, bio-degradable and easily accessible. This study aims to evaluate the efficiency of bio-based materials used both as neat lubricants and additives on friction and wear performance. The evaluated lubricants include oleic acid, a mixture containing oleic acid and dodecyl amine in hexadecane and a neat ionic liquid composed of oleic acid and dodecyl amine. The influence of the additive concentration, ratio between acid and amine, and oscillation frequency under reciprocating contacts has been investigated. Surface analysis was conducted by optical microscope, scanning electron microscopy and energy-dispersive X-ray spectroscopy, and time-of-flight secondary ion mass spectrometry. The results confirm that a small amount of oleic acid as an additive can provide limited friction reduction. Bio-based ionic liquid shows the lowest friction and wear coefficient in all testing conditions. A synergistic effect between oleic acid and dodecyl amine as an additive mixture has been observed when the two components are equimolar and the oscillating frequency is high. Time-of-flight secondary ion mass spectrometry analysis of the wear track indicates that the tribological process enhances the ionic character of the additive mixture, improving the lubrication performance.