Tribological and tribochemical properties of magnetite nanoflakes as additives in oil lubricants

This detailed the tribological and tribochemical properties of magnetite (Fe3O4) nanoflakes used as additives in *40 base oil in a four-ball tribo-tester. The average friction coefficient of the friction pair for lubricant containing the Fe3O4 nanoflakes of 1.5 wt% as a lubricant additive in the base oil is decreased by 18.06% compared to that of solely base oil. The chemical composition of base oil with the Fe3O4 nanoflake additives did not change during the 48-h friction assessment. The decreased saturation magnetization and increased coercivity of magnetite nanoflakes occurred due to the distortion of the basal planes and the presence of hematite (alpha-Fe2O3) generated by the tribochemical reactions during the friction process. The multi-layer low-shear-stress tribochemical lubrication films on the surface of the friction pair could form because the nanoflake particles arrange and adhere onto the surface of the friction pair in an orderly manner, and the tribochemical reactions of the friction pair in the presence of the nanoflakes occur as Fe -> FeO -> Fe3O4 -> gamma-FeOOH -> gamma-Fe2O3 -> alpha-Fe2O3. The formation of the films can improve the tribological properties. (C) 2013 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.