Preparation of platy Co/Al hydrotalcites using aluminum hydroxide and investigation of their tribological properties in base oil

In this study, the synthesis of Co/Al hydrotalcite (layered double hydroxides: LDHs) using insoluble Al(OH) 3 by a hydrothermal method is described. The syntheses were conducted under various conditions. The as-prepared Co/Al-CO 3 2– -LDH was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The tribological properties of the products were evaluated in base oil using four-ball and Plint friction testers. The LDH thus synthesized displays perfect hexagonal platelike morphology having a disk diameter in the range of 0.2–1.5 μm with a thickness of 40 nm. The addition of the product Co/Al-CO 3 2– -LDH, as an additive to the base oil, significantly reduces the friction coefficient (22.3%) and wear (26.1%) compared to base oil alone. The morphology and chemistry of the worn surface were characterized by SEM, atomic force microscopy (AFM), and X-ray absorption near-edge structure (XANES) spectroscopy. The results show that the structural distortion of LDH induced by mechanochemical processes during friction consumes the friction force between the rubbed surfaces, and as a result, the friction and the wear is reduced. Thus, our results show that the LDH sheets absorbed on the worn surface can prevent direct contact between the friction pairs (surfaces) and decreases the roughness of the worn surface.