Tribochemical synergy between phosphate-intercalated layered double hydroxide additives and super high oleic safflower oil on sliding contacts.

In this study, the tribological properties of a series of layered double hydroxides (LDHs) intercalated by various phosphate anions (hydrogen phosphate, orthophosphate, pyrophosphate, and hexametaphosphate) were investigated by ball-on-disc testing in safflower oil which has a super high content of oleic acid (OA). The Mg-Al-NO LDH precursor was first synthesized by a coprecipitation method, and then nitrate anions were substituted by different phosphate anions anion exchange. The successful intercalations were confirmed by X-ray powder diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) analysis. The tribological results indicate that the antiwear properties increased linearly with the basic strength of the phosphate anions. Stronger bases, such as orthophosphate (PO) and pyrophosphate (PO), encourage the dissociation of OA to form a protective oleate tribofilm on steel surfaces, leading to more than 40% wear reduction compared to the base oil. The tribological performance of the best antiwear candidate, PO-LDH, was studied further under different loads and concentrations. A comparison between PO-LDH and other nanomaterials was also carried out with PO-LDH exhibiting a comparable performance against hexagonal boron nitride (BN).