Lanthanum Effect on the Tribological Behaviors of Natural Serpentine as Lubricant Additive

The tribological properties of serpentine powders (Mg6Si4O10(OH)(8), marked as FGM1) and the admixture of 95wt% serpentine powders + 5wt% La2O3 nanoparticles (FGM2) as oil additives were comparatively investigated using an optimal SRV-IV friction and wear tester. The worn surface was characterized by scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectrometry (XPS) and the friction mechanism is discussed. The results show that both FGM1 and FGM2 had excellent tribological performance and 0.5wt% content was the most efficient in reducing friction and wear at 50N. With the addition of La2O3 nanoparticles, the tribological properties were further improved compared to those of serpentine powders alone. A smoother and more compact tribofilm with iron oxides, silicon oxides, graphite, organic compounds, and La-9.33 (SiO4)(6)O-2 was formed on the worn surface and provided further reduced friction and wear.