Preparation of DDP-coated PbS nanoparticles and investigation of the antiwear ability of the prepared nanoparticles as additive in liquid paraffin

PbS nanoparticles of average diameter about 5 nm, which were surface-modified with dialkyldithiophosphate (DDP), were prepared by chemical synthesis. The synthesized DDP-coated PbS nanoparticles were characterized by infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electron diffraction (ED). The antiwear ability of the coated PbS nanoparticles as additive in liquid paraffin was investigated using a four-ball machine. The worn surfaces were analysed with XPS also. It was found that the dispersion capacity and oxidative stability of PbS nanoparticles could be improved effectively by surface modification with DDP. Meanwhile, DDP-coated PbS nanoparticles could improve the antiwear ability of liquid paraffin even at an extremely low concentration. This was attributed to the formation of a chemical reaction boundary film consisting of PbS, PbO, FeS, Fe₂O₃, SO₄^2- and PO₄^3-.