The tribological behaviors of succinimide-modified lanthanum hydroxide nanoparticles blended with zinc dialkyldithiophosphate as additives in liquid paraffin

Lanthanum hydroxide nanoparticles modified with succinimide (coded as Succ-nano La) were prepared in laboratory. The tribological behavior of the synthesized nanoparticles blended with zinc dialkyldithiophosphate (ZDDP) as additives in liquid paraffin (LP) to a total concentration of 5 wt.% was investigated on a four-ball machine. The surface morphologies and elemental distributions of the worn steel ball surfaces were examined with scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), respectively. The chemical states of some typical elements on the worn steel surfaces were analyzed with X-ray photoelectron spectroscopy (XPS). As a result, the best extreme pressure behavior was obtained at a weight fraction of 1:4 for Succ-nano La/ZDDP. The best antiwear ability was obtained at a weight fraction of 2:3 or 3:2 for Succ-nano La/ZDDP, which was accompanied by a parallel improvement in friction-reduction. Surface films consisting of La₂O₃, ZnO₂, sulfides, N-containing organic compounds and P-containing compounds were detected. The improvement in the friction-reduction and antiwear properties was attributed to these tribochemical products.