Synthesis of nanostructured lanthanum fluoborate modified by oleylamine and evaluation of its tribological properties as a lubricating additive in synthetic ester

Lanthanum fluoborate modified by oleylamine [denoted as La(BF4)(3)-OA] was synthesized as a potential lubricant additive by direct precipitation method with sodium tetrafluoroborate and lanthanum nitrate [La(NO3)(3)] as the staring materials and oleylamine (OA) as the surface-modifying agent in distilled water-ethanol mixed solvent. The effects of reaction temperature, OA to La(NO3)(3) ratio, and surfactant cetyltrimethyl ammonium bromide on the size and shape of as-synthesized La(BF4)(3)-OA were investigated. The crystalline structure and morphology of as-obtained La(BF4)(3)-OA were characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy. Moreover, the tribological properties of La(BF4)(3)-OA as an additive in dioctyl sebacate, a synthetic ester, were evaluated with a four-ball machine, and the worn surfaces of the steel balls were analyzed with a field emission scanning electron microscope equipped with an energy dispersive spectrometer accessory. It was found that the as-synthesized La(BF4)(3)-OA exhibits disk-like nanoflake shape and have a diameter of 10-45nm, depending on varying synthetic conditions. As-synthesized La(BF4)(3)-OA as an additive in DIOS possesses excellent antiwear and friction-reduction performance for the steel-steel pair, which is because the as-synthesized additive simultaneously contain tribologically active elements La, B, and F that facilitate the formation of a boundary lubricating and protecting film on sliding steel surfaces thereby avoiding direct contact of the steel-steel pair and significantly reducing the friction and wear. Copyright (c) 2016 John Wiley & Sons, Ltd.