Preparation and Evaluation of Tribological Properties of Cu Nanoparticles Surface Modified by Tetradecyl Hydroxamic Acid

Oil-soluble Cu nanoparticles without phosphorus and sulphur elements were prepared using in situ surface-modification technique with hydrazine hydrate as a reductant and tetradecyl hydroxamic acid (THA) as a modifier. The phase composition, microstructure, and chemical structure of as-synthesized Cu nanoparticles (coded as THA-capped Cu or THA-capped nano-Cu) were analyzed by means of X-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectrometry. The thermal stability of THA-capped Cu was examined using thermogravimetric analysis and differential thermal analysis. The antiwear ability of THA-capped Cu as an additive in liquid paraffin was examined using a four-ball machine, and the morphology of worn steel balls was examined using a scanning electron microscope, an energy dispersive spectrometer and an X-ray photoelectron spectroscopy. It has been found that THA-capped Cu can be well dispersed in some organic solvents. As-synthesized THA-capped Cu as an environmentally friendly additive in liquid paraffin shows excellent antiwear ability for the steel-steel contact. Besides, Cu nanoparticles are able to deposit and fill up micropits and grooves on steel sliding surfaces under a higher load and hence greatly reduced wear of the steel-steel pair thereat by way of self-repairing of worn surfaces of the steel-steel frictional pair, showing promising application as an environmentally acceptable lubricating oil additive.