Water-Based Lubrication of Hard Carbon Microspheres as Lubricating Additives

Because of their superior physical and chemical stability, carbon microspheres have been identified as promising lubricating additives. In this paper, hard carbon microspheres with diameters ranging from approximately 130 to 250 nm were prepared through a hydrothermal method using glucose as the carbon source. The as-prepared carbon microspheres were characterized by a series of complementary techniques including field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray diffraction. It was found that the as-prepared carbon microspheres were spherical with graphitic structure. The effects of applied load, concentration, and particle size of the carbon microspheres as water-based lubricating additives against an opposing smooth silicon surface were systematically studied using a UMT tribometer and a 3D noncontact interferometric microscope. The results showed that carbon microspheres can effectively reduce friction and wear on a smooth silicon surface and the optimal performance was obtained at an applied load of 100 mN, a concentration of carbon microspheres of 0.1 wt% and an average particle size of 200 nm. The superior performance of carbon microspheres as water-based lubricating additives was attributed to having the particles dispersed as individual particles (as opposed to clusters) and also having sufficient physically and chemically stable particles within the contact region which allowed for a rolling friction mechanism to reduce friction.