Hydrothermal Synthesis of Monodisperse Hard Carbon Spheres and Their Water-Based Lubrication

Monodisperse hard carbon spheres (HCSs) with different size from 300 nm to 1 mu m were hydrothermally synthesized and characterized. The tribological performance of green water-based HCSs lubricant systems were studied between glass lens and silicon wafer at various normal loads and concentration on a universal micro-tribotester. The coefficient of friction (COF) increased with the particle size and an average COF of about 0.03 was measured when lubricated by 300 nm HCSs suspensions, whereas for 1-mu m-sized carbon sphere, the average COF was 0.059 for the particle concentration of 1 mg/ml. For a given size of particles, the COF first decreases with increasing concentration, but the trend reverses after a critical concentration as adding more particles in the confined space block their movement causing higher COF. The wear life of the 1 mu m HCSs lubricant was also evaluated at constant load of 2 N for the total shearing length of 8 m. A very low COF of 0.01 was stably achieved for the lubricant with 4 mg/ml HCSs suspension.