The friction of natural and CVD diamond

We present results on the effect of the environment, load and sliding velocity on the tribological properties of natural diamond sliding upon natural and CVD diamond. Under given conditions of sliding, extremely low friction coefficients, of the order of 10−3, have been measured. Our results show that adhesion plays a fundamental role in explaining diamond friction in air, and not only in vacuum as previously thought. We explain the reductions observed in the friction coefficient in terms of the decrease in the adhesive interaction between the two surfaces, following saturation of the dangling bonds by adsorbed species, and by the production of lubricating debris consisting of sp2 hybridised carbon.