Study on solid lubricant properties of carbon onions produced by heat treatment of diamond clusters or particles

Tribological properties of carbon onions prepared by heat treatment of diamond clusters or particles are presented. Diamond clusters used as the source material are heated with an infrared radiation furnace to 1730 degreesC in argon at atmospheric pressure. As a result of heating at 1730 degreesC for 1 min, diamond clusters are transformed into carbon onions. High resolution TEM observation is employed to confirm the formation of carbon onions that have near-spherical and multi-layered concentric structure. The particle size of these carbon onions ranges from 5 to 10 nm that corresponds to the original size of the diamond clusters. This preparation technique is also applied to diamond particles less than 0.5 mum in diameter to produce larger carbon onions. Tribological properties of the carbon onions are examined by ball-on-disc type friction testing using a silicon wafer and a steel ball. Carbon onions, which are spread on the silicon wafer without adhesive, exhibit stable friction coefficients lower than 0.1 both in air and in vacuum at room temperature. The wear rates of steel balls sliding on the silicon wafer on which carbon onions are distributed are much lower than wear rates for sliding on a wafer over which graphite powder is spread. Moreover, it is found that the larger carbon onions prepared from diamond particles show low friction property on the rough surface of silicon discs. (C) 2004 Elsevier Ltd. All rights reserved.