solid lubricant properties of Carbon onions prepared from daimond clusters and particles

Atsushi HIRATA, Masaki IGARASHI and Takahiro KAITO

Department of Mechanical Sciences and Engineering, Tokyo Institute of Technology

2-12-1, O-okayama, Meguro-ku, Tokyo 152-8552, JAPAN

E-mail: ahirata@ctrl.titech.ac.jp, FAX: +81-3-5734-2893, TEL: +81-3-5734-2163

Abstract

Carbon onions have several highly potential properties as solid lubricant, for example, quasi-spherical structure, weak intermolecular bonding as well as high mechanical strength. We have investigated tribological properties of carbon onions prepared by heat treatment of diamond clusters or particles.

A new type of preparation technique was proposed in order to obtain large amount of carbon onions. Ten milligrams of diamond clusters used as source material were heated with an infrared radiation furnace up to approximately 1730 degree C in argon ambient. As a result, heating for one minute at 1730 degree C transformed diamond clusters into carbon onions. Near-round and multi-layer structure of the carbon onions was observed and confirmed by high resolution TEM. The particle size of these carbon onions ranged from 5 to 10 nm that corresponds to the size of diamond clusters. This preparation technique also applied to diamond particles less than 0.5 mm in diameter to produce larger carbon onions.

Tribological properties of the carbon onions were examined by ball-on-disk type friction testing using a doped silicon wafer and a bearing steel ball. The carbon onions were distributed on the silicon wafer without adhesive. The carbon onions exhibited lower and stable friction coefficients in comparison with graphite powders both in air and vacuum at room temperature. The wear rate of a steel ball sliding on the silicon wafer on which carbon onions are distributed was extremely lower than on the wafer over which graphite powders spread Moreover, it is found that the onion displays its superior tribological property on harder disk materials with smoother surface. Larger carbon onions prepared from diamond particles have maintained low friction property on rough surfaces of silicon disks.

Keywords: carbon onion, diamond, cluster, solid lubricant, tribology