Solid Lubrication with Carbon Onions at High Temperature in Vacuum
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1085-T05-07
Solid Lubrication with Carbon Onions at High Temperature in Vacuum Atsushi Hirata, and Shinji Saito Tokyo Institute of Technology, Tokyo, 152-8550, Japan ABSTRACT Solid lubricant performance of carbon onions prepared from diamond nanoparticles through a heat treatment at 1700°C have been examined at high temperatures up to 300°C in air and vacuum. Sliding friction between a silicon disk on which carbon onions were dispersed and a stainless steel ball was measured by means of ball-on-disk type friction testing. Friction coefficients in vacuum decreased with temperatures and became stable above 100°C for longer service life. On the contrary to this, friction coefficients in air increased with temperatures despite Raman spectroscopic analysis and thermogravimetric analysis showed that the structure of carbon onions were stable in air up to 300°C.
INTRODUCTION Nanoscale carbon particles consisting of concentric graphitic multi-shells [1], so called carbon onions, are one of the fullerene-related materials together with C60 and carbon nanotubes. Owing to the surface structure of carbon onions that includes no defect when a graphene sheet of the outermost surface of a carbon onion ideally forms a closed shell, intermolecular reactions of carbon onions with themselves or other materials in contact would become quite weak. As this surface characteristic directly causes small friction, carbon onions have been expected to be a promising solid lubricant. Actually carbon onions have been found to exhibit low friction coefficients and wear rates in both air and vacuum at room temperature [2,3], and their tribological applications to a lubricant additive [4,5] and micro/nano tribology [6] have been investigated. However, solid lubricant properties of carbon onions have not been examined at higher temperatures despite their thermal stability is superior to that of other forms of carbon particles in size of nanometers such as diamond clusters and carbon blacks. In the present study, tribological properties of carbon onions as a solid lubricant were investigated at high temperatures up to 300°C both in air and vacuum.
EXPERIMENTAL DETAILS Carbon onions were prepared by means of heat treatment of diamond nanoparticles approximately 5 nm in diameter, which were made through detonation of trinitrotoluene. A graphite crucible containing a few ten milligrams of diamond nanoparticles was heated using a high frequency induction furnace in an inert ambience. The diamond nanoparticles transformed into carbon onions at 1700°C for several minutes. Carbon onions have been characterized by transmission electron microscopy (TEM), Raman spectroscopy, thermogravimetric analysis and friction measurement using a ball-on-disk tribometer. Friction was measured in air or vacuum at temperatures up to 300°C using a stainless steel ball and a silicon disk covered with the carbon
onions. Table I shows the friction measurement conditions. Friction coefficients were calculated and the surface of the ball was observed with an optical microscop
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