Ultra-low Friction Behavior during Gas Adsorption to a Hard Amorphous Carbon Film

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On a hard amorphous carbon film prepared by electrostatic impact-deposition of carbon black particle, the ultra-low friction behavior under the surface adsorption of gas molecules was investigated by evaluating the structure and the boundary lubrication properties of the film, and the following results are obtained;1.The carbon film is composed with graphitic phase of starting material and its impact-subjected one of amorphous structure, including numerous defects such as dangling bond of carbon. For the film heating beyond 100 C, the amorphous structure gradually transforms to graphitic phase, which reads to the increase in the density of dangling bond.2.Surface adsorption condition for ultra-low friction was revealed with a sliding friction experiment in several atmospheric gases, using the reciprocating motion between coated ball and disc specimens in the manner that the contact point describes a same locus repeatedly. And the following results are obtained; (1)Very low friction was attained for the density state of gas adsorption of hydrogen, water and nitrogen, especially in hydrogen atmosphere the frictional coefficient became of below 0.01. However, it is proved that oxygen gas promotes the interfacial adhesion of carbon film under frictional action. (2)It was clarified that the boundary lubrication in air is considerably affected by water adsorption. In the present experimental condition of reciprocating friction, the low water adsorption for low friction can be attained in an appropriate equilibrium of the desorption and adsorption rates; the former can be dominated by the friction condition, and the latter can be by the atmospheric condition and film quality such as the content of graphite and surface radical.