Nano-tribology at atom-flat surfaces

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In order to understand friction in the atomic level, frictional coefficients were measured both in nano-scale and in millimeters-Ale using well-defined and atom-flat crystal faces. Frictional anisotropy and asymmetry were studied using alkali halide surfaces, and calcite surfaces, respectively. To prepare atom-flat surfaces out of uncleavable crystal faces, various solution treatments were tried. NaC1(110), (111), (113) and (120) faces became locally atom-flat. Among calcite crystal faces, (0001) and {01-16} faces showed signs of stabilization by solution treatments. Atomic models were given for the stabilization of the crystal facesAt NaC1(110) surface, expected frictional anisotropy was clearly detected in frictional force microscopic measurements. Anisotropy was not detected at polar NaC1(111) surface also as was expected. Frictional anisotropy in nano-scale can be intuitively interpreted. Dependence upon relative humidity was also studied.Friction measurements at alkali halide surf … More aces in millimeter-scale, on the other hand, gave results defying simple interpretation. Friction measurements in millimeter-scale were also performed at calcite (10-14) surface which showed clear frictional asymmetry in nano-scale. Asymmetry depending upon scan directions was clearly detected in the larger scale. However, opposite results were obtained compared to in nano-scale. Wear track analyses were performed at the surface by applying much heavier normal load. Observation of the tracks with scanning electron microscopy and atomic force microscopy revealed slip actions at (0001) and {10-14) surfaces. Frictional asymmetry and anisotropy in millimeter-scales can more easily be understood by the presence of these slip surfaces. In this scale, stresses are applied on much larger areas compared to in nano-scale. The model of chemical bonds as mass-spring systems used in explaining asymmetry in nano-scale is not applicable in millimeter-scale.Frictional properties of glass-like-carbon(GLC), a candidate for self-lubricating material, were also studied. Heat treatments at or above 2000 deg. Celsius caused surface graphitization sufficient as a practical material. By treating at even higher temperature, GLC kept the practical range of friction after wearing off of the top layers.Surface structures and frictional properties were studied with furan-resin-derived plastic added with carbon nano-fibers. By spreading the resin using a blade, the fibers lied flat in laminar samples, although in random orientations. Frictional anisotropy measured at the sample was explained by the orientation of the matrix polymer along the spreading direction. The friction coefficient first increased, then, decreased with increasing the fiber content, Heat treatment at 2000 deg. Celsium gave the flattest surface. Fiber structures were lost at 2800 deg. Celsius. Less