Abstract
In this work, effects of running-in process on achieving super-low friction between silicon nitride ball and sapphire disc under lubrication of mixtures of sulfuric acid and glycerin, was investigated. The results revealed that sulfuric acid plays the key role in the running-in process. Owing to this acid, a smooth worn region was generated on the silicon nitride ball through chemical-mechanical abrasion, which provided favorable conditions for super-low friction under elastohydrodynamic lubrication. Meantime, a silica layer formed on part of the worn region through tribochemical reaction during running-in process, contributing to the realization of super-low friction under boundary and mixed lubrication. Moreover, the adsorption of hydrogen ions on friction surfaces generated a repulsive double-layer force that also contributed to super-low friction.
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