Surface charge as a new concept for boundary lubrication of ceramics with water

Abstract

The influencing parameters considered in the present state of the art for determining the thickness of the lubricating film and the lubrication regime under tribological conditions are mostly basic physical, macro-geometrical or mechanical and effects such as surface charge and the associated pH, zeta-potential or solubility are not considered important. However, in this work we present how remarkably these electrochemical parameters affect the properties of the surface layer, the physico-chemical and load-carrying properties of the lubricating film, the tribochemical reactions and the tribolayer failure modes of water-lubricated contacts: more than 25 specific properties were shown/proved or were recognized as potential parameters resulting from surface-charge effects. Under boundary-lubrication conditions, this can result in a significantly different severity of the contact conditions and consequently in friction and wear compared with those predicted with conventional considerations and models. This seems to be especially important not only for water-based but also for other low-viscosity lubricants, which due to thin lubricating films provide poor and/or fragile film conditions. Accordingly, we suggest that a more complete set of tribo-electro-chemical effects should be considered and controlled in a lubricating film and that more tailored models, which also take into account some of these effects, should be developed to enable a more accurate prediction of the contact conditions in future boundary-lubricated systems.