Hydrodynamic Lubrication Theory Considering Electric Double Layer for Very Thin Water Film Lubrication of Ceramics

Abstract

Rubbing of engineering ceramics as silicon nitride against itself in water often shows very low friction.It is generally considered that hydrodynamic lubrication occurs with very thin water film(about 30-70 nm)in water.In this paper, a hydrodynamic lubrication theory of ceramics in water considering the effect of electric double layer is proposed, which has an analogous form to the Reynold's equation.Theoretical results shows that the minimum film thickness increases with the zetapotential of electric double layer.The theoretical results are compared with the experimental results for Al₂O₃, Si₃N₄ and SiC ceramics lubricated.It is found that the load capacity predicted theoretically for these ceramics agree qualitatively with the experimental results.Both the theory and experiments show that ceramics with high zeta-potential will give high load capacity, provided the other condition is the same.