Formation of tribochemical layer of ceramics sliding in water and its role for low friction

The formation of a tribochemical layer on silicon nitride sliding in water is studied. The wear mode changes from mechanically dominated wear to tribochemically dominated wear as sliding distance increases. The silica tribochemical layer is formed on the friction surface and reduces the friction. Introducing an additive that accelerates the formation of colloidal silica makes the running-in distance shorter. The activation energy for tribochemical reaction is estimated to be as small as 1/6–1/8 of that for static reaction.