Atomic-level wear behavior of sliding between silica (010) surfaces

Abstract

Reactive molecular dynamics (ReaxFF) simulations were used to find the atomic-level wear mechanisms occurring at the sliding interface of fully hydroxylated silica (010) as a function of an interfacial water amount. The results showed that there were two kinds of rupture behaviors of surface siloxane bonds. One is resulted from only hydrolysis reaction between surface siloxane bonds and water. The other is also caused by the hydrolysis reaction, but is assisted by the interfacial siloxane bonds. Both rupture behaviors directly lead to tribochemical wear on silica surfaces. In the presence of less than a full monolayer water, the degree of wear induced only by hydrolysis reaction is affected by the change of interfacial shearing actions caused by increasing water molecules. However, the degree of wear assisted by interfacial siloxane bonds is related to the dual role of interfacial water in interfacial siloxane bonds. It is also noted that the load-dependent probability that the occurrence of tribochemical wear is caused by the formation of an interfacial siloxane bond ranges from 18% to 37%. In addition, mechanical wear, characterized by the local lattice distortion at subsurface, was also observed in our simulations. This study shows that even though no interfacial siloxane bond is formed, tribochemical wear of silica can still occur due to stress corrosion, and provides further insights into the wear mechanism of silica.