Atomistic understanding of surface wear process of sodium silicate glass in dry versus humid environments

Abstract

Understanding surface reactions of silicate glass under interfacial shear is critical as it can provide physical insights needed for rational design of more durable glasses. Here, we performed reactive molecular dynamics (MD) simulations with ReaxFF potentials to study the mechanochemical wear of sodium silicate glass rubbed with amorphous silica in the absence and presence of interfacial water molecules. The effect of water molecules on the shear‐induced chemical reaction at the sliding interface was investigated. The dependence of wear on the number of interfacial water molecules in ReaxFF‐MD simulations was in reasonable agreement with the experimental data. Confirming this, the ReaxFF‐MD simulation was used to find further details of atomistic reaction dynamics that cannot be obtained from experimental investigations only. The simulation showed that the severe wear in the dry condition is due to the formation of interfacial Sisubstrate–O–Sicounter_surface bond that convey the interfacial shear stress to the subsurface and the presence of interfacial water reduces the interfacial bridging bond formation. The leachable sodium ions facilitate surface reactions with water‐producing hydroxyl groups and their key role in the hydrolysis reaction is discussed.

Tribochemistry: A Review of Reactive Molecular Dynamics Simulations

“…The suppression of wear by water lubricants was also observed in ReaxFF simulations of sodium silicate sliding on amorphous silica [80,81]. Specifically, water was found to inhibit mechanochemical wear by suppressing the formation of Si silica -O-Si silicate bonds, consistent with experimental trends showing that wear decreased with increasing humidity [80]. Further, experiments revealed subsurface densification of glass during sliding, which was then explained by the simulations as shear-driven change of the subsurface Si-O-Si bond angle and Si-O bond length distributions [81].…”

“…Subsequent simulations were performed at a range of temperatures and with varying amounts of water and revealed that both factors affected the formation of covalent bonds that bridge the two solid surfaces [77]. The suppression of wear by water lubricants was also observed in ReaxFF simulations of sodium silicate sliding on amorphous silica [80,81]. Specifically, water was found to inhibit mechanochemical wear by suppressing the formation of Si silica -O-Si silicate bonds, consistent with experimental trends showing that wear decreased with increasing humidity [80].…”

Investigation on nanoscale material removal process of BK7 and fused silica glass during chemical‐mechanical polishing

“…Based on a general relationship between bond distance and bond order, 37 the ReaxFF‐MD provides us a comprehensive understanding of the formation and dissociation of interfacial bonds during the tribochemical wear process. It has been reported that the glass surface reactivity, 38 as well as the formation and breakage of interfacial Si particle –O–Si glass bridge bonds are the most fundamental mechanisms for the material removal process in the mechanically induced chemical bond removal mode 39,40 …”

“…It has been reported that the glass surface reactivity, 38 as well as the formation and breakage of interfacial Si particle -O-Si glass bridge bonds are the most fundamental mechanisms for the material removal process in the mechanically induced chemical bond removal mode. 39,40 On the other hand, it is worth reminding that there is a threshold force, f, for both BK7 glass and fused silica glass to undergo material removal (as shown in Figure 4). This phenomenon can be understood as follows.…”

Differences in indentation and wear behaviors between the two sides of thermally tempered soda lime silica glass

“…Further studies suggested this unusual wear behavior of SLS glass in humid air could be attributed to the presence of leachable sodium ions (Na + ) and the water activity on the glass surface 21–24 . Since the glass wear in humid air involves chemical reactions of water molecules adsorbed on the glass surface, 25–27 it is usually called “mechanochemical” wear and should be differentiated from ‘mechanical’ wear (or abrasive scratch) occurring in dry condition. The wear behavior of SLS glass can be further affected by the sliding speed 28 and the counter‐surface chemistry 25,29 …”