Chemical Effects on Subcritical Fracture in Silica From Molecular Dynamics Simulations. Issue 11 (5th November 2018)

• Record Type: Journal Article
• Authors: Rimsza, Jessica M.; Jones, Reese E.; Criscenti, Louise J.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 11(2018)
• Page Start: 9341
• Page End: 9354
• Publication Date: 2018-11-05
• Subjects: fracture -- modeling -- mineral -- subcritical stress -- water -- atomistic; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2018JB016120
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Fracture toughness of silicates is reduced in aqueous environments due to water‐silica interactions at the crack tip. To investigate this effect, classical molecular dynamics simulations using the bond‐order‐based reactive force field (ReaxFF) were used to simulate silica fracture. The chemical and mechanical aspects were separated by simulating fracture in (a) a vacuum with dynamic loading, (b) an aqueous environment with dynamic loading, and (c) an aqueous environment with static subcritical mechanical loading to track silica dissolution. The addition of water to silica fracture reduced the silica fracture toughness by ~25%, a trend consistent with experimentally reported results. Analysis of Si─O bonds in the process zone and calculations of dissipation energy associated with fracture indicated that water relaxes the entire process zone and not just the surface. Additionally, the crack tip sharpens during fracture in water and an increased number of microscopic propagation events occur. This results in earlier fracture in systems with increasing mechanical loading in aqueous conditions, despite the lack of significant silica dissolution. Therefore, the threshold for Si─O bond breakage has been lowered in the presence of water and the reduction in fracture toughness is due to structural and energetic changes in the silica, rather than specific dissolution events. Key Points: Fracture toughness (KIC ) of silica estimated from molecular dynamics simulations is reduced by ~25% in aqueous environments Chemical impact on fracture is not additive to mechanical loading but decreases thresholds for Si‐O bond breakage An aqueous environment in a fracture relaxes the silica structure at the fracture tip and in the surrounding process zone