Molecular Simulation of "Hydrolytic Weakening": A Case Study on Silica

Abstract

Water molecules have a great influence on the mechanical performance of silicate materials. In this study, the hydrolytic weakening mechanisms of crystal α-quartz and amorphous silica glass were investigated in light of molecular simulation. A reactive force field was used to simulate the structure, dynamics and mechanical properties of the silica with water molecules during a uniaxial tensile process with loading rates from 0.02 to 0.16 ps-1. Dry silica samples, obtained by the temperature quenching method, and wet silica samples, formed by Grand Canonical Monte Carlo water adsorption, were prepared for mechanical tests. Structurally, water penetrating the silica cavity can form H-bonds with the neighboring bridging oxygen in the silicate network, leading to the elongation of the Si-O bonds and the enlargement of the Si-O-Si angles. Dynamically, the confined water molecules, with a high diffusion rate, collide with the silicate network, reducing the stability of the siloxane bonds. The reactive force field, coupled with the chemical and mechanical responses, provides new insights into the molecular structural evolution. During the tensile process, the siloxane bonds and Si-O-Si angles are initially stretched in the elastic region. Subsequently, the silica network depolymerizes into branch structures and, finally, the structure undergoes a tensioned fracture in a catastrophic manner. When the stress exceeds 30% of the tensile strength, water molecules in the silica system begin to dissociate into two reaction pathways, i.e. one governed by the chemical adsorption of water at a low stress level and the other dominated by the breakage of siloxane bonds at a high stress level. The stress-dependent water dissociation accelerates the depolymerization of the silica network, and brings about further irreversible deformation, which weakens the cohesive force of the silica.

Department(s)

Civil, Architectural and Environmental Engineering

Keywords and Phrases

Adsorption; Depolymerization; Mechanical Properties; Molecular Structure; Molecules; Quartz; Silicates; Tensile Strength; Grand Canonical Monte Carlo; Hydrolytic Reactions; Hydrolytic Weakening; Irreversible Deformation; Mechanical Performance; Molecular Simulations; Reactive Force Field; Temperature Quenching; Silicon; Depolymerization

International Standard Serial Number (ISSN)

1359-6454

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2014 Elsevier, All rights reserved.

Publication Date

01 Nov 2014

Link to Full Text

Share

 
COinS