Computer Simulation Study Of The Mixed Alkali Silicate Glasses

Author : Seung Ho Hahn
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (119 download)

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Download or read book Atomistic-simulations of Silicate Glasses written by Seung Ho Hahn and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Silicate-based glasses are one of the most versatile materials in terms of technological perspective with a wide range of industrial applications. In most cases, glass products are exposed to various aqueous environments (either humid air or liquid water) and subject to physical contact with foreign objects, which leads to deterioration of chemical and mechanical properties of glass surfaces. Therefore, understanding their interactions with adsorbed interfacial water molecules is critical as it can provide physical insights needed for rational design of more durable glasses. Experimental characterization approaches have been applied to tackle difficult problems associated with the complex nature of glass surfaces but they are often limited by the time-scale resolution. As a result, they have failed to offer important structural characteristics and chemical reaction mechanisms under dynamic processes happening at the glass surface. To complement the challenges that experimental endeavors are encountering, this dissertation aims to provide a comprehensive understanding of water interactions of silicate glass surfaces using atomistic-scale simulations techniques. In particular, ReaxFF reactive force field-based molecular dynamics (MD) simulations are employed to study two distinct surface phenomena, i) surface water reaction and ii) surface mechanochemical wear process. These studies represent the surface damage process of silicate glass in the absence and presence of mechanical actions, respectively. The first part of this dissertation describes the water interactions of a silicate glass with readily leachable alkali (sodium) ions. In this study, highly complex surface chemistry, including proton/water exchange with the sodium ions, formation of relatively long-living sodium-hydroxide ionic complexes at the glass surface and eventual dissolution of those ion pairs into the water phase are described. Also, surface mapping of water binding energy to the glass surface is evaluated at different stages of the glass-water reaction, which would be relevant to assess the chemical durability of the glass materials based on the glass network topology. After the transport behavior and glass-water reaction mechanism at the surface has been identified, the mechanochemical wear process of sodium silicate glass rubbed with amorphous silica in the absence and presence of interfacial water molecules is covered in the second part of this dissertation. The effect of water molecules on the shear-induced chemical reaction at the sliding interface was investigated and the dependence of wear on the number of interfacial water molecules in ReaxFF-MD simulations was found to be qualitatively in reasonable agreement with the experimental data. The large-scale atomistic simulation approaches with ReaxFF reactive force field presented in this dissertation alleviates the limitations of DFT calculations and experiments, providing new and meaningful insights on the chemical dynamics associated within the glass-water interface.