Ab initio molecular dynamics simulation of Na-doped aluminosilicate glasses and glass-water interaction

Khagendra Baral,Wai-Yim Ching,Aize Li

doi:10.1063/1.5092617

Khagendra Baral, Wai-Yim Ching + Show 1 more

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https://doi.org/10.1063/1.5092617

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Abstract

The structure and properties of sodium aluminosilicate (NAS) glasses are investigated using ab initio molecular dynamics and density functional calculations. Four NAS glass models of about 700 atoms with composition (SiO2)0.6(Al2O3)0.4-x(Na2O)x with Na/Al ratio R = 0.0, 0.5, 1.0 and 1.5 are constructed corresponding to x = 0, 0.135, 0.20 and 0.24. Detailed information on network coordination, electronic structure, interatomic bonding and partial charge distribution, mechanical and optical properties of these models are presented and fully analyzed. The structural details for each R are discussed in terms of short- and intermediate-range order manifested in the coordination number, atomic pair and bond angle distributions. It is shown that the mechanical strength of NAS glasses decreases with increasing Na content, indicating that pure aluminosilicate glass is stronger than the alkali-doped glasses. We use the novel concept of total bond order density to characterize the internal cohesion of the NAS glasses. In the case of R = 1 NAS model, 12 water molecules are added to investigate the solvation effect and hydrolysis in NAS glass.

Highlights

Alkali aluminosilicate is an important segment of inorganic glass with numerous industrial and technological applications
The NAS-1 model is highly polymerized while NAS-1.5 has a more disruptive network due to the presence of a large number of non-bridging oxygen (NBO)
These figures are just 2D sketches and comprehensive analysis should be discussed in terms of pair distribution function, density, coordination number (CN), bond length (BL) and bond angles (BA) distributions etc

Summary

Introduction

Alkali aluminosilicate is an important segment of inorganic glass with numerous industrial and technological applications. They are found in many geological rock-forming materials and their melts. Sodium aluminosilicate (NAS) is a modified silicate glass widely used in the chemically strengthened glass after ion exchange phenomena as demonstrated in the famous Gorilla Glass.5–7 They exhibit a great variation in physical properties such as density, molar volume, viscosity, refractive index, thermal expansion and thermodynamic properties when Na and Al contents are varied. They show a drastic change at the composition ratio R close to 1.8–12 At this composition, viscosity shows a maximum while activation energy for electrical conductivity goes to a minimum.. A precise atomic-scale understanding of the structural and physiochemical properties of such multi-component glasses is extremely important for their specific applications

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