Regular Article

Diffusion and microstructure in sodium silicate liquids

¹ Simulation in Materials Science Research Group, Advanced Institute of Materials Science, Ton Duc Thang University, Ho Chi Minh City, Vietnam
² Faculty of Electrical and Electronics Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam
³ Department of Computational Physics, Hanoi University of Science and Technology, Hanoi, Vietnam
⁴ Graduate Faculty of Interdisciplinary Research, University of Yamanashi, Yamanashi, Japan
⁵ Computational Astrophysics Laboratory, RIKEN, Saitama 351-0198, Japan

^a e-mail: phamkhachung@tdtu.edu.vn
^b e-mail: lethevinh@tdtu.edu.vn

Received: 26 May 2018
Received in final form: 7 September 2018
Published online: 5 December 2018

Abstract

We use molecular dynamics simulation to investigate the diffusion and microstructure of Na₂O⋅3SiO₂ and Na₂O⋅4SiO₂ liquid. It is shown that the temporal locations of Na are placed nearby O atoms. The O and Si atoms diffuse via the NBO ↔BO and SiO₄ ↔SiO₃ transformations. Meanwhile the diffusion of sodium is realized by mixed hopping-like and cooperative mechanism. Accordingly, Na atoms move from sites to other sites that are located nearby O atoms. Each NBO and BO has two and one sites, respectively. The Na atom prefers to move to NBO sites rather than to BO sites. Furthermore, Na atoms are collectively redistributed between different O atoms as the NBO ↔BO transformation happens. The diffusion pathways for sodium located in overlapped NF_xB_y cells contain large number of NF sites and small amount of BO sites. The dynamics of O atoms is analyzed through specified sets of most mobile and immobile atoms. The simulation showed that the dynamics of O atoms is heterogeneous. During moderately long time, the Si–O network consists of separate immobile domains where the local density of Na atoms is smaller than that in the rest of the network.