Combined experiments and atomistic simulations for understanding the effect of ZnO on the microscopic network of sodium silicate and sodium borosilicate glasses

Abstract

Abstract Considering the beneficial aspects of ZnO doping in silicate and borosilicate glasses for bioactive glass, nuclear waste vitrified glass and many other applications, the combined experiments and molecular dynamics (MD) simulations were performed over wide range of composition. First principles ab-initio MD (AIMD) simulations confirmed the transferability of B-K-S potential model for multi-component glasses. A significant change in glass structure was monitored from short range order parameters: pair correlation function, coordination number, as well as intermediate range order parameters: bond/angle distribution profiles, structure factor and probability of X-O-X\ (X,X\ = Si, B, Zn) connections. Order of connectivity illustrated that hydrolysis of glass will slow down with addition of ZnO in the glass matrix. Successively, the effect of microscopic structure on observable glass properties: chemical durability, mechanical strength, thermal stability and characteristic vibrational spectra was analyzed. Results show good match of MD estimated trend for Young Modulus, glass transition temperature, and leaching data with the experimental observations, hereby, confirm the transferability of applied potential parameters for multi-component (n≥4) glasses. Both the experiments as well as MD simulations report the enhanced chemical durability of glass withZnO addition. Low R (Na2O/B2O3) and high K (SiO2/B2O3) of ZnO doped sodium borosilicate (Zn-NBS) glass surface compared to bare NBS represents the more stable structure of glass surface for Zn-NBS than NBS. During contact with water, Na+ ions were less likely to leach out from glass to aqueous solution for Zn doped glasses. The enhanced chemical resistivity of Zn-NBS was also established from the increasing activation energy for diffusion of Na ions. Likewise, the ring statistics as well as Na cluster size also supported the reduced chemical reactivity of Zn added glasses. The systematic study of linkage between network formers, ring statistics, diffusion dynamics and ion/water migration provides significant understanding of glass dissolution mechanism. Also, results predict the beneficial impact of ZnO doping for improved strength of glass skeleton, which would eventually control the glass degradation due to micro cracking. The combined studies from experiments and MD simulations disclose many interesting microstructure and dynamics due to the presence of ZnO in the glass.