Understanding the correlation of microscopic structure and macroscopic properties of multi-component glass through atomistic simulations

Nuclear power is attracting renewed interest as an alternative power source because it is climate friendly with low greenhouse gas emissions, but its acceptance depends on the safe containment of nuclear waste under geological repositories. For the immobilization of high-level liquid waste (HLLW), borosilicate glass has been considered to be the preferred choice. Selecting suitable glass composition for the vitrification of HLLW is one of the major challenges in nuclear waste reprocessing. The fusion of valuable material properties has led to the acceptance of sodium borosilicate (NBS) glasses for nuclear waste immobilization. The mechanisms associated with these properties are only partially exposed and need further exploration. In that perspective, ZnO doping in borosilicate glasses was studied by performing experiments, classical molecular dynamics (MD), and ab-initio MD (AIMD) simulations. A significant change in glass structure was monitored from short-range order parameters (pair correlation function) and intermediate-range order parameters (angle distribution profiles). Order of connectivity illustrated that the hydrolysis of glass would slow down with the addition of ZnO in the glass matrix. Successively, the effect of microscopic structure on observable glass properties: chemical durability, mechanical strength, and thermal stability, was analyzed. Results show a good match of MD estimated trend for Young Modulus, glass transition temperature, and leaching data with the experimental observations, confirming the transferability of applied potential parameters for multi-component (n≥4) glasses. Both the experiments and MD simulations report the enhanced chemical durability of glass with ZnO addition. The enhanced chemical resistivity of Zn-NBS was also established from the increasing activation energy for the diffusion of Na ions. The combined studies from experiments and atomistic simulations disclose many fascinating microstructures and dynamics due to the presence of ZnO in the glass. The results presented here can be exploited to construe the experimental results and plan future experiments.

Graphical abstract

The chemical, mechanical, and thermal strength of ZnO-incorporated sodium borosilicate glass was demonstrated by combined experiments and molecular dynamics (MD) simulations. The BKS interatomic potential was validated by ab-initio MD (AIMD) simulation. The results show the good mapping of MD-generated radial and angle distribution functions with the AIMD results.