Impact of pressure on structure and properties of hot‐compressed Na₂O–Al₂O₃–SiO₂ glass by molecular dynamics simulations

Abstract

We conduct systematic studies to investigate the impact of pressure on structure and properties of Na2O–Al2O3–SiO2 glass system using molecular dynamics simulations. Glass compositions range from peralkaline, to charge‐balancing, to peraluminous. Hot‐compression operation is applied to as‐prepared glasses with pressure up to 4 GPa. Several key learnings are obtained from the study: (a) Density and elastic moduli increase with increasing Al/Na ratio (RAl/Na) and pressure, which are mainly driven by average internetwork bond angle reduction and void size reduction upon compression. (b) Population of three bonded oxygen (TBO) show some presence in the peralkaline composition space, while gain significantly in the peraluminous regime. Pressure essentially encourages conversion of bridging oxygen to nonbridging and three bonded oxygens. Local nearest neighbor environment of TBO is predominately Al atoms rather than Si atoms regardless of RAl/Na and applied pressure. (c) Analysis of first sharp diffraction peak (FSDP) from neutron scattering suggests that medium‐range structure is compacted and small size rings are noticeably distorted over the hot‐compression process. (d) Ring size distribution analysis shows that pressure has a more pronounced effect on altering medium‐range structure for peralkaline glasses as compared to peraluminous glasses.

Topological hardening through oxygen triclusters in calcium aluminosilicate glasses

“…The preceramic polymer used was allylhydridopolycarbosilane (AHPCS) preceramic polymer, which is commercially available under the tradename StarPCS™ SMP-10. 45 The fabric was first prepregged with SMP-10 polymer containing SiC filler particles. Fillers are typically added in a range of 20-50 weight percent to increase the yield of the prepreg matrix, and also to tailor properties of the CMC.…”

“…However, the percentage of triclusters observed in previous MD simulations, as well as the work here, show roughly ~7-10% triclusters in the tectosilicate composition which is twice the percentage of NBOs for the same glass. Moreover, triclusters have been found to exist in the percalcic regime (although in small amounts) 19,22,45 when theoretically, they should only be present in peraluminous compositions. Furthermore, from this work, the percentage of NBOs decreases to less than 2% at R = 4.…”