Fabrication of nanocrystalline SiO2–ZrO2 glass-ceramic via a high-pressure cold sintering process

The nanocrystalline 0.35SiO2-0.65ZrO2 (65 mol% monoclinic ZrO2) glass-ceramic was successfully fabricated via a high-pressure cold sintering process (CSP), displaying remarkable nano hardness and elastic modulus of 12.5 and 154.8 GPa, respectively. We conducted a thorough investigation of the influence of NaOH solution concentration, liquid-to-solid mass ratio, sintering temperature, and pressure on the phase compositions, microstructural evolution, and densification. Notably, excessive NaOH concentration (>0.7 M) results in the transformation of SiO2 from an amorphous phase to α-quartz, hindering densification. However, below 0.7 M, increasing NaOH concentration enhances the densification processes. Furthermore, higher temperature and pressure contribute to improved densification. It is worth mentioning that there is no grain growth for the ZrO2 phases during the CSP, indicating that the densification of the nanocrystalline 0.35SiO2-0.65ZrO2 glass-ceramic is primarily governed by the glass phase.