Densification and network structural changes in binary aluminosilicate glass via cold sintering process

Abstract

Binary aluminosilicate glasses containing 20–50 wt% Al2O3 were successfully densified through a cold sintering process (CSP) using 1–10 M NaOH solutions. The investigation focused on densification and structural unit changes in the cold-sintered binary aluminosilicate glasses. Specifically, the binary aluminosilicate glass with 40 wt% Al2O3, cold-sintered at 180 °C using 1–10 M NaOH solutions, achieved a relative density of up to 90 % at 10 M NaOH. This was attributed to an enhanced dissolution-precipitation process facilitated by an increased concentration of the NaOH solution. In aluminosilicate glasses with 20–50 wt% Al2O3, the relative densities approached 90 % after CSP at 180 °C using a 10 M NaOH solution. Al(OH)3 formation in the cold-sintered glasses was confirmed, particularly at higher concentrations of NaOH solution (>10 M) and higher contents of Al2O3 (>40 wt%). Changes in Si structural units were observed during CSP, with Al-rich Si units becoming dominant as the concentration of the NaOH solution increased. The higher substitution of Si-O-Si bonds by Si-O-Al bonds led to the precipitation of Al(OH)3, as well as an increased Vickers hardness and biaxial flexural strength of the cold-sintered glasses. These findings demonstrate that the Al2O3 content and NaOH concentration play important roles in the densification and enhancement of the mechanical property in the cold-sintered alumina-rich binary aluminosilicate glasses and offer insights into the optimal conditions for obtaining desirable aluminosilicate materials through CSP.