Precision modulation of microstructure and mechanical properties in gelcasted fused silica ceramics through coordinated solid loading and sintering strategies

In this study, high-performance fused silica ceramics were fabricated from bimodal distribution powders via gelcasting and pressureless sintering. The solid loading of slurries (60–85 vol%) and sintering conditions (1280 °C for 1–6 h) significantly influenced the composition, microstructure, sintering, and mechanical behavior of fused ceramics. Increasing solid loading promoted densification, enhanced bulk density, and inhibited cristobalite precipitation. In contrast, extending holding time enhanced viscous flow and densification, but increased cristobalite precipitation. Therefore, both solid loading and holding time must be optimized to enhance material densification and suppress cristobalite precipitation. Fused silica ceramics prepared under 80 vol% solid loading and 3 h holding time showed optimal overall performance. They achieved a bulk density of 2.00 g/cm 3 , a flexural strength of 71.21 MPa, and a linear thermal expansion coefficient (approximately 10 −6 /°C) within the range from room temperature to 1000 °C. Following 20 thermal shock cycles between room temperature and 1000 °C, the material retained a residual flexural strength of 23.64 MPa, with a corresponding strength retention rate of 33.20 %. This study provides valuable guidance for fabricating high-strength fused silica ceramics via gelcasting and pressureless sintering.