Enhanced Densification and Mechanical Performance of Fused Silica via Gel Casting

The sintering behavior, phase evolution, and mechanical properties of fused silica ceramics were systematically investigated for samples fabricated by gel casting and dry pressing. Gel-cast samples were prepared using an optimized aqueous formulation containing ۵۸ wt.% solids, whereas dry-pressed compacts were produced at ۱۰۰ MPa. All specimens were sintered in air between ۱۱۰۰ °C and ۱۳۰۰ °C for ۵ h. Dilatometric analysis revealed distinct densification characteristics for the two forming methods. Despite their lower initial green density (~۳۰–۳۳% of theoretical), gel-cast bodies exhibited faster and more complete shrinkage than dry-pressed samples (~۵۷–۶۰% of theoretical), achieving near-full densification above ۱۱۵۰ °C. This enhanced sintering efficiency is attributed to the superior microstructural homogeneity of gel-cast green bodies, whose fine and interconnected pore network provides higher capillary driving forces and more efficient mass transport during viscous sintering. In contrast, heterogeneous particle packing in dry-pressed compacts produced isolated pores that impeded densification. Flexural strength increased with sintering temperature but decreased with higher polymer content due to residual porosity formed during burnout. The maximum strength (~۸۵ MPa) was observed for gel-cast specimens sintered at ۱۲۵۰ °C, while a subsequent drop in ۱۳۰۰ °C corresponded to extensive cristobalite crystallization, as confirmed by XRD and SEM. Crystallization induced microcracking and limited further densification. These results demonstrate that microstructural uniformity is more critical than initial green density for achieving dense, high-strength fused silica. Gel casting thus represents a superior forming technique for producing defect-free amorphous silica ceramics below the cristobalite formation threshold.

کلیدواژه ها:

Sintering ، Densification ، Gel Casting ، Fused silica ، Cristobalite