فهرست نشریات علمی دسترسی آزاد ایران

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 58 wt.% solids, whereas dry-pressed compacts were produced at 100 MPa. All specimens were sintered in air between 1100 °C and 1300 °C for 5 h. Dilatometric analysis revealed distinct densification characteristics for the two forming methods. Despite their lower initial green density (~30–33% of theoretical), gel-cast bodies exhibited faster and more complete shrinkage than dry-pressed samples (~57–60% of theoretical), achieving near-full densification above 1150 °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 (~85 MPa) was observed for gel-cast specimens sintered at 1250 °C, while a subsequent drop in 1300 °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.