Effect of solid loading on phase composition, microstructure, mechanical and dielectric properties of fused silica ceramics by gecasting

Abstract

In this study, the fused silica slurries with an ultra-high solid loading of 85 vol%, low viscosity of 0.34 Pa s at 99.4 s−1, and good suspension stability were successfully prepared using two-gradation fused silica raw powders by optimizing the preparation processes. Owing to the inherent characteristics of gelcasting and good dispersion stability of resulting fused silica slurries, all the fused silica ceramics prepared with various solid loadings exhibited a homogeneous bimodal size distribution microstructure after pressureless sintering at 1250 °C for 4 h. Furthermore, a small amount of nanoscale cristobalite was precipitated from fused silica, and solid loading had no significant effect on the crystallization kinetics of cristobalite. A significant increase in solid loading effectively facilitated the densification of fused silica ceramics, enhanced bulk density, decreased sintering shrinkage, and strengthened mechanical properties. However, the increase in solid loading deteriorated dielectric properties within the range of 2–18 GHz. When the solid loading was 85 vol%, the bulk density, linear shrinkage, flexural strength, dielectric constant, and dielectric loss tangent were 2.12 g/cm3, 1.1 %, 72.3 MPa, 3.91–4.36, 0.0081–0.0171, respectively. These properties were favorable making the materials potential applications in the field of microwave transmission.