Porous silica ceramics with closed-cell structure prepared by inactive hollow spheres for heat insulation

摘要

Highly porous silica ceramics (PSCs) with closed-cell structure are fabricated via sintering of randomly packed hollow SiO2 spheres (HSSs), and the influences of sintering parameters, additives and physical features of HSSs on the structure and performance of prepared PSCs are discussed. The results show that the hollow structure of SiO2 spheres is reserved during the sintering process due to its low-activated shells and the sintered necks are finely formed among the hollow spheres, which results in both high porosity and superior strength of final products and thus meets the needs of heat shielding materials. In addition, the optimized PSCs are synthesized with sintering temperature of 1200-1250 degrees C and additive of 4 wt.% H3BO3 combining 6 wt.% Al2O3, and the increase of closed porosity of PSCs brings in the enhanced thermal shielding effect while the strength degrades. Furthermore, the structure analysis reveals that decreased cristobalite phase in the PSCs reduces the glass viscosity and increases the packing density of HSSs, which also prefers to enhance the mechanical strength and thermal insulation. As a result, thermal conductivity of about 0.102-0.218 W/(m.k) and compressive strength of 3.2-14 MPa are obtained in our synthesized products. (C) 2015 Elsevier B.V. All rights reserved.