Structural Evolution of Colloidal Silica Gels to Glass

The gel-to-ceramic evolution of colloidal-derived silica gels was examined by thermal analysis, infrared photoacoustic spectroscopy, physical characterization, and high-temperature calorimetry. Oxygen in the firing atmosphere promoted sintering of colloidal gels relative to firing in a nitrogen or argon atmosphere. Water vapor in the atmosphere promoted consolidation and crystallization to cristobalite. Addition of PVA to the colloidal gel resulted in consolidation and crystallization of the gel at 1000°C, ∼150°C less than gels without the PVA binder. The enthalpy of consolidation of the gels to fused silica glass was approximately − 10 kJ/mol, primarily due to reduction of surface area.