Structure tailoring of alkoxide silica

This study examines the influence of pH in the starting sol on the structure of alkoxide derived silica. The relative rates of hydrolysis and condensation of the alkoxide were altered by pH which yielded materials with different microstructure, stability and sintering behavior. Structural evolution of alkoxide silica during densification was followed in situ by photoacoustic Fourier-transform infrared spectroscopy (PAS). The acid-catalyzed silica gels contained a larger amount of adsorbed water and alcohol than the base-catalyzed gels/precipitates. Hydrogen-bonded surface species in acid-catalyzed gels were removed easily, allowing this material to be densified at 800°C. Although base-catalyzed gels had less hydrogenbonded silanol groups in the green state, it consisted of free silanol groups which maintained a high gel surface area and indicated little sintering below 1000°C.