Viscosity of silica glass prepared from sol–gel powder

The viscosity of silica glass prepared from sol–gel powders was investigated in the temperature range from 1350 to 1500 °C regarding Al doping effects. The viscosity had a peak as a function of Al concentration. The viscosity also depended on the doping method due to the homogeneity of the Al distribution in silica glass. When comparing viscosities at Al concentrations of 10 wt ppm or less, the highest viscosity was obtained for a sample in which Al was introduced with an acetylacetonate complex in the sol–gel process. This viscosity was followed by that for a specimen in which Al doping was accomplished by infiltration of dried gel with an Al nitrate solution and that found for a sample composed of a blend of Al doped and undoped powders. Furthermore, the viscosity of the acetylacetonate-doped material was higher than that of natural quartz glass (NQG) containing Al in a comparable concentration. The activation energies of this material and NQG were higher than that of undoped synthetic silica glass (SQG) in the measured temperature range. It was also found that Al decreased the concentration of OH (hydroxyl) and increased the amount of oxygen deficient defects associated with an emission band of 280 nm in the photoluminescence spectra.