Effect of heat treatment on the high-purity silica glass prepared from amorphous and crystalline powders by small angle X-ray scattering

High-purity silica glass prepared from high-purity amorphous and crystallin e powders by flame fusion and sintering at high temperatures in vacuum, was heat-treated at 1250 degrees C for several periods of time and its structu re was studied using the small-angle X-ray scattering technique. As a resul t, the structure of silica glass was dependent on its thermal history. The structure of as-fused silica glass samples prepared by flame fusion appeare d to be quite similar, even though raw materials with different degrees of homogeneity were used. However, the structure of silica glass behaved diffe rently after heat treatment. This different response of the structure of si lica glass to heat treatment was analyzed in terms of impurity content and viscosity.