Influence of Dehydration/Sintering Conditions on the Distribution of Impurities in Sol-Gel Derived Silica Glass

Use of commercial fumed silica as the starting material for preparation of optical waveguides by sol-gel techniques has been viewed with skepticism. Impurity levels in this material, especially those of transition metal oxides, are too high for waveguide applications. However, we find that during dehydration/consolidation in an atmosphere of CL sub 2 and He from which O sub 2 is excluded that most impurities will be removed as a volatile chloride.