Thermal evolution and densification of R2O-SiO2 gels

Abstract

R2O-SiO2 materials were prepared with 5 mol% of alkaline oxide by the sol-gel method. The gel-glass transition was achieved by treatment in air or in a controlled atmosphere. The samples present a silica network structure to which the alkaline ions are incorporated in a different way as compared to that of conventional glass. Material densification sets in around 350° C. In the temperature range between 500 and 600° C silica devitrification are produced together with condensation-polymerization of many silanol groups which form part of the material. Densification treatments in a helium atmosphere eliminate these residual groups.