Structural Relaxations in Alkali Silicate Systems by Brillouin Light Scattering

The Brillouin light scattering technique was used to investigate the viscoelastic relaxations in alkali silicate systems up to temperatures of 1500°C. The line shape analysis of the Brillouin spectra reveals information about the mechanical rigidity and the viscous dissipation in the scattering medium. Brillouin frequency shifts and the frequency-dependent viscosity coefficients, v ' were measured as a function of temperature. The shapes of the v ' vs temperature curves, and the location of their maxima on the temperature scale, reveal the activation energies and the resonance frequencies of the underlying mechanisms. In binary alkali silicates, small dissipation maxima were observed between the glass transition and the melting temperature, which are attributed to the increased cation mobility as a result of the accelerated disintegration of the silica networks. In mixed alkali systems, multiple dissipation maxima are observed. These are spread over a range of temperatures, which are distinctly higher than in binary systems.