Equilibrium Compressibilities and Density Fluctuations in K₂O–SiO₂ Glasses

Abstract

The density fluctuations contributing to light scattering in a glass are governed by the fictive temperature of the glass and the equilibrium compressibility of the melt. Using ultrasonic velocity data for KzO-Si02 melts, these compressibilities were evaluated, and the magnitude of the density fluctuations were calculated. In this system, the mean-square amplitude of the fluctuations ,reaches a minimum value (about half that of pure SiO,) for a composition of ~2 0 mol% KzO. By extrapolating the equilibrium compressibilities to zero K20 content, the density fluctuations can be calculated for pure SiOz glass; this calculation agrees well with the result obtained from lightscattering measurements.

Structural relaxation in silicate melts and non-Newtonian melt rheology in geologic processes

“…There now exist a number of studies of physical properties of silicate melts that demonstrate a frequency-or strain-rate dependence of the observed property (e.g., acoustic velocities, Laberge et al 1973, Sato and Manghnani 1985, Rivers and Carmichael 1987: viscosity, Li and Uhlmann 1970, Simmons et al 1982. In these studies the timescale of relaxation (or response) of the silicate melt structure is similar in magnitude to, or longer than, the timescale of observation and the observed properties correspond to an unrelaxed state.…”

“…Also, an extensive data set can be extracted from the ultrasonic data on silicate melts (e.g., Laberge et al 1973, Rai et al 1981, Sato and Manghnani 1985, Rivers and Carmichael 1987. Most such studies report the longitudinal viscosity and modulus of liquids.…”

Inhomogeneous structure of inorganic glasses studied by Rayleigh, Mandel'shtam-Brillouin, Raman scattering spectroscopy, and acoustic methods

“…Percentage of CSG can be found through processing of Raman scattering spectra of glasses with variable glass former/modifier percentage ratio by Walles-Katz and Martens technique [16,17]. Concentrations of CSGs can be estimated through mass balance equation if intensities of PSCs and their specific scattering cross-sections (or molar extinction in the case of IR absorption spectra) are known [18].…”

Density fluctuations in oxide glasses investigated by small-angle X-ray scattering

“…In a glass, the description has to take into account that part of the fluctuations that are frozen in at the glass transition. Several descriptions have been proposed (Weinberg, 1963;Wendorff & Fischer, 1973;Laberge et al, 1973;Roe & Curro, 1983;Curro & Roe, 1984;Wright et al, 2005). We followed that of Laberge (Laberge et al, 1973), which assumes that the fluctuations not frozen in below the glass transition arise from long-wavelength propagating vibrational modes due to high-frequency longitudinal phonons.…”