Abstract:
Raman spectra were collected for barium silicate, strontium silicate and calcium silicate melts at temperatures ranging from the glass transition region to temperatures as high as 1600°C. For melts less polymrized than disilicate, the spectra were used to determine the relative abundances of the Q3, Q2 and Q1 tetrahedra and the Si2O2-5, SiO2-3 and Si2O6-77 structural units in the melts. A concentration constant was computed for the reaction: 4SiO2-3 # Si2O2-5 + Si2O6-7 and was found to vary with composition from approximately log10 Kc = 0.5 for barium silicate melts with NBO/Si = 1.143 to log10 Kc = -1.75 for calcium metasilicate melts with NBO/Si = 2. Little difference was found to exist in the structural behavior of the melts on the three alkaline-earth silicate binary joins. Activity coefficients were computed for the SiO2-3 structural unit as a function of bulk composition. The logarithm of the activity coefficients and mole fraction of the structural unit are linearly correlated.