Room temperature Raman spectroscopy and 29Si MAS NMR combined with high temperature Raman spectroscopy and DFT calculation of xMgO-(1-x)CaO–SiO2 glasses and melts

Abstract

In order to study the effect of MgO on the microstructure and macroscopic thermos-physical properties of calcium silicate melt, quantitative analysis of the various silicon-oxygen Q i species in magnesium-calcium silicate glasses and melts at a constant alkalinity has been performed by in-situ high temperature Raman spectroscopy, 29 Si MAS NMR and DFT (Density Functional Theory) calculation. Several cluster models, probably existed in magnesium-calcium silicate glasses and melts, modified by Ca 2+ or Mg 2+ have been designed, their Raman vibrational modes and scattering activities were thus simulated and calculated. A function correlating the wavenumbers of Si-O nb (non-bridge oxygen) of various SiOTs (silicon-oxygen tetrahedrons) with their RSCS (Raman scattering cross sections) was constructed and used to calibrate the experimental Raman spectra. The abundance of each primary Q i species of various magnesium-calcium silicate glasses can be composed by all the deconvoluted hyperfine peaks within the same Q i species. The quantitative description for glasses was proven to be consistent with the result from 29 Si MAS NMR. Thus, Q i species distributions for melts were also quantitatively derived. It demonstrated that the abundances of Q 1 and Q 3 species increased while Q 2 species decreased with the increasing replacing amount of MgO. The relationship between the viscosity and Q i species distributions as well as different cations has been investigated and correlated. Q 3 species was predominantly responsible for the contribution of viscosity of melt.