Effect of silicate structure on thermodynamic properties of calcium silicate melts: Quantitative analysis of Raman spectra

Abstract

The distribution of silicate anionic species (Q(n) units, n=0, 1, 2, 3) and the chemical speciation of oxygen in CaO-SiO2-MO (M=Mn and Mg) slags were investigated by micro-Raman spectroscopic analysis. Furthermore, the thermochemical properties were evaluated using a concentration of free oxygen and a degree of polymerization. A good linear relationship was obtained between sulfide capacity and concentration of free oxygen in the CaO-SiO2 (-MnO) melts at 1500 to 1600 A degrees C. However, even though there was more abundant free oxygen in the CaO-SiO2-MgO system than in the CaO-SiO2 system, the sulfide capacity of the former was lower than the latter, indicating that the sulfur dissolution behavior in the silicate melts cannot be simply explained by the content of free oxygen, because the composition dependency of the stability ratio of oxygen and sulfide ions should be taken into account. The excess free energy of CaO, MgO and MnO linearly decreased as the ln (Q(3)/Q(2)) increased. The effect of the degree of polymerization on the excess free energy of mixing of MgO-containing slag was larger than that of MnO-containing slag, which was explained by the difference of the ionization potential between Mn2+ and Mg2+ ions.