Structure of Na2O–SiO2 melt as a function of composition: In situ Raman spectroscopic study

The structure of x%Na2O·(100−x)%SiO2 glasses and melts (x=33, 40, 50, 55, 60, 67) was studied by in-situ Raman spectroscopy at temperatures from 293 to 1462K. The curve-fitting procedure was applied for data analysis taking into account the second coordination sphere of Si atoms. To obtain a correct interpretation of all bands in Raman spectra, additional types of structural units Q12, Q21 and Q32 were introduced into a description of the glass and melt structures. The conversion coefficients from characteristic Raman bands to concentrations of the corresponding structural units a3=1, a2=1.26, a1=1.53 and a0=2.56 are allowed in the determination of Qn-abundance in sodium silicate melts in the range from 0 to 67mol% Na2O. From these data the dependence of the equilibrium constants kn of the reactions 2Qn↔Qn−1+Qn+1 was determined. It was found that equilibrium constants for di- and metasilicate glasses, k3=0.015 and k2=0.07 are in close agreement with NMR studies. The k3 and k2 increase with increasing temperature up to 0.046 at 1243K and 0.14 at 1462K, respectively, which indicates an increase of the system disorder. The equilibrium constant of the reaction 2Q1↔Q2+Q0 was found to be 0.13±0.03. •We present systematic investigation of sodium silicate melts from O to 67mol% Na2O by in-situ Raman spectroscopy.•We used a curve-fitting procedure taking into account the second coordination sphere of Si atoms.•The conversion coefficients from characteristic Raman bands to concentrations of structural units were calculated.•Qn-abundance in sodium silicate melts in the range from 0 to 67mol% Na2O was determined.•The equilibrium constants kn of the reactions 2Qn↔Qn−1+Qn+1 were determined.