Thermodynamic model and high-temperature Raman spectra of 25Na 2 O·75B 2 O 3 glassforming melts

The temperature dependence of Raman spectra of 25Na2O·75B2O3 melts recorded in the temperature range 321–1142 °C was studied by statistical methods (principal component analysis, PCA, and multivariate curve resolution, MCR) and by the thermodynamic model of Shakhmatkin and Vedishcheva. The PCA of thermally corrected spectra resulted in two independent components. Four components with not negligible abundance were found by the thermodynamic model in the studied temperature range (Na2O·B2O3, Na2O·2B2O3, Na2O·3B2O3, and Na2O·4B2O3). The temperature dependence of Na2O·2B2O3 equilibrium molar amount reaches maximum at ≈670 °C with very low molar amount (0.064 mol). The strong positive correlation was found between the equilibrium molar amounts of Na2O·B2O3 and Na2O·4B2O3. The Malfait spectral decomposition was performed by considering Na2O·3B2O3 and Na2O·4B2O3 as independent system components. The obtained partial Raman spectra correspond to the linear combination of particular Raman spectra of system components, i.e. Na2O·3B2O3 with small admixture of Na2O·2B2O3 for the first partial Raman spectrum and Na2O·4B2O3 with significant admixture of Na2O·B2O3 and with small admixture of Na2O·2B2O3 for the second partial Raman spectrum. The MCR analysis performed for two components resulted in loadings that were practically identical with partial Raman spectra obtained by Malfait decomposition. Both the MCR and the Malfait decomposition reproduced the experimental Raman spectra very well—on the level of experimental error. This result is considered as an example that the correctness of thermodynamic model can be validated by the analysis of temperature dependence of Raman spectra obtained for single glass composition.