Niobate in silicate and phosphate glasses: Effect of glass basicity on crucible dissolution

Using niobium crucibles for melting phosphate and silicate glasses of various modifier oxide contents, therefore varying optical basicity (?), was found to result in dissolution rates niobate during melting. Because their high electronic polarizability, even small concentrations niobates are detectable the Raman spectra glasses. Even <1 mol% Nb2O5 can be identified, as independently confirmed by SEM-EDX analysis. Silica-rich (~60% SiO2, ? ~0.6) did not show significant Nb from crucible, while higher metasilicate (~50% ~0.65) pyrophosphate (~30% P2O5, ~0.7) typical signature at 810–840 cm?1, depending on composition. While is well-dissolved throughout glass, showed a much more intense units near outer surface glass. Measurements along cross-section fractured glass steady decrease strength toward bulk material. Besides correlation with basicity, tendency melts dissolve crucible discussed terms connectivity or polymerization network corresponding melt viscosity.