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

Abstract

Using niobium crucibles for melting phosphate and silicate glasses of various modifier oxide contents, and therefore varying optical basicity (Λ), was found to result in varying dissolution rates of niobate during melting.Because of their high electronic polarizability, even small concentrations of niobates are detectable in the Raman spectra of glasses. Even less than 1 mol% Nb 2 O 5 can be identified, as independently confirmed by SEM-EDX analysis. Silica-rich glasses (~60 % SiO 2, Λ~0.6) did not show significant Nb dissolution from the crucible, while higher basicity metasilicate glasses (~ 50% SiO 2, Λ~0.65) and pyrophosphate glasses (~30% P 2 O 5 , Λ~0.7) did show the typical niobate signature in the Raman spectra at 810-840 cm -1 , depending on composition. While niobium is well dissolved throughout the pyrophosphate glass, metasilicate glasses showed a much more intense Raman signature of niobate units near the outer surface of the glass. Measurements along the cross section of a fractured metasilicate glass showed a steady decrease of the strength of the niobate signature from the surface toward the bulk of the material.Besides correlation with optical basicity, the tendency of melts to dissolve Nb crucible was discussed in terms of the connectivity or polymerization of the network and the corresponding melt viscosity.

Second‐harmonic generation and structural rearrangements in multicomponent antimonite glasses by electrothermal poling

“…It is noted that due to the size of Li, EDX‐SEM is unable to quantify Li 2 O. SiO 2 is detected in all glasses due to crucible dissolution 45 . Crucible dissolution is a common phenomenon when glasses are melted in silica, 46 alumina, 47 or niobium 48 crucibles and so typically platinum is ideally used 47,49 ; but antimonite batches easily react with Pt crucibles in which Sb may alloy into Pt, damaging the crucible. In glasses where all batched elements are detectable, there is a positive correlation observed between PbO content and SiO 2 content.…”

Elucidating photoluminescent properties of Eu‐doped Ca–Al–Si–O(–N) glasses and the local structures of Eu ions

“…However, in the NE-series, the Eu site is introduced to a higher symmetry, even when the samples are doped analogous to the E-series, which could be attributed to the difference in optical basicity between the oxynitride and oxide glasses. The incorporation of nitrogen increases the optical basicity, 36,37 eliminating the need for Eu 2+ ions to function as network modifiers in low-Eu content glasses. The Eu site might exhibit a larger nephelauxetic effect in the NE-series, than that in the E-series, resulting in a shift to longer PL peak wavelengths.…”

Mechanism of hopping conduction in Be–Fe–Al–Te–O semiconducting glasses and glass–ceramics

“…Optical basicity, K, is a parameter that often correlates with the level of depolymerization of a conventional glass network where it will be higher as more non-bridging oxygen atoms and ionic bonds occur than for a more polymerized network with covalent bridging bonds between oxygen and network former atoms [24]. In our previous paper [25], we have shown a correlation between glass basicity calculated on the basis of the glass composition and its role on niobate dissolution from the crucible. Therefore, we examine here the presence of a similar dependence between optical basicity and Al dissolution from the crucible.…”