Incorporation limit of MoO₃ in sodium borosilicate glasses

Abstract

Optimizing the concentration of molybdenum incorporated in a borosilicate glass matrix is essential in the vitrification of high‐level radioactive waste. However, the incorporation limit of MoO3 in fundamental borosilicate systems has been rarely correlated with the local structure of the molybdenum cations. This study investigates the variations in the incorporation limit of MoO3 in ternary sodium borosilicate glass upon varying the B2O3/(SiO2 + B2O3) ratio (i.e., B). The incorporation limit of MoO3 was less than 3 mol% in the low‐B region (B < 0.7), where molybdenum cations mainly existed as [MoO4]2−. However, when B was higher than 0.85, the incorporation limit was higher than 6 mol%, and the Raman spectra indicated the presence of octahedrally coordinated molybdenum cations, essential to stabilize the Mo–O–Mo linkage. The variation in the local structure of molybdenum cations can be explained by the available amount of non‐framework cations compensating for the negative charge near [MoO4]2−. These results allow the development of glass compositions with a high incorporation limit of MoO3 simply by controlling the local structure near the molybdenum cations.

Effect of calcium and potassium oxide addition on the viscosity and fragility of a calcium aluminosilicate melt

“…Raman spectra of the samples were obtained using a micro‐Raman spectrometer (XploRA, Horiba) equipped with a green Ar‐ion laser (532 nm). Raman scattering was performed four times with an exposure time of 100 s in the wavenumber range of 25–1500 cm −1 , and the intensities of the obtained spectra were normalized relative to their integrated intensities 36 . To characterize the detailed compositional dependence of the Raman spectra in the range of 200–1200 cm −1 , the effect of the temperature and excitation line on the normalized intensity ($${I}_{{\mathrm{normalized}}}$$) was corrected by the following equation 37 : $$$$\begin{equation}{I}_{{\mathrm{corrected}}} = {I}_{{\mathrm{normalized}}} \cdot \left\{ {\nu _0^3 \cdot \nu \cdot \frac{{\left[ {1 - {\mathrm{exp}}\left( { - hc\nu /kT} \right)} \right]}}{{{{\left( {{\nu }_0 - \nu } \right)}}^4}}} \right\}\end{equation}$$$$where $$h$$ ( = $$6.62607 \times {10}^{ - 34}$$ J s) is the Planck constant, $$k$$ ( = $$1.38065 \times {10}^{ - 23}$$ J K −1 ) is the Boltzmann constant, c ( = $$2.9979 \times {10}^{10}$$ cm s −1 ) is the speed of light, T is the absolute temperature, $${\nu }_0$$ is the wavenumber of the incident laser light (10 7 /532), and $$\nu $$ is the measured wavenumber in cm −1 .…”

“…Raman scattering was performed four times with an exposure time of 100 s in the wavenumber range of 25-1500 cm −1 , and the intensities of the obtained spectra were normalized relative to their integrated intensities. 36 To characterize the detailed compositional dependence of the Raman spectra in the range of 200-1200 cm −1 , the effect of the temperature and excitation line on the normalized intensity (𝐼 normalized ) was corrected by the following equation 37 :…”