The influence of Mo sources, concentrations and the content of Na2O on the tendency of devitrification of modified R7T7 borosilicate glasses

Abstract

Referring to the R7T7 nuclear waste glass, borosilicate glasses with extra addition of 0.75 and 1.5 mol% MoO3 and with varied contents Na2O were prepared. The samples were examined by XRD, SEM and Raman spectroscopy to identify the devitrification tendency of the glasses during either the cooling or the re-heating process. The results indicate that Raman spectra demonstrated the crystallization of CaMoO4 in glasses which was not detectable by XRD. It is shown that the samples with 0.75 mol% of MoO3 exhibited phase separation during cooling and slightly devitrified upon heating. In contrast, the samples with 1.5 mol% of MoO3 already crystallized as prepared. This trend only depended on the Mo-concentration rather than the Mo-sources. In addition, when the total content of (Na2O+CaO) was kept constant, the crystallization of CaMoO4 was observed when the content of Na2O varied from 5.8 mol% to 9 mol%.