Microstructural Analysis of a Glass Dedicated to the Radioactive Waste Confinement by Raman and FTIR Spectroscopy

This study deals with the structural changes occurring in a Mo-reach glass dedicated to the confinement of Mo-reach radioactive waste that contains different contents of Cs₂O oxide, ranging from 0.3 to 0.6 wt.%. The glass synthesis was carried out by the double melting method at 1380°C, followed by a stage of 2 h at 600°C. Neodymium was an actinide simulator. The glasses were characterized by their physical and microstructural properties using different spectroscopic techniques. As the experiment shows, the glass geometrical density varies between 1.96 and 2.75g/cm³. X-ray diffraction (XRD) analysis shows amorphous features, with traces of crystalline germs, identified as the CaMoO4 powellite phase, which probably formed during glass cooling. Fourier transform infra-red (FTIR) analysis reveals the main chemical bounds in the glasses: Si-O-Si and O-Si-O in SiO₄, B-O-B in BO₃, and Al-O-Al in AlO₄. The addition of Cs₂O raises the rate of polymerization in the glass network and then decreases the number of no-bridged oxygens (NBO). Raman spectroscopic analysis reveals the absorption bands of MoO₄^2– in CaMoO₄. It shows that the Mo environment is altered by the addition of increasing contents of Cs₂O in the glass. This is evidenced by the absorption bands shifts at 319, 792, and 844 cm^–1. The absorption band located at 700 cm^–1, ascribed to the elongation of SiO₄ and AlO₄, is attenuated for 0.4 and 0.6% of the Cs₂O content. It shifts to 680–900 cm^–1 due to the glass high Mo content but increases in intensity with the Cs₂O content, thus disturbing the alkali positions of Ca and Na, with Cs remaining soluble in the glass. One can conclude that a little rise in the Cs₂O content inhibits the phase separation of both Na and Ca molybdates. The glasses analyses do not show particular changes in the lanthanide valences, which are probably in a +III oxidation state. The addition of Cs₂O in this kind of glass network remains an issue with respect to the coherence of its microstructure. However, about 0.6 wt.% of Cs₂O has been incorporated in the glass network, with no Cs₂O phases segregation.

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