Effect of neodymium oxide on the solubility of MoO3 in an aluminoborosilicate glass

High molybdenum and rare earth concentrations in soda–lime aluminoborosilicate glasses may lead to the crystallization of molybdenum-rich phases such as alkali and alkaline-earth molybdates (Na2MoO4, CaMoO4) and also rare earth (RE)-rich phases such as apatite (Ca2RE8(SiO4)6O2) during melt cooling that must be controlled particularly during the preparation of highly radioactive nuclear glassy wasteforms. To understand the effect of neodymium addition (from 0 to 16 wt.% Nd2O3) on the phase separation and the crystallization tendency of molydbate phases and on the structure of a Mo-bearing nuclear glass belonging to the SiO2–B2O3–Al2O3–Na2O–CaO–MoO3 system, crystallization and structural studies have been performed by X-ray diffraction, scanning electron microscopy, electron microprobe analysis, Raman and optical absorption spectroscopies. The results obtained show that the addition of an increasing amount of Nd2O3 induces a significant increase of the solubility of molybdenum in the glass, characterized by a decrease of the phase separation and of the crystallization tendency of molybdate phases. The increase of chemical disorder in the structure of Mo-bearing glasses when Nd2O3 is added – and more precisely in the depolymerized regions where Nd3+ cations and [MoO4]2− entities are located – could be at the origin of the evolution of the molybdenum solubility in the glass.

Research Highlights
► Crystallization of molybdenum-rich and rare earth-rich phases in nuclear glasses.
► Effect of neodymium addition on the crystallization of molybdate phases.
► Effect of neodymium addition on the glass structure.
► Neodymium oxide improves the solubility of molybdenum in the glass.
► Neodymium has a dispersing effect on the molybdate units in the glass.