Effect of neodymium oxide on the solubility of MoO 3 in an aluminoborosilicate glass

Abstract

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 (Na 2MoO 4, CaMoO 4) and also rare earth (RE)-rich phases such as apatite (Ca 2RE 8(SiO 4) 6O 2) 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.% Nd 2O 3) on the phase separation and the crystallization tendency of molydbate phases and on the structure of a Mo-bearing nuclear glass belonging to the SiO 2–B 2O 3–Al 2O 3–Na 2O–CaO–MoO 3 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 Nd 2O 3 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 Nd 2O 3 is added – and more precisely in the depolymerized regions where Nd 3+ cations and [MoO 4] 2− entities are located – could be at the origin of the evolution of the molybdenum solubility in the glass.