Effect of Molybdenum on the Structure and on the Crystallization of SiO ₂ –Na ₂ O–CaO–B ₂ O ₃ Glasses

Abstract

Crystallization of the poorly durable Na 2 MoO 4 phase able to incorporate radioactive cesium must be avoided in SiO 2 –Al 2 O 3 –B 2 O 3 –Na 2 O–CaO glasses developed for the immobilization of Mo‐rich nuclear wastes. Increasing amounts of B 2 O 3 and MoO 3 were added to a SiO 2 –Na 2 O–CaO glass, and crystallization tendency was studied. Na 2 MoO 4 crystallization tendency decreased with the increase of B 2 O 3 concentration whereas the tendency of CaMoO 4 to crystallize increased due to preferential charge compensation of BO 4 − entities by Na + ions. 29 Si MAS NMR showed that molybdenum acts as a reticulating agent in glass structure. Trivalent actinides surrogate (Nd 3+ ) were shown to enter into CaMoO 4 crystals formed in glasses.