MoO 3 is one of the challenging oxides in nuclear waste vitrification in the UK. It has a poor solubility in the conventionally used nuclear waste glasses and its excess presence may cause the formation of "yellow phase" which is highly detrimental to vitrification process. This work investigates the compositional dependence of MoO 3 solubility in borosilicate glasses with varying alkaline earth species as well as the effects of MoO 3 addition on glass structure and properties. Among all alkaline earths Ca is the best in terms of MoO 3 solubility, with 2.84 mol% in calcium borosilicate glass (CBS) without causing any visible phase separation. Magnesium borosilicate glass (MBS) has the lowest MoO 3 solubility (≤1 mol%). XRD results indicate that, while the visibly homogeneous glasses all remain amorphous nature, the visibly heterogeneous glasses contain tiny molybdate crystals. According to SEM results, the separated particles forming within glass matrices are mostly spherical, submicron in diameter and randomly dispersed; the size of these particles are dependent on the extent to which MoO 3 addition is excessive. Compositional analysis for separated phases in CBS glass with excess MoO 3 suggests that the phases are rich in Mo and Ca, while TEM results prove the crystallinity of separated particles whose electron diffraction patterns are in accordance with those of CaMoO 4 . Two Raman bands are observed due to addition of MoO 3 in glass; the bands are assigned tobending and stretching vibrations of MoO 4 2- and their intensities increase with MoO 3 addition. The positions of these bands shift with alkaline earth species in glass, indicating that the local environment of MoO 4 2- is closely associated with alkaline earth cations in glass network. MoO 3 addition to glass also results in decreased glass transition temperature T g , which suggests a depolymerized network due to MoO 4 2- incorporation. Glass density is increased with the increase amount of MoO 3 in glass as long as the glass remains homogeneous.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)