The effect of Cs2O additions on HLW wasteform glasses

Physical parameters and structural characteristics are reported for the mixed alkali borosilicate glass system, xCs2O(100 − x)(MW) (0 ⩽ x ⩽ 9.66) where MW is the BNFL wasteform glass (10.29 mol% Li2O, 10.53 mol% Na2O, 18.57 mol% B2O3, 60.61 mol% SiO2). Glass density was found to increase with x whilst the glass transition temperature (Tg) decreased. The fraction of four-coordinated boron (N4) determined from 11B magic angle spinning nuclear magnetic resonance (MAS NMR) increased with x in a manner consistent with previous reports on the sodium–lithium–borosilicate system and contrary to the Dell model. 29Si MAS NMR was used to identify the fraction of Q4 (B) and Q3 units as a function of x. Raman spectra indicated the presence of reedmergnerite and danburite superstructural units. Mass loss measurements showed a non-linear variation with x, having a maximum between 7 and 8 mol% Cs2O and a correlation was found between the amount of Q3 units in the solid and the volatilization loss from the melt.