Caesium volatilisation in borosilicate glasses: a multinuclear magnetic resonance study

The evaporation of Cs from caesium borosilicate glasses With variable melting times has been quantified using inductively coupled plasma optical emission spectroscopy and Cs-133 NMR spin echo intensities. Caesium is shown to be lost as an oxide or in elemental form, not as a borate or silicate compound. The composition change is associated With a decrease in the fraction of four-coordinated boron, as measured by B-11 MAS NMR, and regular changes in the Cs-133 NMR peak position. Distinct behaviour of the two tetrahedral boron NMR peaks suggests that some degree of phase separation may also occur after long heating times. These results on a simplified model for a nuclear waste glass show that NMR can play a role in determining structural changes due to elemental volatility, and provide valuable information on Which solutions to this problem may be based.