HydrationEffects on the Structural and VibrationalProperties of Yttrium Aluminosilicate Glasses for in Situ Radiotherapy.

The performances of silicate glassesas containment matrices orvectors of radioactive ions in nuclear waste storage and in situ radiotherapyare influenced by the effect of interstitial water on the glass durability.In order to assess how hydration determines changes to atomistic structuralfeatures which control the glass degradation, we have carried outmolecular dynamics simulations of a typical yttrium aluminosilicate(YAS) glass employed in radiotherapy, incorporating different watercontents. The analysis of the models allows us to discuss the wayin which hydroxyl groups are distributed in the glass structure andmodify or disrupt the aluminosilicate glass network. Hydration affectsthe silicate and aluminate connectivity to a different extent, resultingin a different degree of disruption (depolymerization) of the Si andAl network. The simulations also highlight a strong tendency of allhydrated compositions to form Y3+- and OH–-rich domains, separated from the aluminosilicate matrix. The implicationsof these structural effects for the durability and ion release behaviorof the glass are discussed, as well as the vibrational signaturesof the various hydrous species identified in the models. [ABSTRACT FROM AUTHOR]