Malik, J; (2014) Computational modelling of hydrated yttrium-containing silicate glasses for in situ radiotherapy. Doctoral thesis , UCL (University College London).

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Abstract

The application of yttrium-based glasses as radionuclide vectors for in situ radiotherapy relies on the durability of the glass in a physiological system: leaching of activated 90Y ions from the glass matrix into the bloodstream should be minimised as much as possible immediately after injection and before their radioactive decay. In order to understand the relationship between glass composition, structure and durability at an atomistic level, classical molecular dynamics simulations were carried out on different yttrium-containing silicate-based glass compositions, specifically three yttrium aluminosilicate glasses: YAS17, 24 and 30, where 17, 24 and 30 denote the molar % of yttrium, as well as yttrium-containing bioglass (YBG) with and without the presence of phosphorus. Each of the glass compositions listed were hydrated at three levels of included water content. The present simulations primarily aim at understanding how different water content influences the bulk structural features critical for the glass durability, such as the network connectivity and nanosegregation. The dry yttrium glasses were thus hydrated with increasing water amounts, and the analysis of the structures has highlighted marked hydration effects on network-former and network-modifier coordination, as well as on the preferential aggregation of yttrium ions, regulated by surrounding OH groups. Hydration of YAS (with increasing yttria content) and YBG (with and without phosphorus) is shown to increase glass durability through strengthening of the silicate network, which is important for the durability of such glasses in radiotherapy applications. Hydroxyl groups have been found to have a preference to coordinate more towards network modifiers than network formers, which is common to both YAS (with increasing yttria content) and YBG (with and without phosphorus). Other results are also discussed, mainly in the context of the physico-chemical characteristics which make yttrium glasses suitable for in situ radiotherapy.

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