Phosphate based glasses weathering : a solid state NMR investigation…



Phosphate based glasses find widespread applications like water softener (Na2O–P2O5), fertilizer (K2O-CaO-MgO-P2O5), sealing glasses (B2O3-P2O5) or immobilisation matrix for the storage of nuclear waste (Al2O3/Fe2O3-P2O5). All these applications are governed by the interaction between the phosphate glasses and water. Indeed, a controlled dissolution is necessary in case of water softener or fertilizer whereas a complete lack of reactivity is required for the sealing or the radioactive waste confinement matrix applications. It appears thus crucial to monitor the weathering mechanism of this kind of material and we will show in this communication that solid state NMR is a technique of choice to investigate the reactivity between water and phosphate glasses. In a first step, the weathering of a simple phosphate glass (50Na2O-50P2O5) has been investigated by 1D 31P, 1H and 17O MAS-NMR and new insights on structural changes and the underlying mechanisms induced by the hydration were obtained. In a second step, we focused on the weathering of a more complex glass composition (K2O-Al2O3-P2O5). 1D and 2D 31P/27Al correlation MAS-NMR help us to understand how Al2O3 is inserted in the glass network and how it improves the stability of the material.