Structural Features of Sodium Ultraphosphate Glasses Doped with Al2O3

Abstract

The Al₂O₃ substitution for Na₂O, up to 17 mol %, on the glass formation, structural features of a series of sodium ultraphosphate glasses for nuclear waste immobilization was investigated by using Fourier transform infrared spectra and Raman spectra.The results show that the Al₂O₃-containing sodium ultraphosphate glasses in this work predominantly consist of Q² phosphate units and the Al₂O₃ substitution for Na₂O induces the transformation of long phosphate chain units to short chain units such as Q¹ units, the breaking of P=O bonds, and the formation of strong Al–O–P bonds. Moreover, with the Al₂O₃ substitution, the phosphate networks are depolymerized but the entire glass networks are enhanced by cross-linking phosphate chains/units through Al-containing polyhedrons and Al–O–P bonds. Thus, the thermal stability of the NAP glasses are enhanced, as proved by density and DSC analyses. The conclusions provide researchers understanding the role of Al₂O₃ in the molecular structure of sodium ultraphosphate glasses for potential application in nuclear waste immobilization.