Effects of Na₂O/Al₂O₃ Molar Ratio on the Structure and Performances of Borosilicate Glass Wasteforms for Simulated High-Level Radioactive Liquid Waste

The effect of Na₂O/Al₂O₃ molar ratios(n) on the structure and properties of borosilicate glass wasteforms was investigated. The structural changes of borosilicate glass wasteforms with different Na₂O/Al₂O₃ molar ratios were characterized by Fourier transform infrared spectroscopy(FTIR) analysis, and the chemical durability was measured by using dissolution rate(DR) method and direct reading plasma emission spectroscopy(ICP-OES). The results show that: within the studied composition scope, when n<1.0, Al exists as ［AlO₄］ tetrahedron in borosilicate glass wasteforms, but there are large number of triangular ［BO₃］ existed in its structure; with the increase of Na₂O/Al₂O₃ molar ratio (n=1.0), the structure stability of the wasteform increase for the transformations of triangular ［BO₃］ to ［BO₄］ tetrahedron; however, when the molar ratio of Na₂O/Al₂O₃ continually increase (n=1.5 or 2.0), the structure of glass wasteforms become poor, because Al content is very few result in too much decreased ［AlO₄］ content, which plays an important role in influence of the network density at this condition, and excessive alkali metal ions have the effect of broking network in the structure. When Na₂O/Al₂O₃ mole ratio is 1.0, the good structural and chemical stability are obtained. The value of DR for the glass wasteform is 10^-9 g/(cm²•min) order of magnitude after 56 d at 90℃, and the concentration of ions in leached water is the lowest.