Studies on chemical state of uranium in modified sodium borosilicate glass using X-ray photoelectron spectroscopy and X-ray absorption spectroscopy

Highlights: • Modified borosilicate glass 47SiO₂-24B₂O₃-17Na₂O-9.5CaO-1.0Al₂O₃-1.5 TiO₂ was prepared. • 2–8 mol% of UO₃ in the form of U₃O₈ was loaded to the modified borosilicate glass. • Above 6 mol% of UO₃ loading, Na₂U₂O₇ separated out from the glass unravelled by XRD studies. • XPS studies show the presence of U in two different oxidation states (U⁶⁺ and U⁴⁺). • EXAFS studies reveal a decrease in coordination of uranium in glass matrix on increasing uranium loading. The modified sodium borosilicate glass was synthesized by incorporating CaO, TiO₂ and Al₂O₃ to the primary glass forming constituents (SiO₂, B₂O₃ and Na₂O) and on melting the mixture at 1373–1473K/3h by melt quench method. Uranium loaded analogues were synthesized by adding varying amounts of UO₃ (2,4,6 and 8 mol %) to the borosilicate glass forming reagents then on melting at 1373–1473K. The U-loaded matrices were characterized by XRD to ensure the formation of glass matrices. Solubility of uranium in sodium borosilicate glass has been investigated. Further, the glasses were characterized by X-ray photoelectron spectroscopy (XPS) to unravel the oxidation states of uranium in the modified glass composition. X-ray absorption spectroscopy (EXAFS) revealed the chemical environment of uranium in the glass matrix indicating the coordination number of U in glass.