Synopsis: Uranium Oxidation State Finally Revealed

X-ray spectroscopy has revealed the first direct evidence for a particular oxidation state of uranium in two types of uranium oxide.
Synopsis figure
K. Kvashnina et al., Phys. Rev. Lett. (2013)

Uranium is often found in one of several different oxide forms. Understanding how uranium oxides transform from one to another is important for nuclear waste disposal. A new x-ray study of two uranium oxides reveals an oxidation state of uranium that had not previously been observed directly. The results, reported in Physical Review Letters, should improve models for how uranium behaves in geochemical processes and how it might work as a catalyst for industrial purposes.

Nuclear fuel rods typically contain uranium dioxide (UO2), in which the uranium is in the +4 oxidation state, written as U(IV). In this case, one can imagine the uranium makes available four electrons to create chemical bonds. After its use, spent uranium dioxide may be stored in containers, but one worry is that UO2 will oxidize into mixed oxides, such as U4O9 and U3O8, which have more than one oxidation state. These uranium oxide reactions, which can lead to environmental contamination, are not well characterized because of ambiguities in previous studies over the final oxidation states.

Kristina Kvashnina from the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, and her colleagues have performed x-ray spectroscopy experiments on U4O9 and U3O8. Their unique strategy is to probe the transition from the 3d electron shell to the 5f shell in the uranium atom using a setup that provides high-energy resolution. This requires exposing samples to 3.7-kilo-electron-volt x rays from the ESRF synchrotron. The team identified peaks in the absorption spectra that show, for the first time, that U(V) is one of the oxidation states in both U4O9 and U3O8. The authors say that this observation calls for a revision of the current thinking on uranium chemistry. – Michael Schirber


Announcements

More Announcements »

Subject Areas

Materials SciencePhysical Chemistry

Previous Synopsis

Atomic and Molecular Physics

Detecting Molecules on a Chip

Read More »

Next Synopsis

Energy Research

Plant Power

Read More »

Related Articles

Focus: Complex Crystals Form from Heterogeneous Particles
Materials Science

Focus: Complex Crystals Form from Heterogeneous Particles

A suspension containing particles with wide-ranging diameters can crystallize into multiple ordered structures. Read More »

Synopsis: Glassy Fingerprints
Condensed Matter Physics

Synopsis: Glassy Fingerprints

The local structure of glasses and other disordered materials could be extracted from diffraction patterns, according to a proposal for a new technique. Read More »

Synopsis: Electron–Phonon Affair Comes to Light
Condensed Matter Physics

Synopsis: Electron–Phonon Affair Comes to Light

Photoelectron spectroscopy reveals the details of the interaction between electronic and vibrational excitations in a molecular material. Read More »

More Articles