Chemistry of Organic Surface Reactions with Uranium Hexafluoride

Abstract

Despite the importance of UF6 in the nuclear industry, scant data are available on the interaction of UF6 with organic surfaces. To begin to fill this knowledge gap, we have examined, using in situ and ex situ RAIRS spectroscopy, the stability and reactivity of self-assembled monolayer (SAM) surfaces bearing different organic functional groups. Reflection-Absorption InfraRed Spectroscopy (RAIRS) was used both to characterize the model organic surfaces and to monitor reaction progress (if any) during uranium hexafluoride exposure. The results presented here indicate that hexafluoride exposure on amino- and methyl-terminated SAMs results in physisorped UF6 surface layers, or reactive deposition of a species like UO2F2, while fluorinated SAMs are more resistant to hexafluoride attack. Only the NH2-SAM showed compelling evidence for extensive reaction with the SAM chains themselves. RAIRS characterization showed successful consistent creation of SAMfunctionalized surfaces. These prepared surfaces were exposed to gaseous WF6 or UF6 in a custom reaction chamber and any reaction progress monitored with in situ RAIRS. Based on the analysis herein, and with extrapolation from WF6 exposure data, it appears that the fluorinated SAM is resistant to chemical attack by hexafluorides, while amino-terminated SAMs are degraded. All surfaces studied show a relatively dramatic shift in their backbone stretching frequencies, presumably from initial absorption of UF6 perturbing the overall SAM order. Further experiments in the future would help confirm whether the changes seen in the surfaces are true reactions or a physical effect of the adsorption/desorption process.

Publication Title

Chemistry of Uranium

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