Electrospray ionization (ESI) can produce a wide range of gas‐phase uranyl (UO22+) complexes for tandem mass spectrometry studies of intrinsic structure and reactivity. We describe here the formation and collision‐induced dissociation (CID) of [UO2(NO3)3]−and [UO2(NO3)2(O2)]−. Multiple‐stage CID experiments reveal that the complexes dissociate in reactions that involve elimination of O2, NO2, or NO3, and subsequent reactions of interesting uranyl‐oxo product ions with (neutral) H2O and/or O2were investigated. Density functional theory (DFT) calculations reproduce experimental results and show that dissociation of nitrate ligands, with ejection of neutral NO2, is favored for both [UO2(NO3)3]−and [UO2(NO3)2(O2)]−. DFT calculations also suggest that H2O adducts to products such as [UO2(O)(NO3)]−spontaneously rearrange to create dihydroxides and that addition of O2is favored over addition of H2O to formally U(V) species.
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Abstract Surface energy (
γ S) and grain boundary energy (γ GB) of yttrium oxide (Y2O3) were determined by analyzing the heat of sintering (ΔH sintering) using differential scanning calorimetry (DSC). The data allowed quantification of sintering driving forces, which when combined with a thorough kinetic analysis of the process, provide better understanding of Y2O3densification as well as insights into effective strategies to improve its sinterability. The quantitative thermodynamic study revealed moderate thermodynamic driving force for densification in Y2O3(as compared to other oxides) represented by a dihedral angle of 152.7° calculated from its surface and grain boundary energies. The activation energy was determined as 307 ± 61 kJ/mol, consistent with activation energies previously reported for processes relevant to sintering of Y2O3,such as Y3+diffusion and grain boundary mobility. Finally, we propose that a refined deconvolution study on the DSC curve for Y2O3sintering, combined with the associated material's microstructure evolution, may help identify shifts in sintering mechanisms, and therefore, specific activation energies at increasing temperatures.
