arXiv subjects

David Simonne

Publications and source records attributed to David Simonne.

3 recordsLinked to original sources

arXiv2026

Design rules for industrial-scale sintering of UB4-UBC composites with high uranium density

Uranium borides are promising candidate fuel forms for use in advanced nuclear reactors due to their high thermal conductivity and potential for dual use as both fuel and burnable absorber materials. In this work, uranium tetraboride (UB$_4$) and uranium monoboroncarbide (UBC) composites were synthesized using an industrially scalable borocarbothermic reduction method. The high-temperature structural evolution of the as-synthesized borides was investigated using in situ synchrotron X-ray diffraction (SXRD). The oxidation behavior was further characterized using a combination of SXRD and thermogravimetric analysis (TGA), allowing direct comparison with other potential accident-tolerant fuels such as UB$_2$, U$_3$Si$_2$, UC, and UN. The UB$_4$-UBC composite shows higher uranium loading than monolithic UB$_4$ and demonstrates promising oxidation behavior at elevated temperature, pointing to its potential as an improved uranium boride-based fuel form.

cond-mat.mtrl-sci↗

arXiv2025

Transient Surface Oxides Form on Pt(111) - But Vanish During Ammonia Oxidation

Ammonia oxidation on platinum catalysts is pivotal for industrial nitric acid production and environmental abatement, yet the role of surface oxides in this process remains debated. Using operando surface X-ray diffraction (SXRD), crystal truncation rod (CTR) analysis, and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), we reveal that Pt(111) does not form stable surface oxides under ammonia oxidation conditions. Instead, transient hexagonal monolayers and a Pt(111)-(8x8) superstructure emerge under oxygen-rich atmospheres and above the catalyst light-off temperature, but vanish upon ammonia exposure. Real-time mass spectrometry and NAP-XPS demonstrate that the reaction proceeds via a Langmuir-Hinshelwood mechanism, where adsorbed NHx and O species availability dictate selectivity toward NO or N2. Reducing the oxygen pressure by an order of magnitude slows the kinetics of oxide growth, only detected after 24 hr, and facilitated by transient and precursor structures.

cond-mat.mtrl-sci↗

arXiv2025

Multipurpose in situ cell design for 3D X-ray imaging of electrochemical processes

We present the design of a modular multipurpose cell for monitoring the degradation of materials in extreme environments. This cell decouples the reference electrode from the working and counter electrodes, permitting precise electrochemical control and measurement reliability. The design is compatible with 4th generation synchrotron light sources, and its emphasis on modularity facilitates adaptation to different beamlines, where there may be variations in sample stage requirements and X-ray imaging techniques. Experimental tests with the novel design demonstrate its support of real-time corrosion and hydrogen embrittlement measurements under both Bragg Coherent Diffraction Imaging (BCDI) and Dark Field X-ray Microscopy (DFXM) configurations.

physics.ins-det↗