Brian Jaques

The magnetic properties of uranium nitride (UN) surfaces are not well understood experimentally or computationally but they have a significant effect on UN performance as a nuclear fuel. We investigated ferromagnetic (FM), antiferromagnetic (AFM), nonmagnetic (NM), and three hybrid magnetic structures of the most stable UN surface (100). To account for electron correlation and metastability, a U-ramp was performed to an effective Hubbard U-term of 2.0 eV. FM was found to be the most energetically favorable magnetic structure. Type 1 AFM slab was optimized to a new magnetic structure consisting of (100) planes with either all spin-up electrons, all spin-down electrons, or half spin-up and half spin-down electrons on uranium atoms. After OH adsorption to simulate corrosion initiation, the AFM, FM, and NM structures yield relatively similar bond lengths but varying bond angles, adsorption energies, and electronic profiles. Partial charge density maps show varying degradation mechanisms across magnetic structures. Electron localization function reveals more charge localized to AFM uranium atoms with spin-down electrons than uranium atoms with spin-up electrons. This leads to different properties depending on if an adsorbate interacts with a spin-up or spin-down terminated AFM surface. This work supports the physical accuracy of future computational studies toward corroborating with experiments and addressing UN fuel corrosion.

The validation of a ball‐on‐ring, equibiaxial flexural strength method to obtain the transverse rupture strength (TRS) of right cylindrical ceramic specimens was performed in this study. Validation of the test method was achieved using commercially available engineered high purity alumina disks and finite element (FE) model analysis. The validated fixture was then used to obtain the TRS and Weibull statistical analysis of MgO‐partially stabilized zirconia (MSZ) and Y₂O₃‐partially stabilized zirconia (YSZ) ceramic disks. TRS data for alumina, MSZ, and YSZ agreed with the TRS values reported in the literature. A statistically relevant number of samples (N > 30) for each material were tested to allow for a Weibull statistical analysis. Weibull parameters for these materials were within the expected values for engineered ceramics. The characteristic strength for alumina, MSZ, and YSZ were determined to be 289, 786, and 814 MPa, respectively. The Weibull modulus was determined between 10 and 25 for each material, which is typical of engineered ceramics. In addition, FE model results were in close agreement with experimental fracture values for the three ceramic materials tested in this study.

Nuclear energy is the leading clean energy source in the United States with 99 nuclear power plants generating approximately 20% of the country’s electricity. While the growth of the industry helps to reduce our reliance on fossil fuels, there is also an increase in nuclear waste. The demand for on-site dry cask spent nuclear fuel storage has increased due to complications with the Yucca Mountain Project and diminishing pool capacity. A novel dry cask consisting of an aluminum metal matrix for effective thermal conductivity with boron carbide as a neutron absorbing additive was investigated using gravity sand casting techniques. X-ray diffraction, Raman spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and optical microscopy were used to characterize the resultant microstructure, including boron carbide incorporation and heterogeneity. Results indicate vortex and nonvortex mixing in air with boron carbide (1–10 µm diameter) produces large amounts of porosity and insufficient wetting. Use of a larger particle size distribution of boron carbide (20–60 µm diameter) during high speed vortex mixing prior to casting has shown significant dispersion of up to 12 wt% sufficient for neutron shielding with appropriate wall thickness. These results validate the use of gravity sand casting as a means to produce borated aluminum for an effective alternative to fuel storage.

Soft structural textiles, or softgoods, are used within the space industry for inflatable habitats, parachutes and decelerator systems. Evaluating the safety and structural integrity of these systems occurs through structural health monitoring systems (SHM), which integrate non-invasive/non-destructive testing methods to detect, diagnose, and locate damage. Strain/load monitoring of these systems is limited while utilizing traditional strain gauges as these gauges are typically stiff, operate at low temperatures, and fail when subjected to high strain that is a result of high loading classifying them as unsuitable for SHM of soft structural textiles. For this work, a capacitance based strain gauge (CSG) was fabricated via aerosol jet printing (AJP) using silver nanoparticle ink on a flexible polymer substrate. Printed strain gauges were then compared to a commercially available high elongation resistance-based strain gauge (HE-RSG) for their ability to monitor strained Kevlar straps having a 26.7 kN (6 klbf) load. Dynamic, static and cyclic loads were used to characterize both types of strain monitoring devices. Printed CSGs demonstrated superior performance for high elongation strain measurements when compared to commonly used HE-RSGs, and were observed to operate with a gauge factor of 5.2 when the electrode arrangement was perpendicular to the direction of strain.

Adopting black phosphorus (BP) as a material in electronic and optoelectronic device manufacturing requires the development and understanding of a large-scale synthesis technique. To that end, high-energy planetary ball milling is demonstrated as a scalable synthesis route, and the mechanisms and conversion kinetics of the BP phase transformation are investigated. During the milling process, media collisions rapidly compress amorphous red phosphorus (RP) into crystalline, orthorhombic BP flakes, resulting in a conversion yield of ≈90% for ≈5 g of bulk BP powder. Milling conversion kinetics, monitored via ex situ x-ray diffraction, manifest a sigmoidal behavior best described by the Avrami rate model with each impact of sufficient energy (>25 mJ) producing BP nuclei; the process appears to be limited by grain growth. Using a kinematic model for ball trajectories and impact energies, the optimum milling condition is determined to be an impact energy near ≈25 mJ and a milling dose near ≈100 kJ/gram. Photoexcitation of exfoliated BP flakes reveals emission in the near-infrared, indicating the formation of few-layer BP, a promising advance for optoelectronic device applications.

Field reports indicate that many White Sturgeon Acipenser transmontanus ingest hooks internally, but the length of time required for hooks to corrode, facilitating passage through their digestive system, is not well understood. Using a buffered acidic solution to simulate stomach conditions, a laboratory experiment was used to estimate the speed at which sturgeon-sized hooks (2.0-mm wire diameter) lost weight and compression strength and to evaluate whether loss of hook weight and compression strength was affected by hook abrasion, such as may occur when baited hooks are bounced along the bottom of the river or when ingested hooks are ground between hard food items in the gizzard of a sturgeon. After 399 d, hooks lost an estimated 34% of their weight and 70% of their compression strength. Abrading the hooks with stones before and throughout the study accelerated weight loss by 34% (after 399 d) compared with nonabraded hooks but did not accelerate the loss of compression strength. Abrasion increased the variability between hooks in weight loss but not in compression strength. Regardless of hook abrasion, the compression strength of some hooks was reduced essentially to 0 N within 1 year of constant exposure to stomach-like acidic conditions.

Thermoelectric properties of nanostructured half-Heusler Hf0.25Zr0.75NiSn0.99Sb0.01 were characterized before and after 2.5 MeV proton irradiation. A unique high-sensitivity scanning thermal microprobe was used to simultaneously map the irradiation effect on thermal conductivity and Seebeck coefficient with spatial resolution less than 2 μm. The thermal conductivity profile along the depth from the irradiated surface shows excellent agreement with the irradiation-induced damage profile from simulation. The Seebeck coefficient was unaffected while both electrical and thermal conductivities decreased by 24%, resulting in no change in thermoelectric figure of merit ZT. Reductions in thermal and electrical conductivities are attributed to irradiation-induced defects that act as scattering sources for phonons and charge carriers.

Thermoelectric properties of nanostructured half-Heusler Hf0.25Zr0.75NiSn0.99Sb0.01 were characterized before and after 2.5 MeV proton irradiation. A unique high-sensitivity scanning thermal microprobe was used to simultaneously map the irradiation effect on thermal conductivity and Seebeck coefficient with spatial resolution less than 2 μm. The thermal conductivity profile along the depth from the irradiated surface shows excellent agreement with the irradiation-induced damage profile from simulation. The Seebeck coefficient was unaffected while both electrical and thermal conductivities decreased by 24%, resulting in no change in thermoelectric figure of merit ZT. Reductions in thermal and electrical conductivities are attributed to irradiation-induced defects that act as scattering sources for phonons and charge carriers.

The influence of dysprosia addition on the sintering and resulting microstructure of nano‐grained CeO₂ ceramics was investigated as functions of the spark plasma sintering parameters. The addition of Dy₂O₃ (forming a solid solution) resulted in an increase in relative density and a decrease in grain size in sintered samples. The relative density of samples with Dy₂O₃ content of 6 and 10 mol% was over 95% when sintered at 1050°C under 500 MPa for holding times as short as 5 min. The application of high pressure facilitated the consolidation to relatively high densities with minimal grain growth. Heating rate and holding time, however, had insignificant effect on density but a measurable effect on grain size.