The Experts below are selected from a list of 786 Experts worldwide ranked by ideXlab platform
N H De Leeuw - One of the best experts on this subject based on the ideXlab platform.
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a density functional theory study of uranium doped thoria and uranium adatoms on the major surfaces of Thorium Dioxide
Journal of Nuclear Materials, 2016Co-Authors: Ashley E Shields, N H De Leeuw, David SantoscarballalAbstract:Thorium Dioxide is of significant research interest for its use as a nuclear fuel, particularly as part of mixed oxide fuels. We present the results of a density functional theory (DFT) study of uranium-substituted Thorium Dioxide, where we found that increasing levels of uranium substitution increases the covalent nature of the bonding in the bulk ThO2 crystal. Three low Miller index surfaces have been simulated and we propose the Wulff morphology for a ThO2 particle and STM images for the (100), (110), and (111) surfaces studied in this work. We have also calculated the adsorption of a uranium atom and the U adatom is found to absorb strongly on all three surfaces, with particular preference for the less stable (100) and (110) surfaces, thus providing a route to the incorporation of uranium into a growing thoria particle.
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theoretical analysis of uranium doped Thorium Dioxide introduction of a thoria force field with explicit polarization
AIP Advances, 2015Co-Authors: Ashley E Shields, N H De Leeuw, S Ruiz E HernandezAbstract:Thorium Dioxide is used industrially in high temperature applications, but more insight is needed into the behavior of the material as part of a mixed-oxide (MOX) nuclear fuel, incorporating uranium. We have developed a new interatomic potential model including polarizability via a shell model, and commensurate with a prominent existing UO2 potential, to conduct configurational analyses and to investigate the thermophysical properties of uranium-doped ThO2. Using the GULP and Site Occupancy Disorder (SOD) computational codes, we have analyzed the distribution of low concentrations of uranium in the bulk material, where we have not observed the formation of uranium clusters or the dominance of a single preferred configuration. We have calculated thermophysical properties of pure Thorium Dioxide and Th(1−x)UxO2 which generated values in very good agreement with experimental data.
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configurational analysis of uranium doped Thorium Dioxide
IOP Conference Series: Materials Science and Engineering, 2015Co-Authors: Ashley E Shields, Sergio E Ruizhernandez, N H De LeeuwAbstract:While Thorium Dioxide is already used industrially in high temperature applications, more insight is needed about the behaviour of the material as part of a mixed-oxide (MOX) nuclear fuel, incorporating uranium. We have developed a new interatomic potential model, commensurate with a prominent existing UO2 potential, to conduct configurational analyses of uranium-doped ThO2 supercells. Using the GULP and Site Occupancy Disorder (SOD) computational codes, we have analysed the distribution of low concentrations of uranium in the bulk material, but have not observed the formation of uranium clusters or a single dominant configuration.
Marek Danielewski - One of the best experts on this subject based on the ideXlab platform.
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studies of sluggish diffusion effect in co cr fe mn ni co cr fe ni and co fe mn ni high entropy alloys determination of tracer diffusivities by combinatorial approach
Journal of Alloys and Compounds, 2018Co-Authors: Witold Kucza, Juliusz Dąbrowa, Grzegorz Cieślak, Katarzyna Berent, T Kulik, Marek DanielewskiAbstract:Abstract Experimental and theoretical studies of diffusion in quinary Co-Cr-Fe-Mn-Ni and quaternary Co-Cr-Fe-Ni and Co-Fe-Mn-Ni FCC-structured high entropy alloys were performed. The diffusion couples, with Thorium Dioxide markers placed at initial joint positions, were annealed at temperature of 1350 K for 72 or 73 h. The concentration profiles obtained from the quinary system were used to determine tracer diffusivities of all components, by using a combinatorial approach, i.e. the Darken method with thermodynamic description provided by Miedema's scheme combined with the optimization method. The results showed good qualitative agreement with the tracer data from radiotracer experiments. The calculated thermodynamic factor, ranged from tens to hundreds of %, show importance of mixing enthalpy on interdiffusion kinetics. The values determined for 5-component system were then used a priori to simulate the concentration profiles for 4-component ones, showing very good agreement with the experimental data. The results indicate that change of components number did not influence the diffusion kinetics in the investigated systems and do not support existence of the sluggish diffusion effect.
Heinrich Lunsdorf - One of the best experts on this subject based on the ideXlab platform.
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Visualization of the glomerular endothelial glycocalyx by electron microscopy using cationic colloidal Thorium Dioxide
Histochemistry and Cell Biology, 2016Co-Authors: Jan Hegermann, Heinrich Lunsdorf, Matthias Ochs, Hermann HallerAbstract:Biological material itself appears with poor contrast in electron microscopy (EM), due to its composition mostly of light elements. Classical staining agents such as osmium tetroxide, uranyl acetate, and lead citrate preserve and/or stain cellular structures such as membranes, cytoplasm, and organelles well for EM. However, extracellular polymeric substances (EPS) show no or only poor contrast with these staining agents. The endothelial glycocalyx in blood vessels consists mainly of proteoglycans. It can be visualized by EM only by additional staining with heavy metal ions such as copper (Alcian blue, cupromeronic blue), ruthenium (ruthenium red), or lanthanum. Best results are achieved by combined perfusion of fixative and stain. Cationic hydrous Thorium Dioxide colloids (named here cThO_2) trace acidic groups in EPS. We describe here the use of cThO_2 to visualize the glomerular endothelial glycocalyx in the mouse kidney. cThO_2 shows high electron density and binds to a continuous layer of up to a few hundred nanometers thickness on the glomerular endothelium, as well as on epithelia in other blood vessels in perfused animals. The observed staining pattern gives rise to periodic densities, with a spacing varying between 50 and 200 nm, depending on the overall layer thickness, which varies between below 50 up to 300 nm. Due to high electron density of the used cThO_2 particles, the introduced method allows distinct imaging and precise fine structural analysis of the endothelial glycocalyx.
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cationic hydrous Thorium Dioxide colloids a useful tool for staining negatively charged surface matrices of bacteria for use in energy filtered transmission electron microscopy
BMC Microbiology, 2006Co-Authors: Heinrich Lunsdorf, Ingeborg Kristen, Elke BarthAbstract:Background: Synthesis of cationic hydrous Thorium Dioxide colloids (ca. 1.0 to 1.7 nm) has been originally described by Muller [22] and Groot [11] and these have been used by Groot to stain acidic glucosaminoglycans for ultrastructure research of different tissues by conventional transmission electron microscopy. Results: Synthesis of colloidal Thorium Dioxide has been modified and its use as a suitable stain of acidic mucopolysaccharides and other anionic biopolymers from bacteria, either as whole mount preparations or as preembedment labels, is described. The differences in stain behavior relative to commonly used rutheniumred-lysine and Alcian Blue™ electron dense acidic stains has been investigated and its use is exemplified for Pseudomonas aeruginosa adjacent cell wall biopolymers. For the first time thorificated biopolymers, i.e. bacterial outer cell wall layers, have been analysed at the ultrastructural level with electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI), leading to excellent contrast and signal strength for these extracellular biopolymers. Conclusion: Application of cationic hydrous ThO2 colloids for tracing acidic groups of the bacterial surface and/or EPS has been shown to be rather effective by transmission electron microscopy. Because of its high electron density and its good diffusibility it stains and outlines electro-negative charges within these biopolymers. In combination with ESI, based on integrated energy-filtered electron microscopy (EFTEM) Th-densities and thus negative charge densities can be discriminated from other elemental densities, especially in environmental samples, such as biofilms.
Cody A Dennett - One of the best experts on this subject based on the ideXlab platform.
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an integrated experimental and computational investigation of defect and microstructural effects on thermal transport in Thorium Dioxide
Acta Materialia, 2021Co-Authors: Cody A Dennett, Zilong Hua, Amey Khanolkar, Ryan W Deskins, Marat Khafizov, Kaustubh Bawane, Matthew J Mann, Chris A Marianetti, David H Hurley, Anter ElazabAbstract:Abstract Advanced nuclear reactor concepts aim to use fuels that must withstand unprecedented temperature and radiation extremes. In these fuels, thermal energy transport under irradiation is directly related to fuel longevity, reactor safety, and is arguably one of the most important performance metrics. Here we provide a comprehensive, first-principles-informed treatment of phonon mediated thermal transport in a defect-bearing actinide oxide with direct comparison to experimental measurements. Pristine and proton irradiated Thorium Dioxide was chosen as a model system to treat the complexity of thermal transport in the presence of lattice defects. A thermal transport model is implemented using the linearized Boltzmann transport equation (LBTE) with input from first principles calculations and defect evolution models. Density functional theory is used to calculate phonon dispersion in Thorium Dioxide and used as an input to calculate both intrinsic and extrinsic, defect-induced relaxation times. In addition, a defect evolution model is benchmarked using microstructure characterization of as-irradiated Thorium Dioxide using a combination of electron microscopy and optical spectroscopy. The output of the LBTE is compared directly to mesoscopic measurements of thermal conductivity on length scales commensurate with defect accumulation. Parametric measurements of conductivity with irradiation dose and temperature suggest a saturation in the reduction of thermal conductivity with increasing defect generation, which is partially captured in our defect evolution model and LBTE framework. This comprehensive, atomistic- to meso-scale treatment provides the necessary basis to investigate thermal transport under irradiation in more complex systems that exhibit strong electron correlation.
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the influence of lattice defects recombination and clustering on thermal transport in single crystal Thorium Dioxide
APL Materials, 2020Co-Authors: Cody A Dennett, Zilong Hua, Amey Khanolkar, Tiankai Yao, Phyllis K Morgan, Timothy A Prusnick, Narayan Poudel, Aaron French, K Gofryk, Lin ShaoAbstract:Thermal transport is a key performance metric for Thorium Dioxide in many applications where defect-generating radiation fields are present. An understanding of the effect of nanoscale lattice defects on thermal transport in this material is currently unavailable due to the lack of a single crystal material from which unit processes may be investigated. In this work, a series of high-quality Thorium Dioxide single crystals are exposed to 2 MeV proton irradiation at room temperature and 600 °C to create microscale regions with varying densities and types of point and extended defects. Defected regions are investigated using spatial domain thermoreflectance to quantify the change in thermal conductivity as a function of ion fluence as well as transmission electron microscopy and Raman spectroscopy to interrogate the structure of the generated defects. Together, this combination of methods provides important initial insight into defect formation, recombination, and clustering in Thorium Dioxide and the effect of those defects on thermal transport. These methods also provide a promising pathway for the quantification of the smallest-scale defects that cannot be captured using traditional microscopy techniques and play an outsized role in degrading thermal performance.
Witold Kucza - One of the best experts on this subject based on the ideXlab platform.
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studies of sluggish diffusion effect in co cr fe mn ni co cr fe ni and co fe mn ni high entropy alloys determination of tracer diffusivities by combinatorial approach
Journal of Alloys and Compounds, 2018Co-Authors: Witold Kucza, Juliusz Dąbrowa, Grzegorz Cieślak, Katarzyna Berent, T Kulik, Marek DanielewskiAbstract:Abstract Experimental and theoretical studies of diffusion in quinary Co-Cr-Fe-Mn-Ni and quaternary Co-Cr-Fe-Ni and Co-Fe-Mn-Ni FCC-structured high entropy alloys were performed. The diffusion couples, with Thorium Dioxide markers placed at initial joint positions, were annealed at temperature of 1350 K for 72 or 73 h. The concentration profiles obtained from the quinary system were used to determine tracer diffusivities of all components, by using a combinatorial approach, i.e. the Darken method with thermodynamic description provided by Miedema's scheme combined with the optimization method. The results showed good qualitative agreement with the tracer data from radiotracer experiments. The calculated thermodynamic factor, ranged from tens to hundreds of %, show importance of mixing enthalpy on interdiffusion kinetics. The values determined for 5-component system were then used a priori to simulate the concentration profiles for 4-component ones, showing very good agreement with the experimental data. The results indicate that change of components number did not influence the diffusion kinetics in the investigated systems and do not support existence of the sluggish diffusion effect.