scholarly journals Chromium Doped UO2-Based Ceramics: Synthesis and Characterization of Model Materials for Modern Nuclear Fuels

Materials ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6160
Author(s):  
Philip Kegler ◽  
Martina Klinkenberg ◽  
Andrey Bukaemskiy ◽  
Gabriel L. Murphy ◽  
Guido Deissmann ◽  
...  
Keyword(s):  
Reference Sample ◽  
Lattice Parameter ◽  
Model Systems ◽  
Suitable Model ◽  
Nuclear Fuels ◽  
Metallic Particles ◽  
Long Term Stability ◽  
Deep Geological Disposal ◽  
Co Precipitation ◽  
Body Production

Cr-doped UO2 as a modern nuclear fuel type has been demonstrated to increase the in-reactor fuel performance compared to conventional nuclear fuels. Little is known about the long-term stability of spent Cr-doped UO2 nuclear fuels in a deep geological disposal facility. The investigation of suitable model materials in a step wise bottom-up approach can provide insights into the corrosion behavior of spent Cr-doped nuclear fuels. Here, we present new wet chemical approaches providing the basis for such model systems, namely co-precipitation and wet coating. Both were successfully tested and optimized, based on detailed analyses of all synthesis steps and parameters: Cr-doping method, thermal treatment, reduction of U3O8 to UO2, green body production, and pellet sintering. Both methods enable the production of suitable model systems with a similar microstructure and density as a reference sample from AREVA. In comparison with results from the classical powder route, similar trends upon grain size and lattice parameter were determined. The results of this investigation highlight the significance of subtly different synthesis routes on the properties of Cr-doped UO2 ceramics. They enable a reproducible tailor-made well-defined microstructure, a homogeneous doping, for example, with lanthanides or alpha sources, the introduction of metallic particles, and a dust-free preparation.

Visual control of orientation behaviour in the fly: Part I. A quantitative analysis

1976 ◽  
Vol 9 (3) ◽  
pp. 311-375 ◽  
Author(s):  
Werner Reichardt ◽  
Tomaso Poggio
Keyword(s):  
Information Processing ◽  
Quantitative Analysis ◽  
Visual System ◽  
Sensory Information ◽  
Model Systems ◽  
Suitable Model ◽  
Logical Organization ◽  
Integrative Level ◽  
Processing Properties ◽  
Different Levels

An understanding of sensory information processing in the nervous system will probably require investigations with a variety of ‘model’ systems at different levels of complexity.Our choice of a suitable model system was constrained by two conflicting requirements: on one hand the information processing properties of the system should be rather complex, on the other hand the system should be amenable to a quantitative analysis. In this sense the fly represents a compromise.In these two papers we explore how optical information is processed by the fly's visual system. Our objective is to unravel the logical organization of the fly's visual system and its underlying functional and computational principles. Our approach is at a highly integrative level. There are different levels of analysing and ‘understanding’ complex systems, like a brain or a sophisticated computer.

On the transferability of electron density in binary vanadium borides VB, V3B4 and VB2

2015 ◽  
Vol 71 (6) ◽  
pp. 777-787 ◽  
Author(s):  
Bürgehan Terlan ◽  
Lev Akselrud ◽  
Alexey I. Baranov ◽  
Horst Borrmann ◽  
Yuri Grin
Keyword(s):  
Quantum Theory ◽  
Crystal Structures ◽  
Electron Density ◽  
Critical Points ◽  
Atoms In Molecules ◽  
Model Systems ◽  
Suitable Model ◽  
Interatomic Distances ◽  
Systematic Analysis ◽  
A Charge

Binary vanadium borides are suitable model systems for a systematic analysis of the transferability concept in intermetallic compounds due to chemical intergrowth in their crystal structures. In order to underline this structural relationship, topological properties of the electron density in VB, V3B4 and VB2 reconstructed from high-resolution single-crystal X-ray diffraction data as well as derived from quantum chemical calculations, are analysed in terms of Bader's Quantum Theory of Atoms in Molecules [Bader (1990). Atoms in Molecules: A Quantum Theory, 1st ed. Oxford: Clarendon Press]. The compounds VB, V3B4 and VB2 are characterized by a charge transfer from the metal to boron together with two predominant atomic interactions, the shared covalent B—B interactions and the polar covalent B—M interactions. The resembling features of the crystal structures are well reflected by the respective B—B interatomic distances as well as by ρ(r) values at the B—B bond critical points. The latter decrease with an increase in the corresponding interatomic distances. The B—B bonds show transferable electron density properties at bond critical points depending on the respective bond distances.

scholarly journals Emergent colloidal currents across ordered and disordered landscapes

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Dominik Lips ◽  
Ralph L. Stoop ◽  
Philipp Maass ◽  
Pietro Tierno
Keyword(s):  
Magnetic Particles ◽  
Lattice Gas ◽  
Solvable Model ◽  
Model Systems ◽  
Suitable Model ◽  
Many Body ◽  
Emergent Phenomena ◽  
Density Relationship ◽  
Far From Equilibrium ◽  
Experimental Findings

AbstractMany-particle effects in driven systems far from equilibrium lead to a rich variety of emergent phenomena. Their classification and understanding often require suitable model systems. Here we show that microscopic magnetic particles driven along ordered and defective lattices by a traveling wave potential display a nonlinear current-density relationship, which arises from the interplay of two effects. The first one originates from particle sizes nearly commensurate with the substrate in combination with attractive pair interactions. It governs the colloidal current at small densities and leads to a superlinear increase. We explain such effect by an exactly solvable model of constrained cluster dynamics. The second effect is interpreted to result from a defect-induced breakup of coherent cluster motion, leading to jamming at higher densities. Finally, we demonstrate that a lattice gas model with parallel update is able to capture the experimental findings for this complex many-body system.

scholarly journals Crystallographic, Energy Gap, Photoluminescence and Photo-Catalytic Investigation of Cu Doped Cd0.9Zn0.1S Nanostructures by Co-Precipitation Method

2021 ◽  
Author(s):  
P. Raju ◽  
Joseph Prince Jesuraj ◽  
S. Muthukumaran
Keyword(s):  
Crystallite Size ◽  
Energy Gap ◽  
Wavelength Region ◽  
Lattice Parameter ◽  
Precipitation Method ◽  
Optical Absorbance ◽  
Stability Measurement ◽  
Cubic Structure ◽  
The Stability ◽  
Co Precipitation

Abstract The controlled synthesis of Cd0.9Zn0.1S, Cd0.89Zn0.1Cu0.01S and Cd0.87Zn0.1Cu0.03S nanostructures by simple chemical co-precipitation technique was reported. The XRD investigation confirmed the basic CdS cubic structure on Zn-doped CdS and also Zn, Cu dual doped CdS with no secondary/impurity related phases. No modification in cubic structure was detected during the addition of Zn/Cu into CdS. The reduction of crystallite size from 63 Å to 40 Å and the changes in lattice parameter confirmed the incorporation of Cu into Cd0.9Zn0.1S and generation of Cu related defects. The shift of absorption edge along upper wavelength region and elevated absorption intensity by Cu doping can be accredited to the collective consequence of quantization and the generation of defect associated states. The enhanced optical absorbance and the reduced energy gap recommended that Cd0.87Zn0.1Cu0.03S nanostructure is useful to enhance the efficiency of opto-electronic devices. The presence of Cd-S / Zn-Cd-S /Zn/Cu-Cd-S chemical bonding were confirmed by Fourier transform infrared investigation. The elevated green emissions by Cu incorporation was explained by decrease of crystallite size and creation of more defects. Zn, Cu dual doped CdS nanostructures are recognized as the possible and also efficient photo-catalyst for the removal dyes like methylene blue. The enhanced photo-catalytic behaviour of Zn, Cu dual doped CdS is the collective consequences of high density electron-hole pairs creation, enhanced absorbance in the visible wavelength, surface area enhancement, reduced energy gap and the formation of novel defect associated states. The stability measurement signified that Cu doped Cd0.9Zn0.1S exhibits superior dye removal ability and better stability even after 6 repetitive runs with limited photo-corrosion.

Consolidation and properties of Gd0.1Ce0.9O1.95 nanoparticles for solid-oxide fuel cell electrolytes

2006 ◽  
Vol 21 (1) ◽  
pp. 119-124 ◽  
Author(s):  
A.I.Y. Tok ◽  
L.H. Luo ◽  
F.Y.C. Boey ◽  
J.L. Woodhead
Keyword(s):  
Grain Size ◽  
Ionic Conductivity ◽  
Sintering Temperature ◽  
Spherical Shape ◽  
Impedance Analysis ◽  
Lattice Parameter ◽  
Narrow Particle Size Distribution ◽  
Precipitation Process ◽  
Boundary Area ◽  
Co Precipitation

Gd-doped ceria solid solutions have been recognized to be leading electrolytes for use in intermediate-temperature fuel cells. In this paper, the preparation, solubility, and densification of Gd0.1Ce0.9O1.95 ceramics derived from carbonate co-precipitation are reported. The dissolution of Gd2O3 in CeO2 lattice was identified to be completed during the co-precipitation process by studying the lattice parameter as a function of temperature. After calcination at 800 °C for 2 h, the nano-sized Gd0.1Ce0.9O1.95 powder (∼33 nm) with a nearly spherical shape and a narrow particle-size distribution was obtained. This calcined powder has high sinterability and maximum densification rate at ∼1000 °C. Sintering at 1300 °C for 4 h yielded over 97% relative density with near maximum. The grain size increased with increases in sintering temperature. The ionic conductivity of these pellets was tested by alternating current impedance spectroscopy to elucidate the contribution of intragranular and intergranular conductivity to the total ionic conductivity. It was found that sintering temperature does not affect intragranular conductivity, though intergranular conductivity was strongly influenced by grain size, grain boundary area, and relativity density. This pellet sintered at 1500 °C for 4 h showed a high ionic conductivity of 5.90 × 10−2 s/cm when measured at 750 °C. The characterization and structural evaluation of the as-received powders were carried out using x-ray diffraction, transmission electron microscopy, Brunauer–Emmett–Teller, and dilatometer and impedance analysis.

EFFECT OF SURFACTANTS ON THE SIZE, COLOR, PHOTOLUMINESCENCE AND RESISTIVITY OF INDIUM TIN OXIDE NANOPARTICLES PREPARED BY CO-PRECIPITATION METHOD

2012 ◽  
Vol 19 (05) ◽  
pp. 1250054 ◽  
Author(s):  
AYYOOB JAFARI ◽  
YADOLAH GANJKHANLOU ◽  
MAHMOOD KAZEMZAD ◽  
HAMZEH GHORBANI
Keyword(s):  
Tin Oxide ◽  
Indium Tin Oxide ◽  
Lattice Parameter ◽  
Precipitation Method ◽  
Tin Oxide Nanoparticles ◽  
Xrd Patterns ◽  
Ito Nanoparticles ◽  
Xrd Techniques ◽  
Co Precipitation ◽  
Triton X

Indium tin oxide (ITO) nanoparticles were synthesized by co-precipitation method using ammonia as a precipitator in absence/presence of various surfactants (LABS and Triton X-100). The synthesized nanoparticles were investigated by scanning electron microscopy, resistance measurement, photoluminescence (PL) spectroscopy and X-ray diffractometry (XRD) techniques. The XRD patterns of nanoparticles were also studied by Rietveld refinement method for calculation of crystallite size, micro-strain and lattice parameter. The results indicate that by application of LABS and Triton X-100 as surfactant the particle size was increased. Two luminescence bands were observed in PL spectra of ITO nanoparticles with the excitation energy lower than their band gaps. It was found that the ratios of luminescence bands have relation with resistances and colors of ITO nanoparticles. In addition, the band structure of ITO nanoparticles was described considering the obtained results.

Effects of Thermal Treatment on the Structure of Eu:YAG Nanopowder

2007 ◽  
Vol 128 ◽  
pp. 107-114 ◽  
Author(s):  
Maria Luisa Saladino ◽  
Eugenio Caponetti ◽  
Stefano Enzo
Keyword(s):  
Thermal Treatment ◽  
Lattice Strain ◽  
Rietveld Method ◽  
Lattice Parameter ◽  
Spherical Particles ◽  
X Rays ◽  
Garnet Phase ◽  
The Matrix ◽  
Different Temperatures ◽  
Co Precipitation

Eu:YAG nanopowder precursors were obtained by co-precipitation of aluminium, yttrium and europium nitrates solution with ammonia. The hydroxides precursors were calcined at different temperatures from 900 to 1200°C as a function of holding time (1, 2 and 6 hours). The presence of Eu3+ ions in the matrix was confirmed by Energy Dispersive X-rays analysis. X-Ray Diffraction investigation by the Rietveld method shows that the sample treated at 900°C for 1 hour is essentially the garnet phase with the minor presence of hexagonal and monoclinic metastable phases. The Eu3+ ions are incorporated into the garnet phase, as is suggested by the lattice parameter value being larger than that in literature data (homogeneous strain). For the sample treated at 900°C for 1 hour, electron microscopy observations showed agglomerates of spherical particles of mean size about 50 nm. At higher temperature treatments and for longer holding times the minority hexagonal and monoclinic phases totally disappeared. However, the lattice parameters of the cubic garnet phase gradually decreased with temperature, suggesting an expulsion of Eu3+ ions from the solid solution. Simultaneous with this, it was noted that the lattice strain reached a maximum value, but to later decrease, due to the vacancies created by the Eu species initially migrating to the surface of the coherent domains of diffraction. The lattice strain definitely decreased upon more drastic thermal treatments. Meanwhile, FEG-SEM and TEM observations on the same samples confirmed the growth of the garnet particles as a function of the thermal treatment.

Microbes and Microbial Toxins: Paradigms for Microbial- Mucosal Interactions I. Pathophysiological aspects of enteric infections with the lumen-dwelling protozoan pathogenGiardia lamblia

2001 ◽  
Vol 280 (1) ◽  
pp. G1-G6 ◽  
Author(s):  
Lars Eckmann ◽  
Frances D. Gillin
Keyword(s):  
Small Intestine ◽  
B Cell ◽  
Diarrheal Disease ◽  
Clinical Symptoms ◽  
Experimental Studies ◽  
Model Systems ◽  
Mucosal Inflammation ◽  
Suitable Model ◽  
Host Defenses ◽  
Giardia Infection

Giardia lamblia is one of the most important causes of waterborne diarrheal disease worldwide, and giardiasis is the most common protozoan infection of the human small intestine. Symptomatic infection is characterized by diarrhea, abdominal pain, and malabsorption, leading to malnutrition and weight loss, particularly in children. The pathogen resides strictly in the lumen of the small intestine, and infection is typically not accompanied by significant mucosal inflammation. Clinical and experimental studies indicate that B cell-dependent host defenses, particularly IgA, are important for controlling and clearing Giardia infection, although B cell-independent mechanisms also contribute to this outcome. In contrast to antigiardial host defenses, much less is known about the pathophysiological mechanisms underlying the clinical symptoms of giardiasis, partly because of the current lack of suitable model systems. In addition to being an important human enteric pathogen, Giardia is an interesting model organism for gaining basic insights into genetic innovations that led to evolution of eukaryotic cells, since it belongs to the earliest diverging eukaryotic lineage known. The completion of the giardial genome project will increase understanding of the basic biology of the protozoan and will help us to better understand host pathogen-interactions as a basis for developing new vaccination and therapeutic strategies.

The Mixed Magnetic Property of Co0.76Cu0.74[Fe(CN)6]·7.5H2O

2018 ◽  
Vol 71 (11) ◽  
pp. 914
Author(s):  
Yanfang Xia ◽  
Min Liu ◽  
Duxin Li
Keyword(s):  
Magnetic Field ◽  
Magnetic Moment ◽  
Effective Magnetic Moment ◽  
Lattice Parameter ◽  
Precipitation Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffraction Patterns ◽  
Co Precipitation ◽  
The Magnetic Field

Co0.76Cu0.74[Fe(CN)6]·7.5H2O was prepared as a powder by a chemical co-precipitation method. The powder X-ray diffraction patterns were indexed to the typical face-centred cubic structure with the lattice parameter a 10.55(2) Å. The temperature dependence of the χ−1 curve obeys the Curie–Weiss law (χ = C/(T – θ)) in the temperature range of 180–300 K. According to Curie–Weiss law, the calculated θ value is −54.82 K. In the paramagnetic state at 300 K, the effective magnetic moment (μeff = (8χT)1/2) is 3.58 μB per formula unit. The calculated theoretical effective magnetic moment is 4.06 μB. The magnetic field cooling measurements under a 200 Oe applied magnetic field show that the saturation magnetization value at 2 K of the complex Co0.76Cu0.74[Fe(CN)6]·7.5H2O is 1.528 emu g−1.

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