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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Synthesis, structural and magnetic characterisation of the fluorinated compound 15R-BaFeO{sub 2}F

The compounds 15R-BaFeO{sub 2}F and 15R-BaFeO{sub 2.27}F{sub 0.5} have been synthesised by the low temperature fluorination of 15R-BaFeO{sub 3−d}F{sub 0.2} using polyvinylidenedifluoride (PVDF) as a fluorination agent. The materials have been structurally characterised by Rietveld analysis of the X-ray- and HRPD-powder neutron diffraction data. A detailed analysis of bond valence sums suggests that the oxide and fluoride ions order on the different anion sites. A reinvestigation of our recently published structure (Clemens et al., 2013) [34] of 6H-BaFeO{sub 2}F is also reported and incorporation of fluoride in h-type layers is also confirmed in this compound. The magnetic moments for 15R-BaFeO{sub 2}F and 15R-BaFeO{sub 2.25}F{sub 0.5} align in the a/b-plane with antiferromagnetic alignment of the moments between adjacent layers, and are flipped by 90° as compared to the precursor compound. 15R-BaFeO{sub 2}F exhibits very robust antiferromagnetism with a Néel temperature between 300 and 400 °C. - Graphical abstract: The crystal and magnetic structure of the perovskite phase 15R-BaFeO{sub 2}F. - Highlights: • 15R-BaFeO{sub 2}F and 15R-BaFeO{sub 2.27}F{sub 0.5}were prepared via low temperature fluorination using PVDF. • A structural investigation of the compounds BaFeO{sub 2}F is presented in detail. • This analysis suggests ordering of O{sup 2−} and F{sup −} anions between different layers. • 15R-BaFeO{sub 2}F shows antiferromagnetic ordering at 300 K with T{sub N} ∼300–400 °C. • The magnetic moments align in the a/b-plane.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Formation of metastable tetragonal zirconia nanoparticles: Competitive influence of the dopants and surface state

The effect of the surface modification of the nanoparticles of amorphous and crystalline partially stabilized zirconia by fluoride ions on stability of the metastable tetragonal phase was investigated. Based on the DSC, titrimetry and FTIR spectroscopy data it was proven that surface modification of the xerogel resulted from an exchange of the fluoride ions with the basic OH groups. The effect of the powder pre-calcination temperature before modification on the formation of metastable tetragonal phase in partially stabilized zirconia was investigated. It was shown that the main factor of tetragonal zirconia stabilization is the state of nanoparticles surface at pre-crystallization temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Increased radiative lifetime of Tm{sup 3+}:{sup 3}F{sub 4} → {sup 3}H{sub 6} transition in oxyfluoride tellurite glasses

Highlights: • We prepare Tm{sup 3+}-doped tellurite-zinc glasses with F{sup −} substitution. • Thermal stability becomes better with increasing F{sup −} in present glasses. • Tm{sup 3+} 1.8 μm radiative lifetime increases with F{sup −} concentration. • The origin of the increased lifetime has been discussed. - Abstract: The 1.8 μm emission properties of Tm{sup 3+}-doped zinc tellurite glasses modified by the substitution of ZnF{sub 2} are investigated in this paper. The thermal stability, Raman and phonon sideband spectra, transmission and absorption spectra, emission spectra and decay curves are discussed. It is found that substitution of fluoride ions into the zinc tellurite matrix produces dramatic increase in the emission lifetime of Tm{sup 3+} 1.8 μm emission. Absorption, Raman and phonon sideband spectra are used to estimate the local structure of Tm{sup 3+} ions. These analyses indicate structural change around Tm{sup 3+} ions caused by substitution of fluoride ions monitors the increased intrinsic radiative lifetimes. An increase in the measured radiative lifetimes of the Tm{sup 3+}:{sup 3}F{sub 4} → {sup 3}H{sub 6} transition is observed. The origin has been discussed and the reduction of OH{sup −} absorption, decrease of maximum phonon energy and phonon density are considered to be dominant in all of the nonradiative relaxations.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Photon up-conversion production in Tb{sup 3+}–Yb{sup 3+} co-doped CaF{sub 2} phosphors prepared by combustion synthesis

Graphical abstract: Up-conversion luminescence from Tb{sup 3+} obtained by energy transfer from Yb{sup 3+} pairs in CaF{sub 2} powder prepared by combustion synthesis. - Highlights: • Calcium fluoride (CaF{sub 2}) powders were prepared by combustion synthesis. • Rare-earth ions doped in this material were found in interstitial sites. • Cooperative up-conversion was observed in Tb{sup 3+}:Yb{sup 3+}:CaF{sub 2} powder. • Energy transfer between Tb{sup 3+} and pairs of Yb{sup 3+} was analyzed using rate equations. - Abstract: Calcium fluoride (CaF{sub 2}) crystalline powders were successfully prepared by the combustion synthesis method. The powder material containing luminescent rare-earth ions, more specifically terbium (Tb{sup 3+}) and ytterbium (Yb{sup 3+}), was studied by X-ray diffraction, scanning electronic microscopy and optical spectroscopy. These ions are allocated in charge compensated interstitial positions of tetragonal (C{sub 4v}) and trigonal (C{sub 3v}) symmetry sites of the cubic (O{sub h}) CaF{sub 2} lattice. Up-conversion (UC) luminescence in Tb{sup 3+} was achieved using a low power diode laser operating at 975 nm. Tb{sup 3+} is insensitive to near-infrared radiation but UC can be achieved via energy transfer from pairs of Yb{sup 3+} ions to Tb{sup 3+} ions. The UC luminescence dynamics of Tb{sup 3+} was used to study the energy transfer mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A novel elaboration for various morphologies of three-layer TiO2 nanotubes by oxygen bubble mould

Highlights: • Three-layer TiO{sub 2} nanotubes with different morphologies were fabricated. • Some cavities inside middle barrier layer were observed for the first time. • Conventional three-stage current-time curves were transformed into four-stage curves. • Growing process of the three-layer nanotubes was explored systematically. - Abstract: A special three-layer TiO{sub 2} nanotube array has been successfully fabricated. The upper and lower porous layers were formed in the same fluoride-containing electrolyte, while the middle barrier layer was formed in fluoride-free electrolyte. By changing the applied voltage of middle barrier layer, the growth process of the lower layer was explored and compared systematically. The results show that at a critical voltage of barrier layer, the lower layer could barely be seen. Below the critical voltage, complete three-layer TiO{sub 2} nanotubes were achieved, but above the critical voltage, the lower layer failed to appear. Furthermore, some cavities inside the barrier layer were obtained under higher voltage of barrier layer and the conventional three-stage current-time curves were transformed into four-stage curves. Based on the oxygen bubble mould and electronic current model, an explanation for the formation of cavities is firstly proposed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

New insight into UO 2 F 2 particulate structure by micro-Raman spectroscopy

Uranyl fluoride particles produced via hydrolysis of uranium hexafluoride have been deposited on different substrates: polished graphite disks, silver foil, stainless steel and gold-coated silicon wafer, and measured with micro-Raman spectroscopy (MRS). All three metallic substrates enhanced the Raman signal delivered by UO 2 F 2 in comparison to graphite. The fundamental stretching of the U–O band appeared at 867 cm –1 in case of the graphite substrate, while in case of the others it was shifted to lower frequencies (down to 839 cm –1 ). All applied metallic substrates showed the expected effect of Raman signal enhancement; however the gold layer appeared to be most effective. Lastly, application of new substrates provides more information on the molecular structure of uranyl fluoride precipitation, which is interesting for nuclear safeguards and nuclear environmental analysis.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Controlled Formation of Mixed Nanoscale Domains of High Capacity Fe 2 O 3 –FeF 3 Conversion Compounds by Direct Fluorination

In this paper, we report a direct fluorination method under fluorine gas atmosphere using a fluidized bed reactor for converting nanophase iron oxide (n-Fe 2 O 3 ) to an electrochemically stable and higher energy density iron oxyfluoride/fluoride phase. Interestingly, no noticeable bulk iron oxyfluoride phase (FeOF) phase was observed even at fluorination temperature close to 300 °C. Instead, at fluorination temperatures below 250 °C, scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) and X-ray photoelectron spectroscopy (XPS) analysis showed surface fluorination with nominal composition, Fe 2 O 3-x F 2x (x < 1). At fluorination temperatures of 275 °C, STEM-EELS results showed porous interconnected nanodomains of FeF 3 and Fe 2 O 3 coexisting within the same particle, and overall the particles become less dense after fluorination. We performed potentiometric intermittent titration and electrochemical impedance spectroscopy studies to understand the lithium diffusion (or apparent diffusion) in both the oxyfluoride and mixed phase FeF 3 + Fe 2 O 3 composition, and correlate the results to their electrochemical performance. Finally and further, we analyze from a thermodynamical perspective, the observed formation of the majority fluoride phase (77% FeF 3 ) and the absence of the expected oxyfluoride phase based on the relative formation energies of oxide, fluoride, and oxyfluorides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Enhanced surface flashover strength in vacuum of polymethylmethacrylate by surface modification using atmospheric-pressure dielectric barrier discharge

Polymer materials, such as polymethylmethacrylate (PMMA), are widely used as insulators in vacuum. The insulating performance of a high-voltage vacuum system is mainly limited by surface flashover of the insulators rather than bulk breakdown. Non-thermal plasmas are an efficient method to modify the chemical and physical properties of polymer material surfaces, and enhance the surface insulating performance. In this letter, an atmospheric-pressure dielectric barrier discharge is used to treat the PMMA surface to improve the surface flashover strength in vacuum. Experimental results indicate that the plasma treatment method using Ar and CF{sub 4} (10:1) as the working gas can etch the PMMA surface, introduce fluoride groups to the surface, and then alter the surface characteristics of the PMMA. The increase in the surface roughness can introduce physical traps that can capture free electrons, and the fluorination can enhance the charge capturing ability. The increase in the surface roughness and the introduction of the fluoride groups can enhance the PMMA hydrophobic ability, improve the charge capturing ability, decrease the secondary electron emission yield, increase the surface resistance, and improve the surface flashover voltage in vacuum.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Spectral tunability of cerium photoluminescence in nano sized LaF{sub 3}:Ce{sup 3+}

Nano sized LaF{sub 3}:Ce{sup 3+} was synthesized by adopting co-precipitation technique with nominal composition as well as with different molar ratio of reactants La{sup 3+} (Lanthanum) and F{sup −} (Fluoride). All the samples were subjected to X-ray diffraction (XRD), XRF, UV-Vis absorption, and PL characterizations. XRD analysis did not reveal any significant change in the diffraction profile. Particle size variations were observed with respect to change in lanthanum to fluoride molar ratio. An interesting and intense photoluminescence excitation peaks were observed for the samples prepared non-stoichiometrically. The effect of varying nominal reactant composition demonstrates a possibility of introducing tunability in cerium emission in the same host. Life time of cerium has been measured to be in the order of nano seconds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Synthesis of self-organized TiO{sub 2} nanotube arrays: Microstructural, stereoscopic, and topographic studies

In this work, titanium dioxide nanotubes were prepared by using titanium foils via electrochemical anodization in ethylene glycol solutions containing different amounts of water and fluoride in the ranges of 1%–3% and 0.15%–0.5%, respectively, to determine their effects on morphology, optical, and crystalline structure properties. Annealing processes were performed on all samples in the range between 273 and 723 K. Morphology and structure properties of the samples were studied by scanning electron microscopy, X-ray diffraction (XRD), and transmission electron microscopy. Titanium dioxide (TiO{sub 2}) nanotubes, through anodization method, are strongly influenced by conditions, like fluoride concentration and applied voltages. Tube lengths between 2 and 7 μm were obtained, exhibiting different diameters and wall thicknesses. When alternating voltage was applied, the outer surface of the nanotubes exhibited evenly spaced ring-shaped regions, while smooth tubes were observed when constant voltage was applied. Reflection peaks, corresponding to Brookite, Anatase, and Rutile, of TiO{sub 2} phases, were observed from the XRD pattern. These phases were corroborated via μXRD measurements, and the Ti{sub 3}O{sub 5} phase was also observed in detail. Absorption coefficient (α), optical band gap (Eg), and extinction coefficient (ε) of TiO{sub 2} nanotubes were calculated by transmittance spectra in the UV–Vis range. Strong absorption was noted in the UV region from reflectance and absorbance measurements. A correlation between synthesis parameters and physical properties is presented.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Beneficial effect of post-deposition treatment in high-efficiency Cu(In,Ga)Se{sub 2} solar cells through reduced potential fluctuations

World-record power conversion efficiencies for Cu(In,Ga)Se{sub 2} (CIGS) solar cells have been achieved via a post-deposition treatment with alkaline metals, which increases the open-circuit voltage and fill factor. We explore the role of the potassium fluoride (KF) post-deposition treatment in CIGS by employing energy- and time-resolved photoluminescence spectroscopy and electrical characterization combined with numerical modeling. The bulk carrier lifetime is found to increase with post-deposition treatment from 255 ns to 388 ns, which is the longest charge carrier lifetime reported for CIGS, and within ∼40% of the radiative limit. We find evidence that the post-deposition treatment causes a decrease in the electronic potential fluctuations. These potential fluctuations have previously been shown to reduce the open-circuit voltage and the device efficiency in CIGS. Additionally, numerical simulations based on the measured carrier lifetimes and mobilities show a diffusion length of ∼10 μm, which is ∼4 times larger than the film thickness. Thus, carrier collection in the bulk is not a limiting factor for device efficiency. By considering differences in doping, bandgap, and potential fluctuations, we present a possible explanation for the voltage difference between KF-treated and untreated samples.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Cardinal: A Lower-Length-Scale Multiphysics Simulator for Pebble-Bed Reactors

This paper demonstrates a multiphysics solver for pebble-bed reactors, in particular, for Berkeley’s pebble-bed -fluoride-salt-cooled high-temperature reactor (PB-FHR) (Mark I design). The FHR is a class of advanced nuclear reactors that combines the robust coated particle fuel form from high-temperature gas-cooled reactors, the direct reactor auxiliary cooling system passive decay removal of liquid-metal fast reactors, and the transparent, high-volumetric heat capacitance liquid-fluoride salt working fluids (e.g., FLiBe) from molten salt reactors. This fuel and coolant combination enables FHRs to operate in a high-temperature, low-pressure design space that has beneficial safety and economic implications. The PB-FHR relies on a pebble-bed approach, and pebble-bed reactors are, in a sense, the poster child for multiscale analysis. Relying heavily on the MultiApp capability of the Multiphysics Object-Oriented Simulation Environment (MOOSE), we have developed Cardinal, a new platform for lower-length-scale simulation of pebble-bed cores. The lower-length-scale simulator comprises three physics: neutronics (OpenMC), thermal fluids (Nek5000/NekRS), and fuel performance (BISON). Cardinal tightly couples all three physics and leverages advances in MOOSE, such as the MultiApp system and the concept of MOOSE-wrapped applications. Moreover, Cardinal can utilize graphics processing units for accelerating solutions. In this paper, we discuss the development of Cardinal and the verification and validation and demonstration simulations.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2017

Role of Mg{sup 2+}, Sr{sup 2+}, and F{sup –} ions in octacalcium phosphate crystallization

We have synthesized octacalcium phosphate (OCP) in the presence of inorganic additives (magnesium, strontium, and fluoride ions) and studied the composition, morphology, thermal stability, and dynamic dissolution of the samples thus obtained. It has been shown that, in addition to OCP, magnesium and strontium ions favor the formation of brushite and hydroxyapatite (HA), whereas fluoride ions favor the formation of HA and fluorohydroxyapatite (FHA). We have proposed a process for the preparation of powder materials whose resorption kinetics in corrosive liquid media are corrected by adding dopants capable of activating the dissolution process.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Anomalies in the Magnetic Susceptibility in the Second-Order Phase Transitions beyond the Curie Point

Taking into account the inexhaustible interest in studying the peculiarities of physical properties in the neighborhood of phase transitions and the growth of experimental investigations of cobalt fluoride, we have studied the peculiarities of magnetic susceptibility in the vicinity of the critical field H{sub C} at which cobalt fluoride performs the second-order phase transition from the antiferromagnetic phase to the angular phase. It is discovered that in the magnetic field H ‖ C{sub 4}, the magnetic susceptibility becomes infinite at H → H{sub C}. It is shown that as the magnetic field direction deviates from the C{sub 4} axis, the magnetic susceptibility in the critical field H{sub C} proves to be finite. It is also shown that the change in the magnetic susceptibility with the change in the magnetic field considerably decreases at extremely insignificant deviations of the field H from the C{sub 4} axis. Since the calculations are performed in terms of the Landau theory of phase transitions, we pay attention to the similarity and difference between the obtained results and those in the vicinity of the Curie point obtained by using the Landau theory of phase transitions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Nonmonotonic Change in the Tunnel Conductivity of an MIS Structure with a Two-Layer Insulator with an Increase in Its Thickness (by the Example of the Metal/SiO{sub 2}/CaF{sub 2}/Si System)

The effect of increasing the tunnel current in a metal–calcium fluoride–silicon structure with addition of a silicon dioxide layer between fluoride and metal (which seems paradoxical at first glance) has been considered. This effect of nonmonotonic change in the tunnel conductivity with an increase in the insulator thickness may occur at a relatively high bias at the structure and is related to the tunnel-barrier deformation, at which electrons are tunneling through its part formed by the oxide. At low biases, the occurrence/ thickening of an additional layer leads to a natural decrease in the current. Similar behavior is possible in principle for some other combinations of materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

AHTR Refueling Systems and Process Description

The Advanced High-Temperature Reactor (AHTR) is a design concept for a central station-type [1500 MW(e)] Fluoride salt-cooled High-temperature Reactor (FHR) that is currently undergoing development by Oak Ridge National Laboratory for the US. Department of Energy, Office of Nuclear Energy's Advanced Reactor Concepts program. FHRs, by definition, feature low-pressure liquid fluoride salt cooling, coated-particle fuel, a high-temperature power cycle, and fully passive decay heat rejection. The overall goal of the AHTR development program is to demonstrate the technical feasibility of FHRs as low-cost, large-size power producers while maintaining full passive safety. The AHTR is approaching a preconceptual level of maturity. An initial integrated layout of its major systems, structures, and components (SSCs), and an initial, high-level sequence of operations necessary for constructing and operating the plant is nearing completion. An overview of the current status of the AHTR concept has been recently published and a report providing a more detailed overview of the AHTR structures and mechanical systems is currently in preparation. This report documents the refueling components and processes envisioned at this early development phase. The report is limited to the refueling aspects of the AHTR and does not include overall reactor or power plant design information. The report, however, does include a description of the materials envisioned for the various components and the instrumentation necessary to control the refueling process. The report begins with an overview of the refueling strategy. Next a mechanical description of the AHTR fuel assemblies and core is provided. The reactor vessel upper assemblies are then described. Following this the refueling path structures and the refueling mechanisms and components are described. The sequence of operations necessary to fuel and defuel the reactor is then discussed. The report concludes with a discussion of the levels of maturity of the various SSCs to provide guidance for future technology developments. The conceptual design information presented in this report is very preliminary in nature. Significant uncertainty remains about several aspects of the process and even the radiation and mechanical performance of plate-type coated-particle fuel.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2012

Advanced High-Temperature Reactor Dynamic System Model Development: April 2012 Status

The Advanced High-Temperature Reactor (AHTR) is a large-output fluoride-salt-cooled high-temperature reactor (FHR). An early-phase preconceptual design of a 1500 MW(e) power plant was developed in 2011 [Refs. 1 and 2]. An updated version of this plant is shown as Fig. 1. FHRs feature low-pressure liquid fluoride salt cooling, coated-particle fuel, a high-temperature power cycle, and fully passive decay heat rejection. The AHTR is designed to be a “walk away” reactor that requires no action to prevent large off-site releases following even severe reactor accidents. This report describes the development of dynamic system models used to further the AHTR design toward that goal. These models predict system response during warmup, startup, normal operation, and limited off-normal operating conditions. Severe accidents that include a loss-of-fluid inventory are not currently modeled. The scope of the models is limited to the plant power system, including the reactor, the primary and intermediate heat transport systems, the power conversion system, and safety-related or auxiliary heat removal systems. The primary coolant system, the intermediate heat transport system and the reactor building structure surrounding them are shown in Fig. 2. These systems are modeled in the most detail because the passive interaction of the primary system with the surrounding structure and heat removal systems, and ultimately the environment, protects the reactor fuel and the vessel from damage during severe reactor transients. The reactor silo also plays an important role during system warmup. The dynamic system modeling tools predict system performance and response. The goal is to accurately predict temperatures and pressures within the primary, intermediate, and power conversion systems and to study the impacts of design changes on those responses. The models are design tools and are not intended to be used in reactor qualification. The important details to capture in the primary system relate to flows within the reactor vessel during severe events and the resulting temperature profiles (temperature and duration) for major components. Critical components include the fuel, reactor vessel, primary piping, and the primary-to-intermediate heat exchangers (P-IHXs). The major AHTR power system loops are shown in Fig. 3. The intermediate heat transfer system is a group of three pumped salt loops that transports the energy produced in the primary system to the power conversion system. Two dynamic system models are used to analyze the AHTR. A Matlab/Simulink-based model initiated in 2011 has been updated to reflect the evolving design parameters related to the heat flows associated with the reactor vessel. The Matlab model utilizes simplified flow assumptions within the vessel and incorporates an empirical representation of the Direct Reactor Auxiliary Cooling System (DRACS). A Dymola/Modelica model incorporates a more sophisticated representation of primary coolant flow and a physics-based representation of the three-loop DRACS thermal hydraulics. This model is not currently operating in a fully integrated mode. The Matlab model serves as a prototype and provides verification for the Dymola model, and its use will be phased out as the Dymola model nears completion. The heat exchangers in the system are sized using spreadsheet-based, steady-state calculations. The detail features of the heat exchangers are programmed into the dynamic models, and the overall dimensions are used to generate realistic plant designs. For the modeling cases where the emphasis is on understanding responses within the intermediate and primary systems, the power conversion system may be modeled as a simple boundary condition at the intermediate-to-power conversion system heat exchangers.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗