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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 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Experimental study of crossover from capillary to viscous fingering for supercritical CO 2 - water displacement in a homogeneous pore network

Carbon sequestration in saline aquifers involves displacing resident brine from the pore space by supercritical CO 2 (scCO 2 ). The displacement process is considered unstable due to the unfavorable viscosity ratio (logM < 0). The unstable mechanisms that affect scCO 2 - water displacement under reservoir conditions (i.e., 41 °C, 9 MPa) were investigated in a homogeneous micromodel. A wide range of injection rates (logCa = -7.61~-4.73) was studied in two sets of experiments: discontinuous-rate injection, where the micromodel was first cleaned and saturated with water before each injection rate was imposed, and continuous-rate injection, where the rate was increased after quasi-steady conditions were reached for a certain rate. For the discontinuous-rate experiments, capillary fingering and viscous fingering are the dominant mechanisms for low (logCa <= -6.61) and high injection rates (logCa >= -5.21), respectively. Crossover from capillary to viscous fingering was observed for logCa = -5.91~-5.21, resulting in a large decrease in scCO 2 saturation. The discontinuous-rate experimental results confirmed the decrease in nonwetting fluid saturation during crossover from capillary to viscous fingering predicted by numerical simulations by Lenormand et al. (1988).1 Capillary fingering was the only mechanism that dominates all injection rates in the continuous-rate experiment, and resulted in monotonic increase in scCO 2 saturation.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2011

Fluoride-conversion synthesis of homogeneous actinide oxide solid solutions

Here, a novel route to synthesize (U, Th)O2 solid solutions at a relatively low temperature of 1100 C is demonstrated. First, the separate actinide oxides reacted with ammonium bifluoride to form ammonium actinide fluorides at room temperature. Subsequently, this mixture was converted to the actinide oxide solid solution using a two-phased heat treatment, first at 610 C in static air, then at 1100 C in flowing argon. Solid solutions obeying Vegard s Law were synthesized for ThO2 content from 10 to 90 wt%. Microscopy showed that the (U, Th)O2 solid solutions synthesized with this method to have considerably high crystallinity and homogeneity, suggesting the suitability of material thus synthesized for sintering into nuclear fuel pellets at low temperatures.

(U↗
DOE OSTI2026

Selective Bidentate Coordination Reconstructs Residual PbI 2 to Homogenize Interfacial Energetics in Perovskite Solar Cells

Spatially heterogeneous interfacial energetics, often originating from residual lead iodide (PbI 2 ), represent a fundamental bottleneck to both the efficiency and operational stability of perovskite photovoltaics. Conventional PbI 2 passivation strategies based on monodentate ligands or highly polar solvents either interact weakly with PbI 2 or undesirably perturb the underlying three-dimensional perovskite lattice. Here, we report a diammonium bidentate strategy that selectively reconstructs residual PbI 2 into corner-sharing PbI 6 octahedra while preserving the bulk perovskite. Enabled by dual-site coordination, a newly designed thiophene-based bidentate ligand (MeXT) stabilizes PbI 6 units during passivation and establishes spatially homogeneous interfacial energetics. Perovskite solar cells incorporating MeXT achieve 26.19% power conversion efficiency and retain over 80% of their initial efficiency after 1000 h of continuous 1-sun illumination at 75 °C. This dual-anchor coordination passivation strategy establishes a general design principle for selectively treating residual PbI 2 and creating electronically coherent and operationally stable interfaces in perovskite photovoltaics.

ligands↗
DOE OSTI2010

Green Rust Reduction of Chromium Part 2: Comparison of Heterogeneous and Homogeneous Chromate Reduction

White and green rusts are the active chemical reagents of buried scrap iron pollutant remediation. In this work, a comparison of the initial electron-transfer step for the reduction of CrO{sub 4}{sup -2} by Fe{sub (aq)}{sup 2+} and Fe(OH){sub 2}(s) is presented. Using hybrid density functional theory and Hartree-Fock cluster calculations for the aqueous reaction, the rate constant for the homogeneous reduction of chromium by ferrous iron was determined to be 5 x 10{sup -2} M{sup -1} s{sup -1} for the initial electron transfer. Using a combination of Hartree-Fock slab and cluster calculations for the heterogeneous reaction, the initial electron transfer for the heterogeneous reduction of chromium by ferrous iron was determined to be 1 x 10{sup 2} s{sup -1}. The difference in rates is driven by the respective free energies of reaction: 33.4 vs -653.2 kJ/mol. This computational result is apparently the opposite of what has been observed experimentally, but further analysis suggests that these results are fully convergent with experiment. The experimental heterogeneous rate is limited by surface passivation from slow intersheet electron transfer, while the aqueous reaction may be an autocatalytic heterogeneous reaction involving the iron oxyhydroxide product. As a result, it is possible to produce a clear model of the pollutant reduction reaction sequence for these two reactants.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Super‐Droplet Method to Simulate Lagrangian Microphysics of Nuclear Fallout in a Homogeneous Cloud

Abstract Nuclear detonations produce hazardous local and global particles or fallout. Predicting fallout size, chemical components, and location is necessary to inform officials and determine immediate guidance for the public. However, existing nuclear detonation fallout models prescribe the particle size distributions based on limited observations. In this work, we apply the super‐droplet method, which is a numerical modeling technique developed for cloud microphysics, to simulate size distributions of particles in a mushroom cloud formed post‐detonation of a nuclear device. We model fallout formation and evolution with homogeneous nucleation and condensation of a single species and a Monte Carlo coagulation algorithm. We verify the numerical methods representing coagulation and condensation processes against analytical test problems. Additionally, we explore several scenarios for the integral system mass and yield in equivalent kilotons (kt) of TNT (trinitrotoluene). The fallout size distribution median diameter d pg follows a scaling law based on the integral system mass m v 0 kg and yield Y kt: nm. We test the effect of cloud turbulence, enhanced nucleation and growth, and vapor volatility with a sensitivity study. The range in median diameter predictions for simulations of historical tests performed over the Pacific encompass the measurements of particles sampled from the cloud caps. Predicted median particle size ranges up to 217, 123, 86, and 35 nm for historical tests with yields of 0.2, 0.7, 2, and 10 Mt, respectively. This work can be expanded in many different directions to build a more predictive model for fallout formation.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2016

Supramolecular metal-organic frameworks that display high homogeneous and heterogeneous photocatalytic activity for H 2 production

Self-assembly has a unique presence when it comes to creating complicated, ordered supramolecular architectures from simple components under mild conditions. Here, we describe a self-assembly strategy for the generation of the first homogeneous supramolecular metal-organic framework (SMOF-1) in water at room temperature from a hexaarmed [Ru(bpy) 3 ] 2+ -based precursor and cucurbit[8] uril (CB[8]). The solution-phase periodicity of this cubic transition metal-cored supramolecular organic framework (MSOF) is confirmed by small-angle X-ray scattering and diffraction experiments, which, as supported by TEM imaging, is commensurate with the periodicity in the solid state. We further demonstrate that SMOF-1 adsorbs anionic Wells-'Dawson-type polyoxometalates (WD-POMs) in a one-cage-one-guest manner to give WD-POM@SMOF-1 hybrid assemblies. Upon visible-light (500 nm) irradiation, such hybrids enable fast multi-electron injection from photosensitive [Ru(bpy) 3 ] 2+ units to redox-active WD-POM units, leading to efficient hydrogen production in aqueous media and in organic media. The demonstrated strategy opens the door for the development of new classes of liquid-phase and solid-phase ordered porous materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Redox-homogeneous, gel electrolyte-embedded high-mass-loading cathodes for high-energy lithium metal batteries

Lithium metal batteries have higher theoretical energy than their Li-ion counterparts, where graphite is used at the anode. However, one of the main stumbling blocks in developing practical Li metal batteries is the lack of cathodes with high-mass-loading capable of delivering highly reversible redox reactions. To overcome this issue, here we report an electrode structure that incorporates a UV-cured non-aqueous gel electrolyte and a cathode where the LiNi 0.8 Co 0.1 Mn 0.1 O 2 active material is contained in an electron-conductive matrix produced via simultaneous electrospinning and electrospraying. This peculiar structure prevents the solvent-drying-triggered non-uniform distribution of electrode components and shortens the time for cell aging while improving the overall redox homogeneity. Moreover, the electron-conductive matrix eliminates the use of the metal current collector. When a cathode with a mass loading of 60 mg cm -2 is coupled with a 100 µm thick Li metal electrode using additional non-aqueous fluorinated electrolyte solution in lab-scale pouch cell configuration, a specific energy and energy density of 321 Wh kg -1 and 772 Wh L -1 (based on the total mass of the cell), respectively, can be delivered in the initial cycle at 0.1 C (i.e., 1.2 mA cm -2 ) and 25 °C.

25 ENERGY STORAGE↗
DOE OSTI2021

Atomic-scale homogeneous plastic flow beyond near-theoretical yield stress in a metallic glass

Abstract The onset of yielding and the related atomic-scale plastic flow behavior of bulk metallic glasses at room temperature have not been fully understood due to the difficulty in performing the atomic-scale plastic deformation experiments needed to gain direct insight into the underlying fundamental deformation mechanisms. Here we overcome these limitations by combining a unique sample preparation method with atomic force microscopy-based indentation, which allows study of the yield stress, onset of yielding, and atomic-scale plastic flow of a platinum-based bulk metallic glass in volumes containing as little as approximately 1000 atoms. Yield stresses markedly higher than in conventional nanoindentation testing were observed, surpassing predictions from current models that relate yield stress to tested volumes; subsequent flow was then established to be homogeneous without exhibiting collective shear localization or loading rate dependence. Overall, variations in glass properties due to fluctuations of free volume are found to be much smaller than previously suggested.

Yu, Jiaxin↗
DOE OSTI2015

Low-temperature synthesis of homogeneous solid solutions of scheelite-structured Ca 1-x Sr x WO 4 and Sr 1-x Ba x WO 4 nanocrystals

Here, a series of compositionally complex scheelite-structured nanocrystals of the formula A 1-x A’ x WO 4 (A = Ca, Sr, Ba) have been prepared under benign synthesis conditions using the vapor diffusion sol–gel method. Discrete nanocrystals with sub-20 nm mean diameters were obtained after kinetically controlled hydro- lysis and polycondensation at room temperature, followed by composition-dependent thermal aging at or below 60 °C. Rietveld analysis of X-ray diffraction data and Raman spectroscopy verified the synthesis of continuous and phase-pure nanocrystal solid solutions across the entire composition space for A 1-x A’ x WO 4 , where 0 ≤ x ≤ 1. Elemental analysis by X-ray photoelectron and inductively coupled plasma- atomic emission spectroscopies demonstrated excellent agreement between the nominal and experi- mentally determined elemental stoichiometries, while energy dispersive X-ray spectroscopy illustrated good spatial elemental homogeneity within these nanocrystals synthesized under benign conditions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Efficiency analysis of helium-cooled MAS DNP: case studies of surface-modified nanoparticles and homogeneous small-molecule solutions

Despite the growing number of successful applications of dynamic nuclear polarization (DNP)-enhanced magic-angle spinning (MAS) NMR in structural biology and materials science, the nuclear polarizations achieved by current MAS DNP instrumentation are still considerably lower than the theoretical maximum. Here, the method could be significantly strengthened if experiments were performed at temperatures much lower than those currently widely used (~100 K). Recently, the prospects of helium (He)-cooled MAS DNP have been increased with the instrumental developments in MAS technology that uses cold helium gas for sample cooling. Despite the additional gains in sensitivity that have been observed with He-cooled MAS DNP, the performance of the technique has not been evaluated in the case of surfaces and interfaces that benefit the most from DNP. Herein, we studied the efficiency of DNP at temperatures between ~30 K and ~100 K for organically functionalized silica material and a homogeneous solution of small organic molecules at a magnetic field B 0 = 16.4 T. We recorded the changes in signal enhancement, paramagnet-induced quenching and depolarization effects, DNP build-up rate, and Boltzmann polarization. For these samples, the increases in MAS-induced depolarization and DNP build-up times at around 30 K were not as severe as anticipated. In the case of the surface species, we determined that MAS DNP at 30 K provided ~10 times higher sensitivity than MAS DNP at 90 K, which corresponds to the acceleration of experiments by multiplicative factors of up to 100.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Zirconium and hafnium polyhedral oligosilsesquioxane complexes – green homogeneous catalysts in the formation of bio-derived ethers via a MPV/etherification reaction cascade

The polyhedral oligosilsesquioxane complexes, {[(isobutyl) 7 Si 7 O 12 ]ZrOPr i ·(HOPr i )}2 (I), {[(cyclohexyl) 7 Si 7 O 12 ]ZrOPr i ·(HOPr i )} 2 (II), {[(isobutyl) 7 Si 7 O 12 ]HfOPr i ·(HOPr i )} 2 (III) and {[(cyclohexyl) 7 Si 7 O 12 ]HfOPr i ·(HOPr i )} 2 (IV), were synthesized in good yields from the reactions of M(OPr i ) 4 (M = Zr, Hf) with R-POSS(OH) 3 (R = isobutyl, cyclohexyl), resp. I–IV were characterized by 1 H, 13 C and 29 Si NMR spectroscopy and their dimeric solid-state structures were confirmed by X-ray analysis. I–IV catalyze the reductive etherification of 2-hydroxy- and 4-hydroxy and 2-methoxy and 4-methoxybenzaldehyde and vanillin to their respective isopropyl ethers in isopropanol as a “green” solvent and reagent. I–IV are durable and robust homogeneous catalysts operating at temperatures of 100–160 °C for days without significant loss of catalytic activity. Likewise, I–IV selectively catalyze the conversion of 5-hydroxymethylfurfural (HMF) into 2,5-bis(isopropoxymethyl)furane (BPMF), a potentially high-performance fuel additive. Similar results were achieved by using a combination of M(OPr i ) 4 and ligand R-POSS(OH) 3 as a catalyst system demonstrating the potential of this “in situ” approach for applications in biomass transformations. A tentative reaction mechanism for the reductive etherification of aldehydes catalysed by I–IV is proposed.

09 BIOMASS FUELS↗
DOE OSTI2010

Energetic Galerkin BEM for 2D Wave Propagation Problems in Piecewise Homogeneous Media

We consider Dirichlet-Neumann problems for two-dimensional wave propagation analysis in piecewise homogeneous media reformulated in terms of boundary integral equations. The related weak problem is based on a space-time energetic formulation recently introduced for single-domain problems. The discretization phase is carried out by means of Galerkin boundary element method. Numerical results obtained with this procedure will be presented and analyzed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Electrical and kinetical aspects of homogeneous dielectric-barrier discharge in xenon for excimer lamps

A pulsed dielectric-barrier discharge in xenon has been simulated for operating conditions typical to excimer lamps, in which the discharge is considered spatially homogeneous. The computer model developed is based on the xenon plasma chemistry, the circuit, and the Boltzmann equations. First, the validity of the physical model was checked and compared to experimental and theoretical works, and then the model is applied in the case of a sinusoidal voltage at period frequencies in the range of 50 kHz-2 MHz. The results obtained with the present description are in good agreement with experimental measurements and one-dimensional fluid prediction in terms of electrical characteristics and vacuum ultraviolet (vuv) emission. The effect of operation voltage, power source frequency, dielectric capacitance, as well as gas pressure on the discharge efficiency and the 172, 150, and 147 nm photon generation, under the typical experimental operating conditions and for the case of a sinusoidal applied voltage, have been investigated and discussed. Calculations suggest that the overall conversion efficiency from electrical energy to vuv emission in the lamp is greater than 38%, and it will be very affected at high power source frequency and high gas pressure with a significant dependence on the dielectric capacitance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

Fast Transient And Spatially Non-Homogenous Accident Analysis Of Two-Dimensional Cylindrical Nuclear Reactor

The research about fast transient and spatially non-homogenous nuclear reactor accident analysis of two-dimensional nuclear reactor has been done. This research is about prediction of reactor behavior is during accident. In the present study, space-time diffusion equation is solved by using direct methods which consider spatial factor in detail during nuclear reactor accident simulation. Set of equations that obtained from full implicit finite-difference discretization method is solved by using iterative methods ADI (Alternating Direct Implicit). The indication of accident is decreasing macroscopic absorption cross-section that results large external reactivity. The power reactor has a peak value before reactor has new balance condition. Changing of temperature reactor produce a negative Doppler feedback reactivity. The reactivity will reduce excess positive reactivity. Temperature reactor during accident is still in below fuel melting point which is in secure condition.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2011

Effect of hydrogenation on transport and magnetic properties in homogeneous amorphous Mn{sub x}Ge{sub 1-x}:H films

Homogeneous amorphous Mn{sub x}Ge{sub 1-x}:H films were synthesized under thermal nonequilibrium condition by magnetron co-sputtering technology with hydrogen in Ar atmosphere. Compared to the Mn{sub x}Ge{sub 1-x} films without hydrogen, the Mn{sub x}Ge{sub 1-x}:H films with hydrogen show higher concentration of hole carriers, larger conductivity, and higher saturation magnetization. Moreover, it was found that the anomalous Hall resistivity is proportional to the perpendicular magnetization. These electrical and magnetic properties indicate that the ferromagnetism of the Mn{sub x}Ge{sub 1-x}:H films is intrinsic ferromagnetism mediated by the spin-polarized hole carriers.

36 MATERIALS SCIENCE↗