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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Understanding the Effects of Bi Modification on the Properties of Ni-Rich Cathodes

With the skyrocketing market demands for energy storage, lithium ions batteries (LIB) with higher energy density are urgently needed. Cathodes play a critical role in determining the energy density of LIB, and the most popular one is Ni-rich cathode due to its high capacity. However, due to the fast structural degradation, Ni-rich cathode materials should be further modified to achieve higher stability. Herein, we introduce bismuth ions in LiNi 0.83 Co 0.11 Mn 0.06 O 2 cathodes by adding Bi 2 O 3 during sintering to optimize the specific capacity and cycle stability. By adding 0.1% mol Bi, the Li + diffusion and structural stability are effectively optimized, leading to improved electrochemical performances. Further, the modified sample delivers much higher specific capacity (222.9 mAhg -1 , 0.05 C) than unmodified sample (204 mAhg -1 , 0.05 C). Meanwhile, the specific capacity of optimized sample after 100 cycles at 0.33 C is 27.75 mAhg -1 higher than that of unmodified sample. Therefore, this work demonstrates that Bi modification can be regarded as a possible solution to optimizing the electrochemical performance of Ni-rich cathodes.

25 ENERGY STORAGE↗
DOE OSTI2020

Toward Validation of Toxicological Interpretation of Diffusive Gradients in Thin Films in Marine Waters Impacted by Copper

Determination of Mytilus galloprovincialis larvae median effect concentration (EC50), of Cu in coastal marine waters by diffusive gradient in thin-films (DGT), has been shown to effectively reduce the need to consider dissolved organic carbon (DOC) concentration and quality. West coast marine and estuarine organisms’ chronic toxicity test protocol was used to validate previously modelled protective effects, afforded to highly sensitive marine larvae by ligand competition, in five diverse site waters. The results demonstrate significant narrowing of toxicological endpoints, where EC50s ranged from 3.74 – 6.67 µg/L as CDGT Cu versus 8.76 – 26.8 µg/L as CuDISS over a DOC range of 0.74 – 3.11 mg/L. Additionally, DOC quality (characterized by fluorescence excitation and emission matrices) indicates that the heterogeneity of competing Cu binding ligands, in common marine waters, minimizes the need for class determinations toward explaining the degree of protection, when assumptions in criterion maximum concentration (CMC) setting are conservative. A CDGT Cu EC50 of 3.7 µg/L, and corresponding CMC CDGT Cu of 1.8 µg/L, for universal application by regulatory compliance-monitoring programs, are proposed as a superior approach toward both integration of dynamic water quality over effective exposure periods and quantification of biologically-relevant trace Cu speciation and are demonstrated by in situ data.

Diffusive Gradients in Thin-films, copper, seawate↗
DOE OSTI2013

Higher-order compositional modeling of three-phase flow in 3D fractured porous media based on cross-flow equilibrium

Numerical simulation of multiphase compositional flow in fractured porous media, when all the species can transfer between the phases, is a real challenge. Despite the broad applications in hydrocarbon reservoir engineering and hydrology, a compositional numerical simulator for three-phase flow in fractured media has not appeared in the literature, to the best of our knowledge. In this work, we present a three-phase fully compositional simulator for fractured media, based on higher-order finite element methods. To achieve computational efficiency, we invoke the cross-flow equilibrium (CFE) concept between discrete fractures and a small neighborhood in the matrix blocks. We adopt the mixed hybrid finite element (MHFE) method to approximate convective Darcy fluxes and the pressure equation. This approach is the most natural choice for flow in fractured media. The mass balance equations are discretized by the discontinuous Galerkin (DG) method, which is perhaps the most efficient approach to capture physical discontinuities in phase properties at the matrix-fracture interfaces and at phase boundaries. In this work, we account for gravity and Fickian diffusion. The modeling of capillary effects is discussed in a separate paper. We present the mathematical framework, using the implicit-pressure-explicit-composition (IMPEC) scheme, which facilitates rigorous thermodynamic stability analyses and the computation of phase behavior effects to account for transfer of species between the phases. A deceptively simple CFL condition is implemented to improve numerical stability and accuracy. We provide six numerical examples at both small and larger scales and in two and three dimensions, to demonstrate powerful features of the formulation.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Diffusion, atomic transport, and ordering in Al-Zr alloys: FCC and liquid phases

Additive manufacturing of materials with controlled microstructure demands knowledge of atomic scale properties near the solid-liquid transition state. Many of these properties are not affordable by experimental techniques and computer modeling is the possible solution to the problem. In this paper, we present the results of an extended atomistic study of intrinsic atomic transport due to vacancy diffusion in FCC and L12 solid phases and diffusion in the liquid phase of Al-Zr alloys. A deceleration of the overall self-diffusion was observed when Zr was added to Al. The effect was stronger in the solid and weaker in the liquid. Additionally, the effect was strongly temperature dependent in the solid phases, but not in the liquid. Atomic transport was chemically biased: transport of Zr atoms was significantly slower than that of Al atoms, and this bias effect was stronger in the solid phases. The overall diffusion and chemical ordering processes in the liquid state were five to six orders in magnitude faster than in the solid. Chemical short-range order parameters in the liquid saturated at values close to those in the ordered L12 structure of Al3Zr. Chemical and structural ordering in the solid phases was negligible over the modeled microsecond time scale. Here, the results are discussed in view of optimizing additive manufacturing parameters for the controlled formation of metastable L1 2 precipitates.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Hybridizing pseudo-Hamiltonians and non-local pseudopotentials in diffusion Monte Carlo

An accurate treatment of effective core potentials (ECPs) requires care in continuum quantum Monte Carlo (QMC) methods. While most QMC studies have settled on the use of familiar non-local (NL) pseudopotentials with additional localization approximations, these approaches have been shown to result in moderate residual errors for some classes of molecular and solid state applications. Here, we revisit an idea proposed early in the history of QMC ECPs that does not require localization approximations, namely, a differential class of potentials referred to as pseudo-Hamiltonians. We propose to hybridize NL potentials and pseudo-Hamiltonians to reduce residual non-locality of existing potentials. We derive an approach to recast pseudopotentials for 3d elements as hybrid pseudo-Hamiltonians with optimally reduced NL energy. We demonstrate the fidelity of the hybrid potentials by studying atomic ionization potentials of Ti and Fe and the binding properties of TiO and FeO molecules with diffusion Monte Carlo (DMC). We show that localization errors have been reduced relative to potentials with the same NL channels for Sc–Zn by considering the DMC energy change with respect to the choice of approximate localization. While localization error decreases proportionate to the reduced NL energy without a Jastrow, with a Jastrow, the degree of reduction decreases at higher filling of the d-shell. Our results suggest that a subset of existing ECPs may be recast in this hybrid form to reduce the DMC localization error. They also point to the prospect of further reducing this error by generating ECPs within this hybrid form from the start.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Chemically-biased diffusion and segregation impede void growth in irradiated Ni-Fe alloys

Recent irradiations of Ni-Fe concentrated solid solution alloys have demonstrated significant improvement of radiation performance. This improvement is attributed to redistribution of the alloying elements near sinks of point defects (voids, dislocations) due to chemically-biased atomic diffusion, where vacancies have preference to migrate via Fe atoms and interstitials via Ni atoms. In Ni-Fe, all sinks are enriched by Ni atoms, which strongly affects further interactions of radiation-produced mobile defects with voids and dislocations, hence void growth and dislocation climb. Ni-decorated sinks interact stronger with interstitial atoms than vacancies, which enhances dislocation loops growth. At the same time, Ni segregation creates Fe-enriched “channels” for vacancy migration out of the damage region to agglomerate in the outer regions, inaccessible to interstitial atoms. Furthermore, strong effect of chemically-biased diffusion is supported by transmission electron microscope characterization and calls for special attention in designing alloys with desired properties through tuning defect mobilities.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Role of Presolvation and Anharmonicity in Aqueous Phase Hydrated Proton Solvation and Transport

Results from condensed phase ab initio molecular dynamics (AIMD) simulations suggest a proton transfer reaction is facilitated by “presolvation” in which the hydronium is transiently solvated by four water molecules, similar to the typical solvation structure of water, by accepting a weak hydrogen bond from the fourth water molecule. A new version 3.2 multistate empirical valence bond (MS-EVB 3.2) model for the hydrated excess proton incorporating this presolvation behavior is therefore developed. The classical MS-EVB simulations show similar structural properties as those of the previous model but with significantly improved diffusive behavior. The inclusion of nuclear quantum effects in the MS-EVB also provides an even better description of the proton diffusion rate. Finally, to quantify the influence of anharmonicity, a second model (aMS-EVB 3.2) is developed using the anharmonic aSPC/Fw water model, which provides similar structural properties but improved spectroscopic responses at high frequencies.

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

Monte-Carlo simulation of nano-collected current from a silicon sample containing a linear arrangement of uncapped nanocrystals

A Monte-Carlo simulation algorithm is used to study electron beam induced current in an intrinsic silicon sample, which contains at its surface a linear arrangement of uncapped nanocrystals positioned in the irradiation trajectory around the hemispherical collecting nano-contact. The induced current is generated by the use of electron beam energy of 5 keV in a perpendicular configuration. Each nanocrystal is considered as a recombination center, and the surface recombination velocity at the free surface is taken to be zero. It is shown that the induced current is affected by the distance separating each nanocrystal from the nano-contact. An increase of this separation distance translates to a decrease of the nanocrystals density and an increase of the minority carrier diffusion length. The results reveal a threshold separation distance from which nanocrystals have no more effect on the collection efficiency, and the diffusion length reaches the value obtained in the absence of nanocrystals. A cross-section characterizing the nano-contact ability to trap carriers was determined.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Principles of robust innate immune response to viral infections: a multiplex network analysis

The human innate immune response, particularly the type-I interferon (IFN) response, is highly robust and effective first line of defense against virus invasion. IFN molecules are produced and secreted frominfected cells upon virus infection and recognition. They then act as signaling/communicationmolecules to activate an antiviral response in neighboring cells so that those cells become refractory to infection. Previous experimental studies have identified the detailed molecular mechanisms for the IFN signaling and response. However, the principles underlying how host cells use IFN to communicate with each other to collectively and robustly halt an infection is not understood. Here we take a multiplex network modeling approach to provide a theoretical framework to identify key factors that determine the effectiveness of the IFN response against virus infection of a host. In this approach, we consider the virus spread among host cells and the interferon signaling to protect host cells as a competition process on a two-layer multiplex network. We focused on two types of network topology, i.e., the Erdős-Rényi (ER) network and the Geometric Random (GR) network, which represent the scenarios when infection of cells is mostly well mixed (e.g., in the blood) and when infection is spatially segregated (e.g., in tissues), respectively.We show that in general, the IFN response works effectively to stop viral infection when virus infection spreads spatially (a most likely scenario for initial virus infection of a host at the peripheral tissue). Importantly, we show that the effectiveness of the IFN response is robust against large variations in the distance of IFN diffusion as long as IFNs diffuse faster than viruses and they can effectively induce antiviral responses in susceptible host cells. This suggests that the effectiveness of the IFN response is insensitive to the specific arrangement of host cells in peripheral tissues. Thus, our work provides a quantitative explanation of why the IFN response can serve an effective and robust response in different tissue types to a wide range of viral infections of a host.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2015

Emission intensity of the λ = 1.54 μm line in ZnO films grown by magnetron sputtering, diffusion doped with Ce, Yb, Er

The effect of the Er{sup 3+}-ion excitation type on the photoluminescence spectra of crystalline ZnO(ZnO〈Ce, Yb, Er〉) films is determined in the cases of resonant (λ = 532 nm, Er{sup 3+}-ion transition from {sup 4}S{sub 3/2}, {sup 2}H{sub 11/2} levels to {sup 4}I{sub 15/2}) and non-resonant (λ = 325 nm, in the region near the ZnO band-edge emission) excitation. It is shown that resonant excitation gives rise to lines with various emission intensities, characteristic of the Er{sup 3+}-ion intracenter 4f transition with λ = 1535 nm when doping crystalline ZnO films with three rare-earth ions (REIs, Ce, Yb, Er) or with two impurities (Ce, Er) or (Er, Yb), independently of the measurement temperature (T = 83 and 300 K). The doping of crystalline ZnO films with rare-earth impurities (Ce, Yb, Er) leads to the efficient transfer of energy to REIs, a consequence of which is the intense emission of an Er{sup 3+} ion in the IR spectral region at λ{sub max} = 1535 nm. The kick-out diffusion mechanism is used upon the sequential introduction of impurities into semiconductor matrices and during the postgrowth annealing of the ZnO films under study. The crystalline ZnO films doped with Ce, Yb, Er also exhibit intense emission in the visible spectral region at room temperature, which makes them promising materials for optoelectronics.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Ceramic Rolling and Annealing on Mechanical Properties of AlCoCrFeNi{sub 2.1} Eutectic High-Entropy Alloys

It was firstly proved that AlCoCrFeNi{sub 2.1} could optimize the strength-ductility combination by ceramic rolling at room temperature. The technique greatly enhanced the strength of the materials at the price of slight ductility, which is different from the previous studies. When the thickness reduction was 23.06%, the yield strength and compressive strength were 1611.42 and 2212.99 MPa, respectively, with the plastic strain of 28.36%. Such an excellent combination of strength and ductility was attributed to the distribution of the residual stress, the high hydrostatic stress and the shear bands in ceramic rolling process. The plastic strain of the material increased to 38.54%, and the strength reduced to 1900.73 MPa after annealing at 800 °C for 1 h. A lot of like-flower patterns of recrystallized ultrafine grain were observed after annealing at 800 °C due to the sluggish diffusion in HEAs and the effect of ceramic rolling. In addition, after annealing at 800 °C, the fracture mode changed to shearing fracture of microvoid aggregation from cleavage/quasi-cleavage fracture of as-rolled sample due to the deposition of the second phase in the tested sample.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Stochastic models for surface diffusion of molecules

We derive a stochastic model for the surface diffusion of molecules, starting from the classical equations of motion for an N-atom molecule on a surface. The equation of motion becomes a generalized Langevin equation for the center of mass of the molecule, with a non-Markovian friction kernel. In the Markov approximation, a standard Langevin equation is recovered, and the effect of the molecular vibrations on the diffusion is seen to lead to an increase in the friction for center of mass motion. This effective friction has a simple form that depends on the curvature of the lowest energy diffusion path in the 3N-dimensional coordinate space. We also find that so long as the intramolecular forces are sufficiently strong, memory effects are usually not significant and the Markov approximation can be employed, resulting in a simple one-dimensional model that can account for the effect of the dynamics of the molecular vibrations on the diffusive motion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Effect of Heat Treatment on Madagascar Dravite Tourmaline: UV-Visible and Diffuse Reflectance Infrared Spectroscopic Characterization

The color change and chemical behavior of Madagascar dravite when subjected to heating in air atmosphere were studied by energy-dispersive X-ray fluorescence spectrometry, UV-visible (UV-vis) spectroscopy and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Heat treatment was performed with temperatures of 500, 600, and 700°C for 2 h. Colors and color differences were measured and evaluated using CIELAB color measurement. The origin of color and its change after treatment are assessed via UV-vis spectra. The diffuse reflectance infrared spectra of the dravites revealed major absorption bands of OH, BO{sub 3}, Si{sub 6}O{sub 18}, and R–OH (where R = Fe, Mg). The variation of infrared spectra with increasing temperature indicates the deformation of R–OH bonds in an octahedron and, further, the deformation of BO{sub 3} and Si{sub 6}O{sub 18}. The results of color change may be utilized to enhance the color or clarity in dravite tourmaline and for generating satisfactory color.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Effects of irradiation on the interface between U-Mo and zirconium diffusion barrier

Irradiated fuel plates were characterized by microscopy that focused on the interface between U–Mo and Zr. Before irradiation, there were three major sub-layers identified in the U–Mo/Zr interface, namely, UZr 2 , Mo 2 Zr, and U with low Mo. The typical total thickness of this U–Mo/Zr interaction is 2–3 microns. The UZr 2 sub-layer formed during fuel fabrication remains stable after irradiation, without large bubbles/porosity accumulation. However, this sub-layer becomes increasingly discontinuous as burnup increases. The low-Mo sub-layer exhibits numerous sub-micron bubbles/porosity at low burnup. Larger, interconnected porosity in this sub-layer was observed in a medium-burnup fuel specimen. However, at higher burnup, regions with the extra-large bubbles/porosity (i.e., larger than 5 ?m) were observed at least 5 microns away from the original location of this sub-layer. The mechanism for the formation of the extra-large bubbles/porosity is still unclear at this time. In general, the U–Mo/Zr interface in monolithic U–Mo fuels is relatively stable after irradiation. As a result, no large detrimental defects, such as large interfacial bubbles or cracks/delamination, were observed in the fuel plates characterized.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Development of a Novel Accelerator for Neutron Transport Solution Using the Galerkin Spectral Element Methods (Final Report)

This report summarizes the results of a three-year research project sponsored by the U.S. Department of Energy (DOE) Nuclear Energy University Program (NEUP) to develop and implement advanced acceleration schemes for the DOE NEAMS neutronics code PROTEUSSN. The project team included the University of Massachusetts Lowell, The Ohio State University, University of Michigan, and Argonne National Laboratory. The PROTEUS code is a high-fidelity capable deterministic neutron transport code based on unstructured finite element meshes, which solves the steady-state and transient neutron transport problem using the 2nd-order discrete ordinate method (SN2ND), the method of characteristics (MOC), and the advanced nodal transport method (NODAL). The DSA scheme has been implemented in PROTEUS to speed up SN transport calculations. The existing DSA scheme employs a consistent finite element formulation on the same fine mesh structure as the SN solution While the use of consistent discretizations makes the DSA method effective, it does not necessarily make it efficient because the numerical solution of a discretized elliptic diffusion problem itself can be costly, particularly when the problem size becomes large. We developed a new discontinuous Galerkin (DG) discretization of the diffusion equation, called DG-DSA, which can effectively and efficiently accelerate the SN transport iterations. As compared with the previous work, the novelty of our method is that the diffusion equation is solved on a coarse-mesh grid using the DG methods, and the DG diffusion discretization incorporates local hp adaptation, i.e., local adaptation of mesh size and/or polynomial degree, based on local total cross section (or optical thickness). Therefore, the resulting number of degrees of freedom (DOF) of the DG discretization is much less than the conventional consistent DSA discretizations, and thus DG-DSA can achieve significant improvement in computational efficiency. We implemented this scheme in PROTEUS-SN. In addition, we developed a new stabilization scheme named linear prolongation CMFD (lpCMFD). A novel feature of this scheme is that the conventional flat flux ratio–based scaling approach is replaced with a linear interpolation of the scalar flux differences at the coarse-mesh cell edges between the neutron transport and CMFD calculations. Fourier convergence analysis and numerical results show that lpCMFD is unconditionally stable and more effective than other CMFD based on acceleration schemes such as pCMFD, odCMFD. We also developed a new nonlinear diffusion acceleration scheme for solving neutron transport equations. This scheme, called LR-NDA, employs a local refinement approach on the framework of CMFD by solving a local boundary value problem of the scalar flux on the coarse-mesh structure to replace the piecewise constant scalar flux obtained by CMFD. The refined flux is then used to update the scalar flux in the neutron transport source iteration. It has been demonstrated that that LR-NDA is much more effective and stable than CMFD for a wide range of optical thicknesses. LR-NDA is a local adaptive method, which means LR-NDA does not necessarily require local refinement for all the coarse-mesh cells on the problem domain, i.e., it can be used only for relatively optically thick regions where the standard CMFD scheme would encounter the convergence problem.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗