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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 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Stability of gas atomized reactive powders through multiple step in-situ passivation

A method for gas atomization of oxygen-reactive reactive metals and alloys wherein the atomized particles are exposed as they solidify and cool in a very short time to multiple gaseous reactive agents for the in-situ formation of a protective reaction film on the atomized particles. The present invention is especially useful for making highly pyrophoric reactive metal or alloy atomized powders, such as atomized magnesium and magnesium alloy powders. The gaseous reactive species (agents) are introduced into the atomization spray chamber at locations downstream of a gas atomizing nozzle as determined by the desired powder or particle temperature for the reactions and the desired thickness of the reaction film.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Heat-activated Plasmonic Chemical Sensors for Harsh Environments

A passive plasmonics based chemical sensing system to be used in harsh operating environments was investigated and developed within this program. The initial proposed technology was based on combining technologies developed at the SUNY Polytechnic Institute Colleges of Nanoscale Science and Engineering (CNSE) and at the University of Minnesota (UM). Specifically, a passive wireless technique developed at UM was to utilize a heat-activated plasmonic design to passively harvest the thermal energy from within a combustion emission stream and convert this into a narrowly focused light source. This plasmonic device was based on a bullseye design patterned into a gold film using focused ion beam methods (FIB). Critical to the design was the use of thermal stabilizing under and overlayers surrounding the gold film. These stabilizing layers were based on both atomic layer deposited films as well as metal laminate layers developed by United Technologies Aerospace Systems (UTAS). While the bullseye design was never able to be thermally stabilized for operating temperatures of 500oC or higher, an alternative energy harvesting design was developed by CNSE within this program. With this new development, plasmonic sensing results are presented where thermal energy is harvested using lithographically patterned Au nanorods, replacing the need for an external incident light source. Gas sensing results using the harvested thermal energy are in good agreement with sensing experiments, which used an external incident light source. Principal Component Analysis (PCA) was used to reduce the wavelength parameter space from 665 variables down to 4 variables with similar levels of demonstrated selectivity. The method was further improved by patterning rods which harvested energy in the near infrared, which led to a factor of 10 decrease in data acquisition times as well as demonstrated selectivity with a reduced wavelength data set. The combination of a plasmonic-based energy harvesting sensing paradigm with PCA analysis and wavelength down selection offers a novel path towards simplification and integration of plasmonic-based sensing methods using selected wavelengths rather than a full spectral analysis. Integration efforts were designed and modeled for thermal and mass transport considerations by UTAS which led to the 3D printing of scaled models that would serve as the housing for the alternative energy harvesting plasmonic chemical sensor design developed by CNSE.

47 OTHER INSTRUMENTATION↗
DOE OSTI2022

Long–Cycling Sulfide–Based All–Solid–State Batteries Enabled by Electrochemo–Mechanically Stable Electrodes

Anode significantly determines the energy density of all-solid-state Lithium batteries (ASLBs). Silicon (Si) and Lithium (Li) metal are two of the most attractive anodes because of their ultrahigh theoretical capacities. However, most investigations focus on Li metal; the great potential of Si is underrated. This study investigates Si anode's stability, processability, and cost in ASLBs and compares them with Li metal. Moreover, the single-crystal LiNi 0.8 Co 0.1 Mn 0.1 O 2 is stabilized with a lithium silicate (Li 2 SiO x ) through a scalable sol-gel method. ASLBs with a cell-level energy density of 285 Wh kg -1 are obtained through sandwiching Si anode, thin sulfide solid-state electrolyte membrane, and interface stabilized LiNi 0.8 Co 0.1 Mn 0.1 O 2 . The full cell delivered a high capacity of 145 mAh g -1 at C/3 and maintained stability for 1000 cycles. This work inspires commercializing the ASLBs on a large scale with exciting manufacturing lines for large-scale, safe, and economical energy storage.

25 ENERGY STORAGE↗
DOE OSTI2016

Studies on synthesis of reduced graphene oxide (RGO) via green route and its electrical property

Highlights: • RGO-1 and RGO-2 were synthesized by green method using different phytoextracts. • M. indica L., S. tuberosum L. phytoextracts act as reducing and stabilizing agents. • Conjugated structure of graphene is established following partial reduction of GO. • Electrical conductivities of RGO-1 and RGO-2 are higher than GO. - Abstract: An environmentally friendly method has been applied for the preparation of reduced graphene oxide (RGO). This method was developed by using polyphenols that contained a phytoextract of Mangifera indica L. along with Solanum tuberosum L. as reducing agents since they are non-toxic and naturally available. The phytoextracts used in the production of RGO was set between 60 and 70 °C. Graphene oxide (GO) was prepared by modified Hummer’s method as reported in earlier findings. Structural and morphological studies demonstrate that the part of the oxygen functionalities in GO can be removed by following green reduction. Characterizations of the resulting product have been done by X-ray diffraction, FTIR, UV–vis and Raman spectroscopy. FESEM, TEM, EDX spectrum, TGA, DLS and Zeta potential measurements of the samples have also been carried out to study the morphological, thermal and surface charge characteristics. Electrical conductivity was also measured to check the extent of reduction of GO to RGO.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Real-Time Feedback-Based Optimization of Distribution Grids: A Unified Approach

This paper develops an algorithmic framework for real-time optimization of distribution-level distributed energy resources (DERs). The framework optimizes the operation of both DERs that are individually controllable and groups of DERs (i.e., aggregations) that are jointly controlled at an electrical point of connection. From an electrical standpoint, wye and delta single- and multi-phase connections are accounted for. The algorithm enables (groups of) DERs to pursue given performance objectives, while adjusting their (aggregate) powers to respond to services requested by grid operators and to maintain electrical quantities within engineering limits. The design of the algorithm leverages a time-varying bi-level problem formulation capturing various performance objectives and engineering constraints, and an online implementation of primal-dual projected-gradient methods. The gradient steps are suitably modified to accommodate appropriate measurements from the distribution network and the DERs. Stability and convergence claims are established in terms of tracking of the solution of the time-varying optimization problem. Finally, the method is tested in a realistic distribution.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2019

Analysis of Methods of Investigation of the Vibration–Rotation Spectrum of Monomers and Dimers of Sulphur Hexafluoride Isotopes

The stability of the system of sulphur hexafluoride dimer SF{sub 6} under the action of external laser radiation has been estimated using ab initio quantum-chemical calculations of the vibration–rotation spectrum of SF{sub 6} monomers as well as homo- and heterodimers. It is noted that for simple CO molecule as an example, the most widely used method of calculations based on the Hessian matrix approach cannot serve as a reliable instrument in quantitative calculations of some molecular systems. As a potential analog, we have tested the algorithm for obtaining the vibration–rotation spectrum based on molecular dynamics data.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2018

Center for Extended Magnetohydrodrynamic Modeling

This work used the NIMROD code to solve two tokamak regimes found on the DIII-D tokamak. The first regime studied is the Quiescent H-mode regime that has the advantage of enabling tokamak high performance without the deleterious effects of Edge Localized Modes (ELMs). ELMs are a possible impediment to the success of tokamaks as a burning plasma reactor and the QH mode regime provides a mechanism for avoiding it. The QH mode achieves this state due to the appearance of long wavelength instability that saturates instead of reaching an ELM state. NIMROD simulations were able to describe many of the features of a particular discharge, including the importance of shear flow in reaching the state, the role of the parallel heat flux to decorrelate the temperature and velocity fluctations, and in the correlation of density and velocity fluctations to provide the density pumpout. This work resulted in two direct publications and an invited talk. Progress towards these publications resulted in two more publications (verification and solving the Grad-Shafranov equation with scrape-off-layer currents). The second regime studied was the Giant Sawtooth regime whereby energetic particles affect the stability of the 1/1 mode. This work resulted in performance improvements of NIMROD's energetic particle algorithms, and improvements to the drift-kinetic equation infrastructure used by both continuum and energetic particle closure methods. The studies proved more computationally demanding than expected because as the 1/1 is stabilized, the near marginal conditions cause long simulations times. Publication of this work is in progress under other funding.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

Control on the homogeneity and crystallinity of Zn0.5Cd0.5S nanocomposite by different reaction conditions with high photocatalytic activity for hydrogen production from water

Highlights: • The effects of the various reaction conditions are investigated. • Different photocatalytic activities attributed to the different homogeneity and crystallinity of the nanoparticles. • Combination of good crystallinityand homogeneityresulted in an excellent photocatalytic activity. - Abstract: Zn{sub 0.5}Cd{sub 0.5}S nanoparticles with phase homojunctions were prepared by a one-step hydrothermal method with thioacetamide as sulfur source. The effects of the various reaction conditions, such as initial concentrations of Zn and Cd ions, initial content of sulfur source in the reaction mixture, and the temperature rising rate, are investigated. The photocatalytic activities for H{sub 2} evolution from water in the presence of sacrificial reagents of these Zn{sub 0.5}Cd{sub 0.5}S nanoparticles were significantly affected by the reaction conditions. These differences on the photocatalytic activities can be attributed to the different homogeneity and crystallinity of the nanoparticles prepared at different reaction conditions. A faster reaction rate leads to the formation of Zn{sub 0.5}Cd{sub 0.5}S nanoparticles with bad crystallinity, but good homogeneity. On the contrary, a slow reaction rate results in a bad homogeneity, but better crystallinity. Combination of good crystallinity and homogeneity in a Zn{sub 0.5}Cd{sub 0.5}S nanocomposite resulted in an excellent photocatalytic activity. The highest rate of H{sub 2} evolution achieved for these phase-homojunctions materials under visible-light irradiation (λ ≥ 420 nm) reached 1252.7 μmol h{sup −1} with an apparent quantum efficiency of 21.46% at 420 nm. The H{sub 2} evolution rate did not reduce distinctively in a continuous 15 hour test for H{sub 2} evolution, indicating an excellent stability for this material. This work not only demonstrates a facile method to produce highly active phase-homojunctions containing Zn{sub 0.5}Cd{sub 0.5}S solid solutions for photocatalytic hydrogen production from the perspective of controlling various reaction conditions, but also provides new insights into understanding the importance of the homogeneity and crystallinity for enhancing photocatalytic activity and stability of Zn{sub 0.5}Cd{sub 0.5}S solid solutions. It is expected that the strategies of modifying the homogeneity and crystallinity by controlling various reaction conditions can be extracted and used when designing other efficient and robust photocatalysts in the future.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

An Exponential Stability Result of a Timoshenko System with Thermoelasticity with Second Sound and in the Presence of Delay

In this paper, we consider a one-dimensional linear thermoelastic system of Timoshenko type with a delay, where the heat flux is given by Cattaneo’s law. We prove an exponential decay result under a smallness condition on the delay and a stability number introduced first in Santos et al. (J Diff Eqs 253:2715–2733, 2012), using a method different from that of Santos et al. (J Diff Eqs 253:2715–2733, 2012). We also reproduce the polynomial decay of Santos et al. (J Diff Eqs 253:2715–2733, 2012) using the multiplier method in the case of absence of delay. The polynomial decay issue in the presence of a small delay is an open question.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Anderson acceleration and application to the three-temperature energy equations

The Anderson acceleration method is an algorithm for accelerating the convergence of fixed-point iterations, including the Picard method. Anderson acceleration was first proposed in 1965 and, for some years, has been used successfully to accelerate the convergence of self-consistent field iterations in electronic-structure computations. Recently, the method has attracted growing attention in other application areas and among numerical analysts. Compared with a Newton-like method, an advantage of Anderson acceleration is that there is no need to form the Jacobian matrix. Thus the method is easy to implement. In this paper, an Anderson-accelerated Picard method is employed to solve the three-temperature energy equations, which are a type of strong nonlinear radiation-diffusion equations. Two strategies are used to improve the robustness of the Anderson acceleration method. One strategy is to adjust the iterates when necessary to satisfy the physical constraint. Another strategy is to monitor and, if necessary, reduce the matrix condition number of the least-squares problem in the Anderson-acceleration implementation so that numerical stability can be guaranteed. Numerical results show that the Anderson-accelerated Picard method can solve the three-temperature energy equations efficiently. Compared with the Picard method without acceleration, Anderson acceleration can reduce the number of iterations by at least half. A comparison between a Jacobian-free Newton–Krylov method, the Picard method, and the Anderson-accelerated Picard method is conducted in this paper.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Highly Active and Stable Palladium Catalysts on Novel Ceria–Alumina Supports for Efficient Oxidation of Carbon Monoxide and Hydrocarbons

Precious metal catalysts with superior low-temperature activity and excellent thermal stability are highly needed in environmental catalysis field. In this study, a novel two-step incipient wetness impregnation (T-IWI) method was developed for the fabrication of a unique and highly stable CeO 2 /Al 2 O 3 support (CA-T). Pd anchored on CA-T exhibited a much higher low-temperature catalytic activity and superior thermal stability in carbon monoxide (CO) and hydrocarbon (HC) oxidations, compared to Pd anchored on conventional CeO 2 /Al 2 O 3 (CA), which was prepared by a one-step IWI method. After aging treatment at 800 °C, the CO oxidation rate on Pd/CA-T (1.69 mmol/(g Pd s)) at 120 °C was 4.1 and 84.5 times of those on Pd/CA (0.41 mmol/(g Pd s)) and Pd/Al 2 O 3 (0.02 mmol/(g Pd s)), respectively. It was revealed that the CA-T support with well-controlled small CeO 2 particles (ca. 12 nm) possessed abundant defects for Pd anchoring, which created rich Pd-CeO 2 interfaces with strengthened interaction between Pd and CeO 2 where oxygen could be efficiently activated. This resulted in the significantly improved oxidation activity and thermal stability of Pd/CA-T catalysts. The T-IWI method developed herein can be applied as a universal approach to prepare highly stable metal oxide-alumina-based supports, which have broad application in environmental catalyst design, especially for automobile exhaust aftertreatment.

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

Mechanistic Insight into Nanoparticle Surface Adsorption by Solution NMR Spectroscopy in an Aqueous Gel

Abstract Engineering nanoparticle (NP) functions at the molecular level requires a detailed understanding of the dynamic processes occurring at the NP surface. Herein we show that a combination of dark‐state exchange saturation transfer (DEST) and relaxation dispersion (RD) NMR experiments on gel‐stabilized NP samples enables the accurate determination of the kinetics and thermodynamics of adsorption. We used the former approach to describe the interaction of cholic acid (CA) and phenol (PhOH) with ceria NPs with a diameter of approximately 200 nm. Whereas CA formed weak interactions with the NPs, PhOH was tightly bound to the NP surface. Interestingly, we found that the adsorption of PhOH proceeds via an intermediate, weakly bound state in which the small molecule has residual degrees of rotational diffusion. We believe the use of aqueous gels for stabilizing NP samples will increase the applicability of solution NMR methods to the characterization of nanomaterials.

Egner, Timothy K.↗
DOE OSTI2017

Mechanistic Insight into Nanoparticle Surface Adsorption by Solution NMR Spectroscopy in an Aqueous Gel

Engineering nanoparticle (NP) functions at the molecular level requires a detailed understanding of the dynamic processes occurring at the NP surface. Herein we show that a combination of dark-state exchange saturation transfer (DEST) and relaxation dispersion (RD) NMR experiments on gel-stabilized NP samples enables the accurate determination of the kinetics and thermodynamics of adsorption. We used the former approach to describe the interaction of cholic acid (CA) and phenol (PhOH) with ceria NPs with a diameter of approximately 200 nm. Whereas CA formed weak interactions with the NPs, PhOH was tightly bound to the NP surface. Interestingly, we found that the adsorption of PhOH proceeds via an intermediate, weakly bound state in which the small molecule has residual degrees of rotational diffusion. Here we believe the use of aqueous gels for stabilizing NP samples will increase the applicability of solution NMR methods to the characterization of nanomaterials.

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

Design and Simulation for Pre-amplifier of ITER Radial X-ray Camera

The radial X-ray camera, which is used to measure magnetohydrodynamic phenomenon and monitor edge localised mode events, is a key diagnostic system for physics studies in the international thermonuclear experimental reactor (ITER) tokamak. Considering the special requirements of physics measurements and spatial resolution, 144 detector channels are required. The board card of the pre-amplifier is designed to improve the integration, on which 16 signal channels have been integrated. In order to suppress the noise and improve the stability of the pre-amplifier, the target impedance analysis method is applied in the design of the power supply, the trans-impedance amplifier and a two-stage active low pass filter are applied in the design. Simulation with Cadence OrCAD and ANSYS SIwave has been adopted to optimize the characteristics of the pre-amplifier. A test of the pre-amplifier shows its good performance for ITER application. After optimization of the pre-amplifier, the band width is 270 kHz, the amplification is 10{sup 7} V/A, and the noise attenuation is − 30 dB, the noise of the pre-amplifier is reduced to 10 mV (noise of the power supply is included).

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Efficiency enhancement in Si solar cell using 1D quasi-periodic antireflection coating

In order to enhance the efficiency of thin-film Si solar cell, two well-known Fibonacci and Thue–Morse sequences of 1D quasi-periodic structures have been considered to achieve a broadband (300–1100 nm) planar antireflection coating, in this article. As almost non-absorbing materials in the solar spectrum, TiO{sub 2} and SiO{sub 2} with optimized thicknesses are considered to eliminate the reflections in the front side of the solar cell. An optimized bilayer antireflection coating with thicknesses of 54.4 nm and 85.6 nm respectively for the TiO{sub 2} and SiO{sub 2} layers has been obtained. Considering material dispersion and solar power spectrum (AM1.5), maximum efficiency enhancements of 42.78%, 46.15%, and 50% have been achieved for the 3 µm thin-film Si solar cell using the FC(3,1) structure which correspond to the cells without any recombination, with bulk recombination, and with bulk and surface recombinations, respectively. The proposed quasi-periodic multilayer antireflection structures have been investigated and optimized using the TMM and FDTD methods. The electrical characteristic of the design is studied by the drift–diffusion method after extracting the electron–hole pair generation. Also, the stability of the performance of the proposed ARC against induced roughness in practice has been investigated and discussed.

14 SOLAR ENERGY↗
DOE OSTI2017

Calculations of interaction energy between certain components of large multimolecular complexes

A scheme is proposed for calculating the energies of interaction between certain components of large multimolecular systems. These energies are used to model the binding and extraction of metal ions and metal complexes in solutions. The procedure can be extended with ease to calculate the energies of interaction between any two components of an arbitrary polyatomic system. Practical application of the scheme is illustrated taking actinide binding by different sorbents in solutions as examples.

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

High-order conservative difference scheme for a model of nonlinear dispersive equations

A high-order nonlinear conservative difference scheme method is proposed to solve a model of nonlinear dispersive equation: RLW-KdV equation. The existence of the solution was proved by the Brouwer fixed point theorem. The unconditional stability besides uniqueness of the difference scheme are also obtained. The convergence of the proposed method is proved to be fourth-order in space and second-order in time in the discrete L{sup ∞}-norm. An application on the RLW equation is discussed numerically in detail. Furthermore, interaction of solitary waves with different amplitudes are shown. The three invariants of the motion are evaluated to show the conservation properties of the system. The temporal evaluation of a Maxwellian initial pulse is then studied. At last some numerical examples are reported to confirm the theoretical results.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

Effect of substitutional doping and disorder on the phase stability, magnetism, and half-metallicity of Heusler alloys

Spintronics is the fast growing field that will play a key role in optimizing power consumption, memory, and processing capabilities of nanoelectronic devices. Heusler alloys are potential candidates for application in spintronics due to their room temperature (RT) half-metallicity, high Curie temperature, low lattice mismatch with most substrates, and strong control on electronic density of states at Fermi level. In this work, we investigate the effect of substitutional doping and disorder on the half-metallicity, phase stability, and magnetism of Heusler alloys using density functional theory methods. Our study shows that electronic and magnetic properties of half/full-Heusler alloys can be tuned by changing electron-count through controlled variation of chemical compositions of alloying elements. We provide a detailed discussion on the effect of substitutional doping and disorder on the tunability of half-metallic nature of Co 2 MnX and NiMnX based Heusler alloys, where X represents group 13–16 and period 3–6 elements of the periodic table. Based on the idea of electron count and disorder, we predicted a possible existence of thermodynamically stable half-metallic multicomponent bismuthides, for example, (CuNi 3 )Mn 4 Bi 4 and (ZnNi 7 )Mn 8 Bi 8 , through substitution doping at Ni site by specific Cu and Zn composition in half-Heusler NiMnBi. We believe that the design guide based on electron-counts presented for half-metals will play a key role in electronic-structure engineering of novel Heusler alloys for spintronic application, which will accelerate the development and synthesis of novel materials.

36 MATERIALS SCIENCE↗