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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Alternating-current conductivity and dielectric relaxation of bulk iodoargentate

Graphical abstract: The electric modulus shows single dielectric relaxation process in the measured frequency range. - Highlights: • The conduction mechanism is described by quantum mechanical tunneling model. • The applications of dielectric modulus give a simple method for evaluating the activation energy of the dielectric relaxation. • The [Ag{sub 2}I{sub 4}]{sup 2−}1-D chain and [Cu(en){sub 2}]{sup 2+} cation column form the layered stacks by hydrogen bond interactions. - Abstract: An inorganic-organic hybrid compound Cu(en){sub 2}Ag{sub 2}I{sub 4} (en = ethylenediamine) (1) was synthesized and single crystal structurally characterized. Along the [001] direction, the inorganic parts form an infinite 1-D chain and [Cu(en){sub 2}]{sup 2+} cations are separated by inorganic chain. The electrical conductivity and dielectric properties of 1 have been investigated over wide ranges of frequency. The alternating-current conductivities have been fitted to the Almond–West type power law expression with use of a single value of S. It is found that S values for 1 are nearly temperature-independent, which indicates that the conduction mechanism could be quantum mechanical tunneling (QMT) model. The dielectric loss and electric modulus show single dielectric relaxation process. The activation energy obtained from temperature-dependent electric modulus compare with the calculated from the dc conductivity plots.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Pathway modeling of microarray data: A case study of pathway activity changes in the testis following in utero exposure to dibutyl phthalate (DBP)

Pathway activity level analysis, the approach pursued in this study, focuses on all genes that are known to be members of metabolic and signaling pathways as defined by the KEGG database. The pathway activity level analysis entails singular value decomposition (SVD) of the expression data of the genes constituting a given pathway. We explore an extension of the pathway activity methodology for application to time-course microarray data. We show that pathway analysis enhances our ability to detect biologically relevant changes in pathway activity using synthetic data. As a case study, we apply the pathway activity level formulation coupled with significance analysis to microarray data from two different rat testes exposed in utero to Dibutyl Phthalate (DBP). In utero DBP exposure in the rat results in developmental toxicity of a number of male reproductive organs, including the testes. One well-characterized mode of action for DBP and the male reproductive developmental effects is the repression of expression of genes involved in cholesterol transport, steroid biosynthesis and testosterone synthesis that lead to a decreased fetal testicular testosterone. Previous analyses of DBP testes microarray data focused on either individual gene expression changes or changes in the expression of specific genes that are hypothesized, or known, to be important in testicular development and testosterone synthesis. However, a pathway analysis may inform whether there are additional affected pathways that could inform additional modes of action linked to DBP developmental toxicity. We show that Pathway activity analysis may be considered for a more comprehensive analysis of microarray data.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

High active nitrogen flux growth of GaN by plasma assisted molecular beam epitaxy

In the present study, the authors report on a modified Riber radio frequency (RF) nitrogen plasma source that provides active nitrogen fluxes more than 30 times higher than those commonly used for plasma assisted molecular beam epitaxy (PAMBE) growth of gallium nitride (GaN) and thus a significantly higher growth rate than has been previously reported. GaN films were grown using N{sub 2} gas flow rates between 5 and 25 sccm while varying the plasma source's RF forward power from 200 to 600 W. The highest growth rate, and therefore the highest active nitrogen flux, achieved was ∼7.6 μm/h. For optimized growth conditions, the surfaces displayed a clear step-terrace structure with an average RMS roughness (3 × 3 μm) on the order of 1 nm. Secondary ion mass spectroscopy impurity analysis demonstrates oxygen and hydrogen incorporation of 1 × 10{sup 16} and ∼5 × 10{sup 17}, respectively. In addition, the authors have achieved PAMBE growth of GaN at a substrate temperature more than 150 °C greater than our standard Ga rich GaN growth regime and ∼100 °C greater than any previously reported PAMBE growth of GaN. This growth temperature corresponds to GaN decomposition in vacuum of more than 20 nm/min; a regime previously unattainable with conventional nitrogen plasma sources. Arrhenius analysis of the decomposition rate shows that samples with a flux ratio below stoichiometry have an activation energy greater than decomposition of GaN in vacuum while samples grown at or above stoichiometry have decreased activation energy. The activation energy of decomposition for GaN in vacuum was previously determined to be ∼3.1 eV. For a Ga/N flux ratio of ∼1.5, this activation energy was found to be ∼2.8 eV, while for a Ga/N flux ratio of ∼0.5, it was found to be ∼7.9 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Functional Biomimetic Polymers with Antimicrobial Activity

At PNNL, we have developed a completely new class of synthetic biomimetic sequence-defined polymers based on triazine chemistry, which we call TZPs. PNNL's new polymers offer the opportunity to achieve similar functions to natural macromolecules; specifically we designed and synthesized a diversity of test molecules for antimicrobial activity. Antimicrobial activity against a variety of wild type and drug resistant pathogens was found.

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

Kinetic Modeling of the Reaction Rate for Quartz and Carbon Pellet

Kinetic modeling of quartz and carbon pellet at temperatures of 1898 K, 1923 K, and 1948 K (1625 °C, 1650 °C, and 1675 °C) was investigated in this study. The carbon materials used were charcoal, coke, coal, and preheated coal. The overall SiC producing reaction can be described by the reaction SiO 2 + 3C = SiC + 2CO. In the SiC-producing step, the reaction rate of quartz and carbon pellet can be expressed as ((d pct)/(dt)) = (1 - 0.40 × X fix - C -0.86 × F C × pct) × A × exp(-(E/(RT))) The carbon factor F C was used to describe the influence of different carbon materials that effect the gas–solid interface reaction. For charcoal, coke, coal, and preheated coal, the F C values were 0.83, 0.80, 0.94, and 0.83, respectively. The pre-exponential factor A values for the preceding four carbon materials were 1.06 × 10 16 min -1 , 4.21 × 10 15 min -1 , 3.85 × 10 9 min -1 , and 1.00 × 10 25 min -1 , respectively. The activation energies E for the SiC-producing step were 570, 563, 336, and 913 kJ/mole for charcoal, coke, coal, and preheated coal pellets, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Removal potential of toxic 2378-substituted PCDD/F from incinerator flue gases by waste-derived activated carbons

The application of activated carbons has become a commonly used emission control protocol for the removal or adsorption of persistent organic pollutants from the flue gas streams of waste incinerators. In this study, the 2378-substituted PCDD/F removal efficiency of three types of activated carbons derived from the pyrolysis of refuse derived fuel, textile waste and scrap tyre was investigated and compared with that of a commercial carbon. Experiments were carried out in a laboratory scale fixed-bed reactor under a simulated flue gas at 275 deg. C with a reaction period of four days. The PCDD/F in the solid matrices and exhaust gas, were analyzed using gas chromatography coupled with a triple quadrupole mass spectrometer. In the absence of activated carbon adsorbent, there was a significant increase in the concentration of toxic PCDD/F produced in the reacted flyash, reaching up to 6.6 times higher than in the raw flyash. In addition, there was a substantial release of PCDD/F into the gas phase, which was found in the flue gas trapping system. By application of the different commercial, refuse derived fuel, textile and tyre activated carbons the total PCDD/F toxic equivalent removal efficiencies in the exhaust gas stream were 58%, 57%, 64% and 52%, respectively. In general, the removal of the PCDDs was much higher with an average of 85% compared to PCDFs at 41%. Analysis of the reacted activated carbons showed that there was some formation of PCDD/F, for instance, a total of 60.6 {mu}g I-TEQ kg{sup -1} toxic PCDD/F was formed in the refuse derived fuel activated carbon compared to 34 {mu}g I-TEQ kg{sup -1} in the commercial activated carbon. The activated carbons derived from the pyrolysis of waste, therefore, showed good potential as a control material for PCDD/F emissions in waste incinerator flue gases.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Fast crystallization of amorphous Gd{sub 2}Zr{sub 2}O{sub 7} induced by thermally activated electron-beam irradiation

We investigate the ionization and displacement effects of an electron-beam (e-beam) on amorphous Gd{sub 2}Zr{sub 2}O{sub 7} synthesized by the co-precipitation and calcination methods. The as-received amorphous specimens were irradiated under electron beams at different energies (80 keV, 120 keV, and 2 MeV) and then characterized by X-ray diffraction and transmission electron microscopy. A metastable fluorite phase was observed in nanocrystalline Gd{sub 2}Zr{sub 2}O{sub 7} and is proposed to arise from the relatively lower surface and interface energy compared with the pyrochlore phase. Fast crystallization could be induced by 120 keV e-beam irradiation (beam current = 0.47 mA/cm{sup 2}). The crystallization occurred on the nanoscale upon ionization irradiation at 400 °C after a dose of less than 10{sup 17} electrons/cm{sup 2}. Under e-beam irradiation, the activation energy for the grain growth process was approximately 10 kJ/mol, but the activation energy was 135 kJ/mol by calcination in a furnace. The thermally activated ionization process was considered the fast crystallization mechanism.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Emergence of self-organized multivortex states in flocks of active rollers

Active matter, both synthetic and biological, demonstrates complex spatiotemporal self-organization and the emergence of collective behavior. A coherent rotational motion, the vortex phase, is of great interest because of its ability to orchestrate well-organized motion of self-propelled particles over large distances. However, its generation without geometrical confinement has been a challenge. Here, we show by experiments and computational modeling that concentrated magnetic rollers self-organize into multivortex states in an unconfined environment. We find that the neighboring vortices more likely occur with the opposite sense of rotation. Our studies provide insights into the mechanism for the emergence of coherent collective motion on the macroscale from the coupling between microscale rotation and translation of individual active elements. These results may stimulate design strategies for self-assembled dynamic materials and microrobotics.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Contraction of polymer gels created by the activity of molecular motors

Here, we propose a theory based on non-equilibrium thermodynamics to describe the mechanical behavior of an active polymer gel created by the inclusion of molecular motors in its solvent. When activated, these motors attach to the chains of the polymer network and shorten them creating a global contraction of the gel, which mimics the active behavior of a cytoskeleton. The power generated by these motors is obtained by an ATP hydrolysis reaction, which transduces chemical energy into mechanical work. The latter is described by an increment of strain energy in the gel due to an increased stiffness. This effect is described with an increment of the cross-link density in the polymer network, which reduces its entropy. The theory then considers polymer network swelling and species diffusion to describe the transient passive behavior of the gel. We finally formulate the problem of uniaxial contraction of a slab of gel and compare the results with experiments, showing good agreement.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Build plate conduction cooling for thermal management of wire arc additive manufactured components

Wire arc additive manufacturing (WAAM) allows for quick, large component manufacturing with fast deposition rates while leveraging readily available wire feedstock that is significantly cheaper than metal powder. However, the increased deposition rate of this process requires enhanced thermal management as failures can occur due to overheating. A common strategy to mitigate overheating is to dwell, or pause, between individual layers; however, this can significantly increase build times and eliminate the advantage of additive manufacturing being able to manufacture components quickly. To help mitigate this issue, this study explores the use of active cooling to maintain process control and to decrease overall build time. In this work, conductive cooling applied to either the bottom or side of the print substrate was explored. Results from this study showed that bottom build plate active cooling can be used to decrease dwell times by up to 50% and decrease cool-down to room temperature after the building process by up to 75%. Results from this study demonstrate that the use of active cooling strategies for WAAM can be used for better thermal control over the process and should be further investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Kinetics and Mechanisms of Dolime Dissolution in Steelmaking Slag

The kinetics of dolime dissolution containing 20 and 50 pct of magnesium oxide in steelmaking slags has been studied in a high-temperature experiment. The dissolution tests were carried out under static conditions at temperatures of between 1573 K and 1873 K (1300 °C to 1600 °C). Cylindrical samples of dolime were introduced into pre-melted slag at predetermined time intervals. The changes in mass and geometrical parameters of the samples, as well as CaO and MgO concentrations in the melt, were determined to calculate mass transfer and diffusion coefficients. The results revealed that the rate-limiting step in the process of dolime dissolution is diffusion. The increase in MgO content in the initial sample caused a drop in dolime dissolution rate and diffusion coefficients. The prediction of MgO solubility in steel slag, as well as the effect of slag basicity, was carried out using the thermodynamic software FactSage 7.1. In addition, the activation energy of diffusion has been calculated using the dependence of the logarithm of diffusion coefficients on the inverse temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Effects of porous carbon additives and induced fluorine on low dielectric constant polyimide synthesized with an e-beam

We report the synthesis of a polyimide matrix with a low dielectric constant for application as an intercalation material between metal interconnections in electronic devices. Porous activated carbon was embedded in the polyimide to reduce the dielectric constant, and a thin film of the complex was obtained using the spin-coating and e-beam irradiation methods. The surface of the thin film was modified with fluorine functional groups to impart water resistance and reduce the dielectric constant further. The water resistance was significantly improved by the modification with hydrophobic fluorine groups. The dielectric constant was effectively decreased by porous activated carbon. The fluorine modification also resulted in a low dielectric constant on the polyimide surface by reducing the polar surface free energy. The dielectric constant of polyimide film decreased from 2.98 to 1.9 by effects of porous activated carbon additive and fluorine surface modification.

36 MATERIALS SCIENCE↗
DOE OSTI2020

High temperature nanoindentation of Cu–TiN nanolaminates

Here, we examined the high temperature indentation response of physical vapor deposited Cu–TiN multilayered nanocomposites with layer thicknesses ranging from 5 nm to 200 nm. A decrease in hardness with increasing temperature was observed, along with a strong correlation between the hardness and the nanometer-level TiN grain sizes, rather than layer thickness. The apparent activation energies calculated from the high temperature indentation experiments indicated that, for all but the smallest layer thicknesses, the deformation of copper in the nanolaminates dominate the plastic response in these composites. In the finest layer thicknesses, a decrease in the apparent activation energy value indicated possible co-deformation of Cu and TiN.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Temperature influence on luminescent coupling efficiency in concentrator MJ SCs

In the work, presented are the results of investigation of temperature dependencies of the luminescent coupling effectiveness in lattice-matched (LM) GaInP/GaAs/Ge and metamorphic (MM) GaInP/GaInAs/Ge solar cells. The “ordinary” luminescent coupling effectiveness rise has been observed with temperature decrease for GaAs-Ge, GaInP-GaInAs and GaInAs-Ge pairs of subcells, and its limiting values have been defined. A “reverse” behavior of the luminescent coupling effectiveness for the GaInP-GaAs pair has been found, determined emittance potential drop of wideband GaInP p-n junction. It is shown that the established “unusual” behavior of the LC efficiency may be determined by the presence of thermalized centers of non-radiative recombination of charge carriers for the GaInP subcell in GaInP/GaAs/Ge LM structure. Estimation of characteristic parameters for the nonradiative recombination processes in wideband GaInP p-n junction has been carried out, and values for the energy of the nonradiative center thermalization (E{sub nrad2} =79.42meV) and for the activation energy of nonradiative band-to-band recombination (E{sub A}=33.4meV) have been obtained.

14 SOLAR ENERGY↗
DOE OSTI2019

High-Resolution Electron Microscopy and Kinetic Studies of Precipitation Hardening Reactions in Cast Al-5.8Zn-2.2Mg-2.5Cu

Precipitation age hardening (T6) response of Al-5.8Zn-2.2Mg-2.5Cu alloy in near-net-shaped cast condition was investigated. Cast samples were manufactured using the controlled diffusion solidification (CDS) technology combined with a metallic mold tilt pour gravity casting process. This study was conducted using (1) non-isothermal aging during differential scanning calorimetry (DSC) experiments and (2) isothermal aging during which transient bulk and micro-hardness measurements taken at four aging temperatures of 343, 393, 433 and 473 K. A detailed microstructural investigation combined with a quantitative image analysis was carried out on both DSC and hardness specimens using high-resolution electron microscopy (HREM) and energy-dispersive spectroscopy (EDS) elemental mappings. Hardness measurements were analyzed using a kinetic modeling approach (single state variable combined with a kinetic equation that is valid for the Al-Zn-Mg-Cu alloys). The results confirm the formation of hardening phases of GP zone, intermediate hardening metastable phase η′ and equilibrium phase η. The results of calorimetric measurements, electron microscopy and selected area diffraction patterns are in good agreement and confirm transient precipitation/dissolution sequences. A mean value of activation energy Q{sub A} of 75 kJ/mol was evaluated for combined bulk diffusion rate of alloying elements during precipitation of strengthening phases within Al matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Structural, thermal and dielectric studies on the novel solution grown (4-dimethylaminopyridinium) chloroantimonate(III) and chlorobismuthate(III) crystals

Research Highlights: {yields} The one-dimensional (1D) and the zero-dimensional (0D) anionic structure. {yields} The 'crystal bending' discovered in RMX{sub 4}-type analogue. {yields} The low frequency relaxation processes attributed to the dynamics of the organic cations. -- Abstract: The single crystals of the following 4-dimethylaminopyridinium chloroantimonates(III) and chlorobismuthates(III) have been grown by the solvent evaporation method: (C{sub 7}H{sub 11}N{sub 2})SbCl{sub 4}, (C{sub 7}H{sub 11}N{sub 2})BiCl{sub 4} and (C{sub 7}H{sub 11}N{sub 2}){sub 4}Bi{sub 2}Cl{sub 10}. The one-dimensional (1D) structures for (C{sub 7}H{sub 11}N{sub 2})SbCl{sub 4} or (C{sub 7}H{sub 11}N{sub 2})BiCl{sub 4} and the zero-dimensional (0D) one for (C{sub 7}H{sub 11}N{sub 2}){sub 4}Bi{sub 2}Cl{sub 10} have been solved by the single-crystal X-ray diffraction method. (C{sub 7}H{sub 11}N{sub 2})SbCl{sub 4} and (C{sub 7}H{sub 11}N{sub 2})BiCl{sub 4} appeared to be isomorphous and crystallize in the monoclinic space group, C2/c, whereas (C{sub 7}H{sub 11}N{sub 2}){sub 4}Bi{sub 2}Cl{sub 10} in the orthorhombic one, Imma. The molecular arrangements in the subsequent crystal lattices have been studied. For all three compounds by using the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) no structural phase transition has been detected in temperature region between 100 and 400 K. Nevertheless, the dielectric relaxation processes in temperature region 100-450 K and frequency range between 100 Hz and 2 MHz have been found in all crystals studied. The experimental results of the real and imaginary parts of the dielectric permittivity allow us to estimate the parameters of the relaxation processes, i.e. macroscopic relaxation times, {tau}, and activation energies, E{sub A}. The dynamics of the dipolar organic cations is expected to contribute to the relaxations process in the crystals under investigation.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Determining the activation energies and slip systems for dislocation nucleation in body-centered cubic mo and face-centered cubic Ni single crystals

Nanoindentation tests were performed on single crystals of Mo and Ni. The critical shear stress for the first pop-in was {approx}1/7 of the shear modulus in both crystals. The dependence of pop-in probability on load was understood in terms of a thermally activated dislocation nucleation process. Comparison of the activation energies suggests nucleation of full dislocations in Mo and partial dislocations in Ni. The activation energy analysis also offers information on the specific slip system on which dislocations are nucleated.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Calculation of self-diffusion coefficients in iron

On the basis of available P-V-T equation of state of iron, the temperature and pressure dependence of self-diffusion coefficients in iron polymorphs (α, δ, γ and ε phases) have been successfully reproduced in terms of the bulk elastic and expansivity data by means of a thermodynamical model that interconnects point defects parameters with bulk properties. The calculated diffusion parameters, such as self-diffusion coefficient, activation energy and activation volume over a broad temperature range (500-2500 K) and pressure range (0-100 GPa), compare favorably well with experimental or theoretical ones when the uncertainties are considered.

36 MATERIALS SCIENCE↗