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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Oxidation kinetics of biochar from woody and herbaceous biomass

The goal of this study was to determine oxidation kinetics for biochar produced from fast pyrolysis of various biomass feedstocks. In particular, the role of inherent ash content on the oxidation rate was evaluated. Thermogravimetric analysis (TGA) and fluidized bed combustion experiments were used to explore oxidation kinetics of six fast pyrolysis produced biochars with diverse ash content. Here, the reaction rates varied by a factor of three under chemical kinetic-limited conditions, demonstrating inorganic content impacts oxidation rate. Chemical kinetic rate coefficients were proposed as a function of compositional parameters to determine overall fit and impact. Potassium content was found to have a positive correlation, best describing the differences in the oxidation kinetic rate coefficients. Additionally, feedstocks were subjected to a 1 M HCl acid wash mitigating the catalytic activity of the metals. Acid washed biochars had lower oxidation kinetic rates compared to their unwashed counterparts, indicating the removal of catalytically active metals reduced oxidation rate. Gas composition (CO/CO 2 ) was measured during fluidized bed experiments for both acid-washed and unwashed biochars, which varied between the six biochars. Formation of CO 2 was greatly affected by catalytic metals, finding potassium content to correlate well with a higher percentage of CO 2 formation as compared to CO. Comparison of oxidation rates were made between the two experimental apparatuses to measure the effect of attrition on biochar oxidation.

09 BIOMASS FUELS↗
DOE OSTI2021

Drying model of a high salt content cementitious waste form: Effect of capillary forces and salt solution

Highlights: • Drying model for a high salt content cementitious waste form is developed. • Water vapor diffusion and capillary liquid flow are distinguished. • Capillary and salt solution effects are considered in vapor-liquid equilibrium. A water transport model coupling capillary liquid flow with vapor diffusion is developed to describe the drying process for a cementitious waste form with high salinity porewater. Vapor-liquid equilibrium is formulated as the driving force for vapor diffusion and the model accounts for pore capillary and high salinity effects on water thermodynamic activity. Pore filling and porewater surface tension as a function of pore size distribution and water saturation have been quantified for the material. Geochemical speciation modeling is used to simulate porewater activity as a function of composition over the range of saturation. The theoretical relationship between relative humidity and water saturation generally agrees with experimental measurement, and the developed model is capable of predicting drying rates under various external relative humidity conditions. The model was developed to be incorporated into reactive transport models considering the effects of drying such as salt redistribution and efflorescence.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microbial communities for bioprocessing: lessons learned from nature

Microbial bioprocessing has evolved from the use of undefined natural consortia to the construction of synthetic communities tailored to specific processes and bioproducts. This evolution is enabled by recent advances in biotechnology, including cultivation of non-model microbes, metabolic engineering, bioinformatics, and numerical modeling. Equipped with these powerful tools, engineers have designed co-cultures and consortia with an expanded set of capabilities, mainly via ‘bottom-up’ approaches that tether isolates together in culture. We present a brief review of the opportunities, challenges, and recent developments in consortia-based bioprocessing with a focus on lignocellulosic biomass conversion. With improved understanding of microbial community composition and function, we further present a vision to harness defined consortia down-selected from nature via ‘top down’ approaches.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Experimental and fuel-surrogates modeling study of the high-pressure pyrolysis of specialty cetane number fuels: implications for fall-off in ethylene unimolecular dissociation

Single pulse shock tube experiments were conducted at 50 atm nominal pressure and 4 ms nominal reaction time over a temperature range of 900–1800 K, to study the pyrolysis speciation of a multi-component jet fuel, F-24, and six cetane number (CN) specialty fuels - CN30, CN35, CN40, CN45, CN50, and CN55. Gas chromatography (GC) was used to qualitatively and quantitatively analyze the post shock gases. The relationship between the formation of key pyrolysis species and the chemically controlled combustion propensity as reflected by the cetane number of each fuel was examined. A surrogate-based mechanism from the CRECK Modelling Group and chemical-functional group based optimized surrogates (CFGO) were used to simulate the pyrolysis speciation results. The model was able to capture the chemistry of most species except two important pyrolysis intermediates – ethylene and acetylene. Chemical kinetic analyses were performed to identify the important reactions which affect the chemistry of these species; however, the rate parameters of critical reactions were found to be unsuitable for simulating the present high-pressure studies. Here, to address this unsuitability, a theory-based fall-off analysis for three reactions representing the decomposition of ethylene and subsequent formation of acetylene was performed, and these are included in an updated version of the CRECK mechanism. This update resolves discrepancies between the experimental results and simulations for ethylene and acetylene. Reaction flux analyses using the updated surrogate model were also performed to identify the important reaction pathways responsible for the formation of crucial species and to provide an analysis of the chemistry of complex multi-component fuel systems. The fundamental reactions responsible for driving pyrolysis chemistry were greatly influenced by the chemical functional groups present in these fuels. In addition to updating the rate parameters of specific reactions to improve modeling, this study also emphasizes the effectiveness of the fuel-surrogate approach, where surrogates representing the chemical functional group composition of the parent fuel serve as a valuable tool for predicting the combustion chemistry of novel fuels.

Chemical Kinetics↗
DOE OSTI2015

PyDII: A python framework for computing equilibrium intrinsic point defect concentrations and extrinsic solute site preferences in intermetallic compounds

Point defects play an important role in determining the structural stability and mechanical behavior of intermetallic compounds. To help quantitatively understand the point defect properties in these compounds, we developed PyDII, a Python program that performs thermodynamic calculations of equilibrium intrinsic point defect concentrations and extrinsic solute site preferences in intermetallics. The algorithm implemented in PyDII is built upon a dilute-solution thermodynamic formalism with a set of defect excitation energies calculated from first-principles density-functional theory methods. The analysis module in PyDII enables automated calculations of equilibrium intrinsic antisite and vacancy concentrations as a function of composition and temperature (over ranges where the dilute solution formalism is accurate) and the point defect concentration changes arising from addition of an extrinsic substitutional solute species. To demonstrate the applications of PyDII, we provide examples for intrinsic point defect concentrations in NiAl.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Sea cucumber ( Holothuria glaberrima ) intestinal microbiome dataset from Puerto Rico, generated by shotgun sequencing

The sea cucumber (H. glaberrima) is a species found in the shallow waters near coral reefs and seagrass beds in Puerto Rico. To characterize the microbial taxonomic composition and functional profiles present in the sea cucumber, total DNA was obtained from their intestinal system, fosmid libraries constructed, and subsequent sequencing was performed. The diversity profile displayed that the most predominant domain was Bacteria (76.56 %), followed by Viruses (23.24 %) and Archaea (0.04 %). Within the 11 phyla identified, the most abundant was Proteobacteria (73.16 %), followed by Terrabacteria group (3.20 %) and Fibrobacterota, Chlorobiota, Bacteroidota (FCB) superphylum (1.02 %). The most abundant species were Porvidencia rettgeri (21.77 %), Pseudomonas stutzeri (14.78 %), and Alcaligenes faecalis (5.00 %). The functional profile revealed that the most abundant functions are related to transporters, MISC (miscellaneous information systems), organic nitrogen, energy, and carbon utilization. The data collected in this project on the diversity and functional profiles of the intestinal system of the H. glaberrima provided a detailed view of its microbial ecology. These findings may motivate comparative studies aimed at understanding the role of the microbiome in intestinal regeneration.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2018

Exposure to traffic-related air pollution and the composition of the gut microbiota in overweight and obese adolescents

Highlights: • Traffic-related air pollution (TRAP) was positively correlated with fasting glucose. • TRAP exposure was correlated with specific gut microbial taxa. • These taxa partially explained the correlation between TRAP and fasting glucose. • TRAP exposure may negatively impact metabolic health via the gut microbiota. Traffic-related air pollution (TRAP) exposure has been linked to type 2 diabetes and metabolic dysfunction in humans. Animal studies suggest that air pollutants may alter the composition of the gut microbiota, which may negatively impact metabolic health through changes in the composition and/or function of the gut microbiome.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Current status and outlook for ATRP

Atom transfer radical polymerization (ATRP) is one of the most often used controlled radical polymerization techniques. It employs very small amounts (ppm) of Cu complexes in the presence of various chemical reducing agents but also external stimuli such as light, electrical current or mechanical forces. It can be carried out in bulk, in solution, and in dispersed media. ATRP has been successfully used to prepare various polymers with controlled architecture and well-defined topology, composition, and functionality, as well as bioconjugates and organic–inorganic hybrids. This article summarizes the current status and also an outlook for ATRP.

ATRP↗
DOE OSTI2022

Sodium diffusion in heterogeneous porous media: Connecting laboratory experiments and simulations

Sodium has been suggested as a tracer for brine in reservoir formations where a significant amount of sodium ion is found mainly in the aqueous phase. Fortunately, the most abundant sodium isotope, 23 Na, is Nuclear Magnetic Resonance (NMR) active, making it possible to study the structure and dynamical properties of both bulk and pore confined fluid systems. We investigated the diffusion of key dissolved sodium species in bulk solution and porous media as a function of composition, ionic strength, and permeability of the carbonate samples using NMR relaxometry and pulsed-field gradient (PFG) NMR techniques. We use Indiana limestone as an example of natural porous media and water as a freely diffusible tracer and carrier. We demonstrate apparent diffusion measurement of sodium based on changes in spin–spin relaxation time (T 2 ) signal in pore confinement. The diffusion rate of sodium decreases with increasing counter-ion size. This effect is greater at higher ionic strengths and lower chemical potentials in porous media. The reactive transport code, CrunchFlow, was used to complement the NMR experiments to simulate diffusion behavior in porous media. Combining these two methods provides a powerful approach to estimating effective diffusion coefficients in heterogeneous matrices. The modeling considers the influence of physical properties (porosity and tortuosity) and chemical properties (geochemical composition and chemical gradients). The results presented in this work highlight the advantage of measuring apparent diffusivity using NMR T 2 relaxometry in conjunction with numerical simulation to derive effective diffusivity and the corresponding matrix properties (i.e., tortuosity) of the system.

58 GEOSCIENCES↗
DOE OSTI2016

Diffusion of water-soluble sorptive drugs in HEMA/MAA hydrogels

In this work, we measure and, for the first time, theoretically predict four prototypical aqueous-drug diffusion coefficients in five soft-contact-lens material hydrogels where solute-specific adsorption is pronounced. Two-photon fluorescence confocal microscopy and UV/Vis-absorption spectrophotometry assess transient solute concentration profiles and concentration histories, respectively. Diffusion coefficients are obtained for acetazolamide, riboflavin, sodium fluorescein, and theophylline in 2-hydroxyethyl methacrylate/methacrylic acid (HEMA/MAA) copolymer hydrogels as functions of composition, equilibrium water content (30–90%), and aqueous pH (2 and 7.4). At pH 2, MAA chains are nonionic, whereas at pH 7.4, MAA chains are anionic (pKa ≈ 5.2). All examined prototypical drugs specifically interact with HEMA and nonionic MAA (at pH 2) moieties. Conversely, none of the prototypical drugs adsorb specifically to anionic MAA (at pH 7.4) chains. As expected, diffusivities of adsorbing solutes are significantly diminished by specific interactions with hydrogel strands. Despite similar solute size, relative diffusion coefficients in the hydrogels span several orders of magnitude because of varying degrees of solute interactions with hydrogel-polymer chains. To provide a theoretical framework for the new diffusion data, we apply an effective-medium model extended for solute-specific interactions with hydrogel copolymer strands. Sorptive-diffusion kinetics is successfully described by local equilibrium and Henry's law. All essential parameters are determined independently. Predicted diffusivities are in good agreement with experiment.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Controlling microstructure and B2 ordering kinetics in Fe–Al system through additive manufacturing

Multi-material fabrication between steel and aluminum is challenging because of the formation of several intermetallic phases. Embrittling B2 ordered intermetallics form in the steel rich side and are stable till about 60% of Al dilution in steel. In this work by using multi-length scale characterization coupled with integrated computational process and thermokinetic modeling, we show that the ordered B2 intermetallics in the steel rich side of the Fe–Al system forms via a nucleation and growth mechanism. The extent of B2 ordered intermetallics can be controlled by modifying the directed energy deposition-additive manufacturing (DED-AM) process parameters. Our findings lay the foundation for enabling fabrication of crack-free functionally graded compositions between the two alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Synthesis, structure, and optical properties of BiCuOCh (Ch=S, Se, and Te)

Crystals of BiCuOSe were grown from a salt flux, and the crystal structure was determined by single-crystal X-ray diffraction. BiCuOSe adopts the tetragonal layered structure of LnCuOCh (Ln=lanthanide; Ch=S, Se, and Te) with bond lengths and bond angles in good agreement with those published for powders. Powders comprising mixed chalcogenides across the series BiCuOCh (Ch=S, Se, and Te) were made by reacting Bi{sub 2}O{sub 2}Ch and Cu{sub 2}Ch. Band gaps determined via infrared diffuse reflectance from powders are E{sub g}=0.82 eV for BiCuOSe, 0.89 eV for BiCuOS{sub 0.5}Se{sub 0.5}, and 1.07 eV for BiCuOS. The band gap of BiCuOSe inferred from infrared transmission measurements on single crystals is in good agreement with the value obtained from diffuse reflectance from the powder. - Graphical abstract: IR absorption of BiCuOCh powders from diffuse reflection (left scale) and polished BiCuOSe single crystal from transmission (right scale). Spectra are normalized to the maximum absorption. Inset: band gap as a function of composition. Highlights: Black-Right-Pointing-Pointer BiCuOSe single crystals are synthesized, and the band gap is measured by direct transmission. Black-Right-Pointing-Pointer A new powder synthesis of BiCuOCh{sub 1-x}Ch Prime {sub x} is demonstrated. Black-Right-Pointing-Pointer Band gaps of BiCuO(S{sub 1-x}Se{sub x}) are determined from diffuse reflection from powders.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Towards new binary compounds: Synthesis of amorphous phosphorus carbide by pulsed laser deposition

We have recently undertaken comprehensive computational studies predicting possible crystal structures of the as yet unknown phosphorus carbide as a function of composition. In this work, we report the synthesis of amorphous phosphorus-carbon films by pulsed laser deposition. The local bonding environments of carbon and phosphorus in the synthesised materials have been analysed by x-ray photoelectron spectroscopy; we have found strong evidence for the formation of direct P-C bonding and hence phosphorus carbide. There is a good agreement between the bonding environments found in this phosphorus carbide material and those predicted in the computational work. In particular, the local bonding environments are consistent with those found in the {beta}-InS-like structures that we predict to be low in energy for phosphorus:carbon ratios between 0.25 and 1. Highlights: Black-Right-Pointing-Pointer We have synthesised amorphous phosphorus-carbon films by pulsed laser deposition. Black-Right-Pointing-Pointer X-ray photoelectron spectroscopy results indicate formation of direct P-C bonds and hence phosphorus carbide. Black-Right-Pointing-Pointer Local bonding environments are consistent with those in predicted structures.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Diffusion model of the non-stoichiometric uranium dioxide

Uranium dioxide (UO{sub 2}), which is used in light water reactors, exhibits a large range of non-stoichiometry over a wide temperature scale up to 2000 K. Understanding diffusion behavior of uranium oxides under such conditions is essential to ensure safe reactor operation. The current understanding of diffusion properties is largely limited by the stoichiometric deviations inherent to the fuel. The present DICTRA-based model considers diffusion across non-stoichiometric ranges described by experimentally available data. A vacancy and interstitial model of diffusion is applied to the U–O system as a function of its defect structure derived from CALPHAD-type thermodynamic descriptions. Oxygen and uranium self and tracer diffusion coefficients are assessed for the construction of a mobility database. Chemical diffusion coefficients of oxygen are derived with respect to the Darken relation and migration energies of defects are evaluated as a function of stoichiometric deviation. - Graphical abstract: Complete description of Oxygen–Uranium diffusion as a function of composition at various temperatures according to the developed Dictra model. - Highlights: • Assessment of a uranium–oxygen diffusion model with Dictra. • Complete description of U–O diffusion over wide temperature and composition range. • Oxygen model includes terms for interstitial and vacancy migration. • Interaction terms between defects help describe non-stoichiometric domain of UO{sub 2±x}. • Uranium model is separated into mobility terms for the cationic species.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Hydrogenation induced structure and property changes in GdGa

Hydrides GdGaH{sub x} were obtained by exposing the Zintl phase GdGa with the CrB structure to a hydrogen atmosphere at pressures from 1.5 to 50 bar and temperatures from 50 to 500 °C. Structural analysis by powder X-ray diffraction suggests that conditions with hydrogen pressures in a range between 15 and 50 bar and temperatures below 500 °C afford a uniform hydride phase with the NdGaH{sub 1.66} structure (Cmcm, a=3.9867(7) Å, b=12.024(2) Å, c=4.1009(6) Å) which hosts H in two distinct positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by Gd atoms, whereas H2 atoms are inserted between Ga atoms. The assignment of the NdGaH{sub 1.66} structure is corroborated by first principles DFT calculations. Modeling of phase and structure stability as a function of composition resulted in excellent agreement with experimental lattice parameters when x=1.66 and revealed the presence of five-atom moieties Ga-H2-Ga-H2-Ga in GdGaH{sub 1.66}. From in situ powder X-ray diffraction using synchrotron radiation it was established that hydrogenation at temperatures above 200 °C affords a hydride with x≈1.3, which is stable up to 500 °C, and that additional H absorption, yielding GdGaH{sub 1.66}, takes place at lower temperatures. Consequently, GdGaH{sub 1.66} desorbs H above T=200 °C. Without the presence of hydrogen, hydrides GdGaH{sub x} decompose at temperatures above 300 °C into GdH{sub 2} and an unidentified Gd-Ga intermetallics. Thus the hydrogenation of GdGa is not reversible. From magnetic measurements the Curie-Weiss constant and effective magnetic moment of GdGaH{sub 1.66} were obtained. The former indicates antiferromagnetic interactions, the latter attains a value of ~8 μ{sub B} which is typical for compounds containing Gd{sup 3+}ions. - Graphical abstract: Ferromagnetic GdGa absorbs hydrogen in two steps to yield antiferromagnetic GdGaH{sub 1.66}. Display Omitted - Highlights: • Elucidation of hydrogen uptake behavior of the rare earth gallide GdGa by in situ diffraction. • H-incorporation in GdGa leads to the formation of chain-like polyanions Ga-H-Ga-H-Ga. • H-incorporation in GdGa changes magnetism from ferromagnetic to antiferromagnetic.

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

On the kinetics of transgranular particle embrittlement during simulated carburizing in steel containing grain-refining additions of aluminum and niobium plus aluminum

Here, the kinetics of toughness degradation resulting from transgranular particle embrittlement are evaluated as a function of composition and processing history for simulated carburizing operations in air-melt steel containing grain-refining additions of aluminum and aluminum plus niobium. The kinetics of particle embrittlement are inherently linked to the ripening of AlN precipitates after extended austenitization in steel containing carbon contents representative of both the case and core of a carburized component. Embrittlement in steel containing AlN occurs with an activation energy similar to the value for aluminum diffusion in austenite, although an AlN volume fraction effect on the embrittlement kinetics is manifested as decreases in activation energy with decreases in the [Al]/[N] ratio of steel. In contrast, the presence of niobium substantially retards the kinetics of particle embrittlement in steel containing 120–200 ppm N. Observations of AlN precipitates coated with Nb(C,N) indicate that the decreases in embrittlement kinetics are related to a reduction in the potential for AlN ripening during austenitization.

36 MATERIALS SCIENCE↗