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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Real-time process monitoring for direct ink write additive manufacturing

Direct ink write (DIW) printing of reactive resins presents a unique challenge due to the time-dependent nature of the rheological and chemical properties of the ink. As a result, careful print optimization or process control is important to obtain consistent, high quality prints. The present invention uses a flow-through characterization cell for in situ chemical monitoring of a resin ink during DIW printing. Additionally, in-line extrusion force monitoring can be combined with off-line post inspection using machine vision. By combining in-line spectroscopy and force monitoring, it is possible to follow reaction kinetics (for example, curing of a reactive resin) and viscosity changes during printing, which can be used for a closed-loop process control. Additionally, the capability of machine vision to automatically identify and quantify print artifacts can be incorporated on the printing line to enable real-time, AI-assisted quality control of the printed products. Together, these techniques can form the building blocks of an optimized process control strategy when complex reactive ink must be used to produce printed hardware.

Cook, Adam W.↗
DOE OSTI2024

Electrochemical Manipulation and Radiolytic Evaluation of Organic Phase Neptunium

Post for LDRD Annual Poster Session Under envisioned used nuclear fuel reprocessing conditions, neptunium (Np) is present in a mixture of extractable Np(IV)/Np(VI) and inextractable Np(V) species, the distribution of which is dependent on several factors that lead to the unintentional partitioning of Np into various phases and product streams, reducing process and cost efficiency. With this in mind, we tested an innovative approach to precisely control the oxidation state distribution of Np using novel, high surface area, optically transparent, ligand modified tin-doped indium oxide electrodes (LMEs). These proof-of-concept experiments employed a variety of radiation and electrochemistry (echem) techniques to determine: electrode radiation stability; aqueous echem behavior of Np at nITO|P3 electrode surfaces; radiation-induced Np-extractant reaction kinetics; and non-aqueous echem of Np in diethylhexyl butyramide (DEHBA) solutions.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Pulse Radiolysis Study of Radiation Effect on Molten Salt

The molten salt reactor concept, where nuclear fuel is dissolved in a molten salt that also serves as the heat transfer fluid, is a leading candidate for next generation nuclear reactors. This necessitates a thorough understanding of radiation effects on molten salt media to support the design, development, and deployment of such reactors. Early, pioneering pulse radiolysis molten salt experiments observed key primary radiolysis products such as the solvated electron (esolv?) and dichloride radical anion (Cl2??), but left many fundamental mechanistic and reactivity questions unanswered. Here we report on the reaction kinetics of esolv? and Cl2?? in molten LiCl-KCl eutectic salt doped with Zn2+ ion, using electron pulse radiolysis to observe the transient behavior from nanosecond to microsecond time scales. Experiments were performed at the BNL Laser-Electron Accelerator Facility using a recently-developed high-temperature sample holder. Prompt formation of esolv? and Cl2?? are observed; esolv? decays within hundreds of nanoseconds while Cl2?? decays more slowly by second-order kinetics, more likely by cross-recombination rather than disproportionation. This work was supported as part of the Molten Salts in Extreme Environments Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science.

38 - RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCL↗
DOE OSTI2026

Chemical and Radiological Compatibility Testing of 3D Printed Materials

To dramatically increase the adaptability, performance, and safety of processes in support of the Defense Waste Processing Facility (DWPF), Savannah River National Lab (SRNL) plans to perform chemical and radiological compatibility testing on a wide variety of 3D printed materials of interest. The 3D printing process provides numerous strategic operational benefits such as rapid prototyping of complex designs and geometry specific to the needs of the nuclear waste disposition process, as well as on-demand rapid prototyping and iteration with materials that aren’t as accessible through traditional manufacturing methods. Reaction chemistry in simulated waste batches can be matched closely to its radioactive counterpart, but glass reactor vessels have limitations. Vessel geometry can play a big factor in mixing transport limitations, process chemistry, and degradation reaction kinetics. In addition, additive manufacturing allows for much more detailed vessel design than traditional alternatives. Waste processing techniques in DWPF also encounter extreme chemical environments including high pH, strong acids, abrasive slurries, and significant irradiation. To meet these challenges, a matrix of various polymer, ceramic, and metal additive manufacturing materials have been exposed to a suite of chemical environments of interest as well as radioactive dose (such as gamma radiation from 60 Co) to properly test their durability under these conditions. Mass change has been monitored over a period of up to a week in these conditions, as well as added characterization for surface modification through Scanning Electron Microscopy/Electron Dispersive X-ray analysis (SEM/EDX). Further chemical characterization has been monitored through Fourier-Transform InfraRed Spectroscopy (FTIR), with planned investigation via thermal and tensile strength degradation. While the direct product of this research is identification of material(s) that can withstand specific hazardous environments encountered by the mercury water wash tank in DWPF process simulation experiments, the reference base of materials will be used for many other nuclear processes in the pursuit of rapidly developed, cost-efficient, and highly specific devices for environmental remediation and much more.

Wilson, Nathan W. [Savannah River National Laborat↗
DOE OSTI2024

Broadband Rotational Spectroscopy in Uniform Supersonic Flows: Chirped Pulse/Uniform Flow for Reaction Dynamics and Low Temperature Kinetics

ConspectusThe study of gas-phase chemical reactions at very low temperatures first became possible with the development and implementation of the CRESU (French acronym for Reaction Kinetics in Uniform Supersonic Flows) technique. CRESU relies on a uniform supersonic flow produced by expansion of a gas through a Laval (convergent-divergent) nozzle to produce a wall-less reactor at temperatures from 10 to 200 K and densities of 1016-1018 cm-3 for the study of low temperature kinetics, with particular application to astrochemistry. In recent years, we have combined uniform flows with revolutionary advances in broadband rotational spectroscopy to yield an instrument that affords near-universal detection for novel applications in photodissociation, reaction dynamics, and kinetics. This combination of uniform supersonic flows with chirped-pulse Fourier-transform microwave spectroscopy (Chirped-Pulse/Uniform Flow, CPUF) permits detection of any species with a modest dipole moment, thermalized to the uniform temperature of the gas flow, with isomer, conformer, and vibrational state specificity. In addition, the use of broadband, high-resolution, and time-dependent (microsecond time scale) micro- and mm-wave spectroscopy makes it an ideal tool for characterizing both transient and stable molecules, as well as studying their spectroscopy and dynamics.In this Account, we review recent advances made using the CPUF technique, including studies of photodissociation, radical-radical reaction dynamics, and low temperature kinetics. These studies highlight both the strength of universal and multiplexed detection and the challenges of coupling it to a high-density collisional environment. Product branching and product evolution as a function of time have been measured for astrochemically relevant systems, relying on the detailed characterization of these flow conditions via experiments and fluid dynamics simulations. In the photodissociation of isoxazole, an unusual heterocyclic molecule with a very low-energy conical intersection, we have identified 7 products in 5 reaction channels and determined the product branching, pointing to both direct and indirect pathways. We have also approached the same system from separated NO and C3H3 reactants to explore a broader range of the potential energy surface, demonstrating the power of multichannel branching measurements for complex radical-radical reactions. We determined the product branching in the C3H2 isomers in the photodissociation of the propargyl radical and identified the importance of a hydrogen atom catalyzed isomerization to the lowest energy cyclic form. This then motivated a study of direct D-H exchange reaction in radicals, in which we demonstrate that it is an important and overlooked pathway for deuterium fractionation in astrochemical environments. Recently, we have shown the measurement of low temperature kinetics inside an extended Laval nozzle, after which a shock-free secondary expansion to low temperature and density affords an ideal environment for detection by rotational spectroscopy. These results highlight the power and potential of the CPUF approach, and future prospects will also be discussed in light of these developments.

Dias, Nureshan↗
DOE OSTI2021

Electrocatalysts Development for Hydrogen Oxidation Reaction in Alkaline Media: from Mechanism Understanding to Materials Design

Anion exchange member (AEM) fuel cells have gained great attention recently mainly owing to the advantages of non-precious metal catalysts application. Despite of the similar oxygen reduction reaction (ORR) kinetics in acid and base, the reaction kinetics of hydrogen oxidation reaction (HOR) is two orders of magnitude slower in alkaline systems than in acid. To understand the slower kinetics of HOR in base, two major interpretations have been proposed, including 1) hydrogen binding energy as a major descriptor for HOR in both acid and base; and 2) bifunctional theory based on the contributions from both hydrogen and hydroxide adsorption for HOR in alkaline electrolyte. Here, we discuss the possible HOR mechanisms in alkaline electrolytes with the corresponding Tafel behavior change. Besides the discussion of traditional Tafel-Volmer and Heyrovsky-Volmer HOR mechanisms, the recently proposed hydroxide adsorption step is discussed to illustrate the HOR mechanism difference in acid and base. We further correlate the hydroxide adsorption step involved mechanism with HOR catalyst design, and summarize its role in HOR and HER activities improvement in alkaline electrolyte over the same catalyst. The representative works of alkaline HOR catalyst development were briefly introduced, and the strategy of strengthening interaction between H2 desorption and H2O recombination was finally proposed for future HOR catalyst design in alkaline environment.

Hydrogen oxidation reaction, Hydrogen evolution re↗
DOE OSTI2021

Key Chemical Kinetic Steps in Reaction Mechanisms for Fuels from Biomass: A Perspective

Detailed chemical kinetic modeling has been a significant part of combustion research since the entry of the computer into the research community. For most of that time, fuels have largely been provided from petrochemicals, and the combustion chemistry that was developed reflected that source of fuels. Furthermore, renewable fuels from biomass have always made important contributions as fuel sources. Current trends show that renewable fuels are gaining an even more important role as fuel sources, and chemical kinetic modeling of those fuels is playing an essential role in these advances. Interactions between fuels research and chemical kinetic modeling are discussed in this paper, with emphasis on the close and continuous coupling between them. In many cases, new fuels from biomass have structural or compositional features never before seen in real fuels, so entirely new reaction mechanisms are required.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2024

Kinetics of the reaction of ferrous ions with hydroxyl radicals in the temperature range 25–300 °C

Here, the kinetics and mechanism of the reaction between OH radicals and ferrous ions in the temperature range 25–300 °C were studied using pulse radiolysis. At temperatures <150 °C the rate of reaction is essentially independent of temperature, while at temperatures >150 °C the activation energy is 45.8 ± 3.0 kJ mol —1 . The change in activation energy is attributed to a change in the dominant mechanism from hydrogen atom transfer (HAT) to dissociative ligand interchange. The kinetic isotope effect (KIE) was measured by repeating experiments in heavy water. A value of 2.9 was measured at room temperature where HAT is the dominant mechanism. The KIE decreases to zero at temperatures > 150 °C as ligand interchange becomes dominant and the O–H bond is no longer involved in the reaction.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

Iron (IV) Formation and the pH Dependent Kinetics of the Fenton Reaction

Despite its widespread importance for biological and environmental chemistry and decades of study, the mechanism underlying the Fenton reaction is still a matter of some controversy. Here, to elucidate the pH dependence of this complex reaction, a new kinetic model is developed to explain the increase in rate and mechanistic shift that occurs from acidic to neutral conditions. This mechanism originated from a re-analysis of a previously proposed model, which neglected explicit iron speciation, leading to unrealistic rate constants. Accounting for speciation suggests a much faster formation rate of Fe(IV), which is estimated to be on the order of 10 6 M −1 s −1 . Expanding on prior kinetic studies that include speciation under acidic conditions, we propose a unified kinetic model that captures the pH-dependent rate acceleration in Fe(II) oxidation by H 2 O 2 , which is a significant step toward resolving the long-standing mechanistic ambiguity of Fenton chemistry.

Cohen, Liron [Lawrence Berkeley National Laborator↗
DOE OSTI2022

Reaction mechanism and kinetics for N 2 reduction to ammonia on the Fe–Ru based dual-atom catalyst

Environmental and energy considerations demand that the Haber-Bosch process for reducing N 2 to NH 3 be replaced with electrochemical ammonia synthesis where the H atoms come from water instead of from H 2 . But a practical realization of electrochemical N 2 reduction reaction (NRR) requires the development of new generation electrocatalysts with low overpotential and high Faraday efficiency (FE). A major problem here is that the hydrogen evolution reaction (HER) competes with NRR. Herein, we consider new generation dual-site catalysts involving two different metals incorporated into a novel two-dimensional C 3 N–C 2 N heterostructure that provides a high concentration of well-defined but isolated active sites that bind two distinct metal atoms in a framework that facilitates electron transfer. We report here the mechanism and predicted kinetics as a function of applied potential for both NRR and HER for the (Fe–Ru)/C 3 N–C 2 N dual atom catalyst. These calculations employ the grand canonical potential kinetics (GCP-K) methodology to predict reaction free energies and reaction barriers as a function of applied potential. The rates are then used in a microkinetic model to predict the turn-over-frequencies (TOF) as a function of applied potential. At U = 0 V, the FE for NRR is 93%, but the current is only 2.0 mA cm –2 . The onset potential (at 10 mA cm –2 ) for ammonia on Fe–Ru/C 3 N–C 2 N is –0.22 V RHE . This leads to a calculated TOF of 434 h –1 per Fe–Ru site. In conclusion, we expect that the mechanisms for NRR and HER developed here will help lead to new generations of NRR with high TOF and FE.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Theoretical study of the reaction mechanism and kinetics of the phenyl + propargyl association

Potential energy surface for the phenyl + propargyl radical recombination reaction has been studied at the CCSD(T)-F12/cc-pVTZ-f12//B3LYP/6-311G** level of theory for the closed-shell singlet species and at the triplet–singlet gap CASPT2/cc-pVTZ-CCSD(T)-F12/cc-pVTZ-f12//CASSCF/cc-pVTZ level of theory for the diradical species. High-pressure limit rate constants for the barrierless channels were evaluated with variable reaction coordinate transition state theory (VRC-TST). Rice–Ramsperger–Kassel–Marcus Master Equation (RRKM-ME) calculations have been performed to assess temperature- and pressure-dependent phenomenological rate constants and product branching ratios. Here, the entrance channels of the radical association reaction produce 3-phenyl-1-propyne and phenylallene which can further dissociate/isomerize into a variety of unimolecular and bimolecular products. Theoretical evidence is presented that, at combustion relevant conditions, the phenyl + propargyl recombination provides a feasible mechanism for the addition of a second five-member ring to the first six-member aromatic ring producing the prototype two-ring species indene and indenyl. Rate expressions for all important reaction channels in a broad range of temperatures and pressures have been generated for kinetic modeling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Modeling the Environment-Dependent Kinetics of Oxygen Reduction Reaction – a Continuum Model for Electric Double Layer

Here, for proton-exchange-membrane fuel cells (PEMFCs) to achieve broad commercialization, improved energy-conversion efficiency with minimal Pt-based electrocatalyst is required. Because the sluggish rate of oxygen reduction reaction (ORR) limits the efficiency of PEMFCs, the efficiency improvement requires a better understanding of ORR kinetics and mechanism to design better catalyst. To understand the ORR mechanism, theoretical and experimental analyses have been conducted. While previous studies reasonably explained the catalyst-dependent activity on single crystal catalysts in 0.1 M perchloric acid solution, the explicit effect of electrolyte and related microenvironments is not thoroughly understood. The change in the electrolyte alters the electric-double-layer (EDL) structure and thus the local microenvironment at the electrode/electrolyte interface. Thus, the structure of the EDL should be carefully analyzed to uncover the electrolyte-dependent reaction kinetics. In this talk, we propose a multiscale continuum model to predict the EDL structure and examine the effect of perchloric acid concentration on ORR activity on Pt (111). The model includes Density Potential Functional Theory (DPFT) for electron density and Modified Poisson Boltzmann equation for species’ density and electric potential. Also, the interaction between adsorbents and electric field is taken into account by minimizing the grand potential. After model validation with experimentally measured double-layer capacity data as a function of applied potential and concentration, the effect of the perchloric acid concentration (0.02 M – 0.2 M) on ORR activity is analyzed and discussed. It is shown that the model reproduces the specific activity obtained in the experiments when assuming the oxygen adsorption is limiting the rate, which can be attributed to the large energetic barrier for solvent reorganization. Then, extension of the model to PEMFC ionomer electrolytes will be introduced. Overall, the model framework and findings provide insights into the ORR mechanism and guidance on how to tailor catalyst materials for increased PEMFC performance.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2021

Predicted Reaction Mechanisms, Product Speciation, Kinetics, and Detonation Properties of the Insensitive Explosive 2,6-Diamino-3,5-dinitropyrazine-1-oxide (LLM-105)

2,6-Diamino-3,5-dinitropyrazine-1-oxide (LLM-105) is a relatively new and promising insensitive high-explosive (IHE) material that remains only partially characterized. IHEs are of interest for a range of applications and from a fundamental science standpoint, as the root causes behind insensitivity are poorly understood. In this work, we adopt a multitheory approach based on reactive molecular dynamic simulations performed with density functional theory, density functional tight-binding, and reactive force fields to characterize the reaction pathways, product speciation, reaction kinetics, and detonation performance of LLM-105. We compare and contrast these predictions to 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), a prototypical IHE, and 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX), a more sensitive and higher performance material. The combination of different predictive models allows access to processes operative on progressively longer timescales while providing benchmarks for assessing uncertainties in the predictions. We find that the early reaction pathways of LLM-105 decomposition are extremely similar to TATB; they involve intra- and intermolecular hydrogen transfer. Additionally, the detonation performance of LLM-105 falls between that of TATB and HMX. We find agreement between predictive models for first-step reaction pathways but significant differences in final product formations. Predictions of detonation performance result in a wide range of values, and one-step kinetic parameters show the similar reaction rates at high temperatures for three out of four models considered.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Theoretical Kinetics Predictions for Reactions on the NH 2 O Potential Energy Surface

Recent modeling studies of ammonia oxidation, which are motivated by the prospective role of ammonia as a zero-carbon fuel, have indicated significant discrepancies among the existing literature mechanisms. In this study, high-level theoretical kinetics predictions have been obtained for reactions on the NH 2 O potential energy surface, including the NH 2 + O, HNO + H, and NH + OH reactions. These reactions have previously been highlighted as important reactions in NH 3 oxidation with high sensitivity and high uncertainty. The potential energy surface is explored with coupled cluster calculations, including large basis sets and high-level corrections to yield high-accuracy (~0.2 kcal/mol 2σ uncertainty) estimates of the stationary point energies. Variational transition state theory is used to predict the microcanonical rate constants, which are then incorporated in master equation treatments of the temperature- and pressure-dependent kinetics. For radical–radical channels, the microcanonical rates are obtained from variable reaction coordinate transition state theory implementing directly evaluated multireference electronic energies. The analysis yields predictions for the total rate constants as well as the branching ratios. We find that the NO + H 2 channel contributes 10% of the total NH 2 + O flux at combustion temperatures, although this channel is not included in modern NH 3 oxidation mechanisms. Modeling is used to illustrate the ramifications of these rate predictions on the kinetics of NH 3 oxidation and NO x formation. Finally, the present results for NH 2 + O are important for predicting the chain branching and formation of NO in the oxidation of NH 3 and thermal DeNO x .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Reaction Profiles and Kinetics for Radical–Radical Hydrogen Abstraction via Multireference Coupled Cluster Theory

Radical-radical abstractions in hydrocarbon oxidation chemistry are disproportionation reactions that are generally exothermic with little or no barrier yet are underappreciated and poorly studied. Such challenging multireference electronic structure problems are tackled here using the recently developed state-specific multireference coupled cluster methods Mk-MRCCSD and Mk-MRCCSD(T), as well as the companion perturbation theory Mk-MRPT2 and the established MRCISD, MRCISD+Q, and CASPT2 approaches. Reaction paths are investigated for five prototypes involving radical-radical hydrogen abstraction: H + BeH → H 2 + Be, H + NH 2 → H 2 + NH, CH 3 + C 2 H 5 → CH 4 + C 2 H 4 , H + C2H 5 → H 2 + C 2 H 4 , and H + HCO → H 2 + CO. Full configuration interaction (FCI) benchmark computations for the H + BeH, H + NH 2 , and H + HCO reactions prove that Mk-MRCCSD(T) provides superior accuracy for the interaction energies in the entrance channel, with mean absolute errors less than 0.3 kcal mol(-1) and percentage deviations less than 10% over the fragment separations of relevance to kinetics. To facilitate combustion studies, energetics for the CH 3 + C 2 H 5 , H + C 2 H 5 , and H + HCO reactions were computed at each level of theory with correlation-consistent basis sets (cc-pVXZ, X = T, Q 5) and extrapolated to the complete basis set (CBS) limit. These CBS energies were coupled with CASPT2 projected vibrational frequencies along a minimum energy path to obtain rate constants for these three reactions. The rigorous Mk-MRCCSD(T)/CBS results demonstrate unequivocally that these three reactions proceed with no barrier in the entrance channel, contrary to some earlier predictions. Mk-MRCCSD(T) also reveals that the economical CASPT2 method performs well for large interfragment separations but may deteriorate substantially at shorter distances.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Kinetics and mechanisms of polycondensation reactions between aryl halides and bisphenol A

Aryl chlorides (ArCl) or aryl fluorides (ArF) were used in polycondensation reactions to form poly(arylene ether sulfone)s (PAES). Interestingly, the kinetics of the ArF reaction fit a third-order rate law, which is attributed to the activation of the carbon–fluorine bond by two potassium cations (at least one bound to phenolate), which form a three-body complex. Here, the ArCl monomer follows a second-order rate law, where a two-body complex forms at the initial state of the aromatic nucleophilic substitution (S N Ar) pathway. These metal cation-activated complexes act as intermediates during the attack by the nucleophile. This finding was reproduced with either the potassium or the sodium counterion (introduced via potassium carbonate or sodium carbonate). Through a combination of experimental analysis of reaction kinetics and computational calculations with density functional theory (DFT) methods, the present work extends the fundamental understanding of polycondensation mechanisms for two aryl halides and highlights the importance of the CX–metal interaction(s) in the S N Ar reaction, which is translational to other ion-activated substitution reactions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

The reaction NH 2 + CH 2 O: Kinetic measurements and computational studies

The reaction of amidogen with formaldehyde is relevant to astrochemistry and couples nitrogen and carbon chemistry in flames. The first measurements of the temperature dependence of the rate constant k were made, over 409–643 K, and are summarized as k = 7.1 × 10 −12 exp(−18.2 kJ mol −1 /RT) cm 3 molecule −1 s −1 with a confidence interval of ±20%. These results address a controversy over the presence of a significant barrier in the addition/elimination pathway leading to the production of formamide between theoretical models that include the zero-point energy of all modes at the transition state and a model that excludes transitional modes. The latter would lead to a negligible barrier, which is inconsistent with the experiments. Contrary to earlier claims, CCSDT(Q)-corrected energies combined with transition state theory yield quantitative accord with the measurements.

Astrochemistry↗