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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 1,081 records · Page 60
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Reactivity Worth Measurement of Control Rods of CFBR-II with Inverse Kinetics Method

CFBR-II is a Godiva type metal HEU fast burst reactor. Reactivity adjustment of the reactor depends on three metal HEU rods (CPI, CP2 and CP3), which have positive reactivity worth. Reactivity effectiveness curves of the three rods are important to safe operation and control of CFBR-I. To measure the reactivity, two different techniques were used: the asymptotic period method (APM) and the inverse kinetic method(IKM). The APM is the most common used method on fast burst reactor, which measured the asymptotic power period then determined reactivity with the in-hour equation. This method only works for positive periods (super criticality state). The IKM can measured continuously reactivity changes by analyzing the variation of reactor power level with the inverse kinetic equation, which works for both subcritical and super critical state. We will mainly discuss how to measure reactivity effectiveness curves of control rods by the IKM.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Operando Neutron Imaging of Lithium Flux and Gradient Cathode Design for Enhanced Kinetics in High‐Loading All‐Solid‐State Li─S Batteries

All-solid-state Li–sulfur batteries (ASSLSBs) are considered promising candidates for next-generation energy storage owing to their inherent safety, high energy density, and abundant sulfur resources. However, slow redox kinetics greatly limit sulfur utilization during solid-solid sulfur reactions, leading to significant challenges to achieve efficient performance in high-mass-loading ASSLSBs. Here, operando neutron image is employed to directly visualize, for the first time, that sluggish Li + transport kinetics and the uneven distribution of Li + during cathodic reactions are critical factors limiting sulfur conversion. To address this issue, gradient cathode architectures comprising three and five layers are designed, in which catholyte concentrations are strategically varied to optimize Li-ion flux and enhance ionic conductivity of the whole composite cathode electrode. Operando neutron imaging distinctly visualizes and confirms that three-layer gradient approach significantly enhances Li-ion mobility, resulting in more uniform redox reactions and greatly improved sulfur utilization compared to traditional non-gradient structures. Consequently, the three-layer gradient cathode achieves superior rate performance and reduced electrode polarization at high sulfur mass loadings of 4.5 and 6.0 mg cm −2 . Furthermore, the applicability and scalability of this design are demonstrated in a five-layer gradient cathode architecture, achieving an impressive discharge specific capacity increase from 656 mAh g −1 (three-layer gradient) to 1232 mAh g −1 at 1/20 C for ultra-high sulfur loading of 7.5 mg cm −2 . In conclusion, this innovative gradient cathode design offers substantial advancements in understanding and overcoming Li-ion transport limitations, paving the way toward practical, high-energy-density ASSLSBs.

25 ENERGY STORAGE↗
DOE OSTI2019

In Situ Optical Absorption Studies of Point Defect Kinetics and Thermodynamics in Oxide Thin Films

The authors discuss the use of in situ optical absorption to probe point defect equilibria and kinetics in oxides, with particular attention to thin films and high-temperature measurements evaluating changes in oxygen content. The introduction notes the effect of point defects on oxide behavior, including differences in thin films versus bulk materials, and describes methods to evaluate point defect equilibria and kinetics; advantages of optical absorption among these methods are highlighted. Section 2 provides an overview of how optical absorption and point defect concentrations are related, including various possible structural and electronic origins of defect-mediated absorption changes corresponding to oxygen content changes. Section 3 traces the development of historical understanding of optical absorption in nonstoichiometric oxides and emergence of thin film applications and measurement approaches that resulted. Section 4 details the procedure for determining surface exchange coefficients from optical transmission relaxation measurements and provides specific examples of how this approach uniquely has enabled new insights into thin film surface exchange behavior with and without current collectors. Section 5 provides examples of optically derived diffusivity measurements and comparisons of bulk and thin film defect equilibria. Section 7 outlines potential opportunities and future developments in this area, and Section 7 concludes the manuscript.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Enantioselective Kinetic Resolution/Desymmetrization of Para</em-Quinols: A Case Study in Boronic-Acid-Directed Phosphoric Acid Catalysis

A chiral phosphoric acid-catalyzed kinetic resolution and desymmetrization of para-quinols operating via oxa-Michael addition was developed and subsequently subjected to mechanistic study. Good to excellent s-factors/enantioselectivities were obtained over a broad range of substrates. Kinetic studies were performed, and DFT studies favor a hydrogen bonding activation mode. The mechanistic studies provide insights to previously reported chiral anion phase transfer reactions involving chiral phosphate catalysts in combination with boronic acids.

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

Toward Higher Voltage Solid-State Batteries by Metastability and Kinetic Stability Design

The energy density of battery systems is limited largely by the electrochemical window of the electrolyte. Here, the combined thermodynamic and kinetic effects of mechanically induced metastability are shown to greatly widen the operational voltage window of solid-state batteries based on ceramic-sulfide electrolytes. Solid electrolyte voltage stability up to 10 V is achieved with minimal degradation, far beyond the capability of organic liquid electrolytes. Furthermore, combined experiment, ab initio computation, and theoretical modeling identify the nature of mechanically constrained Li 10 GeP 2 S 12 decomposition both within the bulk and at interfaces with cathode materials at very high voltages. Previously unclear kinetic processes are identified that, when properly implemented, can potentially allow solid-state full cells with remarkably high operational voltages.

25 ENERGY STORAGE↗
DOE OSTI2019

Reduction Kinetics of Perovskite Oxides for Selective Hydrogen Combustion in the Context of Olefin Production

Chemical looping represents a novel approach for generating light olefins in which thermal cracking or catalytic dehydrogenation is coupled with selective hydrogen combustion (SHC) by a metal oxide redox catalyst, which enables autothermal operation, increased per-pass conversion, and greater-than-equilibrium yields. Recent studies indicate that Na 2 WO 4 -promoted perovskite oxides are effective redox catalysts with high olefin selectivity. Herein, kinetic parameters, rates, and reaction models for the reduction of unpromoted and Na 2 WO 4 -promoted CaMnO 3 redox catalysts by H 2 , C 2 H 4 , and C 2 H 6 , is reported. Reduction rates of CaMnO 3 under ethylene and ethane are significantly lower than under H 2 . Additionally, model fitting of reduction kinetics show good agreement with reaction order–controlled models for CaMnO 3 reduction and predict greater oxygen site dependence and higher activation energy for CaMnO 3 reduction by C 2 H 4 as compared with H 2 . Avrami–Erofe'ev nucleation and growth models provide the best fit to the reduction of Na 2 WO 4 /CaMnO 3 in H 2 and in C 2 H 4 . After Na 2 WO 4 promotion, the reduction rate of CaMnO 3 is three orders of magnitude lower in ethylene in comparison to hydrogen, consistent with its superior selectivity to hydrogen combustion. The models developed can be applied toward reactor design and optimization in the context of enhanced olefin production via SHC under a cyclic redox scheme.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Contrasting Chemical Kinetic Parameters for Near In‐Service‐Temperature Aging and High‐Temperature Thermal Decomposition of Triaminotrinitrobenzene Formulations

Triaminotrinitrobenzene-based high explosives such as LX-17 offer high energy density and exceptional safety, yet their long-term aging behavior at low temperatures remains poorly understood. In this study, several legacy and new production lots of LX-17 were subjected to accelerated aging experiments below 100°C, during which the formation rate of the initial degradation product, monofurazan (F1), was monitored. Kinetic analysis was performed using a sample-age-aware computational approach, yielding activation energy estimates of 82–91 kJ mol −1 for the low-temperature initiation step—markedly lower than the ∼200 kJ mol −1 associated with high-temperature thermal decomposition. Extrapolation from established cookoff models supports the conclusion that the dominant degradation mechanism at low temperatures differs from that at high temperatures. In conclusion, our results provide a unified kinetic framework that bridges the gap between in-service conditions and high-temperature damage.

Chemistry - Chemical explosives↗
DOE OSTI2019

Kinetic Simulations of Cu Doping in Chlorinated CdSeTe PV Absorbers

This paper reports on 1D kinetic modeling of p-type doping formation in Cu-doped chlorinated CdSeTe photovoltaic (PV) absorbers with graded Se profiles. Following the recent progress in kinetic simulations of the defect chemistry in stoichiometric CdTe films, this work extends simulation capabilities to a domain of semiconductor alloy films with graded stoichiometries. The defect formation energies and ionization levels, as well as the diffusion and reaction barriers used in the reaction-diffusion equations are calculated from the first principles. A new formalism is employed to account for the uncertainty of the defect formation energies in semiconductor alloys caused by unknown local surrounding. Finally, the developed methodology is used to model a practical fabrication process of p-type doping formation in graded CdSeTe absorbers and to study the effect of alloy stoichiometry on the doping activation.

14 SOLAR ENERGY↗
DOE OSTI2024

Enhancing the Reaction Kinetics and Stability of Co‐Free Li‐Rich Cathode Materials via a Multifunctional Strategy

Co-free Li-rich layered oxides (CFLLOs) with anionic redox activity are among the most promising cathode materials for high-energy-density and low-cost lithium-ion batteries (LIBs). However, irreversible oxygen release often causes severe structural deterioration, electrolyte decomposition, and the formation of unstable cathode-electrolyte interface (CEI) film with high impedance. Additionally, the elimination of cobalt elements further deteriorates the reaction kinetics, leading to reduced capacity and poor rate performance. Here, in this study, a multifunctional strategy is proposed, incorporating Li 2 MnO 3 phase content regulation, micro-nano structure design, and heteroatom substitution. The increased content of Li 2 MnO 3 phase enhances the capacity through oxygen redox. The smaller nanoscale primary particles induce greater tensile strain and introduce more grain boundaries, thereby improving the reaction kinetics and reactivity, while the larger micron-sized secondary particles help to reduce interfacial side reactions. Furthermore, Na⁺ doping modulates the local coordination environment of oxygen, stabilizing both the anion framework and the crystal structure. As a result, the designed cathode exhibits enhanced rate performance, delivering a capacity of 158 mAh g⁻¹ at 5.0 C and improved cyclic stability, with a high capacity retention of 99% after 400 cycles at 1.0 C. This multifunctional strategy holds great promise for advancing the practical application of CFLLOs in next-generation LIBs.

Co-free Li-rich layered oxide↗
DOE OSTI2018

Equilibrium, Kinetic and Thermodynamic Studies Of Lead (II) Sorption on Hydrolyzed Starch Graft Copolymers

Hydrolyzed starch graft poly (acrylic acid) and starch graft poly(acrylonitrile) copolymers were used as a sorbents for the removal of Pb(II) from aqueous solution in batch process. The sorbents were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. The effect of contact time, initial concentration and temperature were assessed to optimize the conditions for maximum sorption of the metal ions. The experimental data were analyzed by Langmuir, Freundlich, Temkin, Dubinin Radushkevich and Sips isotherm models. The Freundlich and the Sips isotherms confirmed the applicability of the models. The sorption capacity of the sorbent was found to be 118.61 mg/g for starch graft poly (acrylic) acid and 115.83 mg/g for starch graft poly (acrylonitrile). The Sorption kinetics was assessed by Lagergren pseudo first order, pseudo second order, Elovich equation, Intraparticle diffusion and the liquid film diffusion models. The experimental data fitted very well with the Elovich equation and the Intraparticle kinetic models. The thermodynamic analysis showed that the sorption was a spontaneous and endothermic process. The results indicated that starch graft copolymers can be used as an effective sorbents for Pb (II) removal from aqueous media.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Reaction Kinetics of CFRP Degradation in Supercritical Fluids

The reaction kinetics models of carbon fiber-reinforced plastic (CFRP) degradation in supercritical fluids were established by analyzing the chain scission reaction of a cross-linked network in CFRP. The effect of reaction time and temperature on the residual resin content from the recycled carbon fiber was investigated. The reaction order of CFRP degradation was estimated, and the reaction rate constant was calculated at different reaction temperatures. Reaction kinetics equations of CFRP degradation in different supercritical fluids were also proposed. Results indicated that CFRP degradation was mainly due to the scission of the C–C, C–O, and –O– bonds in the linear chain segment and of the C–N bond in the cross-linked segment of an epoxy resin cure system. The reaction order was 2 or 2.5. The monofilament tensile strength of recycled carbon fiber in supercritical n-butanol and n-propanol, which had higher degradation reaction rates, decreased by about 2% compared with that of the original carbon fiber.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Kinetic Models for Topological Nearest-Neighbor Interactions

We consider systems of agents interacting through topological interactions. These have been shown to play an important part in animal and human behavior. Precisely, the system consists of a finite number of particles characterized by their positions and velocities. At random times a randomly chosen particle, the follower, adopts the velocity of its closest neighbor, the leader. We study the limit of a system size going to infinity and, under the assumption of propagation of chaos, show that the limit kinetic equation is a non-standard spatial diffusion equation for the particle distribution function. We also study the case wherein the particles interact with their K closest neighbors and show that the corresponding kinetic equation is the same. Finally, we prove that these models can be seen as a singular limit of the smooth rank-based model previously studied in Blanchet and Degond (J Stat Phys 163:41–60, 2016). The proofs are based on a combinatorial interpretation of the rank as well as some concentration of measure arguments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Physical Kinetics of Electrons in a High-Voltage Pulsed High-Pressure Discharge with Cylindrical Geometry

Results of theoretical modeling of the phenomenon of a high-voltage discharge in nitrogen at atmospheric pressure are presented, based on a consistent kinetic theory of the electrons. A mathematical model of a nonstationary high-pressure discharge has been constructed for the first time, based on a description of the electron component from first principles. The physical kinetics of the electrons are described with the help of the Boltzmann kinematic equation for the electron distribution function over momenta with only ionization and elastic collisions taken into account. A detailed spatiotemporal picture of a nonstationary discharge with runaway electrons under conditions of coaxial geometry of the gas diode is presented. The model describes in a self-consistent way both the process of formation of the runaway electron flux in the discharge and the influence of this flux on the rate of ionization processes in the gas. Total energy spectra of the electron flux incident on the anode are calculated. The obtained parameters of the current pulse of the beam of fast electrons correlate well with the known experimental data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

A Mathematical Model for the Multiphase Transport and Reaction Kinetics in a Ladle with Bottom Powder Injection

A computation fluid dynamics-population balance model-simultaneous reaction model (CFD-PBM-SRM) coupled model has been proposed to study the multiphase flow behavior and refining reaction kinetics in a ladle with bottom powder injection, and some new and important phenomena and mechanisms are presented. For the multiphase flow behavior, the effects of bubbly plume flow, powder particle motion, particle-particle collision and growth, particle-bubble collision and adhesion, and powder particle removal into top slag are considered. For the reaction kinetics, the mechanisms of multicomponent simultaneous reactions, including Al, S, Si, Mn, Fe, and O, at the multi-interface, including top slag-liquid steel interface, air-liquid steel interface, powder droplet-liquid steel interface, and bubble-liquid steel interface, are presented, and the effect of sulfur solubility in the powder droplet on the desulfurization is also taken into account. Model validation is carried out using hot tests in a 2-t induction furnace with bottom powder injection. The result shows that the powder particles gradually disperse in the entire furnace; in the vicinity of the bottom slot plugs, the desulfurization product CaS is liquid phase, while in the upper region of the furnace, the desulfurization product CaS is solid phase. The predicted sulfur contents by the present model agree well with the measured data in the 2-t furnace with bottom powder injection.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Carbothermic Reduction Kinetics of Phosphorous Vaporization from Tri-calcium Phosphate (TCP) Under Microwave Rapid Heating With/Without the Presence of Fe{sub 3}O{sub 4}

The kinetics of vapor phase dephosphorization from tri-calcium phosphate (TCP) by carbothermic reduction was studied with and without the presence of Fe{sub 3}O{sub 4}. Microwave heating was utilized to obtain large variations in the heating rate (HR). In the reduction of TCP alone, the phosphorous removal fraction (RF; equal to ∆P{sub 2}O{sub 5}/P{sub 2}O{sub 5}{sup 0}, where ∆P{sub 2}O{sub 5} is the weight change and P{sub 2}O{sub 5}{sup 0} is the P{sub 2}O{sub 5} weight before heating) decreased as the HR increased. In other words, a shorter residence time at a high temperature resulted in a smaller reduction fraction of TCP. An apparently third-order reaction was postulated to account for the kinetics using a fitting simulation based on the additive law of the reaction progress. On the other hand, the phosphorous removal (dephosphorization) rate (RR; equal to ∆P{sub 2}O{sub 3}/t{sub MW}, where t{sub MW} is the microwave heating time period) increased as the HR increased above 1200 °C. The reduction ratio of Fe{sub 3}O{sub 4} above 1100 °C is higher than 97 pct regardless of the heating rate. The reduction of TCP in the presence of Fe{sub 3}O{sub 4} showed that RF increased slightly with increasing HR despite a shorter residence time at a high temperature. The RR also increased with the HR even though RF decreased to half of the values observed in the cases without Fe{sub 3}O{sub 4} for temperatures above 1200 °C. The practicality and optimal operation conditions of phosphorus vapor removal were discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Study on Kinetic Mechanism of Bastnaesite Concentrates Decomposition Using Calcium Hydroxide

The thermal decomposition of bastnaesite concentrates using calcium hydroxide was studied. Calcium hydroxide can effectively inhibit the emission of fluorine during roasting by transforming it to calcium fluoride. The decomposition rate increased with increasing reaction temperature and amount of calcium hydroxide. The decomposition kinetics were investigated. The decomposition reaction was determined to be a heterogeneous gas–solid reaction, and it followed an unreacted shrinking core model. By means of the integrated rate equation method, the reaction was proven to be kinetically first order. Different reaction models were fit to the experimental data to determine the reaction control process. The chemical reaction at the phase interface controlled the reaction rate in the temperatures ranging from 673 K to 773 K (400 °C to 500 °C) with an apparent activation energy of 82.044 kJ·mol{sup −1}. From 773 K to 973 K (500 °C to 700 °C), diffusion through the solid product’s layer became the determining step, with a lower activation energy of 15.841 kJ·mol{sup −1}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Kinetics of Reduction of Low-Grade Nickel Laterite Ore Using Carbon Monoxide

Reduction of a low-grade nickel laterite ore with carbon monoxide to produce Fe-Ni alloy was investigated using a thermo-gravimetric analysis (TGA) method. Non-isothermal reduction tests with a fixed heating rate of 10 °C/min from room temperature to 1200 °C were carried out to determine the different reduction stages and reaction products in each state. Combining measured mass losses with theoretically calculated values together with X-ray diffraction analysis, the products of different reduction stages were identified and a reaction path was established. Isothermal reduction tests with temperatures ranging from 500 °C to 1100 °C were performed to evaluate the temperature dependence of the reduction kinetics. Various kinetic models were fitted to the experimental data to further determine the rate-controlling step in the isothermal tests. Then, two groups of TG experiments were carried out to study the effect of CO flow rate and sample mass on the rate of reaction. The results indicated that the reduction rate increases with the increase of the reduction temperature from 500 °C to 1100 °C. More alloy products are formed and the apparent activation energies increase from 8.6 to 14.7 kJ/mol with the increase of the reduction temperature from 700 °C to 1100 °C. Accordingly, it was proposed that diffusion of CO in the gas bulk and through the pores of the laterite ore sample bed are the rate limiting steps.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Kinetic Modeling of the Silicothermic Reduction of Manganese Oxide from Slag

A model was developed to describe the mixed rate control kinetics in systems with MnO-SiO{sub 2}-CaO-Al{sub 2}O{sub 3} slags and Fe-Si metal droplets. During the reaction of Fe-Si droplets and slag, Mn{sup 2+} transport was found to be part of controlling the system but could not sufficiently describe all initial conditions (chiefly, changes to initial silicon content). The current model describes the kinetics of the stated system and offers answers to the question of rate control; the model has been fitted to nine datasets of varying initial conditions including initial [Si], initial (MnO), initial droplet size, and reaction temperature. The fitted mass transfer coefficients for metal and slag were 2.3 × 10{sup −4} and 6.7 × 10{sup −4} m/s, respectively; these values are constant across the nine datasets. Previous claims about the efficiency of silicon usage in reducing manganese have been modified; it appears that the formation of silica is favored throughout the reaction, but that the formation of a silicon monoxide gas layer on the metal surface dramatically impacts the rate of reaction. As a measure of overall fit of the model, the average of the root-mean-square errors for all datasets is 14 pct. Mass transport in slag is twice as influential on rate control as the metal phase. The simultaneous transport of both Mn{sup 2+} and silicate dimers controls mass transport in the slag. Both [Si] and [Mn] can control from the metal side but are dependent on the initial conditions.

36 MATERIALS SCIENCE↗