Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “kinetics”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,603 records · Page 89
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Thermal Stability of a Eutectic Mixture of Bis(2,2-dinitropropyl) Acetal and Formal: Part C. Kinetic Compensation Effect

Here, the aging behavior of a eutectic mixture of bis(2,2-dinitropropyl) acetal and formal [called NP here] has been studied in various atmospheres [dry (air or nitrogen) versus wet] at temperatures 70 °C and below. The properties of aged samples were analyzed using Fourier transform infrared (FTIR) spectroscopy, Karl Fischer (KF) titration, liquid chromatography/mass spectrometry (LC/MS), and thermogravimetric analysis (TGA) over a period of three years. The results indicate that at aging temperatures up to 55 °C, the initial rates of water production from nitrous acid (HONO) formation and decomposition into the water, NO, and NO 2 follows a 1st order rate law and the rate constants follow an Arrhenius law as a function of temperature. The activation energies and pre-factors for water and volatiles production yield a single linear kinetic compensation plot, suggesting a common degradation pathway between NP and the various combinations of its constituents. Within a narrow temperature range, around 55 °C, a trace amount of water in NP stabilizes its properties by preventing HONO elimination. When the aging temperature is substantially higher than 55 °C, the nature of the degradation mechanism changes. It is suspected that the degradation products of NO x , water, and HNO 3 serve as catalysts to auto-catalyze (kinetics beyond the 1st order) and further degrade NP. The effect of headspace volume on this auto-catalytic process will be discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Migration Kinetics of Surface Ions in Oxygen-Deficient Perovskite During Topotactic Transitions

Oxygen diffusivity and surface exchange kinetics underpin the ionic, electronic, and catalytic functionalities of complex multivalent oxides. Towards understanding and controlling the kinetics of oxygen transport in emerging technologies, it is highly desirable to reveal the underlying lattice dynamics and ionic activities related to oxygen variation. In this study, the evolution of oxygen content is identified in real-time during the progress of a topotactic phase transition in La 0.7 Sr 0.3 MnO 3-δ epitaxial thin films, both at the surface and throughout the bulk. Using polarized neutron reflectometry, a quantitative depth profile of the oxygen content gradient is achieved, which, alongside atomic-resolution scanning transmission electron microscopy, uniquely reveals the formation of a novel structural phase near the surface. Surface-sensitive X-ray spectroscopies further confirm a significant change of the electronic structure accompanying the transition. The anisotropic features of this novel phase enable a distinct oxygen diffusion pathway in contrast to conventional observation of oxygen motion at moderate temperatures. The results provide insights furthering the design of solid oxygen ion conductors within the framework of topotactic phase transitions.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Imaging Lateral Drift Kinetics to Understand Causes of Outdoor Degradation in Silicon Heterojunction Photovoltaic Modules

Lateral drift currents caused by partial or patterned illumination of photovoltaic cells have important implications for laser-based screening methods and luminescence imaging of fielded and lab-stressed modules. This study investigates the kinetics of carrier drift and bulk recombination following patterned illumination in commercial silicon heterojunctions with intrinsic thin layer (HIT) modules, comparing the kinetics between a ten-year field-weathered module versus a control module that is stored indoors. The measurement of the microwave photoconductance decay (uPCD) transients in the modules, both coincident with the photoexcitation and in nonilluminated cell regions, reveals carrier drift on the 100 us timescale, followed by millisecond bulk lifetimes. Importantly, the uPCD transients are consistent with luminescence spreading over the cell, which is imaged using a time-gated InGaAs array camera. The weathered HIT module shows slower lateral drift and faster bulk lifetimes compared with the control, suggesting increased series resistance and accelerated nonradiative recombination in this module, attributable to degradation of the transparent conductive oxide and degradation of the passivation layer, respectively. These results provide a novel example of using time-resolved measurements directly on full photovoltaic modules to reveal causes of degradation, providing insight for further development of module imaging and screening capabilities.

14 SOLAR ENERGY↗
DOE OSTI2017

Influence of Alloying Elements and Effect of Stress on Anisotropic Hydrogen Diffusion in Zr-Based Alloys Predicted by Accelerated Kinetic Monte Carlo Simulations

The formation of hydrides degrades the toughness of Zr-based claddings, and thus is one of the primary concerns regarding cladding integrity during fuel operation and used fuel storage. However, the formation mechanism of hydrides, particularly the nucleation mechanism, is yet to be fully understood. To explore the nucleation process, atomic scale studies including density functional theory, molecular dynamics and kinetic Monte Carlo have been used to investigate H diffusion, segregation, and the possible nucleation paths of hydrides. Here, density functional theory calculations are used to parameterize a kinetic Monte Carlo model, which can accurately predict the effective H diffusivity in various Zr-based claddings including Zircaloy, Zirlo and Zr-2.5Nb. Assisted by density functional theory calculations, a recently developed charge-optimized-many-body potential is further improved and used to investigate the possible nucleation paths of hydrides. It’s shown that the formation of face-centered hydrides starts with coherent zeta-phase, shearing of which in the basal plane changes the hcp stacking into fcc and leads to the formation of gamma-hydride nuclei. The shearing involves a negligible barrier and negligible strain accumulation in the matrix by adopting three equivalent shear partials. The results obtained at the atomic scale are consistent with previous theory and experiments, and improves the current understanding on how and how fast hydride forms in Zr based cladding.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Kinetic control of phase evolution and defect-mediated recombination in AACVD-grown copper antimony sulphide thin films

Copper antimony sulphide (CAS) is a multinary chalcogenide semiconductor in which small deviations from stoichiometry can drive phase competition and strong defect-mediated modulation of optoelectronic properties. However, the systematic roles of copper precursor fraction and deposition time in governing phase evolution, off-stoichiometry, and recombination dynamics in aerosol-assisted chemical vapour deposition (AACVD)-grown undoped CAS thin films remain insufficiently understood. In this work, undoped CAS thin films were deposited by AACVD using Cu(dedtc)2 and Sb(dedtc)3 single-source precursors at 550 °C and a carrier gas flow rate of 150 sccm, while the Cu(dedtc)2 mole fraction (x = 0.15 – 0.55) and deposition time (1 – 2 hours) were systematically varied to probe how growth kinetics influence phase composition, microstructure, and defect-mediated optical properties without post-deposition annealing or extrinsic doping. Increasing copper precursor content drives phase evolution toward tetrahedrite-dominant CAS films at intermediate Cu(dedtc)2 mole fractions, with the film deposited at x = 0.35 exhibiting the strongest tetrahedrite character within the parameter space examined. The films are also copper-rich, antimony-poor, and sulphur-deficient, consistent with off-stoichiometric growth and intrinsic defect formation, plausibly including copper interstitials, Cu-on-Sb antisites, and sulphur vacancies. These growth-dependent compositional deviations are accompanied by tunable indirect optical bandgaps of approximately 1.60 – 2.18 eV and weak visible photoluminescence governed by defect-mediated recombination. Time-resolved photoluminescence reveals bi-exponential decay behaviour with lifetimes of approximately 0.1 – 3.6 ns, with emission dominated by slower donor–acceptor pair recombination and a smaller contribution from faster trap-assisted pathways. Collectively, these results establish an explicit kinetic process–structure–defect–property relationship for AACVD-grown CAS thin films and provide a growth–structure–property framework relevant to future optimization of CAS-based optoelectronic and energy materials.

36 MATERIALS SCIENCE↗
DOE OSTI2017

A degradation function consistent with Cocks–Ashby porosity kinetics

Here, the load carrying capacity of ductile materials degrades as a function of porosity, stress state and strain-rate. The effect of these variables on porosity kinetics is captured by the Cocks–Ashby model; however, the Cocks–Ashby model does not account for material degradation directly. This work uses a yield criteria to form a degradation function that is consistent with Cocks–Ashby porosity kinetics and is a function of porosity, stress state and strain-rate dependence. Approximations of this degradation function for pure hydrostatic stress states are also explored.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Spectra and Kinetics of YAG:0.5%Er{sup 3+} Radiation Under Pulsed Laser Thermal Excitation

The dependences of single-crystal YAG:0.5%Er{sup 3+} spectra in the range 200–1700 nm and the kinetics of the integrated emission on the excitation-energy density W of a single CO{sub 2}-laser pulse of ~100 ns FWHM duration at λ{sub ex} = 10.6 μm were investigated experimentally. The spectra changed qualitatively when W exceeded the generation threshold W{sub t} of laser plasma near the single-crystal surface. The YAG:0.5%Er{sup 3+} spectra at W < Wt were represented by peaks of selective emission (SE) of Er{sup 3+} multiplets on the continuous spectrum background. New emission peaks and additional background corresponding to emission spectra in a laser-induced air plasma with intensities much higher than the SE peaks appeared due to air ionization near the crystal surface at W > W{sub t}. Oscillograms of the integral emission in the range 600–1700 nm were characterized by a pulse-front duration of τ{sub f} = 1.0–1.6 μs and a decay time τ{sub d} ≈ 2.5 μs if W changed by one order of magnitude. The kinetics of the integrated emission intensity were explained by calculating the single-crystal temperature and the populations of Er{sup 3+} energy levels during conversion of thermal energy into SE during unsteady energy transfer by internal radiation and thermal conductivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

First-principles-based kinetic Monte Carlo studies of diffusion of hydrogen in Ni–Al and Ni–Fe binary alloys

The diffusion of dilute hydrogen in fcc Ni–Al and Ni–Fe binary alloys was examined using kinetic Monte Carlo method with input kinetic parameters obtained from first-principles density functional theory. The simulation involves the implementation of computationally efficient energy barrier model that describes the configuration dependence of the hydrogen hopping. The predicted hydrogen diffusion coefficients in Ni and Ni 89.4 Fe 10.6 are compared well with the available experimental data. In Ni–Al, the model predicts lower hydrogen diffusivity compared to that in Ni. Overall, diffusion prefactors and the effective activation energies of H in Ni–Fe and Ni–Al are concentration dependent of the alloying element. Furthermore, the changes in their values are the results of the short-range order (nearest-neighbor) effect on the interstitial diffusion of hydrogen in fcc Ni-based alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Thermal Kinetic Inductance Detectors for Ground-Based Millimeter-Wave Cosmology

We show measurements of thermal kinetic inductance detectors (TKIDs) intended for millimeter-wave cosmology in the 200–300 GHz atmospheric window. The TKID is a type of bolometer which uses the kinetic inductance of a superconducting resonator to measure the temperature of the thermally isolated bolometer island. We measure bolometer thermal conductance, time constant, and noise equivalent power. We also measure the quality factor of our resonators as the bath temperature varies to show they are limited by effects consistent with coupling to two-level systems.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Development of a Data Acquisition System for Kinetic Inductance Detectors: Wide Dynamic Range and High Sampling Rate for Astronomical Observation

Microwave kinetic inductance detectors have a variety of potential applications in astronomical observations. We built a data acquisition system for kinetic inductance detectors combining a dedicated analog board and a commercially available digital board to meet the requirements of astronomical measurements, such as observation of the cosmic microwave background. This paper reports the status of the development of the data acquisition system. We have already achieved simultaneous readout through 120 channels using a direct down-conversion method to decode the signal. A variety of software has been developed and tested using the functionalities of the system and actual detectors.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Development of Thermal Kinetic Inductance Detectors Suitable for X-ray Spectroscopy

We report on the development of thermal kinetic inductance detectors (TKIDs) suitable to perform X-ray spectroscopy measurements. The aim is to implement MKIDs sensors working in thermal quasi-equilibrium mode to detect X-ray photons as pure calorimeters. The thermal mode is a variation on the MKID classical way of operation that has generated interest in recent years. TKIDs can offer the MKIDs inherent multiplexibility in the frequency domain, a high spatial resolution comparable with CCDs, and an energy resolution theoretically limited only by thermodynamic fluctuations across the thermal weak links. Microresonators are built in Ti/TiN multilayer technology with the inductive part thermally coupled with a metal absorber on a suspended SiN membrane, to avoid escape of phonons from the film to the substrate. The mid-term goal is to optimize the single-pixel design in terms of superconducting critical temperatures, internal quality factors, kinetic inductance and spectral energy resolution. The final goal is to realize a demonstrator array for a next generation thousand pixels X-ray spectrometer. In this contribution, the status of the project after one year of developments is reported, with detailed reference to the microresonators design and simulations and to the fabrication process.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Kinetic Inductance Traveling Wave Amplifier Designs for Practical Microwave Readout Applications

Abstract A Kinetic Inductance Traveling Wave Amplifier (KIT) utilizes the nonlinear kinetic inductance of superconducting films, particularly niobium titanium nitride (NbTiN), for parametric amplification. These amplifiers achieve remarkable performance in terms of gain, bandwidth, and compression power and frequently approach the quantum limit for noise. However, most KIT demonstrations have been isolated from practical device readout systems. Using a KIT as the first amplifier in the readout chain of an unoptimized microwave SQUID multiplexer coupled to a transition-edge sensor microcalorimeter, we see an initial improvement in the flux noise [1]. One challenge in KIT integration is the considerable microwave pump power required to drive the non-linearity. To address this, we have initiated efforts to reduce the pump power by using thinner NbTiN films and an inverted microstrip transmission line design. In this article, we present the new transmission line design, fabrication procedure, and initial device characterization—including gain and added noise. These devices exhibit over 10 dB of gain with a 3 dB bandwidth of approximately 5.5–7.25 GHz, a maximum practical gain of 12 dB, and typical gain ripple under 4 dB peak to peak. We observe an appreciable impedance mismatch in the NbTiN transmission line, which is likely the source of the majority of the gain ripple. Finally, we perform an initial noise characterization and demonstrate system-added noise of three quanta or less over nearly the entire 3 dB bandwidth.

Physics↗
DOE OSTI2018

Development of Novel Biodegradable Enrofloxacin–Silica Composite for In Vitro Drug Release Kinetic Studies

A sustained drug delivery system is developed by using nonionic polymer to formulate drug release rate from silica capsules. To serve this purpose, silica capsules filled with poly(ethylene glycol) (PEG) were incorporated with a veterinary antibiotic drug enrofloxacin (ENF); as a model hydrophobic drug by using a general and facile sol–gel route. The physicochemical properties of the prepared drug-loaded composites were investigated by scanning electron microscope (SEM), nitrogen adsorption, Fourier transform infrared spectroscopy and thermal analysis (TGA). The impact of the media’s ionic strength on the drug release was evaluated over a range of 0–0.4 M to simulate the gastrointestinal feed in two physiological pH conditions. Sodium chloride was applied for ionic concentration adjustment due to its ability to salt out polymers in the midrange of the lyotropic series. Simultaneously, the drug release kinetics was evaluated by fitting experimental data to common empirical (zero-order, first order and Higuchi) and semi-empirical (Ritger–Peppas and Sahlin–Peppas) models. The drug release kinetics from capsules revealed a non-Fickian diffusion and pure relaxation-controlled release. Of these models, Sahlin–Peppas equation best fit the release data of ENF. To determine the best model, non-linear regressions were carried out.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Equilibrium, Kinetic and Thermodynamic Studies on Methylene Blue Adsorption by Konjac Glucomannan/Activated Carbon Aerogel

Activated carbon (AC) is a common adsorbent used for the purification of aqueous solutions, yet its poor aqueous dispersion may negatively affects its practicability significantly. In the present study, the fabrication of an AC aerogel immobilized with konjac glucomannan (KGM/AC) for environmental protection was reported, and the parameters (e.g. AC content in aerogel, solution pH, adsorption duration, adsorption temperature and adsorbent dosage) were analyzed systematically using methylene blue (MB) as a model adsorbate. Further, to explore the adsorption equilibrium isotherm at equilibrium, the adsorption data were respectively fitted to Langmuir and Freundlich models, while kinetics study was conducted to explain the adsorption mechanism and predict the adsorption efficiency. Besides, the effect of temperature on the adsorption behavior was assessed using Van’t Hoff equation. According to the experimental and calculative results, the adsorption data at equilibrium could be well geared into the Langmuir model, and the adsorption kinetics behavior was better consistent with the pseudo-second-order expression as well as the intra-particle diffusion model. The Brunauer, Emmett and Teller surface area of KGM/AC aerogel was 352.44 m{sup 2}/g. KGM/AC aerogel exhibited the maximal capacity of adsorption of 416.67 mg/g at 323 K, and its adsorption behavior toward MB was endothermic and spontaneous in nature.

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

A Simple Kinetic Model for the Phase Transition of the van der Waals Fluid

A simple kinetic model, which is presumably minimum, for the phase transition of the van der Waals fluid is presented. In the model, intermolecular collisions for a dense gas has not been treated faithfully. Instead, the expected interactions as the non-ideal gas effect are confined in a self-consistent force term. Collision term plays just a role of thermal bath. Accordingly, it conserves neither momentum nor energy, even globally. It is demonstrated that (i) by a natural separation of the mean-field self-consistent potential, the potential for the non-ideal gas effect is determined from the equation of state for the van der Waals fluid, with the aid of the balance equation of momentum, (ii) a functional which monotonically decreases in time is identified by the H theorem and is found to have a close relation to the Helmholtz free energy in thermodynamics, and (iii) the Cahn–Hilliard type equation is obtained in the continuum limit of the present kinetic model. Numerical simulations based on the Cahn–Hilliard type equation are also performed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Determination of kinetic properties of Sm(III)/Sm(II) reaction in LiCl–KCl molten salt using cyclic voltammetry and electrochemical impedance spectroscopy

Electrochemical and kinetic properties of samarium (Sm) in LiCl-KCl eutectic salt were explored at various concentrations and temperatures. Cyclic voltammetry (CV) were performed to determine diffusion coefficient and the rate constant (k0). In addition, electrochemical impedance spectroscopy (EIS) was conducted for additional understandings on the kinetic behaviors of Sm(III)/Sm(II) couple. The values of the diffusion coefficients were in the range of 3.54 × 10 -6 to 9.58 × 10 -5 cm 2 s -1 and the values of k 0 were estimated to be in the range of 0.63 × 10 -2 to 1.11 × 10 -2 cm s -1 . The values of i 0 for Sm(III)/Sm(II) were computed by obtaining the charge transfer resistance from the curve fitting analysis, ranging from 1.04 ×10 -3 to 2.97×10 -3 A cm -2 .

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Optical behavior and TL kinetics of Eu{sup 3+} and Tb{sup 3+} doped zirconate thermoluminescent phosphors

The influence of Tb{sup 3+} and Eu{sup 3+} ions on the optical behavior and TL kinetics of the synthesized phosphors were analyzed here. The AZrO{sub 3} (A = Ca, Ba, Sr) phosphors activated with Eu{sup 3+} and Tb{sup 3+} ions were prepared using solid state reaction technique. The doping concentration of Eu{sup 3+} and Tb{sup 3+} ions is varied from 0 to 2 mol% for each. The PXRD analysis is done to study various crystallographic aspects of synthesized phosphors. It confirms the crystalline structure, phase purity and homogeneity of synthesized phosphors. The FESEM and TEM analyses show formation of particles with irregular shape and variable dimensions. The agglomeration of these particles is a resultant of prolonged heat treatments involved in solid state reaction method at elevated temperatures. The study of TL spectra of UV and gamma irradiated phosphors set forth their second order kinetics. The electrons were trapped in trap centers with high trap depth and hence high amount of energy (~ 3 eV) is required to vacate them. The doping of trivalent rare earth impurity ions in the perovskite host lattice leads to formation of these traps centers. With enhanced TL intensity and low fading characteristics, these phosphors are suitable alternatives for TL mapping and sensing applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Performance efficiency and kinetic studies of water purification using ZnO and MgO nanoparticles for potassium permanganate

Zinc oxide (ZnO) and Magnesium oxide (MgO) nanoparticles (NPs) have been synthesized by solid–solid reaction technique. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) were used to investigate the structural properties of ZnO and MgO NPs. XRD indicates that structural of ZnO NPs has a hexagonal structure with space group P63mc. On the other hand, MgO NPs is cubic structure with space group Fm 3-bar m. The photocatalytic efficiency of both ZnO and MgO NPs as a catalyst was illustrated by studying the extreme quantity of potassium permanganate (KMnO{sub 4}) degradation rate in wastewater. KMnO{sub 4} achieved 17% and 25% degradation rate in 180 min for ZnO and MgO NPs, respectively. The experimental data were examined by the kinetic models of pseudo-first and second order as well as intra-particle diffusion. The obtained data is expressed well by the second-order kinetic model for both NPs. Moreover, according to the experimental results, MgO NPs has high-performance water purification as a comparison of ZnO NPs effect.

77 NANOSCIENCE AND NANOTECHNOLOGY↗