Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “reaction 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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The effect of Co alloying content on the kinetics of reaction zone growth in tungsten fiber reinforced superalloy composites

A Co-free modified superalloy similar in composition to Waspaloy is investigated in an effort to understand the effect of Co on reaction zone growth kinetics and verify the chemistry dependence of reaction zone growth in the matrix of tungsten fiber reinforced superalloy composites. The values of the parabolic rate constant, characterizing the kinetics of reaction zone growth, for the Waspaloy matrix and the C-free alloy as well as five other alloys from a previous study confirm the dependence of reaction zone growth kinetics on cobalt content of the matrix. The Co-free alloy composite exhibits the slowest reaction zone growth among all tungsten fiber reinforced composites studied to date.

Rodriguez, A.↗
DOE OSTI2026

Suppressing proximity effects during rapid serial two-photon lithography through tuning of reaction–diffusion kinetics

The ability of two-photon lithography (TPL) to print deterministic nanoporous 3D structures is highly valuable for many applications. However, it is challenging to print such structures rapidly due to the proximity effects that cause closely spaced features to enlarge and merge. A key challenge is the limited understanding of the origins and spatiotemporal dynamics of the long-range proximity effects that extend beyond the optical focal spot. Here, we empirically investigate these proximity effects in serial TPL using custom-made acrylate-based photoresists. We demonstrate that the complex spatiotemporal dynamics of the proximity effects can be explained through the kinetics of the reaction–diffusion photopolymerization mechanisms that underlie the curing process. Specifically, we show that the proximity effects arise due to comparable timescales of reaction and diffusion of oxygen. Furthermore, we demonstrate that long-range proximity effects can be suppressed by introducing phenolic inhibitors, which reduce oxygen consumption through non-inhibiting side reactions and promote faster termination of curing reactions. These insights enabled improving the linewidths from >400 to 260 nm during printing of nanoporous 3D woodpiles at scanning speeds of 50 mm s −1 . Thus, the knowledge generated here can be applied to deterministically tune the proximity effects and enable rapid printing of high-resolution nanoporous 3D structures.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Single-Atom Doping at the Molecule–Metal Interface: How Rh Affects Surface Explosion Kinetics

Controlling chemical reactions at interfaces is central to many fields, including atmospheric, environmental, and biological chemistry as well as catalysis and corrosion. We performed a fundamental study of how catalytically active Rh atoms placed at and above a molecule-metal interface influence the surface reaction kinetics of tartaric acid (TA) decomposition. Specifically, TA decomposition on Cu(100) exhibits autocatalytic decomposition kinetics involving a slow initiation step followed by fast decomposition of the molecular layer. These so-called “surface explosions” are extremely sensitive to initial conditions, making it fundamentally interesting to study how the placement of reactive atoms affects the reaction rate. Temperature-programmed reaction (TPR) experiments reveal that Rh atoms embedded in the Cu(100) surface beneath TA (TA/Rh/Cu) or atop the TA layer (Rh/TA/Cu) reduce the decomposition temperature and modify the reaction rate constants. Isothermal TPR analysis reveals that Rh enhances both the initiation rate constant, k i , and the explosion rate constant, k e , facilitating explosive decomposition at lower temperatures. This result provides evidence that both the initiation and explosion steps occur at the metal-molecule interface and are accelerated by the presence of Rh at this interface. This study illustrates how small amounts of reactive elements may be used to control nonlinear kinetic processes at interfaces.

desorption↗
DOE OSTI2025

Cross-Scale Catalyst Modeling Applied to H 2 Storage and Release via Formic Acid

Here, we propose the Systems-to-Atoms (S2A) modeling framework that integrates the kinetics of reaction chemistry and structural configurations across various length scales with the aim of establishing a versatile template for multiscale modeling of reactive flow problems and to predict the operando activity of catalyst materials. The approach encompasses a microkinetic model to analyze surface reactions on individual facets of catalyst nanoparticles coupled with the computation of average surface reaction rates for catalyst nanoparticles of specific size distributions. Macro-homogeneous surface reaction kinetics are derived as a function of catalyst loading and used as input parameters for the continuum-scale reactor model. The cross-scale framework enables the optimization of catalyst utilization through reactor design and operating strategy. To demonstrate the framework, we studied the storage and release of hydrogen from formic acid, a promising liquid organic hydrogen carrier (LOHC), over Pd, Pt, and Cu catalysts. The framework predicts observed trends in formic acid dehydrogenation activity for catalysts with comparable weight loadings and metal particle diameters, demonstrating satisfactory quantitative alignment. Finally, the seamless transmission of parameter uncertainties between scales is also discussed.

08 HYDROGEN↗
NASA NTRS1990

Compatibility of Fe-40Al with various fibers

Chemical reaction can occur at the fiber/matrix interface of intermetallic matrix composites, leading to a degradation of mechanical properties. Fe-40Al matrix composites were fabricated using SiC, B, W, Mo-base, and Al2O3 fibers. Composite samples were heat treated up to 1500 K to study the reaction kinetics, and reaction rates were determined from reaction zone thickness measurements. The Al2O3 and W fibers were found to be compatible with the Fe-40Al matrix, while the Mo-based fibers reacted moderately and the B and SiC fibers reacted severely. Experimental results are compared to theoretical thermodynamic predictions.

Draper, S. L.↗
NASA NTRS2016

Materials Outgassing Rate Decay in Vacuum at Isothermal Conditions

As a laboratory for scientific research, the International Space Station has been in Low Earth Orbit for nearly 20 years and is expected to be on-orbit for another 10 years. The ISS has been maintaining a relatively pristine contamination environment for science payloads. Materials outgassing induced contamination is currently the dominant source for sensitive surfaces on ISS and modeling the outgassing rate decay over a 20 to 30 year period is challenging. Materials outgassing is described herein as a diffusion-reaction process using ASTM E 1559 rate data. The observation of -1/2 (diffusion) or non-integers (reaction limited) as rate decay exponents for common ISS materials indicate classical reaction kinetics is unsatisfactory in modeling materials outgassing. Non-randomness of reactant concentrations at the interface is the source of this deviation from classical reaction kinetics. A diffusion limited decay was adopted as the result of the correlation of the contaminant layer thicknesses on returned ISS hardware, the existence of high outgassing silicone exhibiting near diffusion limited decay, and the confirmation of non-depleted material after ten years in the Low Earth Orbit.Keywords: Materials Outgassing, ASTM E 1559, Reaction Kinetics, Diffusion, Space Environments Effects, Contamination

Huang, Alvin Y.↗
NASA NTRS2003

Termolecular ion-molecule reactions in Titan's atmosphere. IV. A search made at up to 1 micron in pure hydrocarbons

The results of a study of ion-molecule reactions occurring in pure methane, acetylene, ethylene, ethane, propyne, propene, propane, and diacetylene at pressures up to 40 microns of pressure are reported. A variety of experimental methods are used: The standard double resonance in an ICR, for determination of the precursor ions and the modulated double resonance ejection in an ICR, for the determination of the daughter ions. The FA-SIFT technique was used for validation and examination of termolecular reactions with rate coefficients that are less than 10(-26) cm(6) s(-1). An extensive database of reaction kinetics already exists for many of these reactions. The main point of this study was the determination of the accuracy of this database and to search for any missing reactions and reaction channels that may have been omitted from earlier investigations. A specific objective of this work was to extend the study to the highest pressures possible to find out if there were any important termolecular reaction channels occurring. A new approach was used here. In the pure hydrocarbon gases the mass spectra were followed as a function of the pressure changes of the gas. An initial guess was first made using the current literature as a source of the reaction kinetics that were expected. A model of the ion abundances was produced from the solution of the partial differential equations in terms of reaction rate coefficients and initial abundances. The experimental data was fitted to the model for all of the pressures by a least squares minimization to the reaction rate coefficients and initial abundances. The reaction rate coefficients obtained from the model were then compared to the literature values. Several new channels and reactions were discovered when the modeled fits were compared to the actual data. This is all explained in the text and the implications of these results are discussed for the Titan atmosphere.

Hydrocarbons, Acyclic/analysis↗
NASA NTRS1991

Origin of fatty acid synthesis - Thermodynamics and kinetics of reaction pathways

The primitiveness of contemporary fatty acid biosynthesis was evaluated by using the thermodynamics and kinetics of its component reactions to estimate the extent of its dependence on powerful and selective catalysis by enzymes. Since this analysis indicated that the modern pathway is not primitive because it requires sophisticated enzymatic catalysis, an alternative pathway of primitive fatty acid synthesis is proposed that uses glycolaldehyde as a substrate. In contrast to the modern pathway, this primitive pathway is not dependent on an exogenous source of phosphoanhydride energy. Furthermore, the chemical spontaneity of its reactions suggests that it could have been readily catalyzed by the rudimentary biocatalysts available at an early stage in the origin of life.

Weber, Arthur L.↗
NASA NTRS1981

Investigation of the hydrogenation of SiCl4

A laboratory scale pressure reactor was constructed to study the 3 SiCl + 2H2 + Si yields 4 SiHCl3 reaction at pressures up to 500 psig. Reaction kinetic measurements were carried out as a function of reactor pressure, reaction temperature and H2/SiCl4 feed ratio. Based on the reaction kinetic data, the hydroclorination of SiCl4 and m.g. silicon metal is found to be an efficient process to produce SiHCl3 in good conversions and in high yields. Copper is an effective catalyst. Results of the corrosion study show that conventional nickel chromium alloys are suitable material of construction for the hydrochlorination reactor. The hydrochlorination reaction is relatively insensitive to external process parameters such as silicon particle size distribution and the impurities in the m.g. silicon metal.

Mui, J. Y. P.↗
DOE OSTI2025

Decoupling electrode kinetics to elucidate reaction mechanisms in alkaline water electrolysis

Alkaline water electrolysis (AWE) presents key advantages, including reduced material costs, enhanced operational stability, and compatibility with non-precious metal catalysts, positioning it as a scalable route for hydrogen production. In this study, we introduce a minimally invasive single-cell configuration incorporating a reference electrode via diaphragm extension to form an internal ion channel. This setup, combined with an interfaced potentiostat and auxiliary electrometer, enables real-time, independent monitoring of anode and cathode behavior, offering high-resolution electrochemical diagnostics. While it is well established that the hydrogen evolution reaction (HER) exhibits sluggish kinetics in alkaline media, our study reveals that this limitation persists even in practical AWE systems where nickel-based substrates are used as electrodes. This observation is supported by both experimental data and voltage breakdown modeling. Arrhenius-type analysis reveals that localized electric fields induced by catalysts shift the reaction kinetics from classical Butler–Volmer behavior toward a Marcus-like regime, where interfacial molecular dynamics and bimolecular charge transfer dominate. We propose a semi-empirical model and a surficial reaction mechanism to describe these dynamics. This work underscores the critical need for cathode innovation and provides a rational framework for designing advanced catalysts and electrode architectures to optimize AWE performance.

08 HYDROGEN↗
DOE OSTI2025

Mitigated Dissimilar Mass Transfer with Aluminized RAFM Steels in Flowing PbLi at 650°C

To evaluate dissimilar material interactions in flowing eutectic Pb-16at. %Li between fusion-relevant materials and to establish a maximum operating temperature of future blanket designs, a series of thermal convection loop (TCL) experiments with flowing PbLi have been conducted. Following a 1000-h, 550°C to 650°C TCL experiment, a thin reaction product was observed on the surface of monolithic, high-purity SiC. To identify the source of the observed dissimilar material interaction and to understand the reaction kinetics, an identical 2000-h TCL exposure was conducted, but less reaction of the SiC specimen was observed. Characterization of the FeCrAlMo (alloy APMT) loop tubing and the PbLi-exposed austenitic stainless steel (SS) assembly parts suggested that the formation of the reaction layer on the surface of the PbLi-exposed SiC did not originate from the coated reduced activation ferritic martensitic (RAFM) steel, but from the dissolved loop materials (liquid metal exposed APMT tubing and type 316 SS fittings). Here, the results, after 2000 h, suggest that the dissimilar material reaction between the Al-coated RAFM steel and the SiC has very slow reaction kinetics within a temperature gradient of 550°C to 650°C.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Effect of Electrolyte Ions on Iridium Oxide-Based Water Oxidation Catalysis

The oxygen evolution reaction often limits the efficiency of renewable fuel syntheses due to its sluggish reaction kinetics. Of the factors that have been studied to improve this important reaction is how the choice of the electrolyte may alter the reaction kinetics. Despite its importance, sys-tematic studies of this effect have been relatively rare. Herein, we report an effort toward correcting this deficiency by investigating the effect of nitrate on water oxidation catalyzed by IrO x . The results show that nitrate can suppress the reaction, resulting in a decrease of the rate and an increase in the Tafel slope. The effect was found to be consistent with a microkinetic model incorporating competitive adsorption between reac-tion intermediates and nitrate, suggesting that the reaction mechanism was unaffected by anion identity. Moreover, this blocking effect exhibited dependence on the cations, following a trend Li + ≈ Na + ≈ K + > Cs + > TEA + . The results are expected to find broad applications in electrocatalysis.

Tafel slope analysis↗
DOE OSTI2025

Modeling kinetic effects of charged vacancies on electromechanical responses of ferroelectrics: Rayleighian approach

Understanding the time-dependent effects of charged vacancies on the electromechanical responses of materials is at the forefront of research for designing materials exhibiting metal-insulator transitions and memristive behavior. A Rayleighian approach is used to develop a model for studying the nonlinear kinetics of the reaction leading to generation of vacancies and electrons via the dissociation of vacancy-electron pairs. Also, diffusion and elastic effects of charged vacancies are considered to model polarization-electric potential and strain-electric potential hysteresis loops. The model captures multiphysics phenomena by introducing couplings among polarization, the electric potential, stress, strain, and concentrations of charged (multivalent) vacancies and electrons (treated as classical negatively charged particles), where the concentrations can vary due to association-dissociation reactions. A derivation of coupled time-dependent equations based on the Rayleighian approach is presented. Three limiting cases of the governing equations are considered, highlighting the effects of (1) nonlinear reaction kinetics on the generation of charged vacancies and electrons, (2) Vegard's law (i.e., the concentration-dependent local strain) on asymmetric strain-electric potential relations, and (3) coupling between a fast component and the slow component of the net polarization on the polarization-electric-field relations. The Rayleighian approach discussed in this work should pave the way for developing a multiscale modeling framework in a thermodynamically consistent manner while capturing multiphysics phenomena in ferroelectric materials. Published by the American Physical Society 2025

Kumar, Rajeev (ORCID:0000000194943488)↗