Search NASA⌕ Search

SEARCH · Search NASA

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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Brewster angle-cavity ringdown spectroscopy for low temperature plasma measurements in multiphases

Here we report on the development of a Brewster angle-cavity ringdown spectroscopy (BA-CRDS) system for low temperature plasma diagnostics. The system can measure gas species in solutions, with a detection limit (minimum detectable absorbance) of 9.1 × 10 -5 , which is equivalent to a detection limit of 0.04 parts per billion for measuring OH radicals in water at 308 nm. With higher reflectivity ringdown mirrors and improved design of a Brewster angle cell, the detection limit can potentially be up to 10 -6 or lower. In this exploratory study, the absorption cross sections of HgBr 2 and H 2 O 2 in the aqueous phase at 256 nm are measured to be (1.8 ± 0.1) × 10 -18 cm 2 and (5.2 ± 0.5) × 10 -20 cm 2 , respectively. Furthermore, temporal profiles of absorbance from distilled water, HgBr 2 , and H 2 O 2 solutions when interacting with a helium atmospheric plasma jet are individually characterized at different plasma powers, gas flow rates, and/or solute concentrations. The observed linear temporal profiles of absorbance from the plasma-interacted water suggest formation of H 2 O 2 from plasma-generated OH radicals, while the nonlinear temporal profiles from the plasma-treated HgBr 2 solutions reveal possible removal of HgBr 2 by OH radicals. Our results demonstrate that the new BA-CRDS system is a powerful tool for quantification of reactive plasma species in multiphases or other complex settings.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

2,4–dinitroanisole transformation during advanced oxidation with ultraviolet light emitting diodes and hydrogen peroxide

This study investigated the kinetics and reaction mechanisms associated with advanced oxidation of 2,4-dinitroanisole (DNAN) with light emitting diodes (LEDs) in the UV/H2O2 process. The pseudo first-order reaction rate constants for DNAN oxidation depended on the H 2 O 2 /DNAN molar ratio and were between 0.017 and 0.026 min –1 . Hydroxyl radical scavenging was strongly implicated by the experimental results. High mass spectrophotometric chromatograms showed the presence of several by-products, including three with ecotoxicity that is greater than that of DNAN. Transformation pathways were analysed using Density Functional Theory (DFT), which helped to predict the presence of experimentally detected DNAN by-products by considering Mulliken charges. Furthermore, this study is the first to elucidate DNAN transformation mechanisms using both experimental studies and computational chemistry.

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

Baselining Activity and Stability of ORR Catalysts and Electrodes for Proton Exchange Membrane Fuel Cells for Heavy-Duty Applications

Activity and stability of electrodes with Pt and PtCo alloy catalysts supported on high surface area carbon, hereafter to as a-Pt/C and d-PtCo/C, were evaluated for heavy-duty applications. Both catalysts had nearly identical Pt loading (50-wt% Pt on carbon and 0.25 mg Pt cm −2 ) and had undergone thermal treatment to stabilize them by growing the average particle size to 4–5 nm. Both were subjected to 90,000 (90 k) standard accelerated stress tests (AST) cycles consisting of 0.6–0.95 V square wave potentials, 3-s hold at upper and lower potential limits in H 2 /N 2 at 1.5 atm, 80 °C and 100% RH. Test protocols were developed to monitor the performance losses and characterize them in terms of activity for the oxygen reduction reaction (ORR), oxygen transport in the electrode and proton transport in the membrane and cathode catalyst layer. Despite the nearly double initial ORR activity, the PtCo/C electrode degraded faster due to the leaching of Co from the catalyst that had started even before the imposition of the AST potential cycles. Commensurate with Co leaching, Co poisoning of ionomer is responsible for the inferior performance of d-PtCo/C electrode at high current densities both before and after AST.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Performance and Durability of Hybrid Fuel Cell Systems for Class-8 Long Haul Trucks

Hybrid fuel cell-battery configurations are investigated that overcome thermal management issues in fuel cell powertrains for heavy-duty Class 8 trucks. The battery is sized so that it has sufficient capacity to provide supplemental power and energy on a hill climb transient at end-of-life. A dynamic load sharing strategy is developed to distribute the power demand between the fuel cell system (FCS) and the energy storage system in a manner that optimizes their lifetimes. The FCS end-of-life is identified as the terminal point beyond which the stack cannot generate the rated power with target power density at 0.7 V and 40 °C ambient temperature. Reaching the target lifetime with a-Pt/C cathode catalyst in one hybrid configuration requires voltage clipping to 813 mV, idle power limited to 50 kW, catalyst overloading to 0.45 mg cm -2 total Pt in anode and cathode, and 44% active membrane area oversizing. The stack and FCS drive cycle efficiencies decrease by 4.2% and 5.4%, respectively, during the electrode lifetime. Further, the FCS performance, durability and cost are compared with the targets of 68% peak efficiency, 0.30 mg cm -2 total Pt loading, 2.5 kW/g PGM Pt group metal (PGM) loading, 750 mW cm -2 power density, 25,000-h lifetime and $80/kW cost.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2022

Hyperbranched PDMAEMA-functionalized SiO 2 microparticles: ATRP polymerization and grafting in a continuous flow reactor

Flow chemistry offers high reaction yield, kinetic control, improved safety, reliability, scalability, and greater degree of process control. Herein, hyperbranched polymer-grafted silica microparticles (HP-SMPs) are synthesized in a commercially available flow reactor through atom transfer radical polymerization. Initiator-anchored silica microparticles are obtained by in situ silanization in the flow reactor. Hyperbranched poly[2-(dimethylamino)ethylmethacrylate] chains are grafted onto the initiator-anchored SMPs through inimer–monomer ratio control. To demonstrate the efficiency and universality of this approach in grafting polymers onto SMPs, multiple hyperbranched polymeric structures are obtained by varying the inimer concentration. Dye absorption test is conducted to demonstrate the potential applications of HP-SMPs.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Predictive Engineering of Interfaces and Cathodes for High-Performance All Solid-State Lithium-Sulfur Batteries

The primary goal of this project is to leverage data-driven methods and machine learning strategies to develop accurate multi-physics models for all-solid-state Li-S battery (ASLSB) materials that can capture electrochemical and transport phenomena over atomic to mesoscopic length/timescales. These models will be rigorously validated by synthesis and advanced characterization experiments. The team will leverage the predictive power of these models, alongside synthesis/characterization experiments and battery fabrication to address longstanding issues at the electrode/electrolyte interfaces in ASLSBs. The project’s proposed technology involves the following: (1) halide-doped solid sulfide electrolytes that can concurrently provide high Li + ion conductivity and suppress dendrite growth; (2) novel mesoporous cathode composed of super-P and carbon nanotubes co-infiltrated with sulfur and sulfide electrolyte, which hold potential to allow high sulfur loading and optimal ion/electron pathways; and (3) functionalization of sulfide electrolyte with ionic liquids to improve physical contact and minimize impedance at the cathode/electrolyte interface. Successful development of proposed predictive models (at multiple scales) will bridge this knowledge gap and will advance fundamental understanding of reaction chemistry, kinetics, charge transfer, and dendrite growth at electrified SSIs. This will enable predictive design of effective strategies to mitigate interfacial problems in ASSLSBs, including poor interfacial contact, interfacial impedance to Li + ion transport, and poor electron/ion conduction within cathodes. Ultimately, the fundamental knowledge gained will lead to development of high-performance ASSLSBs.

25 ENERGY STORAGE↗
DOE OSTI2021

Developing a Fundamental Knowledge Base for the Interaction of Ruthenium with Natural and Engineered Iron-Bearing Materials

The intent of this project is to build a fundamental knowledge base concerning the redox coupling between Ru and Fe in heterogeneous systems with predictive applications towards the fate, speciation, and transport of Ru in the environment and its capture using available technologies. RuNOCl 3 and Fe 3+ are redox active over a broad range of pH. Initial assessment of effect of redox coupling between Ru and Fe indicates that Fe(III) in ferrihydrite can oxidize Ru 2+ in RuNOCl3 to Ru(IV) during coprecipitation at ambient conditions and alkaline pH. Further, evidence suggests that Ru(IV) is incorporated in the structure of fh. Likewise, Fe 3+ (aq) also reduces Ru 2+ in RuNOCl 3 in the homogenous system at acidic pH although the kinetics of reaction appear to be slow. Rufh annealed to 500 0C transforms to Ru(III) doped hematite. AIMD informed EXAFS indicates that Ru substitutes for Fe(III) in regular octahedral sites of hematite but requires three distinct configurations involving edge-sharing protonated Fe vacancies and straight substitution with no local defects. Fe 2+ (aq) appears to oxidize at the surface of RuO 2 , but the amount is too low to reasonably expect detectable reduced Ru. Future experiments at higher pH are warranted to make Fe 2+ (aq) less stable (i.e., make more redox active). We also demonstrated that we can functionalize Si aerogels with Fe(II) and Fe(III) but likely need to go to higher T to make Feo nanoparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High-Performance AEM LTE with Advanced Membranes, Ionomers and PGM-Free Electrodes

Alkaline low temperature electrolysis (LTE) systems enjoy several potential advantages over acid-based LTE systems including facile oxygen evolution reaction (OER) kinetics and electrodes that can use little to no platinum group metals (PGM). The polymer membranes and membrane electrode assembly (MEA) structures going into alkaline electrochemical systems have seen significant advances in recent years. The objective of this project is to combine state-of-the-art alkaline polymer electrolyzer components into one optimized membrane electrode assembly (MEA) system to achieve DOE low temperature electrolysis (LTE) goals. The benefit of individual component advances cannot be fully appreciated until all aspects and components of the MEA are working at an equally high level of performance. New electrode fabrication methods were developed where solvent cast catalyst/ionomer solutions were used in place of insoluble ionomers to significantly improve adhesion. The membranes were improved in terms of durability and mechanical properties. The OER and HER catalysts were improved and made more durable.

08 HYDROGEN↗
DOE OSTI2026

Hybrid Fuel Cell Systems for Heavy-Duty Trucks: Configuration, Heat Rejection, and Performance

Low-temperature polymer electrolyte membrane fuel cell systems can achieve higher efficiency than diesel engines, but heat rejection remains a major challenge in class-8 heavy-duty fuel cell trucks. For the same rated power, the radiator heat load is greater than that in a diesel engine, while the allowable operating temperatures are lower. This work proposes and evaluates 400 kWe fuel cell–battery hybrid (FCH) platforms and operating strategies that manage heat rejection without enlarging the radiator frontal area. Three FCH platforms are identified, each varying in fuel cell system (FCS) rated power, battery energy storage system (ESS) capacity, and maximum stack coolant exit temperature (T h1 ). All three satisfy key system and vehicle requirements, including 175 kWe FCS power at top sustained speed, 400 kWe FCH power on a 6% grade climb, a target stack power density (PD) of 750 mW e /cm 2 , and heat rejection constraints. The first FCH has the smallest FCS, the largest ESS, and a T h1 of 90 °C. The second achieves the highest PD of 840 mW e /cm 2 at a T h1 of 95 °C. The third has the largest FCS, the smallest ESS, and a T h1 of 102 °C. At a Th1 of 115 °C, the platform can be configured as a stand-alone 400 kWe(net) FCS without hybridization, but the achievable PD drops to 460 mW e /cm 2 .

25 ENERGY STORAGE↗
DOE OSTI2021

Modeling of Thermal Decomposition of TATB-Based Explosive for Safety Analysis

We investigate and model the cook-off behavior of LX-17 to understand the response of explosive systems in abnormal thermal environments. Decomposition has been explored via conventional ODTX (One-Dimensional Time-to-eXplosion), PODTX (ODTX with pressure-measurement), TGA (Thermo-Gravimetric Analysis), and DSC (Differential Scanning Calorimetry) experiments under isothermal and ramped temperature profiles. The data were used to fit reaction rate parameters for proposed schemes in an ALE3D computational model. This model includes chemical reactions, thermo- and hydro-dynamics, and material properties, including thermal expansion, compressibility, and strength. These parameterizations were carried out utilizing a Python evolutionary optimization method on LLNL’s high-performance computing clusters. Additional experiments are being developed to further characterize and monitor decomposition intermediates to improve the model. Once experimentally validated, this model will be scalable to several applications involving LX-17. Furthermore, the optimization methodology developed herein should be applicable to other high explosive materials.

Chemistry - Chemical explosives↗
DOE OSTI2021

Transamericium Radiation-Induced Redox Chemistry

The actinide series boasts many unique physical and chemical features worthy of study. However, the chemical influence of their inherent radiation field is often overlooked, especially as we begin to explore the late actinides (transamericium) in more detail than ever possible before. - Absorption of ionizing radiation induces the formation of a variety of transient and steady-state radicals, ions, and molecular degradation products. Many of these radiolysis products are strongly redox active and exhibit significant reactivity with a number of actinides, e.g., neptunium and americium. Here we present results from the first-ever time-resolved picosecond pulsed electron radiolysis measurements for the reaction of the late actinides (curium and californium) with reactive transients pertinent to actinide manipulations in aqueous solution, i.e., the hydrated electron (eaq–), the hydrogen atom (H•), and hydroxyl (•OH) and nitrate (•NO3) radicals.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Synthesis and Characterization of Pd-based Nanomaterials

Bimetallic nanoparticles (BNPs) consist of two different types of metals or alloys that are bonded together. Unique properties such as optical, electronic, thermal, and catalytic effects differ for each type of BNP. Important BNPs range from Au-Pd, Ag- Pt, Au-Pt, and Ag-Ni. Pd bimetallic nanoparticles are of interest due to their many applications such as catalysis and sensing. Bimetallic catalysts have increase reaction rates and have improved catalyst stability through the geometry and ligand distribution. Pd nanoparticles are considered to be a strong catalyst due to their high activity at low temperatures and high tolerance to moisture. The catalytic properties of bimetallic nanoparticles depend on the structural properties such as size and shape. Core-shell, hollow structure, and multi-shell alloy are three possible structures nanoparticles can form as bimetallic catalysts. BNPs can be synthesized through different methods to control the size, shape, and structure. To obtain different morphologies, a variety of methods can be performed. Different methods can range from the usage of the glancing angle deposition (GLAD) to the galvanic replacement reaction, but the methods all depend on the properties of the metals. The galvanic displacement reaction was the method used to obtain Pd-based nanoparticles. This reaction is best know for obtaining hollow shaped NPs. To determine what redox process was preformed, the activity series of metals was used. From the activity series of metals, silver (Ag) was selected to preform Pd-based nanoparticles. Objectives: Synthesize Ag nanoparticles and Ag-Pd nanoparticles to understand the morphology. Characterize the synthesized nanoparticles using scanning electron microscopy (SEM), phase analysis light scattering (PALS), dynamic light scattering (DLS), energy dispersive X-ray spectroscopy (EDS), and UV-Vis spectroscopy. Results: In the UV-Vis spectrum, the Ag-Pd bimetallic NP's plasmon band decreased as the volume of palladium increased. The surface charge increases as the concentration of palladium increases. The Pd{sup 2+} ions interact with the sodium citrate surface, and decrease the negative charge. Conclusion: Ag-Pd nanoparticles were successfully created and stabilized with sodium citrate. The addition of Pd decreased the prominent plasmon band of the Ag nanoparticles. The SEM analysis showed that Ag nanoparticles had a well-defined structure, while the Ag-Pd nanoparticles showed hollow and rough structure. The EDX analysis confirmed the presence of silver and palladium. This material can be used in many industrial and research fields such as organic synthesis, fuel cells, and environmental sensing and remediation.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Chromate Removal by Long Life IX Resins Without Continuous pH Adjustment - 20083

Long life resins are available for chromate removal from water but have traditionally had the disadvantage of requiring pH adjustment, first to reduce pH before treatment, and then to raise pH following treatment. The requirement for double pH adjustment leads to a significant increase in TDS, added complexity, risks associated with the use of strong acids and bases, and the ongoing costs of purchasing and using these chemicals. The mechanism of removal in long life resins used for chromate removal is ion exchange, followed by reduction of hexavalent chromium to trivalent chromium, followed by immobilization of trivalent chromium within the IX resin polymer. The second step is rate limiting and pH dependent and is the reason why lowering pH before treatment has until now been necessary. However, there is a reasonably simple way to use these long life resins that does not require continuous pH adjustment. By taking a portion of the treatment vessels off line and soaking them in a low pH solution, the rate constant for the reduction step is increased sufficiently to catch up, making the ion exchange step the limiting factor. The long life resin is effectively regenerated by the low pH soaks. Rejuvenated resin beds can then be put back on line and operated at the natural pH of the feedwater. This method of operation is protected by US Patent no. US20150136706A1. (author)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Deposition Behavior of Supersaturated Silicic Acid on the Surfaces of Chlorite and Sericite around Geological Repository - 20138

Around the repository for HLW underground, cementitious materials used for the repository may complicate the migration of radionuclides in the host rock by the alteration of groundwater to a high alkaline condition. Specially, the alkaline groundwater dissolves silicate minerals of host rocks but the plenty of silicic acid dissolved from host rocks in groundwater will become supersaturated and deposit on the surface of flow-paths after decreasing the pH value to about 8 with dispersion and dilution. The deposition of silicic acid is presumed to recover and improve the barrier performance of host rocks for the radionuclide migration because of the narrowing of flow paths and the decrease of the permeability. In this study, the deposition behavior of supersaturated silicic acid was examined by the deposition experiments and the deposition rate constants, k [m/s], were evaluated from the experimental data. As the minerals of the surface of flow-paths, this study focused on chlorite and sericite, hydrothermally-altered minerals distributed to fill fractures of granite. In the experiments, deposition behavior of silicic acid on the powder of chlorite or sericite was observed after the pH of the solution was adjusted to 8 in order to make the silicic acid supersaturated. The solution of CaCl{sub 2} and NaCl were added into a silicic acid to simulate Ca{sup 2+} from the cementitious materials of the repository, Na{sup +} of the saline groundwater in Japan. From the results, the value of k was estimated to be about the order of 10{sup -10}∼10{sup -9} m/s for both chlorite and sericite and the value was almost the same as those for amorphous silica in the previous study. Therefore, the deposition of silicic acid may be assessed by similar apparent deposition rate constants even in actual underground containing various silicate minerals. Moreover, the Damkoehler number which is the dimensionless number expressed by the ratio of characteristic time of mass transfer and chemical reaction was calculated to be 10{sup 4} or more from the value of k. This value shows that the deposition reaction of silicic acid was estimated as much more predominant than the groundwater flow under the situation simulated in this study. These results suggest that the deposition of supersaturated silicic acid on the flow paths composed with various silicate minerals will be able to retard the migration of radionuclides because of narrowing micro flow-paths. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Influences of Mg Ions and Al Ions on Deposition Behavior of Supersaturated Silicic Acid - 20261

Silicic acid can change into various species such as deposit, colloidal, and soluble form under certain conditions: for example, gradual pH changes around geological disposal repositories. In particular, silicic acid deposits narrow groundwater flow paths, thereby restricting the flow of groundwater. Such effects may contribute to a delay in radionuclide migration. Previous studies have reported that silicic acid supersaturated in sodium and calcium ions can narrow the flow paths. This study examined the effect of magnesium (Mg) and aluminum (Al) ions on the deposition of supersaturated silicic acid on the solid phase. The deposition behavior of supersaturated silicic acid on the solid phase was investigated in a batch system while changing the initial supersaturation concentration, the coexisting ion concentration, and the amount of added solid phase. In the presence of Mg ions, silicic acid precipitation increased with increasing Mg ion concentration due to the influence of the electrolyte, and crosslinking reactions. The coexistence of Al ions significantly suppressed silicic acid deposition due to the formation of a covering on the solid surface during Al ion hydrolysis under conditions of high Al concentration (1.4 mM). On the basis of these experimental results, the apparent deposition rate constant of silicic acid was estimated to be in the range from 10{sup -11} to 10{sup -10} m/s. The Damkoehler number (the dimensionless number expressed by the ratio of the characteristic time of mass transfer and the chemical reaction constant) was sufficient to cause the clogging of the host rock by deposition. This suggests that supersaturated silicic acid deposition, regardless of the presence of Mg ions (and Al ions), contributes to improving barrier performance against radionuclide migration in the host rock. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Savannah River Site High Level Radioactive Waste Tank Sample Thermolytic Hydrogen Generation - 20346

To support the revision of flammability calculations and controls for the Savannah River Site (SRS) High-Level Radioactive Waste (HLW) tanks, Savannah River National Laboratory (SRNL) conducted laboratory measurements with the goal of quantifying hydrogen produced in HLW by non-radiolytic chemical reactions (i.e., thermolysis). Testing was performed with HLW tank supernate samples that represented a cross section of types of waste at SRS, including tanks that store typical evaporator concentrate, dissolved salt-cake, dilute recycle stream from the Defense Waste Processing Facility (DWPF), evaporator concentrate of the recycle stream from DWPF, fresh waste from the canyon separations facility, and waste that has been through salt processing cesium removal. Non-radioactive simulant testing included the classes of organic compounds historically introduced into the HLW tanks that were recently shown to be the most active toward the thermolytic generation of hydrogen. The reaction rate equations developed for thermolytic hydrogen generation from each class of organic compound showed direct proportionality to organic compound concentration and hydroxide concentration. Simulant testing identified that highly concentrated waste with high hydroxide concentration had the highest rates of thermolytic hydrogen generation. Using the radioactive tank sample thermolysis measurements at high temperatures and the mechanistic salt dependence of the simulant models, a global model was developed for tank waste thermolytic hydrogen generation as a function of total organic carbon content of SRS HLW. Through the primary functionality of the global model (organic carbon and free hydroxide concentration), the relative reactivity of the organic carbon in the waste was quantified. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗