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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1954

Study of Some Dielectric Properties of Suspensions of Magnesium Particles in Mineral Oil

The variation of dielectric constant has been measured as a function of the concentration of magnesium particles; the shape, size, and degree of oxidation of the particles; the temperature; and the frequency of oscillation. The variation of dielectric constant and settling rate was investigated as a function of time. Also investigated were the effects of particle concentration, shape and time on dielectric losses.

Altshuller, Aubrey P↗
DOE OSTI2022

Tuning Strong Metal–Support Interaction Kinetics on Pt-Loaded TiO 2 (110) by Choosing the Pressure: A Combined Ultrahigh Vacuum/Near-Ambient Pressure XPS Study

Pt catalyst particles on reducible oxide supports often change their activity significantly at elevated temperatures due to the strong metal–support interaction (SMSI), which induces the formation of an encapsulation layer around the noble metal particles. However, the impact of oxidizing and reducing treatments at elevated pressures on this encapsulation layer remains controversial, partly due to the “pressure gap” between surface science studies and applied catalysis. In the present work, we employ synchrotron-based near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) to study the effect of O 2 and H 2 on the SMSI-state of well-defined Pt/TiO 2 (110) catalysts at pressures of up to 0.1 Torr. Further, by tuning the O 2 pressure, we can either selectively oxidize the TiO 2 support or both the support and the Pt particles. Catalyzed by metallic Pt, the encapsulating oxide overlayer grows rapidly in 1 × 10 –5 Torr O 2 , but orders of magnitude less effectively at higher O 2 pressures, where Pt is in an oxidic state. While the oxidation/reduction of Pt particles is reversible, they remain embedded in the support once encapsulation has occurred.

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

Calcination Heterogeneity in Li-Rich Layered Oxides: A Systematic Study of Li 2 CO 3 Particle Size

Li- and Mn-rich (LMR) layered oxide positive-electrode materials exhibit high energy density and have earth-abundant compositions relative to conventional Ni-, Mn-, and Co-oxides (NMCs). The lithiation of coprecipitated precursors is a key part of the synthesis and offers opportunities for tuning the properties of LMR materials. Whereas the morphology of transition metal precursors has received substantial attention, that of Li sources has not. Using Li 1.14 Mn 0.57 Ni 0.29 O 2 as a model system, in this work, we establish a detailed understanding of LMR calcination pathways via in situ and ex situ diffraction, spectroscopy, microscopy, and thermogravimetry. Our work shows that a large Li 2 CO 3 particle size modulates a previously misunderstood thermogravimetric feature present at the Li 2 CO 3 melting point during layered oxide calcination and causes heterogeneity at larger length scales (inter-secondary particle) than previously reported (intra-secondary particle). We found that electrochemical performance is largely insensitive to this heterogeneity. Finally, this work highlights the sensitivity of layered oxide calcination pathways to synthesis conditions and suggests design rules to minimize calcination heterogeneity in layered oxides beyond LMR.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Impact of Particle Size on the Vapor-Phase Oxidative Coupling of Methanol and Dimethylamine over Palladium–Gold Nanoparticles

Oxidative coupling of methanol and dimethylamine in the presence of O 2 in the vapor phase over dilute Pd in Au bimetallic catalysts occurs via the dissociation of O 2 on Pd and selective oxidation of methanol on Au. Here, we synthesize a series of silica-supported PdAu alloy nanoparticle catalysts of varied Pd:Au ratios with ~5 nm particle diameter and show that these catalysts have increased selectivity to dimethylformamide across all Pd:Au ratios (~95%), distinct from observations over larger PdAu nanoparticles (~15–25 nm diameter) of similar Pd:Au ratios. Small monometallic Pd particles are more selective than large monometallic Pd particles, and small Au nanoparticles are reactive and selective for oxidative coupling (while large Au nanoparticles are inactive). Rates per surface metal atom were similar over PdAu nanoparticles of all sizes and increased monotonically with increasing Pd content for the small nanoparticles. Further, apparent reaction kinetics demonstrate distinct apparent methanol reaction order and apparent activation energy relative to those reported over larger nanoparticles of similar Pd:Au ratios. Unlike larger PdAu nanoparticles, the rate of dimethylformamide formation is not promoted by cofed water over small PdAu nanoparticles. The results of the kinetic studies are used to propose a series of elementary steps, derive a plausible rate expression, and regress rate and equilibrium constants. These results suggest high coverages of surface methoxy species and low coverages of adsorbates derived from dimethylamine. Taken together, these results demonstrate the sensitivity of the rates, selectivities, and kinetics of oxidative coupling reactions to the size of bimetallic nanoparticles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Dependence of Uranium Oxide Polymorphism on Plasma Synthesis Conditions

Here, we synthesized uranium oxide nanoparticles using a plasma flow reactor (PFR) and studied the effects of three different experimental parameters on the resulting morphologies and speciation of the particles: (1) collection duration, (2) collection substrate temperature, and (3) radial collection position due to radial temperature gradients in the PFR. We also induced three distinct temperature histories along the axis of the plasma flow reactor by varying the gas flow rates downstream of the plasma torch. Transmission electron microscopy (TEM) analyses of collected particles showed two phases of uranium oxides (fcc-UO 2 and α-UO 3 ). The chemical compositions of the resulting uranium oxide particles were not altered by the three parameters investigated in this work but varied based on the temperature history induced. Preheating of the collection substrate led to deposition of fewer particles, which is attributed to a reduction in thermophoretic force caused by the reduced temperature gradient for preheated substrates. The relative amounts of UO 2 to UO 3 and particle size varied depending on the cooling history employed during synthesis.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
NASA NTRS1982

Carbon-catalyzed oxidation of SO2 by NO2 and air

A series of experiments was performed using carbon particles (commercial furnace black) as a surrogate for soot particles. Carbon particles were suspended in water, and gas mixtures were bubbled into the suspensions to observe the effect of carbon particles on the oxidation of SO2 by air and NO2. Identical gas mixtures were bubbled into a blank containing only pure water. After exposure each solution was analyzed for pH and sulfate. It was found that NO2 greatly enhances the oxidation of SO2 to sulfate in the presence of carbon particles. The amount of sulfate found in the blanks was significantly less. Under the conditions of these experiments no saturation of the reaction was observed and SO2 was converted to sulfate even in a highly acid medium (pH or = 1.5).

Rogowski, R. S.↗
NASA NTRS1992

The structure of premixed particle-cloud flames

The structure of premixed flames propagating in combustible systems, containing uniformly distributed volatile fuel particles, in an oxidizing gas mixture, is analyzed. It is presumed that the fuel particles vaporize first to yield a gaseous fuel of known chemical structure, which is subsequently oxidized in the gas phase. The analysis is performed in the asymptotic limit, where the value of the characteristic Zeldovich number, based on the gas-phase oxidation of the gaseous fuel is large, and for values of phi(u) greater than or equal to 1.0, where phi(u) is the equivalence ratio based on the fuel available in the fuel particles. The structure of the flame is presumed to consist of a preheat vaporization zone where the rate of the gas-phase chemical reaction is small, a reaction zone where convection and the rate of vaporization of the fuel particles are small and a convection zone where diffusive terms in the conservation equations are small. For given values phi(u) the analysis yields results for the burning velocity and phi(g) where phi(g) is the effective equivalence ratio in the reaction zone. The analysis shows that even though phi(u) greater than or equal to 1.0, for certain cases the calculated value of phi(g) is less than unity. This prediction is in agreement with experimental observations.

Seshadri, K.↗
NASA NTRS1990

Titanium oxide Magneli phases in four chondritic porous interplanetary dust particles

Detailed analytical electron microscope analyses of four fine-grained chondritic porous interplanetary dust particles (IDPs) reveal the presence of titanium oxide Magneli phases, Ti(n)O(2n-1) (n = 4, 5, 6), and rare Ti-metal. The association of Magneli phases, Ti-metal, and carbonaceous material in chondritic IDPs, along with the grain size distributions of Ti-metal and Magneli phases and equilibrium dissociation pressures for these oxygen-deficient Ti-oxides, support in situ solid carbon gasification in these extraterrestrial particles. The active catalyst in this process is titanium metal that may be of interstellar origin. A model is proposed that explains the higher solid carbon content of chondritic IDPs relative to bulk carbon abundances typical for carbonaceous chondrite matrices that represent another type of more metamorphosed undifferentiated solar system bodies.

Rietmeijer, E. J. M.↗
DOE OSTI2020

Review on the growth, properties and applications of self-assembled oxide–metal vertically aligned nanocomposite thin films—current and future perspectives

Self-assembled oxide–metal nanocomposite thin films have aroused great research interest owing to their wide range of functionalities, including metamaterials with plasmonic and hyperbolic optical properties, and ferromagnetic, ferroelectric and multiferroic behaviors. Oxide–metal nanocomposites typically self-assemble as metal particles in an oxide matrix or as a vertically aligned nanocomposite (VAN) with metal nanopillars embedded in an oxide matrix. Among them, the VAN architecture is particularly interesting due to the vertical strain control and highly anisotropic structure, enabling the epitaxial growth of materials with large lattice mismatch. In this review, the driving forces behind the formation of self-assembled oxide–metal VAN structures are discussed. Specifically, an updated in-plane strain compensation model based on the areal strain compensation concept has been proposed in this review, inspired by the prior linear strain compensation model. It provides a guideline for material selection for designing VAN systems, especially those involving complex orientation matching relationships. Based on the model, several case studies are discussed, comparing the microstructure and morphology of different oxide–metal nanocomposites by varying the oxide phase. Specific examples highlighting the coupling between the electrical, magnetic and optical properties are also discussed in the context of oxide–metal nanocomposites. Finally, future research directions and needs are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Temperature dependence of corrosion behavior of a dual-phase Fe 50 Mn 30 Co 10 Cr 10 high entropy alloy in supercritical water at 380–650 °C

Corrosion behavior of a dual-phase Fe 50 Mn 30 Co 10 Cr 10 HEA subjected to supercritical water at different temperatures was investigated. Both weight gain and oxide film thickness increased with increasing temperatures. An outer layer with polyhedral MnFe 2 O 4 particles and an inner layer containing a mixture of CrMn 1.5 O 4 and Fe 3 O 4 were formed at 380 °C. Mn 2 O 3 outer and CrMn 1.5 O 4 inner layers developed at 550 and 650 °C, but the loose granular Mn 2 O 3 particles at 550 °C transformed into a compact oxide film at 650 °C. Besides, Cr 2 O 3 oxide particles were observed along the grain boundaries. Finally, the corrosion mechanism at different temperatures was also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Overview of the Alaskan Layered Pollution and Chemical Analysis (ALPACA) Field Experiment

The Alaskan Layered Pollution And Chemical Analysis (ALPACA) field experiment was a collaborative study designed to improve understanding of pollution sources and chemical processes during winter (cold climate and low-photochemical activity), to investigate indoor pollution, and to study dispersion of pollution as affected by frequent temperature inversions. A number of the research goals were motivated by questions raised by residents of Fairbanks, Alaska, where the study was held. This paper describes the measurement strategies and the conditions encountered during the January and February 2022 field experiment, and reports early examples of how the measurements addressed research goals, particularly those of interest to the residents. Outdoor air measurements showed high concentrations of particulate matter and pollutant gases including volatile organic carbon species. During pollution events, low winds and extremely stable atmospheric conditions trapped pollution below 73 m, an extremely shallow vertical scale. Tethered-balloon-based measurements intercepted plumes aloft, which were associated with power plant point sources through transport modeling. Because cold climate residents spend much of their time indoors, the study included an indoor air quality component, where measurements were made inside and outside a house to study infiltration and indoor sources. In the absence of indoor activities such as cooking and/or heating with a pellet stove, indoor particulate matter concentrations were lower than outdoors; however, cooking and pellet stove burns often caused higher indoor particulate matter concentrations than outdoors. The mass-normalized particulate matter oxidative potential, a health-relevant property measured here by the reactivity with dithiothreiol, of indoor particles varied by source, with cooking particles having less oxidative potential per mass than pellet stove particles.

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

Mutual modulation between surface chemistry and bulk microstructure within secondary particles of nickel-rich layered oxides

Abstract Surface lattice reconstruction is commonly observed in nickel-rich layered oxide battery cathode materials, causing unsatisfactory high-voltage cycling performance. However, the interplay of the surface chemistry and the bulk microstructure remains largely unexplored due to the intrinsic structural complexity and the lack of integrated diagnostic tools for a thorough investigation at complementary length scales. Herein, by combining nano-resolution X-ray probes in both soft and hard X-ray regimes, we demonstrate correlative surface chemical mapping and bulk microstructure imaging over a single charged LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) secondary particle. We reveal that the sub-particle regions with more micro cracks are associated with more severe surface degradation. A mechanism of mutual modulation between the surface chemistry and the bulk microstructure is formulated based on our experimental observations and finite element modeling. Such a surface-to-bulk reaction coupling effect is fundamentally important for the design of the next generation battery cathode materials.

25 ENERGY STORAGE↗
DOE OSTI2023

Stabilized lithium metal oxide electrode material and method of preparation

A stabilized lithium metal oxide cathode material comprises microparticles of lithium metal oxide in which individual particles thereof a core of lithium metal oxide and a coating of a different lithium metal oxide surrounding the core. There is an interface layer between the cores and the coatings in which there are gradients of metal ions in the direction of coating to core. The materials are made by a three stage process involving coprecipitating precursor metal hydroxide core particles at a controlled pH; coprecipitating a different metal hydroxide coating on the particles without controlling the pH; and then calcining the resulting coated precursor particles with lithium hydroxide to form the stabilized lithium metal oxide material.

Lipson, Albert L.↗
DOE OSTI2024

Stabilized lithium metal oxide electrode material and method of preparation

A stabilized lithium metal oxide cathode material comprises microparticles of lithium metal oxide in which individual particles thereof a core of lithium metal oxide and a coating of a different lithium metal oxide surrounding the core. There is an interface layer between the cores and the coatings in which there are gradients of metal ions in the direction of coating to core. The materials are made by a three stage process involving coprecipitating precursor metal hydroxide core particles at a controlled pH; coprecipitating a different metal hydroxide coating on the particles without controlling the pH; and then calcining the resulting coated precursor particles with lithium hydroxide to form the stabilized lithium metal oxide material.

Lipson, Albert L.↗
DOE OSTI2025

Maximizing Calendering Effects Through the Mechanical Pulverization of Co-Free Nickel-Rich Cathodes in Lithium-Ion Cells

Calendering is a technique used to maximize the volumetric energy density of battery electrodes. However, higher amounts of calendering result in increased tortuosity and particle cracking. We propose a novel packing structure of electrode particles to maximize calendering benefits while minimizing particle fracture. Cobalt-free layered oxide cathode LiNi0.92Mn0.04Al0.04O2 (NMA) particles are pulverized through ball-milling and coated with lithium phosphate. Pulverized and pristine NMA are fabricated into “bimodal” electrodes, whereas “unimodal” electrodes consist of only pristine NMA. Each electrode type was made into 30% porosity, 40% porosity, and uncalendered coin cell samples. X-ray diffraction suggests that the unimodal samples suffer from more particle fracture than the bimodal samples when calendered to the same porosity of 30%. Electrochemical impedance spectroscopy suggests that the bimodal electrodes exhibit lower surface film resistance. This is supported by enhanced capacity retention for the bimodal samples after 100 cycles.

25 ENERGY STORAGE↗
DOE OSTI2020

Conversion of Uranium Metal to Uranyl Sulfate Solution

Experiments involving conversion of uranium (U) metal to U 3 O 8 , followed by dissolution to form uranyl sulfate solution, were performed with batches of up to 300 g of U metal. The focus was to identify major U species formed during the oxidation process, determine the particle size distribution of the uranium oxide product, and identify the size of the dissolution vessel needed to accommodate the exothermic reaction during the conversion of U 3 O 8 to uranyl sulfate using 30% hydrogen peroxide and H 2 SO 4 . The information obtained in this study will be used for designing full-scale processes to convert kilogram quantities of U metal to uranyl sulfate solution with a concentration of 300 g U/L.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2020

Inorganic Sulfur Species Formed upon Heterogeneous OH Oxidation of Organosulfates: A Case Study of Methyl Sulfate

In this report recent studies reveal that organosulfates at the particle surface can be oxidized by gas-phase OH radicals with significant rates. Inorganic sulfur species, such as the bisulfate ion (HSO 4 - ) and sulfate ion (SO 4 2- ), can be formed upon these heterogeneous oxidation processes through the formation and subsequent reactions of sulfate radical anions (SO 4 •- ) in the particle phase. However, the amount of inorganic sulfur species produced in these heterogeneous oxidation reactions is not known. We investigate the heterogeneous OH oxidation of sodium methyl sulfate (CH 3 SO 4 Na), the smallest organosulfate detected in atmospheric particles, using an oxidation flow reactor at a relative humidity of 75%. We quantify the kinetics by measuring the decay of CH 3 SO 4 Na and the amount of HSO 4 - and SO 4 2- formed upon oxidation using ion chromatography. Kinetic measurements determine the heterogeneous OH reaction rate to be (5.72 ± 0.14) x 10 -13 cm 3 molecule -1 s -1 , with an effective OH uptake coefficient, γ eff , of 0.31 ± 0.06. The molar yield of inorganic sulfur species, defined as the total number of moles of HSO 4 - and SO 4 2- formed per mole of CH 3 SO 4 Na consumed upon oxidation, is found to be significant and has an average value of 0.62 ± 0.18 upon oxidation. A kinetic model is developed to describe the kinetics and inorganic sulfur species formation upon oxidation. Model simulations suggest that CH 3 SO 4 Na tends to decompose rapidly into formaldehyde and SO 4 •- , and the reaction of SO 4 •- with CH 3 SO 4 Na plays a significant role in both governing the kinetics and the formation of inorganic sulfur species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗