Search NASA⌕ Search

SEARCH · Search NASA

Results for “METAL PARTICLE”

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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Particle interspacing effects on the mechanical behavior of a Fe–TiB 2 metal matrix composite using FFT-based mesoscopic field dislocation mechanics

This paper presents an application to metal matrix composites (MMCs) of an enhanced elasto-viscoplastic Fast Fourier Transform (EVP-FFT) formulation coupled with a phenomenological continuum Mesoscale Field Dislocation Mechanics (MFDM) theory. Contrary to conventional crystal plasticity, which only accounts for plastic flow and hardening induced by statistically stored dislocations (SSDs), MFDM-EVP-FFT also describes the evolution of polarized geometrically necessary dislocation (GND) density and its effect on both plastic flow and hardening. Numerical results for a Fe–TiB 2 MMC made of a ferrite matrix (α-Fe) and elastic ceramic particles (TiB 2 ) are presented. Full-field simulations are performed using synthetic periodic unit cells representative of the MMC, with single-crystalline and polycrystalline matrix, for different particle interspacing distances. A strong dependence of the predicted equivalent stress, cumulated plastic strain and GND density fields with particle interspacing distance is observed, in contrast with conventional crystal plasticity. Correlations between these mechanical fields and microstructural features, and their influence on local and global mechanical behavior are examined for the different MMC microstructures.

42 ENGINEERING↗
DOE OSTI2021

In situ mechanical reinforcement of polymer hydrogels via metal-coordinated crosslink mineralization

Biological organic-inorganic materials remain a popular source of inspiration for bioinspired materials design and engineering. Inspired by the self-assembling metal-reinforced mussel holdfast threads, we tested if metal-coordinate polymer networks can be utilized as simple composite scaffolds for direct in situ crosslink mineralization. Starting with aqueous solutions of polymers end-functionalized with metal-coordinating ligands of catechol or histidine, here we show that inter-molecular metal-ion coordination complexes can serve as mineral nucleation sites, whereby significant mechanical reinforcement is achieved upon nanoscale particle growth directly at the metal-coordinate network crosslink sites.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Deciphering the morphology of transition metal carbonate cathode precursors

The performance and life of Li-ion battery cathode materials are determined by both the composition (crystal structure and transition metal ratio) and the morphology (particle size, size distribution, and surface area). Careful control of these two aspects is the key to long lasting, high-energy batteries that can undergo fast charge. Developing such cathodes requires manipulation of the synthesis conditions, namely the coprecipitation process to develop the precursor and a calcination step to lithiate and convert it to a transition metal oxide. In this paper, we utilize a combination of controlled synthesis, microscopic and spectroscopic characterization, and multi-scale mathematical modeling to shed light on the synthesis of cathode precursors. The complex interplay between the various chemical reactions in the co-precipitation process is studied to provide experimentalists with guidance on achieving composition control during synthesis. Further, the formation of a variety of morphologies of the primary particles and the driving force for agglomeration is mathematically described, for the first time, based on an energy minimization approach. Results suggest that the presence of Ni and/or Co significantly lowers the reaction rate constant compared to Mn, resulting in agglomerated growth in the former and single crystal growth in the latter. Modeling studies are used to provide a phase map describing the synthesis conditions needed to control the secondary particle size and corresponding size distribution. Finally, this paper represents an important step in developing a computationally guided approach to the synthesis of battery cathode materials.

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

Tailoring Carbide Dispersed Steels: A Path to Increased Strength and Hydrogen Tolerance

The use of transition metal carbides is reported for use as a hydrogen trapping mechanism for ferritic and austenitic steel materials. The program combined computational modeling and simulations to guide experiments towards candidate metal carbide traps, both for interfacial and interior trapping. It was found that interfacial trapping is less effective than interior trapping, with the group IVB transition metal carbides being the most effect internal traps with a loss of carbon. The sub-stoichiometric rocksalt structure accommodate the hydrogen atoms in its octahedral interstices. Using percolation theory, carbon loss of approximately 25% or more was sufficient to ensure an interconnected network of vacancies for such trapping from the surface to the internal sites within the carbide. Using this as a guide, the program developed a means to provide a uniform dispersion of ZrC nanoparticles with either Fe or 304L micron-scale powders which was then consolidated by direct current sintering. Electrolytic hydrogen diffusivity studies confirmed the reduction of hydrogen diffusion in the matrix with increasing ZrC content, which was a linear response over the sample range studied (0.01 to 1.0 wt.%). The consolidated material was micro-tensile tested in either a non-hydrogen or hydrogen charge condition and compared to a control with no carbides. Additions up to 0.05 wt.% ZrC increased the yield strength with no loss in ductility in either the non-hydrogen or hydrogen tested condition. ZrC concentrations above this amount further increased the yield strength at the expense of ductility. While these samples had a lower absolute ductility value prior to failure, the relative change in ductility between the non-hydrogen and hydrogen charge states was less for the carbides than that of the control. Metal-rich ZrC nanoparticles were fabricated through a conformal coating process yielding ZrC0.66 particles that were then incorporated into a metal matrix. Notch fatigue testing in a hydrogen environment was conducted where the number of cycles to failure was found to be less in the control than that of the carbide addition. However, the spread in experimental data and the number of samples tested limits a conclusive outcome based on defects noticed in the gauge section of all the powder processed samples. The collective outcomes of this report provide further insight into the mechanisms by which carbides act as hydrogen traps; a means to process such carbides through powder metallurgy; and their associated mechanical performance in either a non-hydrogen or hydrogen-charged condition.

08 HYDROGEN↗
DOE OSTI2023

Monolayer organic thin films as particle-contamination–resistant coatings

Abstract Three organic monolayers coatings were developed and tested for their effectiveness to increase cleaning efficiency of attached microscale particles by air flows. The experiments were performed using silica substrates coated with these organic thin films and subsequently exposed to stainless-steel and silica microparticles as a model of contamination. Laser-induced–damage tests confirmed that the coatings do not affect the laser-induced–damage threshold values. The particle exposure results suggest that although the accumulation of particles is not significantly affected under the experimental conditions used in this work, the coated substrates exhibit significantly improved cleaning efficiency with a gas flow. A size-distribution analysis was conducted to study the adsorption and cleaning efficiency of particles of different sizes. It was observed that larger size (> 5-μm) particles can be removed from coated substrates with almost 100% efficiency. It was also determined that the coatings improve the cleaning efficiency of the smaller particles (≤ 5 μm) by 17% to 30% for the stainless steel metal and 19% to 38% for the silica particles.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Primary Radiation Damage Formation in Solids

The processes that give rise to changes in the microstructure and the physical and mechanical properties of solid metals and ceramics exposed to energetic particles are initiated by essentially elastic collisions between atoms in what has been called an atomic displacement cascade. These processes are similar in metals and ceramics, with some differences related to the ionic and covalent bonding in ceramics compared to metallic bonding. The formation and evolution of primary radiation damage mechanisms are described to provide an overview of how stable defects are formed by displacement cascades, as well as the nature and morphology of the defects themselves. The impact of the primary variables cascade energy and irradiation temperature are discussed, along with a range of secondary factors that can influence damage formation.

Zarkadoula, Eva↗
DOE OSTI2026

Design of a SiC-Si moving packed-bed particle-to-sCO 2 heat exchanger for high temperature concentrating solar power applications

Particle-based concentrating solar power systems integrated with sCO 2 power cycles offer high thermal efficiencies but require durable heat exchangers to transfer heat from high-temperature particles to the sCO 2 working fluid. Here, this study presents the design and optimization of a silicon carbide-silicon moving packed-bed heat exchanger for fabrication via binder jetting additive manufacturing. The heat exchanger was designed to withstand a 20 MPa sCO 2 pressure and operate at particle inlet temperatures up to 750 °C. The final design features 152 sCO 2 channels distributed across 19 plates, with elliptical corners and a minimum wall thickness of 3 mm. Flow restrictors at the sCO 2 channel inlets significantly improved flow uniformity, reducing thermal stresses and achieving a structural reliability of 99 % under representative operating conditions. The heat exchanger delivers a thermal duty of 9 kW and a volumetric power density of approximately 1 MW/m 3 in the channel region. Sensitivity studies confirmed the heat exchanger’s robustness under varying operating conditions, demonstrating its viability as a high-performance alternative to metallic heat exchangers for particle-based high-temperature concentrating solar power applications.

Barua, Bipul [Argonne National Laboratory (ANL), A↗
DOE OSTI2022

Dynamical Change of Valence States and Structure in NiCu 3 Nanoparticles during Redox Cycling

Alloyed materials are promising candidates to improve catalytic processes. Ni–Cu nanoparticles are used for various reactions, including processes with biomass-derived components. However, dynamical restructuring effects alter the catalytic properties and can deactivate the sample. To understand these structural modifications, a multimodal investigation of NiCu 3 /C was performed to determine compositional and morphological changes during a redox cycle to simulate reduction and oxidation of the catalyst during reaction. We exploit a novel correlative, multimodal approach that combines in situ X-ray absorption spectroscopy (XAS) and in situ scanning transmission electron microscopy and electron energy-loss spectroscopy (STEM-EELS) to describe changes that occur in the sample in realistic conditions. In the fresh sample, there are two morphologies present: core–shell and hollow. Segregation of Cu was observed in both types of particles after synthesis, with Cu being more oxidized in the hollow structures. Upon reduction for 2 h under H 2 at 400 °C, the Cu was reduced, although segregation of Cu and Ni was still observed. Subsequent exposure to O 2 at 400 °C led to a strong reoxidation of Cu with the formation of hollow particles with compositional heterogeneities. The oxidation of metals and segregation phenomena can be related to known catalytic properties of NiCu 3 /C particles, especially regarding the hydrodeoxygenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran.

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

Cooperative roles of water and metal-support interfaces in the selective hydrogenation of cinnamaldehyde over cobalt boride catalysts

Chemoselectivity in the hydrogenation of carbonyl over alkene bonds is valuable for producing industrial chemicals. In this study, we investigate the role of water in the selective hydrogenation of cinnamaldehyde on cobalt and cobalt boride catalysts by combining rate measurements, in situ characterization, and computational calculations. Ex situ and in situ spectroscopic analyses indicate that the boron species do not significantly modify the intrinsic electronic properties of cobalt. However, during thermal treatments, they exsolve from the bulk phase and become enriched on the surface, forming acidic species that enhance the activity and selectivity of carbonyl bond hydrogenation by three and two times, respectively. A small amount of water is able to promote hydrogenation. When titania, ceria, and zirconia are used as supports, metal-support interactions result in smaller particles that show a drop in selectivity toward the desirable unsaturated alcohol. Overall, the combination of the presence of boron species and strong metal-support interactions protects the catalysts from water attack, resulting in enhanced stability.

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

Understanding Flow Characteristics in Metal Additive Manufacturing

In fluid flow, the frictional effects from interior surfaces of flow components create pressure loss across the surface. Understanding this inherent pressure loss due to friction and other phenomena is important when designing a flow system. For conventional manufacturing, friction loss has been empirically studied and is well known in the engineering community. However, newer manufacturing techniques, such as laser powder bed fusion (LPBF), an additive manufacturing technique, need to be understood. The inherent flow conditions resulting from the additive processes were studied. Test samples were printed with the flow path oriented in the vertical direction with different channel diameters to characterize the inherent fundamental flow properties of the process. Moody diagrams were replicated for a greater understanding of possibilities and shortfalls when implementing LPBF into design applications. Experimental flow testing revealed that greater effective sand grain roughness resulted from this process when compared to conventional machining methods. This roughness did not correlate well to the average roughness measured with a laser scanning microscope but was consistent with the average particle size of the powder metal feedstock.

42 ENGINEERING↗
DOE OSTI2020

Understanding the Deactivation of Ag–ZrO 2 /SiO 2 Catalysts for the Single-step Conversion of Ethanol to Butenes

Ag–ZrO 2 /SBA-16 has recently been found to be efficient for catalyzing the single-step conversion of ethanol to butene (1- and 2-butene mixtures) in the presence of H 2 . The reaction proceeds via a cascading sequence of reactions over mixed metal and Lewis sites, with the catalyst composition tuned to selectively favor butene formation. However, the catalyst slowly deactivates when evaluated over long reaction times. Here, we evaluated the lifetime of the Ag–ZrO 2 /SBA-16 catalyst system for ethanol-to-butene conversion at 325 °C for up to 800 hours on stream. Several characterization techniques were used to elucidate the mechanism(s) by which catalyst deactivation occurs. Coke deposition, Ag particle sintering, and Ag 0 -to-Ag + oxidation state change were identified to be the major causes of catalyst deactivation. Coke deposits cover primarily Lewis acid sites which are responsible for aldol condensation, Meerwein-Ponndorf-Verley (MPV) reduction, and dehydration reactions. Ag particle sintering and Ag oxidation state change leads to a reduction in the number of metallic Ag sites responsible for the dehydrogenation/hydrogenation steps. The fresh catalyst likely experiences hydrothermal sintering in the early stage of reaction and permanently loses some active Lewis acid sites before reaching a new structural steady state. The deactivation of Lewis acid sites leads to a decrease in overall ethanol conversion, whereas the deactivation of the metallic Ag sites decreases the butene selectivity. For catalyst regeneration, oxidative calcination (at 500 °C) followed by reduction (at 325 °C) successfully removes all the coke species on the catalyst surface and restores the metallic Ag particles of the 4Ag–4ZrO 2 /SBA-16 catalysts.

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

Iridium-Doped Nanosized Zn–Al Layered Double Hydroxides as Efficient Water Oxidation Catalysts

Layered double hydroxides (LDHs) are an ideal platform to host catalytic metal centers for water oxidation (WO) owing to the high accessibility of water to the interlayer region, which makes all centers potentially reachable and activated. In this paper, we report the syntheses of three iridium-doped zinc–aluminum LDHs (Ir-LDHs) nanomaterials (1–3, with about 80 nm of planar size and a thickness of 8 nm as derived by field emission scanning electron microscopy and powder X-ray diffraction studies, respectively), carried out in the confined aqueous environment of reverse micelles, through a very simple and versatile procedure. These materials exhibit excellent catalytic performances in WO driven by NaIO 4 at neutral pH and 25 °C, with an iridium content as low as 0.5 mol % (~0.8 wt %), leading to quantitative oxygen yields (based on utilized NaIO 4 , turnover number up to ~10,000). Nanomaterials 1–3 display the highest ever reported turnover frequency values (up to 402 min –1 ) for any heterogeneous and heterogenized catalyst, comparable only to those of the most efficient molecular iridium catalysts, tested under similar reaction conditions. The boost in activity can be traced to the increased surface area and pore volume (>5 times and 1 order of magnitude, respectively, higher than those of micrometric materials of size 0.3–1 μm) estimated for the nanosized particles, which guarantee higher noble metal accessibility. X-ray absorption spectroscopy (XAS) studies suggest that 1–3 nanomaterials, as-prepared and after catalysis, contain a mixture of isolated, single octahedral Ir(III) sites, with no evidence of Ir–Ir scattering from second-nearest neighbors, excluding the presence of IrO 2 nanoparticles. The combination of the results obtained from XAS, elemental analysis, and ionic chromatography strongly suggests that iridium is embedded in the brucite-like structure of LDHs, having four hydroxyls and two chlorides as first neighbors. These results demonstrate that nanometric LDHs can be successfully exploited to engineer efficient WOCs, minimizing the amount of iridium used, consistent with the principle of the noble-metal atom economy.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Radio-Frequency Resonances and Damping in Metallic Magnetic Calorimeter Sensors

Metallic magnetic calorimeters (MMCs) are particle detectors that combine ultra-high energy resolution with a predictable and smooth response based on the physics of paramagnetism. For best energy resolution, MMCs are read out with dc SQUID preamplifiers. Since the ac Josephson effect also makes dc SQUIDs broadband RF sources in the 1–100 GHz range, the SQUID can potentially excite RF modes of the MMC sensor, with negative consequences. Further, the importance of this possibility is magnified in direct-coupled MMCs, where the MMC sensor is part of the SQUID loop to maximize performance. For these reasons, the RF behavior of MMC sensors must be investigated. In this report, we present the results of exploratory RF simulations of MMC sensor modes and damping, and we assess three approaches to damp the parallel-meander direct-coupled MMC without excessive noise increase.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Predicting Morphological Evolution during Coprecipitation of MnCO 3 Battery Cathode Precursors Using Multiscale Simulations Aided by Targeted Synthesis

The performance of lithium-ion batteries is intimately linked to both the structure and the morphology of the cathode material, which in turn is critically linked to the synthesis conditions. However, few studies focus on understanding synthesis, especially during the coprecipitation of metal oxide precursors, a process that largely determines the final morphology of the material. In this paper, we go beyond the typical equilibrium particle shape analysis conducted in the literature and incorporate kinetic aspects of morphology evolution. We perform these studies using controlled synthesis on a well-defined metal salt system (MnCO 3 ) combined with multiscale simulations and high-resolution microscopy. Results show that with increasing metal concentration, the particles transition from rhombohedral to cubic to spherical shapes. Computational analysis using density functional theory (DFT) reveals that rhombohedral shaped particles evolve under equilibrium conditions. Phase field techniques indicate that at higher metal concentrations, fast growth kinetics of the precipitates result in the transition to cubic and, subsequently, spherical shapes, accompanied by a decrease in particle size. This study, while limited to the one metal salt system, provides an approach to shed light on the synthesis process of mixed transition metal salts, gradient materials, and other cathode materials of interest to the battery community.

25 ENERGY STORAGE↗
DOE OSTI2024

Reductive catalytic fractionation of cotton stalks: catalytic strategy for tuning the selectivity of phenolic monomers

Pretreatment of lignocellulosic biomass is a primary step to delink lignin from the lignin-carbohydrate complex for bioethanol production and other value-added products. Presently, these processes yield lignin (technical) with significant structural changes compared to native lignin and make it difficult to valorize. Reductive catalytic fractionation (RCF) is an advanced pretreatment process to valorize native lignin to selective phenolic monomers before capitalizing on carbohydrates. Herein, cotton stalks (CS) were pretreated with ethanol: water mixture catalyzed by bimetallic, Ru-Ni/HY (RNY) and Ru-Fe/HY (RFY), and trimetallic, Ru-Fe-Ni/HY (RFNY), catalysts using the endogenously produced H 2 . The favorable catalytic properties of the RFNY catalyst, including high reducibility, acidity, metal dispersion, the synergistic effect of all the metals, and appropriate pore and particle size resulted in the highest catalytic activity. Maximum 92% delignification efficiency was achieved with 91% holocellulose retention. The extracted lignin after depolymerization in the same step produced a 19 wt.% yield of phenolic monomers. Increasing the duration of the reaction from 2 to 6 h increased the selectivity to saturated alkyl chain phenolics (1 to 16 wt.%) at the expense of hemicellulose (50 to 9%). The fate of carbohydrates left behind after the RCF (CS-RCF) process was analyzed through enzymatic saccharification and compared with raw CS and acid-pretreated CS. In conclusion, CS-RCF yielded maximum glucose yield (45 g/L) within an incubation period of 72 h.

09 BIOMASS FUELS↗
DOE OSTI2021

Lanthanum-based double perovskite nanoscale motifs as support media for the methanol oxidation reaction

In this report we have not only analyzed the performance of perovskite oxides as support media for the methanol oxidation reaction (MOR) but also examined the impact and significance of various reaction parameters on their synthesis. Specifically, we have generated (a) La 2 NiMnO 6 , LaMnO 3 , and LaNiO 3 nanocubes with average sizes of ~200 nm, in addition to a series of La 2 NiMnO 6 (b) nanocubes possessing average sizes of ~70 and 400 nm and (c) anisotropic nanorods characterized by average diameters of 40-50 nm. All of these samples, when used as supports for Pt nanoparticles, exhibited activities which were at least twice that measured for Pt/C. We have investigated and correlated the effect of varying perovskite (i) composition, (ii) size, and (iii) morphology upon the measured MOR activity. (i) The Ni-containing perovskites yielded generally higher performance metrics than LaMnO 3 alone, suggesting that the presence of Ni is favorable for MOR, a finding supported by a shift in the Pt d-band in XPS. (ii) MOR activity is enhanced as the perovskite size increases in magnitude, suggesting that a growth in the perovskite particle size enables favorable, synergistic metal–support interactions. (iii) A comparison of the nanorods and nanocubes of a similar diameter implied that the one-dimensional morphology achieved a greater activity, a finding which can be attributed not only to the anisotropic structure but also to a desirable surface structure. Overall, these data yield key insights into the tuning of metal–support interactions via rational control over the composition, size, and morphology of the underlying catalyst support.

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

Effect of Catalyst and Catalyst Layer Composition on Catalyst Support Durability

Polymer electrolyte membrane fuel cells (PEMFCs) are efficient, zero-emission engines for the automotive sector. However, cost and durability are major barriers for the commercialization of PEMFCs. Degradation of the carbon support in the cathode catalyst layer due to high potential excursions caused by unmitigated events like H 2 starvation, or start-up/shutdown are still a major durability issue in PEMFCs. Catalyst support durability was studied by accelerated stress tests (ASTs) that included repeated potential cycling from 1.0 to 1.5 V. The effect of catalyst layer composition on carbon corrosion was studied using membrane electrode assemblies with different catalysts (Pt, PtCo), catalyst composition (catalyst wt.%, supports), ionomer composition (loading, and equivalent weights). The corrosion of the carbon support is similar between Pt and PtCo catalysts. However, the performance degradation rate is higher for the alloy catalysts due to differences in catalyst particle size and the transition metal’s leaching accelerating the performance degradation. The carbon loss is lower for catalysts with lower initial carbon loading (or higher catalyst wt.%), which is better for durability. However, the cumulative loss of carbon is identical for electrodes with the same catalyst support irrespective of catalyst and ionomer composition in the catalyst layer.

25 ENERGY STORAGE↗
DOE OSTI2024

Capacity Fade of Graphite/NMC811: Influence of Particle Morphology, Electrolyte, and Charge Voltage

LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) is an important Li-ion battery cathode material; however, there is a tradeoff between delivered capacity and capacity retention. As the charge potential increases the capacity rises but at the expense of capacity retention. The decrease in capacity retention has been ascribed to several factors including particle cracking, surface reconstruction, transition metal dissolution, and electrolyte reactivity. The present study compares 4.1 and 4.3 V charging limits in commercially relevant graphite/NMC811 pouch cells for single crystal (SC) and polycrystalline (PC) NMC811 with ethylene carbonate (EC)-containing or EC-free electrolytes. The electrochemistry is rationalized through analysis of electrochemical impedance spectroscopy, positive electrode X-ray photoelectron spectroscopy, soft X-ray absorption spectroscopy, X-ray diffraction, and negative electrode mapping by X-ray fluorescence. Graphite/SC-NMC811 cells show high-capacity retention at 4.1 V but exhibit degradation at 4.3 V charging potentials. The EC-free electrolyte cells led to higher capacity fade, especially when charged to 4.3 V. Cathode dissolution and deposition on the negative electrode from PC-NMC811 cells was higher than for samples from SC-NMC811 cells. This study reveals the impact of material type, charge voltage, and electrolyte composition on the reactions at the positive electrode, their influence on the negative electrode, and evolution with cycle number.

36 MATERIALS SCIENCE↗