Fibering of ceramics by mechanical deformation
Ceramic fibers formation by particles mechanical deformation by extrusion in W matrix, describing grain structure of various extruded metal oxides
Jech, R. W.↗
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Fibering ceramics by mechanical deformation
Ceramic fibers formation by particles mechanical deformation by extrusion in W matrix, describing grain structure of various extruded metal oxides
Jech, R. W.↗
Conceptual design of a hybrid Ge:Ga detector array
For potential applications in space infrared astronomy missions such as the Space Infrared Telescope Facility and the Large Deployable Reflector, integrated arrays of long-wavelength detectors are desired. The results of a feasibility study which developed a design for applying integrated array techniques to a long-wavelength (gallium-doped germanium) material to achieve spectral coverage between 30 and 200 microns are presented. An approach which builds up a two-dimensional array by stacking linear detector modules is presented. The spectral response of the Ge:Ga detectors is extended to 200 microns by application of uniaxial stress to the stack of modules. The detectors are assembled with 1 mm spacing between the elements. Multiplexed readout of each module is accomplished with integration sampling of a metal-oxide-semiconductor (MOS) switch chip. Aspects of the overall design, including the anticipated level of particle effects on the array in the space environment, a transparent electrode design for 200 microns response, estimates of optical crosstalk, and mechanical stress design calculations are included.
Parry, C. M.↗
Feasibility Testing of Silver Electrolysis for Disinfection of Spacecraft Potable Water Systems
Anodic dissolution of silver electrodes, or “silver electrolysis,” is being investigated as a means of introducing biocidal silver into potable water on exploration spacecraft. A proof-of-concept prototype of a silver electrolysis reactor was developed, and feasibility was demonstrated for imparting a target silver concentration into a spacecraft water system. Prototype testing showed that the primary initial concerns related to the technology - inefficiencies of electrolysis in low conductivity water, the potential formation of resistive oxides on the electrode surfaces, and the potential for release of electrolytically-generated silver particles to the effluent water - were not problematic over the duration of the feasibility testing. The testing also demonstrated advantages of the technology, including the ability to consistently deliver silver at targeted concentrations and the ability to directly correlate the silver concentration to measurements of water conductivity. On the other hand, the reliability of the system has not yet been demonstrated. During prototype testing, intermittent periods of poor reactor performance manifested as a decrease in voltage accompanied by a decrease in silver output. It was determined that the cause of this behavior was silver-based deposits on inter-electrode wetted surfaces forming a conductive “bridge” between electrodes. Ongoing testing and refinement of the prototype reactor design seek to elucidate the root cause the bridging phenomenon and identify associated mitigation strategies. Once resolved, long-term performance testing is planned as part of continued development of the electrolytic silver dosing system.
Silver↗
JWST Reveals CO Ice, Concentrated CO 2 Deposits, and Evidence for Carbonates Potentially Sourced From Ariel’s Interior
The Uranian moon Ariel exhibits a diversity of geologically young landforms, with a surface composition rich in CO 2 ice. The origin of CO 2 and other species, however, remains uncertain. We report observations of Ariel’s leading and trailing hemispheres, collected with NIRSpec (2.87–5.10 μm) on the James Webb Space Telescope. These data shed new light on Arielʼs spectral properties, revealing a double-lobed CO 2 ice scattering peak centered near 4.20 and 4.25 μm, with the 4.25 μm lobe possibly representing the largest CO 2 Fresnel peak yet observed in the solar system. A prominent 4.38 μm 13 CO 2 ice feature is also present, as is a 4.90 μm band that results from 12 CO 2 ice. The spectra reveal a 4.67 μm 12 CO ice band and a broad 4.02 μm band that might result from carbonate minerals. The data confirm that features associated with CO 2 and CO are notably stronger on Ariel’s trailing hemisphere compared to its leading hemisphere. We compared the detected CO 2 features to synthetic spectra of CO 2 ice and mixtures of CO 2 with CO, H 2 O, and amorphous carbon, finding that CO 2 could be concentrated in deposits thicker than ∼10 mm on Ariel’s trailing hemisphere. Comparison to laboratory data indicates that CO is likely mixed with CO 2 . The evidence for thick CO 2 ice deposits and the possible presence of carbonates on both hemispheres suggests that some carbon oxides could be sourced from Ariel’s interior, with their surface distributions modified by charged particle bombardment, sublimation, and seasonal migration of CO and CO 2 from high to low latitudes.
Uranian satellites↗
Local nm-Scale Imaging of Electrical Contact for Series Resistance Degradation of Silicon Solar Cells
We report on an electrical conduction mechanism for series resistance (Rs) degradation observed in a utility scale solar farm by nm-scale imaging of the local resistance at the Ag/Si interface of c-Si cell front metallization. Our previous work showed that the I-V measurement of individual cells demonstrated exclusively the cell Rs degradation, and the "beads pattern" of electroluminescence indicated the degradation at the Ag grid of front metallization. Scanning spreading resistance microscopy (SSRM) imaging, which is based on the contact mode of atomic force microscopy and taken on the cross-sections of Ag/Si contact, revealed the electrical conduction pathway of Ag particles in point or small area contact with Si cell emitter. The SSRM results illustrated that the number of electrical contacts in the degraded cell decreased largely compared with the unaffected cell, demonstrating the direct cause of the Rs degradation. This reduction in electrical contact in the degraded cell could be caused by a structural change in the Ag grid during long-term field service: The Ag particles in contact with Si aggregate into the Ag bulk and a highly resistive ceramic oxide is formed in a "belt" shape at the Ag/Si interface. This resistive belt with a thickness of ~1 m blocks the current conduction from cell emitter to the Ag grid. The degraded cell shows both a morphological and chemical difference in the screen-printed finger contact compared to the unaffected cell, which likely caused the different degradation susceptibility during the long-term field service. Our results demonstrate an example of the multi-scale characterization approach for understanding photovoltaic degradation mechanisms.
ENGINEERING,SOLAR ENERGY↗
Large contribution of organics to condensational growth and formation of cloud condensation nuclei (CCN) in the remote marine boundary layer
Marine low clouds strongly influence global climate, and their radiative effects are particularly susceptible to the concentration of cloud condensation nuclei (CCN). One major source of CCN is the condensational growth of pre-CCN particles, and sulfate has long been considered the major condensing species in the remote marine boundary layer. While some studies have suggested that secondary organic species can contribute to particle growth, its importance remains unclear. Here we present the first long-term observational evidence that organics play an important role in particle growth over remote oceans. To the contrary of traditional thinking, sulfate dominated condensational growth for only a small (~18 %) fraction of the 62 observed growth events, even fewer than the organic-dominated events (24 %). During most (58 %) growth events, the major condensing species included both organics and sulfate. Potential precursors of the secondary organics are volatile organic compounds from ocean biological activities and those produced by the air–sea interfacial oxidation. Our results indicate that the condensation of secondary organics contributes strongly to the growth of pre-CCN particles and thereby the CCN population over remote oceans.
54 ENVIRONMENTAL SCIENCES↗
Experimental investigation of low velocity and high temperature solid particle impact erosion wear
Next generation Concentrating Solar Power (CSP) plants utilizing solid particles as the heat transfer medium (HTM) are expected to achieve greater operational efficiencies. However, the erosion from the solid particles can cause significant damage to component materials. Low particle speeds (1–2 m/s) are proposed as a means of preventing excessive damage to containment materials. Within the current investigation, solid particle erosion of three potential containment materials, stainless-steel grade 316L, a nickel alloy (Inconel 740H), and a refractory material (Tufcrete 60 M), are examined at a particle impact speed of 1.6 m/s. CarboBead-HSP 40/70 particles, a candidate HTM for CSP systems, impact the specimens at a relatively high impact angle of 60° based on containment design criteria. Experiments were conducted at ambient temperature and 800 °C to examine erosion of the materials at very low impact speeds and determine how temperature effects erosion. Initial results revealed surprising outcomes inconsistent with available literature: ambient temperature erosion of SS316L is an order of magnitude lower than IN740H, but erosion (erosion-corrosion) of SS316L at 800 °C surpasses IN740H by two orders of magnitude. Furthermore, results suggest removal of oxide layers (erosion-corrosion) is responsible for the significant erosion that was observed even at these low particle speeds.
36 MATERIALS SCIENCE↗
X-ray Diffraction Studies of the Structure and Thermochemistry of Alkaline-Earth Oxide-Coated Thermionic Cathodes
NASA LeRC has a broad, active cathode technology development program in which both experimental and theoretical studies are being employed to further development of thermionic cathodes for use as electron sources in vacuum devices for communications and other space applications. One important type of thermionic cathode under development is the alkaline-earth oxide-coated (BaO, SrO, CaO) cathode. Significant improvements in the emission characteristics of this cathode have been obtained through modification of the chemical composition and morphology of the oxide coating, with the best result thus far coming from the addition of In2O3 and Sc2O3. Whereas the In2O3 produces a finer, more uniform particle structure, the exact chemical state and role of the Sc2O3 in the emission enhancement is unknown. The purpose of this cooperative agreement is to combine the studies of the surface chemistry and electron emission at NASA LeRC of chemically modified oxide coatings with a study of the thermochemistry and crystal structure using X-ray diffraction equipment and expertise at Clark Atlanta University (CAU). The study at CAU is intended to provide the description and understanding of the structure and thermochemistry needed for further improvement and optimization of the modified coatings. A description of the experimental procedure, preliminary X-ray diffraction test results, together with the design of an ultrahigh vacuum chamber necessary for high temperature thermochemistry studies will be presented.
Karikari, E. K.↗
Aerosol iron speciation and seasonal variation of iron oxidation state over the western Antarctic Peninsula
The iron (Fe) speciation and oxidation state have been considered critical factors affecting Fe solubility in the atmosphere and bioavailability in the surface ocean. In this study, elemental composition and Fe speciation in aerosol samples collected at the Palmer Station in the West Antarctic Peninsula were determined using synchrotron-based X-ray fluorescence (XRF) and X-ray Absorption Near-Edge Structure (XANES) spectroscopy. The elemental composition of coarse-mode (>1 mu m) Fe-containing particles suggests that the region's crustal emission is the primary source of aerosol Fe. The Fe minerals in these aerosol particles were predominantly hematite and biotite, but minor fractions of pyrite and ilmenite were observed as well. The Fe oxidation state showed an evident seasonal variation. Further, the Fe(II) content accounted for 71% of the total Fe in the austral summer, while this fraction dropped to 60% in the austral winter. Multivariate linear models involving meteorological parameters suggested that the wind speed, relative humidity, and solar irradiance were the factors that significantly controlled the percentage of Fe(II) in the austral summer. On the contrary, no relationship was found between these factors and the Fe(II) percentage in the austral winter, suggesting that atmospheric photoreduction and regional dust emission were limited. Moreover, the snow depth was significantly (p < 0.05) correlated with the aerosol Fe concentration, confirming the limiting effect of snow/ice cover on the regional dust emission. Given that the Antarctic Peninsula has experienced rapid warming during recent decades, the ice-free areas in the Antarctic Peninsula may act as potential dust sources.
54 ENVIRONMENTAL SCIENCES↗
Observation of coherently coupled cation spin dynamics in an insulating ferrimagnetic oxide
Many technologically useful magnetic oxides are ferrimagnetic insulators, which consist of chemically distinct cations. In this work, we examine the spin dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite (Ni 0.65 Zn 0.35 Al 0.8 Fe 1.2 O 4 ) under continuous microwave excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance to separately probe Fe 2+/3+ and Ni 2+ cations on different sublattice sites. Our results show that the precessing cation moments retain a rigid, collinear configuration to within ≈2°. Moreover, the effective spin relaxation is identical to within <10% for all magnetic cations in the ferrite. Thus, we validate the oft-assumed “ferromagnetic-like” dynamics in the resonantly driven ferrimagnetic oxide: the magnetic moments from different cations precess as a coherent, collective magnetization, despite the high contents of nonmagnetic Zn 2+ and Al 3+ diluting the exchange interactions.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Transition metal-based bimetallic MOFs and MOF-derived catalysts for electrochemical oxygen evolution reaction
The oxygen evolution reaction (OER) is a critical electrochemical reaction in water splitting and rechargeable metal–air batteries. It plays a pivotal role in achieving high-efficiency clean-energy production and energy storage in these devices. Transition metal-based bimetallic MOFs (TMB MOFs) with two different metal ions possess specific synergistic effects, which could exhibit OER performance and stability superior to those of the corresponding monometallic MOFs for water oxidation. Benefiting from the diversity of chemical composition and structural type, TMB MOFs can also serve as precursors and templates to obtain alloy-particle-decorated carbon materials with high surface area, or metal compounds such as bimetallic sulfides, phosphides, and hydroxides with atomic-level mixing of heterometallic elements. These materials with high-density active sites exhibit much improved catalytic activity in the water oxidation reaction. Furthermore, this article aims to review the recent progress with TMB MOFs and their derivatives in relation to applications as electrocatalysts in OER, including analysis of the mechanism of the OER process with the assistance of DFT calculations and in situ or operando techniques.
36 MATERIALS SCIENCE↗
Relating FTS Catalyst Properties to Performance
During the reporting period June 23, 2011 to August 31, 2013, CAER researchers carried out research in two areas of fundamental importance to the topic of cobalt-based Fischer-Tropsch Synthesis (FTS): promoters and stability. The first area was research into possible substitute promoters that might be used to replace the expensive promoters (e.g., Pt, Re, and Ru) that are commonly used. To that end, three separate investigations were carried out. Due to the strong support interaction of γ-Al2O3 with cobalt, metal promoters are commonly added to commercial FTS catalysts to facilitate the reduction of cobalt oxides and thereby boost active surface cobalt metal sites. To date, the metal promoters examined have been those up to and including Group 11. Because two Group 11 promoters (i.e., Ag and Au) were identified to exhibit positive impacts on conversion, selectivity, or both, research was undertaken to explore metals in Groups 12 - 14. The three metals selected for this purpose were Cd, In, and Sn. At a higher loading of 25%Co on alumina, 1% addition of Cd, In, or Sn was found to-on average-facilitate reduction by promoting a heterogeneous distribution of cobalt consisting of larger lesser interacting cobalt clusters and smaller strongly interacting cobalt species. The lesser interacting species were identified in TPR profiles, where a sharp low temperature peak occurred for the reduction of larger, weakly interacting, CoO species. In XANES, the Cd, In, and Sn promoters were found to exist as oxides, whereas typical promoters (e.g., Re, Ru, Pt) were previously determined to exist in an metallic state in atomic coordination with cobalt. The larger cobalt clusters significantly decreased the active site density relative to the unpromoted 25%Co/Al2O3 catalyst. Decreasing the cobalt loading to 15%Co eliminated the large non-interacting species. The TPR peak for reduction of strongly interacting CoO in the Cd promoted catalyst occurred at a measurably lower temperature than in the unpromoted catalyst. Nevertheless, the Co clusters remained slightly larger, on average, in comparison with the unpromoted 15%Co/Al2O3 reference catalyst. None of the promoted catalysts (i.e., with Cd, In, or Sn) exhibited surface Co0 site densities higher than that of the unpromoted catalyst. In activity testing, the activities were even much lower than what was expected from the H2-TPD results. Two possible explanations were proposed: (1) the promoters may be located on the surfaces of cobalt particles, blocking surface Co0 but being able to desorb hydrogen or (2) the promoters may facilitate Co oxidation during FTS, as previously observed by Huffman and coworkers when K was added to cobalt catalysts.
Zirconia↗
The orbital characteristics of debris particle rings as derived from IDE observations of multiple orbit intersections with LDEF
During the first 346 days of the LDEF's almost 6 year stay in space, the metal oxide silicon detectors of the Interplanetary Dust Experiment (IDE) recorded over 15,000 impacts, most of which were separated in time by integer multiples of the LDEF orbital period (called multiple orbit event sequences, or MOES). Simple celestial mechanics provides ample reason to expect that a good deal of information about the orbits of the impacting debris particles can be extracted from these MOES, and so a procedure, based on the work of Greenberg, has been developed and applied to one of these events, the so-called 'May swarm'. This technique, the 'Method of Differential Precession,' allows for the determination of the geometrical elements of a particle orbit from the change in the position of the impact point with time. The application of this approach to the May swarm gave the following orbital elements for the orbit of the particles striking LDEF during this MOES: a = 6746.5 km; 0.0165 less than e less than 0.025; i = 66.55 deg; Omega(sub 0) = 179.0 deg plus or minus 0.2 deg; omega = 178.1 deg plus or minus 0.2 deg.
Cooke, William J.↗
Stability of ceramic matrix materials in molten hydroxide under oxidizing and reducing conditions
The degradation mechanism of ceramic matrix materials used as molten hydroxide electrolyte support for steam electrolysis cells, is not well documented. In this study, we have investigated the structural and chemical stability of non-oxide and oxide ceramics (SiC, YSZ, Li 2 ZrO 3, LiAlO 2 , and SrZrO 3 ) in the presence of molten hydroxide under oxidizing and reducing conditions with humidity levels of 3 and 85% at 550 °C. SiC, YSZ, Li 2 ZrO 3 and LiAlO 2 showed structural and chemical changes due to dissolution of the ceramic particles in the hydroxide melt followed by precipitation. The SrZrO 3 powder, on the other hand, remained both chemically and structurally stable during 500 h test under both oxidizing and reducing atmospheres. The findings of a stable ceramic matrix in molten hydroxide contribute to the enhancement of the durability and performance of intermediate temperature water electrolysis system.
08 HYDROGEN↗
Oxide mixture and complex oxide coatings for cathode materials
Cathode active materials are provided. The cathode active material can include a plurality of cathode active compound particles. A coating is disposed over each of the cathode active compound particles. The coating can include at least one of ZrO 2 , La 2 O 3 , a mixture of Al 2 O 3 and ZrO 2 or a mixture of Al 2 O 3 and La 2 O 3 . The battery cells that include the cathode active material are also provided.
Wang, Dapeng↗
Elucidating the phase transformations and grain growth behavior of O3-type sodium-ion layered oxide cathode materials during high temperature synthesis
Understanding the formation mechanism of layered oxide cathodes via solid-state synthesis is imperative to achieving controllability over their materials properties and electrochemical behaviors. In this work, we investigate the phase and microstructure evolution during the synthesis of NaNi 1/3 Fe 1/3 Mn 1/3 O 2 , a model sodium-ion layered oxide cathode, using a combination of imaging, diffraction, and spectroscopic techniques. We unravel the synthetic mechanistic pathways involved in the high-temperature calcination reaction, as well as elaborate the synthesis-microstructure-performance relationship of this material. The formation of the final layered oxide phase involves a gradual transformation through a sodiated oxyhydroxide intermediate. During the reaction, the precursor dehydration reaction dominates at 250–550 °C, while the major sodiation reaction occurs at 550–850 °C. Alongside multiple stages of phase transformations, the final grain structure formation occurs through the continuous growth of the (003) and (104) facets. During the reaction, Mn acts as the charge-compensating element and exhibits depth-dependent characteristics. When the sodiation reaction dominates over dehydration, the reaction intermediates undergo gradual electronic structure changes with increasing temperature, as indicated by the spectral features of TM3d-O2p hybrid states. Calcination duration is also a critical parameter governing the microstructure, surface reactivity, phase fraction distribution and electrochemical performance of the material. The optimal calcination duration was determined to be 18 hours at 850 °C under the conditions evaluated here. Calcination beyond this duration was found to be detrimental to electrochemical performance due to Na and O loss and heterogeneous sodium distribution throughout the particles. Our work sheds light on the complex crystallographic-chemical-microstructural evolution of sodium ion layered oxide cathodes and provides insight into precisely tuning material properties which are intimately linked to battery performances.
25 ENERGY STORAGE↗
Hydrogen Plasma Reduction
Hydrogen plasma increases efficiency by strategically using energy to break bonds within the regolith to liberate oxygen instead of heating the entire bed of regolith. The energy used by the plasma system would be imparted into the H2 gas, forming highly energetic ions, electrons, and neutrals that would interact with the regolith surface. The energized atomic and ionic H2 provide the energy needed to make reduction of SiO2 (Silicon Dioxide) and other regolith mineral oxides favorable. What’s more, the high-energy plasma interaction occurs in a small, localized volume, and thus requires relatively little energy. The lunar regolith is well-suited for the process as the fine particles naturally available provide a high surface area for the plasma to interact with. The process would require a system to collect the regolith composed of metal oxides (MxOy) and load it into a reactor. An H2 plasma would pass over the surface (potentially at a low pressure, reducing complexity of the system as it would not require large increases in pressure from the lunar vacuum), then the gases from the plasma reaction would be collected and processed, and the spent regolith would be carried away. The gross reaction temperature would be near ambient (due to the localized nature of the plasma), eliminating the necessity of a regolith heating mechanism or handling of molten regolith. Also, the H2 used in the plasma could be subsequently recovered from the water produced by the plasma reaction. Thus, this approach would not require significant amounts of added commodities.
Elspeth Petersen↗