Enhanced MgF2 and LiF Over-Coated Al Mirrors for FUV Space Astronomy
We reported gains in Far-Ultraviolet (FUV) reflectivity of Al+MgF2 and Al+LiF mirrors by employing a-step process during PVD coating deposition of these materials.
Quijada, Manuel↗
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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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Investigation of Abnormal Grain Growth in a Friction Stir Welded and Spin-Formed Al-Li Alloy 2195 Crew Module
In order to improve manufacturing efficiency and reduce structural mass and costs in the production of launch vehicle structures, NASA is pursuing a wide-range of innovative, near-net shape manufacturing technologies. A technology that combines friction stir welding (FSW) and spin-forming has been applied to manufacture a single-piece crew module using Aluminum-Lithium (AL-Li) Alloy 2195. Plate size limitations for Al-Li alloy 2195 require that two plates be FSW together to produce a spin-forming blank of sufficient size to form the crew module. Subsequent forming of the FSW results in abnormal grain growth (AGG) within the weld region upon solution heat treatment (SHT), which detrimentally impacts strength, ductility, and fracture toughness. The current study seeks to identify microstructural factors that contribute to the development of AGG. Electron backscatter diffraction (EBSD) was used to correlate driving forces for AGG, such as stored energy, texture, and grain size distributions, with the propensity for AGG. Additionally, developmental annealing treatments prior to SHT are examined to reduce or eliminate the occurrence of AGG by promoting continuous, or uniform, grain growth
Tayon, Wesley A.↗
A Compendium of Scale Surface Microstructures: Ni(pt)al Coatings Oxidized at 1150 C for 2000 1-h Cycles
The surface structure of scales formed on Ni(Pt)Al coatings was characterized by SEM/EDS/BSE in plan view. Two nominally identical {100} samples of aluminide coated CMSX4 single crystal were oxidized at 1150 C for 2000 1-h cycles and were found to produce somewhat disparate behavior. One sample, with less propensity for coating grain boundary ridge deformation, presented primarily alpha-Al2O3 scale structures, with minimal weight loss and spallation. The original scale structure, still retained over most of the sample, consisted of the classic theta-alpha transformation-induced ridge network structure, with approx. 25 nm crystallographic steps and terraces indicative of surface rearrangement to low energy alumina planes. The scale grain boundary ridges were often decorated with a fine, uniform distribution of (Hf,Ti)O2 particles. Another sample, producing steady state weight losses, exhibited much interfacial spallation and a complex assortment of different structures. Broad areas of interfacial spalling, crystallographically-faceted (Ni,Co)(Al,Cr)2O4 spinel, with an alpha-Al2O3 base scale, were the dominant features. Other regions exhibited nodular spinel grains, with fine or (Ta,Ti)-rich (rutile) particles decorating or interspersed with the spinel. While these features were consistent with a coating that presented more deformation at extruded grain boundaries, the root cause of the different behavior between the duplicate samples could not be conclusively identified.
Smialek, James L.↗
Unusual Oxidative Limitations for Al-MAX Phases
Alumina-forming MAX phases are well-known for their excellent oxidation resistance, rivaling many metallic NiAl, NiCrAl, and FeCrAl counterparts and with upper temperature capability possible to approximately1400C. However a number of limitations have been emerging that need to be acknowledged to permit robust performance in demanding applications. Ti2AlC and Ti3AlC2 possess excellent scale adhesion, cyclic oxidation/moisture/volatility resistance, and TBC compatibility. However they are very sensitive to Al content and flux in order to maintain an exclusive Al2O3 scale without runaway oxidation of ubiquitous TiO2 transient scales. Accelerated oxidation has been shown to occur for Al-depleted, damaged, or roughened surfaces at temperatures less than 1200C. Conversely, Cr2AlC is less sensitive to transients, but exhibits volatile losses at 1200C or above if common Cr7C3 impurity phases are present. Poor scale adhesion is exhibited after oxidation at 1150C or above, where spallation occurs at the Cr7C3 (depletion zone) interface. Delayed spallation is significant and suggests a moisture-induced phenomenon similar to non-adherent metallic systems. Re-oxidation of this surface does not reproduce the initial pure Al2O3 behavior, but initiates a less-protective scale. Cr2AlC has also been shown to have good long term bonding with superalloys at 800C, but exhibits significant Beta-NiAl + Cr7C3 diffusion zones at 1100C and above. This may set limits on Cr2AlC as a high temperature TBC bond coat on Ni-based superalloys, while improving corrosion resistance in lower temperature applications.
oxidation resistance↗
Development of Large Bandgap Materials Using Reactive Growth in Al-SI Eutectic for Optical and RF Applications
Carbon was utilized as reactive element to modify the microstructure using forced mixing during crystallization of the Al-Si alloy by rotation and stirring. We nucleated the material on SiC substrates while the Al-Si melt was rotated with a speed of 30rpm in a graphite crucible. Several experiments were performed and parameters such as time of mixing, soaking temperature, rotation rate of the substrate and rate of cooling during the solidification was changed. We observed dendrite and cell morphologies during the solidification of rotating melt. The microstructure was characterized by optical microscopy and SEM-EDX and compositional spectroscopy. The effect of carbon impurities was studied on the solidifying microstructure. When we used the longer soak time of the melt in presence of carbon impurities we observed the destruction of dendritic morphology and the formation of cellular and colony structures. Similar approach has been used for Ga2O3, a novel large bandgap material also.
Singh, N. B.↗
Low-Loss Thin-Film Al-On-Si Microwave Resonators for Astronomy Applications Designing and Characterizing the Next Generation of Microwave Detectors
We present measurements of prototype thin film Al microwave kinetic inductance detectors (MKIDs) intended for application in the sub-mm astronomy balloon experiment EXCLAIM. The device we show is dark, or non-optically coupled, and contains 16 coplanar waveguide (CPW) resonators etched into a 261 nm sputter deposited Al layer on a Si wafer. The resonators span the f0 = 3.5 - 4 GHz range, and include both lambda=2 and lambda=4 resonators. Each resonator is coupled to the feedline using one of three alternating coupling designs. We performed transmission line measurements of the device for a series of excitation powers ranging from -90 dBm to -30 dBm, and at a series of base temperatures ranging from 73 mK to 400 mK. We observed quality factors of up to Qi 107 at a base temperature of 73 mK. The lambda=2 and lambda=4 resonators performed similarly, achieving comparable Qi values. The results of these measurements are actively informing the fi nal design of the EXCLAIM instrument. EXCLAIM will incorporate six spectrometers, each containing an array of over 300 resonators in the 420-540 GHz range.
Carrie Volpert↗
Synthesis and Characterization of Fe(III)-Fe(II)- Mg- Al Smectite Solid Solutions and Implications for Planetary Science
This study demonstrates the synergies and limits of multiple measurement types for the detection of smectite chemistry and oxidation state on planetary surfaces to infer past geochemical conditions. Smectite clay minerals are common products of water-rock interactions throughout the solar system, and their detection and characterization provides important clues about geochemical conditions and past environments if sufficient information about their composition can be discerned. Here, we synthesize and report on the spectroscopic properties of a suite of smectite samples that span the intermediate compositional range between Fe(II), Fe(III), Mg, and Al end-member species using bulk chemical analyses, X-ray diffraction, Vis/IR reflectance spectroscopy, UV and green-laser Raman spectroscopy, and Mössbauer spectroscopy. Our data show that smectite composition and the oxidation state of octahedral Fe can be reliably identified in the near infrared on the basis of combination and fundamental metal-OH stretching modes between 2.1–2.9 μm, which vary systematically with chemistry. Smectites dominated by Mg or Fe(III) have spectrally distinct fundamental and combination stretches, whereas Al-rich and Fe(II)-rich smectites have similar fundamental minima near 2.76 μm, but have distinct combination M-OH features between 2.24 and 2.36 μm. We show that with expanded spectral libraries that include intermediate composition smectites and both Fe(III) and Fe(II) oxidation states, more refined characterization of smectites from MIR data is now possible, as the position of the 450 cm–1 absorption shifts systematically with octahedral Fe content, although detailed analysis is best accomplished in concert with other characterization methods. Our data also provide the first Raman spectral libraries of smectite clays as a function of chemistry, and we demonstrate that Raman spectroscopy at multiple excitation wavelengths can qualitatively distinguish smectite clays of different structures and can enhance interpretation by other types of analyses. Our sample set demonstrates how X-ray diffraction can distinguish between dioctahedral and trioctahedral smectites using either the (02,11) or (06,33) peaks, but auxiliary information about chemistry and oxidation state aids in specific identifications. Finally, the temperature-dependent isomer shift and quadrupole splitting in Mössbauer data are insensitive to changes in Fe content but reliability differentiates Fe within the smectite mineral structure.
Valerie K Fox↗
Al-Mg Isotopic Constraints on the Condensation Age of Fine-Grained Refractory Inclusions in Reduced Cv3 Chondrites
Fine-grained Ca-Al-rich inclusions (FGIs) in carbonaceous chondrites are interpreted as aggregates of direct condensates from the solar nebula that escaped extensive melting. Thus far, a few high-precision SIMS Al-Mg chronology studies of FGIs from CV3 chondrites have been reported. Argued that (26Al/27Al)0 of all FGIs are close to the bulk refractory inclusion value of ~5.2×10−5 which may define a time zero for the FGI condensation. A similar (26Al/27Al)0 value was also inferred from an amoeboid olivine aggregate (AOA), which also represents a direct condensate from the solar nebula. In contrast, reported significant variations in (26Al/27Al)0 of FGIs, ranging from ~5.2×10−5 to ~3.4×10−5, and concluded that their formation continued over at least ~0.4 Ma after the canonical value. These contrasting results suggest that the chronological significance for the formation age spread of FGIs in CV3 chondrites is still poorly constrained.
J. Han↗
Hot Cracking Behavior and Beam-Induced Grain Refinement in Electron Beam Freeform Fabricated Al 7075
Electron beam freeform fabrication (EBF 3 ) is a high deposition rate, wire-based directed energy deposition (DED) additive manufacturing (AM) process used to print metallic parts in a vacuum environment. While high specific strength 7xxx-series Al alloys are of interest in the aerospace and automotive industries, these alloys suffer from hot cracking issues during fusion welding and AM. In this work, linear deposits of Al 7075 were fabricated with EBF 3 to study the effects of baseplate thickness, preheat temperature, and beam focus on hot cracking behavior. Solidification cracks were observed in the first deposition layer, and by the third layer coalesced into large “macrocracks” running vertically through the build height. Fine, intergranular liquation “microcracks” appeared between macrocracks below the root of the final deposit layer fusion zone. Increasing the substrate preheat temperature from 165°C to 320°C deepened the partially melted zone and resulted in a more than twofold increase in the liquation microcrack density. Analysis of Scheil solidification diagrams revealed that fugitive losses of Zn and Mg during deposition increased the susceptibility to solidification cracking and promoted substrate liquation cracking. Focused electron beam (EB) conditions combined with a high aspect ratio elliptical raster pattern resulted in bands of refined, equiaxed grains. The refined microstructure suppressed solidification macrocracking and caused a nearly fivefold reduction in liquation crack density, demonstrating that beam-induced grain refinement may be a promising low-cost method for reducing hot cracking during AM.
aluminum↗
A Coordinated Mineralogical and Oxygen Isotopic Study of Refractory Ca-Al-Rich Inclusions
Refractory Ca-Al-rich inclusions (CAIs) in primitive chondritic meteorites represent the oldest solids that formed in our Solar System. Coordinated analyses using multiple ion and electron-beam techniques are vital to fully understand complex nebular and asteroidal processes that CAIs may have experienced in the context of the formation and early evolution of our Solar System. We report the results of a coordinated mineralogical and oxygen isotopic study of unique grossite bearing CAIs from reduced CV (Vigarano type) carbonaceous chondrites using transmission electron microscopy and secondary ion mass spectrometry. Grossite (CaAl 4 O 7 ) occurs in cores of nodules in fine grained CAIs that likely represent aggregates of nebular condensates. In many occurrences, grossite has been partially replaced by hercynite [(Fe,Mg,Zn)Al 2 O 4 ], which displays complex microstructures and compositions, and magnetite nanoparticles. This grossite alteration likely occurred via crystallographically controlled metasomatic reactions with Zn, Fe-rich aqueous fluids on the parent asteroid. The constituent phases of grossite bearing CAIs show heterogeneous oxygen isotopic compositions . That is, grossite and perovskite are 16 O poor and melilite is variably 16 O-depleted in contrast to solar like, 16 O-rich hibonite and spinel. The observed oxygen isotopic distribution is interpreted as a result of mineralogically controlled oxygen isotopic exchange with an 16 O-poor fluid on the parent asteroid. Collectively, we conclude that the presence of limited fluids played an important role in preferential alteration of grossite to hercynite and magnetite and various degrees of 16 O depletion in grossite, perovskite, and melilite during thermal metamorphism on the CV chondrite parent asteroid.
Jangmi Han↗
Global Model Estimates of Atmospheric Al, Ca, Fe, Si, and Ti from Dust and Non-Dust Aerosols Informed by EMIT Surface Mineralogy and Evaluated Against Observations
Atmospheric deposition of micro-nutrients like Fe has been shown to be important for ocean biogeochemistry. The largest source of atmospheric Fe and other elements (e.g., Ca, Al, Si, and Ti) is desert dust, although there are significant non-dust sources in some regions. However, past estimates of these elements have been substantially uncertain due to limited information about the composition of the desert source regions. Here we use elemental distributions estimated from new Earth Surface Mineral Dust Source Investigation (EMIT) observations, which provide mineralogical composition at the surface of the Earth based on imaging spectroscopy measurements from the International Space Station. We add in other sources of these elements (anthropogenic and natural) and compare to a compilation of available surface concentration data from stations over land and from shipborne observations. Our results suggest that the modeled distribution is similar to available observations, but discrepancies still exist in both natural desert dust regions as well as regions dominated by anthropogenic sources. Global budgets for the elements Ca, Al, Fe, Si, and Ti suggest that desert dust remains the dominant source for these elements but anthropogenic or volcanic sources are also important for these elements. Changes in elemental distributions since preindustrial times were also estimated.
aerosols↗
Nucleation and Antiphase Twin Control in Bi 2 Se 3 via Step‐Terminated Al 2 O 3 Substrates
The epitaxial synthesis of high-quality 2D layered materials is an essential driver of both fundamental physics studies and technological applications. Bi 2 Se 3 , a prototypical 2D layered topological insulator, is sensitive to defects imparted during the growth, either thermodynamically or due to the film-substrate interaction. Here, in this study, it is shown that step-terminated Al 2 O 3 substrates with a high miscut angle (3°) can effectively suppress a particular hard-to-mitigate defect, the antiphase twin. Systematic investigations across a range of growth temperatures and substrate miscut angles confirm that atomic step edges act as preferential nucleation sites, stabilizing a single twin domain. First-principles calculations suggest that there is a significant energy barrier for twin boundary formation at step edges, supporting the experimental observations. Detailed structural characterization indicates that this twin-selectivity is lost through the mechanism of the 2D layers overgrowing the step edges, leading to higher twin density as the thickness increases. These findings highlight the complex energy landscape unique to 2D materials that is driven by the interplay between substrate properties, nucleation dynamics, and defect formation, and overcoming and controlling these are critical to improve material quality for quantum and electronic applications.
36 MATERIALS SCIENCE↗
Materials Data on Al(Ag3S2)3 by Materials Project
Ag9AlS6 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are nine inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded in a 3-coordinate geometry to three S2- atoms. There are a spread of Ag–S bond distances ranging from 2.51–2.71 Å. In the second Ag1+ site, Ag1+ is bonded in a 3-coordinate geometry to three S2- atoms. There are a spread of Ag–S bond distances ranging from 2.52–2.78 Å. In the third Ag1+ site, Ag1+ is bonded in a 2-coordinate geometry to three S2- atoms. There are a spread of Ag–S bond distances ranging from 2.47–3.11 Å. In the fourth Ag1+ site, Ag1+ is bonded in a 3-coordinate geometry to three S2- atoms. There are one shorter (2.51 Å) and two longer (2.68 Å) Ag–S bond lengths. In the fifth Ag1+ site, Ag1+ is bonded in a 2-coordinate geometry to three S2- atoms. There are a spread of Ag–S bond distances ranging from 2.46–2.92 Å. In the sixth Ag1+ site, Ag1+ is bonded in a distorted bent 150 degrees geometry to three S2- atoms. There are a spread of Ag–S bond distances ranging from 2.46–3.25 Å. In the seventh Ag1+ site, Ag1+ is bonded in a 2-coordinate geometry to three S2- atoms. There are a spread of Ag–S bond distances ranging from 2.48–2.95 Å. In the eighth Ag1+ site, Ag1+ is bonded in a distorted linear geometry to two S2- atoms. There are one shorter (2.41 Å) and one longer (2.47 Å) Ag–S bond lengths. In the ninth Ag1+ site, Ag1+ is bonded in a 3-coordinate geometry to three S2- atoms. There are a spread of Ag–S bond distances ranging from 2.54–2.61 Å. Al3+ is bonded in a tetrahedral geometry to four S2- atoms. There are a spread of Al–S bond distances ranging from 2.24–2.30 Å. There are six inequivalent S2- sites. In the first S2- site, S2- is bonded in a 4-coordinate geometry to four Ag1+ atoms. In the second S2- site, S2- is bonded in a 5-coordinate geometry to four Ag1+ and one Al3+ atom. In the third S2- site, S2- is bonded in a distorted see-saw-like geometry to three Ag1+ and one Al3+ atom. In the fourth S2- site, S2- is bonded in a 5-coordinate geometry to four Ag1+ and one Al3+ atom. In the fifth S2- site, S2- is bonded in a 7-coordinate geometry to six Ag1+ and one Al3+ atom. In the sixth S2- site, S2- is bonded in a 5-coordinate geometry to five Ag1+ atoms.
36 MATERIALS SCIENCE↗
Materials Data on Al(SeCl)4 by Materials Project
AlCl4(Se)4 crystallizes in the orthorhombic Pca2_1 space group. The structure is zero-dimensional and consists of thirty-two selenium molecules and eight AlCl4 clusters. In each AlCl4 cluster, Al3+ is bonded in a tetrahedral geometry to four Cl1- atoms. There are a spread of Al–Cl bond distances ranging from 2.13–2.17 Å. There are four inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Al3+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Al3+ atom. In the third Cl1- site, Cl1- is bonded in a single-bond geometry to one Al3+ atom. In the fourth Cl1- site, Cl1- is bonded in a single-bond geometry to one Al3+ atom.
36 MATERIALS SCIENCE↗
Materials Data on Al(FeO2)2 by Materials Project
AlFe2O4 is Spinel structured and crystallizes in the trigonal R-3m space group. The structure is three-dimensional. there are two inequivalent Fe+2.50+ sites. In the first Fe+2.50+ site, Fe+2.50+ is bonded to six O2- atoms to form FeO6 octahedra that share corners with six equivalent AlO4 tetrahedra and edges with six FeO6 octahedra. All Fe–O bond lengths are 2.11 Å. In the second Fe+2.50+ site, Fe+2.50+ is bonded to six equivalent O2- atoms to form FeO6 octahedra that share corners with six equivalent AlO4 tetrahedra and edges with six equivalent FeO6 octahedra. All Fe–O bond lengths are 2.07 Å. Al3+ is bonded to four O2- atoms to form AlO4 tetrahedra that share corners with twelve FeO6 octahedra. The corner-sharing octahedra tilt angles range from 54–55°. There is one shorter (1.79 Å) and three longer (1.82 Å) Al–O bond length. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a rectangular see-saw-like geometry to three Fe+2.50+ and one Al3+ atom. In the second O2- site, O2- is bonded in a rectangular see-saw-like geometry to three equivalent Fe+2.50+ and one Al3+ atom.
36 MATERIALS SCIENCE↗
Materials Data on Al(CoO2)2 by Materials Project
Co2AlO4 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent Co+2.50+ sites. In the first Co+2.50+ site, Co+2.50+ is bonded in a square co-planar geometry to four O2- atoms. There is two shorter (1.85 Å) and two longer (1.91 Å) Co–O bond length. In the second Co+2.50+ site, Co+2.50+ is bonded in a square co-planar geometry to four O2- atoms. There is two shorter (1.85 Å) and two longer (1.91 Å) Co–O bond length. Al3+ is bonded in a distorted square co-planar geometry to four O2- atoms. All Al–O bond lengths are 1.88 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Co+2.50+ and one Al3+ atom. In the second O2- site, O2- is bonded in a trigonal non-coplanar geometry to two Co+2.50+ and one Al3+ atom.
36 MATERIALS SCIENCE↗
Materials Data on Al(NiO2)2 by Materials Project
Ni2AlO4 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent Ni+2.50+ sites. In the first Ni+2.50+ site, Ni+2.50+ is bonded in a square co-planar geometry to four O2- atoms. There is two shorter (1.84 Å) and two longer (1.88 Å) Ni–O bond length. In the second Ni+2.50+ site, Ni+2.50+ is bonded in a square co-planar geometry to four O2- atoms. There is two shorter (1.84 Å) and two longer (1.88 Å) Ni–O bond length. Al3+ is bonded in a 4-coordinate geometry to four O2- atoms. All Al–O bond lengths are 1.89 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ni+2.50+ and one Al3+ atom. In the second O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Ni+2.50+ and one Al3+ atom.
36 MATERIALS SCIENCE↗
Materials Data on Al(NF2)3 by Materials Project
AlNF6N2 crystallizes in the cubic Fm-3m space group. The structure is three-dimensional and consists of eight ammonia molecules and one AlNF6 framework. In the AlNF6 framework, Al3+ is bonded to six equivalent F1- atoms to form AlF6 octahedra that share corners with six equivalent NF6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Al–F bond lengths are 1.86 Å. N1+ is bonded to six equivalent F1- atoms to form NF6 octahedra that share corners with six equivalent AlF6 octahedra. The corner-sharing octahedral tilt angles are 0°. All N–F bond lengths are 1.92 Å. F1- is bonded in a linear geometry to one Al3+ and one N1+ atom.
36 MATERIALS SCIENCE↗