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36 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ba(AlSi)2 by Materials Project

BaAl2Si2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ba2+ is bonded in a 7-coordinate geometry to seven Si4- atoms. There are a spread of Ba–Si bond distances ranging from 3.29–3.62 Å. There are two inequivalent Al3+ sites. In the first Al3+ site, Al3+ is bonded to four Si4- atoms to form a mixture of corner and edge-sharing AlSi4 tetrahedra. There are three shorter (2.56 Å) and one longer (2.58 Å) Al–Si bond lengths. In the second Al3+ site, Al3+ is bonded to four Si4- atoms to form a mixture of corner and edge-sharing AlSi4 tetrahedra. There are a spread of Al–Si bond distances ranging from 2.52–2.58 Å. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 4-coordinate geometry to four equivalent Ba2+ and four Al3+ atoms. In the second Si4- site, Si4- is bonded in a 7-coordinate geometry to three equivalent Ba2+ and four Al3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba(AlSi)2 by Materials Project

BaAl2Si2 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Ba2+ is bonded in a 6-coordinate geometry to six equivalent Si4- atoms. There are two shorter (3.32 Å) and four longer (3.39 Å) Ba–Si bond lengths. Al3+ is bonded in a T-shaped geometry to three equivalent Si4- atoms. There are two shorter (2.54 Å) and one longer (2.58 Å) Al–Si bond lengths. Si4- is bonded in a 7-coordinate geometry to three equivalent Ba2+, three equivalent Al3+, and one Si4- atom. The Si–Si bond length is 2.41 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(AlSi)2 by Materials Project

Al2Si2Sr crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Sr2+ is bonded to six equivalent Si4- atoms to form SrSi6 octahedra that share corners with twelve equivalent AlSi4 tetrahedra, edges with six equivalent SrSi6 octahedra, and edges with six equivalent AlSi4 tetrahedra. All Sr–Si bond lengths are 3.18 Å. Al3+ is bonded to four equivalent Si4- atoms to form AlSi4 tetrahedra that share corners with six equivalent SrSi6 octahedra, corners with six equivalent AlSi4 tetrahedra, edges with three equivalent SrSi6 octahedra, and edges with three equivalent AlSi4 tetrahedra. The corner-sharing octahedra tilt angles range from 24–50°. There are three shorter (2.54 Å) and one longer (2.60 Å) Al–Si bond lengths. Si4- is bonded to three equivalent Sr2+ and four equivalent Al3+ atoms to form a mixture of distorted edge and corner-sharing SiSr3Al4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr3(AlSi)2 by Materials Project

Al2Si2Sr3 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. there are two inequivalent Sr sites. In the first Sr site, Sr is bonded to eight equivalent Al and four equivalent Si atoms to form a mixture of face and edge-sharing SrAl8Si4 cuboctahedra. All Sr–Al bond lengths are 3.45 Å. All Sr–Si bond lengths are 3.62 Å. In the second Sr site, Sr is bonded in a 7-coordinate geometry to two equivalent Al and five equivalent Si atoms. Both Sr–Al bond lengths are 3.32 Å. There are four shorter (3.32 Å) and one longer (3.38 Å) Sr–Si bond lengths. Al is bonded in a 2-coordinate geometry to six Sr, one Al, and two equivalent Si atoms. The Al–Al bond length is 2.58 Å. Both Al–Si bond lengths are 2.52 Å. Si is bonded in a 2-coordinate geometry to seven Sr and two equivalent Al atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sm(AlSi)2 by Materials Project

Al2Si2Sm crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Sm2+ is bonded to six equivalent Si4- atoms to form SmSi6 octahedra that share corners with twelve equivalent AlSi4 tetrahedra, edges with six equivalent SmSi6 octahedra, and edges with six equivalent AlSi4 tetrahedra. All Sm–Si bond lengths are 3.02 Å. Al3+ is bonded to four equivalent Si4- atoms to form AlSi4 tetrahedra that share corners with six equivalent SmSi6 octahedra, corners with six equivalent AlSi4 tetrahedra, edges with three equivalent SmSi6 octahedra, and edges with three equivalent AlSi4 tetrahedra. The corner-sharing octahedra tilt angles range from 22–54°. There are three shorter (2.52 Å) and one longer (2.53 Å) Al–Si bond lengths. Si4- is bonded to three equivalent Sm2+ and four equivalent Al3+ atoms to form a mixture of distorted corner and edge-sharing SiSm3Al4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ca(AlSi)2 by Materials Project

CaAl2Si2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ca2+ is bonded to six equivalent Si4- atoms to form CaSi6 octahedra that share corners with twelve equivalent AlSi4 tetrahedra, edges with six equivalent CaSi6 octahedra, and edges with six equivalent AlSi4 tetrahedra. All Ca–Si bond lengths are 3.04 Å. Al3+ is bonded to four equivalent Si4- atoms to form AlSi4 tetrahedra that share corners with six equivalent CaSi6 octahedra, corners with six equivalent AlSi4 tetrahedra, edges with three equivalent CaSi6 octahedra, and edges with three equivalent AlSi4 tetrahedra. The corner-sharing octahedra tilt angles range from 21–52°. There are three shorter (2.52 Å) and one longer (2.60 Å) Al–Si bond lengths. Si4- is bonded to three equivalent Ca2+ and four equivalent Al3+ atoms to form a mixture of distorted edge and corner-sharing SiCa3Al4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(AlSi)2 by Materials Project

Al2CeSi2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ce is bonded to six equivalent Si atoms to form distorted CeSi6 octahedra that share corners with twelve equivalent AlSi4 tetrahedra, edges with six equivalent CeSi6 octahedra, and edges with six equivalent AlSi4 tetrahedra. All Ce–Si bond lengths are 3.03 Å. Al is bonded to four equivalent Si atoms to form distorted AlSi4 tetrahedra that share corners with six equivalent CeSi6 octahedra, corners with six equivalent AlSi4 tetrahedra, edges with three equivalent CeSi6 octahedra, and edges with three equivalent AlSi4 tetrahedra. The corner-sharing octahedra tilt angles range from 22–53°. There are three shorter (2.52 Å) and one longer (2.54 Å) Al–Si bond lengths. Si is bonded to three equivalent Ce and four equivalent Al atoms to form a mixture of distorted corner and edge-sharing SiCe3Al4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nd(AlSi)2 by Materials Project

NdAl2Si2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Nd2+ is bonded to six equivalent Si4- atoms to form NdSi6 octahedra that share corners with twelve equivalent AlSi4 tetrahedra, edges with six equivalent NdSi6 octahedra, and edges with six equivalent AlSi4 tetrahedra. All Nd–Si bond lengths are 3.05 Å. Al3+ is bonded to four equivalent Si4- atoms to form AlSi4 tetrahedra that share corners with six equivalent NdSi6 octahedra, corners with six equivalent AlSi4 tetrahedra, edges with three equivalent NdSi6 octahedra, and edges with three equivalent AlSi4 tetrahedra. The corner-sharing octahedra tilt angles range from 22–53°. There are three shorter (2.52 Å) and one longer (2.53 Å) Al–Si bond lengths. Si4- is bonded to three equivalent Nd2+ and four equivalent Al3+ atoms to form a mixture of distorted edge and corner-sharing SiNd3Al4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Quantification and prediction of solidification textures under additive manufacturing conditions

Crystallographic textures are a major determinant of the macroscale anisotropic properties of polycrystalline metallic alloys produced in a wide range of additive manufacturing (AM) processes. Here, we introduce a statistical method that can accurately quantify the degree of orientational order of textures despite the large random fluctuations in the orientation of individual grains inherent in AM processes. The method, demonstrated for laser and resolidification of AlSi thin films, extends Z-scoring to a dynamical regime to assess the statistical significance of observed textures compared to randomly generated ones at different stages of solidification. We further show that, combined with phase-field modeling, this method can be used to infer fundamental anisotropic properties of the solid-liquid interface that are essential for texture prediction, and are compared here to the results of atomistic simulations. In addition, phase-field modeling reveals that, even at rapid AM solidification rates, the observed 〈110〉-dominated textures in the AlSi thin films are controlled predominantly by the anisotropy of the interface free-energy and sheds light on the physical mechanism of grain competition. These results significantly enhance both the existing tools for the quantification and prediction of AM crystallographic textures and our basic understanding of their formation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Secondary corundum‐bearing assemblages in Allende Ca,Al‐rich inclusions: Mineralogy, petrology, oxygen, and aluminum–magnesium isotope systematics

Here, we report on the mineralogy, petrology, oxygen, and aluminum–magnesium isotopic systematics of the secondary corundum-bearing assemblages in type B CAIs 3529Z and 3529G and fluffy type A (FTA) CAI ALH-2 from Allende (CV > 3.6). In 3529Z and 3529G, 2–5 μm-sized euhedral-to-subhedral corundum grains associate with secondary alumoåkermanite [(Ca,Na) 2 AlSi 2 O 7 ], grossular, spinel, grossite, celsian, kushiroite, and wadalite. In ALH-2, 2–5 μm-sized euhedral-to-subhedral corundum grains associate with secondary grossular, nepheline, spinel, and kushiroite. In 3529Z and 3529G, corundum and associated secondary grossite, spinel, alumoåkermanite, grossular, and kushiroite have similar 16 O-poor compositions (Δ 17 O = −2.2 ± 1.5‰); primary spinel is 16 O-rich (Δ 17 O ~ −23‰); Al,Ti-diopside shows a range of Δ 17 O (from ~ −24‰ to ~ −15‰); anorthite and melilite are 16 O-depleted to various degrees (−6.5‰ ≤ Δ 17 O ≤ −4.5‰ and Δ 17 O = −2.7 ± 0.8‰, respectively). In ALH-2, corundum shows a range of Δ 17 O, from ~ −9‰ to ~ −1‰; primary hibonite and spinel are 16 O-rich (Δ 17 O ~ −23‰); melilite and perovskite are 16 O-poor (Δ 17 O = −2.6 ± 1.5‰ and −3.1 ± 1.3‰, respectively). On the Al-Mg isotope diagram ( 26 Mg* versus 27 Al/ 24 Mg), primary Al,Ti-diopside, hibonite, melilite, and spinel in the Allende CAIs studied along the canonical isochron with inferred initial 26 Al/ 27 Al ratio [( 26 Al/ 27 Al) 0 ] of ~5 × 10 −5 . All secondary minerals have resolved excesses of 26 Mg*: alumoåkermanite, corundum, and grossite plot below the canonical isochron, whereas most spinel analyses plot above it. An internal isochron defined by the coexisting secondary corundum and alumoåkermanite in 3529Z has ( 26 Al/ 27 Al) 0 = (7.5 ± 2.6) × 10 −7 . We conclude that the corundum-bearing assemblages in Allende CAIs resulted from metasomatic alteration of primary melilite and anorthite, ~4–5 Ma after their crystallization. Metasomatic alteration of CAIs in the Allende parent asteroid by an aqueous fluid having Δ 17 O of ~ −3 ± 2‰ modified the O-isotope composition of their primary melilite, anorthite, and Ti-rich pyroxene; O-isotope compositions of primary hibonite, spinel, and low-Ti pyroxene escaped this modification.

Geosciences↗
NASA NTRS1972

Dissociation energies of some high temperature molecules containing aluminum

The Knudsen cell mass spectrometric method has been used to investigate the gaseous molecules Al2, AlSi,AlSiO, AlC2, Al2C2, and AlAuC2. Special attention was given to the experimental considerations and techniques needed to identify and to measure ion intensities for very low abundance molecular species. Second- and third-law procedures were used to obtain reaction enthalpies for pressure calibration independent and isomolecular exchange reactions. Dissociation energies for the molecules were derived from the measured ion intensities, free-energy functions obtained from estimated molecular constants, and auxiliary thermodynamic data. The bonding and stability of these aluminum containing molecules are compared with other similar species.

Stearns, C. A.↗
NASA NTRS1985

Studies of the Crystallization Process of Aluminum-Silicon Alloys Using a High Temperature Microscope

It is shown that primary silicon crystals grow polyhedral in super-eutectic AlSi melts and that phosphorus additives to the melt confirm the strong seeding capacity. Primary silicon exhibits strong dendritic seeding effects in eutectic silicon phases of various silicon alloys, whereas primary aluminum does not possess this capacity. Sodium addition also produces a dendritic silicon network growth in the interior of the sample that is attributed to the slower silicon diffusion velocity during cooling.

Justi, S.↗
NASA NTRS1986

Ada technology support for NASA-GSFC

Utilization of the Ada programming language and environments to perform directorate functions was reviewed. The Mission and Data Operations Directorate Network (MNET) conversion effort was chosen as the first task for evaluation and assistance. The MNET project required the rewriting of the existing Network Control Program (NCP) in the Ada programming language. The DEC Ada compiler running on the VAX under WMS was used for the initial development efforts. Stress tests on the newly delivered version of the DEC Ada compiler were performed. The new Alsys Ada compiler was purchased for the IBM PC AT. A prevalidated version of the compiler was obtained. The compiler was then validated.

Source record↗
NASA NTRS1986

Using Ada (R) on a workstation for large projects

Alsys has implemented validated Ada compilers that are hosted and targeted on a variety of microprocessor-based workstations, including the IBM PC/AT. The availability of Ada compilers for these kinds of inexpensive, widely available machines considerably enhances the development options for large efforts such as the NASA Space Station, and this is addressed from both an implementation and a user perspective. First, the issue of large program development on a workstation is discussed: how the compiler must handle this, and how an inherently decentralized approach can be managed. Next, the focus is on code efficiency and the compiler and run-time design decisions that help meet this goal are described. It is concluded with a presentation of benchmarks that are quite encouraging with respect to the run-time efficiency of Ada code compared with other languages.

Avakian, Arra S.↗
NASA NTRS1990

A study of the portability of an Ada system in the software engineering laboratory (SEL)

A particular porting effort is discussed, and various statistics on analyzing the portability of Ada and the total staff months (overall and by phase) required to accomplish the rehost, are given. This effort is compared to past experiments on the rehosting of FORTRAN systems. The discussion includes an analysis of the types of errors encountered during the rehosting, the changes required to rehost the system, experiences with the Alsys IBM Ada compiler, the impediments encountered, and the lessons learned during this study.

Jun, Linda O.↗
NASA NTRS2003

Design of Hybrid Solid Polymer Electrolytes: Structure and Properties

This paper reports synthesis, structure, and properties of novel hybrid solid polymer electrolytes (SPE's) consisting of organically modified aluminosilica (OM-ALSi), formed within a poly(ethylene oxide)-in-salt (Li triflate) phase. To alter the structure and properties we fused functionalized silanes containing poly(ethylene oxide) (PEO) tails or CN groups.

Bronstein, Lyudmila M.↗
NASA NTRS2012

ISS-Experiments of Columnar-to-Equiaxed Transition in Solidification Processing

The main topic of the research project CETSOL in the framework of the Microgravity Application Promotion (MAP) programme of the European Space Agency (ESA) is the investigation of the transition from columnar to equiaxed grain growth during solidification. Microgravity environment allows for suppression of buoyancy-driven melt flow and for growth of equiaxed grains free of sedimentation and buoyancy effects. This contribution will present first experimental results obtained in microgravity using hypo-eutectic AlSi alloys in the Materials Science Laboratory (MSL) on-board the International Space Station (ISS). The analysis of the experiments confirms the existence of a columnar to equiaxed transition, especially in the refined alloy. Temperature evolution and grain structure analysis provide critical values for the position, the temperature gradient and the solidification velocity at the columnar to equiaxed transition. These data will be used to improve modeling of solidification microstructures and grain structure on different lengths scales.

Sturz, Laszlo↗
NASA NTRS2012

Chemical Heterogeneity on Mercury's Surface Revealed by the MESSENGER X-ray Spectrometer

We present the analysis of 205 spatially resolved measurements of the surfacecomposition of Mercury from MESSENGERs X-Ray Spectrometer. The surfacefootprints of these measurements are categorized according to geological terrain. Northernsmooth plains deposits and the plains interior to the Caloris basin differ compositionallyfrom older terrain on Mercury. The older terrain generally has higher MgSi, SSi, andCaSi ratios, and a lower AlSi ratio than the smooth plains. Mercurys surface mineralogyis likely dominated by high-Mg mafic minerals (e.g., enstatite), plagioclase feldspar, andlesser amounts of Ca, Mg, andor Fe sulfides (e.g., oldhamite). The compositionaldifference between the volcanic smooth plains and the older terrain reflects differentabundances of these minerals and points to the crystallization of the smooth plains from amore chemically evolved magma source. High-degree partial melts of enstatite chondritematerial provide a generally good compositional and mineralogical match for much ofthe surface of Mercury. An exception is Fe, for which the low surface abundance onMercury is still higher than that of melts from enstatite chondrites and may indicate anexogenous contribution from meteoroid impacts.

Chemical heterogeneity↗