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27 records · Page 2
All sourcesNASA NTRSDOE OSTI
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↗