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10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ca(ScS2)2 by Materials Project

Ca(ScS2)2 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ca2+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Ca–S bond distances ranging from 2.92–3.22 Å. There are two inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing ScS6 octahedra. The corner-sharing octahedra tilt angles range from 48–61°. There are a spread of Sc–S bond distances ranging from 2.54–2.65 Å. In the second Sc3+ site, Sc3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing ScS6 octahedra. The corner-sharing octahedra tilt angles range from 48–61°. There are a spread of Sc–S bond distances ranging from 2.56–2.63 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent Ca2+ and three equivalent Sc3+ atoms. In the second S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent Ca2+ and three Sc3+ atoms. In the third S2- site, S2- is bonded to two equivalent Ca2+ and three equivalent Sc3+ atoms to form a mixture of distorted edge and corner-sharing SCa2Sc3 square pyramids. In the fourth S2- site, S2- is bonded to two equivalent Ca2+ and three Sc3+ atoms to form a mixture of distorted edge and corner-sharing SCa2Sc3 trigonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(ScS2)2 by Materials Project

Mg(ScS2)2 is Spinel structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Mg2+ is bonded to four equivalent S2- atoms to form MgS4 tetrahedra that share corners with twelve equivalent ScS6 octahedra. The corner-sharing octahedral tilt angles are 57°. All Mg–S bond lengths are 2.46 Å. Sc3+ is bonded to six equivalent S2- atoms to form ScS6 octahedra that share corners with six equivalent MgS4 tetrahedra and edges with six equivalent ScS6 octahedra. All Sc–S bond lengths are 2.59 Å. S2- is bonded to one Mg2+ and three equivalent Sc3+ atoms to form a mixture of distorted corner and edge-sharing SMgSc3 trigonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ScS2 by Materials Project

ScS2 is Rutile structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Sc3+ is bonded to six equivalent S+1.50- atoms to form a mixture of edge and corner-sharing ScS6 octahedra. The corner-sharing octahedral tilt angles are 47°. There are two shorter (2.54 Å) and four longer (2.57 Å) Sc–S bond lengths. S+1.50- is bonded in a distorted trigonal planar geometry to three equivalent Sc3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Mg(ScS2)2 by Materials Project

Mg(ScS2)2 crystallizes in the tetragonal I-42d space group. The structure is three-dimensional. Mg2+ is bonded in a 4-coordinate geometry to eight equivalent S2- atoms. There are four shorter (2.53 Å) and four longer (3.11 Å) Mg–S bond lengths. Sc3+ is bonded in a 8-coordinate geometry to eight equivalent S2- atoms. There are a spread of Sc–S bond distances ranging from 2.56–3.07 Å. S2- is bonded in a 6-coordinate geometry to two equivalent Mg2+ and four equivalent Sc3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Sr(ScS2)2 by Materials Project

SrSc2S4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Sr2+ is bonded in a 8-coordinate geometry to eight S2- atoms. There are a spread of Sr–S bond distances ranging from 3.03–3.20 Å. There are two inequivalent Sc3+ sites. In the first Sc3+ site, Sc3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing ScS6 octahedra. The corner-sharing octahedra tilt angles range from 48–59°. There are a spread of Sc–S bond distances ranging from 2.55–2.63 Å. In the second Sc3+ site, Sc3+ is bonded to six S2- atoms to form a mixture of edge and corner-sharing ScS6 octahedra. The corner-sharing octahedra tilt angles range from 48–59°. There are a spread of Sc–S bond distances ranging from 2.57–2.67 Å. There are four inequivalent S2- sites. In the first S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent Sr2+ and three equivalent Sc3+ atoms. In the second S2- site, S2- is bonded to two equivalent Sr2+ and three Sc3+ atoms to form a mixture of distorted edge and corner-sharing SSr2Sc3 trigonal bipyramids. In the third S2- site, S2- is bonded to two equivalent Sr2+ and three equivalent Sc3+ atoms to form a mixture of distorted edge and corner-sharing SSr2Sc3 square pyramids. In the fourth S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent Sr2+ and three Sc3+ atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Reassessment of a reported S-delay under Trindade

A correction to a paper by Okal and Anderson (1975) about multiple ScS travel-time anomalies is presented. Data for ScS2 surface bounces in the South Atlantic Ocean have been reanalyzed. From these data an ScS2-S residual of 23.6 seconds was found by Okal and Anderson (1975). This corresponded to an ScS2 surface bounce point under Trindade island and was inferred to be due to very slow upper mantle associated with the Trindade hot spot. The analysis presented here invalidates this conclusion. The nature of the upper mantle under Trindade is an open issue.

Nataf, H. C.↗
NASA NTRS1984

Fatigue behavior of continuous fiber silicon-carbide-aluminum composites

Four lay-ups of continuous fiber silicon carbide (SCS2) fiber/aluminum matrix composites were tested to assess fatigue mechanisms including stiffness loss when cycled below their respective fatigue limits. The lay-ups were 0 (sub 8), 0(sub 2)/ + or - 45 (sub 2s), 0/90 (sub 2s),and 0/ + or 45/90 (subs). The data were compared with predictions from the author's previously published shakedown model which predicts fatigue-induced stiffness loss in metal matrix composites. A fifth lay-up, + or - 45 (sub 2s), was tested to compare shakedown and fatigue limits. The particular batch of silicon-carbide fibers tested in this program had a somewhat lower modulus (340 GPa) than expected and displayed poor bonding to the aluminum matrix. Good agreement was obtained between the stiffness loss model and the test data. The fatigue damage below the fatigue limit was primarily in the form of matrix cracking. The fatigue limit corresponded to the laminate shakedown for the + or - 45 (sub 2s) laminate.

Johnson, W. S.↗
NASA NTRS1986

Fatigue behavior of continuous-fiber silicon carbide/aluminum composites

Four lay-ups of continuous fiber silicon carbide (SCS2) fiber/aluminum matrix composites were tested to assess fatigue mechanisms including stiffness loss when cycled below their respective fatigue limits. The lay-ups were 0 (sub 8), 0(sub 2)/ + or - 45 (sub 2s), 0/90 (sub 2s), and 0/ + or - 45/90 (subs). The data were compared with predictions from the author's previously published shakedown model which predicts fatigue-induced stiffness loss in metal matrix composites. A fifth lay-up, + or - 45 (sub 2s), was tested to compare shakedown and fatigue limits. The particular batch of silicon-carbide fibers tested in this program had a somewhat lower modulus (340 GPa) than expected and displayed poor bonding to the aluminum matrix. Good agreement was obtained between the stiffness loss model and the test data. The fatigue damage below the fatigue limit was primarily in the form of matrix cracking. The fatigue limit corresponded to the laminate shakedown for the + or - 45 (sub 2s) laminate.

Johnson, W. S.↗
NASA NTRS2019

Terrestrial Single-Station Analog for Constraining the Martian Core and Deep Interior: Implications for InSight

We used a terrestrial single-station seismometer to quantify the uncertainty of InSight (INterior explorations using Seismic Investigations, Geodesy and Heat Transport) data for determining Martian core size. To mimic Martian seismicity, we formed a catalog using 917 terrestrial earthquakes, from which we randomly selected events. We stacked ScS amplitudes on modeled arrival times and searched for where ScS produced coherent seismic amplitudes. A core detection was defined by a coherent peak with small offset between predicted and user-selected arrival times. Iterating the detection algorithm with varying signal-to-noise (SNR) ranges and quantity of events determined the selection frequency of each model and quantified core depth uncertainty. Increasing the quantity of events reduced core depth uncertainty while increasing the recovery rate, while increasing event SNR had little effect. Including ScS2 multiples increased the recovery rate and reduced core depth uncertainty when we used low quantities of events. The most-frequent core depths varied by back azimuth, suggesting our method is sensitive to the presence of mantle heterogeneities. When we added 1° in source distance errors, core depth uncertainty increased by up to 11 km and recovery rates decreased by <5%. Altering epicentral distances by 25% added ~35 km of uncertainty and reduced recovery rates to <50% in some cases. From these experiments, we estimate that if InSight can detect five events with high location precision (<10% epicentral distance errors), that there is at least an 88% chance of core depth recovery using ScS alone with uncertainty in core depth approaching 18 km and decreasing as more events are located.

Marusiak, Angela G.↗
NASA NTRS2019

Terrestrial Single-Station Analog for Constraining the Martian Core and Deep Interior: Implications for InSight

We used a terrestrial single-station seismometer to quantify the uncertainty of InSight (INterior explorations using Seismic Investigations, Geodesy and Heat Transport) data for determining Martian core size. To mimic Martian seismicity, we formed a catalog using 917 terrestrial earthquakes, from which we randomly selected events. We stacked ScS amplitudes on modeled arrival times and searched for where ScS produced coherent seismic amplitudes. A core detection was defined by a coherent peak with small offset between predicted and user-selected arrival times. Iterating the detection algorithm with varying signal-to-noise (SNR) ranges and quantity of events determined the selection frequency of each model and quantified core depth uncertainty. Increasing the quantity of events reduced core depth uncertainty while increasing the recovery rate, while increasing event SNR had little effect. Including ScS2 multiples increased the recovery rate and reduced core depth uncertainty when we used low quantities of events. The most-frequent core depths varied by back azimuth, suggesting our method is sensitive to the presence of mantle heterogeneities. When we added 1° in source distance errors, core depth uncertainty increased by up to 11 km and recovery rates decreased by <5%. Altering epicentral distances by 25% added ~35 km of uncertainty and reduced recovery rates to <50% in some cases. From these experiments, we estimate that if InSight can detect five events with high location precision (< 10% epicentral distance errors), that there is at least an 88% chance of core depth recovery using ScS alone with uncertainty in core depth approaching 18 km and decreasing as more events are located.

Angela G Marusiak↗