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30 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Tm(CrSi)2 by Materials Project

TmCr2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Tm3+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Tm–Si bond lengths are 2.97 Å. Cr+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of corner and edge-sharing CrSi4 tetrahedra. All Cr–Si bond lengths are 2.40 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Tm3+, four equivalent Cr+2.50+, and one Si4- atom. The Si–Si bond length is 2.43 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Nd(CrSi)2 by Materials Project

NdCr2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Nd3+ is bonded in a body-centered cubic geometry to eight equivalent Si4- atoms. All Nd–Si bond lengths are 3.06 Å. Cr+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CrSi4 tetrahedra. All Cr–Si bond lengths are 2.41 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Nd3+, four equivalent Cr+2.50+, and one Si4- atom. The Si–Si bond length is 2.60 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Gd(CrSi)2 by Materials Project

GdCr2Si2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. Gd3+ is bonded in a body-centered cubic geometry to eight Si4- atoms. There are three shorter (3.00 Å) and five longer (3.01 Å) Gd–Si bond lengths. There are two inequivalent Cr+2.50+ sites. In the first Cr+2.50+ site, Cr+2.50+ is bonded to four Si4- atoms to form a mixture of edge and corner-sharing CrSi4 tetrahedra. All Cr–Si bond lengths are 2.41 Å. In the second Cr+2.50+ site, Cr+2.50+ is bonded to four Si4- atoms to form a mixture of edge and corner-sharing CrSi4 tetrahedra. There are one shorter (2.40 Å) and three longer (2.41 Å) Cr–Si bond lengths. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 9-coordinate geometry to four equivalent Gd3+, four Cr+2.50+, and one Si4- atom. The Si–Si bond length is 2.50 Å. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to four equivalent Gd3+, four Cr+2.50+, and one Si4- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Tb(CrSi)2 by Materials Project

TbCr2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Tb3+ is bonded in a body-centered cubic geometry to eight equivalent Si4- atoms. All Tb–Si bond lengths are 3.00 Å. Cr+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CrSi4 tetrahedra. All Cr–Si bond lengths are 2.41 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Tb3+, four equivalent Cr+2.50+, and one Si4- atom. The Si–Si bond length is 2.48 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ce(CrSi)2 by Materials Project

CeCr2Si2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ce3+ is bonded in a body-centered cubic geometry to eight equivalent Si4- atoms. All Ce–Si bond lengths are 3.06 Å. Cr+2.50+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CrSi4 tetrahedra. All Cr–Si bond lengths are 2.42 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Ce3+, four equivalent Cr+2.50+, and one Si4- atom. The Si–Si bond length is 2.52 Å.

36 MATERIALS SCIENCE↗
NASA NTRS1974

Improved coating for silica fiber based ceramic Reusable Surface Insulation (CRSI)

A series of coatings was developed for the space shuttle type silica fiber insulation system and characterized for optical and physical properties. Reentry simulation tests were run using a radiant panel and also using a hypersonic plasma arc. The coatings produced had improved physical and optical properties as well as greater reuse capability over the GE version of the JSC-0042 coating.

Ormiston, T. J.↗
NASA NTRS2004

Thin-Film Ceramic Thermocouples Fabricated and Tested

The Sensors and Electronics Technology Branch of the NASA Glenn Research Center is developing thin-film-based sensors for surface measurement in propulsion system research. Thin-film sensors do not require special machining of the components on which they are mounted, and they are considerably thinner than wire- or foil-based sensors. One type of sensor being advanced is the thin-film thermocouple, specifically for applications in high-temperature combustion environments. Ceramics are being demonstrated as having the potential to meet the demands of thin-film thermocouples in advanced aerospace environments. The maximum-use temperature of noble metal thin-film thermocouples, 1500 C (2700 F), may not be adequate for components used in the increasingly harsh conditions of advanced aircraft and next-generation launch vehicles. Ceramic-based thermocouples are known for their high stability and robustness at temperatures exceeding 1500 C, but are typically in the form of bulky rods or probes. As part of ASTP, Glenn's Sensors and Electronics Technology Branch is leading an in-house effort to apply ceramics as thin-film thermocouples for extremely high-temperature applications as part of ASTP. Since the purity of the ceramics is crucial for the stability of the thermocouples, Glenn's Ceramics Branch and Case Western Reserve University are developing high-purity ceramic sputtering targets for fabricating high-temperature sensors. Glenn's Microsystems Fabrication Laboratory, supported by the Akima Corporation, is using these targets to fabricate thermocouple samples for testing. The first of the materials used were chromium silicide (CrSi) and tantalum carbide (TaC). These refractory materials are expected to survive temperatures in excess of 1500 C. Preliminary results indicate that the thermoelectric voltage output of a thin-film CrSi versus TaC thermocouple is 15 times that of the standard type R (platinum-rhodium versus platinum) thermocouple, producing 20 mV with a 200 C temperature gradient. The photograph on the left shows the CrSi-TaC thermocouple in a test fixture at Glenn, and the resulting output signal is shown on the right. The temperature differential across the sample, from the center of the sample inside the oven to the sample mount outside the oven, is measured using a type R thermocouple on the sample.

Wrbanek, John D.↗
DOE OSTI2022

Electronic and magnetic properties of iridium-based novel Heusler alloys

We report half-metallicity and magnetism including exchange splitting are the most significant physical parameters to predict and design a candidate material for spintronic applications. We report here an ab-initio investigation on chemical formation and dynamical stability along with electronic structure and magnetic properties of Ir 2 Cr (Si, Ge) and IrRhCr (Si, Ge) Heusler alloys. The negative formation and cohesive energies with positive phonon dispersions confirm the stabilities of these alloys. Electronic structure calculations reveal that Ir 2 Cr (Si, Ge) and IrRhCrSi alloys are half-metallic ferromagnets with unprecedented exchange splitting. In addition, IrRhCrGe also shows semi-metallic nature. All of these materials follow Slater Pauling rule with large magnetic moments and 100% spin-polarization. With Cr bearing the majority of the local magnetic moment and exchange splitting, a ferromagnetic state is more stable than a nonmagnetic state. The electronic charge distribution and population analysis confirm mixed ionic and covalent bonding. The magnetocrystalline anisotropy energy, with the easy magnetization along the [1 1 1] direction, is significantly high in Ir 2 CrGe. Elastic constants such as shear (G), bulk (B), Young’s moduli, and Poisson’s ratio indicate that the IrRhCrSi and IrRhCrGe alloys are mechanically stable, and Ir 2 CrSi and Ir 2 CrGe are mechanically unstable. The Pugh’s (B/G) and Poisson’s ratios confirm that the stable alloys are ductile.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrFeSi2 by Materials Project

FeSi(CrSi) is beta-prime palladium aluminum-derived structured and crystallizes in the monoclinic P2_1 space group. The structure is three-dimensional. Cr5+ is bonded in a 7-coordinate geometry to seven Si4- atoms. There are a spread of Cr–Si bond distances ranging from 2.34–2.54 Å. Fe3+ is bonded in a 7-coordinate geometry to seven Si4- atoms. There are a spread of Fe–Si bond distances ranging from 2.25–2.53 Å. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 7-coordinate geometry to three equivalent Cr5+ and four equivalent Fe3+ atoms. In the second Si4- site, Si4- is bonded in a 7-coordinate geometry to four equivalent Cr5+ and three equivalent Fe3+ atoms.

36 MATERIALS SCIENCE↗
NASA NTRS2002

SHARC II: A Caltech Submillimeter Observatory Facility Camera with 384 Pixels

SHARC II is a background-limited 350 micron and 450 micron facility camera for the Caltech Submillimeter Observatory undergoing commissioning in 2002. The key component of SHARC II is a 12 x 32 array of doped silicon 'pop-up' bolometers developed at NASA/Goddard. Each 1 mm x 1 mm pixel is coated with a 400 Omega/square bismuth film and located lambda/4 above a reflective backshort to achieve greater than 75% absorption efficiency. The pixels cover the focal plane with greater than 90% filling factor. At 350 microns, the SHARC II pixels are separated by 0.65 lambda/D. In contrast to the silicon bolometers in the predecessor of SHARC II, each doped thermistor occupies nearly the full area of the pixel, which lowers the 1/f knee of tile detector noise to less than 0.03 Hz, under load, at tile bath temperature of 0.36 K. The bolometers are AC-biased and read in 'total power' mode to take advantage of the improved stability. Each bolometer is biased through a custom approx. 130 MOmega CrSi load resistor at 7 K and read with a commercial JFET at 120 K. The JFETs and load resistors are integrated with the detectors into a single assembly to minimize microphonic noise. Electrical connection across the 0.36 K to 4 K and 4 K to 120 K temperature interfaces is accomplished with lithographed metal wires on dielectric substrates. In the best 25% of winter nights on Mauna Kea, SHARC II is expected to have an NEFD at 350 micron of 1 Jy Hz(sup -1/2) or better. The new camera should be at least 4 times faster at detecting known point sources and 30 times faster at mapping large areas compared to the prior instrument.

Dowell, C. Darren↗
NASA NTRS2014

Comparison of the Thermal Expansion Behavior of Several Intermetallic Silicide Alloys Between 293 and 1523 K

Thermal expansion measurements were conducted on hot-pressed CrSi(sub 2), TiSi(sub 2), W Si(sub 2) and a two-phase Cr-Mo-Si intermetallic alloy between 293 and 1523 K during three heat-cool cycles. The corrected thermal expansion, (L/L(sub 0)(sub thermal), varied with the absolute temperature, T, as (deltaL/L(sub 0)(sub thermal) = A(T-293)(sup 3) + B(T-293)(sup 2) + C(T-293) + D, where A, B, C and D are regression constants. Excellent reproducibility was observed for most of the materials after the first heat-up cycle. In some cases, the data from the first heatup cycle deviated from those determined in the subsequent cycles. This deviation was attributed to the presence of residual stresses developed during processing, which are relieved after the first heat-up cycle.

silicides↗