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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Zr-Hf-Ta fractionation during lunar evolution

Zr/Hf ratios and other elemental data in 68 samples of various mare basalts, KREEP units, and lunar glasses have been determined using instrumental neutron activation analysis coupled with coincidence-anticoincidence counting for greater precision. The data are presented in order to quantify further the amount of Zr/Hf fractionation that has occurred during primordial crystallization and cumulate remelting or by any other process. Models of Zr-Hf evolution are developed to place additional constraints on the bulk lunar composition and on the effects of minor phases that may be responsible for the observed fractionations. The Hf-Ta fractionation in lunar compositions is also reviewed in order to characterize normal Hf(4+) versus Ta(4+) behavior and to delineate possible effects due to the oxidation of Ta(4+) to Ta(5+) during late-stage ilmenite crystallization.

Hughes, S. S.↗
NASA NTRS1989

HF sideband generation in the ionosphere

The temporal development of sidebands excited near sunrise by two strong HF waves separated by a few hertz is presented. Sidebands are not observed before sunrise when the ionospheric critical frequency is less than the heater frequency. As the ionospheric density increases following sunrise and overdense conditions are established, strong sidebands emerge. Even though these results favor a mechanism which phase modulates the reflected HF wave over one which first downconverts the HF power to ULF before exciting sidebands, it is possible that either mechanism could at times contribute to sideband production.

Noble, S. T.↗
NASA NTRS1989

Microstructure and tensile properties of Fe-40 at. pct Al alloys with C, Zr, Hf, and B additions

The influence of small additions of C, Zr, and Hf, alone or in combination with B, on the microstructure and tensile behavior of substoichiometric FeAl was investigated. Tensile properties were determined from 300 to 1100 K on powder which was consolidated by hot extrusion. All materials possessed some ductility at room temperature, although ternary additions generally reduced ductility compared to the binary alloy. Adding B to the C- and Zr-containing alloys changed the fracture mode from intergranular to transgranular and restored the ductility to approximately 5 percent elongation. Additions of Zr and Hf increased strength up to about 900 K. Fe6Al6Zr and Fe6Al6Hf precipitates, both with identical body-centered tetragonal structures, were identified as the principal second phase in these alloys. Strength decreased steadily as temperature increased above 700 K, as diffusion-assisted mechanisms became operative. Although all alloys had similar strengths at 1100 K, Hf additions significantly improved high-temperature ductility by suppressing cavitation.

Gaydosh, D. J.↗
NASA NTRS1993

Spectroscopic ellipsometry studies of HF treated Si (100) surfaces

Both ex situ and in situ spectroscopic ellipsometry (SE) measurements were employed to investigate the effect of HF cleaning on Si surfaces. The hydrogen-terminated (H-terminated) Si surface was modeled as an equivalent dielectric layer, and monitored in real time by SE measurements. The SE analyses indicate that, after a 20-sec 9:1 HF dip without rinse, the Si (100) surface was passivated by the hydrogen termination and remained chemically stable. Roughness of the HF-etched bare Si (100) surface was observed, in an ultrahigh vacuum chamber (UHV), and analyzed by the in situ SE. Evidence for desorption of the H-terminated Si surface layer, after being heated to about 550 C in the UHV chamber, is presented and discussed. This is the first use of an ex situ and in situ real-time, nondestructive technique capable of showing state of passivation, the rate of reoxidation, and the surface roughness of the H-terminated Si surfaces.

Yao, Huade↗
NASA NTRS1993

Spectroscopic ellipsometry studies of HF treated Si (100) surfaces

Both ex situ and in situ spectroscopic ellipsometry (SE) measurements were employed to investigate the effects of HF cleaning on Si surfaces. The hydrogen-terminated (H-terminated) Si surface was modeled as an equivalent dielectric layer, and monitored in real time by SE measurements. The SE analyses indicate that after a 20-s 9:1 HF dip without rinse, the Si(100) surface was passivated by the hydrogen termination and remained chemically stable. Roughness of the HF-etched bare Si(100) surface was observed, in an ultrahigh vacuum (UHV) chamber, and analyzed by the in situ SE. Evidence for desorption of the H-terminated Si surface-layer, after being heated to approximately 550 C in the UHV chamber, is presented and discussed. This is the first use of an ex situ and in situ real-time, nondestructive technique capable of showing state of passivation, the rate of reoxidation, and the surface roughness of the H-terminated Si surfaces.

Yao, Huade↗
NASA NTRS1994

Balloon measurements of stratospheric HCl and HF by far infrared emission spectroscopy

We have analyzed atmospheric thermal emission spectra obtained with the balloon-borne FIRS-2 far infrared Fourier transform spectrometer during balloon flights from Palestine, Texas on May 12-13, 1988 and from Fort Sumner, New Mexico on September 26-27, 1989 and on July 4-5, 1990. Seven and two pure rotational transition lines in 100-205 cm(exp -1) range are analyzed for deriving vertical profiles of stratospheric HCl and HF, respectively. We obtain both the daytime and nighttime average vertical profiles from 15 to 50 km. We compare these profiles with the ones obtained in June, 1983 with the first version of FIRS spectrometer during the Balloon Intercomparison Campaign (BIC-2). BIC-2 results were revised to be consistent with the present analysis which uses the latest spectral parameters. According to our comparison results no increase is recognized for HCl but about 3 percent per year increase for HF from 1983 to 1990, assuming a linear trend. These annual increase rates are smaller than those reported by other groups. Recently Rinsland et al. (1991) and Wallace and Livingston (1991) reported long term behavior of total HCl and HF observed on Kit Peak between 1977 and 1990. As Kit Peak is located near both balloon launching sites, Palestine and Fort Sumner, we think our results are favorably comparable with theirs. Comparison results with ours and ground-based measurements will be presented and discussed.

Shibasaki, Kazuo↗
NASA NTRS1996

Crystallography of the NiHfSi Phase in a NiAl (0.5 Hf) Single-Crystal Alloy

Small additions of Hf to conventionally processed NiAl single crystals result in the precipitation of a high density of cuboidal G-phase along with a newly identified silicide phase. Both of these phases form in the presence of Si which is not an intentional alloying addition but is a contaminant resulting from contact with the ceramic shell molds during directional solidification of the single-crystal ingots. The morphology, crystal structure and Orientation Relationship (OR) of the silicide phase in a NiAl (0.5 at.%Hf) single-crystal alloy have been determined using transmission electron microscopy, electron microdiffraction and energy dispersive X-ray spectroscopy. Qualitative elemental analysis and indexing of the electron microdiffraction patterns from the new phase indicate that it is an orthorhombic NiHfSi phase with unit cell parameters, a = 0.639 nm, b = 0.389 nm and c = 0.72 nm, and space group Pnma. The NiHfSi phase forms as thin rectangular plates on NiAl/111/ planes with an OR that is given by NiHfSi(100))(parallel) NiAl(111) and NiHfSi zone axes(010) (parallel) NiAl zone axes (101). Twelve variants of the NiHfSi phase were observed in the alloy and the number of variants and rectangular morphology of NiHfSi plates are consistent with symmetry requirements. Quenching experiments indicate that nucleation of the NiHfSi phase in NiAI(Hf) alloys is aided by the formation of NiAl group of zone axes (111) vacancy loops that form on the NiAl /111/ planes.

Garg, A.↗
NASA NTRS2007

Lu-Hf and Sm-Nd Isotopic Studies of Shergottites and Nakhlites: Implications for Martian Mantle Sources

We present a new Lu-Hf and Sm-Nd isotope systematics study of four enriched shergottites (Zagami, Shergotty, NWA856 and Los Angeles), and three nakhlites (Nakhla, MIL03346 and Yamato 000593) in order to further understand processes occurring during the early differentiation of Mars and the crystallization of its magma ocean. Two fractions of the terrestrial petrological analogue of nakhlites, the Archaean Theo's flow (Ontario, Canada) were also measured. The coupling of Nd and Hf isotopes provide direct insights on the mineralogy of the melt sources. In contrast to Sm/Nd, Lu/Hf ratios can be very large in minerals such as garnet. Selective partial melting of garnet bearing mantle sources can therefore lead to characteristic Lu/Hf signatures that can be recognized with Hf-176/Hf-177Hf ratios.

Debaille, V.↗
DOE OSTI2022

Evaluation and Comparison of a New Robust Waveform Against Direct Sequence Spread Spectrum for HF

This paper provides a comprehensive performance comparison between a filter bank multicarrier spread-spectrum (FBMC-SS) waveform and a current robust military waveform; namely, MIL-STD-188-110D, Waveform 0, proposed for communications through ionospheric/skywave HF channels. Waveform 0 is effectively a direct sequence spread spectrum waveform that uses the Walsh multi-codes to enhance the information transmission rate. It may thus be referred to as Walsh-DSSS. FBMC-SS, on the other hand, makes use of filter banks to provide excellent performance when the received signal is subject to partial band interference. Successful application of FBMC-SS for communications across skywave HF channels has been previously demonstrated, both theoretically and through experimental work. However, very little has been done to contrast FBMC-SS against Walsh-DSSS. The goal of this paper is to first add new features to FBMC-SS to bring it on par with Walsh- DSSS. These features include: (i), introduction of multi-codes that achieve a comparable (or better) data rate to the Walsh-DSSS; and (ii), addition of a scrambling step applied to the multi-codes to make the receiver detection robust against widely spread multipaths. With this established, in the second part of the paper, we examine the performance of the developed FBMC-SS against Walsh-DSSS when both are applied for communications across skywave HF channels. The two waveforms are compared both through a theoretical study and through experimental works across several skywave channels ranging from hundreds to thousands of kilometers.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2020

Materials Data on Hf(PS3)2 by Materials Project

Hf(PS3)2 crystallizes in the orthorhombic Fdd2 space group. The structure is three-dimensional. Hf4+ is bonded in an octahedral geometry to six S2- atoms. There are two shorter (2.54 Å) and four longer (2.57 Å) Hf–S bond lengths. P4+ is bonded in a trigonal non-coplanar geometry to three S2- atoms. There are a spread of P–S bond distances ranging from 2.03–2.05 Å. There are three inequivalent S2- sites. In the first S2- site, S2- is bonded in an L-shaped geometry to one Hf4+ and one P4+ atom. In the second S2- site, S2- is bonded in a water-like geometry to one Hf4+ and one P4+ atom. In the third S2- site, S2- is bonded in an L-shaped geometry to one Hf4+ and one P4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(CuP)2 by Materials Project

Hf(CuP)2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Hf4+ is bonded to six equivalent P3- atoms to form HfP6 octahedra that share corners with twelve equivalent CuP4 tetrahedra, edges with six equivalent HfP6 octahedra, and edges with six equivalent CuP4 tetrahedra. All Hf–P bond lengths are 2.66 Å. Cu1+ is bonded to four equivalent P3- atoms to form CuP4 tetrahedra that share corners with six equivalent HfP6 octahedra, corners with six equivalent CuP4 tetrahedra, edges with three equivalent HfP6 octahedra, and edges with three equivalent CuP4 tetrahedra. The corner-sharing octahedra tilt angles range from 17–55°. There are three shorter (2.31 Å) and one longer (2.40 Å) Cu–P bond lengths. P3- is bonded to three equivalent Hf4+ and four equivalent Cu1+ atoms to form a mixture of distorted corner and edge-sharing PHf3Cu4 pentagonal bipyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(FeSi)2 by Materials Project

Hf(FeSi)2 crystallizes in the orthorhombic Pbcm space group. The structure is three-dimensional. Hf4+ is bonded in a 6-coordinate geometry to eight Si4- atoms. There are a spread of Hf–Si bond distances ranging from 2.70–3.07 Å. There are two inequivalent Fe2+ sites. In the first Fe2+ site, Fe2+ is bonded in a 5-coordinate geometry to five Si4- atoms. There are a spread of Fe–Si bond distances ranging from 2.28–2.40 Å. In the second Fe2+ site, Fe2+ is bonded in a 7-coordinate geometry to two equivalent Fe2+ and five Si4- atoms. Both Fe–Fe bond lengths are 2.51 Å. There are a spread of Fe–Si bond distances ranging from 2.38–2.48 Å. There are two inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 9-coordinate geometry to four equivalent Hf4+ and five Fe2+ atoms. In the second Si4- site, Si4- is bonded in a 11-coordinate geometry to four equivalent Hf4+, five Fe2+, and two equivalent Si4- atoms. Both Si–Si bond lengths are 2.51 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(SiNi)2 by Materials Project

Hf(NiSi)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Hf4+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Hf–Si bond lengths are 2.89 Å. Ni2+ is bonded to four equivalent Si4- atoms to form a mixture of corner and edge-sharing NiSi4 tetrahedra. All Ni–Si bond lengths are 2.26 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Hf4+, four equivalent Ni2+, and one Si4- atom. The Si–Si bond length is 2.31 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(SeCl6)2 by Materials Project

Hf(SeCl6)2 crystallizes in the orthorhombic Fdd2 space group. The structure is three-dimensional. Hf4+ is bonded to six Cl1- atoms to form HfCl6 octahedra that share corners with two equivalent SeCl6 octahedra and edges with two equivalent SeCl6 octahedra. The corner-sharing octahedral tilt angles are 48°. There are a spread of Hf–Cl bond distances ranging from 2.44–2.49 Å. Se4+ is bonded to six Cl1- atoms to form distorted SeCl6 octahedra that share a cornercorner with one HfCl6 octahedra and an edgeedge with one HfCl6 octahedra. The corner-sharing octahedral tilt angles are 48°. There are a spread of Se–Cl bond distances ranging from 2.19–2.96 Å. There are six inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Se4+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Se4+ atom. In the third Cl1- site, Cl1- is bonded in a distorted water-like geometry to one Hf4+ and one Se4+ atom. In the fourth Cl1- site, Cl1- is bonded in a single-bond geometry to one Se4+ atom. In the fifth Cl1- site, Cl1- is bonded in a distorted single-bond geometry to one Hf4+ and one Se4+ atom. In the sixth Cl1- site, Cl1- is bonded in a distorted water-like geometry to one Hf4+ and one Se4+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(CoSi)2 by Materials Project

Hf(CoSi)2 crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Hf4+ is bonded in a distorted body-centered cubic geometry to eight equivalent Si4- atoms. All Hf–Si bond lengths are 2.89 Å. Co2+ is bonded to four equivalent Si4- atoms to form a mixture of edge and corner-sharing CoSi4 tetrahedra. All Co–Si bond lengths are 2.24 Å. Si4- is bonded in a 9-coordinate geometry to four equivalent Hf4+, four equivalent Co2+, and one Si4- atom. The Si–Si bond length is 2.33 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(MoO4)2 by Materials Project

HfMo2O8 crystallizes in the trigonal P-31c space group. The structure is two-dimensional and consists of two HfMo2O8 sheets oriented in the (0, 0, 1) direction. there are two inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded to six O2- atoms to form HfO6 octahedra that share corners with six equivalent MoO4 tetrahedra. All Hf–O bond lengths are 2.07 Å. In the second Hf4+ site, Hf4+ is bonded to six equivalent O2- atoms to form HfO6 octahedra that share corners with six equivalent MoO4 tetrahedra. All Hf–O bond lengths are 2.08 Å. Mo6+ is bonded to four O2- atoms to form MoO4 tetrahedra that share corners with three HfO6 octahedra. The corner-sharing octahedra tilt angles range from 9–23°. There are a spread of Mo–O bond distances ranging from 1.73–1.82 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a bent 150 degrees geometry to one Hf4+ and one Mo6+ atom. In the second O2- site, O2- is bonded in a linear geometry to one Hf4+ and one Mo6+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one Mo6+ atom. In the fourth O2- site, O2- is bonded in a linear geometry to one Hf4+ and one Mo6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Hf(Nb2B3)4 by Materials Project

Hf(Nb2B3)4 crystallizes in the orthorhombic Immm space group. The structure is three-dimensional. Hf4+ is bonded to twelve B2- atoms to form a mixture of edge and face-sharing HfB12 cuboctahedra. There are eight shorter (2.48 Å) and four longer (2.53 Å) Hf–B bond lengths. There are four inequivalent Nb+2.50+ sites. In the first Nb+2.50+ site, Nb+2.50+ is bonded in a 7-coordinate geometry to seven B2- atoms. There are a spread of Nb–B bond distances ranging from 2.40–2.58 Å. In the second Nb+2.50+ site, Nb+2.50+ is bonded in a 7-coordinate geometry to seven B2- atoms. There are a spread of Nb–B bond distances ranging from 2.39–2.59 Å. In the third Nb+2.50+ site, Nb+2.50+ is bonded in a 7-coordinate geometry to seven B2- atoms. There are a spread of Nb–B bond distances ranging from 2.39–2.58 Å. In the fourth Nb+2.50+ site, Nb+2.50+ is bonded to twelve B2- atoms to form a mixture of edge and face-sharing NbB12 cuboctahedra. There are eight shorter (2.48 Å) and four longer (2.51 Å) Nb–B bond lengths. There are six inequivalent B2- sites. In the first B2- site, B2- is bonded in a 9-coordinate geometry to six Nb+2.50+ and three B2- atoms. There is one shorter (1.82 Å) and two longer (1.85 Å) B–B bond length. In the second B2- site, B2- is bonded in a 9-coordinate geometry to six Nb+2.50+ and three B2- atoms. Both B–B bond lengths are 1.85 Å. In the third B2- site, B2- is bonded in a 9-coordinate geometry to four equivalent Hf4+, two equivalent Nb+2.50+, and three B2- atoms. There is one shorter (1.84 Å) and two longer (1.85 Å) B–B bond length. In the fourth B2- site, B2- is bonded in a 9-coordinate geometry to seven Nb+2.50+ and two equivalent B2- atoms. In the fifth B2- site, B2- is bonded in a 9-coordinate geometry to seven Nb+2.50+ and two equivalent B2- atoms. In the sixth B2- site, B2- is bonded in a 9-coordinate geometry to two equivalent Hf4+, five Nb+2.50+, and two equivalent B2- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2023

APC Nb 3 Sn superconductors based on internal oxidation of Nb–Ta–Hf alloys

In the last few years, a new type of Nb 3 Sn superconducting composite, containing a high density of artificial pinning centers (APC) generated via an internal oxidation approach, has demonstrated a significantly superior performance relative to present, state-of-the-art commercial Nb3Sn conductors. This was achieved via the internal oxidation of Nb-4at.%Ta-1at.%Zr alloy. On the other hand, our recent studies have shown that internal oxidation of Nb–Ta–Hf alloys can also lead to dramatic improvements in Nb 3 Sn performance. Here in this work we follow up on this latter approach, fabricating a 61-stack APC wire based on the internal oxidation of Nb-4at.%Ta-1at.%Hf alloy, and compare its critical current density (J c ) and irreversibility field with APC wires made using Nb-4at.%Ta-1at.%Zr. A second goal of this work was to improve the filamentary design of APC wires in order to improve their wire quality and electromagnetic stability. Our new modifications have led to significantly improved residual resistivity ratio and stability in the conductors, while still keeping non-Cu J c at or above the conductor J c specification required by the proposed Future Circular Collider. Further improvement via optimization of the wire recipe and design is ongoing. Finally, additional work needed to make APC conductors ready for applications in magnets is discussed.

43 PARTICLE ACCELERATORS↗