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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

C/He abundances in WC stars

Recombination theory has been used to determine the C/He abundances in 17 southern WC stars from spectra in the H and K bands. An LTE treatment of C II provides C/He values in the 0.04-0.3 range, by number, and maximum allowance for possible non-LTE effects yields values in the 0.1-0.7 range, by number. C/He is shown to decrease from WC4 to WC7. The ionization balance is found to be lower than in previous reports. He(+)/He(2+) values are between 2.6 and 3.0 for WC5-8 stars, increasing to 7 for WC9 stars. Continuum slopes and corrections for the emission line contributions to the H and K magnitudes are evaluated.

Smith, Lindsey F.↗
NASA NTRS1989

A case study of a WC planetary nebula nucleus - Henize 2-99

The WC spectrum of the nucleus of the planetary nebula Henize 2-99. Fluxes are given, emission lines are identified, and blends are described. The most powerful emissions are C III, C II, and C IV. O, H, and Si lines are also observed, but little stellar nitrogen is found except for N V. The interstellar extinction is estimated at c = 0.9 + or - 0.2. Blackbody, Zanstra, and Stoy temperatures are found to be 70,000 K, 26,000 K, and 27,000 K, respectively. It is shown that He 2-99 is binebulous with a prominent enhancement in H-alpha along the minor axis. The structural characteristics of He 2-99 are very similar to BD +30 deg 3639 and NGC 40.

Kaler, James B.↗
NASA NTRS1989

Mid-infrared spectra of WC 9 stars - The composition of circumstellar and interstellar dust

Broad emission features at about 7.7 microns and absorption features at about 6 and 10 microns observed from the WC 9 stars AFGL 2104 and Ve 2-45 are analyzed. The 7.7-micron feature is shown to resemble the well-known PAH band attributed to CC stretching modes in carbonaceous materials. The results suggest a low H abundance in the outflow of these objects, and that, given a strong UV source, all C-rich dust-enshrouded objects will show (some of) the IR emission bands. It is noted that at least 6 percent of the C and 4 percent of the O are locked up in C=O groups in interstellar silicates.

Cohen, M.↗
NASA NTRS1993

C III spectra in WC Wolf-Rayet stars - Does collisional excitation dominate?

A direct comparison of the spectra emitted by an improved collisionally excited C III atomic model, with observations of C III spectra in Wolf-Rayet WC stars, shows agreement for UV, visible, and near-infrared lines including lines usually considered to be recombination lines. The agreement implies high-density and temperature source conditions corresponding to log (Ne Te) is greater than 16 as a lower limit, whereas most current modeling assumes log (Ne Te) is less than 15.5. This raises questions concerning the photoionization/recombination assumptions on which most WR modeling is based. Recent models are discussed from this point of view.

Kastner, S. O.↗
NASA NTRS1995

An IRAS-based search for new Dusty Late-Type WC Wolf-Rayet stars

I have examined all Infrared Astronomical Satellite (IRAS) data relevant to the 173 Galactic Wolf-Rayet (W-R) stars in an updated catalog, including the 13 stars newly discovered by Shara and coworkers. Using the W-R coordinates in these lists, I have examined the IRAS Point Source Catalog (PSC), the Faint Source Catalog, and the Faint Source Reject Catalog, and have generated one-dimensional spatial profiles ('ADDSCANs') and two-dimensional full-resolution images ('FRESCOs'). The goal was to assemble the best set of observed IRAS color indices for different W-R types, in particular for known dusty late-type WC Wolf-Rayet (WCL) objects. I have also unsuccessfully sought differences in IRAS colors and absolute magnitudes between single and binary W-R stars. The color indices for the entire ensemble of W-R stars define zones in the IRAS color-color plane. By searching the PSC for otherwise unassociated sources that satisfy these colors, I have identified potential new W-R candidates, perhaps too faint to have been recognized in previous optical searches. I have extracted these candidates' IRAS low-resolution spectrometer (LRS) data and compared the spectra with the highly characteristic LRS shape for known dusty WCL stars. The 13 surviving candidates must now be examined by optical spectroscopy. This work represents a much more rigorous and exhaustive version of the LRS study that identified IRAS 17380 - 3031 (WR98a) as the first new W-R (WC9) star discovered by IRAS. This search should have detected dusty WCL stars to a distance of 7.0 kpc from the Sun, for the absolute value of l greater than 30 deg, and to 2.9 kpc even in the innermost Galaxy. For free-free-dominated W-R stars the corresponding distances are 2.5 and 1.0 kpc, respectively.

Cohen, Martin↗
NASA NTRS1995

An IRAS-Based Search for New Dusty Late-Type WC Wolf-Rayet Stars

I have examined all Infrared Astronomical Satellite (IRAS) data relevant to the 173 Galactic Wolf-Rayet (W-R) stars in an updated catalog, including the 13 stars newly discovered by Shara and coworkers. Using the W-R coordinates in these lists, I have examined the IRAS Point Source Catalog (PSC), the Faint Source Catalog, and the Faint Source Reject Catalog, and have generated one-dimensional spatial profiles, 'ADDSCANs', and two-dimensional full-resolution images, 'FRESCOS'. The goal was to assemble the best set of observed IRAS color indices for different W-R types, in particular for known dusty late-type WC Wolf-Rayet (WCL) objects. I have also unsuccessfully sought differences in IRAS colors and absolute magnitudes between single and binary W-R stars. The color indices for the entire ensemble of W-R stars define zones in the IRAS color-color ([12] - [25], [25] - [60])-plane. By searching the PSC for otherwise unassociated sources that satisfy these colors, I have identified potential new W-R candidates, perhaps too faint to have been recognized in previous optical searches. I have extracted these candidates' IRAS low-resolution spectrometer (LRS) data and compared the spectra with the highly characteristic LRS shape for known dusty WCL stars. The 13 surviving candidates must now be ex amined by optical spectroscopy. This work represents a much more rigorous and exhaustive version of the LRS study that identified IRAS 17380 - 3031 (WR98a) as the first new W-R (WC9) star discovered by IPAS. This search should have detected dusty WCL stars to a distance of 7.0 kpc from the Sun, for l is greater than 30 degrees, and to 2.9 kpc even in the innermost galaxy. For free-free-dominated W-R stars the corresponding distances are 2.5 and 1.0 kpc, respectively.

Cohen, Martin↗
DOE OSTI2020

Materials Data on WC by Materials Project

WC1 is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. W4+ is bonded to six equivalent C4- atoms to form a mixture of edge and corner-sharing WC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All W–C bond lengths are 2.19 Å. C4- is bonded to six equivalent W4+ atoms to form a mixture of edge and corner-sharing CW6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on WC by Materials Project

WC1 is Tungsten Carbide structured and crystallizes in the hexagonal P-6m2 space group. The structure is three-dimensional. W4+ is bonded to six equivalent C4- atoms to form a mixture of distorted corner, edge, and face-sharing WC6 pentagonal pyramids. All W–C bond lengths are 2.21 Å. C4- is bonded to six equivalent W4+ atoms to form a mixture of distorted corner, edge, and face-sharing CW6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(WC)4 by Materials Project

UW4C4 crystallizes in the tetragonal P4/m space group. The structure is three-dimensional. there are two inequivalent U4+ sites. In the first U4+ site, U4+ is bonded in a body-centered cubic geometry to eight equivalent C4- atoms. All U–C bond lengths are 2.57 Å. In the second U4+ site, U4+ is bonded in a body-centered cubic geometry to eight equivalent C4- atoms. All U–C bond lengths are 2.50 Å. There are two inequivalent W3+ sites. In the first W3+ site, W3+ is bonded in a rectangular see-saw-like geometry to four C4- atoms. There are a spread of W–C bond distances ranging from 2.15–2.19 Å. In the second W3+ site, W3+ is bonded to four C4- atoms to form corner-sharing WC4 trigonal pyramids. There are a spread of W–C bond distances ranging from 2.08–2.11 Å. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to two equivalent U4+ and four W3+ atoms to form a mixture of corner, edge, and face-sharing CU2W4 octahedra. The corner-sharing octahedra tilt angles range from 0–68°. In the second C4- site, C4- is bonded to two equivalent U4+ and four W3+ atoms to form a mixture of corner, edge, and face-sharing CU2W4 octahedra. The corner-sharing octahedra tilt angles range from 0–67°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on WC by Materials Project

WC1 is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. W4+ is bonded in a body-centered cubic geometry to eight equivalent C4- atoms. All W–C bond lengths are 2.37 Å. C4- is bonded in a body-centered cubic geometry to eight equivalent W4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on WC by Materials Project

WC1 is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. W4+ is bonded to four equivalent C4- atoms to form corner-sharing WC4 tetrahedra. All W–C bond lengths are 2.04 Å. C4- is bonded to four equivalent W4+ atoms to form corner-sharing CW4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on U(WC)4 by Materials Project

UW4C4 crystallizes in the tetragonal P4/m space group. The structure is three-dimensional. there are two inequivalent U4+ sites. In the first U4+ site, U4+ is bonded in a body-centered cubic geometry to eight equivalent C4- atoms. All U–C bond lengths are 2.49 Å. In the second U4+ site, U4+ is bonded in a body-centered cubic geometry to eight equivalent C4- atoms. All U–C bond lengths are 2.53 Å. There are two inequivalent W3+ sites. In the first W3+ site, W3+ is bonded to four C4- atoms to form corner-sharing WC4 trigonal pyramids. There are one shorter (2.09 Å) and three longer (2.11 Å) W–C bond lengths. In the second W3+ site, W3+ is bonded in a rectangular see-saw-like geometry to four C4- atoms. There are a spread of W–C bond distances ranging from 2.13–2.16 Å. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to two equivalent U4+ and four W3+ atoms to form a mixture of edge, face, and corner-sharing CU2W4 octahedra. The corner-sharing octahedra tilt angles range from 0–67°. In the second C4- site, C4- is bonded to two equivalent U4+ and four W3+ atoms to form a mixture of edge, face, and corner-sharing CU2W4 octahedra. The corner-sharing octahedra tilt angles range from 0–68°.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Mechanical evaluation of WC-Co materials with varying microstructures

Tungsten carbide–cobalt materials are useful in a variety of extreme applications due to a desirable blend of properties, yet the technology has not significantly changed since their initial development in the 1920s. The mechanical properties of this class of materials is highly dependent on two variables, the size of the tungsten carbide grains, and the amount of binder phase present in the final body. In this study, the amount of binder phase is isolated across three commercial materials from the same manufacturer with three different grain sizes to investigate the effect on mechanical properties. The mechanical properties investigated are indentation hardness, flexure and tensile strength, as well as fracture toughness. In general, an increase in hardness and tensile strength with decreasing grain size was observed, while the fracture toughness showed the opposite trend with toughness increasing with increasing grain size. The flexure strength results did not show a correlation to grain size. Fractographic analysis identified the dominant strength-limiting flaw for each sample, which largely were in the form of porosity. Other flaws types, such as inclusions from the milling process, clusters of large grains, and machining cracks from the surface finishing process, were also identified. Finally, Weibull analysis was performed and deemed appropriate for analysis of these materials, but strength-size scaling was not conducted due to the variability in the strength-limiting feature between the different specimen geometries.

36 MATERIALS SCIENCE↗