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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Fused slurry silicide coatings for columbium alloys reentry heat shields. Volume 1: Evaluation analysis

The R-512E (Si-20Cr-20Fe) fused slurry silicide coating process was optimized to coat full size (20in x 20in) single face rib and corrugation stiffened panels fabricated from FS-85 columbium alloy for 100 mission space shuttle heat shield applications. Structural life under simulated space shuttle lift-off stresses and reentry conditions demonstrated reuse capability well beyond 100 flights for R-512E coated FS-85 columbium heat shield panels. Demonstrated coating damage tolerance showed no immediate structural failure on exposure. The FS-85 columbium alloy was selected from five candidate alloys (Cb-752, C-129Y, WC-3015, B-66 and FS-85) based on the evaluation tests which have designed to determine: (1) change in material properties due to coating and reuse; (2) alloy tolerance to coating damage; (3) coating emittance characteristics under reuse conditions; and (4) new coating chemistries for improved coating life.

Fitzgerald, B.↗
NASA NTRS1974

The effects of composition on mechanical properties of W-4Re-Hf-C alloys

Studies were made of the effects of alloy composition on the mechanical behavior of as-worked W-4Re-Hf-C alloys containing up to about 0.8 mol % Hfc. Extracted second-phase particles were analyzed and related to alloy composition and creep strength. While strengthening is attributed to HfC particles, the presence of excess hafnium or carbon (above the calculated amounts for stoichiometric HfC) in swaged W-4Re-Hf-C alloys generally causes a reduction of the high-temperature (1930 C) tensile strength; maximum creep strength is, however, indicated for alloys with a slight (about 0.05 to 0.1 at. %) excess of hafnium. Particle strengthening is reduced by WC in solid solution with HfC for allow compositions with an excess of carbon. The low-temperature ductility of worked W-4Re-Hf-C alloys appears to be far more dependent on the amount of excess C or Hf present than on the HfC particle content in the range studies.

Witzke, W. R.↗
NASA NTRS1974

Photoelectric spectrophotometry of Wolf-Rayet stars

Photoelectric spectrum scans of five southern Wolf-Rayet stars in the spectral range lambda lambda 4600-4720 were analyzed to study the variability of brightness and of emission line strengths. No variations of any kind in short time scale were found. However, in WC stars night-to-night variations of three to four percent were detected in the emission line strengths.

Bahng, J. D. R.↗
NASA NTRS1975

Photoelectric spectrophotometry of Wolf-Rayet stars

Photoelectric spectrum scans of five southern Wolf-Rayet stars in the spectral range 4600-4720 A were analyzed to study the variability of brightness and of emission line strengths. No variations of any kind in short time scale were found. However, in WC stars night-to-night variations of 3 to 4 per cent were detected in the emission line strengths.

Bahng, J. D. R.↗
NASA NTRS1977

Application of diffusion barriers to high modulus fibers

Barrier layers were coated onto high-modulus fibers, and nickel and titanium layers were overcoated as simulated matrix materials. The objective was to coat the high-strength fibers with unreactive selected materials without degrading the fibers. The fibers were tungsten, niobium, and single-crystal sapphire, while the materials used as barrier coating layers were Al2O3, Y2O3, TiC, ZrC, WC with 14% Co, and HfO2. An ion-plating technique was used to coat the fibers. The fibers were subjected to high-temperature heat treatments to evaluate the effectiveness of the barrier layer in preventing fiber-metal interactions. Results indicate that Al2O3, Y2O3, and HfO2 can be used as barrier layers to minimize the nickel-tungsten interaction. Further investigation, including thermal cycling tests at 1090 C, revealed that HfO2 is probably the best of the three.

Veltri, R. D.↗
NASA NTRS1978

An atlas of Copernicus ultraviolet spectra of Wolf-Rayet stars

An atlas of Copernicus UV scans is presented, and line identifications are tabulated, for the Wolf-Rayet stars Gamma-2 Vel (WC 8 + O7), HD 50896 (= EZ CMa; WN 5), and HD 92740 (WN 7). The atlas covers the wavelength ranges from 946.8 to 3182 A for Gamma-2 Vel, from 1012 to 1294 A for HD 50896, and from 1051 to 1243 A for HD 92740. The wavelengths include corrections for components of satellite velocity, earth velocity, and stellar heliocentric velocity; each spectral feature is classified as interstellar, photospheric, emission, UV-displaced P Cygni line absorption, or P Cygni line emission. UV-edge velocities of the P Cygni profiles are estimated, P Cygni profile types are discussed, and the results are compared with Copernicus scans of OB stars exhibiting UV P Cygni profiles. It is noted that: (1) the line-strength ratio of molecular hydrogen to atomic species appears to be substantially greater in the scans of the WN stars than in the Gamma-2 Vel scans; (2) some of the P Cygni profiles in Gamma-2 Vel differ significantly from the corresponding profiles in OB stars; and (3) there may be a slight inverse correlation between ejection velocities and excitation potentials in Gamma-2 Vel.

Johnson, H. M.↗
NASA NTRS1979

Catalog of far-ultraviolet objective-prism spectrophotometry: Skylab experiment S-019, ultraviolet steller astronomy

Ultraviolet stellar spectra in the wavelength region from 1300 to 5000 A (130 to 500) were photographed during the three manned Skylab missions using a 15 cm aperture objective-prism telescope. The prismatic dispersion varied from 58 A mm/1 at 1400 A to 1600 A mm/1 at 3000 A. Approximately 1000 spectra representing 500 stars were measured and reduced to observed fluxes. About 100 stars show absorption lines of Si IV, C IV, or C II. Numerous line features are also recorded in supergiant stars, shell stars, A and F stars, and Wolf-Rayet stars. Most of the stars in the catalog are of spectral class B, with a number of O and A type stars and a sampling of WC, WN, F and C type stars. Spectrophotometric results are tabulated for these 500 stars.

Henize, K. G.↗
NASA NTRS1978

Static evaluation of surface coatings for compliant gas bearings in an oxidizing atmosphere to 650 C

Hard wear-resistant coatings and soft low shear strength coatings were developed for an air-lubricated compliant journal bearing for a future automotive gas turbine engine. The coatings were expected to function in either 540 or 650 C ambient. Soft lubricant coatings were generally limited in temperature. Therefore emphasis was on the hard wear-resistant coatings. The coating materials covered were TiC, B4C, Cr3C2, WC, SiC, CrB2, TiB2, Cr2O3, Al2O3, Si3N4, Tribaloy 800, CaF2, CaF2-BaF2 eutectic, Ni-Co, silver, CdO-graphite and proprietary compounds. The coatings on test coupons were subjected to static oven screening tests. The test consisted of exposure of material samples in an oven for 300 h at the maximum temperature (540 or 650 C) and ten temperature cycles from room temperature to the maximum service temperature. On the basis of the specimen examinations the following coatings were recommended for future wear tests: TiC (sputtered), Cr2O3 (sputtered), Si3N4 (sputtered), CdO and graphite (fused), Kaman DES (a proprietary coating), CrB2 (plasma sprayed), Cr3C2 (detonation gun) and NASA PS-106 (plasma sprayed).

Bhushan, B.↗
NASA NTRS1980

Airborne lightning characterization

A WC-130 aircraft was instrumented with wideband electromagnetic field sensors and flown near active thunderstorms to obtain data on the characteristics of nearby and direct strike lightning. An electric field ground station and time-of-arrival network provided time correlated data to identify the three dimensional locations of the discharge and the different events in the lightning flash. A description of the sensors, calibration procedures, and recording equipment is presented. Data are presented on return stroke characteristics in the 5 to 50 km range.

Baum, R. K.↗
NASA NTRS1981

Non-noble catalysts and catalyst supports for phosphoric acid fuel cells

Four different samples of the cubic alloys W sub x-1 Ti sub x C sub 1-y were prepared and found to be active and CO tolerant. When the activities of these cubic alloys were weighted by the reciprocal of the square of the W exchange, they displayed magnitudes and dependence on bulk C deficiency comparable to those of highly active forms of WC. It is concluded that they may offer important insight into the nature of the active sites on, and means for improving the performance of, W-C anode catalysts for use in phosphoric acid fuel cells.

Mcalister, A. J.↗
NASA NTRS1981

Spectral energy distributions of hot stars with circumstellar dust

Combined spectral energy distribution curves of six Ae/Be stars (BD+61 deg 154, AB Aur, V380 Ori, HD 259431, ZCMa, and BD+40 deg 4124), five peculiar shell stars (HD 31648, HD 45677, HD 50138, HD 163296, and HD 190073), and the peculiar central object in the Red Rectangle nebula (HD 44179), obtained with the IUE and a variety of ground-based optical and infrared telescope systems, are presented, covering the wavelength range of approximately 1300 A to 12.5 microns. The observations are reviewed, and include ultraviolet observations, low-resolution absolute visual spectrophotometry, moderate-resolution relative visual spectrophotometry, and infrared photometry. For most of the objects the ratio of the flux deficiency for lambda equals less than 1 micron to the flux excess for lambda equals greater than 1 micron is approximately unity. Only two of the objects (AB Aur and HD 163296) possess a strong emission feature at 9.7 microns, while one other (HD 31648) may have a weak 9.7 micron emission feature. Most of the objects have a broad, smooth, infrared emission curve resembling those seen in some WC stars. It is concluded that the dust surrounding these stars may be different from that seen in the diffuse interstellar medium.

Sitko, M. L.↗
NASA NTRS1981

Non-noble catalysts and catalyst supports for phosphoric acid fuel cells

Tungsten carbide, which is active for hydrogen oxidation, is CO tolerant and has a hexagonal structure is discussed. Titanium carbide is inactive and has a cubic structure. Four different samples of the cubic alloys W sub x-1Ti sub XC sub 1-y were found to be active and CO tolerant. When the activities of these cubic alloys are weighted by the reciprocal of the square to those of highly forms of WC. They offer important insight into the nature of the active sites on W-C anode catalysts for use in phosphoric acid fuel cells.

Mcalister, A. J.↗
NASA NTRS1982

Ultraviolet, visual, and infrared observations of the WC7 variable HD 193793

Low-resolution IUE data are used to explore the ultraviolet extinction toward the Wolf-Rayet star HD 193793 and to search for ultraviolet variability that might relate to the infrared variability. High-dispersion IUE observations are used to investigate the nature of the stellar wind of the star and to search for anomalies in the interstellar line spectrum that might be expected to be found toward a star that has recently formed a dust shell. Finally, the ultraviolet and new visual and infrared data are combined to investigate the full energy distribution of this unusual source. The energy distribution is found to extend from 0.12 to 12.5 microns, and the ultraviolet data suggest a normal WC-7 type star. A wind terminal speed of about 3000 km/s is implied by the data, as well as an E(B-V) value of 0.85. The dereddened ultraviolet to visual energy distribution is consistent with a star having effective temperature of about 43,000 K.

Fitzpatrick, E. L.↗
NASA NTRS1982

Wolf-Rayet phenomena

An outline is presented of what is currently known about the properties of stars showing Wolf-Rayet (W-R) phenomena, taking into account also the directions in which future work is leading. W-R spectra are found to be primarily an emission line spectrum superimposed on a 'hot' continuous spectrum. P Cygni absorption components are observed for some lines in some stars. A fact not realized when Thomas (1968) discussed W-R spectra is that a very few W-R stars have intrinsic absorption lines. On the basis of the spectroscopic observations, it could now be inferred that an optically thick stellar wind is involved. Many of the WN subtypes do contain some carbon. The WC subtypes contain little or no nitrogen. Attention is given to absolute visual magnitudes of W-R stars, the heterogeneity of W-R spectra, transition W-R spectra, mass loss rates, very luminous W-R objects, theoretical aspects of stellar structure and stellar winds, and evolutionary scenarios.

Conti, P. S.↗
NASA NTRS1985

Neutron-rich nuclei in cosmic rays and Wolf-Rayet stars

Wolf-Rayet stars figure prominently in astrophysical research. As a bonus, they seem to offer, in the recent past, an interesting connection between classical astronomy and high energy astrophysics due to their unusual composition and their huge mechanical power. The material flowing from WC stars (carbon-rich WR stars) contains gas which has been processed through core-helium burning, i.e., considerably enriched into 12C,16O, 22Ne, and 25,26Mg. This composition is reminiscent of the cosmic ray source anomalies. Encouraging agreement is obtained with observation in the mass range 12 A 26 assuming acceleration of wind particles at the shock that delineates the WR cavity, and adequate dilution with normal cosmic rays, but silicon poses.

Prantzos, N.↗
NASA NTRS1985

Analysis of ultraviolet atmospheric eclipses in the Wolf-Rayet binary CV Serpentis

While no eclipses deeper than 0.04 mag are noted in the present UV spectra, covering one-half of an orbital cycle of CV Ser, in the electron scattering continuum at 2400-3200 A or in fine error sensor observations, marked atmospheric eclipses of up to 0.5 mag depth are observed in individual strong lines and over large ranges of the continuum at shorter wavelengths. The flux above the continuum in the C II 1247 A, Si IV 1400 A, and Si IV 1723 lines showed similar phase dependence with emission weakening, as well as with the emission's going into absorption as phase progresses from superior to inferior conjunction of the WC star (primary eclipse). These observations show effects very similar to the behavior of WN stars in the UV.

Eaton, J. A.↗
NASA NTRS1987

Optical spectroscopy of IRAS sources with infrared emission bands. 1: IRAS 21282+5050 and the diffuse interstellar bands

Spectroscopy of the starlike optical counterpart to IRAS 21282+5050, a source with the hydrocarbon infrared emission band spectrum, shows an 07(f)-(WC11) planetary nebula nucleus suffering an extinction of 5.7 mag. Emission line widths in the WC spectrum are only approx. 100 km/s, indicating a very slow stellar wind. Optical diffuse interstellar bands (DIBs) are prominent. Five DIBs are strongly enhanced, namely lamda lamda 5797, 6196, 6203, 6283, and 6613. The presence of circumstellar hydrocarbon molecules may explain both the infrared emission bands and the enhanced DIBs.

Cohen, Martin↗
NASA NTRS1988

Carbon and nitrogen lines in the spectra of Wolf-Rayet stars

The one-representative-point radiative transfer theory of Castor and van Blerkom (1970) is used to predict the relative energies in emission lines of the ions of carbon and nitrogen in Wolf-Rayet atmospheres for a wide range of parameters. The predicted ratios are compared with observed relative energies of lines in the visible and ultraviolet spectral ranges of six Wolf-Rayet stars. It is found that the lower levels of C II, C III, N III, and N IV are strongly overpopulated relative to their populations in LTE. The differences between WC and WN spectra appear to be due chiefly to a difference in electron temperature in the line-emitting regions. The typical volume of stars studied is estimated to be in the range of 10 to the 41st to 10 to the 44th cu cm. Possible ways in which the line-emitting regions may be arranged around the star are discussed, noting that the high-temperature line-emitting plasma may lie in a thin annular disk approximately 10 to the 15th cm from the star.

Bhatia, A. K.↗