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At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

The origin and history of the metal and sulfide components of chondrules

Instrumental and radiochemical neutron activation analysis is used to determine the concentrations of 14 siderophile and other nonlithophilic elements in 31 chondrules from the extremely unequilibrated chondrite Semarkona. The results are presented in tables and graphs, characterized in detail, and compared with the results obtained for lithophile elements in the same samples by Grossman and Wasson (1983). The elements studied are found to be significantly more fractionated than the lithophile elements, with variations in chondrule/whole-rock abundances of up to a factor of 1000, a mean ratio of 0.2, and differences between Ni-rich and Ni-depleted chondrules. It is argued that the metal and sulfides in the chondrules represent the composition of the solar nebula before chondrule formation and already contained the siderophile and chalcophile elements, although some Fe was contained in silicates along with Ni, Co, Au, Ge and Se. The segregation of metals during a molten stage is considered of minor importance.

Grossman, J. N.↗
NASA NTRS1983

A potential energy scaling Monte Carlo simulation of thin film nucleation and growth

The initial growth of thin Ge fims on the (100) surface of an Fe substrate is investigated theoretically by means of Monte Carlo simulations based on a potential-energy-scaling technique. The substrate is modeled as a 20 x 20-square array with periodic boundary conditions, as described by Heinbockel et al. (1983), and the movement of surface atoms under the influence of the substrate interaction potential and the lateral interaction of neighboring atoms is explored via continuous updating (on the time scale of single events) of the potential energy at each site in the array. Results for the clustering of nine dispersed atoms over 1.0 s at 600 K and for deposition at 5 x 10 to the -14th/sq cm s over 2.0 s at 500 K are presented graphically.

Outlaw, R. A.↗
NASA NTRS1985

Bocaiuva - A silicate-inclusion bearing iron meteorite related to the Eagle-Station pallasites

On the basis of its metal composition, the unique Bocaiuva meteorite, which consists of major metal having a high Ge/Ga ratio and minor silicates, appears distantly related to certain iron meteorites with similar Ge contents and similar Ge/Ga ratios. Detailed comparisons with six such irons shows, however, that none of these is closely related to Bocaiuva. The composition and texture of the Bocaiuva metal-silicate assembly indicate mixing in an impact event. It is suggested that the Eagle-Station pallasites were also formed by impact heating rather than by a long-lived internal heat source.

Malvin, D. J.↗
NASA NTRS1985

AES and LEED study of the zinc blende SiC(100) surface

Auger and LEED measurements have been carried out on the (100) surface of zinc blende SiC. Two different phases of the clean surface, in addition to two kinds of oxygen-covered surfaces, have been obtained, identified, and discussed. In the oxygen-covered surface, the oxygen is bonded to the Si. The carbon-rich phase is reconstructed (2 x 1), similar to the (100) clean surfaces of Si, Ge, and diamond. The Si-topped surface is reconstructed. A model of alternating Si dimers is suggested for this surface.

Dayan, M.↗
NASA NTRS1985

Far-infrared transmittance of boron-implanted germanium at liquid-helium temperatures

The transmission of far-infrared radiation of 100-microns-wavelength through Ge wafers ion implanted with B was measured at a temperature of approximately 4 K. Transmittance ranged from approximately 0.5 to 0.08 for doses from 3 x 10 to the 12th to 3 x 10 to the 15th/sq cm. The resistivity at temperatures between 4 and 1 K, and the impurity profiles of the implanted layers were also measured and correlated with the infrared transmittance.

Hadek, V.↗
NASA NTRS1985

Fluid Dynamics and Thermodynamics of Vapor Phase Crystal Growth

The ground-based research effort under this program is concerned with systematic studies of the effects of variations: (1) of the relative importance of buoyancy-driven convection, and (2) of diffusion and viscosity conditions on crystal properties. These experimental studies are supported by thermodynamic characterizations of the systems, based on which fluid dynamic parameters can be determined. The specific materials under investigation include: the GeSe-GeI4, Ge-GeI4, HgTe-HgI2, and Hg sub (1-x)Cd sub (x) Te-HgI2 systems. Mass transport rate studies of the GeSe-GeI system as a function of orientation of the density gradient relative to the gravity vector demonstrated the validity of flux anomalies observed in earlier space experiments. The investigation of the effects of inert gases on mass flux yielded the first experimental evidence for the existence of a boundary layer in closed ampoules. Combined with a thorough thermodynamic analysis, a transport model for diffusive flow including chemical vapor transport, sublimation, and Stefan flow was developed.

Wiedemeier, H.↗
NASA NTRS1985

Bulk Formation of Metallic Glasses and Amorphous Silicon from the Melt

By using metallic glass compositions with a high relative glass transition temperature, such as Pd40Ni40P20, homogeneous nucleation also becomes negligible. Large (5g) masses of this alloys were obtained using a molten B2O3 flux. Presently, bulk glass formation in iron based glasses is being investigated. It is expected that if an undercooling of about 250K can be achieved in a Ge or Si melt, formation of the amorphous semiconductor phase (rather than the crystal) may be kinetically favored. The volumetric behavior of undercooled liquid Ga droplet dispersion is investigated by dilatometry. A theoretical model (both analytical and numerical) was developed for transient nucleation in glass forming melts. The model, originally designed for isothermal conditions, was extended to continuous quenching. It is being applied to glass formation in various metallic and oxide systems. A further refinement will be the inclusion of diffusion controlled interfacial rearrangements governing the growth of the crystal embryos.

Spaepen, F.↗
NASA NTRS1985

MCZ: Striations in CZ silicon crystals grown under various axial magnetic field strengths

Suppression of fluid flow instabilities in the melt by the axial magnetic field in Czochralski silicon crystal growth (AMCZ) is investigated precisely by a high-sensitivity striation etching in conjunction with temperature measurements. The magnetic strength (B) was varied up to 4.0 kG, incremented in 0.5 kG/5 cm crystal length. The convection flow was substantially suppressed at B 1.0 kG. A low oxygen level of 2-3 ppma and a high resistivity of 400 ohm-cm is achieved in the AMCZ silicon crystals at B 1.0 kG. Details of the striation formation as a function of B are presented. Computer simulation of the magnetohydrodynamics of the AMCZ silicon crystal growth are discussed briefly with regard to the solute, especially oxygen segregation at B=0, 1.0, and 2.0 kG. Earlier studies in the inverted Bridgman growth of InSb and Ge, which have established the cause and effect relationship between the convection in the melt and the striation formation as well as the suppression of the convections in the melt by transverse magnetic field are reviewed.

Kim, G. K. M.↗
NASA NTRS1986

Crystal growth of device quality GaAs in space

It was established that the findings on elemental semiconductors Ge and Si regarding crystal growth, segregation, chemical composition, defect interactions, and materials properties-electronic properties relationships are not necessarily applicable to GaAs (and to other semiconductor compounds). In many instances totally unexpected relationships were found to prevail. It was further established that in compound semiconductors with a volatile constituent, control of stoichiometry is far more critical than any other crystal growth parameter. It was also shown that, due to suppression of nonstoichiometric fluctuations, the advantages of space for growth of semiconductor compounds extend far beyond those observed in elemental semiconductors. A novel configuration was discovered for partial confinement of GaAs melt in space which overcomes the two major problems associated with growth of semiconductors in total confinement. They are volume expansion during solidification and control of pressure of the volatile constituent. These problems are discussed in detail.

Gatos, H. C.↗
NASA NTRS1985

Infrared and far-infrared laser magnetic resonance spectroscopy of the GeH radical - Determination of ground state parameters

The GeH radical has been detected in its ground 2 Pi state in the gas phase reaction of fluorine atoms with GeH4 by laser magnetic resonance techniques. Rotational transitions within both 2 Pi 1/2 and 2 Pi 3/2 manifolds have been observed at far-infrared wavelengths and rotational transitions between the two fine structure components have been detected at infrared wavelengths (10 microns). Signals have been observed for all five naturally occurring isotopes of germanium. Nuclear hyperfine structure for H-1 and Ge-73 has also been observed. The data for the dominant isotope (/Ge-74/H) have been fitted to within experimental error by an effective Hamiltonian to give a set of molecular parameters for the X 2 Pi state which is very nearly complete. In addition, the dipole moment of GeH in its ground state has been estimated from the relative intensities of electric and magnetic dipole transitions in the 10 micron spectrum to be 1.24(+ or - 0.10) D.

Brown, J. M.↗
NASA NTRS1985

Net thrust calculation sensitivity of an afterburning turbofan engine to variations in input parameters

The calculated value of net thrust of an aircraft powered by a General Electric F404-GE-400 afterburning turbofan engine was evaluated for its sensitivity to various input parameters. The effects of a 1.0-percent change in each input parameter on the calculated value of net thrust with two calculation methods are compared. This paper presents the results of these comparisons and also gives the estimated accuracy of the overall net thrust calculation as determined from the influence coefficients and estimated parameter measurement accuracies.

Hughes, D. L.↗
NASA NTRS1985

Chemical compositional study of 35 iron meteorites and its application in taxonomy

Structural and compositional data are reported as a guide to the classification of 35 iron meteorites. The Xinjiang iron meteorite, previously classified as III AB, is reclassified as III E on the basis of its lower Ga/Ni and Ge/Ni ratios, its wider, swollen kamacite bands, and the ubiquitous presence of haxonite, (Fe,Ni)22C. The Dongling (III CD) appears not to be a new meteorite, but to be paired with the Nantan. Four Antarctic iron meteorites, IAB Allan Hills A77250, A77263, A77289, and A77290, are classified as a paired meteorite because of their similarities in structure and in concentrations of various elements. It is shown that Cu shares certain properties with Ga and Ge, which makes them excellent taxonomic parameters.

Wang, D.↗
NASA NTRS1985

High-resolution observations of X-ray transitions in Fe XXV-XXIII

The wavelengths of X-ray transitions in Fe XXV-XXIII have been measured using a high-resolution spectrum reflected from the Ge(13-1) planes. A number of transitions have been resolved for the first time in solar flare spectra, and the contributions of the Fe XXIV n = 3 satellites to the Fe XXV parent lines are discussed. The QED contributions to the wavelengths of the Fe XXIV n = 3 satellite transitions have been determined.

Seely, J. F.↗
NASA NTRS1984

Power Sources Symposium, 31st, Atlantic City, NJ, June 11-14, 1984, Proceedings

The present conference on electrochemical power sources encompasses systems of such types as the thermoelectric, advanced rechargeable, lithium reserve, rechargeable, and nonrechargeable, nickel-cadmium and nickel-hydrogen rechargeable, lead-acid, nickel-zinc and nickel-iron rechargeable, nickel-cadmium and nickel-hydrogen rechargeable, and fuel cells. Attention is given to Si-Ge alloy multicouple technology, sodium-sulfur battery development status, the safety aspects of a rechargeable lithium C cell, fiber-structure electrodes for nickel-cadmium batteries, energy density improvements in Li/carbon monofluoride cells, zinc-air button cell technology, catalyzed cathodes for Li/SOCl2 cells, the effect of polymer structure on the rate capability of the lithium-iodine cell, and a methanol fuel cell powerplant.

Source record↗
NASA NTRS1985

X-29 initial flight test results

It is announced that the X-29 forward-swept-wing (FSW) aircraft has been built, with flight testing under way and proceeding smoothly. The X-29 is a single-seat, single-engine supersonic aircraft that blends an optimized FSW, a close-coupled near-coplar canard, an F-5A forward fuselage module employing two side-mounted engine inlets, and a new aft fuselage. An F404-GE-400 engine with afterburner provides about 16,000 lb of thrust. The X-29 was designed to be near neutrally stable in the supersonic region to minimize drag; it becomes highly unstable transonically and subsonically, which dictates the use of a computerized fly-by-wire flight control system capable of stabilizing the aircraft. The X-29 advanced technology demonstrator began flight testing on Dec. 14, 1984; by Sept. 26, 1985, its envelope had been expanded to 0.75 Mach, 350 knots estimated airspeed, and 30,000 feet altitude. The aircraft has flown with very few problems and aerodynamic, structural, and control system results have correlated well with predictions. Areas where prediction and performance are not so well correlated are noted.

Ishmael, S. D.↗
NASA NTRS1986

Theoretical electric dipole moments of SiH, GeH and SnH

Accurate theoretical dipole moments have been computed for the X2Pi ground states of Si(-)H(+) (0.118 D), Ge(+)H(-) (0.085 D), and Sn(+)H(-) (0.357 D). The trend down the periodic table is regular and follows that expected from the electronegativities of the group IV atoms. The dipole moment of 1.24 + or - 0.1 D for GeH recently derived by Brown, Evenson and Sears (1985) from the relative intensities of electric and magnetic dipole transitions in the 10-micron spectrum of the X2Pi state is seriously questioned.

Pettersson, L. G. M.↗
NASA NTRS1986

Design, construction and long life endurance testing of cathode assemblies for use in microwave high-power transmitting tubes

The cathode life test program sponsored by NASA Lewis Research Center at Watkins-Johnson Company has been in continuous operation since 1972. Its primary objective has been to evaluate the long life capability of barium dispenser cathodes to produce emission current densities of 2 A sq. cm. or more in an operational environment simulating that of a highpower microwave tube. The life test vehicles were equipped with convergent flow electron guns, drift space tubes with solenoid magnets for electron beam confinement and water-cooled depressed collectors. A variety of cathode types has been tested, including GE Tungstate, Litton Impregnated, Philips Type B and M, Semicon types S and M, and Spectra-Mat Type M. Recent emphasis has been on monitoring the performance of Philips Type M cathodes at 2 A sq. cm. and Sprectra-Mat and Semicon Type M cathodes at 4 A sq. cm. These cathodes have been operated at a constant current of 616 mA and a cathode anode voltage on the order of 10 kV. Cathode temperatures were maintained at 1010 C true as measured from black body holes in the backs of the cathodes. This report presents results of the cathode life test program from July l982 through April l986. The results include hours of operation and performance data in the form of normalized emission current density versus temperature curves (Miram plots).

Batra, R.↗
NASA NTRS1986

NOAA 26.5 Ah LEO characterization test

The General Electric (GE) 26.5 Ah NOAA-G flight nickel-cadmium cells were obtained from RCA-Astro Electronics to undergo performance characterization testing at the Goddard Space Flight Center (GSFC). This lot of cells was manufactured with passivated positive plate, to control nickel structure attack duing active material impregnation, and less electrolyte than normal (less than 3cc/Ah). The cells were tested in a parametric low Earth orbit (LEO) cycling regime that was previously used to test and characterize standard 50 Ah cells. Life cycle testing at the Naval Weapons Support Center (NWSC), in Crane, followed. The results of the test showed nominal performance in comparison with previous test data on the standard 50. Life cycle testing in the NOAA orbital regime is continuing at NWSC.

Morrow, G. W.↗