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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Thermoelectric properties of Co(x)Ni(4-x)Sb(12-y)Sn(y) ternary skutterudites

Thermoelectric materials based on the skutterudite crystal structure have demonstrated enhanced performance (ZT greater than 1), along with good thermal stability and favorable mechanical properties. Binary skutterudites, with single and multiple fillers, have been intensively studied in recent years. Compared to binary skutterudites, the ternary systems have received less attention, e.g. Ni4Sb8Sn4. Ternary skutterudites are isoelectronic variants of binary skutterudites; cation substitutions appear to be isostructural to their binary analogues. In general, ternary skutterudites exhibit lower thermal conductivity. Ternary systems of Ni4Bi8Ge4, Ni4Sb8Ge4, and Ni4Sb8Sn4 were investigated using combined solidification and sintering steps. Skutterudite formation was not achieved in the Ni4Bi8Ge4 and Ni4Sb8Ge4 systems; skutterudite formation occurred in Ni4Sb8Sn4 system. P-type material was achieved by Co substitution for Ni. Thermoelectric properties were measured from 298 K to 673 K for Ni4Sb8Sn4, Ni4 Sb7Sn5 and Co2Ni2Sb7Sn5. N-type Ni4Sb8Sn4 exhibit the highest figure of merit of 0.1 at 523 K.

Seebeck Effect↗
NASA NTRS1981

Antimony in iron meteorites

Sb concentrations determined by radiochemical neutron activation analysis in 60 iron meteorites range from 0.2 ng/g to 36 microg/g. The meteorites with the highest Sb concentrations are those of the nonmagmatic groups IAB and IIICD, while meteorites with the lowest Sb concentrations are found in groups IVA and IVB. In all groups Sb is positively correlated with Ni; slopes on log Sb vs log Ni plots decrease with increasing Ni. This decrease may reflect an increasing tendency to avoid schreibersite during the analysis of high-Ni meteorites because Sb partitions strongly into schreibersite. It is found that schreibersite from New Westville is enriched in Cr, Ni, Ge, As, Sb, and Au and depleted in Fe, Co, Ir; the Sb content in schreibersite is 540 times higher than the bulk metal value.

Willis, J.↗
NASA NTRS1990

Effects of antimony substitution on bismuth based superconductors

The effect of Sb substitution and simultaneous substitution of Pb and Sb on the superconducting transition temperatures in the BiSrCaCuO system is investigated. The 2:2:2:3 phase is of particular interest since any small increase in the transition temperature could be of great interest. More that 90 different samples were prepared based on 2:2:2:3 stoichiometry in the BiSrCaCuO system. After this preliminary attempt, four different families of samples were investigated. In the first family of samples, Bi was substituted by Sb to form Bi(1.9)Sb(0.1)Sr2Ca2Cu3O(y). The second group of samples were prepared by simultaneous addition of Pb and Sb with nominal composition Bi(1.8)Pb(0.1)Sb(0.1)Sr2Ca2Cu3O(y). The third and fourth groups were prepared to determine the effect created when the Pb concentration is increased with the nominal compositions being Bi(1.7)Pb(0.1)Sr2Ca2Cu3O(y) and Bi(1.6)Sb(0.1)Sr2Ca2Cu3O(y). The results of these investigations are presented with a discussion.

Barrientos, Alfonso↗
NASA NTRS2007

Coating Thermoelectric Devices To Suppress Sublimation

A technique for suppressing sublimation of key elements from skutterudite compounds in advanced thermoelectric devices has been demonstrated. The essence of the technique is to cover what would otherwise be the exposed skutterudite surface of such a device with a thin, continuous film of a chemically and physically compatible metal. Although similar to other sublimation-suppression techniques, this technique has been specifically tailored for application to skutterudite antimonides. The primary cause of deterioration of most thermoelectric materials is thermal decomposition or sublimation - one or more elements sublime from the hot side of a thermoelectric couple, changing the stoichiometry of the device. Examples of elements that sublime from their respective thermoelectric materials are Ge from SiGe, Te from Pb/Te, and now Sb from skutterudite antimonides. The skutterudite antimonides of primary interest are CoSb3 [electron-donor (n) type] and CeFe(3-x)Co(x)Sb12 [electron-acceptor (p) type]. When these compounds are subjected to typical operating conditions [temperature of 700 C and pressure <10(exp -5) torr (0.0013 Pa)], Sb sublimes from their surfaces, with the result that Sb depletion layers form and advance toward their interiors. As the depletion layer advances in a given device, the change in stoichiometry diminishes the thermal-to-electric conversion efficiency of the device. The problem, then, is to prevent sublimation, or at least reduce it to an acceptably low level. In preparation for an experiment on suppression of sublimation, a specimen of CoSb3 was tightly wrapped in a foil of niobium, which was selected for its chemical stability. In the experiment, the wrapped specimen was heated to a temperature of 700 C in a vacuum of residual pressure <10(exp -5) torr (0.0013 Pa), then cooled and sectioned. Examination of the sectioned specimen revealed that no depletion layer had formed, indicating the niobium foil prevented sublimation of antimony at 700 C. This was a considerable improvement, considering that uncoated CoSb3 had been found to decompose to form the lowest antimonide at the surface at only 600 C. Evidently, because the mean free path of Sb at the given temperature and pressure was of the order of tens of centimeters, any barrier closer than tens of centimeters (as was the niobium foil) would have suppressed transport of Sb vapor, thereby suppressing sublimation of Sb

Sakamoto, Jeffrey↗
NASA NTRS1975

Improved Schottky barrier solar cells

Schottky barrier (SB) solar cells have been fabricated for solar energy conversion using GaAs and GaAs 0.78P0.22. Conversion efficiencies of 9% for air mass zero and 12% for terrestrial sun were observed for antireflection coated GaAs0.78P0.22 SB cells. The corresponding efficiencies for GaAs SB cells were 7% and 10%, respectively. These efficiencies are for cells with no interfacial layer effect. The short circuit current density for GaAs SB cells has been improved. The use of an ellipsometer to determine the optimum antireflection coating parameters is illustrated.

Yeh, Y.-C. M.↗
NASA NTRS1977

Germanium-silicon solid solutions

An experiment on melting and directional crystallization of an antimony (Sb) doped germanium silicon (GeSi) solid solution was designed for the Apollo-Soyuz Test Project (ASTP) to study the possibility of using zero-g conditions for obtaining solid-solution monocrystals with uniformly distributed components. Crystallization in the zero-g environment did not occur under ideal stationary growth and segregation conditions. Crystallization under zero-g conditions revealed the heterogeneous nature of Si and Sb distribution in the cross sections of crystals. The presence of the radial thermal gradient in the multipurpose furnace could be one of the reasons for such Si and Sb distribution. The structure of space-grown crystals correlates with the nature of heterogeneities of Si and Sb distribution in crystals. The type of surface morphology and the contour observed in space-grown crystals were never observed in ground-based crystals and indicate the absence of wetting of the graphitized walls of the ampoule by the melt during melting and crystallization.

Zemskov, V. S.↗
NASA NTRS1979

Serenitatis multi-ringed basin - Regional geology and basin ring interpretation

New topographic data allow a reassessment of the ring structure and distribution of facies of the Serenitatis basin (SB) and correlation with the younger and essentially same-size Orientale basin. Three major rings of the main (southern) SB are mapped: the Linne ring, outlined by mare ridges, average diameter 420 km; the Haemus ring, outlined by basin-facing scarps and massifs with crenulated borders, 610 km; and the Vitruvius ring, outlined by basin-facing linear scarps and massifs, 880 km. The second ring is interpreted as the rim of the transient cavity, while Serenitatis ejecta should be present in significant amounts at the junction of the Serenitatis and Imbrium third rings. The new reconstruction indicates that portions of the SB are better preserved than previously thought, consistent with recent stratigraphic and sample studies that suggest an age (as young as 3.87 plus or minus 0.04 b.y.) for SB which is older than, but close to, the time of formation of the Imbrium basin.

Head, J. W., III↗
NASA NTRS1980

Interplanetary sector boundaries 1971-1973

The large-scale morphology and internal structure of sector boundaries (SB) are investigated, using observations at 1 AU of interplanetary SB crossings. It was found that the durations of the SBs were either relatively short (less than about 10 min) or relatively long (longer than about 3 hours). Using the minimum variance technique, it was found that the SB surfaces were inclined appreciably with respect to the ecliptic at this epoch of the solar cycle (1971-1973). Magnetic holes were found in thick SBs at a rate about three times that elsewhere. In addition, an analysis of tangential discontinuities showed that their orientations were generally not related to the orientations of the SB surface, but their characteristics were very similar to those for discontinuities outside the SBs.

Klein, L.↗
NASA NTRS1981

An integrated transportation and operations comparison of space and ground based OTV's

This paper presents the results of a comparison of space vs. ground basing of orbital transfer vehicles (OTV). The comparison was done assuming an 11-year mission model beginning in 1995 and averaging over 100 MT of payloads per year to GEO. When analyzed from a total transportation standpoint, the launch system employed had the greatest impact on the basing mode comparison. A launch fleet consisting of both a basic STS and a Shuttle derivative cargo vehicle provided the least cost. Only a small advantage (3%) was found in flight performance for the space based (SB) OTV once it incorporated the necessary provisions for space debris protection and on-orbit maintenance. Propellant storage and transfer losses associated with the SB OTV amounted to 12% of the actual flight propellant requirement. Turnaround of the SB OTV required a crew of 3 and 40% duty cycle. The life cycle cost comparison including all involved space elements indicated less than a 10% difference between basing modes. The SB OTV however is judged to provide more flexibility in launch manifesting, simplified recovery operations and greater potential for improvement.

Davis, E. E.↗
NASA NTRS1988

Powerful warm infrared sources in early-type galaxies

IRAS far-infrared sources have been identified with 129 S0, Sa, Sb, and Sc galaxies in a statistically complete sample of 738 galaxies brighter than 14.5 mag and smaller than 4.0 arcmin. In most cases, the far-IR colors and the ratios of far-IR flux to radio flux density are those of normal galactic disks and/or starbursts. The most powerful far-IR sources in S0 and Sa galaxies are just as powerful as the strongest far-IR sources in Sb and Sc galaxies. Bright-IR sources in S0 and Sa galaxies are warm; those in Sc galaxies are cool. Sb galaxies have both warm and cool IR sources. Bright warm IR sources occur much more frequently in barred galaxies than in galaxies without bars for types S0, Sa, and Sb. Bright, cool IR sources are found with increasing frequency along the Hubble sequence, regardless of the presence or absence of a bar. At least some 'S0' galaxies with warm, bright IR sources have peculiar morphologies and ambiguous classifications.

Dressel, L. L.↗
NASA NTRS1993

A demonstration of TDRS orbit determination using differential tracking observables from GPS ground receivers

A Global Positioning System (GPS) flight receiver provides a means of precisely determining orbits for satellites in low to moderate altitude orbits. Above 5000 km altitude, however, relatively few GPS satellites are visible. We present a new approach to orbit determination for satellites at higher altitudes. Modification of GPS ground receivers enables a beacon from the orbiter to be tracked simultaneously with GPS data. The orbit accuracy expected from this GPS-like tracking (GLT) technique in principle could be comparable to accuracies of GPS orbits. Present-day GPS orbit quality from a daily semi-automated analysis system at the Jet Propulsion Laboratory is at the 30 - 50 cm level: expected accuracies for orbiters with GLT are calculated to be in the few-meter range for altitudes up to 100000 km. For geosynchronous satellites, however, there are unique challenges due to geometrical limitations and to the lack of strong dynamical signature in tracking data. We examine two approaches for tracking Tracking and Data Relay Satellites (TDRS) geostationary orbiters. One uses GLT with a global network; the other relies on a small `connected element' ground network with a distributed clock for short baseline differential carrier phase (SB Delta Phi). In priciple, both could meet 50-m TDRS operational requirements. However there are practical difficulties with either pure GLT or SB Delta Phi tracking schemes for present-day TDRS satellites. We describe an experiment planned for late 1993 which will combine aspects of both GLT and SB Delta Phi to demonstrate a new approach for tracking TDRS which offers a number of operationally convenient and attractive features. The TDRS demo will in effect ba a proof of concept experiment for both the GLT and SB Delta Phi approaches to tracking spacecraft.

Lichten, Stephen M.↗
NASA NTRS2009

Cold-Flow Testing of a Proposed Integrated Center-Body Diffuser/Steam Blocker Concept for Plum Brook Station's B-2 Test Facility

The center-body diffuser (CBD) steam blocker (SB) system is a concept that incorporates a set of secondary drive nozzles into the envelope of a CBD, such that both nozzle systems (i.e., the rocket engine and the steam blocking nozzles) utilize the same supersonic diffuser, and will operate either singularly or concurrently. In this manner, the SB performs as an exhaust system stage when the rocket engine is not operating, and virtually eliminates discharge flow on rocket engine shutdown. A 2.25-percent scale model of a proposed SB integrated into a diffuser for the Plum Brook B-2 facility was constructed and cold-flow tested for the purpose of evaluating performance characteristics of various design options. These specific design options addressed secondary drive nozzle design (method of steam injection), secondary drive nozzle location relative to CBD throat, and center-body throat length to diameter (L/D) ratios. The objective of the test program is to identify the desired configuration to carry forward should the next phase of design proceed. The tested scale model can provide data for various pressure ratios; however, its design is based on a proposed B-2 spray chamber (SC) operating pressure of 4.0 psia and a steam supply pressure of 165 psia. Evaluation of the test data acquired during these tests indicate that either the discrete axial or annular nozzle configuration integrated into a CBD, with an annular throat length of 1.5 L/D at the nominal injection position, would be suitable to carry forward from the SB's perspective. Selection between these two then becomes more a function of constructability and implementation than performance. L/D also has some flexibility, and final L/D selection can be a function of constructability issues within a limited range.

Edwards, Daryl A.↗