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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Low work function silicon collector for thermionic converters

To improve the efficiency of present thermionic converters, single crystal silicon was investigated as a low work function collector material. The experiments were conducted in a test vehicle which resembled an actual thermionic converter. Work function as low as 1.0eV was obtained with an n-type silicon. The stabilities of the activated surfaces at elevated temperatures were tested by raising the collector temperature up to 829 K. By increasing the Cs arrival rate, it was possible to restore the originally activated low work function of the surface at elevated surface temperatures. These results, plotted in the form of Rasor-Warner curve, show a behavior similar to that of metal electrode except that the minimum work function was much lower with silicon than with metals.

Chang, K. H.↗
NASA NTRS1976

Rolling-element fatigue lives of AISI 52100 steel balls with several synthetic lubricants

Rolling-element fatigue tests were run with three synthetic lubricants with and without antiwear additives and with a paraffinic mineral oil at race temperatures of 336 to 353 K (146 146 to 175 F). The five-ball fatigue tester was used with steel balls to evaluate the relative fatigue lives with each of six lubricant-additive combinations. The tests were run at 5,520 MPa (800,000psi) maximum Hertz stress, 10,000 rpm shaft speed, and 30 deg contact angle. The lubricants tested have similar kinetic viscosities at 372 K (210 F) ranging from 0.034 to 0.089 sq cm/sec (3.4 to 8.9 cS). At these conditions, the mode of failure in the five-ball fatigue tester was classical subsurface rolling-element fatigue. The baseline for comparison of fatigue life was the paraffinic mineral oil without additives. The effects of the synthetic lubricants and their additives, which are useful for boundary lubrication, oxidation or foam inhibition, were evaluated.

Parker, R. J.↗
NASA NTRS1974

The simultaneous determination of 20 trace elements in terrestrial, lunar and meteoritic material by radiochemical neutron activation analysis

A radiochemical neutron activation method has been developed and applied to determine the content of 20 trace elements (Ag, Au, Bi, Br, Cd, Co, Cs, Cu, Ga, Ge, In, Ir, Ni, Rb, Re, Sb, Te, Tl, and Zn) in 45 terrestrial, 230 lunar, and 70 meteoritic samples. Results obtained for the U.S.G.S. standard basalt BCR-1 indicate that the inherent precision for most elements is 10% or better. The values obtained for the trace elements investigated are compared to those previously reported in the literature. Data for Type I carbonaceous chondrites show their compositions to be far more uniform than previously supposed. The values obtained for several elements represent significant revisions in the accepted cosmic abundances. These new values include: Zn, 1250; Cd, 1.51; and Ir, 0.72 atoms/million Si atoms. Further results have provided insight into the meteoritic material and accretion of the moon, and give evidence of lunar highland vulcanism.

Keays, R. R.↗
NASA NTRS1976

H2CO emission at 2 millimeters in dark clouds

The paper reports the detection of the 2-mm emission line due to the 2(12)-1(11) transition of H2CO at two positions in the Taurus dark cloud and one position in the dark cloud L134 N. The profiles of the observed emissions are plotted, and peak radiation temperatures at 2 mm are determined for the three positions. These radiation temperatures are used along with data on the 2-mm H2CO absorption line and computed cross sections for H2-H2CO collisions to deduce the molecular hydrogen density and the ortho-H2CO column density in the two clouds. The results are shown to support previous theoretical estimates of the H2CO/H2 and the H2(C-12)O/H2(C-13)O ratios. It is concluded that if the abundances of CS and HCN in the clouds are equal to that of H2CO, emissions from these molecules should be easily detectable.

Evans, N. J., II↗
NASA NTRS1976

Substorm phenomena and the uniqueness of the geostationary orbit for observation of dynamic processes in the magnetosphere

During the Spring equinox, both ATS-6 and ATS-5 were in geosynchronous orbit with a separation of about 11 deg longitude. A ground-based campaign was undertaken by Eather, Mende, and Judge to observe aurora at the foot of the ATS field line with a variety of instruments. Initial results support the injection boundary hypothesis of Mauk and McIlwain. Also during this period, the Cs-ion thrusters on both spacecraft were exercized in a deliberate attempt to control the spacecraft potential. Some success was achieved, and the presence of a sheath with a potential minimum about ATS-5 has been demonstrated (the sheath about ATS-6 is observed directly).

Deforest, S. E.↗
NASA NTRS1976

Chemical fractionations in meteorites. IX - C3 chondrites

Radiochemical neutron activation is applied to the analysis of four C3V chondrites and three C3O chondrites for 17 trace elements (U, Re, Ir, Ni, Au, Sb, Ge, Ag, Rb, Cs, Bi, Tl, Br, Se, Te, In, and Cd). It is shown that both classes exhibit a typical chondritic step pattern, reflecting loss of volatiles during chondrule formation. It appears that the H2S/H2 ratio is the key variable to account for the condensation of chalcophile elements as a function of H2S. C3O's seem to have condensed in a region where enough metallic Fe was present to buffer the H2S pressure, whereas C3V's condensed in a more oxidized region where H2S was in excess. Accretion temperatures for both subclasses is determined. Sb and Au show variable depletion, presumably reflecting variable loss during chondrule formation.

Anders, E.↗
NASA NTRS1976

Ultraviolet response of semitransparent multialkali photocathodes

The UV spectral sensitivity of two semitransparent visible sensitive photocathodes for spaceborne applications, a trialkali, Cs-Na2KSB, and a bialkali, K2CsSb, both on MgF2 substrates. Results show that for extended wavelength coverage, the bialkali photocathode affords increased quantum yield as compared with the trialkali type, and that the latter has a more variable responsivity with wavelength.

Sobieski, S.↗
NASA NTRS1977

Spectroscopic determination of electrical conductivity in an MHD duct from absolute intensity measurements

Measurements of the electrical conductivity in the NASA Lewis cesium seeded, H2-O2 MHD duct have been previously reported. In order to corroborate the above measurements and to analyze the possibility of nonuniform seed injection as a cause of the deviations, a spectroscopic investigation of the plasma conductivity has been undertaken. Transverse profiles of the absolute integrated intensity were measured from the optically thin lines of CSI-.5664 microns and .5636 microns. Radial profiles of emission coefficient were obtained from the measured transverse profiles of intensity by Abel inversion. Radial profiles of electrical conductivity were then obtained under two different assumptions. In the first, the Cs seed fraction is assumed uniform and equal to the measured flow rate at the time when the temperature and conductivity were obtained. In the second method, the local temperature and pressure are taken to be those given by a one-dimensional channel calculation including heat transfer and friction. In this case profiles of conductivity and seed fractions are obtained. The results of the two methods are compared to the previously measured conductivity.

Wang, S. Y.↗
NASA NTRS1977

Cross sections for charge transfer between mercury ions and other metals

Cross sections for charge transfer between several ions and metals of interest to the NASA electro propulsion program have been measured. Specifically, the ions considered were Hg(+), Xe(+) and Cs(+) and the metals Mo, Fe, Al, Ti, Ta, and C. Measurements were made in the energy regime from 1 to 5,000 eV. In general, the cross sections for charge transfer were found to be less than 10 to the minus 15 power sq cm for most processes over the total energy range. Exceptions are Hg(+) in collision with Ti and Ta. The results obtained for each reaction are given in both graphical and numerical form in the text. For quick reference, the data at several ion velocities are condensed into one table given in the summary.

Vroom, D. A.↗
NASA NTRS1975

Quantitative multielement analysis using high energy particle bombardment

Charged particles ranging in energy from 0.8 to 4.0 MeV are used to induce resonant nuclear reactions, Coulomb excitation (gamma-rays), and X-ray emission in both thick and thin targets. Quantitative analysis is possible for elements from Li to Pb in complex environmental samples, although the matrix can severely reduce the sensitivity. It is necessary to use a comparator technique for the gamma-rays while for X-rays an internal standard can be used. A USGS standard rock is analyzed for a total of 28 elements. Water samples can be analyzed either by nebulizing the sample doped with Cs or Y a thin Formvar film or by extracting the sample onto ion exchange resin which is pressed into a pellet.

Clark, P. J.↗
NASA NTRS1976

A fractographic study of the edge-sliding mode in fracture toughness testing

A fractographic study of Mode II fracture surfaces has been conducted for the purpose of identifying the microstructural mechanisms responsible for fracture in the edge-sliding mode. A compact shear (CS) specimen was employed to generate the fracture surfaces and also to establish Mode II fracture toughness values for Ti-6Al-4V, A533-B steel, and several aluminum alloys. In all tests, one of the two edge cracks sustained complete Mode II fracture while the other exhibited only a limited amount of subcritical crack growth. Mode II fracture surfaces, which were unique in appearance, have been examined by optical and scanning electron microscopy. It was determined that shear (or parabolic) microvoid coalescence was the dominant mechanism for Mode II fracture. It was also established that most of the surface abrasions were created by the relative sliding of the fracture surfaces during unstable fracture rather than the crack initiation process.

Jones, D. L.↗
NASA NTRS1976

Composition of the projectiles that bombarded the lunar highlands

Twenty highland samples from Apollo 14, 15, and 17 and the eucrites Juvinas and Morre County were analyzed by radiochemical neutron activation for Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Os, Pd, Rb, Re, Sb, Se, Te, Tl, U, and Zn. The meteoritic components of 82 highland rocks were recalculated with the new corrections for the indigenous contribution and were classified by discriminant and cluster analysis as well as ternary diagrams, using Ir, Re, Au and Ni as diagnostic elements. To characterize these groups more fully, average abundances of meteoritic volatiles (Sb, Ge, Ag, Se, Te, and Bi) were calculated from regressions against Ir.

Gros, J.↗
NASA NTRS1977

Spectroscopic determination of electrical conductivity in an MHD duct from absolute intensity measurements

Measurements of the electrical conductivity in the NASA Lewis cesium seeded, H2-O2 MHD duct made by applying a voltage across the channel from one end electrode to the other, measuring the current, and using the inner electrodes as probes to monitor the voltage distribution along the channel were found to be in good agreement with theory except at low combustion pressures and/or high ratios of seed/oxygen mass flows. To corroborate these measurements and to analyze the possibility of nonuniform seed injection as a cause of the above deviations, a spectroscopic investigation of the plasma conductivity was undertaken. Radial profiles of emission coefficient were obtained from measured transverse profiles of the absolute integrated intensity by Abel inversion. Radial profiles of electrical conductivity were then obtained under two different assumptions. In the first the Cs seed fraction is assumed uniform and equal to the measured flow rate at the time when the temperature and conductivity were obtained. In the second method the local temperature and pressure are taken to be those given by a one-dimensional channel calculation including heat transfer and friction. The results of the two methods are compared to the previously measured conductivity.

Wang, S. Y.↗
NASA NTRS1977

'Mysterite' - A late condensate from the solar nebula

An attempt is made to clarify the nature of 'mysterite', a material that had been postulated to explain the overabundance of Tl, Bi, and Ag in certain chondrites. Four dark clasts and a vein sample from the H6 chondrite Supuhee were analyzed by radiochemical neutron activation analysis for Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Ni, Os, Rb, Re, Sb, Se, Te, Tl, and Zn. One of the clasts is enriched in all volatile elements, while the other four samples are enriched only in the siderophile volatiles Ag, Bi, and Tl. The enrichments range up to 100 times typical H6 chondrite abundances. The proportions of Ag, Bi, and Tl suggest the presence of at least two, Tl-rich and Tl-poor, varieties of mysterite. The former seems to dominate in Supuhee and Krymka, and the latter in Mezo-Madaras. Apparently mysterite is a late condensate from the solar nebula that collected volatiles left behind by earlier generations of chondrites. It was incorporated in Supuhee and perhaps in other chondrites (mainly of low petrologic types) during brecciation events.

Higuchi, H.↗
NASA NTRS1977

Status of research on advanced thermionic converters

It is shown that it is possible to controllably and continuously elevate the electron temperature in the plasmatron thermionic energy converter from the emitter temperature to the maintenance electron temperature for the diode arc mode. This ability and the apparent validity of an elementary analytical model of the plasma should make possible the optimization and evaluation of operation under strong ionization conditions for which the plasma resistance should be acceptably low. Measurement of the vacuum space charge arising from the emission from a surface in cesium vapor indicates the presence of a substantial negative ion emission current. Apparatus has been constructed for identifying and directly measuring the flux of positive, negative and neutral species emitted from an electrode surface in a cesium vapor diode. The primary purpose of the investigation is to determine the influence of negative ion emission on the effective work function of thermionic converter electrodes. Initial data indicate the presence of H(-), Cs(-) and possibly C(-) and CH(-).

Hatch, G. L.↗
NASA NTRS1977

Rotational excitation of linear molecules by collisions with atoms - Comparison of classical and quantum methods

Exact quantum results for the rotational excitation of rigid linear molecules by collisions with atoms are compared with classical trajectory results. The systems studied are CO-He, CS-H2, OCS-H2, HCl-He, and HCl-Ar at collision energies up to 500/cm. Total cross sections and state to state rate constants are compared. The classical results are found to be in good agreement with the quantum results on the average. Differences arising from the existence of purely quantum effects are clearly evident, but consistent and predictable. Two methods of extracting state selective information from moments of the classical distribution are examined and found to be less reliable than the usual histogram method. In conjunction with previous comparisons of classical and quantum results these calculations provide a useful measure of the limitations and reliability of classical trajectories.

Chapman, S.↗
NASA NTRS1977

Geochemical zoning and early differentiation in the moon

The volatile elements (e.g., Rb, Pb, Tl, Bi, Cs) seem to have been depleted at the time of lunar accretion. Accordingly, it may be assumed that the moon initially accreted from refractory material. The good correlation between volatile/involatile element ratios (e.g., Cs/U, K/La, K/Zr) in both highland and maria samples means that element distribution in lunar crustal rocks is not governed by volatility differences. This and other evidence encourages the view that the moon was accreted homogeneously. A consequence of homogeneous accretion theories is that very efficient large-scale element fractionation is required to account both for the high near-surface concentrations of refractory elements (e.g., Th, U, REE, Zr, Ba, etc.) and for the Ca-Al-rich crust.

Taylor, S. R.↗
NASA NTRS1977

Physics and chemistry of MoS2 intercalation compounds

An investigation is made of the physics and chemistry of MoS2 intercalation compounds. These compounds may be separated into two groups according to their stoichiometry, structure and superconducting properties. The first group consists of Na, Ca, and Sr intercalates, and the second group consists of K, Rb, and Cs intercalates. Particular attention is given to the structure of the electronic energy band and to the normal state and superconducting properties of these compounds.

Woollam, J. A.↗