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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Impedance measurements on a spiral-wound nickel/metal hydride cell cycled in a simulated Leo orbit

A spiral-wound size C cell was cycled at 25 C in a low earth orbit (LEO) regime at 50 percent depth of discharge (DOD) with approximately five percent over-charge. The nominal capacity was 3.5 AH. The cell was cycled for 2000 cycles. Capacity checks and impedance measurements over the complete range of state of charge were made upon receipt and after 500, 1000, and 2000 cycles. The capacity of the cell was essentially unchanged until after the impedance measurements at 2000 cycles. Only small changes in the impedance parameters were observed, but there was somewhat more scatter in the data after 2000 cycles. When the cell was returned to LEO cycling after 2000 cycles, only 38 percent of the capacity could be obtained. It is believed that the cell failed because of an equipment failure at the end of the final impedance measurements which allowed an over-discharge.

Reid, Margaret A.↗
NASA NTRS1997

Burp Charging Nickel Metal Hydride Cells

The SKYNET 4 constellation consists of three spacecraft which were launched between December 1988 and August 1990. The spacecraft are three-axis stabilized geostationary earth-orbiting military communications satellites with a design life of seven years on station. With the mission objective achieved all the batteries continue to give excellent performance. This paper presents a review of the history of the six batteries from cell procurement to the end of their design life and beyond. Differences in operational strategies are discussed and the lifetime trends in performance are analyzed. The combination of procurement acceptance criteria and the on-station battery management strategy utilized are presented as the prime factors in achieving completely successful battery performance throughout the mission.

Darcy, Eric↗
NASA NTRS2001

Resonances in Positronium Hydride

Recently, Ho and his colleagues have calculated the positions and widths of a series of resonances in the Ps+H scattering system, using the complex -rotation method and have compared them with estimates that I made many years ago using a quite different technique. I assumed that the resonance mechanism was the existence in the rearrangement channel [e+ + H-] of an infinite series of perturbed Coulomb bound states. Although these must be broadened and shifted by coupling with the open scattering channel, I expected them to lie very close to the actual resonance positions. To verify this, I did a model calculation for S-waves, including the coupling, and found that the first two resonances were not shifted very far from their unperturbed position. The new, detailed calculation agrees with this result, but when the P-wave was examined it was found, surprisingly, that the lowest resonance indeed moved up in energy by a large amount. With the help of Joseph DiRienzi of the College of Notre Dame of Maryland I am now extending the old calculation to P- and D-waves, in an attempt to understand this unexpected energy shift. Results will be presented at the Workshop.

Drachman, Richard J.↗
NASA NTRS2001

Resonances in Positronium Hydride

We re-examine the problem of calculating the positions and widths of the lowest-lying resonances in the Ps + H scattering system which consists of two electrons, one positron and one proton. The first of these resonances, for L=0, was found by the methods of complex rotation and stabilization, and later described as a Feshbach resonance lying close to a bound state in the closed-channel e (+) + H (-) system. Recently, results for the L=1 and 2 scattering states were published, and it was found, surprisingly, that there is a larae shift in the positions of these resonances. In this work we repeat the analysis for L=1 and find an unexpected explanation for the shift.

DiRienzi, Joseph↗
NASA NTRS2002

D-Wave Resonances in Positronium Hydride

The problem of calculating the position and width of the lowest-lying (L = 0, 1) resonances in the Ps + H scattering system has recently been re-examined by the authors [1]. In the model used, resonances axe assumed generated by bound Rydberg states in the closed re-arranged channel [e(+) + H(-)]. This infinite series of Coulomb bound states are shifted somewhat by the coupling with the open scattering channel [Ps + H]. Estimates using this approach, first carried out by one of the authors [2] using a simple form of scattering wavefunction, indicated an anticipated small shift of resonance away from the Rydberg energy in the S-wave (L = 0). More recent results by Ho and Yan [3] using the complex-rotation method showed unexpected significant shifting in the P (L = 1) and D (L = 2)-wave resonance energies from their respective unperturbed values. Our re-calculation of the resonances [I I for L = 0 and I indicates that, in each case, reasonably consistent resonance energies are obtained by coupling the two lowest lying states (IS and 2S for L = 0 and 2P and 3P for L = 1). For each L it is the higher state (2S and 3P, respectively) that produces the resonance. The lower state (1S and 2P, respectively) is effective only in increasing the non-resonant phase shift. In this work we extend the model to L = 2 (D-waves). Our results show that, unlike the S and P-waves, the 313-state alone produces a resonant energy that is very close to the result of Yan and Ho [3]. Inclusion of the 4D-state produces a second resonance in the scattering system shifted up slightly from its unperturbed Rydberg energy.

Drachman, Richard J.↗
NASA NTRS2002

D-wave Resonances in Positronium Hydride

We have recently reexamined the problem of calculating the positions and widths of the lowest-lying S- and P-state resonances in the Ps+H scattering system. The resonances are generated by bound Rydberg states in the closed rearranged channel (e(+)+H(-)), shifted somewhat by coupling with the open scattering channel. This picture had been successfully applied for S-waves, but more recent results showed unexpectedly large shifts in both P- and D-wave resonances. Our recalculation for the S- and P-waves showed that the series of resonances begins with the second Rydberg state, giving rise to an apparent large shift. Now we have extended the calculations to D states. Here we find the expected results: The 3D Rydberg state produces a resonance very close to the result of Yan and Ho, and inclusion of the 4D state gives a second resonance only slightly shifted.

Drachman, Richard J.↗
NASA NTRS2002

D-wave Resonances in Positronium Hydride

In a previous paper [Phys. Rev. A 65, 032721 (2002)] we re-examined a model describing the structure of the low-energy Ps-H resonances as being due to quasi-bound states of the positron in the perturbed Coulomb potential of the H-ion appearing in the closed, rearranged channel. In particular, we wished to understand why the lowest p-state resonance was so far away from the lowest quasi-bound (2p) state. We found that the lowest resonance actually corresponds to the first excited [3p] state, while the lowest state is not recognizable as a resonance. In the present work we repeat our analysis, but this time for the lowest d state. We find that the lowest [3d] state does correspond to a resonance shifted moderately.

DiRienzi, Joseph↗
NASA NTRS1957

Blow-Out Velocities of Solutions of Hydrocarbons and Boron Hydride - Hydrocarbon Reaction Products in a 1 7/8-Inch-Diameter Combustor

Blow-out velocities were determined for JP-4 solutions containing: (1) 10 % ethylene - decaborane reaction product, (2) 10% and 20% acetylene - diborane reaction product, and (3) 5.5%, 15.7%, and 30.7% methylacetylene - diborane reaction product. These were compared with blow-out velocities for JP-4, propylene oxide, and neohexane and previously reported data for JP-4 solutions of pentaborane. For those reaction products investigated, the blow-out velocities at a fixed equivalence ratio were higher for those materials containing higher boron concentrations; that is, blow-out velocity increased in the following order: (1) methylacetylene - diborane, (2) acetylene - diborane, and (3) ethylene - decaborane reaction products.

Morris, James F.↗
NASA NTRS2002

Evaluation of hydride compressor elements for the Planck sorption cryocooler

Hydrogen sorption crycoolers are being developed for the European Space Agency Planck mission to provide nominal 19 K cooling to instruments for measuring the temperature anisotropy of the cosmic microwave background with extreme sensitivity and resolution.

sorption cryocoolers metal hydides gas gap heat sw↗
NASA NTRS1972

Investigation of the reaction of 5Al-2.5Sn titanium with hydrogen at subzero temperature

An investigation of the effect of temperature on the surface hydriding reaction of 5Al-2.5Sn titanium exposed to hydrogen at 250 psig was made. The temperature range studied extended from 160 F to -160 F. Reaction conditions were controlled so as to expose a vacuum-cleaned, oxide-free alloy surface to an ultrapure hydrogen atmosphere. Reaction times up to 1458 hours were studied. The hydriding reaction was extremely sensitive to experimental variables and the reproducibility of reaction behavior was poor. However, it was demonstrated that the reaction proceeded quite rapidly at 160 F; as much as 1 mil surface hydriding being observed after exposure for 162 hours. The amount of hydriding appeared to decrease with decreasing temperature at 75 F, -36 F, and -76 F. No surface hydriding was detected either by vacuum fusion analysis or by metallographic examination after exposure for 1458 hours at -110 F or -160 F. Tensile properties were unaffected by surface hydriding of the severity developed in this program (up to 1 mil thick) as determined by slow strain rate testing of hydrided sheet tensile samples.

Williams, D. N.↗
NASA NTRS1971

Tensile properties of titanium electrolytically charged with hydrogen

Yield strength, ultimate tensile strength, and elongation were studied for annealed titanium electrolytically charged with hydrogen. The hydrogen was present as a surface hydride layer. These tensile properties were generally lower for uncharged titanium than for titanium with a continuous surface hydride; they were greater for uncharged titanium than for titanium with an assumed discontinuous surface hydride. We suggest that the interface between titanium and titanium hydride is weak. And the hydride does not necessarily impair strength and ductility of annealed titanium. The possibility that oxygen and/or nitrogen can embrittle titanium hydride is discussed.

Smith, R. J.↗
NASA NTRS1973

The reaction of a titanium alloy with hydrogen gas at low temperatures.

An investigation of the effect of temperature on the surface hydriding reaction of Ti-5Al-2.5Sn alloy exposed to hydrogen at 250 psig was made. The temperature range studied extended from 160 to -160 F. Reaction conditions were controlled so as to expose a vacuum-cleaned, oxide-free alloy surface to an ultra-pure hydrogen atmosphere. Reaction times up to 1458 hr were studied. The hydriding reaction was extremely sensitive to experimental variables and the reproducibility of reaction behavior was poor. However, it was demonstrated that the reaction proceeded quite rapidly at 160 F; as much as 1 mil surface hydriding was observed after exposure for 162 hr. The amount of hydriding was observed to decrease with decreasing temperature at 75, 36, and -76 F. No surface hydriding was detected either by vacuum fusion analysis or by metallographic examination after exposure for 1458 hr at -110 or -160 F.

Williams, D. N.↗
NASA NTRS1975

Hydrogen interactions with metals

Review of the literature on the nature and extent of hydrogen interactions with metals and the role of hydrogen in metal failure. The classification of hydrogen-containing systems is discussed, including such categories as covalent hydrides, volatile hydrides, polymeric hydrides, and transition metal hydride complexes. The use of electronegativity as a correlating parameter in determining hydride type is evaluated. A detailed study is made of the thermodynamics of metal-hydrogen systems, touching upon such aspects as hydrogen solubility, the positions occupied by hydrogen atoms within the solvent metal lattice, the derivation of thermodynamic functions of solid solutions from solubility data, and the construction of statistical models for hydrogen-metal solutions. A number of theories of hydrogen-metal bonding are reviewed, including the rigid-band model, the screened-proton model, and an approach employing the augmented plane wave method to solve the one-electron energy band problem. Finally, the mechanism of hydrogen embrittlement is investigated on the basis of literature data concerning stress effects and the kinetics of hydrogen transport to critical sites.

Mclellan, R. B.↗
NASA NTRS1991

Evaluation of a hydrogen resistant titanium aluminide alloy

The Ti-24Al-11Nb (Ti-24-11) alloy heat treated to the fine basketweave microstructure was shown previously to be hydrogen tolerant. In order to assess its limit of hydrogen tolerance, the tensile, creep, fracture toughness, and sustained load crack growth behaviors of this alloy were studied as a function of hydrogen content. All test specimens were thermally charged with internal hydrogen and tested at 25 and 600 C. Coupon specimens were used for developing the hydrogen charging procedures and for studying compatibility of the alloy with high temperature, high pressure gaseous hydrogen. The mechanical test results indicated that the fine basketweave microstructure was tolerant to hydride embrittlement for hydrogen contents up to approximately 1500 wt. ppm, providing that the hydride formed was of the TiH2 type. On the other hand, hydrogen charging experiments indicated that the Ti-24-11 alloy was severely cracked and pulverized under zero load when the hydrogen content exceeded 3000 wt. ppm. X-ray diffraction results revealed that the dichotomous behaviors might be due to the formation of TiH(1.924) type hydrides at higher hydrogen contents. Thus, hydrogen embrittlement in the Ti-24-11 alloy with the fine basketweave microstructure depends on hydrogen content and the nature of the hydrides formed.

Chan, K. S.↗