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Bowman, R. C., Jr.

Publications and source records attributed to Bowman, R. C., Jr..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2006

Solid State NMR Studies of the Aluminum Hydride Phases

Several solid state NMR techniques including magic-angle-spinning (MAS) and multiple-quantum (MQ) MAS experiments have been used to characterize various AlH3 samples. MAS-NMR spectra for the 1H and 27Al nuclei have been obtained on a variety of AlH3 samples that include the (beta)- and (gamma)- phases as well as the most stable (alpha)-phase. While the dominant components in these NMR spectra correspond to the aluminum hydride phases, other species were found that include Al metal, molecular hydrogen (H2), as well as peaks that can be assigned to Al-O species in different configurations. The occurrence and concentration of these extraneous components are dependent upon the initial AlH3 phase composition and preparation procedures. Both the (beta)-AlH3 and (gamma)-AlH3 phases were found to generate substantial amounts of Al metal when the materials were stored at room temperature while the (alpha)-phase materials do not exhibit these changes.

phase compositions↗
NASA NTRS2003

20 K continuous cycle sorption coolers for the Planck flight mission

In this paper we present the level of maturity of the hydrogen sorption cooler technology at JPL by describing the design and how it has been validated at the subsystem and system levels. In addition, we will describe how such systems could be advantageously used for other space missions with similar needs and cooler attributes.

sorption cooler 20 K hydride Planck↗
NASA NTRS2000

Degradation behavior of LaNi(sub 4.87)Sn(sub 0.22)H(sub x) at elevated temperature

Partial substitution of tin for nickel in the LaNi(sub 5) alloy greatly enhances the stability and durability of the hydride phase during both gas phase and electrochemical cycling. Effects observed included reduction in hydrogen storage capacity, decreases in the plateau pressures, increased slopes of the plateaus, and smaller hysteresis ratios.

metal hydrides hydrogen storage↗
NASA NTRS2000

Degradation study of the ZrNiH(sub 1.5) system

The ZrNi hydride has been assessed as reversible hydrogen storage material in actuators of gas gap heat switches for applications involving hydride compressors in closed-cycle Joule-Thomson sorption cryocoolers.

metal hydrides gas gap heat switches hydrogen stor↗
NASA NTRS2000

Degradation behavior at elevated temperature of LaNisub5-xSnsubxHsubz for x between 0.20 and 0.25

Systematic studies of the hydriding behavior of LaNi(sub 5-x)Sn(sub x)H(sub z) alloys with tin contents in the range between 0.20 and 0.25 have revealed changes in the pressure-composition-temperature (PCT) isotherms measured after heating the hydrides above 450 K. These changes are indications of degradation processes and increased disorder within the alloy structure.

metal hydrides gas gap heat switches hydrogen stor↗
NASA NTRS2000

Assessment of Zr-Fe-V getter alloy for gas-gap heat switches

A commercial Zr-V-Fe alloy (i.e., SAES Getters trade name alloy St-172) has been assessed as reversible hydrogen storage material for use in actuators of gas gap heat switches. Two prototype actuators containing the SAES St-172 material were built and operated for several thousand cycles to evaluate performance of the metal hydride system under conditions simulating heat switch operation.

metal hydrides gas gap heat switches hydrogen stor↗
NASA NTRS1999

Development of Gas Gap Heat Switch Actuator for the Planck Sorption Cryocooler

We present the general principles of gas gap heat switches that impact their performances for the Planck cryocooler, develop two figures of merit relevant to this application, and present initial characterization results of switches using uranium or ZrNi as the hydriding material.

Gas Gap Heat Switch Actuator Cryocooler↗
NASA NTRS1998

Hydrogen Desorption and Adsorption Measurements on Graphite Nanofibers

Graphite nanofibers were synthesized and their hydrogen desorption and adsorption properties are reported for 77 and 300 K. Catalysts were made by several different methods including chemical routes, mechanical alloying and gas condensation.

graphite nanofibers hydrogen desorption adsorption↗
NASA NTRS1997

Electrochemical Properties of LaNi (sub 5-x) Ge (sub x) Alloys in Ni-MH Batteries

Electrochemical studies were performed on LaNi (sub 5-x) Ge (sub x) metal hydride alloys with 0 <= x <= 0.5. We carried out single-electrode studies to understand the effects of the Ge substituent on the hydrogen absorption characteristics, the electrochemical capacity, and the electrochemical kinetics of hydrogen absorption and desorption.

hydrogen absorption electrochemical capacity elect↗
NASA NTRS1996

Hybriding Behavior of Gas-Atomized AB(sub 5) Alloys

The Hydriding characteristics of some AB(sub 5) alloys produced by high pressure gas atomization (HPGA) have been examined during reactions with hydrogen gas, and in electrochemical cells.

metal hydrides gas atomization electrochemical hyd↗
NASA NTRS1996

Electrochemical Studies on LaNi(sub 5-x)Sn(sub x) Metal Hydride Alloys

Electrochemical studies were performed on LaNi(sub 5-x)Sn(sub x) with 0(less than or equal to)x(less than or equal to)0.5. We measured the effect of the Sn substituent on the kinetics of charge transfer and diffusion during hydrogen absorption and desorption, and the cyclic lifetimes of LaNi(sub 5-x)Sn(sub x) electrodes in 250 mAh laboratory test cells. We report beneficial effects of making small substitutions of Sn for Ni in LaNi(sub 5) on the performance of metal hydride alloy anode in terms of cyclic lifetime, capacity and kinetics. The optimal concentration of Sn in LaNi(sub 5-x)Sn(sub x) alloys for negative electrodes in alkaline rechargable secondary cells was found to lie in the range 0.25(less than or equal to)x(less than or equal to)0.3.

metal hydride alloys hydrogen absorption↗
NASA NTRS1996

Electrochemical Evaluation of LaNi(sub 5-x)Ge(sub x) Metal Hydride Alloys

We report a detailed evaluation of Ge-substituted LaNi(sub 5) for electrochemical application as a negative electrode inalkaline rechargeable cells. Alloys with small substitutions of Ge for Ni show operating pressures, chargeability, cyclic lifetime, and kinetics for hydrogen absorption and desorption all superior to those found in many substituted LaNi(sub 5) alloys.

alkaline cells recharchable cells rechargeable bat↗
NASA NTRS1993

(abstract) Development of Sorbent Bed Assembly for a Periodic 10K Solid Hydrogen Cryocooler

A closed-cycle 10K sorption cryocooler is being fabricated for microgravity testing during a future space shuttle mission. A critical component of this cryogenic refrigerator is the metal hydride sorbent bed assembly (SBA). The SBA uses hydrides which absorb hydrogen gas at low pressure, (i.e., about 0.25 MPa from liquid hydrogen at 25K and below 0.2 kPa from solid hydrogen near 10K) and subsequently delivers hydrogen at nearly 10 MPa to a storage reservoir to repeat the Joule-Thomson (J-T) expansion process. The SBA includes three independent hydride beds where two contain LaNi(sub 4.8)Sn(sub 0.2) alloy and the third ZrNi. Detailed descriptions will be given for the three beds, which have specialized design features to enhance performance at each step of operation. In particular, two beds must rapidly absorb hydrogen in order for the J-T cold stage to reach 10K within two minutes from a 65K holding temperature. Performance characterization results will be compared to model analyses of the SBA.

applications microgravity↗
NASA NTRS1988

Photoreflectance Study of Boron Ion-Implanted (100) Cadmium Telluride

Ion implanted (100) cadmium telluride was studied using the contactless technique of photoreflectance. The implantations were performed using 50- to 400-keV boron ions to a maximum dosage of 1.5 x 10(16)/sq cm, and the annealing was accomplished at 500 C under vacuum. The spectral measurements were made at 77 K near the E(0) and E(1) critical points; all the spectra were computer-fitted to Aspnes' theory. The spectral line shapes from the ion damaged, partially recovered and undamaged, or fully recovered regions could be identified, and the respective volume fraction of each phase was estimated.

Amirtharaj, P. M.↗
NASA NTRS1983

NMR studies of electronic structure in crystalline and amorphous Zr2PdH/x/

The proton Knight shifts and spin-lattice relaxation times have been measured in crystalline and amorphous Ze2PdH(x). Core polarization from the Zr d-band dominates the proton hyperfine interactions. The density of Fermi level d-electron states is reduced in the amorphous phase relative to the electron density in crystalline Zr2PdH(x).

Bowman, R. C., Jr.↗