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Structure and properties of metal hydrides prepared by mechanical alloying

Description: Our research examines the structure and reversible hydrogen storage capacity of alloys based on the LaNi{sub 5} intermetallic. The alloys are prepared by mechanical alloying (MA), a technique particularly useful when alloying LaNi{sub 5} with low melting point elements such as tin and calcium. In LaNi{sub 5-y}Sn{sub y}, x-ray diffraction and Rietveld analysis show that tin preferentially occupies the Ni(3g) sites in the LaNi{sub 5} structure, and the unit cell volume increases linearly with tin content to a maximum tin solubility of 7.33 atomic percent (LaNi{sub 4.56}Sn{sub 0.44}). The addition of tin to LaNi{sub 5} causes (a) a logarithmic decrease in the plateau pressures for hydrogen absorption and desorption, which is consistent with the corresponding increase in the volume of the LaNi{sub 5} unit cell; (b) a decrease in the hysteresis between the pressures for hydride formation and decomposition, which is in agreement with a recent theoretical model for the effect; and (c) a linear decrease in the hydrogen storage capacity. Effect (c) is explained by a rigid-band model whereby electrons donated by the tin atoms occupy holes in the 3d band of LaNi{sub 5}, which could otherwise be occupied by electrons donated by the hydrogen atoms. Thermodynamic van`t Hoff analysis for these alloys show an increase in hydride formation enthalpy and no change in entropy with increasing tin concentration. LaNi{sub 5} with calcium additions shows enhanced kinetics of hydrogen absorption/desorption. The powder particles prepared by MA have a larger surface area than particles of the same overall size prepared by arc casting. All LaNi{sub 5}-based alloys prepared by MA in an inert environment require no activation for hydrogen absorption and suffer less comminution upon hydriding/dehydriding.
Date: September 1, 1995
Creator: Wasz, M.L. & Schwarz, R.B.
Partner: UNT Libraries Government Documents Department

Electrochemical and in situ neutron diffraction investigations of La-Ni-Al-H alloys

Description: Li/metal hydride batteries are a strong contender to replace Ni/Cd batteries. Since the role of alloying components is not yet understood, a combination of electrochemical and neutron diffraction techniques has been designed to investigate metal hydrides. In this work, several Al-substituted LaNi{sub 5} alloys were investigated for their specific capacity (measured by mAh/La and symbolized by x in LaNi{sub 5-y}Al{sub y}H{sub x}), impedance, and cycling stability. Neutron diffraction was used to study the electrochemically induced phase transformation and structure change during charge/discharge.
Date: May 1, 1996
Creator: Peng, W.; Redey, L.; Vissers, D.R.; Myles, K.M.; Carpenter, J.; Richardson et al.
Partner: UNT Libraries Government Documents Department

Mathematical modeling of the nickel/metal hydride battery system

Description: A group of compounds referred to as metal hydrides, when used as electrode materials, is a less toxic alternative to the cadmium hydroxide electrode found in nickel/cadmium secondary battery systems. For this and other reasons, the nickel/metal hydride battery system is becoming a popular rechargeable battery for electric vehicle and consumer electronics applications. A model of this battery system is presented. Specifically the metal hydride material, LaNi{sub 5}H{sub 6}, is chosen for investigation due to the wealth of information available in the literature on this compound. The model results are compared to experiments found in the literature. Fundamental analyses as well as engineering optimizations are performed from the results of the battery model. In order to examine diffusion limitations in the nickel oxide electrode, a ``pseudo 2-D model`` is developed. This model allows for the theoretical examination of the effects of a diffusion coefficient that is a function of the state of charge of the active material. It is found using present data from the literature that diffusion in the solid phase is usually not an important limitation in the nickel oxide electrode. This finding is contrary to the conclusions reached by other authors. Although diffusion in the nickel oxide active material is treated rigorously with the pseudo 2-D model, a general methodology is presented for determining the best constant diffusion coefficient to use in a standard one-dimensional battery model. The diffusion coefficients determined by this method are shown to be able to partially capture the behavior that results from a diffusion coefficient that varies with the state of charge of the active material.
Date: September 1, 1995
Creator: Paxton, B.K.
Partner: UNT Libraries Government Documents Department

Thermal aging of LaNi{sub 5-x}Mn{sub x} hydrides

Description: The LaNi{sub 5-x}Mn{sub x}-hydrides have potential applications in cryocooling devices for non-mechanical method to compress hydrogen gas. Thermal aging behavior of LaNi{sub 5-x}Mn{sub x}-hydrides of compositions x=0.4 and x=1.5 has been investigated. The hydriding properties of the La{sub 1.02}Ni{sub 4.6}Mn{sub 0.4} alloy do not change significantly after thermal aging at 453K for 260 hours. X-ray diffraction analyses of this aged alloy do not reveal the presence of any new phases but the Bragg peaks become broader. Line profile analyses show anisotropic microstrains with an average <e{sup 2}>{sup 1/2} value of {approximately}5x10{sup -3}. Thermal aging of the other hydride, LaNi{sub 3.5}Mn{sub 1.5} hydride, at 623K for 280 hours, showed significant disproportionation; the hydrogen capacity reduced significantly from an H/M value of 0.75 in the activated condition to {approximately}0.15 after aging. X-ray diffraction analyses showed disproportionated lanthanum dihydride, metallic Ni, and Mn phases. The Bragg peaks were very broad indicative of microstrains or small crystalline domains.
Date: February 1, 1997
Creator: Bagchi, S.; Chandra, D. & Cathey, W.N.
Partner: UNT Libraries Government Documents Department

Sn-substituted LaNi{sub 5} alloys for metal hydride electrodes

Description: This research examines the efficacy of tin additions to LaNi{sub 5} in improving the hydrogen storage capacity of the material during charging/discharging. Alloys were prepared using high energy ball milling (mechanical alloying), a technique superior to arc casting for alloying elements with a wide disparity in melting points. Characterization by X-ray diffraction and Rietveld analysis shows that tin preferentially occupies the Ni(3g) sites in the LaNi{sub 5} structure, and the unit cell volume increases linearly with tin content to the maximum tin solubility of 7.33 atomic percent (LaNi{sub 4.56}Sn{sub 0.44}). The authors found that powders prepared by mechanical alloying and not exposed to air require no activation to induce hydrogen absorption. The hydrogen storage capacity in the gas and electrochemical phase was measured as a function of tin content. They found that with increasing tin, the plateau pressure decreases logarithmically, whereas the hydrogen storage capacity decreases linearly.
Date: May 1, 1995
Creator: Wasz, M.L.; Schwarz, R.B.; Srinivasan, S. & Sridhar Kumar, M.P.
Partner: UNT Libraries Government Documents Department

Automated apparatus for Sieverts' studies of metal hydrides. [U deuteride; La/sub 5. 25/ Ni hydride]

Description: An automated system, controlled by a small desktop computer, that carries out Sieverts' experiments on metal hydride systems is described. Data (equilibrium pressures versus temperatures at constant hydrogen-to-metal ratios) are recorded for later analysis and plotting. The computer also controls valve positions during the experiments. Results for two metal hydride systems, the uranium deuteride system in the plateau region and the La/sub 5/ /sub 25/Ni hydride system at low concentrations, are presented as examples. Data included on the latter system have not been reported previously. The techniques used in Sieverts' experiments and the sources of errors are discussed.
Date: December 1, 1980
Creator: Carstens, D.H.W. & David, W.R.
Partner: UNT Libraries Government Documents Department

Electronic band structure and optical properties of the cubic, Sc, Y and La hydride systems

Description: Electronic band structure calculations are used to interpret the optical spectra of the cubic Sc, Y and La hydride systems. Self-consistent band calculations of ScH/sub 2/ and YH/sub 2/ were carried out. The respective joint densities of states are computed and compared to the dielectric functions determined from the optical measurements. Additional calculations were performed in which the Fermi level or band gap energies are rigidly shifted by a small energy increment. These calculations are then used to simulate the derivative structure in thermomodulation spectra and relate the origin of experimental interband features to the calculated energy bands. While good systematic agreement is obtained for several spectral features, the origin of low-energy interband transitions in YH/sub 2/ cannot be explained by these calculated bands. A lattice-size-dependent premature occupation of octahedral sites by hydrogen atoms in the fcc metal lattice is suggested to account for this discrepancy. Various non-self-consistent calculations are used to examine the effect of such a premature occupation. Measurements of the optical absorptivity of LaH/sub x/ with 1.6 < x < 2.9 are presented which, as expected, indicate a more premature occupation of the octahedral sites in the larger LaH/sub 2/ lattice. These experimental results also suggest that, in contrast to recent calculations, LaH/sub 3/ is a small-band-gap semiconductor.
Date: January 1, 1980
Creator: Peterman, D. J.
Partner: UNT Libraries Government Documents Department

Metal hydride/chemical heat-pump development project. Phase I. Final report

Description: The metal hydride/chemical heat pump (MHHP) is a chemical heat pump containing two hydrides for the storage and/or recovery of thermal energy. It utilizes the heat of reaction of hydrogen with specific metal alloys. The MHHP design can be tailored to provide heating and/or cooling or temperature upgrading over a wide range of input and ambient temperatures. The system can thus be used with a variety of heat sources including waste heat, solar energy or a fossil fuel. The conceptual design of the MHHP was developed. A national market survey including a study of applications and market sectors was conducted. The technical tasks including conceptual development, thermal and mechanical design, laboratory verification of design and material performance, cost analysis and the detailed design of the Engineering Development Test Unit (EDTU) were performed. As a result of the market study, the temperature upgrade cycle of the MHHP was chosen for development. Operating temperature ranges for the upgrader were selected to be from 70 to 110/sup 0/C (160 to 230/sup 0/F) for the source heat and 140 to 190/sup 0/C (280 to 375/sup 0/F) for the product heat. These ranges are applicable to many processes in industries such as food, textile, paper and pulp, and chemical. The hydride pair well suited for these temperatures is LaNi/sub 5//LaNi/sub 4/ /sub 5/Al/sub 0/ /sub 5/. The EDTU was designed for the upgrade cycle. It is a compact finned tube arrangement enclosed in a pressure vessel. This design incorporates high heat transfer and low thermal mass in a system which maximizes the coefficient of performance (COP). It will be constructed in Phase II. Continuation of this effort is recommended.
Date: February 1, 1982
Creator: Argabright, T.A.
Partner: UNT Libraries Government Documents Department

Hydrogen recovery from supplemented natural gas by metal hydrides

Description: A metal hydride process employing LaNi/sub 4/ /sub 7/Al/sub 0/ /sub 3/ for recovery of hydrogen from supplemented natural gas is being developed. Experimental studies performed to date involved determination of the equilibrium hydrogen capacity of the alloy, measurement of the adsorption behavior of contaminant gases, and measurement of rates of hydrogen absorption by the alloy. The results were used as the basis for a preliminary process design and cost estimate.
Date: January 1, 1981
Creator: Huang, D.T.J.; Reidinger, F. & Hill, F.B.
Partner: UNT Libraries Government Documents Department

Temperature and concentration dependence of hydrogen site occupancy in several rare-earth dihydrides

Description: Neutron inelastic scattering and diffraction techniques were used to study the hydrogen site distribution in several rare earth dihydrides as a function of temperature and concentration. For Y, La, and Ce the fraction of hydrogen on octahedral sites is approximately a constant from 15K to 200K followed by a decrease with increasing temperature. A model is presented which qualitatively explains this behavior.
Date: January 1, 1985
Creator: Goldstone, J.A.; Eckert, J.; Richards, P.M. & Venturini, E.L.
Partner: UNT Libraries Government Documents Department

Deuteron nuclear magnetic resonance investigation of LaNi$sub 5$D/sub x/ compounds

Description: The $sup 2$D quadrupole interaction was observable in all the samples of LaNi$sub 5$D/sub x/ up to a critical temperature T/sub c/ at which the intensity of the quadrupole interaction spectrum disappeared and only a narrow unsplit line remained. The critical temperatures were 360$sup 0$K for the x = 3.6 sample and 380$sup 0$K for the x = 5.7, 6.7 samples. Based on preliminary electric field gradient (EFG) calculations, it appears likely that several quadrupole interactions are being observed from inequivalent deuterium sites in the lattice. In the temperature range T greater than or equal to 300$sup 0$K, it appears that diffusional averaging is not entirely isotropic and that the deuterium still occupies certain interstitial sites preferentially. The temperature dependence of the $sup 2$D characteristic quadrupole frequency ($nu$/sub Q/) and the disappearance of the $sup 2$D quadrupole interaction signal were found to be compatible with desorption of the deuterium from the LaNi$sub 5$ lattice with increasing temperature. Spectra obtained from D$sub 2$ gas samples under various experimental conditions (pure gas, gas above LaNi$sub 5$D$sub 6$.$sub 7$, and gas within or on LaNi$sub 5$ at 77$sup 0$K) may provide evidence for the identification of the solid-solution $alpha$-phase or for the existence of an adsorbed deuterium surface film on the LaNi$sub 5$. In addition, the spectra suggest that at 77$sup 0$K rapid deuterium exchange between the gas and surface contributes to spin-lattice relaxation and, hence, to broadening of the NMR resonance. (auth)
Date: October 1, 1975
Creator: Nelson, S.O.
Partner: UNT Libraries Government Documents Department

AN IN-REACTOR RADIOMETRIC CALORIMETER

Description: A twin isothermal resistance-bridge calorimeter for use in a pool-type nuclear reactor is described. Measurements of fission energy in U/sup 235/ foils and derivation of the thermal neutron flux are given as examples of its use. (auth)
Date: September 11, 1963
Creator: Gunn, S.R.
Partner: UNT Libraries Government Documents Department

Aging effects in palladium and LaNi sub 4. 25 Al sub 0. 75 tritides

Description: Palladium and LaNi{sub 5-x}Al{sub x} (x=0.30, 0.75, 0.85), which form reversible hydrides, are used for tritium processing and storage in the Savannah River Site (SRS) tritium facilities. As part of a program to develop technology based on the use of reversible metal hydrides for tritium processing and storage, the effects of aging on the thermodynamic behavior of palladium and LaNi{sub 4.25}Al{sub 0. 75} tritides are under investigation. During aging, the {sup 3}He tritium decay product remains in the tritide lattice and changes the thermodynamics of the tritium-metal tritide system. Aging effects in 755-day-aged palladium and 1423-day-aged LaNi{sub 4.25}Al{sub 0.75} tritides will be reported. Changes in the thermodynamics were determined by measuring tritium desorption isotherms on aging samples. In palladium, aging decreases the desorption isotherm plateau pressure and changes the {alpha}-phase portion of the isotherm. Aging-induced changes in desorption isotherms are more drastic in LaNi{sub 4.25}Al{sub 0.75}. Among the changes noted are: (1) decreased isotherm plateau pressure, (2) increased isotherm plateau slope, and (3) appearance of deep-trapped tritium, removable only by exchange with deuterium.
Date: January 1, 1991
Creator: Nobile, A.; Wermer, J.R. & Walters, R.T.
Partner: UNT Libraries Government Documents Department

Bandstructure calculations for metal hydrogen systems

Description: The factors contributing to hydride stability are discussed for a variety of metal hydride systems. The formation of a low-lying hydrogen associated state is a common feature. A significant transition metal character is also found in these states.
Date: January 1, 1979
Creator: Switendick, A.C.
Partner: UNT Libraries Government Documents Department

Hydrides of CeNi/sub 5/, MmNi/sub 5/, Ca/sub 0/ /sub 2/(Ce/sub 0/ /sub 65/Mm/sub 0/ /sub 35/)/sub 0/ /sub 8/Ni/sub 5/, Ca/sub 0/ /sub 2/Ce/sub 0/ /sub 8/Ni/sub 5/, Ca/sub 0/ /sub 2/Mm/sub 0/ /sub 8/Ni/sub 5/, and mixed CeNi/sub 5//MmNi/sub 5/

Description: Six intermetallic alloys (CeNi/sub 5/, MmNi/sub 5/, Ca/sub 0/ /sub 2/(Ce/sub 0/ /sub 65/Mm/sub 0/ /sub 35/)/sub 0/ /sub 8/Ni/sub 5/, Ca/sub 0/ /sub 2/Ce/sub 0/ /sub 8/Ni/sub 5/, Ca/sub 0/ /sub 2/Mm/sub 0/ /sub 8/Ni/sub 5/, and a mixed alloy, CeNi/sub 5//MmNi/sub 5/) were investigated with respect to their suitability to provide high hydrogen capacity and their potential for use in providing substantial hydrogen pressure at both low and high temperatures. A second phase of our investigation dealt with ball-milling and hydriding and dehydriding cycles to produce fine particles for use in hydride powder transfer studies. A summary of several Van't Hoff plots is also included for hydride-forming alloys.
Date: September 1, 1982
Creator: Lakner, J.F. & Chow, T.S.
Partner: UNT Libraries Government Documents Department

Hydrogen storage and purification systems. II. August 1972-June 1974

Description: Pressure-composition isotherms are given for the following systems: FeTi-H/sub 2/ (0, 30, 40, 55, 70/sup 0/C); Fe/sub 0/ /sub 95/V/sub 0/ /sub 05/Ti/sub 1/ /sub 0/-H/sub 2/ (40/sup 0/C); Fe/sub 1/ /sub 0/Cu/sub 0/ /sub 1/Ti/sub 1/ /sub 0/-H/sub 2/ (40/sup 0/C); Fe/sub 0/ /sub 9/Mo/sub 0/ /sub 1/Ti-H/sub 2/ (40/sup 0/C); two (Fe, Cr, Ti)-H/sub 2/ (40/sup 0/C); three (Fe, Mn, Ti)-H/sub 2/ (40, 70/sup 0/C); Fe/sub 0/ /sub 8/Mn/sub 0/ /sub 2/Ti-H/sub 2/ (61/sup 0/C); Fe/sub 0/ /sub 9/Mn/sub 0/ /sub 1/Ti/sub 1/ /sub 0/-H/sub 2/ (30, 40, 50/sup 0/C); CoTi-H/sub 2/ (123, 138, 154/sup 0/C); Mg/sub 2/Al/sub 3/-H/sub 2/ (302, 326/sup 0/C); LaNi/sub 5/-H/sub 2/ (40/sup 0/C); and La/sub 4/ /sub 75/Pt/sub 0/ /sub 25/-H/sub 2/ (40/sup 0/C).
Date: August 1, 1974
Creator: Reilly, J.J. & Wiswall, R.H. Jr.
Partner: UNT Libraries Government Documents Department