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Sample records for alh3 vliyanie dobavok

  1. Decomposition kinetics of the AlH3 polymorphs.

    PubMed

    Graetz, Jason; Reilly, James J

    2005-12-01

    Aluminum hydride polymorphs (alpha-AlH3, beta-AlH3, and gamma-AlH3) were prepared by organometallic synthesis. Hydrogen capacities approaching 10 wt % at desorption temperatures less than 100 degrees C have been demonstrated with freshly prepared AlH3. The temperature-dependent rate constants were determined by measuring the isothermal hydrogen evolution between 60 degrees C and 140 degrees C. Fractional decomposition curves showed good fits using both the second and third-order Avrami-Erofeyev equations, indicating that the decomposition kinetics are controlled by nucleation and growth of the aluminum phase in two and three dimensions. The large activation energies measured for the AlH3 polymorphs suggest that the decomposition occurs via an activated complex mechanism with complexes consisting of approximately nine AlH3 molecules (1-2 unit cells for alpha-AlH3).

  2. Trapped H2 in AlH3

    NASA Astrophysics Data System (ADS)

    Conradi, Mark; Senadheera, Lasitha; Carl, Erik; Ivancic, T. M.; Bowman, R. C., Jr.; Hwang, S. J.; Udovic, T. J.

    2007-03-01

    Trapped molecular hydrogen has been discussed for years in H-storage systems such as NaAlH4. Here we report proton NMR and neutron vibration spectroscopy (NVS) evidence for H2 in AlH3 samples. In static sample NMR, a sharp line appears on top of the broad AlH3 solid signal. MAS further sharpens this line and identifies it as H2 by its chemical shift. Upon cooling, the line broadens and disappears near 20K, confirming the H2 identification. NVS reports energy-gain peaks at the H2 rotational energy (J=1 to 0).

  3. Point-defect-mediated dehydrogenation of AlH3

    NASA Astrophysics Data System (ADS)

    Ismer, Lars; Janotti, Anderson; Van de Walle, Chris G.

    2010-11-01

    Based on hybrid density functional calculations, we propose a microscopic mechanism for the dehydrogenation of AlH3. Our results indicate that mass transport mediated by positively charged hydrogen vacancies (VH+) is likely the rate-limiting mechanism. The calculated activation energy of 1.72 eV is in good agreement with experimental values. The high formation energy and hence low concentration of VH+ explains why AlH3 does not decompose at room temperature, although it is thermodynamically unstable. Issues of maintaining charge neutrality are addressed.

  4. Surface changes on AlH3 during the hydrogen desorption

    NASA Astrophysics Data System (ADS)

    Kato, Shunsuke; Bielmann, Michael; Ikeda, Kazutaka; Orimo, Shin-ichi; Borgschulte, Andreas; Züttel, Andreas

    2010-02-01

    Surface change of α-AlH3 during the hydrogen desorption was investigated by means of in situ x-ray photoelectron spectroscopy combined with thermal desorption spectroscopy. The surface of AlH3 covered by an oxide layer significantly changes upon hydrogen desorption and the hydrogen desorption rate increases remarkably. In this study, the role of the surface oxide layer on AlH3 in view of the hydrogen desorption kinetics was investigated. AlH3 only decomposes into Al and H2 at the free surface and not in the bulk. Therefore, a closed surface oxide layer prevents the thermodynamically unstable AlH3 from decomposition.

  5. Pressure induced band gap opening of AlH3

    NASA Astrophysics Data System (ADS)

    Geshi, Masaaki; Fukazawa, Taro

    2013-02-01

    Pressure-induced band gap opening (PIBGO) of AlH3 with a Pm3barn structure is verified by using first-principles calculations. With increasing pressure, the semimetallic band structures change to the indirect band gap semiconducting band structure at about 300 GPa. The key points of this phenomenon are (1) the moderately large difference of electronegativity between aluminium and hydrogen and (2) the orthogonality between the 3s states and 2s states of Al. We have been confirmed that the structure is stable up to and including 500 GPa resulting from the structural relaxation and phonon calculations. The band gap is more accurately confirmed by GW calculations than done by DFT-GGA ones. The band gap may open at about 200 GPa. This phenomenon may be verified by means of a leading-edge experimental technique.

  6. Accelerated thermal decomposition of AlH3 for hydrogen-fueled vehicles

    NASA Astrophysics Data System (ADS)

    Sandrock, G.; Reilly, J.; Graetz, J.; Zhou, W.-M.; Johnson, J.; Wegrzyn, J.

    2005-02-01

    The potential for using aluminum hydride, AlH3, for vehicular hydrogen storage is explored. It is shown that particle-size control and doping of AlH3 with small levels of alkali-metal hydrides (e.g. LiH) results in accelerated desorption rates. For AlH3 20 mol % LiH, 100 °C desorption kinetics are nearly high enough to supply vehicles. It is highly likely that 2010 gravimetric and volumetric vehicular system targets (6 wt % H2 and 0.045 kg/L) can be met with onboard AlH3. However, a new, low-cost method of off-board regeneration of spent Al back to AlH3 is needed.

  7. Development and Test of a Highly Energetic AlH3 Difluoramino Propellant.

    DTIC Science & Technology

    The object of this program was to combine the difluoramine binder with the AlH3 to produce a propellant having high theoretical impulse and high...shelf life of the TVOPA/ AlH3 propellants. Stripping of an inert diluent at 140F for 16 hours reduced the gassing rate and improved the shelf life...markedly. Using this mix process with a more stable AlH3 , a shelf life of 5 years for large web grains stored at 70 F may be feasible. In process hazards

  8. Dynamical stability of the cubic metallic phase of AlH3 at ambient pressure

    NASA Astrophysics Data System (ADS)

    Kim, Duck Young; Scheicher, Ralph H.; Ahuja, Rajeev

    2009-03-01

    We have characterized the high-pressure cubic phase of AlH3 using density functional theory to determine mechanical as well as electronic properties and lattice dynamics from the response function method [1]. Metallization in AlH3 under pressure has been studied, which is of great interest not only from a fundamental physics point of view for the study of phenomena related to metallic hydrogen, but also, because metallic AlH3 possesses weaker Al-H bonds than other insulating phases [2]. Our phonon calculations show the softening of a particular mode with decreasing pressure, indicating the onset of a dynamical instability that continues to persist at ambient conditions. We find from analyzing the atomic and electronic interactions using theoretical calculations that finite-temperature effects lead to the desired stabilization of metallic AlH3 at ambient conditions.[0pt] [1] PRB 78, 100102(R) (2008). [0pt] [2] APL 92, 201903 (2008).

  9. Catalytic effect of Ti and Ni on dehydrogenation of AlH3: A first principles investigation

    NASA Astrophysics Data System (ADS)

    Yu, H. Z.; Dai, J. H.; Song, Y.

    2015-08-01

    Ab initio calculations were performed for the M-doped (M = Ti or Ni) AlH3 to investigate influence of dopants Ti and Ni on the dehydrogenation properties of AlH3. It was found that Ti and Ni prefer to substitute for Al atom in both the bulk phase and the slab surface. However a large amount of energy was needed for Ni to dope into AlH3 making that Ni might not a suitable catalyst for AlH3. Mechanisms that Ti improved the dehydrogenation properties of AlH3 were clarified. Ti greatly decreased the dehydrogenation energy of AlH3 by weakening the interaction between Al and H atoms, its influence on the dehydrogenation of AlH3 was however sensitive to the occupation behavior. The calculations indicated that the catalytic effect of Ti was weaker if Ti substitutes for Al than its interstitial occupation.

  10. Doping of AlH3 with alkali metal hydrides for enhanced decomposition kinetics

    NASA Astrophysics Data System (ADS)

    Sandrock, Gary; Reilly, James

    2005-03-01

    Aluminum hydride, AlH3, has inherently high gravimetric and volumetric properties for onboard vehiclular hydrogen storage (10 wt% H2 and 0.148 kg H2/L). Yet it has been widely neglected because of its kinetic limitations for low-temperature H2 desorption and the thermodynamic difficulties associated with recharging. This paper considers a scenario whereby doped AlH3 is decomposed onboard and recharged offboard. In particular, we show that particle size control and doping with small levels of alkali metal hydrides (e.g., LiH) results in accelerated H2 desorption rates nearly high enough to supply fuel-cell and ICE vehicles. The mechanism of enhanced H2 desorption is associated with the formation of alanate windows (e.g., LiAlH4) between the AlH3 particles and the external gas phase. These alanate windows can be doped with Ti to further enhance transparency, even to the point of accomplishing slow decomposition of AlH3 at room temperature. It is highly likely 2010 gravimetric and volumetric vehicular system targets (6 wt% H2 and 0.045 kg/L) can be met with AlH3. But a new, low-cost method of offboard regeneration of spent Al back to AlH3 is yet needed.

  11. First-principles study of structural stabilities of AlH3 under high pressure

    NASA Astrophysics Data System (ADS)

    Feng, Wenxia; Cui, Shouxin; Feng, Min

    2014-07-01

    The structural stabilities and electronic properties of AlH3 under high pressure are investigated by using the plane-wave pseudopotential method. Our results demonstrate that the sequence of the pressure-induced phase transition is Fd 3 bar m(β) → cmcm(α ') → R 3 bar c(α) → Pnma(hp 1) → Pm 3 bar n(hp 2), and the transition pressures are 0.49, 0.91, 47, and 70 GPa, respectively. Im 3 bar m , Pnnm(γ) and P63/m structures are not stable in the 0-100 GPa. β, α ', α, and hp1 structures of AlH3 are nonmetals, while Pm 3 bar n structure of AlH3 is metallic, and the pressure-induced metallization is ascribed to phase transition under higher compression.

  12. Unexpected acidity enhancement triggered by AlH3 association to phosphines.

    PubMed

    Martín-Sómer, Ana; Lamsabhi, Al Mokhtar; Mó, Otilia; Yáñez, Manuel

    2012-06-28

    The complexes formed by the interaction between a series of phosphines R-PH(2) (R = H, CH(3), c-C(3)H(5), C(6)H(5)) and AlH(3) have been investigated through the use of high-level G4 ab initio calculations. These very stable complexes behave as much stronger acids than the isolated phosphines. This dramatic acidity enhancement, which can be as high as 174 kJ mol(-1), results from a much greater stabilization of the anionic deprotonated species with respect to the neutral one, upon AlH(3) association. This effect depends quantitatively on the nature of the substituent R and is smaller for R = C(6)H(5) because of the conjugation of the P lone pair with the aromatic system. More unexpectedly, however, the phosphine-alane complexes, RPH(2):AlH(3), are more acidic than the corresponding phosphine-borane RPH(2):BH(3) analogues. This unexpected result is due to the enhanced stability of the anionic deprotonated species for complexes involving AlH(3), because the delocalization of the newly created P lone pair with the P-Al bonding density is more favorable when the Lewis acid is aluminum trihydride than when it is borane.

  13. Electron band structure of the high pressure cubic phase of AlH3

    NASA Astrophysics Data System (ADS)

    Shi, Hongliang; Zarifi, Niliffar; Yim, Wai-Leung; Tse, J. S.

    2012-07-01

    The electronic band structure of the cubic Pm3n phase of AlH3 stable above 100 GPa is examined with semi-local, Tran-Blaha modified Becke-Johnson local density approximation (TB-mBJLDA), screened hybrid density functionals and GW methods. The shift of the conduction band to higher energy with increasing pressure is predicted by all methods. However, there are significant differences in detail band structure. In the pressure range from 90 to160 GPa, semi-local, hybrid functional and TB-mBJLDA calculations predicted that AlH3 is a poor metal. In comparison, GW calculations show a gap opening at 160 GPa and AlH3 becomes a small gap semi-conductor. From the trends of the calculated band shifts, it can be concluded that the favourable conditions leading to the nesting of Fermi surfaces predicted by semi-local calculation have disappeared if the exchange term is included. The results highlight the importance of the correction to the exchange energy on the band structure of hydrogen dominant dense metal hydrides at high pressure hydrides and may help to rationalize the absence of superconductivity in AlH3 from experimental measurements.

  14. Lewis base complexes of AlH3: prediction of preferred structure and stoichiometry.

    PubMed

    Humphries, Terry D; Munroe, Keelie T; Decken, Andreas; McGrady, G Sean

    2013-05-21

    The structures adopted by a range of complexes AlH3·nL, (n = 1 or 2), have been explored in detail to identify the factors that determine the value of n, and whether a monomeric or dimeric arrangement is preferred for the 1 : 1 complexes. Single-crystal X-ray diffraction, vibrational and NMR spectroscopies, and thermal analysis data have been collected, DFT calculations have been performed for AlH3·nL species, and pK(a) values have been collated for a series of amine and phosphine ligands L. The pK(a) of the ligand L exerts an important influence on the type of complex formed: as the basicity of L increases, a monomeric structure is favoured over a dimeric arrangement. Dimeric amine complexes form if pK(a) < 9.76, while monomeric complexes are preferred when pK(a) > 9.99. The steric requirements of L also influence the structural preference: bulky ligands with large cone angles (>163°) tend to favour formation of monomers, while smaller cone angles (<125°) encourage the formation of dimeric or 1 : 2 adducts. The steric bulk of the ligand appears to be more important for phosphine complexes, with smaller phosphines being unable to stabilise the complex at ambient temperatures even through dimerisation. Raman spectroscopy and DFT calculations have been particularly helpful in elucidating the stoichiometric preferences of complexes that have been contentious; these include AlH3·NMe2Et, AlH3·NMe3 and AlH3·nEt2O.

  15. Electrical conductivity of aluminum hydride AlH3 at high pressure and temperature

    NASA Astrophysics Data System (ADS)

    Shakhray, Denis; Molodets, Alexander; Fortov, Vladimir; Khrapak, Aleksei

    2009-06-01

    A study of electrophysical and thermodynamic properties of alane AlH3 under multi shock compression has been carried out. The increase in specific electroconductivity of alane at shock compression up to pressure 100 GPa have been measured. High pressures and temperatures were obtained with explosive device, which accelerates the stainless impactor up to 3 km/sec. The impact shock is split into a shock wave reverberating in alane between two stiff metal anvils. The conductivity of shocked alane increases in the range up to 60-75 GPa and is about 30 1/Ohm*cm. In this region the semiconductor regime is true for shocked alane. The conductivity of alane achieves approximately 500 1/Ohm*cm at 80-90 GPa. In this region conductivity is interpreted in frames of the conception of the ``dielectric catastrophe'', taking into consideration significant difference between electronic states of isolated AlH3 molecule and condensed alane.

  16. Stability of ferromagnetic phase in Fe-doped AlH3

    NASA Astrophysics Data System (ADS)

    Nisar, J.; Scheicher, R. H.; Peng, X.; Ahuja, R.

    2009-03-01

    We have carried out a systematic theoretical investigation of Fe-doped AlH3 to study its magnetic properties and to assess the stability of the ferromagnetic phase in this material. All calculations were performed using the projector augmented-wave method and generalized-gradient approximation (GGA) as well as GGA+U. The magnetic moment is found to be constant at 1.1 μB per Fe-atom in the ferromagnetic configuration for distances between adjacent Fe atoms varying from 3.25 Å to 7.41 Å. We conclude that the ferromagnetic phase in Fe-doped AlH3 is stable both for near and far configurations of Fe. The stability of the ferromagnetic phase is due to the holes created by Fe-doping and the larger level splitting of the interacting gap states within the ferromagnetic phase.

  17. Kinetics of hydrogen desorption from MgH2 and AlH3 hydrides

    NASA Astrophysics Data System (ADS)

    Terent'ev, P. B.; Gerasimov, E. G.; Mushnikov, N. V.; Uimin, M. A.; Maikov, V. V.; Gaviko, V. S.; Golovatenko, V. D.

    2015-12-01

    Kinetic parameters of the process of thermal decomposition of the MgH2 hydride (obtained by the method of the mechanoactivation of magnesium in a hydrogen atmosphere) and of the commercial AlH3 hydride have been studied upon the rapid heating in the range of temperatures of 150-510°C at hydrogen pressures of 0-2 atm. The time dependences of the amount of hydrogen released by the metal hydrides at different temperatures and pressures have been determined. It has been shown that the activation energies of the hydrogen desorption are 135 kJ/mol for MgH2 and 107 kJ/mol for AlH3. The maximum rates of hydrogen desorption from the investigated metal hydrides have been established, and the temperatures and initial pressures that ensure the maximum rate and maximum volume of the hydrogen release have been determined.

  18. AlH3 and Al2H6: Magic Clusters with Unmagical Properties

    NASA Astrophysics Data System (ADS)

    Rao, B. K.; Jena, P.; Burkart, S.; Ganteför, G.; Seifert, G.

    2001-01-01

    Enhanced stability, low electron affinity, and high ionization potential are the hallmarks of a ``magic'' cluster. With an electron affinity of 0.28 eV, ionization potential of 11.43 eV, and a large binding energy, AlH3 satisfies these criteria. However, unlike other magic clusters that interact only weakly with each other, two AlH3 clusters bind to each other with an energy of 1.54 eV. The resulting Al2H6, while also a magic cluster in its own right, possesses the most unusual property that the difference between its adiabatic and vertical detachment energy is about 2 eV-the largest of any known cluster. These results, based on density functional theory, are verified experimentally through photodetachment spectroscopy.

  19. Undamped low-energy plasmon in AlH3 at high pressure

    NASA Astrophysics Data System (ADS)

    Gurtubay, I. G.; Rousseau, B.; Bergara, A.

    2010-08-01

    Pressure strongly modifies electronic and optical properties of solids. In this work we report ab initio time-dependent density-functional theory calculations of the dielectric response of the high-pressure metallic phase of aluminum hydride (AlH3) within the random-phase approximation. Besides the conventional free-electronlike plasmon, which is highly damped, low-energy transitions between states near the Fermi level that appear in this metallized phase give rise to a low-energy undamped collective mode. This feature is expected to induce an abrupt edge in the experimentally measured reflectivity just below 1 eV and also affect electronic correlations close to the Fermi energy. Our work shows that AlH3 is basically a hydrogen sublattice weakly perturbed by Al atoms.

  20. First-principles prediction of low-energy structures for AlH3

    NASA Astrophysics Data System (ADS)

    Sun, Shoutian; Ke, Xuezhi; Chen, Changfeng; Tanaka, Isao

    2009-01-01

    We report density-functional calculations that predict ten different low-energy structures for aluminum hydride AlH3 with space groups Pnma , P6/mmm , I4/mcm , P4/mbm , P4/nmm , Pm3¯m , P21/m , P21/c , Pbcm , and P4/n . Phonon calculations within harmonic approximation reveal unstable modes in the P6/mmm , I4/mcm , P4/mbm , P4/nmm , Pm3¯m , P21/m , and P21/c structures, indicating that they are unstable at low temperatures. The calculations show that the thermodynamic stabilities for AlH3 with space groups Pnma , Pbcm , and P4/n are overall close to the existing α - and γ-AlH3 . From x-ray powder-diffraction patterns, the simulated main-peak positions for AlH3 (P4/n) are in good agreement with experimental δ-AlH3 . A full Rietveld analysis reveals that the fitting space groups R3¯c , Pbcm , and Pnma to the experimental x-ray powder-diffraction pattern of α-AlH3 gives almost the same satisfactory result.

  1. Theoretical study of the vibrational properties of NaAlH4 with AlH3 vacancies.

    PubMed

    Zhang, Feng; Wang, Yan; Chou, M Y

    2011-01-01

    It has been suggested that the diffusion of AlH3 vacancies plays an essential role in the decomposition of NaAlH4, a prototypical material for hydrogen storage. We find from first-principles calculations that the AlH3 vacancy induces several isolated vibrational modes that are highly localized in the vacancy region with frequencies within the phonon gaps of pure NaAlH4 in both the alpha and gamma phases. Thus, the proposed existence of AlH3 vacancies in the dehydrogenation reaction of NaAlH4 can be possibly confirmed with the experimental detection of these unique vibrational modes associated with the AlH3 vacancy.

  2. High pressure Raman and visible absorption study of AlH3

    NASA Astrophysics Data System (ADS)

    Shimura, N.; Takeichi, T.; Kume, T.; Sasaki, S.; Shimizu, H.; Ohmura, A.; Ikeda, K.; Nakamori, Y.; Orimo, S.

    2010-03-01

    Raman and visible absorption spectra of AlH3 were measured at high pressures in order to clarify the structural and electronic phase transitions. For the Raman results, abrupt decrease in Raman intensity was found at 30 GPa, implying that there exists a structural transition from the α phase to higher pressure phase. Correspondingly, the spectral change in the optical absorption was observed at almost the same pressure of 30 GPa. From the absorption measurements, the band gap is expected to close at the pressure higher than 50 GPa.

  3. Phonon, IR, and Raman spectra, NMR parameters, and elastic constant calculations for AlH3 polymorphs.

    PubMed

    Vajeeston, P; Ravindran, P; Fjellvåg, H

    2011-10-06

    The electronic structure, lattice dynamics, and mechanical properties of AlH(3) phases have been studied by density functional calculations. The chemical bonding in different polymorphs of AlH(3) are evaluated on the basis of electronic structures, charge density analysis, and atomic charges, as well as bond overlap population analysis and the Born effective charges. The phonon dispersion relations and phonon density of states of all the polymorphs of AlH(3) are calculated by direct force-constant method. Application of pressure induces seqauence of phase transitions in β-AlH(3) which are understood from the phonon dispersive curves of the involved phases. The previously predicted phases (Chem. Mater. 2008, 20, 5997) are found to be dynamically stable. The calculated single crystal elastic constants reveal that all the studied AlH(3) polymorphs are easily compressible. The chemical bonding of these polymorphs have noticeable covalent character (except the hp2 phase) according to the present chemical bonding analyses. For all these polymorphs, the NMR-related parameters, such as isotropic chemical shielding, quadrupolar coupling constant, and quadrupolar asymmetry, are also calculated. All IR- and Raman-active phonon frequencies, as well as the corresponding intensities, are calculated for all the AlH(3) polymorphs and are compared with available experimental results.

  4. Metallization of aluminum hydride AlH3 at high multiple-shock pressures

    NASA Astrophysics Data System (ADS)

    Molodets, A. M.; Shakhray, D. V.; Khrapak, A. G.; Fortov, V. E.

    2009-05-01

    A study of electrophysical and thermodynamic properties of alane AlH3 under multishock compression has been carried out. The increase in specific electroconductivity of alane at shock compression up to pressure 100 GPa has been measured. High pressures and temperatures were obtained with an explosive device, which accelerates the stainless impactor up to 3 km/s. A strong shock wave is generated on impact with a holder containing alane. The impact shock is split into a shock wave reverberating in alane between two stiff metal anvils. This compression loads the alane sample by a multishock manner up to pressure 80-90 GPa, heats alane to the temperature of about 1500-2000 K, and lasts 1μs . The conductivity of shocked alane increases in the range up to 60-75 GPa and is about 30(Ωcm)-1 . In this region the semiconductor regime is true for shocked alane. The conductivity of alane achieves approximately 500(Ωcm)-1 at 80-90 GPa. In this region, conductivity is interpreted in frames of the conception of the “dielectric catastrophe,” taking into consideration significant differences between the electronic states of isolated molecule AlH3 and condensed alane.

  5. In situ X-ray diffraction measurement of the hydrogenation and dehydrogenation of aluminum and characterization of the recovered AlH3

    NASA Astrophysics Data System (ADS)

    Saitoh, H.; Sakurai, Y.; Machida, A.; Katayama, Y.; Aoki, K.

    2010-03-01

    Pristine aluminum was hydrogenated to form AlH3 at 8.9 GPa and 600 °C. The cyclic formation and decomposition of the hydride were measured by in situ synchrotron X-ray diffraction measurement. AlH3 synthesized under high pressure and temperature was recovered at ambient conditions. The recovered AlH3 was characterized by conventional powder X-ray diffraction measurement and Raman spectroscopy. The results of the characterization were consistent with that obtained for chemically prepared AlH3 and indicated that single phase α-AlH3 was obtained.

  6. Dehydriding reaction of AlH3: in situ microscopic observations combined with thermal and surface analyses

    NASA Astrophysics Data System (ADS)

    Ikeda, K.; Muto, S.; Tatsumi, K.; Menjo, M.; Kato, S.; Bielmann, M.; Züttel, A.; Jensen, C. M.; Orimo, S.

    2009-05-01

    The dehydriding reaction of single-phase α- AlH3 was investigated by in situ microscopic observations combined with thermal and surface analyses. Before the dehydriding reaction, primary AlH3 particles of size 100 nm-1 µm were thought to be covered by an oxide layer with a thickness of less than 5 nm. Both the precipitation/grain-growth of metallic Al of size 1-50 nm and an increase in 'boundary space' were clearly observed inside the particles, while the morphologies of the particles covered by the layer did not change during the dehydriding reaction. This preliminary report provides fundamental information for a further study of AlH3 as a possible hydrogen storage material.

  7. Dehydriding reaction of AlH3: in situ microscopic observations combined with thermal and surface analyses.

    PubMed

    Ikeda, K; Muto, S; Tatsumi, K; Menjo, M; Kato, S; Bielmann, M; Züttel, A; Jensen, C M; Orimo, S

    2009-05-20

    The dehydriding reaction of single-phase alpha- AlH3 was investigated by in situ microscopic observations combined with thermal and surface analyses. Before the dehydriding reaction, primary AlH3 particles of size 100 nm-1 microm were thought to be covered by an oxide layer with a thickness of less than 5 nm. Both the precipitation/grain-growth of metallic Al of size 1-50 nm and an increase in 'boundary space' were clearly observed inside the particles, while the morphologies of the particles covered by the layer did not change during the dehydriding reaction. This preliminary report provides fundamental information for a further study of AlH3 as a possible hydrogen storage material.

  8. Density Functional Studies of NaAlH_4, NaH and AlH_3

    NASA Astrophysics Data System (ADS)

    Aguayo, Aaron; Singh, David J.

    2004-03-01

    We report electronic structure investigations of the bonding of the alanate NaAlH4 and the related materials NaH and AlH_3. The results are based on density functional calculations using the LAPW method. All three compounds are insulators. AlH3 has a substantially covalent electronic structure with a band gap of approximately 2 eV, while NaAlH4 and NaH both show larger band gaps of approximately 4 eV and are much more ionic. This ionic character is stabilized by the Madelung energy in the respective crystal structures. We discuss the implications for H storage.

  9. Watching the dehydrogenation of alane (AlH3) in a TEM

    NASA Astrophysics Data System (ADS)

    Beattie, Shane; Humphries, Terry; Weaver, Louise; McGrady, Sean

    2008-03-01

    Alane (AlH3) is a promising candidate for on-board hydrogen storage applications. Its theoretical gravimetric capacity is 10.1 percent and decomposition is achieved with modest heating (60-200 deg C). We studied the dehydrogenation of alane, insitu, in a TEM. Alane powder was loaded into the TEM and heated at 80 deg C. We were able to `watch' the dehydrogenation of the alane to aluminum. Electron diffraction and dark fiend images are used to show how and where the aluminum crystallites grow. Although crystalline aluminum phases were successfully identified, some of the sample remained amorphous. We will discuss the nature of the amorphous material and present images clearly identifying the nature of the aluminum crystallites.

  10. Giant anharmonicity suppresses superconductivity in AlH3 under pressure

    NASA Astrophysics Data System (ADS)

    Rousseau, Bruno; Bergara, Aitor

    2010-09-01

    The anharmonic self-energy of two zone boundary phonons were computed to lowest order for AlH3 in the Pm3¯n structure at 110 GPa. The wave vector and branch index corresponding to these modes are situated in a region of phase space providing most of the electron-phonon coupling. The self-energies are found to be very large and the anharmonic contribution to the linewidth of one of the modes studied could be distinguished from the electron-phonon linewidth. It is found that anharmonicity suppresses the electron-phonon coupling parameter λ , providing a possible explanation for the disagreement between experiment and previous theoretical studies of superconductivity in this system.

  11. Chemical Bonding of AlH3 Hydride by Al-L2,3 Electron Energy-Loss Spectra and First-Principles Calculations

    PubMed Central

    Tatsumi, Kazuyoshi; Muto, Shunsuke; Ikeda, Kazutaka; Orimo, Shin-Ichi

    2012-01-01

    In a previous study, we used transmission electron microscopy and electron energy-loss (EEL) spectroscopy to investigate dehydrogenation of AlH3 particles. In the present study, we systematically examine differences in the chemical bonding states of Al-containing compounds (including AlH3) by comparing their Al-L2,3 EEL spectra. The spectral chemical shift and the fine peak structure of the spectra were consistent with the degree of covalent bonding of Al. This finding will be useful for future nanoscale analysis of AlH3 dehydrogenation toward the cell. PMID:28816996

  12. Ultra-low diffusion barriers for the AlH3-related vacancies in γ-NaAlH4

    NASA Astrophysics Data System (ADS)

    Zhang, Feng; Wang, Yan; Chou, Mei-Yin

    2011-03-01

    It has been suggested that the diffusion of AlH3 -related vacancies plays an essential role in the decomposition of NaAlH4 , a prototypical material for hydrogen storage[1,2]. We find from first-principles calculations that the diffusion barrier for both the neutral AlH3 vacancy and the charged AlH4- vacancy in the newly proposed γ -phase of NaAlH4 is only about 0.1 eV, much lower than the barrier for the diffusion of corresponding vacancies in the conventional α -phase 0.5 eV, calculated with the same method. Possible schemes to facilitate the α --> γ phase transformation in order to improve the kinetics of the decomposition reaction of NaAlH4 will also be discussed.

  13. Elastic, superconducting, and thermodynamic properties of the cubic metallic phase of AlH3 via first-principles calculations

    NASA Astrophysics Data System (ADS)

    Wei, Yong-Kai; Ge, Ni-Na; Ji, Guang-Fu; Chen, Xiang-Rong; Cai, Ling-Cang; Zhou, Su-Qin; Wei, Dong-Qing

    2013-09-01

    The lattice dynamic, elastic, superconducting, and thermodynamic properties of the high-pressure cubic metallic phase AlH3 are studied within density function theory. The calculated elastic modulus and phonon dispersion curves at various pressures indicate that the cubic phase is both mechanically and dynamically stable above 73 GPa. The superconducting transition temperature was calculated using Allen-Dynes modification of the McMillan formula based on the Bardeen-Cooper-Schrieffer theory. It is found that Tc approaches a linear decrease in the low pressure range at the rate dTC/dP ≈-0.22 K/GPa but gradually decreases exponentially at higher pressure, and then it becomes 0 K upon further compression. The calculations indicate that Tc is about 2.042 K at 110 GPa, in agreement with experimental results. The soft phonon modes, especially the lowest acoustic mode, contribute almost 79% to the total electron-phonon coupling parameter sλ for cubic AlH3 at 73 GPa. However, they disappear gradually with increasing pressure, showing a responsibility for the variation of Tc. The thermodynamic properties of cubic AlH3, such as the dependence of thermal expansion coefficient αV on pressure and temperature, the specific heat capacity CP, as well as the electronic specific heat coefficient Cel, were also investigated by the quasi-harmonic approximation theory.

  14. Theoretical study of the vibrational properties of NaAlH4 with AlH3 vacancies

    NASA Astrophysics Data System (ADS)

    Chou, Mei-Yin; Zhang, Feng; Wang, Yan

    2011-03-01

    We investigate from first-principles calculations the vibrational properties in the presence of the AlH3 vacancy in both α and γ phases of NaAlH4 . When AlH3 is removed from an AlH4- anion, the remaining H recombines with another neighboring AlH4- anion and forms an AlH52 - unit with slightly deformed D3 h symmetry. For both α - and γ -NaAlH4 , the AlH3 vacancy induces several isolated phonon modes that are highly localized on the AlH52 - unit with frequencies within the band gap separating the Al-H stretching modes and Al-H bending modes in pure NaAlH4 . Similar localized phonon modes also exist in the gap separating the Al-H bending modes and the modes involving the rotation of AlH4- anions for the γ phase. On the other hand, for both α and γ phases of NaAlH4 with charged AlH4- vacancies, no isolated phonon modes were found to be localized in the vacancy region with frequencies within the band gap of the pure crystal. These theoretical findings suggest further experimental studies to identify the defects that are involved in the decomposition of NaAlH4 .

  15. Photoelectron spectroscopy of the aluminum hydride anions: AlH2-, AlH3-, Al2H6-, Al3H9-, and Al4H12-

    NASA Astrophysics Data System (ADS)

    Zhang, Xinxing; Wang, Haopeng; Collins, Evan; Lim, Alane; Ganteför, Gerd; Kiran, Boggavarapu; Schnöckel, Hansgeorg; Eichhorn, Bryan; Bowen, Kit

    2013-03-01

    We report measurements of the negative ion photoelectron spectra of the simple aluminum hydride anions: AlH2-, AlH3-, Al2H6-, Al3H9-, and Al4H12-. From these spectra, we measured the vertical detachment energies of the anions, and we estimated the electron affinities of their neutral counterparts. Our results for AlH2-, AlH3-, and Al2H6- were also compared with previous predictions by theory.

  16. Photoelectron spectroscopy of the aluminum hydride anions: AlH2(-), AlH3(-), Al2H6(-), Al3H9(-), and Al4H12(-).

    PubMed

    Zhang, Xinxing; Wang, Haopeng; Collins, Evan; Lim, Alane; Ganteför, Gerd; Kiran, Boggavarapu; Schnöckel, Hansgeorg; Eichhorn, Bryan; Bowen, Kit

    2013-03-28

    We report measurements of the negative ion photoelectron spectra of the simple aluminum hydride anions: AlH2(-), AlH3(-), Al2H6(-), Al3H9(-), and Al4H12(-). From these spectra, we measured the vertical detachment energies of the anions, and we estimated the electron affinities of their neutral counterparts. Our results for AlH2(-), AlH3(-), and Al2H6(-) were also compared with previous predictions by theory.

  17. Lewis base complexes of AlH3: structural determination of monomeric and polymeric adducts by X-ray crystallography and DFT calculations.

    PubMed

    Humphries, Terry D; Munroe, Keelie T; Decken, Andreas; McGrady, G Sean

    2013-05-21

    The AlH3 adducts of TMEDA (Me2NCH2CH2NMe2), DIOX (O(CH2CH2)2O), TEA (Et3N), BDMA (PhNMe2), and TMPDA (Me2NCH2CH2CH2NMe2) have each been characterised by single-crystal X-ray diffraction at low temperature, by (1)H, (14)N and (27)Al NMR and FT-Raman and FT-IR spectroscopy, and by DFT calculations and elemental analysis. Hence, AlH3·TMEDA and AlH3·DIOX are both shown to adopt a polymeric structure, with the bidentate ligand bridging two Al centres, each of which adopts a trigonal bipyramidal (TBP) arrangement with equatorial hydride moieties. The 1 : 2 adduct AlH3·2BDMA is monomeric but the geometry at the Al centre resembles closely that of the polymeric TMEDA and DIOX complexes. AlH3·TEA alone adopts a monomeric structure in which the Al centre is tetrahedrally coordinated by three hydride and one amine ligand. The Al-L bond distance of 2.0240(17) Å for AlH3·TEA is the shortest of all the complexes in this study, and AlH3·TEA also possesses the shortest Al-H bonds. AlH3·DIOX has the shortest Al-L bond distance of the polymeric species (2.107(14) Å) on account of the higher electronegativity of the oxygen donor. The structure of AlH3·TMEDA was determined at low temperature (monoclinic space group P2(1)/c), and salient features are compared to the previous room temperature study, for which a highly disordered orthorhombic space group (P2(1)2(1)2(1)) was reported. The polymeric structures appear to be stabilised by a number of intermolecular interactions and unconventional hydrogen bonds; these are most pronounced for AlH3·DIOX, whose chains are connected by highly directional C-H···H-Al bonding with an H···H distance of 2.32(6) Å.

  18. Dynamical stability of the cubic metallic phase of AlH3 at ambient pressure: Density functional calculations

    NASA Astrophysics Data System (ADS)

    Kim, D. Y.; Scheicher, R. H.; Ahuja, R.

    2008-09-01

    We have characterized the high-pressure cubic phase of AlH3 from ab initio using density functional theory to determine mechanical as well as electronic properties and lattice dynamics (phonon-dispersion relations) from the response function method. Our zero-temperature phonon calculations show the softening of a particular mode with decreasing pressure, indicating the onset of a dynamic instability that continues to persist at ambient conditions. This instability can, however, be removed when finite electronic temperature effects are considered in the calculations. We furthermore identify a particular momentum transfer in the phonon-dispersion relation, matching a corresponding momentum transfer in the electronic band structure.

  19. Temperature behavior of the AlH3 polymorph by in situ investigation using high resolution Raman scattering.

    PubMed

    Giannasi, A; Colognesi, D; Fichtner, M; Röhm, E; Ulivi, L; Ziparo, C; Zoppi, M

    2011-02-10

    A Raman investigation of the AlH(3) polymorph has been carried out at a low temperature (20 K) under helium atmosphere (2 bar). The pristine material was composed of three polymorphs, namely, the α, β, and γ phases. The β phase has been removed by warming the sample to 70 °C, while further heating at 100 °C was used to remove the γ phase. This allowed us to evidence, on a purely experimental basis, the characteristic Raman spectrum for each phase. Raman spectra, for the three phases, have been also calculated using density functional theory, and the results have been compared to the present experimental data, allowing for a univocal assignment, to each phase, of its characteristic spectral features.

  20. A structural study of bis-(trimethylamine)alane, AlH 3·2NMe 3, by variable temperature X-ray crystallography and DFT calculations

    NASA Astrophysics Data System (ADS)

    Humphries, Terry D.; Sirsch, Peter; Decken, Andreas; Sean McGrady, G.

    2009-04-01

    The structure of AlH 3·2NMe 3 has been investigated by single-crystal X-ray diffraction over the range of 296-173 K. Over this temperature range a phase change is observed from Cmca to Pbcm where the methyl groups convert from a statistically disordered conformation to adopt a mutually eclipsed conformation at lower temperatures. Measurement of the unit cell dimensions shows a decrease in the lengths of the a and b axes, and an increase in that of the c axis as the temperature is lowered, with inflections apparent between 223 and 233 K in the region of the phase change. Low-temperature DSC measurements reveal the change from Pbcm to Cmca to occur at 218.3 K, with an enthalpy of 107.7 J mol -1. The molecular structure of AlH 3·2NMe 3 is compared with those of related amine adducts of Group 13 hydrides, either measured experimentally or calculated using DFT methods. 1H, 13C and 27Al NMR spectroscopy has also been utilized to characterize AlH 3·2NMe 3 and its 1:1 counterpart AlH 3·NMe 3.

  1. Intrinsic and mechanically modified thermal stabilities of α-, β- and γ-aluminum trihydrides AlH3

    NASA Astrophysics Data System (ADS)

    Orimo, S.; Nakamori, Y.; Kato, T.; Brown, C.; Jensen, C. M.

    2006-04-01

    The intrinsic and mechanically modified thermal stabilities of the α-, β-, and γ-phases of AlH3 have been experimentally determined. The thermogravimetric profiles of the α- and γ-phases exhibit dehydriding reactions in the temperature range of 370 450 K. The amounts of hydrogen released are nearly 9 mass %. The profile of the β-phase shows the continuous dehydriding reactions, which differs from the other two phases. The values of the enthalpy of dehydriding reactions ΔHdehyd. are determined to be 6.0±1.5, -3˜-5 and 1.0±0.5 kJ/mol H2 for the α-, β- and γ-phases, respectively. The milling-time dependences of the powder X-ray diffraction measurement and thermal analyses indicate the occurrence of the dehydriding reactions both in the α- and γ-phases during milling, but there is no drastic change in the β-phase.

  2. Initial gas phase reactions between Al(CH3)3/AlH3 and ammonia: theoretical study.

    PubMed

    Lisovenko, Anna S; Morokuma, Keiji; Timoshkin, Alexey Y

    2015-01-29

    Mechanisms of initial stages of gas phase reactions between trimethylaluminum and ammonia have been explored by DFT studies. Subsequent substitution of CH3 groups in AlMe3 by amido groups and substitution of hydrogen atoms in ammonia by AlMe2 groups have been considered. Structures of Al(CH3)x(NH2)3-x, NHx(Al(CH3)2)3-x (x = 0-3) and related donor-acceptor complexes, dimerization products, and reaction pathways for the methane elimination have been obtained. The transition state for the first methane elimination from Al(CH3)3NH3 adduct is the highest point on the reaction pathway; subsequent processes are exothermic and do not require additional activation energy. In excess ammonia, subsequent methane elimination reactions may lead to formation of [Al(NH2)3]2, while in excess trimethylaluminum, formation of N(AlMe2)3 is feasible. Formation of [AlMe2NH2]2 dimer is very favorable thermodynamically. Studies on model reactions between AlH3 and NH3 indicate that reaction barriers obtained for hydrogen-substituted species may serve as an upper estimate in studying the reactivity of methyl-substituted analogues in more complex systems.

  3. Formation of Al2H7- anions--indirect evidence of volatile AlH3 on sodium alanate using solid-state NMR spectroscopy.

    PubMed

    Felderhoff, Michael; Zibrowius, Bodo

    2011-10-14

    After more than a decade of intense research on NaAlH(4) doped with transition metals as hydrogen storage material, the actual mechanism of the decomposition and rehydrogenation reaction is still unclear. Early on, monomeric AlH(3) was named as a possible transport shuttle for aluminium, but never observed experimentally. Here we report for the first time the trapping of volatile AlH(3) produced during the decomposition of undoped NaAlH(4) by an adduct of sodium alanate and crown ether. The resulting Al(2)H(7)(-) anion was identified by solid-state (27)Al NMR spectroscopy. Based on this indirect evidence of volatile alane, we present a simple description of the processes occurring during the reversible dehydrogenation of NaAlH(4).

  4. Preparation of monopodal and bipodal aluminum surface species by selective protonolysis of highly reactive [AlH3(NMe2Et)] on silica.

    PubMed

    Sauter, D W; Chiari, V; Aykac, N; Bouaouli, S; Perrin, L; Delevoye, L; Gauvin, R M; Szeto, K C; Boisson, C; Taoufik, M

    2017-09-12

    The synthesis and characterization of silica-grafted monopodal and bipodal aluminum hydrides has been achieved starting from 200 °C- and 700 °C-annealed silica and [AlH3(NMe2Et)]. The mechanism by which aluminum trishydride reacts with isolated and vicinal silanols, assisted by the amine, has been investigated computationally at the ωB97XD-DFT level.

  5. Al-H σ-bond coordination: expanded ring carbene adducts of AlH3 as neutral bi- and tri-functional donor ligands.

    PubMed

    Abdalla, Joseph A B; Riddlestone, Ian M; Tirfoin, Remi; Phillips, Nicholas; Bates, Joshua I; Aldridge, Simon

    2013-06-21

    Thermally robust expanded ring carbene adducts of AlH3 have been synthesized with a view to probing their ligating abilities via Al-H σ-bond coordination. While κ(2) binding to the 14-electron [Mo(CO)4] fragment is readily demonstrated, interaction with [Mo(CO)3] results in μ:κ(1),κ(1) and μ:κ(2),κ(2) bridging linkages rather than terminal κ(3) binding.

  6. Reaction kinetics for the solid state synthesis of the AlH3/MgCl2 nano-composite by mechanical milling.

    PubMed

    Duan, C W; Hu, L X; Sun, Y; Zhou, H P; Yu, H

    2015-09-14

    The process of mechanical milling has been proved to be a cost-effective way to synthesize the AlH3/MgCl2 nano-composite by using MgH2 and AlCl3 as reagents. However, so far there is no comprehensive knowledge of the kinetics of this process. In an effort to predict the reaction progress and optimize the milling parameters, the kinetics of the synthesis of the AlH3/MgCl2 nano-composite by mechanical milling of MgH2 and AlCl3 is experimentally investigated in the present work. The reaction progress or the transformation fraction upon milling for different times is evaluated using the isothermal hydrogen desorption test of the as-milled samples at 220 °C, which is much lower than the threshold temperature for the de-hydriding of the reagent MgH2 but enough for the de-hydriding of the as-synthesized nano-sized AlH3. The effects of milling parameters on the reaction kinetics as well as the underlying mechanism are discussed by referring to the mechanical energy input intensity, the vial temperature and the Gibbs free energy change for the reaction. Furthermore, it is found that the Johnson-Mehl-Avrami (JMA) model can well describe the kinetics theoretically. By fitting the experimental data with the JMA expression, the theoretical kinetics expressions, the equation parameters, and the activation energy are obtained.

  7. Addition of ammonia to AlH3 and BH3. Why does only aluminum form 2:1 adducts?

    PubMed

    Czerw, M; Goldman, A S; Krogh-Jespersen, K

    2000-01-24

    The electronic structures of the mono- and bisammonia adducts EH3NH3 and EH3(NH3)2, E = B and Al, have been investigated using ab initio electronic structure methods. Geometries were optimized at the MP2/cc-pVTZ level. Higher-level correlated methods (MP4(SDTQ), QCISD(T), CCSD(T)), as well as the G2 and CBS-Q methods, were used to obtain accurate bond dissociation energies. The E-N bond dissociation energy (De) is computed near 33 kcal/mol (E = B) and 31 kca/mol (E = Al), respectively. Whereas the Al-N bond energy pertaining to the second ammonia molecule in AlH3(NH3)2 is 11-12 kcal/mol, only a transition-state structure may be located for the species BH3(NH3)2. We analyze factors which may distinguish Al from B with respect to the formation of stable bisamine adducts. The most significant difference relates to electronegativity and hence the propensity of boron to engage in predominantly covalent bonding, as compared with the bonding of aluminum with ammonia, which shows substantial electrostatic character. Neither steric factors nor the participation of d-orbitals is found to play an important role in differentiating aluminum from boron. The lesser electronegativity of third-row elements appears to be the critical common feature allowing the formation of hypercoordinate complexes of these elements in contrast to their second-row analogues. Consideration of some group 14 analogues and hard/soft acid/base effects supports this view.

  8. Ab initio studies on phase transition, thermoelastic, superconducting and thermodynamic properties of the compressed cubic phase of AlH3

    NASA Astrophysics Data System (ADS)

    Wei, Yong-Kai; Ge, Ni-Na; Chen, Xiang-Rong; Ji, Guang-Fu; Cai, Ling-Cang; Gu, Zhuo-Wei

    2014-03-01

    The phase transition, thermoelastic, lattice dynamic, and thermodynamic properties of the cubic metallic phase AlH3 were obtained within the density-function perturbation theory. The calculated elastic modulus and phonon dispersion curves under various pressures at 0 K indicate the cubic phase is both mechanically and dynamically stable above 73 GPa. The superconducting transition temperature Tc was calculated using the Allen-Dynes modification of the McMillan formula based on BCS theory. The calculations show that Tc for the cubic phase AlH3 is 8.5 K (μ*=0.1) at the onset of this phase (73 GPa), while decreases to 5.7 K at 80 GPa and almost disappears at 110 GPa, consisting with experimental phenomenon that there was no superconducting transition observed down to 4 K over a wide pressure range 110-164 GPa. It is found that the soft phonon mode for branch 1, namely, the lowest acoustic mode, plays a crucial role in elevating the total EPC parameter λ of cubic AlH3. And the evolution of Tc with pressure follows the corresponding change of this soft mode, i.e. this mode is responsible for the disappearance of Tc in experiments. Meanwhile, the softening of this lowest acoustic mode originates from the electronic momentum transfer from M to R point. This phenomenon provides an important insight into why drastic changes in the diffraction pattern were observed in the pressure range of 63-73 GPa in Goncharenko's experiments. Specifically, once finite electronic temperature effects are included, we find that dynamical instabilities can be removed in the phonon dispersion for P ≥63 GPa, rendering the metastability of this phase in the range of 63-73 GPa, and Tc (15.4 K) becomes remarkably high under the lowest possible pressure (63 GPa) compared with that of under 73 GPa (8.5 K). Our calculations open the possibility that finite temperature may allow cubic AlH3 to be dynamically stabilized even for pressures below 73 GPa. It is reasonable to deduced that if special techniques, such as rapid decompression, quenching, and annealing, are implemented in experiments, higher Tc can be observed in hydrides or hydrogen-rich compounds under much lower pressure than ever before.

  9. Automated calculation of fundamental frequencies: Application to AlH3 using the coupled-cluster singles-and-doubles with perturbative triples method

    NASA Astrophysics Data System (ADS)

    Ruden, T. A.; Taylor, P. R.; Helgaker, T.

    2003-07-01

    An automated scheme for calculating numerical derivatives of functions is presented and applied to the Taylor expansion of potential energy surfaces. The computational cost is reduced by invoking the symmetry properties of noncubic groups. The scheme is applied to the quartic force field of isotopomers of AlH3 by numerical differentiation of the CCSD(T) energy, using the cc-pCVQZ basis for the harmonic part of the potential and the cc-pCVTZ basis for the anharmonic part. From this force field, zero-order vibrational corrections to the geometry and the fundamental frequencies are calculated by second-order perturbation theory. The results are compared with experiment and previous calculations.

  10. Mechanistic models for LAH reductions of acetonitrile and malononitrile. Aggregation effects of Li+ and AlH3 on imide-enamide equilibria.

    PubMed

    Glaser, Rainer; Ulmer, Laura; Coyle, Stephanie

    2013-02-01

    The results are reported of an ab initio study of the addition of LiAlH(4) to acetonitrile and malononitrile at the MP2(full)/6-311+G* level considering the effects of electron correlation at higher levels up to QCISD(T)/6-311++G(2df,2pd) and including ether solvation. All imide (RCH(2)CH═N(-)) and enamide (RCH(-)CH═NH ↔ RCH═CHN(-)H) adducts feature strong interactions between the organic anion and both Li(+) and AlH(3). The relative stabilities of the tautomeric LAH adducts are compared to the tautomer preference energies of the LiH adducts and of the hydride adducts of the nitriles. Alane affinities were determined for the lithium ion pairs formed by LiH addition to the nitriles. The results show that alane binding greatly affects the imide-enamide equilibria and that alane complexation might even provide a thermodynamic preference for the imide intermediate. While lithium enamides of malononitrile are much more stable than lithium imides, alane binding dramatically reduces the enamide preference so that both tautomers are present at equilibrium. Implications are discussed regarding to the propensity for multiple hydride reductions and with regard to the mechanism of reductive nitrile dimerization. A detailed mechanism is proposed for the formation of 2-aminonicotinonitrile (2ANN) in the LAH reduction of malononitrile.

  11. A parallel vectorized implementation of triple excitations in CCSD(T) - Application to the binding energies of the AlH3, AlH2F, AlHF2 and AlF3 dimers

    NASA Technical Reports Server (NTRS)

    Rendell, Alistair P.; Lee, Timothy J.; Komornicki, Andrew

    1991-01-01

    An efficient method for various noniterative estimates of connected triple excitations in coupled-cluster theory is outlined and related to a similar expression occurring in Moller-Plesset perturbation theory. The method is highly vectorized and capable of utilizing multiple processors on a shared-memory machine, leading to computational rates in excess of one billion floating-point operations per second on four processors of a CRAY Y-MP. Using the new procedure, the binding energies of the D(2h) diborane-type dimers of AlH3, AlH2F, AlHF2, and AlF3 have been determined to be 32, 40, 20, and 47 kcal/mol, respectively. For Al2F6, the correlation procedure includes 232 molecular orbitals and over 1.5 x 10 to the 6th single and double coupled-cluster amplitudes, effectively accounting for over 2 x 10 to the 9th connected triple excitations.

  12. Volume dependence of AlH3 band gap at high pressures

    NASA Astrophysics Data System (ADS)

    Shakhray, D. V.; Golyshev, A. A.; Kim, V. V.; Molodets, A. M.; Fortov, V. E.

    2011-06-01

    The volume dependence of the band gap for aluminum hydride (alane) is compared at high static and dynamic pressures. Room temperature high pressure isotherm data and multiple-shock conductivity data were used for the reconstruction of the volume dependence of the alane band gap in the pressure range 50-75 GPa. The traditional exponential relationship for the temperature dependence of semiconductor conductivity with the power law volume dependence of the aluminum hydride band gap is suggested in the regions of volumes 11.5-12.5 cm3/mol, pressures 50-75 GPa and temperatures 1270-1370 K.

  13. Regeneration of AlH3 studied with Raman and Infrared Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lacina, David; Wegrzyn, J.; Reilly, J. J.; Graetz, Jason

    2010-03-01

    Aluminum hydride compounds are known to exhibit a 10% by weight hydrogen storage capacity that makes them suited for technologies that require hydrogen as a fuel. The current challenge associated with this material is how to regenerate the hydride from the spent fuel and H2 gas. We employ a two-step process to regenerate the hydride compound which first requires the formation of a stable aluminum hydride adduct using a tertiary amine. This is followed by a second step consisting of adduct separation and hydride recovery, involving transamination to create a less stable adduct. We present results which show that alane-amines can be formed by hydrogenation of catalyzed aluminum in a solvent at low pressures using one of several tertiary amines. Raman and infrared spectroscopy was performed on the products of these reactions to better understand the structure of the alane amines that are formed, as well as the hydrogenation reactions that take place. A vibrational analysis of the regeneration products performed with Raman and infrared spectroscopy is presented and will help clarify the molecular and vibrational structures of these alane amine adducts.

  14. Materials Data on AlH3 (SG:167) by Materials Project

    SciTech Connect

    Kristin Persson

    2014-11-02

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  15. Formation and decomposition of AlH3 in the aluminum-hydrogen system

    NASA Astrophysics Data System (ADS)

    Saitoh, H.; Machida, A.; Katayama, Y.; Aoki, K.

    2008-10-01

    The pressure-temperature diagram of hydrogen-aluminum system was determined for a pressure range of 0-10GPa and a temperature range of 27-800°C by in situ x-ray diffraction measurements. Pristine aluminum was hydrogenated to trihydride at 8.9GPa and 600°C. The cyclic formation and decomposition of the hydride resulted in lowering of the hydrogenation conditions down to 4.9GPa and 330°C. Transparent single crystals were recovered at ambient conditions.

  16. Materials Data on AlH3 (SG:58) by Materials Project

    SciTech Connect

    Kristin Persson

    2014-07-09

    Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations

  17. An insight into the process and mechanism of a mechanically activated reaction for synthesizing AlH3 nano-composites.

    PubMed

    Duan, Congwen; Hu, Lianxi; Sun, Yu; Zhou, Haiping; Yu, Huan

    2015-10-07

    The reaction pathway as well as the mechanism of the solid state reaction between MgH2 and AlCl3 has been a mystery so far. Based on SEM, TEM and NMR (Nuclear Magnetic Resonance) analyses, an amorphous intermediate (AlH6)n was preferentially formed and recrystallized as a γ phase at the final stage of the reaction. As a novel finding, this research provides a deep insight into the process and mechanism of this mechanically activated reaction.

  18. Thermal Stability and Kinetic Studies of LMH-1

    DTIC Science & Technology

    was extracted from AlH3 - 1451 and is believed to be responsible for nucleation sites which result in the decomposition of AlH3 . Pound quantities of stabilized AlH3 have been successfully used in high energy propellant formulations.

  19. Development and Test of a Highly Energetic DOMINO Propellant

    DTIC Science & Technology

    This program was designed to demonstrate a practical high energy propellant containing a difluoroamino binder, AlH3 , and the advanced oxidizer...polyester binders, (2) scale-up of TVOPA/ AlH3 propellants, and (3) an evaluation of difluoroamino binders with HAP. A high impulse TVOPA- AlH3 propellant

  20. Kinetics of Thermal Decomposition of Aluminum Hydride: I-non-Isothermal Decomposition Under Vacuum and in Inert Atmosphere (Argon)

    DTIC Science & Technology

    2005-05-06

    during decomposition, hydrogen gas is liberated and the initial polyhedral AlH3 crystals yield a final mix of amorphous aluminium and aluminium crystals...fastest is due to growth of the crystals. Thus, during decomposition, hydrogen gas is liberated and the initial polyhedra AlH3 crystals yield a final mix...Thermal stability; VTS ____________________________________________________________________________________ 1. Introduction Alane, AlH3 , is a

  1. HIGH ENERGY PROPELLANT INGREDIENT RESEARCH AND DEVELOPMENT.

    DTIC Science & Technology

    Studies on the preparation and properties of AlH3 -1451 continued. Magnesium has been incorporated into product made by the continuous...construction; a larger scale crystallizer has been fabricated from FEP stock items. Structure studies of AlH3 -1451 show the decomposition mechanism...involves loss of hydrogen and formation of aluminum nuclei and anion vacancies. Density measurements of Mg-doped AlH3 -1451 show that magnesium forms a

  2. Complex Metal Hydrides. High Energy Fuel Components for Solid Propellant Rocket Motors.

    DTIC Science & Technology

    of beryllium-hydrogen chemistry (2) a study of the redistribution of AlH3 -BeCl2, BeH2-BeCl2 and AlH3 -AlCl3 in ether solvent (3) a study of the...formation and properties of ether soluble AlH3 (4) a study involving the preparation of a series of complex metal hydrides of zinc (e.g., Li2ZnH4) (5) a

  3. HIGH ENERGY PROPELLANT INGREDIENT RESEARCH AND DEVELOPMENT.

    DTIC Science & Technology

    Studies on the preparation and properties of AlH3 -1451 possessing improved thermal stability have continued. Incorporation of magnesium into the... AlH3 -1451 lattice in concentrations greater than 1% via the continuous process has been accomplished. Teflon FEP shows excellent promise as a material...the reaction between aluminum chloride and lithium aluminum hydride. The controlling parameters for the direct nucleation of AlH3 -1451 have been

  4. Kinetics of Thermal Decomposition of Aluminum Hydride in Argon

    DTIC Science & Technology

    2005-05-01

    investigate the decomposition kinetics of alane ( AlH3 ) in argon atmosphere and to shed light on the mechanism of alane decomposition. Two kinetic models...fastest is due to growth of the crystals. Thus, during decomposition, hydrogen gas is liberated and the initial polyhedra AlH3 crystals yield final...INTRODUCTION Recently, the interest in alane ( AlH3 ) as a solid rocket fuel has been renewed presumably after the development of new methods of

  5. Investigation of Hydrogen Storage in Single Walled Carbon Nanotubes for Fuel Cells

    DTIC Science & Technology

    2009-07-17

    four systems(NH3, AlH3 , NiH3 and BH3) theoretically investigated, the single walled Carbon Nanotube (SWCNT) functionalized with BH3 is found to be...storage medium We have taken the (5, 5) single walled carbon nanotube for our study. The AlH3 molecule is allowed to approach the CNT from large...distances, to determine the energetically preferred absorption position of AlH3 . The AlH3 molecule is attached to the SWCNT and this system is denoted

  6. Development of Alternating Current Potential Drop (ACPD) Procedures for Crack Detection in Aluminum Aircraft Panels

    DTIC Science & Technology

    1993-12-01

    SPECIMEN ALH3 6 . o . . . o . o. . . . . . . o 26 4. SUMMARY OF RIVETED PANEL TESTS . . o . . . . . 31 S. COMPARISON BETWEEN SEN AND VISUAL CRACK LENGTHS IN...first two specimens ALH3 1 and ALH3 2 attempted to determine the difference between-the two current lead geometries. The results showed that the single...in tests with specimens ALH3 4 and those following it, including all the riveted tests and tests on one hole specimens ALH 1 6 and those following it

  7. Crystal Lattice Doping Studies of High Energy Propellant Ingredients

    DTIC Science & Technology

    The kinetics of the thermal decomposition of both pure and Mg doped AlH3 have been determined, by using both isothermal constant volume and...doped AlH3 is different from that for the pure AlH3 . To help resolve these discrepancies the electrical conductance of these same samples has also...been measured as a function of temperature and time. From these two studies a model for the thermal decomposition of AlH3 has been developed. Also

  8. Chemical Hydride Hydrogen Sources for Small Fuel Cells.

    DTIC Science & Technology

    1997-09-30

    This report details and investigation into the feasibility of thermal decomposition (non-hydrolytic) of aluminum hydride ( AlH3 ) for hydrogen...production. A unique new process, referred to as the self-sustaining (SS) reaction, was developed, along with a prototype generator and cartridges of AlH3 for

  9. Pre- and Post-Burning Analysis of Nano-Alluminized Propellants. Comparison of Four Russian Nano-Al Powders

    DTIC Science & Technology

    2004-12-01

    propellants, metallized with various amounts of AlH3 . Metal Oxidizer Binder AP micro-Al 18% type 05 Al 68% AP 14% HTPB AN 15% type 06 Al 68% AN...formulations and may lead to very large burning particles of the order up to 1000 µm. Just the opposite was observed for AP formulations containing AlH3

  10. DEVELOPMENT AND EVALUATION OF ADVANCED SOLID PROPELLANTS.

    DTIC Science & Technology

    Intensive investigations were conducted on improving the thermal stability and crystallization of AlH3 . Areas considered included the solubility in...and surveillance of both neat and formulated propellants at 25 and 40 C. A study of the kinetics of AlH3 and BeH3 using flash heating with UV

  11. Hydrazine bisalane is a potential compound for chemical hydrogen storage. A theoretical study.

    PubMed

    Nguyen, Vinh Son; Swinnen, Saartje; Leszczynski, Jerzy; Nguyen, Minh Tho

    2011-09-14

    Electronic structure calculations suggest that hydrazine bisalane (AlH(3)NH(2)NH(2)AlH(3), alhyzal) is a promising compound for chemical hydrogen storage (CHS). Calculations are carried out using the coupled-cluster theory CCSD(T) with the aug-cc-pVTZ basis set. Potential energy surfaces are constructed to probe the formation of, and hydrogen release from, hydrazine bisalane which is initially formed from the reaction of hydrazine with dialane. Molecular and electronic characteristics of both gauche and trans alhyzal are determined for the first time. The gauche hydrazine bisalane is formed from starting reactants hydrazine + dialane following a movement of an AlH(3) group from AlH(3)AlH(3)NH(2)NH(2) rather than by a direct attachment of a separate AlH(3) group, generated by predissociation of dialane, to AlH(3)NH(2)NH(2). The energy barriers for dehydrogenation processes from gauche and transalhyzal are in the range of 21-28 kcal mol(-1), which are substantially smaller than those of ca. 40 kcal mol(-1) previously determined for the isovalent hydrazine bisborane (bhyzb) system. H(2) release from hydrazine bisalane is thus more favored over that from hydrazine bisborane, making the Al derivative an alternative candidate for CHS.

  12. Cubic and orthorhombic structures of aluminum hydride Al H3 predicted by a first-principles study

    NASA Astrophysics Data System (ADS)

    Ke, Xuezhi; Kuwabara, Akihide; Tanaka, Isao

    2005-05-01

    The most stable structure of aluminum hydride AlH3 is believed to be a hexagonal symmetry. However, using the density functional theory, we have identified two more stable structures for the AlH3 with the cubic and orthorhombic symmetries. Based on the quasiharmonic approximation, the cubic and orthorhombic AlH3 are almost degenerate when the zero-point energies are included. The geometric and electronic structures, the phonon, and the thermodynamic properties for the hexagonal, cubic, and orthorhombic AlH3 have been studied by means of density functional theory and direct ab initio force constant approach. The calculated electronic structures, phonon density of states, and thermodynamic functions [including S(T) and H(T)-H(0) ] for the three hydrides are similar. The results show that these three hydrides have negative enthalpies of formation, but positive free energies of formation. This conclusion is the same as that made by Wolverton for the hexagonal AlH3 [Phys. Rev. B 69, 144109 (2004)]. The thermodynamic properties indicate that the orthorhombic and cubic AlH3 should be more difficult to dissociate than the hexagonal AlH3 .

  13. Long-term sustainable aluminum precursor solution for highly conductive thin films on rigid and flexible substrates.

    PubMed

    Lee, Hye Moon; Seo, Jung Yoon; Jung, Areum; Choi, Si-Young; Ko, Seung Hwan; Jo, Jeongdai; Park, Seung Bin; Park, Duckshin

    2014-09-10

    To fabricate the highly conductive Al film via a solution process, AlH3 etherates have been a unique Al source despite their chemical instability in solvents and thus lack of long-term sustainability. Herein, we suggest an innovative solution process to overcome the aforementioned drawbacks in AlH3 etherates; AlH3 aminates powder, which can be stored in low temperature surroundings and redissolved in solvents whenever it is needed. Since refrigeration of AlH3 aminates, AlH3{N(CH3)3}, was very effective to prevent its chemical degradation, Al film with excellence and uniformity in electrical and mechanical properties was successfully fabricated even by the 180-day stored AlH3{N(CH3)3} dissolved in solvents. Moreover, the applicability of long-term stored AlH3{N(CH3)3} to electronic devices was experimentally demonstrated by the successful operation of LED lamps connected to the Al pattern films on glass, PET, and paper substrates.

  14. A STUDY OF REACTIONS FOR THE PREPARATION OF PERFLUOROALKYLALUMINUM COMPOUNDS

    DTIC Science & Technology

    was treated with AlH3 :NMe3 in ether, (CF2:CF)3Al:NMe3 resulted; and the compound (CF2:CF)2AlH:NMe3 could be isolated from a synproportionation of AlH3 ...NMe3 and (CF2:CF)3Al:NMe3. CF3AlH2:NMe3, in polymeric form, was synthesized from the reaction of AlH3 :NMe3 with (CF3)2Hg. (Author)

  15. Combustion of Alane and Aluminum with Water for Hydrogen and Thermal Energy Generation

    DTIC Science & Technology

    2010-01-01

    17–24]. Alane is a covalently bonded hydride which often appears in a polymeric form ( AlH3 )n and has at least seven known non- solvated forms. The...most stable polymorph is a- AlH3 [19,25,26]. Alane decomposition or dehy- drogenation (an endothermic process) has been found to be dependent on particle...Steady-state and one-dimensional approxi- mations are invoked. The entire region of interest is divided into six zones: (1) Al/ AlH3 -ice preheat zone

  16. HIGH ENERGY PROPELLANT INGREDIENT RESEARCH AND DEVELOPMENT

    DTIC Science & Technology

    Studies of the preparation and properties of AlH3 -1451 have continued. Magnesium has been incorporated into product made by the continuous...propellant containing magnesium-doped, in situ DPA-treated AlH3 -1451 shows a twofold improvement in stability over standard hydride at both 25 and 40 C...Magnesium-doped, in situ DPA-treated, and magnesium-doped, aged AlH3 -1451 are remarkably stable at 60 C. Propellant containing aged, magnesium-doped

  17. Stability and Compatibility Studies on Advanced Rocket Propellant Components

    DTIC Science & Technology

    ingredients studied include: Perchlorates--HAP, HP-2, DOAP and AP (for comparison); N-F materials--P-BEP, TVOPA and P-722; Fuel-- AlH3 ; and numerous state-of-the-art binder prepolymers and curatives.

  18. Hydrogen Storage Solutions in Support of DoD Warfighter Portable Power Applications

    DTIC Science & Technology

    2009-04-01

    Table 3 have a high volumetric hydro- gen capacity. For example Alane ( AlH3 ) has twice the hydrogen capacity of liquid hydrogen, making it a good...MHCoE is AlH3 . This material is able to readily release 10 wt% hydrogen at practical conditions but it requires more than 100,000 atmospheres of pressure...and so far have shown some success using both electrochemical and chemical synthesis methods, respectively.[6] While the materials being developed by

  19. Coordination preference of Ga in hydrides.

    PubMed

    Klaveness, A; Swang, O; Kjekshus, A; Fjellvåg, H

    2006-12-25

    Aluminum and gallium show some interesting differences in their coordination chemistry. Solid GaH3 is unknown, in contrast to solid AlH3. Ga equivalents of Li3AlH6, Na3AlH6, and other hydrides whose structure contain AlH(3-)6 ions, are unknown. We relate these differences to an instability of the hexacoordinated gallium moiety.

  20. Ammonia-Based Hydrogen Source for Fuel Cell Applications

    DTIC Science & Technology

    2006-01-01

    reaction [6], and ammonia–aluminum hydride ( AlH3 ) reaction [7]. Metal hydrides are metals either ionically or covalently bonded with hydrogen, which is...occurs at temperatures greater than 250 ◦C, except for AlH3 (150 ◦C) and LiAlH4 (180 ◦C) [14]. In addition, metal hydrides with higher H2 content dis

  1. Chemical hydride hydrogen sources for small fuel cells. Final report, 1 February-30 August 1997

    SciTech Connect

    Serebrennikov, V.A.; Cleland, J.G.; Damle, A.S.; Turner, M.W.

    1997-09-30

    This report details an investigation into the feasibility of thermal decomposition (non-hydrolytic) of aluminum hydride (AlH3) for hydrogen production. A unique new process, referred to as the self-sustaining (SS) reaction, was developed, along with a prototype generator and cartridges of AlH3 for use in the generator. Tests performed indicate repeatable, rapid hydrogen production and a safe reaction. Issues of controllability are addressed for future work.

  2. Studying aluminum hydride by means of thermal analysis

    NASA Astrophysics Data System (ADS)

    Milekhin, Yu. M.; Koptelov, A. A.; Matveev, A. A.; Baranets, Yu. N.; Bakulin, D. A.

    2015-07-01

    Chemical reactions and physical transformations that occur upon heating aluminum hydride (AlH3, alane), stored for 25 years, in the temperature range of 50-1200°C in an atmosphere of nitrogen, argon, and air are studied by means of thermogravimetric analysis and differential scanning calorimetry. The heat of thermal decomposition and the hydrogen content are determined for the AlH3 samples and are found to be 318 ± 25 J/g and 9.32 ± 0.24 wt %, respectively. It is established that the estimated enthalpy of formation of AlH3 in stoichiometric composition (Δf H ≈ -10.3 kJ/mol) agrees with the literature data. After the release of hydrogen, the mass of the precipitate increases by 0.5 ± 0.3%, relative to the initial mass of the AlH3 samples; the most likely reason for this effect is the adsorption of nitrogen (argon) in the micropores and mesopores that form. Thermal phenomena associated with the crystallization of the amorphous aluminum that forms after hydrogen is released from the alane particles are analyzed. It is established that the aluminum contained in initial AlH3 samples is almost completely transformed into aluminum nitride and oxide (AlN and Al3O3) upon heating to 1200°C in nitrogen and air, respectively.

  3. Formation and bonding of alane clusters on Al(111) surfaces studied by infrared absorption spectroscopy and theoretical modeling.

    PubMed

    Chaudhuri, Santanu; Rangan, Sylvie; Veyan, Jean-Francois; Muckerman, James T; Chabal, Yves J

    2008-08-13

    Alanes are believed to be the mass transport intermediate in many hydrogen storage reactions and thus important for understanding rehydrogenation kinetics for alanates and AlH3. Combining density functional theory (DFT) and surface infrared (IR) spectroscopy, we provide atomistic details about the formation of alanes on the Al(111) surface, a model environment for the rehydrogenation reactions. At low coverage, DFT predicts a 2-fold bridge site adsorption for atomic hydrogen at 1150 cm(-1), which is too weak to be detected by IR but was previously observed in electron energy loss spectroscopy. At higher coverage, steps are the most favorable adsorption sites for atomic H adsorption, and it is likely that the AlH3 molecules form (initially strongly bound to steps) at saturation. With increasing exposures AlH3 is extracted from the step edge and becomes highly mobile on the terraces in a weakly bound state, accounting for step etching observed in previous STM studies. The mobility of these weakly bound AlH3 molecules is the key factor leading to the growth of larger alanes through AlH3 oligomerization. The subsequent decomposition and desorption of alanes is also investigated and compared to previous temperature programmed desorption studies.

  4. Hydrogen release from systems containing phosphine, borane, alane and galane: A mechanistic study

    NASA Astrophysics Data System (ADS)

    Nguyen, Vinh Son; Majumdar, D.; Leszczynski, Jerzy; Nguyen, Minh Tho

    2013-10-01

    The H2 release mechanism from phosphine borane and phosphine alane was investigated using quantum chemical methods (MP2/aug-cc-pVTZ geometry optimization and coupled-cluster energies were obtained through complete basis set extrapolation, CCSD(T)/CBS). The effect of catalysts borane, alane and galane on the processes was also explored. As the energy barriers for the release of H2 from BH3PH3 and AlH3PH3 are much higher than the B-P and Al-P bond energies, the presence of inherent catalysts can reduce substantially such energy barriers (using BH3 for BH3PH3, while AlH3 and GaH3 for AlH3PH3), and these systems could be useful as probable hydrogen source.

  5. Atomic Simulations of Alane Phase Transformations and Dehydrogenation Mechanisms

    NASA Astrophysics Data System (ADS)

    Opalka, Susanne; Saxe, Paul; Lovvik, Ole Martin

    2007-03-01

    Density functional theory atomic ground state, molecular dynamics, and direct method lattice dynamic simulations were used to mechanistically probe phase transformations between the various crystallographically refined α, α', β, and γ AlH3 phases. Lattice dynamic predictions of the AlH3 structures provided an ideal test case for systematically accessing the accuracy of the vibrational thermodynamic property contributions with the harmonic approximation. The predicted transformation pathways involved coordinated tilting and rotation mechanisms, similar to that observed in perovskite structures. Further simulations were conducted to elucidate the mechanism for α AlH3 phase decomposition to the Al and H2 products and to identify probable barriers to reversible rehydrogenation.

  6. Calculations suggest facile hydrogen release from water using boranes and alanes as catalysts

    NASA Astrophysics Data System (ADS)

    Swinnen, Saartje; Nguyen, Vinh Son; Sakai, Shogo; Nguyen, Minh Tho

    2009-04-01

    Producing H 2 from water is a very challenging task. Using quantum chemical calculations with the MP2 and CCSD(T) methods and the aug-cc-pVnZ basis sets (extrapolated to CBS), we investigated the possibilities of B 2H 6, AlH 3, Al 2H 6 and AlH 3BH 3 to act as catalysts in the reactions that split water. Hydrogen production from H 2O is greatly accelerated in the presence of alane, dialane or borane-alane in such a way that reaction H 2O + Al 2H 6 is a nearly spontaneous process. The main catalytic effect of AlH 3 arises from the occurrence of a strong dihydrogen bond of the type Al-H δ-- δ+H-O within a cyclic transition structure.

  7. The infrared spectrum of Al2H6 in solid hydrogen.

    PubMed

    Andrews, Lester; Wang, Xuefeng

    2003-03-28

    Although many volatile binary boron hydride compounds are known, binary aluminum hydride chemistry is limited to the polymeric (AlH3)(n) solid. The reaction of laser-ablated aluminum atoms and pure H2 during codeposition at 3.5 kelvin, followed by ultraviolet irradiation and annealing to 6.5 kelvin, allows dimerization of the intermediate AlH3 photolysis product to form Al2H6. The Al2H6 molecule is identified by seven new infrared absorptions that are accurately predicted by quantum chemical calculations for dibridged Al2H6, a molecule that is isostructural with diborane.

  8. Cubic metallic phase of aluminum hydride showing improved hydrogen desorption

    NASA Astrophysics Data System (ADS)

    Scheicher, R. H.; Kim, D. Y.; Lebègue, S.; Arnaud, B.; Alouani, M.; Ahuja, R.

    2008-05-01

    We report on our results calculated from density functional theory and GW of the dehydrogenation properties in a cubic phase of AlH3. The metallic nature of the electronic structure entails a more favorable hydrogen removal energy which is lowered by 75% compared to the insulating hexagonal phase. This remarkable reduction in the Al-H bond strength bears important consequences for feasible applications of AlH3 as an on-board hydrogen storage material for mobile applications. We suggest that the cubic phase could be prepared and stabilized experimentally at ambient pressure by off-board quenching.

  9. Electronic structure of the complex hydride NaAlH4

    NASA Astrophysics Data System (ADS)

    Aguayo, A.; Singh, D. J.

    2004-04-01

    Density-functional calculations of the electronic structure of the complex hydride NaAlH4 and the reference systems NaH and AlH3 are reported. We find a substantially ionic electronic structure for NaAlH4, which emphasizes the importance of solid-state effects in this material. The relaxed hydrogen positions in NaAlH4 are in good agreement with the recent experiment. The electronic structure of AlH3 is also ionic. Implications for the binding of complex hydrides are discussed.

  10. Novel Reagents for Chemical Vapor Deposition of Intermetallic Alloys.

    DTIC Science & Technology

    1994-10-31

    AlH3 :NMe3 yielded Al(CH2SiMe3)3. NMe3 and ’Hf(CH2SiMe3)H3’. Carbon blocks coated with this mixture produced a HfAlC2 coating which was effective in protecting the substrate from air oxidation at high temperatures. jg

  11. LYNX: A Linked Eulerian and Lagrangian Code. Volume II. LYNX Computer Listing

    DTIC Science & Technology

    1975-11-01

    Al_H2»Sbl 0SB2»GN2-ALH2»Sb2 DSB3»GN3-ALH2»S83 DSB|2«€MI2-ALH2»SriI2 ALH3 "AL«H3 DSl«DS81* ALH3 «Snl DS2»DS82*ALM3«SB2 0S3»OS83* ALH3 «S03 DS|2«DSB12... ALH3 «SÖ12 Sbl»SBl*OSBl SB2»SB2*DSB2 SB3»SP3*0S83 SBl2«Sd|2*üSai2 S1»SI+05I S2»S2*0S2 »30! ’ * 3 r 0 a 15 ""Ob lb i r Q a 5 Jr35lb 0005 17

  12. HIGH ENERGY PROPELLANT INGREDIENT RESEARCH.

    DTIC Science & Technology

    percent. Conductivity studies of the LiAlH4-AlCl3 reaction in ether-toluene (1:1) under a variety of conditions confirm the existence of a maximum in the curve at 2:1 molar ratios of LiAlH4: AlH3 . (Author)

  13. Convenient method for the synthesis of rare-earth hydrides by the use of a conventional very high pressure technique

    NASA Astrophysics Data System (ADS)

    Wakamori, Koji; Filipek, Stanisl/aw M.; Sawaoka, Akira

    1983-10-01

    This paper describes a new method for synthesizing massive rare-earth hydrides with high hydrogen contents. The method can substantially reduce the time for synthesizing rare-earth hydrides compared to a conventional method. Thermally decomposed gas from a hydride was used to synthesize another hydride under very high pressure. AlH3 and MgH2 were used as hydrogen sources. When AlH3 was used as a solid source of hydrogen, SmH2.95 was obtained under the pressure of 4.0 GPa at 300 °C in 30 min. When MgH2 was used, SmH2.95 was obtained under 3.0 GPa at 250 °C for 1 h, or under 4.0 GPa at 200 °C for 1.5 h.

  14. Molecular aluminum hydrides identified by inelastic neutron scattering during H2 regeneration of catalyst-doped NaAlH4.

    PubMed

    Fu, Qi Jia; Ramirez-Cuesta, A J; Tsang, Shik Chi

    2006-01-19

    Catalyst-doped sodium aluminum hydrides have been intensively studied as solid hydrogen carriers for onboard proton-exchange membrane (PEM) fuel cells. Although the importance of catalyst choice in enhancing kinetics for both hydrogen uptake and release of this hydride material has long been recognized, the nature of the active species and the mechanism of catalytic action are unclear. We have shown by inelastic neutron scattering (INS) spectroscopy that a volatile molecular aluminum hydride is formed during the early stage of H2 regeneration of a depleted, catalyst-doped sodium aluminum hydride. Computational modeling of the INS spectra suggested the formation of AlH3 and oligomers (AlH3)n (Al2H6, Al3H9, and Al4H12 clusters), which are pertinent to the mechanism of hydrogen storage. This paper demonstrates, for the first time, the existence of these volatile species.

  15. VizieR Online Data Catalog: ALHAMBRA fields type-I AGN with ELDAR (Chaves-Montero+, 2017)

    NASA Astrophysics Data System (ADS)

    Chaves-Montero, J.; Bonoli, S.; Salvato, M.; Greisel, N.; Diaz-Garcia, L. A.; Lopez-Sanjuan, C.; Viironen, K.; Fernandez-Soto, A.; Povic, M.; Ascaso, B.; Arnalte-Mur, P.; Masegosa, J.; Matute, I.; Marquez, I.; Cenarro, A. J.; Abramo, L. R.; Ederoclite, A.; Alfaro, E. J.

    2017-08-01

    The catalogues ALH2L and ALH3L contain type-I AGN in the ALHAMBRA fields identified by using the 2- and 3-lines mode of ELDAR with the publicly available multi-band data of the ALHAMBRA survey, respectively, and they contain 585 and 494 sources. For each type-I AGN coordinates, redshift, best-fit template, PSF ALHAMBRA magnitudes, Stellarity, and properties of the AGN emission lines detected by ELDAR are given. (2 data files).

  16. Low-pressure Structural Modification of Aluminum Hydride

    DTIC Science & Technology

    2011-02-01

    pressure release. 15. SUBJECT TERMS High - pressure , Diamond anvil cell, aluminum hydride 16. SECURITY CLASSIFICATION OF...loaded into the diamond anvil cell using a specialized high - pressure gas loading system (18). The in-situ pressure within the diamond anvil cell was...Visible Absorption Study of AlH3. Journal of Physics: Conference Series 2010, 215, 012047. 18. Jayaraman, A. Diamond Anvil Cell and High -

  17. Understanding and Quantifying the Reactivity of Energetic NanoParticles and NanoComposites

    DTIC Science & Technology

    2015-01-05

    Aerosol Synthesis and Reactivity of Thin Oxide Shell Aluminum Nanoparticles via Fluorocarboxylic Acid Functional Coating, Particle & Particle...Received Paper G. Feng,, S. Chowdhury, G. Jian,, M.R Zachariah. Modified Aerosol Routes to Core-Shell Nano-Energetic Materials Synthesis , Materials...Hydride (- AlH3 ) was also conducted. In this study the ignition characteristics were determined through the use of two separate modified T-jump

  18. Influence of Aluminum Passivation on the Reaction Mechanism: Flame Propagation Studies

    DTIC Science & Technology

    2009-01-01

    Combustion, Aluminum Particles, Passivation of Aluminum Particles, AI synthesis techniques 17. SECURITY CLASSIFICATION 118. SECURITY CLASSIFICATION 119...shell. The type of Al without an alumina passivation shell was further prepared using two different synthesis techniques. Physical property information...prepared from catalytic decomposition of AlH3 *N(Me)Pyr and desig- nated as (Al-C13F27)cd; and the second was prepared from triethylaluminum

  19. Vacancy Mechanism of the Photolysis of Aluminum Hydride

    NASA Astrophysics Data System (ADS)

    Goryaev, M. A.

    2000-01-01

    Within the framework of the thermodynamic model of formation of intrinsic defects in a lattice during the decay of photoexcitations in a solid, the formation of hydrogen vacancies in aluminum hydride is analyzed. The evolution of a system with excess vacancy concentration leads to the formation of micropores under the crystal surface. The results of calculations agree well with the experimental data on photochemically induced absorption obtained in electron-microscopic studies of AlH3 decomposition.

  20. Solid State NMR Studies of the Aluminum Hydride Phases

    NASA Technical Reports Server (NTRS)

    Hwang, Son-Jong; Bowman, R. C., Jr.; Graetz, Jason; Reilly, J. J.

    2006-01-01

    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.

  1. Solid State NMR Studies of the Aluminum Hydride Phases

    NASA Technical Reports Server (NTRS)

    Hwang, Son-Jong; Bowman, R. C., Jr.; Graetz, Jason; Reilly, J. J.

    2006-01-01

    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.

  2. Alanes formation on the Al(111) surface

    NASA Astrophysics Data System (ADS)

    Rangan, Sylvie; Veyan, Jean-Francois; Chabal, Yves J.; Chaudhuri, Santanu; Muckerman, James T.

    2008-03-01

    Alane clusters (AlxHy) are believed to be the ubiquitous intermediates in hydrogen storage reactions for a wide variety of alanates (LiAlH4, NaAlH4) currently considered for hydrogen storage. The formation and behavior of alanes at surfaces appear to control and limit the efficiency of hydrogen storage. In particular, hydrogen adsorption on the Al(111) surface leads to the coexistence of several adsorbed species, the concentration of which is affected by the step density, the surface coverage and the temperature. We combine density functional theory (DFT) and surface infra-red (IR) absorption spectroscopy to uncover the mechanisms for alane formation on Al(111) surfaces. At low coverage, DFT predicts a two-fold bridge site adsorption for atomic hydrogen, consistent with previous Electron Energy Loss Spectroscopy measurements. At higher coverage, the formation of small chemisorbed AlH3 occurs at the step edges. With increasing coverage AlH3 is extracted from the step edge and becomes highly mobile on the terraces in a weakly bound state. This mobility is the key factor leading to the growth of larger alanes through AlH3 oligomerization. For these large alanes, previous Thermal Programmed Desorption studies are discussed and compared to the thermal stability observed in IR.

  3. pardInvestigation of the Direct Hydrogenation of Aluminum to Alane in Supercritical Fluids

    NASA Astrophysics Data System (ADS)

    Jensen, Craig; McGrady, Sean; Ayabe, Reyna; Reddy, Ben

    2007-03-01

    Alane, AlH3 has many of the properties that are requisite for materials to be considered viable for onboard hydrogen storage applications. Most notibly, it contains 10.1 wt% hydrogen and undergoes dehydrogenation at appreciable rates at temperatures below 100^oC. However, the very low, >= 6 kJ/mol, enthalpy of dehydrogenation of AlH3 prohibits subsequent re-hydrogenation through standard gas-solid techniques except at very high pressures or very low temperatures. The extremely low solubility of gaseous H2 in conventional organic solvents also vitiates a solution-based approach. Re-hydrogenation of Al using a supercritical fluid potentially offers a workable approach since the fluid can act as a solvent, at the same time remaining completely miscible with permanent gases like hydrogen. Recently, it has been found that mixtures of NaH and Al can be hydrogenated to sodium alanate, NaAlH4 under modest pressures and temperatures in supercritical fluids. We have now extended these studies to the hydrogenation of Al to AlH3. The results of these studies and experimental details will be reported.

  4. Al6H18: A baby crystal of γ-AlH3

    NASA Astrophysics Data System (ADS)

    Kiran, B.; Kandalam, Anil K.; Xu, Jing; Ding, Y. H.; Sierka, M.; Bowen, K. H.; Schnöckel, H.

    2012-10-01

    Using global-minima search methods based on the density functional theory calculations of (AlH3)n (n = 1-8) clusters, we show that the growth pattern of alanes for n ≥ 4 is dominated by structures containing hexa-coordinated Al atoms. This is in contrast to the earlier studies where either linear or ring structures of AlH3 were predicted to be the preferred structures in which the Al atoms can have a maximum of five-fold coordination. Our calculations also reveal that the Al6H18 cluster, with its hexa-coordination of the Al atoms, resembles the unit-cell of γ-AlH3, thus Al6H18 is designated as the "baby crystal." The fragmentation energies of the (AlH3)n (n = 2-8) along with the dimerization energies for even n clusters indicate an enhanced stability of the Al6H18 cluster. Both covalent (hybridization) and ionic (charge) contribution to the bonding are the driving factors in stabilizing the isomers containing hexa-coordinated Al atoms.

  5. The catalyzed hydrogen sorption mechanism in alkali alanates.

    PubMed

    Kocabas Atakli, Züleyha Özlem; Callini, Elsa; Kato, Shunsuke; Mauron, Philippe; Orimo, Shin-Ichi; Züttel, Andreas

    2015-08-28

    The hydrogen sorption pathways of alkali alanates were analyzed and a mechanism for the catalytic hydrogen sorption was developed. Gibbs free energy values of selected intermediate steps were calculated based on experimentally determined thermodynamic data (enthalpies and entropies) of individual hydrides: MAlH4, M3AlH6, and MH. The values of the activation energies, based on the intermediates M(+), H(-), MH, and AlH3, were obtained. The mechanism of the catalytic activity of Ti is finally clarified: we present an atomistic model, where MAlH4 desorbs hydrogen through the intermediates M(+), H(-), MH, and AlH3 to the hexahydride M3AlH6 and finally the elemental hydride MH. The catalyst acts as a bridge to transfer M(+) and H(-) from MAlH4(-) to the neighboring AlH4(-), forming AlH6(3-) and finally isolated MH, leaving AlH3 behind, which spontaneously desorbs hydrogen to give Al and 1.5H2. The proposed mechanism is symmetric in the direction of hydrogen desorption as well as readsorption processes.

  6. Al6H18: a baby crystal of γ-AlH3.

    PubMed

    Kiran, B; Kandalam, Anil K; Xu, Jing; Ding, Y H; Sierka, M; Bowen, K H; Schnöckel, H

    2012-10-07

    Using global-minima search methods based on the density functional theory calculations of (AlH(3))(n) (n = 1-8) clusters, we show that the growth pattern of alanes for n ≥ 4 is dominated by structures containing hexa-coordinated Al atoms. This is in contrast to the earlier studies where either linear or ring structures of AlH(3) were predicted to be the preferred structures in which the Al atoms can have a maximum of five-fold coordination. Our calculations also reveal that the Al(6)H(18) cluster, with its hexa-coordination of the Al atoms, resembles the unit-cell of γ-AlH(3), thus Al(6)H(18) is designated as the "baby crystal." The fragmentation energies of the (AlH(3))(n) (n = 2-8) along with the dimerization energies for even n clusters indicate an enhanced stability of the Al(6)H(18) cluster. Both covalent (hybridization) and ionic (charge) contribution to the bonding are the driving factors in stabilizing the isomers containing hexa-coordinated Al atoms.

  7. Cubic Metallic Phase of Aluminum Hydride Showing Improved Hydrogen Desorption

    NASA Astrophysics Data System (ADS)

    Scheicher, Ralph H.; Kim, Duck Young; Ahuja, Rajeev

    2009-03-01

    AlH3 is of great interest for hydrogen storage applications, with a particularly attractive feature being its large hydrogen capacity of 10 wt.%. Here we report the results of our density functional theory study of the dehydrogenation properties in a cubic phase of AlH3. The metallic nature of the electronic structure entails a more favorable hydrogen removal energy which is lowered by 75% compared to the insulating hexagonal phase. This remarkable reduction in the Al--H bond strength might bear important consequences for feasible applications of AlH3 as an on-board hydrogen storage material for mobile applications. Suggestions are made how the cubic phase could be prepared and stabilized at ambient pressure by off-board quenching. See also: R. H. Scheicher, D. Y. Kim, S. Lebègue, B. Arnaud, M.Alouani, and R. Ahuja, Appl. Phys. Lett. 92, 201903 (2008) and D. Y. Kim, R. H. Scheicher, and R. Ahuja, Phys. Rev. B 78, 100102(R) (2008).

  8. Synthesis and characterization of thermally robust amidinato group 13 hydride complexes.

    PubMed

    Cole, Marcus L; Jones, Cameron; Junk, Peter C; Kloth, Marc; Stasch, Andreas

    2005-07-18

    The reactivity of two sterically bulky amidines, ArNC(R)N(H)Ar (Ar=2,6-diisopropylphenyl; R=H (HFiso); tBu, (HPiso)) towards LiMH4, M=Al or Ga, [AlH3(NMe3)], and [GaH3(quin)] (quin=quinuclidine) has been examined. This has given rise to a variety of very thermally stable aluminum and gallium hydride complexes. The structural motif adopted by the prepared complexes has been found to be dependent upon both the amidinate ligand and the metal involved. The 1:1 reaction of HFiso with LiAlH4 yielded dimeric [{AlH3(mu-Fiso)Li(OEt2)}2]. Amidine HFiso reacts in a 1:1 ratio with [AlH3(NMe3)] to give the unusual hydride-bridging dimeric complex, [{AlH2(Fiso)}2], in which the Fiso- ligand is nonchelating. The equivalent reaction with the bulkier amidine, HPiso, yielded a related hydride-bridging complex, [{AlH2(Piso)}2], in which the Piso- ligand is chelating. In contrast, the treatment of [GaH3(quin)] with one equivalent of HFiso afforded the four-coordinate complex [GaH2(quin)(Fiso)], in which the Fiso- ligand acts as a localized monodentate amido-imine ligand. The 2:1 reactions of HFiso with [AlH3(NMe3)] or [GaH3(quin)] gave the monomeric complexes [MH(Fiso)2], which are thermally robust and which exhibit chelating amidinate ligands. In contrast, HPiso did not give 2:1 complexes in its reactions with either of the Group 13 trihydride precursors. For sake of comparison, the reactions of [AlH3(NMe3)] and [GaH3(quin)] with the bulky carbodiimide ArN=C=NAr and the thiourea Ar(H)NC(=S)N(H)Ar were examined. These last reactions afforded the five-coordinate thioureido complexes, [MH{N(Ar)C[N(H)(Ar)]S}2], M=Al or Ga.

  9. Thermodynamic properties of molecular borane phosphines, alane amines, and phosphine alanes and the [BH(4)(-)][PH(4)(+)], [AlH(4)(-)][NH(4)(+)], and [AlH(4)(-)][PH(4)(+)] salts for chemical hydrogen storage systems from ab initio electronic structure theory.

    PubMed

    Grant, Daniel J; Dixon, David A

    2005-11-10

    The heats of formation for the molecules BH(3)PH(3), BH(2)PH(2), HBPH, AlH(3)NH(3), AlH(2)NH(2), HAlNH, AlH(3)PH(3), AlH(2)PH(2), HAlPH, AlH(4)(-), PH(3), PH(4), and PH(4)(+), as well as the diatomics BP, AlN, and AlP, have been calculated by using ab initio molecular orbital theory. The coupled cluster with single and double excitations and perturbative triples method (CCSD(T)) was employed for the total valence electronic energies. Correlation consistent basis sets were used, up through the augmented quadruple-zeta, to extrapolate to the complete basis set limit. Additional d core functions were used for Al and P. Core/valence, scalar relativistic, and spin-orbit corrections were included in an additive fashion to predict the atomization energies. Geometries were calculated at the CCSD(T) level up through at least aug-cc-pVTZ and frequencies were calculated at the CCSD(T)/aug-cc-pVDZ level. The heats of formation of the salts [BH(4)(-)][PH(4)(+)](s), [AlH(4)(-)][NH(4)(+)](s), and [AlH(4)(-)][PH(4)(+)](s) have been estimated by using an empirical expression for the lattice energy and the calculated heats of formation of the two component ions. The calculations show that both AlH(3)NH(3)(g) and [AlH(4)(-)][NH(4)(+)](s) can serve as good hydrogen storage systems that release H(2) in a slightly exothermic process. In addition, AlH(3)PH(3) and the salts [AlH(4)(-)][PH(4)(+)] and [BH(4)(-)][PH(4)(+)] have the potential to serve as H(2) storage systems. The hydride affinity of AlH(3) is calculated to be -70.4 kcal/mol at 298 K. The proton affinity of PH(3) is calculated to be 187.8 kcal/mol at 298 K in excellent agreement with the experimental value of 188 kcal/mol. PH(4) is calculated to be barely stable with respect to loss of a hydrogen to form PH(3).

  10. Theoretical exploration of hydrogen loss from Al3H9.

    PubMed

    Nold, Christopher P; Head, John D

    2012-05-03

    The Al(3)H(9) and Al(3)H(7) potential energy surfaces were explored using quantum chemistry calculations to investigate the H(2) loss mechanism from Al(3)H(9), which provide new insights into hydrogen production from bulk alane, [AlH(3)](x), a possible energy storage material. We present results of B3LYP/6-311++G(d,p) calculations for the various Al(3)H(9) and Al(3)H(7) optimized local minima and transition state structures along with some reaction pathways for their interconversion. We find the energy for Al(3)H(9) decomposition into Al(2)H(6) and AlH(3) is slightly lower than that for H(2) loss and Al(3)H(7) formation, but the calculations show that H(2) loss from Al(3)H(9) is a lower energy process than for losing hydrogen from either Al(2)H(6) or AlH(3). We found four transition state structures and reaction pathways for Al(3)H(9) → Al(3)H(7) + H(2), where the lowest energy activation barrier is around 25-73 kJ/mol greater than the experimental value for H(2) loss from bulk alane. Intrinsic reaction coordinate calculations show that the H(2) loss pathway involves considerable rearrangement of the H atom positions around a single Al center. Three of the pathways start with the formation of an AlH(3) moiety, which then enables a terminal H on the AlH(3) to get within 1.1 to 1.2 Å of a nearby bridging H atom. The bridging and terminal H atoms eventually combine to form H(2) and leave Al(3)H(9). One implication of these H(2) loss reaction pathways is that, since the H atoms in bulk alanes are all at bridging positions, if a similar H(2) loss mechanism were to apply to bulk alane, then H(2) loss would most likely occur on the bulk alane surface or at a defect site where there should be more terminal H atoms available for reaction with nearby bridging H atoms.

  11. Point-defect-mediated dehydrogenation of alane

    NASA Astrophysics Data System (ADS)

    Ismer, Lars

    2011-03-01

    For the engineering of better hydrogen storage materials a systematic understanding of their hydrogen sorption kinetics is crucial. Theoretical studies on metal hydrides have indicated that in many cases point defects control mass transport and hence hydrogen uptake and release. Manipulating point-defect concentrations thus allows control over hydrogen sorption kinetics, opening up new engineering strategies. However, in some cases the relevance of kinetic limitations due to point defects is still under debate; kinetic inhibition of hydrogen sorption has also been attributed to surface effects, e.g. oxide layers or low recombination rates. We present a systematic analysis of the dehydrogenation kinetics of alane (AlH3), one of the prime candidate materials for hydrogen storage. Using hybrid-density functional calculations we determine the concentrations and mobilities of point defects and their complexes. Kinetic Monte Carlo simulations are used to describe the full dehydrogenation reaction. We show that under dehydrogenation conditions charged hydrogen vacancy defects form in the crystal, which have a strong tendency towards clustering. The vacancy clusters denote local nuclei of Al phase, and the growth of these nuclei eventually drives the AlH3/Al transformation. However, the low concentration of vacancy defects limits the transport of hydrogen across the bulk, and hence acts as the rate-limiting part of the process. The dehydrogenation is therefore essentially inactive at room temperature, explaining why AlH3 is metastable for years, even though it is thermodynamically unstable. Our derived activation energy and dehydrogenation curves are in excellent agreement with the experimental data, providing evidence for the relevance of bulk point-defect kinetics. Work performed in collaboration with A. Janotti and C. G. Van de Walle, and supported by DOE.

  12. Growth of aluminum on Si using dimethyl-ethyl amine alane

    NASA Astrophysics Data System (ADS)

    Neo, Yoichiro; Niwano, Michio; Mimura, Hidenori; Yokoo, Kuniyoshi

    1999-04-01

    The paper describes growth of aluminum on a hydrogen terminated Si (100) surface using dimethyl-ethyl amine alane. The growth rate depends on the substrate temperature with an activation energy of 0.56 eV at the temperature ranging from 150 to 250°C. Selective growth of Al into 1.5-μm diameter via-holes is successfully demonstrated at the substrate temperature of 150°C. In situ FTIR measurements suggest that growth of Al occurs by the chemical reaction between AlH 3 and a hydrogen terminated Si surface.

  13. Adhesion of oxide layer to metal-doped aluminum hydride surface: Density functional calculations

    NASA Astrophysics Data System (ADS)

    Takezawa, Tomoki; Itoi, Junichi; Kannan, Takashi

    2017-07-01

    The density functional theory (DFT) calculations were carried out to evaluate the adhesion energy of the oxide layer to the metal-doped surface of hydrogen storage material, aluminum hydride (alane, AlH3). The total energy calculations using slab model revealed that the surface doping of some metals to aluminum hydride weakens the adhesion strength of the oxide layer. The influence of titanium, iron, cobalt, and zirconium doping on adhesion strength were evaluated. Except for iron doping, the adhesion strength becomes weak by the doping.

  14. Ring-expansion reaction of oximes with aluminum reductants.

    PubMed

    Cho, Hidetsura; Iwama, Yusuke; Mitsuhashi, Nakako; Sugimoto, Kenji; Okano, Kentaro; Tokuyama, Hidetoshi

    2012-06-14

    The ring-expansion reactions of heterocyclic ketoximes and carbocyclic ketoximes with several reductants such as AlHCl2, AlH3 (alane), LiAlH4, LiAlH(OtBu)3, and (MeOCH2CH2O)2AlH2Na (Red-Al) were examined. Among reductants, AlHCl2 (LiAlH4:AlCl3 = 1:3) in cyclopentyl methyl ether (CPME) has been found to be a suitable reagent for the reaction, and the rearranged cyclic secondary amines were obtained in good to excellent yields.

  15. Pressure-induced hydrogen-dominant metallic state in aluminum hydride.

    PubMed

    Goncharenko, Igor; Eremets, M I; Hanfland, M; Tse, J S; Amboage, M; Yao, Y; Trojan, I A

    2008-02-01

    Two structural transitions in covalent aluminum hydride AlH3 were characterized at high pressure. A metallic phase stable above 100 GPa is found to have a remarkably simple cubic structure with shortest first-neighbor H-H distances ever measured except in H2 molecule. Although the high-pressure phase is predicted to be superconductive, this was not observed experimentally down to 4 K over the pressure range 120-164 GPa. The results indicate that the superconducting behavior may be more complex than anticipated.

  16. Oxidation-reduction processes upon interaction of aluminum oxide melt with molybdenum and tungsten in a hydrogen-containing atmosphere

    NASA Astrophysics Data System (ADS)

    Kostomarov, D. V.

    2017-07-01

    A thermodynamic analysis of the processes occurring in the Mo-W-Al2O3 system at T = 2400 K and a total pressure of 1 bar, set by controlled reducing Ar + H2 atmosphere, has been performed. It is found that the basic components of the system do not interact directly, although may be actively involved in chemical reactions with participation of other components to undergo numerous cyclic oxidation-reduction processes. Particular attention is paid to the processes involving such chemically active reagents as H2O2, HO2, H2 (H), gaseous Al, and its hydrides (AlH, AlH2, AlH3).

  17. Metallization of aluminum hydride at high pressures: A first-principles study

    NASA Astrophysics Data System (ADS)

    Pickard, Chris J.; Needs, R. J.

    2007-10-01

    We have used first-principles density-functional-theory electronic structure methods and a random searching technique to identify stable high pressure phases of aluminum hydride (AlH3) . We find a transition from the insulating low-pressure α phase to an insulating layered structure of space group Pnma at 34GPa , and a transition to a semimetallic Pm3¯n phase at 73GPa . These phases are predicted to be stable against dehydridation (the evolution of H2 molecules), and they could be formed at pressures easily attainable within diamond-anvil-cell experiments.

  18. Hydrogen permeation pathways for the hydrogenation reaction of aluminum

    NASA Astrophysics Data System (ADS)

    Saitoh, H.; Machida, A.; Katayama, Y.; Aoki, K.

    2010-09-01

    The hydrogenation of aluminum is inhibited by the slow diffusion of hydrogen in its hydride AlH3, which covers the surface of aluminum in the initial stages of the reaction. Thus, permeation pathways for hydrogen are introduced by either mixing aluminum powder with boron nitride powder or alloying aluminum with gallium at 10 at. % Ga. The aluminum in the composite or alloy is reacted with hydrogen at high pressure and temperature. In both cases, the hydrogenation reaction yields are significantly enhanced, confirming that boron nitride and the liquid phase produced by partial melting of the alloy work efficiently as hydrogen permeation pathways.

  19. On the existence of MH(n) species with M = Al, Ga and n = 4, 5, 6. Computational study of structures, stabilities and bonding.

    PubMed

    Moc, Jerzy; Bober, Karolina; Panek, Jarosław

    2005-12-01

    Based on second-order perturbation theory (MP2) predictions with large 6-311 + + G(3df, 3pd) basis set we have reviewed the possible structures and stabilities of a series of neutral MH(n)(M = Al, Ga; n = 4, 5, 6) species. For AlH4 and AlH5, our results confirm the previous theoretical findings, which indicate the dihydrogen C(s) complexes (2A') AlH2(H2) and (1A') AlH3(H2), respectively, as the lowest energy isomers. We found, similarly, C(s) (2A') GaH2(H2) and (1A') GaH3(H2) van der Waals complexes as the most stable species of the gallium analogues GaH4 and GaH5. The calculated H2 dissociation energies (D(e)) for AlH2(H2) and AlH3(H2) are of the order 1.8-2.5 kcalmol(-1), whereas this range of values for GaH2(H2) and GaH3(H2) is 1.4-1.8 kcalmol(-1) . Symmetry-adapted perturbation theory (SAPT) was used to analyze the interaction energies of these dihydrogen complexes (for n = 5) to determine why the Ga species show a smaller binding energy than the Al species. The SAPT partitioning of the interaction energy showed significant differences between AlH3(H2) and GaH3(H2), resulting from the much stronger "hydride" character of the aluminum species. The experimental observation of AlH2(H2) and AlH3(H2), and likely GaH3(H2), via low-temperature matrix isolation has been reported recently by Pullumbi et al. and Andrews et al., supporting the theoretical predictions. For n = 6, we found the degenerate C2(2A) and C(s)(2A') MH2(H2)2 "double H2" type van der Waals complexes as the lowest energy species for both M = Al and Ga.

  20. Pressure-Induced Hydrogen-Dominant Metallic State in Aluminum Hydride

    NASA Astrophysics Data System (ADS)

    Goncharenko, Igor; Eremets, M. I.; Hanfland, M.; Tse, J. S.; Amboage, M.; Yao, Y.; Trojan, I. A.

    2008-02-01

    Two structural transitions in covalent aluminum hydride AlH3 were characterized at high pressure. A metallic phase stable above 100 GPa is found to have a remarkably simple cubic structure with shortest first-neighbor H-H distances ever measured except in H2 molecule. Although the high-pressure phase is predicted to be superconductive, this was not observed experimentally down to 4 K over the pressure range 120 164 GPa. The results indicate that the superconducting behavior may be more complex than anticipated.

  1. A Lewis Acid-Base Computational Chemistry Exercise for Advanced Inorganic Chemistry

    NASA Astrophysics Data System (ADS)

    Anderson, Wayne P.

    2000-02-01

    A computational chemistry exercise dealing with Lewis acids and bases has been developed for use in advanced inorganic chemistry courses. The exercise employs ab initio or semiempirical quantum mechanical calculations to investigate the adducts of the Lewis acids BH3, BF3, BCl3, AlH3, and AlCl3 with the Lewis bases NH3 and PH3. Adducts of BCl3 with pyridine, 3,5-dimethylpyridine, and 2,6-dimethylpyridine are also investigated. Binding energies, geometric changes upon adduct formation, structural reorganizational energies, and partial atomic charges are calculated. Factors influencing binding energies between Lewis acids and bases can be inferred from the results.

  2. Towards direct synthesis of alane: A predicted defect-mediated pathway confirmed experimentally

    DOE PAGES

    Wang, Lin -Lin; Herwadkar, Aditi; Reich, Jason M.; ...

    2016-08-18

    Here, alane (AlH3) is a unique energetic material that has not found a broad practical use for over 70 years because it is difficult to synthesize directly from its elements. Using density functional theory, we examine the defect-mediated formation of alane monomers on Al(111) in a two-step process: (1) dissociative adsorption of H2 and (2) alane formation, which are both endothermic on a clean surface. Only with Ti dopant to facilitate H2 dissociation and vacancies to provide Al adatoms, both processes become exothermic. In agreement, in situ scanning tunneling microscopy showed that during H2 exposure, alane monomers and clusters formmore » primarily in the vicinity of Al vacancies and Ti atoms. Moreover, ball milling of the Al samples with Ti (providing necessary defects) showed a 10 % conversion of Al into AlH3 or closely related species at 344 bar H2, indicating that the predicted pathway may lead to the direct synthesis of alane from elements at pressures much lower than the 104 bar expected from bulk thermodynamics.« less

  3. A benign synthesis of alane by the composition-controlled mechanochemical reaction of sodium hydride and aluminum chloride

    DOE PAGES

    Hlova, Ihor; Goldston, Jennifer F.; Gupta, Shalabh; ...

    2017-05-30

    Solid-state mechanochemical synthesis of alane (AlH3) starting from sodium hydride (NaH) and aluminum chloride (AlCl3) has been achieved at room temperature. The transformation pathway of this solid-state reaction was controlled by a stepwise addition of AlCl3 to the initial reaction mixture that contained sodium hydride in excess of stoichiometric amount. As in the case of previously investigated LiH–AlCl3 system, complete selectivity was achieved whereby formation of unwanted elemental aluminum was fully suppressed, and AlH3 was obtained in quantitative yield. Reaction progress during each step was investigated by means of solid-state NMR and powder X-ray diffraction, which revealed that the overallmore » reaction proceeds through a series of intermediate alanates that may be partially chlorinated. The NaH–AlCl3 system presents some subtle differences compared to LiH–AlCl3 system particularly with respect to optimal concentrations needed during one of the reaction stages. Based on the results, we postulate that high local concentrations of NaH may stabilize chlorine-containing derivatives and prevent decomposition into elemental aluminum with hydrogen evolution. As a result, complete conversion with quantitative yield of alane was confirmed by both SSNMR and hydrogen desorption analysis.« less

  4. Novel methods for synthesizing halide-free alane without the formation of adducts

    NASA Astrophysics Data System (ADS)

    Dinh, Long V.; Knight, Douglas A.; Paskevicius, Mark; Buckley, Craig E.; Zidan, Ragaiy

    2012-04-01

    Many of the current synthesis methods for aluminum hydride (alane—AlH3) involve reacting AlCl3 and LiAlH4 in solvents. The reaction requires the formation of an alane adduct such as AlH3ṡ[(C2H5)2O] prior to obtaining crystallized stable α-AlH3. This process requires several hours of pumping in a vacuum system to remove the ether and convert the alane etherate into stable α-alane. This crystallization process is both costly and hazardous because a large amount of highly flammable material (e.g. ether) is removed by vacuum pumps over several hours. Conversely, the work presented herein describes novel methods to synthesize adduct-free alane. It is demonstrated here that AlH3 can form by mixing AlCl3 and LiAlH4 in the solid state and heating to 75∘C; only α-AlH3 was obtained. The α-AlH3 product can be washed with minimal solvents leading to zero formation of alane adducts. In addition, the unwanted LiCl by-product is also removed during the solvent wash, resulting in halide-free α-alane. Although simply mixing and heating the reactants led to a 40% yield of alane, having the reactants compacted and mechanically pressed while heating increases the yield to 60% crystalline α-AlH3.

  5. Towards Direct Synthesis of Alane: A Predicted Defect-Mediated Pathway Confirmed Experimentally.

    PubMed

    Wang, Lin-Lin; Herwadkar, Aditi; Reich, Jason M; Johnson, Duane D; House, Stephen D; Peña-Martin, Pamela; Rockett, Angus A; Robertson, Ian M; Gupta, Shalabh; Pecharsky, Vitalij K

    2016-09-08

    Alane (AlH3 ) is a unique energetic material that has not found a broad practical use for over 70 years because it is difficult to synthesize directly from its elements. Using density functional theory, we examine the defect-mediated formation of alane monomers on Al(111) in a two-step process: (1) dissociative adsorption of H2 and (2) alane formation, which are both endothermic on a clean surface. Only with Ti dopant to facilitate H2 dissociation and vacancies to provide Al adatoms, both processes become exothermic. In agreement, in situ scanning tunneling microscopy showed that during H2 exposure, alane monomers and clusters form primarily in the vicinity of Al vacancies and Ti atoms. Moreover, ball milling of the Al samples with Ti (providing necessary defects) showed a 10 % conversion of Al into AlH3 or closely related species at 344 bar H2 , indicating that the predicted pathway may lead to the direct synthesis of alane from elements at pressures much lower than the 10(4)  bar expected from bulk thermodynamics. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  6. Electronic and vibrational properties of γ-AlH3

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Yan, Jia-An; Chou, M. Y.

    2008-01-01

    Aluminum hydride (alane) AlH3 is an important material in hydrogen storage applications. It is known that AlH3 exists in multiply forms of polymorphs, where α-AlH3 is found to be the most stable with a hexagonal structure. Recent experimental studies on γ-AlH3 reported an orthorhombic structure with a unique double-bridge bond between certain Al and H atoms. This was not found in α-AlH3 or other polymorphs. Using density functional theory, we have investigated the energetics, and the structural, electronic, and phonon vibrational properties for the newly reported γ-AlH3 structure. The current calculation concludes that γ-AlH3 is less stable than α-AlH3 by 1.2KJ/mol , with the zero-point energy included. Interesting binding features associated with the unique geometry of γ-AlH3 are discussed from the calculated electronic properties and phonon vibrational modes. The binding of H-s with higher energy Al-p,d orbitals is enhanced within the double-bridge arrangement, giving rise to a higher electronic energy for the system. Distinguishable new features in the vibrational spectrum of γ-AlH3 were attributed to the double-bridge and hexagonal-ring structures.

  7. Synthesis and Structural Characterization of (1,4-Dihydropyrid-1-yl)aluminum Complexes.

    PubMed

    Hensen, Karl; Lemke, Alexander; Stumpf, Thorsten; Bolte, Michael; Fleischer, Holger; Pulham, Colin R.; Gould, Robert O.; Harris, Steven

    1999-10-18

    The reaction between LiAlH(4) and pyridine, 4-methylpyridine, or 3,5-dimethylpyridine results in hydride transfer to the pyridine ring to give tetrakis(pyridine)lithium tetrakis(1,4-dihydropyrid-1-yl)aluminate(III), 1, tetrakis(4-methylpyridine)lithium tetrakis(1,4-dihydro-4-methylpyrid-1-yl)aluminate(III), 2, or tetrakis(3,5-dimethylpyridine)lithium tetrakis(3,5-dimethyl-1,4-dihydropyrid-1-yl)aluminate(III), 3, respectively. We claim that 1, instead of lithium tetrakis(1,4-dihydropyrid-1-yl)aluminate(III), is the compound which is known as Lansbury's reagent. Treatment of trimethylamine-alane, AlH(3).NMe(3), with pyridine yields tris(1,4-dihydropyrid-1-yl)(pyridine)aluminum, 4. It could be shown that AlH(3).NMe(3) initially reduces pyridine to 1,2-dihydropyridine, which is subsequently converted into its 1,4-isomer. The X-ray crystal structures of 1-4 were determined. While the differences between Al-N distances within each of the compounds 1-3 are not significant, 4 exhibits two distinctly different types of Al-N bonds, the dative bond between Al and N(pyridine), d(Al-N) = 1.959(2) Å, and the covalent bonds between Al and N(1,4-dihydropyrid-1-yl), d(av)(Al-N) = 1.833 Å.

  8. Electronic structure and optical properties of lightweight metal hydrides

    NASA Astrophysics Data System (ADS)

    van Setten, M. J.; Popa, V. A.; de Wijs, G. A.; Brocks, G.

    2007-01-01

    We study the dielectric functions of the series of simple hydrides LiH, NaH, MgH2 , and AlH3 , and of the complex hydrides Li3AlH6 , Na3AlH6 , LiAlH4 , NaAlH4 , and Mg(AlH4)2 , using first-principles density-functional theory and GW calculations. All compounds are large gap insulators with GW single-particle band gaps varying from 3.5eV in AlH3 to 6.6eV in LiAlH4 . Despite considerable differences between the band structures and the band gaps of the various compounds, their optical responses are qualitatively similar. In most of the spectra the optical absorption rises sharply above 6eV and has a strong peak around 8eV . The quantitative differences in the optical spectra are interpreted in terms of the structure and the electronic structure of the compounds. In the simple hydrides the valence bands are dominated by the hydrogen atoms, whereas the conduction bands have mixed contributions from the hydrogens and the metal cations. The electronic structure of the aluminium compounds is determined mainly by aluminium hydride complexes and their mutual interactions.

  9. Selected boron, aluminum, and gallium trihalide and trihydride anions

    NASA Astrophysics Data System (ADS)

    Brzeski, Jakub; Czapla, Marcin; Skurski, Piotr; Simons, Jack

    2017-01-01

    Ab initio methods with flexible orbital basis sets are used to examine the electron binding strengths of tri-fluorides, tri-chlorides, and tri-hydrides of B, Al, and Ga. The adiabatic electron affinities are found to increase with increasing atomic number of the central atom. For any given central atom M (M = B, Al, Ga), the adiabatic and vertical electronic stability for MCl3 is larger than that of the corresponding MF3. The tri-hydrides have quite different electron binding strengths than the corresponding tri-halides. BH3 has a very small EA (ca. 0.02 eV) and its anion is planar whereas the tri-halide anions and AlH3- and GaH3- are non-planar. AlH3 and GaH3 have considerably smaller EAs (ca. 0.3 eV) than the Al and Ga tri-halides (0.9-1.8 eV). In all, these anions provide species whose electron binding strengths span a considerable range (0.3-1.8 eV).

  10. First-Principles Studies of Phase Stability and Reaction Dynamics in Complex Metal Hydrides

    NASA Astrophysics Data System (ADS)

    Chou, Mei-Yin

    2009-03-01

    Complex metal hydrides are believed to be one of the promising materials for developing hydrogen storage systems that can operate under desirable conditions. At the same time, these are also a class of materials that exhibit intriguing properties. We have applied state-of-the-art computational techniques to study the structural, dynamic, and electronic properties of these materials. This talk will focus on the critical role played by the Ti catalyst in helping hydrogen cycling in the alanates, which remains a challenging topic for this hydrogen storage material. We have performed a series of calculations to address the hydrogen interaction on the aluminum surface in the presence of the Ti ``dopant,'' focusing on the effect of near-surface alloying on the Al(100) surface. It is found that Ti occupies subsurface sites near the Al surface. This subsurface Ti arrangement not only enhances H binding with the Al surface layer, but also improves H mobility on the surface. Based on existing experimental data and our preliminary results, we propose a model in which the catalyst does not enter the bulk, but facilitates hydrogen dissociation-recombination near the surface. In the dehydrogenation cycle, the catalyst kinetically facilitates the release and decomposition of AlH3 from the solid-state alanate. In the hydrogenation cycle, the catalyst helps the adsorption of hydrogen and the formation of AlH3 oligomers on Al surfaces. The implication of Ti as a catalyst for the hydrogenation reactions will be discussed.

  11. Heat capacity of α-AlH3 and α-AlD3 at temperatures up to 1000 K

    NASA Astrophysics Data System (ADS)

    Antonov, V. E.; Kolesnikov, A. I.; Markushkin, Yu E.; Palnichenko, A. V.; Ren, Y.; Sakharov, M. K.

    2008-07-01

    The densest α modification of AlH3 and AlD3 is thermodynamically stable at high hydrogen pressures. At ambient pressure, α-AlH3 and α-AlD3 rapidly and irreversibly decompose to Al and H2 or D2 gas when heated to about 420 and 520 K, respectively. In the present paper, the heat capacities at constant volume (CV) and at constant pressure (CP) are calculated for α-AlH3 and α-AlD3 at a pressure of 1 atm and temperatures 0-1000 K using the phonon densities of states determined earlier by inelastic neutron scattering at helium temperatures (Kolesnikov et al 2007 Phys. Rev. B 76 064302). The CP(T) dependence of AlH3 is also measured at temperatures 6-30 K and 130-320 K and that of AlD3 at 130-320 K in order to compensate for the scatter in the literature data and to improve the accuracy of the calculated CV and CP dependences at low temperatures.

  12. Direct deposition of highly conductive aluminum thin film on substrate by solution-dipping process.

    PubMed

    Lee, Hye Moon; Choi, Si-Young; Jung, Areum

    2013-06-12

    A solution-dipping process consisting of 2 steps, including (i) a catalytic treatment of the substrate and (ii) an immersion of the catalytically treated substrate into an aluminum precursor solution of AlH3{O(C4H9)2}, is suggested for the low-cost and simple preparation of aluminum thin film. This process can be applied to electric devices in the way of not only various film geometry including large area (□ 100 mm (W) × 100 mm (L)) or patterned structure but also the diverse substrate selectivity including rigid or flexible substrate. More interestingly, preparations of aluminum film in this study can be unprecedentedly accomplished at room temperature with the help of chemical catalyst to decompose AlH3{O(C4H9)2} into Al, 1.5H2, and O(C4H9)2. Beyond the previously reported processes, the prepared Al films via solution-dipping process are comparable or even superior to Ag, Au, and Al films prepared by other solution processes and furthermore are found to be excellent in mechanical durability against external deformation.

  13. Secondary Amine Stabilized Aluminum Hydrides Derived from N,N'-Di-tert-butylethylenediamines.

    PubMed

    Gardiner, Michael G.; Lawrence, Stacey M.; Raston, Colin L.

    1996-02-28

    The metalation of substituted N,N'-di-tert-butylethylenediamines by various aluminum hydride sources has been investigated. HN(t-Bu)CH(t-Bu)CH(2)N(H)(t-Bu) forms a dimeric lithium chelated adduct of LiAlH(4), [{[HN(t-Bu)CH(t-Bu)CH(2)N(H)(t-Bu)]Li(&mgr;-H)(2)AlH(2)}(2)], 4, which thermally decomposes to yield the tetrameric lithium diamidoaluminum hydride [{Li[N(t-Bu)CH(t-Bu)CH(2)N(t-Bu)]AlH(2)}(4)], 5. The same diamine reacts with AlH(3).NMe(3) or AlH(3) diethyl etherate to give the secondary amine stabilized amidoaluminum hydride species [{HN(t-Bu)CH(t-Bu)CH(2)N(t-Bu)}AlH(2)], 2. Similarly, the same aluminum hydride sources react with the diamine rac-HN(t-Bu)CH(Me)CH(Me)N(H)(t-Bu) to yield [{rac-HN(t-Bu)CH(Me)CH(Me)N(t-Bu)}AlH(2)], 3. Compounds 2 and 3 are stable with respect to elimination of hydrogen to form diamidoaluminum hydrides, but can be converted to the alane rich species, [H(2)Al{N(t-Bu)CH(t-Bu)CH(2)N(t-Bu)}AlH(2)],6, and [H(2)Al{rac-N(t-Bu)CH(Me)CH(Me)N(t-Bu)}AlH(2)], 7, by reaction with AlH(3).NMe(3) under special conditions. The varying reactivity of the three aluminum hydride sources in these reactions has enabled mechanistic information to be gathered, and the effect of the different steric requirements in the diamines on the stability of the complexes is discussed. Crystals of 3are monoclinic, space group P2(1)/n (No. 14), with a = 8.910(4), b = 14.809(1), and c = 12.239(6) Å, beta = 109.76(2) degrees, V = 1520(1) Å(3), and Z = 4. Crystals of 4 are orthorhombic, space group Pbca (No. 61), with a = 15.906(9), b = 24.651(7), and c = 9.933(7) Å, V = 3895(3) Å(3), and Z = 4. Crystals of 6 are monoclinic, space group P2(1)/c (No. 14), with a = 8.392(1), b = 17.513(2), and c = 12.959(1) Å, beta = 107.098(8) degrees, V = 1820.4(3) Å(3), and Z = 4.

  14. Alane adsorption and dissociation on the Si(0 0 1) surface

    NASA Astrophysics Data System (ADS)

    Smith, R. L.; Bowler, D. R.

    2017-10-01

    We used DFT to study the energetics of the decomposition of alane, AlH3, on the Si(0 0 1) surface, as the acceptor complement to PH3. Alane forms a dative bond with the raised atoms of silicon surface dimers, via the Si atom lone pair. We calculated the energies of various structures along the pathway of successive dehydrogenation events following adsorption: AlH2, AlH and Al, finding a gradual, significant decrease in energy. For each stage, we analyse the structure and bonding, and present simulated STM images of the lowest energy structures. Finally, we find that the energy of Al atoms incorporated into the surface, ejecting a Si atom, is comparable to Al adatoms. These findings show that Al incorporation is likely to be as precisely controlled as P incorporation, if slightly less easy to achieve.

  15. Synthesis of square-planar aluminum(III) complexes.

    PubMed

    Thompson, Emily J; Myers, Thomas W; Berben, Louise A

    2014-12-15

    The synthesis of two four-coordinate and square planar (SP) complexes of aluminum(III) is presented. Reaction of a phenyl-substituted bis(imino)pyridine ligand that is reduced by two electrons, Na2((Ph)I2P(2-)), with AlCl3 afforded five-coordinate [((Ph)I2P(2-))Al(THF)Cl] (1). Square-planar [((Ph)I2P(2-))AlCl] (2) was obtained by performing the same reaction in diethyl ether followed by lyphilization of 2 from benzene. The four-coordinate geometry index for 2, τ4, is 0.22, where 0 would be a perfectly square-planar molecule. The analogous aluminum hydride complex, [((Ph)I2P(2-))AlH] (3), is also square-planar, and was characterized crystallographically and has τ4=0.13. Both 2 and 3 are Lewis acidic and bind 2,6-lutidine.

  16. Advances in the electrochemical regeneration of aluminum hydride

    NASA Astrophysics Data System (ADS)

    Martínez-Rodríguez, Michael J.; García-Díaz, Brenda L.; Teprovich, Joseph A.; Knight, Douglas A.; Zidan, Ragaiy

    2012-03-01

    In previous work, a reversible cycle that uses electrolysis and catalytic hydrogenation of spent Al(s) for the regeneration of alane (AlH3) was reported. In this study, the electrochemical synthesis of alane is improved. Advances in the electrochemical regeneration of alane have been achieved via the use of lithium aluminum hydride (LiAlH4) and lithium chloride (LiCl). Lithium chloride reacts in a cyclic process and functions as an electro-catalytic additive that enhances the electrochemical process by increasing the cell efficiency and the alane production. Electrochemical techniques are used to show that the increased rate of alane generation is due to the electro-catalytic effect of lithium chloride, rather than an electrolyte enhanced effect.

  17. Stability Studies of Aluminum Hydride

    NASA Astrophysics Data System (ADS)

    Tang, Xia; Laube, Bruce; Anton, Donald; Hwang, Son-Jong; Bowman, Robert

    2007-03-01

    Aluminum hydride has attracted research attention recently as a promising hydrogen storage material due to its high gravimetric, volumetric storage capacity and very low enthalpy. AlH3 forms several phases, all of which are sensitive to moisture. In this study, the discharge kinetics of a stabilized form of alpha aluminum hydride newly synthesized was evaluated. Its desorption kinetics were measured in the temperature range of 60-120^oC at one atmosphere of hydrogen pressure. The material was stable at ambient temperature and no significant dehydrogenation was observed at 60^oC after 70 hours. Approximately 10 wt% hydrogen was rapidly (quantify in wt%/min.) released at 100^oC with no additional catalization. The activation energy for desorption was measured at 97.0 KJ/mole H2. The surface and bulk characterization methods Auger, SEM, XRD, and solid state NMR were used to investigate the mechanism of stabilization.

  18. A Highly diastereoselective synthesis of (1R)-(+)-camphor-based chiral allenes and their asymmetric hydroboration-oxidation reactions.

    PubMed

    Hung, Shang-Cheng; Wen, Yen-Fang; Chang, Jia-Wen; Liao, Chun-Chen; Uang, Biing-Jiun

    2002-02-22

    Synthesis of camphor derived chiral allenes and their hydroboration-oxidation reactions are described. Reaction of (1R)-(+)-camphor with alkynyllithium followed by the reduction of the resulted propargyl alcohol derivatives using AlH3 furnished chiral allenes 2a-g in excellent yields with high diastereoselectivity. Reduction of the propargyl alcohols with aluminum hydride proceeded through selective intermolecular anti-addition of hydride ion. The stereochemistry of the chiral allenes 2 was assigned based on lanthanide shift studies and chemical correlations. Diastereoselectivity was observed in the hydroboration-oxidation of 2 which produced a mixture of (E,R) and (E,S) stereoisomers in a ratio of 6:1 to 18:1.

  19. Aluminium Diphosphamethanides: Hidden Frustrated Lewis Pairs.

    PubMed

    Styra, Steffen; Radius, Michael; Moos, Eric; Bihlmeier, Angela; Breher, Frank

    2016-07-04

    The synthesis and characterisation of two aluminium diphosphamethanide complexes, [Al(tBu)2 {κ(2) P,P'-Mes*PCHPMes*}] (3) and [Al(C6 F5 )2 {κ(2) P,P'-Mes*PCHPMes*}] (4), and the silylated analogue, Mes*PCHP(SiMe3 )Mes* (5), are reported. The aluminium complexes feature four-membered PCPAl core structures consisting of diphosphaallyl ligands. The silylated phosphine 5 was found to be a valuable precursor for the synthesis of 4 as it cleanly reacts with the diaryl aluminium chloride [(C6 F5 )2 AlCl]2 . The aluminium complex 3 reacts with molecular dihydrogen at room temperature under formation of the acyclic σ(2) λ(3) ,σ(3) λ(3) -diphosphine Mes*PCHP(H)Mes* and the corresponding dialkyl aluminium hydride [tBu2 AlH]3 . Thus, 3 belongs to the family of so-called hidden frustrated Lewis pairs.

  20. Metallic and superconducting gallane under high pressure

    NASA Astrophysics Data System (ADS)

    Gao, Guoying; Wang, Hui; Bergara, Aitor; Li, Yinwei; Liu, Guangtao; Ma, Yanming

    2011-08-01

    Using our newly developed particle swarm optimization algorithm on crystal structural prediction, we characterized the pressure-induced structural transition sequence of gallane (GaH3). As has been observed in alane (AlH3), enthalpy calculations reveal that the Pm3¯n structure of GaH3 becomes stable above 160 GPa, below which it is unstable with respect to elemental decomposition. Interestingly, the Pm3¯n structure is metallic, and the application of the Allen-Dynes modified McMillan equation reveals a high superconducting transition temperature (Tc), which reaches 86 K at 160 GPa and increases with decreasing pressure (Tc = 102 K at 120 GPa). Our band structure calculations demonstrate that GaH3 within the Pm3¯n structure is a highly ionic solid, where the ionicity of H atoms plays an important role in the predicted high temperature superconductivity.

  1. A density functional theory study of the one-dimensional alane

    NASA Astrophysics Data System (ADS)

    Cui, Yan-Hong; Wang, Jian-Guo; Xu, W.

    2010-01-01

    The AlH1-6, Al2H1-7, Al3H1-9, AlmH3m (m = 4-10), and the periodic helical structure of the one-dimensional (1D) alane are studied by means of density functional theory calculations. The helical isolated structure is more stable than those in the corresponding cyclic and other geometries. A new periodic 1D helical alane structure is predicted for the first time. The stability of this periodic 1D helical alane structure has been confirmed by its large average binding energy based on AlH3, large energy gap of highest occupied molecular orbital and lowest unoccupied molecular orbital, and the typically double helical π-orbital which parallels its bone structure.

  2. Reaction of dimethylethylamine alane and ammonia on Si(100) during the atomic layer growth of AlN: static SIMS, TPSIMS, and TPD

    NASA Astrophysics Data System (ADS)

    Kuo, J. S.; Rogers, J. W.

    2000-05-01

    Dimethylethylamine alane [DMEAA; AlH 3:N(CH 3) 2(CH 2CH 3)] has been used as an Al source in the chemical vapor deposition of AlN. In the atomic layer growth mode, ammonia and DMEAA interact selectively by nucleophilic displacement. In the first part of this study, the surface adsorption and reaction processes are characterized with static secondary-ion mass spectrometry and temperature-programmed secondary-ion mass spectrometry. The secondary ion emission from DMEAA-covered Si surface shares similar general characteristics with the gas phase cracking pattern. The secondary ion emission spectrum is interpreted according to a unimolecular ion decomposition mechanism and is used as the fingerprint for the presence of molecular DMEAA. During the surface reaction between DMEAA and ammonia, the intensity of the fingerprint peaks diminish, representing the departure of the amine ligand. The thermal stability of DMEAA and its decomposition behavior on Si are also examined.

  3. Alane adsorption and dissociation on the Si(0 0 1) surface.

    PubMed

    Smith, R L; Bowler, D R

    2017-10-04

    We used DFT to study the energetics of the decomposition of alane, AlH3, on the Si(0 0 1) surface, as the acceptor complement to PH3. Alane forms a dative bond with the raised atoms of silicon surface dimers, via the Si atom lone pair. We calculated the energies of various structures along the pathway of successive dehydrogenation events following adsorption: AlH2, AlH and Al, finding a gradual, significant decrease in energy. For each stage, we analyse the structure and bonding, and present simulated STM images of the lowest energy structures. Finally, we find that the energy of Al atoms incorporated into the surface, ejecting a Si atom, is comparable to Al adatoms. These findings show that Al incorporation is likely to be as precisely controlled as P incorporation, if slightly less easy to achieve.

  4. Parametrization of a reactive force field for aluminum hydride.

    PubMed

    Ojwang, J G O; van Santen, Rutger A; Kramer, Gert Jan; van Duin, Adri C T; Goddard, William A

    2009-07-28

    A reactive force field, REAXFF, for aluminum hydride has been developed based on density functional theory (DFT) derived data. REAXFF(AlH(3)) is used to study the dynamics governing hydrogen desorption in AlH(3). During the abstraction process of surface molecular hydrogen charge transfer is found to be well described by REAXFF(AlH(3)). Results on heat of desorption versus cluster size show that there is a strong dependence of the heat of desorption on the particle size, which implies that nanostructuring enhances desorption process. In the gas phase, it was observed that small alane clusters agglomerated into a bigger cluster. After agglomeration molecular hydrogen was desorbed from the structure. This thermodynamically driven spontaneous agglomeration followed by desorption of molecular hydrogen provides a mechanism on how mobile alane clusters can facilitate the mass transport of aluminum atoms during the thermal decomposition of NaAlH(4).

  5. Parametrization of a reactive force field for aluminum hydride

    NASA Astrophysics Data System (ADS)

    Ojwang, J. G. O.; van Santen, Rutger A.; Kramer, Gert Jan; van Duin, Adri C. T.; Goddard, William A.

    2009-07-01

    A reactive force field, REAXFF, for aluminum hydride has been developed based on density functional theory (DFT) derived data. REAXFFAlH3 is used to study the dynamics governing hydrogen desorption in AlH3. During the abstraction process of surface molecular hydrogen charge transfer is found to be well described by REAXFFAlH3. Results on heat of desorption versus cluster size show that there is a strong dependence of the heat of desorption on the particle size, which implies that nanostructuring enhances desorption process. In the gas phase, it was observed that small alane clusters agglomerated into a bigger cluster. After agglomeration molecular hydrogen was desorbed from the structure. This thermodynamically driven spontaneous agglomeration followed by desorption of molecular hydrogen provides a mechanism on how mobile alane clusters can facilitate the mass transport of aluminum atoms during the thermal decomposition of NaAlH4.

  6. A density functional theory study of the one-dimensional alane.

    PubMed

    Cui, Yan-Hong; Wang, Jian-Guo; Xu, W

    2010-01-15

    The AlH(1-6), Al(2)H(1-7), Al(3)H(1-9), Al(m)H(3m) (m = 4-10), and the periodic helical structure of the one-dimensional (1D) alane are studied by means of density functional theory calculations. The helical isolated structure is more stable than those in the corresponding cyclic and other geometries. A new periodic 1D helical alane structure is predicted for the first time. The stability of this periodic 1D helical alane structure has been confirmed by its large average binding energy based on AlH(3), large energy gap of highest occupied molecular orbital and lowest unoccupied molecular orbital, and the typically double helical pi-orbital which parallels its bone structure.

  7. Stable High-Energy Density Super-Atom Clusters of Aluminum Hydride

    NASA Astrophysics Data System (ADS)

    Lian, Ke-yan; Jiang, Yuan-fei; Fei, De-hou; Feng, Wei; Jin, Ming-xing; Ding, Da-jun; Luo, Yi

    2012-04-01

    With the concept of super-atom, first principles calculations propose a new type of super stable cage clusters AlnH3n that are much more energetic stable than the well established clusters, AlnHn+2. In the new clusters, the aluminum core-frame acts as a super-atom with n vertexes and 2n Al-Al edges, which allow to adsorb n hydrogen atoms at the top-site and 2n at the bridge-site. Using Al12H36 as the basic unit, stable chain structures, (Al12H36)m, have been constructed following the same connection mechanism as for (AlH3)n linear polymeric structures. Apart from high hydrogen percentage per molecule, calculations have shown that these new clusters possess large heat of formation values and their combustion heat is about 4.8 times of the methane, making them a promising high energy density material.

  8. Enhanced Anharmonicity Under Pressure

    NASA Astrophysics Data System (ADS)

    Errea, Ion; Rousseau, Bruno; Bergara, Aitor

    2012-07-01

    Contradicting common sense, pressure does not monotonically harden the phonons in many systems but makes some specific modes soften at given points of the first Brilloiun zone, even inducing dynamical instabilities that drive structural phase transitions. As the harmonic part of the ionic potential becomes smaller, higher order terms turn out to be more and more important. In AlH3, for instance, anharmonicity suppresses the predicted high superconducting transition temperature at 110 GPa in agreement with experiments. Furthermore, anharmonicity stabilizes the high-pressure simple cubic phase of calcium even at zero temperature, explaining its mechanical stability. We will review the calculations performed in these two systems and show that anharmonicity can be tackled making use of perturbation theory or the so called self-consistent harmonic approximation.

  9. Cyclic and linear polymeric structures of AlnH3n (n=3 7) molecules

    NASA Astrophysics Data System (ADS)

    Kawamura, Hiroaki; Kumar, Vijay; Sun, Qiang; Kawazoe, Yoshiyuki

    2003-06-01

    AlH3 and Al2H6 are very stable molecules with high ionization potentials and low electron affinities. Yet, we report the findings of higher aluminum hydrides, AlnH3n (n=3 7) with cyclic or linear polymeric structures that are even more stable. These represent the possibilities of associating higher contents of hydrogen with aluminum clusters. We use first-principles calculations with a plane-wave basis as well as a linear combination of atomic-orbitals method. The binding energies and the highest occupied lowest unoccupied molecular-orbital gaps of these molecules are significantly higher as compared to the values for the three-dimensional structures of hydrogenated aluminum clusters. The energetic and fragmentation behavior shows that these molecules should be stable up to a size of at least n=4 in cyclic or polymeric forms.

  10. Hydrogenation of passivated aluminum with hydrogen fluid

    NASA Astrophysics Data System (ADS)

    Saitoh, H.; Machida, A.; Katayama, Y.; Aoki, K.

    2009-04-01

    Hydrogenation conditions of passivated aluminum were examined in a pressure and temperature range of 6-10 GPa and 300-800 °C, respectively. The relationship between the hydrogenation reaction yields and holding time was analyzed by Johnson-Mehl-Avrami equation. An Avrami exponent n of 0.3 indicated that the reaction decreased with time due to the low diffusivity of hydrogen in AlH3. The oxide layer on passivated aluminum seemed to be partly removed or modified by pressure-temperature treatment above 6 GPa and 600 °C in hydrogen fluid. The hydrogenation pressure of 9 GPa for the passivated aluminum was reduced to 6 GPa.

  11. Infrared spectroscopic observation of the group 13 metal hydroxides, M(OH)1,2,3 (M =Al, Ga, In, and Tl) and HAl(OH)2.

    PubMed

    Wang, Xuefeng; Andrews, Lester

    2007-03-15

    Reactions of laser-ablated Al, Ga, In, and Tl atoms with H2O2 and with H2 + O2 mixtures diluted in argon give new absorptions in the O-H and M-O stretching and O-H bending regions, which are assigned to the metal mono-, di-, and trihydroxide molecules. Isotopic substitutions (D2O2, 18O2, 16,18O2, HD, and D2) confirm the assignments, and DFT calculations reproduce the experimental results. Infrared spectra for the Al(OH)(OD) molecule verify the calculated C2v structure. The trihydroxide molecules increase on annealing from the spontaneous reaction with a second H2O2 molecule. Aluminum atom reactions with the H2 + O2 mixtures favor the HAl(OH)2 product, suggesting that AlH3 generated by UV irradiation combines with O2 to form HAl(OH)2.

  12. DFT and CCSD(T) study of the AH3- (A = Al, Ga) isomerization, [Ga2(μ-H)(μ-H2)]- and [Ga2(μ-H3)]- unprecedented hydrido-bimetallic structures

    NASA Astrophysics Data System (ADS)

    Guermoune, Abdeladim; Jarid, Abdellah

    2007-03-01

    Total potential energy surfaces (PES) are scanned in order to study the isomerization of the AH3- (A = Al, Ga) anions. AlH3- PES is characterized by six minima and seven transition structures which are connectable with themselves. Indeed of these 12 same extrema, the GaH3- PES has three other minima and four TSs. These structures exhibit an activated H 2 molecule in one or both Ga atoms coordination sphere where the Ga atom seems imply its metallic character via its occupied d-orbital. We have also localized two unusual structures: a minimum having M 2(μ-H)(μ-H 2)-like structure and a transition with M 2(μ-H 3)-like arrangement where the H 3 entity is coordinated to both Ga atoms. The connectivity of all these extrema brings to the fore an eventual fluxional behaviour of these compounds.

  13. Dry mechanochemical synthesis of alane from LiH and AlCl3.

    PubMed

    Hlova, Ihor Z; Gupta, Shalabh; Goldston, Jennifer F; Kobayashi, Takeshi; Pruski, Marek; Pecharsky, Vitalij K

    2014-01-01

    A mechanochemical process for the synthesis of alane (AlH3) starting from lithium hydride (LiH) and aluminium chloride (AlCl3) at room temperature and the underlying reaction pathway have been studied. In contrast to a conventional process using the same two reactants dissolved in diethyl ether, our approach enables a solvent-free synthesis, thereby directly leading to adduct-free alane. The method described here is quick and efficient, resulting in the quantitative conversion of all aluminium in the starting mixture to alane. Both the intermediate compounds formed during the reaction and the final products have been characterized by powder X-ray diffraction, solid-state (27)Al NMR spectroscopy, and temperature programmed desorption analysis of the as-milled mixtures. We show that excess LiH in the starting mixture (with an optimal ratio of 9LiH : 1AlCl3) is essential for the formation and stability of Al-H bonds, initially in the form of alanates and, eventually, as alane. Further processing of this mixture, gradually adding AlCl3 to reach the ideal 3LiH : 1AlCl3 stoichiometry, appears to restrict the local accumulation of AlCl3 during the ball-milling process, thereby preventing the formation of unstable intermediates that decompose to metallic Al and molecular hydrogen. We also demonstrate that under the milling conditions used, a moderate hydrogen pressure of ca. 300 bar is required to suppress competing reactions that lead to the formation of metallic Al at room temperature. The identification of the reaction intermediates at each stage of the synthesis provides significant insight into the mechanism of this solid-state reaction, which may potentially afford a more rational approach toward the production of AlH3 in a simple solvent-free process.

  14. Calculation of the 13C NMR shieldings of the C0 2 complexes of aluminosilicates

    NASA Astrophysics Data System (ADS)

    Tossell, J. A.

    1995-04-01

    13C NMR shieldings have been calculated using the random-phase-approximation, localized-orbital local-origins version of ab initio coupled Hartree-Fuck perturbation theory for CO 2 and and for several complexes formed by the reaction of CO 2 with molecular models for aluminosilicate glasses, H 3TOT'H3 3-n, T,T' = Si,Al. Two isomeric forms of the CO 2-aluminosilicate complexes have been considered: (1) "CO 2-like" complexes, in which the CO 2 group is bound through carbon to a bridging oxygen and (2) "CO 3-like" complexes, in which two oxygens of a central CO 3 group form bridging bonds to the two TH 3 groups. The CO 2-like isomer of CO 2-H 3SiOSiH 3 is quite weakly bonded and its 13C isotropic NMR shielding is almost identical to that in free CO 2. As Si is progressively replaced by Al in the - H terminated aluminosilicate model, the CO 2-like isomers show increasing distortion from the free CO 2 geometry and their 13C NMR shieldings decrease uniformly. The calculated 13C shielding value for H 3AlO(CO 2)AlH 3-2 is only about 6 ppm larger than that calculated for point charge stabilized CO 3-2. However, for a geometry of H 3SiO(CO 2) AlH 3-1, in which the bridging oxygen to C bond length has been artificially increased to that found in the - OH terminated cluster (OH) 3SiO(CO 2)Al(OH) 3-1, the calculated 13C shielding is almost identical to that for free CO 2. The CO 3-like isomers of the CO 2-aluminosili-cate complexes show carbonate like geometries and 13C NMR shieldings about 4-9 ppm larger than those of carbonate for all T,T' pairs. For the Si,Si tetrahedral atom pair the CO 2-like isomer is more stable energetically, while for the Si,Al and Al,Al cases the CO 3-like isomer is more stable. Addition of Na + ions to the CO 3-2 or H 3AlO(CO 2)AlH 3-2 complexes reduces the 13C NMR shieldings by about 10 ppm. Complexation with either Na + or CO 2 also reduces the 29Si NMR shieldings of the aluminosilicate models, while the changes in 27Al shielding with Na + or CO 2 complexation are much smaller. Complexation with CO 2 greatly increases the electric field gradient at the bridging oxygen of H 3AlOAlH 3-2, raising it to a value similar to that found for SiOSi linkages. Comparison of these results with the experimental 13C NMR spectra support the formation of CO 2-like complexes at SiOSi bridges in albite glasses and CO 3-like complexes at SiOAl and AlOAl bridges in albite and nepheline glasses. Changes in the calculated shieldings as Na + ions are added to the complexes suggest that some of the observed complexes may be similar in their CO 2-aluminosilicate interactions, but different with respect to the positions of the charge-compensating Na + ions.

  15. Hydrogen in aluminum: First-principles calculations of structure and thermodynamics

    NASA Astrophysics Data System (ADS)

    Wolverton, C.; Ozoliņš, V.; Asta, M.

    2004-04-01

    Despite decades of study, several key aspects of the Al-H system remain the subject of considerable debate. In an effort to elucidate some of these unknowns, we perform a systematic study of this system using first-principles density-functional calculations. We show that generalized gradient approximation (GGA) calculations provide an accurate picture of energetics, phase stability and structure, diffusion, and defect binding in the Al-H system. A series of calculations for hydrides in the M-H systems (M=Al, Ba, Ca, K, Mg, La, Li, Na, Ni, Pd, Sc, Sr, Ti, V, and Y) also shows that the GGA calculations are a quantitatively accurate predictor of hydride formation energies. For Al-H, we find: (i) In agreement with experiment, the observed metastable hydride, AlH3 is found to have a small, negative formation enthalpy at ambient conditions, but a strongly positive formation free energy. (ii) Linear response calculations of AlH3 yield vibrational frequencies, phonon densities of states (DOS), and heat capacities in excellent agreement with experimental measurements, and suggest the need for a reinterpretation of measured phonon DOS. (iii) Atomic relaxation and anharmonic vibrational effects both play an important role in the tetrahedral versus octahedral interstitial site preference of H in Al. (iv) The calculated heat of solution of H in the preferred tetrahedral site is large and positive (+0.71 eV), consistent with experimental solubility data and with Al as an endothermic hydrogen absorber. (v) Interstitial H interacts strongly with Al vacancies (□), with a calculated H-□ binding energy of 0.33 eV. (vi) In the absence of vacancies, the calculated migration energy of H between the tetrahedral and octahedral interstitial sites is 0.18 eV, but for H migrating away from an Al vacancy, the migration energy increases to 0.54 eV. Vacancy trapping of H can therefore provide an explanation for observed disparate H migration barriers.

  16. Ultrafast bulk diffusion of AlHx in high-entropy dehydrogenation intermediates of NaAlH4 [Highly mobile AlHx species and the dehydogenation kinetics of NaAlH4

    DOE PAGES

    Zhang, Feng; Wood, Brandon C.; Wang, Yan; ...

    2014-07-21

    Using first-principles molecular dynamics (FPMD) and total-energy calculations, we demonstrate low-barrier bulk diffusion of Al-bearing species in γ-NaAlH4, a recently proposed high-entropy polymorph of NaAlH4. For charged AlH4– and neutral AlH3 vacancies, the computed barriers for diffusion are <0.1 eV, and we directly observe the predicted diffusive pathways in FPMD simulations at picosecond time scales. In contrast, such diffusion in the α phase is inaccessible to FPMD, consistent with much higher barriers. The transport behavior of γ-NaAlH4, in addition to key dynamical and structural signatures, is consistent with experimental observations of high-mobility species, strongly supporting the idea that an intermediatemore » transition from the α phase to a high-entropy polymorph facilitates the hydrogen-releasing decomposition of NaAlH4. Lastly, our results provide an answer to longstanding questions regarding the responsible agent for the experimentally observed efficient Al transport during dehydrogenation and suggest that mass transport and phase transformation kinetics are coupled. Implications for understanding the (de)hydrogenation of undoped and catalyzed NaAlH4 are discussed.« less

  17. Aluminum compounds in calcium chloride extracts from podzolic soil and their possible sources

    NASA Astrophysics Data System (ADS)

    Tolpeshta, I. I.; Sokolova, T. A.

    2008-06-01

    Aluminum concentrations in organoaluminum complexes, mineral polymers, Al(H2O){6/3+}, Al(OH)(H2O){5/2+}, Al(OH)2(H2O){4/+}, AlH3SiO{4/2+}, and Al(OH)3(H2O){3/0} extracted with 0.001 M CaCl2 from the main genetic horizons of a podzolic soil on two-layered deposits were determined experimentally and calculated from thermodynamic equations. It was found that aluminum bound in organic complexes was predominant in extracts from the AE horizon, and mineral polymer aluminum compounds prevailed in extracts from the E and IIBD horizons. In the AE horizon, organoaluminum compounds were a major source of aluminum, which passed into solution predominantly by exchange reactions. In the E horizon, aluminum hydroxide interlayers in soil chlorites were the main source of aluminum, which passed into solution by dissolution reactions. In extracts from the IIBD horizon, aluminum was solubilized by the dissolution of aluminosilicates inherited from the parent rock.

  18. Dihydrogen bonding vs metal-σ interaction in complexes between H2 and metal hydride.

    PubMed

    Alkorta, Ibon; Elguero, Jose; Solimannejad, Mohammad; Grabowski, Sławomir J

    2011-01-20

    The complexes formed by hydrogen with metal hydrides (LiH, NaH, BeH(2), MgH(2), BH(3), AlH(3), Li(2)H(2), Na(2)H(2), Be(2)H(4), and Mg(2)H(4)) have been theoretically studied at the MP2/aug-cc-pVTZ, MP2/aug-cc-pVQZ and CCSD(T)/aug-cc-pVTZ//CCSD/aug-cc-pVTZ levels of theory. The hydrogen molecule can act as a Lewis acid or base. In the first case, a dihydrogen bonded complex is obtained and in the second an interaction between the σ-bond of the hydrogen molecule and an empty orbital of the metal atoms is found. Quantum theory of atoms in molecules and natural bond orbitals methods have been applied to analyze the intermolecular interactions. Additionally, the cooperativity effects are analyzed for selected complexes with two H(2) molecules where both kinds of interactions exist simultaneously.

  19. Synthesis and Hydrogen Desorption Properties of Aluminum Hydrides.

    PubMed

    Jeong, Wanseop; Lee, Sang-Hwa; Kim, Jaeyong

    2016-03-01

    Aluminum hydride (AlH3 or alane) is known to store maximum 10.1 wt.% of hydrogen at relatively low temperature (< 100 degrees C), which partially fulfills the U.S. department of energy requirements for gravimetric loading capacity. However, its detailed mechanisms of appearing of different phases, structural stability, and dynamics of hydrogen desorption are still not clear. To understand the desorption properties of hydrogen in alane, thermodynamically stable α-AlH3 was synthesized by employing an ethereal reaction method. The dependence of pathways on phase formation and the properties of hydrogen evolution were investigated, and the results were compared with the ones for γ-AlH3. It was found that γ-AlH3 requires 10 degrees C higher than that of γ-AlH3 to form, and its decomposition rate demonstrated enhanced endothermic stabilities. For desorption, all hydrogen atoms of alane evolved under an isothermal condition at 138 degrees C in less than 1 hour, and the sample completely transformed to pure aluminum. Our results show that the total amount of desorbed hydrogen from α-AlH3 exceeded 9.05 wt.%, with a possibility of further increase. Easy synthesis, thermal stability, and a large amount of hydrogen desorption of alane fulfill the requirements for light-weight hydrogen storage materials once the pathway of hydrogen cycling is provided.

  20. Development and evaluation of portable and wearable fuel cells for soldier use

    NASA Astrophysics Data System (ADS)

    Thampan, T.; Shah, D.; Cook, C.; Novoa, J.; Shah, S.

    2014-08-01

    A number of fuel cell systems have been recently developed to meet the U.S. Army's soldier power requirements. The operation and performance of these systems are discussed based on laboratory results and limited soldier evaluation. The systems reviewed are primarily intended for soldier use in an austere environment with minimum access to resupply and vehicular transportation. These applications require high power and energy density sources that are portable (300 W) and wearable (20 W) to minimize the soldier's load burden. Based on soldier field evaluations of portable fuel cell systems, improvements in power density and compatibility with logistical fuels are required to be successfully deployed. For soldier worn applications, a novel chemical hydride system has shown significant advances in power and energy density while maintaining a small form factor. The use of a high energy dense fuel cartridge (800 Wh kg-1) based on AlH3 (Alane) thermolysis, allows a power density of (28 W kg-1) which offers promising weight savings compared to the standard military batteries.

  1. Mechanistic studies of CO2 reduction to methanol mediated by an N-heterocyclic germylene hydride.

    PubMed

    Tan, Gengwen; Wang, Wenyuan; Blom, Burgert; Driess, Matthias

    2014-04-28

    The labile germylene hydride L(Cy)GeH is capable of activating CO2 affording the corresponding formate L(Cy)GeOCH([double bond, length as m-dash]O) (2) (L(Cy) = cyclo-C6H8-1-NAr-2-C(Ph)NAr, Ar = 2,6-iPr2C6H3). Compound and the previously reported LGeOCH([double bond, length as m-dash]O) (L = CH(MeC[double bond, length as m-dash]NAr)2, Ar = 2,6-iPr2C6H3) (2) could be further converted to methanol with the AlH3 · NMe3 alane-amine adduct as a hydrogen source upon workup with water. A plausible mechanism for the conversion of the formate complexes to methanol is proposed based on additional results from the conversion of with the milder hydride delivery agent LAlH2.

  2. Synthesis of aluminum hydrazides by hydroalumination of 2,3-diazabutadienes--formation of an Al4(N2)3 cage compound and an Al3(N2)3 macrocyclic ligand.

    PubMed

    Uhl, W; Molter, J; Neumüller, B

    2001-04-01

    Treatment of 1,1,4,4-tetramethyl-2,3-diazabutadiene with the alane adduct [AlH3(NMe2Et)] yielded the hydrazine derivative (AlH2)2-(AlH)2(N2iPr2)3 (1) by the hydroalumination of both C N double bonds. Compound 1 has a complicated cage structure formed by three hydrazido groups and four aluminium atoms. As a particularly interesting structural motif it contains a N-N group side-on-coordinated to one aluminium atom through its lone pairs of electrons. Sublimation of 1 gave a heterocubane-type compound (HAlNiPr)4 (2) by the complete cleavage of all N-N bonds, one face of which is bridged by weakly coordinated diisopropyldiazene with a N-N double bond. Repeated sublimation gave the pure, unsupported heterocubane molecule 3. Heating of the rough product of the reaction of alane and diazabutadiene to 90 degrees C in a closed vessel yielded another product Al(AlH2)3(N2iPr2)3 (4), which contains a cyclic chelating ligand formed by three hydrazido groups and three aluminium atoms. This heterocycle coordinates a fourth aluminum atom in the molecular center by close contacts to all six nitrogen atoms. A strongly flattened, distorted octahedral coordination sphere results for the inner metal atom.

  3. Vacancy-mediated hydrogen desorption in NaAl H4

    NASA Astrophysics Data System (ADS)

    Araújo, C. Moysés; Li, S.; Ahuja, R.; Jena, P.

    2005-10-01

    First-principles calculations based on density functional theory are carried out to understand the mechanisms responsible for hydrogen desorption from Ti-doped sodium-alanate (NaAlH4) . While the energy needed to remove a hydrogen atom from NaAlH4 with Ti substituted either at the Na site or at Al site is found to be significantly lower than that from the pristine NaAlH4 , the presence of Na vacancies is shown to play an even larger role: It is not only an order of magnitude smaller than that from Ti-doped sodium-alanate, but the removal of hydrogen associated with a Na vacancy is exothermic with respect to formation of H2 molecule. Furthermore, we show that the unusual stabilization of the magic AlH3 cluster in the vacancy containing sodium-alanate is responsible for this diminished value of the hydrogen-removal energy. It is suggested that this role of vacancies can be exploited in the design and synthesis of complex light-metal hydrides suitable for hydrogen storage.

  4. Solution processed aluminum paper for flexible electronics.

    PubMed

    Lee, Hye Moon; Lee, Ha Beom; Jung, Dae Soo; Yun, Jung-Yeul; Ko, Seung Hwan; Park, Seung Bin

    2012-09-11

    As an alternative to vacuum deposition, preparation of highly conductive papers with aluminum (Al) features is successfully achieved by the solution process consisting of Al precursor ink (AlH(3){O(C(4)H(9))(2)}) and low temperature stamping process performed at 110 °C without any serious hydroxylation and oxidation problems. Al features formed on several kinds of paper substrates (calendar, magazine, and inkjet printing paper substrates) are less than ~60 nm thick, and their electrical conductivities were found to be as good as thermally evaporated Al film or even better (≤2 Ω/□). Strong adhesion of Al features to paper substrates and their excellent flexibility are also experimentally confirmed by TEM observation and mechanical tests, such as tape and bending tests. The solution processed Al features on paper substrates show different electrical and mechanical performance depending on the paper type, and inkjet printing paper is found to be the best substrate with high and stable electrical and mechanical properties. The Al conductive papers produced by the solution process may be applicable in disposal paper electronics.

  5. Density Functional Theory Based Kinetic Monte Carlo Approach for Understanding Atomistic Mechanisms for Reversible Hydrogen Storage in Metal Hydrides: Application to Alane Formation on Ti Doped Al Surfaces

    NASA Astrophysics Data System (ADS)

    Karim, A.; Muckerman, J.; Sutter, P.; Muller, E.

    2008-03-01

    We describe a density functional kinetic Monte Carlo approach enabling us to study and simulate the steady-state situation of dissociative adsorption of hydrogen along with diffusion and reaction of Al and H atoms leading towards the formation of alane species on Ti-doped Al surfaces. In the first step, density functional theory is used in conjunction with the nudged elastic band/drag method to obtain the energetics of the relevant atomistic processes of Al and H diffusion and their reactions on Al surfaces with different concentration of dopant Ti atoms. Subsequently, the kinetic Monte Carlo method is employed, which accounts for the spatial distribution, fluctuations, and evolution of chemical species at Ti-doped Al surfaces under steady-state conditions. This DFT-based KMC approach provides an insight into the kinetics of alanes at technologically relevant pressure and temperature conditions. Our computed production rates of AlH3 on Al surfaces are in agreement with experimental data. We also obtained temperature programmed desorption spectra of different alane species, which is agreeing well with experiments.

  6. Multiscale modelling of Interaction of Alane Clusters on Al(111) surface: A Reactive Force Field and Infrared Absorption Spectroscopy Approach

    NASA Astrophysics Data System (ADS)

    Ojwang, Julius; van Duin, Adri; Goddard, William, III; van Santen, Rutger

    2010-10-01

    Alanes are believed to be the ubiquitous facilitators of mass transport of aluminum atoms during the thermal decomposition of NaAlH4. Alanes also take part on decomposition of AlH3, another important material for hydrogen storage. We have used interplay of theoretical simulations (reactive force field and density functional theory) and experiments (IR reflection absorption spectroscopy) to address the issue of the role of alanes as facilitators of mass transport of aluminum atoms. We have obtained valuable details on the mechanism of formation and agglomeration of alanes on Al(111) surface. Our simulations show that, on the Al(111) surface, alanes oligomerize into larger alanes. The identification of these string like intermediates as a precursor to the bulk hydride phase allows us to explain the loss of resolution in surface IR experiments with increasing hydrogen coverage on single crystal Al(111) surface. This is in excellent agreement with the experimental works of Go et al. (E. Go, K. Thuermer, J.E. Reutt-Robey, Surf. Sci.,437:377(1999)).

  7. Monomeric Alanes: Synthesis, Structure, and Thermolysis of MesAl(H)N(SiMe(3))(2) and a One-Pot Synthetic Route to Mes(2)AlH (Mes = -C(6)H(2)-2,4,6-t-Bu(3)).

    PubMed

    Wehmschulte, Rudolf J.; Power, Philip P.

    1998-05-04

    The reaction of (MesAlH(2))(2) (Mes = -C(6)H(2)-2,4,6-t-Bu(3)) with HN(SiMe(3))(2) affords the monomeric amidoarylalane MesAl(H)N(SiMe(3))(2), 1. This product can also be synthesized by the reaction of [MesAlH(2)](2) with LiN(SiMe(3))(2), which, in addition, yields the byproducts LiAlH(2){N(SiMe(3))(2)}(2), 3, and MesH. Thermolysis of 1 at 175-180 degrees C affords three different the related and the imide [MesAlN(SiMe(3))](n)(), 5. In addition, the previously reported monomeric alane Mes(2)AlH was synthesized in ca. 70% yield by a one-pot reaction between LiMes (generated in situ) and AlH(3).NMe(3). All products were spectroscopically characterized, and the structure of 1 was determined by X-ray crystallography. The Al-N distance (1.819(2) Å) in 1 is relatively long. However, it has a substantial, 18.5 kcal mol(-)(1), Al-N rotation barrier which is attributed to steric congestion rather than Al-N pi bonding.

  8. Defect-mediated Alane formation on Ti-doped Al(111) surfaces: a DFT study

    NASA Astrophysics Data System (ADS)

    Herwadkar, Aditi; Wang, Lin-Lin; Johnson, Duane D.

    2011-03-01

    Understanding of Alane (AlH3) formation on Al surface remains elusive, including interpreting STM results under various conditions. Using density functional theory calculations, we study Alane formation on close-packed (111) and stepped surfaces with {111} and {100} microfacets of Al, with and without Ti as a catalyst. We find that Ti dopants act as catalyst in the formation of Alane on Al(111) via a vacancy-mediated mechanism. Additionally, we find the Alane formation energy at steps is 40 % less than that from the flat surface. We assess the energetics of various surface-defect configurations to understand the concerted roles that Ti dopants, surface vacancies, and step defects play in Alane formation. Work was supported in part by Department of Energy, Office of Basic Energy Science under contract DEFC36-05GO15064 (Sandia Metal-Hydride Center of Excellence), DE-FG02-03ER15476, DE-FG02-03ER46026, and DE-AC02-07CH11358 at the Ames Laboratory operated by Iowa State University.

  9. Lattice dynamics of α-AlH3 and α-AlD3 by inelastic neutron scattering: High-energy band of optical bond-stretching vibrations

    NASA Astrophysics Data System (ADS)

    Kolesnikov, A. I.; Antonov, V. E.; Markushkin, Yu. E.; Natkaniec, I.; Sakharov, M. K.

    2007-08-01

    Inelastic neutron scattering (INS) spectra of trigonal α-AlH3 and α-AlD3 have been measured in a wide range (5-150meV) of energy transfers with a much better statistical accuracy than previously using the inverted-geometry NERA-PR spectrometer at JINR, Dubna. The studied energy interval covers the range of low-frequency lattice vibrations and a broad band of optical H vibrations. By using a direct-geometry HRMECS spectrometer at ANL, Argonne, the AlH3 hydride was also examined by INS at energy transfers up to 315meV in the regime of small momentum transfers. This significantly enhanced the contribution from the one-phonon neutron scattering and allowed an observation and accurate examination of one more, high-energy band of optical H vibrations predicted theoretically [C. Wolverton , Phys. Rev. B 69, 144109 (2004)]. Combining the obtained experimental data, the entire spectrum of phonon density of states was reconstructed for both α-AlH3 and α-AlD3 .

  10. Ultrafast Bulk Diffusion of AlHxin High-Entropy Dehydrogenation Intermediates of NaAlH4

    SciTech Connect

    Zhang, Feng; Wood, Brandon C; Wang, Yan; Wang, Cai-Zhuang; Ho, Kai-Ming; Chou, Mei-Yin

    2014-08-14

    Using first-principles molecular dynamics (FPMD) and total-energy calculations, we demonstrate low-barrier bulk diffusion of Al-bearing species in γ-NaAlH4, a recently proposed high-entropy polymorph of NaAlH4. For charged AlH4– and neutral AlH3 vacancies, the computed barriers for diffusion are <0.1 eV, and we directly observe the predicted diffusive pathways in FPMD simulations at picosecond time scales. In contrast, such diffusion in the α phase is inaccessible to FPMD, consistent with much higher barriers. The transport behavior of γ-NaAlH4, in addition to key dynamical and structural signatures, is consistent with experimental observations of high-mobility species, strongly supporting the idea that an intermediate transition from the α phase to a high-entropy polymorph facilitates the hydrogen-releasing decomposition of NaAlH4. Our results provide an answer to longstanding questions regarding the responsible agent for the experimentally observed efficient Al transport during dehydrogenation and suggest that mass transport and phase transformation kinetics are coupled. Implications for understanding the (de)hydrogenation of undoped and catalyzed NaAlH4 are discussed.

  11. Thermal- and photoactivation of aluminum hydride decomposition

    NASA Astrophysics Data System (ADS)

    Gabis, I. E.; Elets, D. I.; Kuznetsov, V. G.; Baraban, A. P.; Dobrotvorskii, M. A.; Dobrotvorskii, A. M.

    2012-11-01

    Processes occurring in the phase of AlH3 dehydrogenation incubation that precedes the active decomposition of the hydride and is evidently accompanied by a change in its material properties are investigated by thermal desorption spectroscopy and barometry. The electronic structures of α-AlH3 and α-AlH3:V(H0) (i.e., aluminum hydride with a neutral hydrogen atom removed) are calculated by the density functional method. It is shown that hydrogen vacancies are the source of nuclei for the metallic phase, and their emergence could be thermally activated. It is established that UV irradiation also leads to the formation of hydrogen vacancies in α-AlH3. A description of the probable mechanism for the accumulation of hydrogen vacancies at elevated temperatures and finally to the appearance of metallic phase nuclei is offered. It is shown that UV irradiation allows us to lower the temperature of the dehydrogenation of α-AlH3 crystals.

  12. Unusual Properties of Al_2H_6

    NASA Astrophysics Data System (ADS)

    Ganteför, G.; Burkart, S.; Seifert, G.; Rao, B. K.; Jena, P.

    2000-03-01

    Ab initio calculations based on density functional theory and generalized gradient approximation reveal the structure of Al_2H6 to be that of di-borane (B_2H_6) even though the chemistry of Al and B clusters are different. With an electron affinity of 0.44 eV and ionization potential of 10.14 eV, Al_2H6 bears the signature of a "magic" cluster. Unlike magic clusters in metallic systems, Al_2H6 is born out of the coalescence of two AlH3 which are also "magic" by themselves as dictated by their low electron affinity (0.28 eV) and high ionization potential (11.43 eV). The most striking property of Al_2H_6, however, is that its vertical electron detachment energy is about 2 eV higher than its adiabatic electron affinity signifying vast changes between the geometries of the anion and the neutral cluster. These predictions are verified experimentally by photodetachment spectroscopy.

  13. Hard-soft acid-base interactions of silylenes and germylenes.

    PubMed

    Oláh, Julianna; De Proft, Frank; Veszprémi, Tamás; Geerlings, Paul

    2005-03-03

    A detailed investigation of the electrophilic and nucleophilic character of singlet silylenes and germylenes, divalent compounds of silicon and germanium, respectively, substituted by first- and second-row elements is presented. In a first part, the Lewis acid properties of these compounds were studied through their complexation reaction with the Lewis bases NH3, PH3, and AsH3. The results indicate that this complexation is most favorable with the hardest base NH3, classifying these compounds as hard Lewis acids. This is confirmed by the linear correlation between the interaction energies and the value of the electrostatic potential, used as an approximation to the local hardness, near the empty p orbital of these compounds, indicating a charge-controlled interaction in the complex. Also the electrophilicity index, proposed by Parr et al., computed both at the global and the local level, correlates linearly with the complexation energies of the compounds with NH3. The Lewis base character of these silylenes has been investigated, through their interaction with the acids BH3 and AlH3. Also in this case, the electrostatic potential can be used to probe the reactivity of the compounds. It will finally be demonstrated that an increasing stability of the silylenes and germylenes is accompanied by an increase in their nucleophilicity and a decrease of the electrophilicity.

  14. Kinetics of bulk and surface mass transport in complex metal hydrides

    NASA Astrophysics Data System (ADS)

    Gunaydin, Hakan

    2009-03-01

    Metal hydrides can be used to store hydrogen in high gravimetric and volumetric densities. However, the kinetics of hydrogen release and uptake are slow in complex metal hydrides. Clarification of the mechanism of hydrogen release and uptake in complex metal hydrides can aid in a rational design of new hydrogen storage materials with fast kinetics or catalysts that will catalyze the rate of hydrogen release from the existing materials. The release of hydrogen in metal hydrides requires the transport of hydrogen and/or heavier species. The kinetics of such mass transport in metal hydrides can be the rate-limiting process for the release of hydrogen. For example, the rate-determining step for the release of hydrogen from NaAlH4 is the creation and diffusion of neutral AlH3 defects in NaAlH4. The release of hydrogen from LiH destabilized LiNH2 also proceeds via the creation of neutral point defects. The mechanism of mass transport in prototypical hydrogen storage materials such as NaAlH4 and LiNH2 and the mechanism of hydrogen diffusion in aluminum will be discussed.

  15. Hydrido and chloro gallium and aluminium complexes with the tridentate bis(2-dimethylaminoethyl)amide ligand.

    PubMed

    Luo, Bing; Kucera, Benjamin E; Gladfelter, Wayne L

    2006-10-07

    Five-coordinate gallium and aluminium dihydrides, H2Ga[N(CH2CH2NMe2)2] () and H2Al[N(CH2CH2NMe2)2] (), were synthesized and found to be volatile and thermally stable. and reacted with H3Ga(NMe3) and H3Al(NMe3), respectively, to form H2Ga[N(CH2CH2NMe2)2]GaH3 () and H2Al[N(CH2CH2NMe2)2]AlH3 (), in which the amido nitrogen bridged between the MH2 and MH3 groups (M=Ga or Al). A mixed metal complex, H2Al[N(CH2CH2NMe2)2]GaH3 () was obtained from the reaction of with H3Al(NMe3) or with H3Ga(NMe3), and a crystal consisting of a mixture of and was structurally characterized. The five-coordinate chloro derivative, Cl2Ga[N(CH2CH2NMe2)2] (), was synthesized and characterized.

  16. Al-Coated Conductive Fibrous Filter with Low Pressure Drop for Efficient Electrostatic Capture of Ultrafine Particulate Pollutants.

    PubMed

    Choi, Dong Yun; Jung, Soo-Ho; Song, Dong Keun; An, Eun Jeong; Park, Duckshin; Kim, Tae-Oh; Jung, Jae Hee; Lee, Hye Moon

    2017-05-17

    Here, we demonstrate a new strategy of air filtration based on an Al-coated conductive fibrous filter for high efficient nanoparticulate removals. The conductive fibrous filter was fabricated by a direct decomposition of Al precursor ink, AlH3{O(C4H9)2}, onto surfaces of a polyester air filter via a cost-effective and scalable solution-dipping process. The prepared conductive filters showed a low sheet resistance (<1.0 Ω sq(-1)), robust mechanical durability and high oxidative stability. By electrostatic force between the charged fibers and particles, the ultrafine particles of 30-400 nm in size were captured with a removal efficiency of ∼99.99%. Moreover, the conductive filters exhibited excellent performances in terms of the pressure drop (∼4.9 Pa at 10 cm s(-1)), quality factor (∼2.2 Pa(-1) at 10 cm s(-1)), and dust holding capacity (12.5 μg mm(-2)). After being cleaned by water, the filtration efficiency and pressure drop of the conductive filter was perfectly recovered, which indicates its good recyclability. It is expected that these promising features make the conductive fibrous filter have a great potential for use in low-cost and energy-efficient air cleaning devices as well as other relevant research areas.

  17. Analysis of the bonding in XH3Cu+ (XB, Al, Ga) complexes

    NASA Astrophysics Data System (ADS)

    Corral, Inés; Mó, Otilia; Yáñez, Manuel

    High-level density functional theory (DFT) calculations on XH3Cu+ (XB, Al, Ga) complexes show that the attachment of the metal cation to the base takes place through agostic-type interactions. These interactions that can be viewed as dative bonds from the σXH bonding orbitals of the base toward low-lying empty 4s orbitals of the metal cation, and back-donations from the lone pairs of the metal into the σ *XH antibonding orbitals of the neutral, are particularly favored when the XH bonds have a high X+δH-δ polarity. Accordingly, the AlH3 and GaH3 Cu+ binding energies are very similar, but much larger than that of BH3. Depopulation of the σXH bonding orbital and the concomitant population of the σ *XH antibonding orbital involved in the agostic interaction result in a significant weakening of the corresponding XH linkages, whose bond length increases and whose stretching frequency appears red-shifted.

  18. Pair-correlated coupled cluster theory: An alternative multireference coupled cluster method

    NASA Astrophysics Data System (ADS)

    Li, Shuhua; Ma, Jing; Jiang, Yuansheng

    2003-04-01

    We describe an alternative multireference coupled cluster (MRCC) method, pair-correlated coupled cluster (PCCC) theory, for treating the ground state of closed-shell systems with degeneracy or quasidegeneracy. With the separated electron pair (SEP) wave function as a reference, the PCCC wave function is truncated according to how many electron pairs are explicitly correlated. The inclusion of only two-pair correlation defines the PCCC2 scheme, and the inclusion of up to three-pair correlation gives the PCCC3 scheme. The PCCC theory is well defined within the natural orbital (of the SEP reference) description and size extensive. We present the formalism of the PCCC theory by taking the PCCC2 scheme as an example, and implement the PCCC2 and PCCC3 schemes at the ab initio level with various basis sets. Then illustrative applications are presented for systems such as the perpendicular insertion reaction path of Be into H2, the simultaneous bond stretching in AlH3 and H2O. The results show that the overall performance of PCCC methods is competitive to that of the RCCSD(T) or UCCSD(T) method at stretched geometries, but slightly inferior to that of the CCSD(T) method at the equilibrium geometry.

  19. Vacancy-mediated dehydrogenation of sodium alanate

    PubMed Central

    Gunaydin, Hakan; Houk, Kendall N.; Ozoliņš, Vidvuds

    2008-01-01

    Clarification of the mechanisms of hydrogen release and uptake in transition-metal-doped sodium alanate, NaAlH4, a prototypical high-density complex hydride, has fundamental importance for the development of improved hydrogen-storage materials. In this and most other modern hydrogen-storage materials, H2 release and uptake are accompanied by long-range diffusion of metal species. Using first-principles density-functional theory calculations, we have determined that the activation energy for Al mass transport via AlH3 vacancies is Q = 85 kJ/mol·H2, which is in excellent agreement with experimentally measured activation energies in Ti-catalyzed NaAlH4. The activation energy for an alternate decomposition mechanism via NaH vacancies is found to be significantly higher: Q = 112 kJ/mol·H2. Our results suggest that bulk diffusion of Al species is the rate-limiting step in the dehydrogenation of Ti-doped samples of NaAlH4 and that the much higher activation energies measured for uncatalyzed samples are controlled by other processes, such as breaking up of AlH4− complexes, formation/dissociation of H2 molecules, and/or nucleation of the product phases. PMID:18299582

  20. The Department of Energy's Hydrogen Storage Activities: Challenges and Needs in Chemistry and Chemical Dynamics

    NASA Astrophysics Data System (ADS)

    Satyapal, Sunita; Ordaz, Grace; Petrovic, John; Read, Carole; Thomas, George

    2006-03-01

    Hydrogen storage is a key area of research funded by the Department of Energy. Hydrogen, the simplest diatomic molecule known, has the highest energy content of all known fuels by mass, but the practical storage of sufficient hydrogen on-board a vehicle is a significant technological challenge. Hydrogen can be stored via various mechanisms within materials such as metal hydrides (e.g. LiBH4, AlH3) chemical hydrides (e.g. organic liquids), and nanostructured sorbents (e.g. carbon nanotubes, clathrates). Examples of mechanisms include physisorption, chemisorption, dissociative adsorption or combinations of the above. In addition to weight and volume, the kinetics of hydrogen charging and discharging as well as durability must be addressed. A fundamental understanding of hydrogen storage to help optimize materials is critical. The technical requirements for hydrogen storage, as well as some of the promises and challenges will be presented, with a focus on what chemical dynamics and chemistry can offer in solving the challenge of hydrogen storage for transportation applications.

  1. Aluminum compounds containing eta1- and/or eta5-bidentate dianionic pyrrolyl-methylamide ligands.

    PubMed

    Chen, Ya-Chi; Lin, Che-Yu; Li, Chun-Yin; Huang, Jui-Hsien; Chang, Ling-Chueh; Lee, Ting-Yu

    2008-01-01

    A series of dialuminum compounds have been synthesized and their reactivity and application for lactide polymerization have been studied. The reaction of AlH3 x NMe3 with [C4H3NH(2-CH2NHtBu)] in diethyl ether generated a dimeric aluminum hydride compound, [[[C4H3N(2-CH2NtBu)]AlH]2] (1). The structure of 1 was confirmed by spectroscopy of a deuterated analogue of 1 with an Al--D function. Direct treatment of [C4H3NH(2-CH2NHtBu)] with LiAlH4 in diethyl ether resulted in colorless crystals of [[Li[micro-eta1:eta5-C4H3N(2-CH2NtBu)]2Al]2] (2) in 80 % yield after recrystallization from a toluene solution. The micro-eta1:eta5-pyrrolyl protons exhibit high-field shifts at delta=5.73, 6.15, and 6.72 comparable to a similar eta5-bonding mode in the literature. Treatment of 1 with 1 equiv acetone oxime or acetone in dichloromethane gave [[[C4H3N(2-CH2NtBu)]Al[varkappaO,varkappaN-(ON==CMe2)

  2. Thermochemistry of Alane Complexes for Hydrogen Storage: A Theoretical and Experimental Investigation

    PubMed Central

    2011-01-01

    Knowledge of the relative stabilities of alane (AlH3) complexes with electron donors is essential for identifying hydrogen storage materials for vehicular applications that can be regenerated by off-board methods; however, almost no thermodynamic data are available to make this assessment. To fill this gap, we employed the G4(MP2) method to determine heats of formation, entropies, and Gibbs free energies of formation for 38 alane complexes with NH3−nRn (R = Me, Et; n = 0−3), pyridine, pyrazine, triethylenediamine (TEDA), quinuclidine, OH2−nRn (R = Me, Et; n = 0−2), dioxane, and tetrahydrofuran (THF). Monomer, bis, and selected dimer complex geometries were considered. Using these data, we computed the thermodynamics of the key formation and dehydrogenation reactions that would occur during hydrogen delivery and alane regeneration, from which trends in complex stability were identified. These predictions were tested by synthesizing six amine−alane complexes involving trimethylamine, triethylamine, dimethylethylamine, TEDA, quinuclidine, and hexamine and obtaining upper limits of ΔG° for their formation from metallic aluminum. Combining these computational and experimental results, we establish a criterion for complex stability relevant to hydrogen storage that can be used to assess potential ligands prior to attempting synthesis of the alane complex. On the basis of this, we conclude that only a subset of the tertiary amine complexes considered and none of the ether complexes can be successfully formed by direct reaction with aluminum and regenerated in an alane-based hydrogen storage system. PMID:22962624

  3. A new bulky iminophosphonamide as an N,N'-chelating ligand: synthesis and structural characterization of heteroleptic group 13 element complexes.

    PubMed

    Prashanth, Billa; Singh, Sanjay

    2014-11-28

    A sterically demanding iminophosphonamine ligand [(2,6-iPr2C6H3N)P(Ph2)(NtBu)]H (LH) and its lithium derivative [(2,6-iPr2C6H3N)P(Ph2)(NtBu)](Li·2THF) (1) were used to prepare complexes of group 13 elements. The reaction of LH with AlH3·NMe2Et and AlMe3 respectively, affords [LAlH2]2 (2) and LAlMe2 (3). The lithium derivative 1 when treated with the MCl3 compound of group 13 yields [(2,6-iPr2C6H3N)P(Ph2)(NtBu)]MCl2 (M = B (4); Al (5); and Ga (6). Compound 3 on reaction with a Lewis acid B(C6F5)3 generates the cationic complex [{(2,6-iPr2C6H3N)P(Ph2)(NtBu)}AlMe](+) [MeB(C6F5)3](-) (7) that slowly undergoes rearrangement to yield [(2,6-iPr2C6H3N)P(Ph2)(NtBu)]AlMe(C6F5) (8) and MeB(C6F5)2. Compounds 1-8 were characterized using multinuclear NMR, EI-MS and IR techniques and the solid state structure of 1-6 and 8 was elucidated by single crystal X-ray diffraction analyses.

  4. Aluminum forms in drinking water and risk of Alzheimer's disease.

    PubMed

    Gauthier, E; Fortier, I; Courchesne, F; Pepin, P; Mortimer, J; Gauvreau, D

    2000-11-01

    The objective of this study was to assess the relation between long-term exposure to different aluminum (Al) forms in drinking water and Alzheimer's disease (AD). The study participants were selected from a random sample of the elderly population (> or = 70 years of age) of the Saguenay-Lac-Saint-Jean region (Quebec). Sixty-eight cases of Alzheimer's disease diagnosed according to recognized criteria were paired for age (+/-2 years) and sex with nondemented controls. Aluminum speciation was assessed using established standard analytical protocols along with quality control procedures. Exposure to Al forms (total Al, total dissolved Al, monomeric organic Al, monomeric inorganic Al, polymeric Al, Al(3+), AlOH, AlF, AlH(3)SiO(2+)(4), AlSO(4)) in drinking water was estimated by juxtaposing the subject's residential history with the physicochemical data of the municipalities. The markers of long-term exposures (1945 to onset) to Al forms in drinking water were not significantly associated with AD. On the other hand, after adjustment for education level, presence of family cases, and ApoE varepsilon4 allele, exposure to organic monomeric aluminum estimated at the onset of the disease was associated with AD (odds ratio 2.67; 95% CI 1.04-6.90). On average, the exposure estimated at the onset had been stable for 44 years. Our results confirm prime the importance of estimation of Al speciation and consideration of genetic characteristics in the assessment of the association between aluminum exposure and Alzheimer's disease. Copyright 2000 Academic Press.

  5. Site and chirality selective chemical modifications of boron nitride nanotubes (BNNTs) via Lewis acid-base interactions.

    PubMed

    Sundaram, Rajashabala; Scheiner, Steve; Roy, Ajit K; Kar, Tapas

    2015-02-07

    The pristine BNNTs contain both Lewis acid (boron) and Lewis base (nitrogen) centers at their surface. Interactions of ammonia and borane molecules, representatives of Lewis base and acid as adsorbates respectively, with matching sites at the surface of BNNTs, have been explored in the present DFT study. Adsorption energies suggest stronger chemisorption (about 15-20 kcal mol(-1)) of borane than ammonia (about 5-10 kcal mol(-1)) in both armchair (4,4) and zigzag (8,0) variants of the tube. NH3 favors (8,0) over the (4,4) tube, whereas BH3 exhibits the opposite preference, indicating some chirality dependence on acid-base interactions. A new feature of bonding is found in BH3/AlH3-BNNTs (at the edge site) complexes, where one hydrogen of the guest molecule is involved in three-center two-electron bonding, in addition to dative covalent bond (N: → B). This interaction causes a reversal of electron flow from borane/alane to BNNT, making the tube an electron acceptor, suggesting tailoring of electronic properties could be possible by varying strength of incoming Lewis acids. On the contrary, BNNTs always behave as electron acceptor in ammonia complexes. IR, XPS and NMR spectra show some characteristic features of complexes and can help experimentalists to identify not only structures of such complexes but also the location of the guest molecules and design second functionalizations. Interaction with several other neutral BF3, BCl3, BH2CH3 and ionic CH3(+) acids as well as amino group (CH3NH2 and NH2COOH) were also studied. The strongest interaction (>100 kcal mol(-1)) is found in BNNT-CH3(+) complexes and H-bonds are the only source of stability of NH2COOH-BNNT complexes.

  6. Thermochemistry of Alane Complexes for Hydrogen Storage: A Theoretical and Experimental Investigation.

    PubMed

    Wong, Bryan M; Lacina, David; Nielsen, Ida M B; Graetz, Jason; Allendorf, Mark D

    2011-04-21

    Knowledge of the relative stabilities of alane (AlH(3)) complexes with electron donors is essential for identifying hydrogen storage materials for vehicular applications that can be regenerated by off-board methods; however, almost no thermodynamic data are available to make this assessment. To fill this gap, we employed the G4(MP2) method to determine heats of formation, entropies, and Gibbs free energies of formation for 38 alane complexes with NH(3-n)R(n) (R = Me, Et; n = 0-3), pyridine, pyrazine, triethylenediamine (TEDA), quinuclidine, OH(2-n)R(n) (R = Me, Et; n = 0-2), dioxane, and tetrahydrofuran (THF). Monomer, bis, and selected dimer complex geometries were considered. Using these data, we computed the thermodynamics of the key formation and dehydrogenation reactions that would occur during hydrogen delivery and alane regeneration, from which trends in complex stability were identified. These predictions were tested by synthesizing six amine-alane complexes involving trimethylamine, triethylamine, dimethylethylamine, TEDA, quinuclidine, and hexamine and obtaining upper limits of ΔG° for their formation from metallic aluminum. Combining these computational and experimental results, we establish a criterion for complex stability relevant to hydrogen storage that can be used to assess potential ligands prior to attempting synthesis of the alane complex. On the basis of this, we conclude that only a subset of the tertiary amine complexes considered and none of the ether complexes can be successfully formed by direct reaction with aluminum and regenerated in an alane-based hydrogen storage system.

  7. Understanding the borane analogy in Al(n)H(n+4) (n = 5-19): unprecedented stability of a non-Wade-Mingos cluster Al(8)H(12) fused by two T(d)-like Al(4)H(6).

    PubMed

    Fu, Li-Juan; Jin, Lin; Shao, Chang-Bin; Ding, Yi-Hong

    2010-06-07

    Contrasting the boranes B(n)H(n+4) with rich chemistry, the alanes Al(n)H(n+4) remain largely unknown in laboratory, except for the simplest Al(2)H(6). Though recent experimental and theoretical studies have proved Al(n)H(n+2) to be the borane analogues, whether or not the borane analogy can exist for the more complicated Al(n)H(n+4) is still unclear. In this paper, we find that at the B3PW91/TZVP level, Al(n)H(n+4) each has a nido-single cluster ground structure as B(n)H(n+4) for n < 12. For n >or= 12, the fusion cluster becomes energetically more competitive than the single cluster also as B(n)H(n+4). Thus, concerning the ground structures, the alanes Al(n)H(n+4) (n = 5-19) could be considered as the borane analogues. Remarkably, Al(8)H(12) has a novel closo(4)-closo(4) cluster fused by two T(d)-like subunits Al(4)H(6), lying only 0.49 kcal/mol above the single cluster. The Born-Oppenheimer molecular dynamic simulation shows that the closo(4)-closo(4) fusion cluster intrinsically has high kinetic stability, which can be ascribed to the rigidity of the T(d)-Al(4)H(6) subunit. Since T(d)-Al(4)H(6) has been experimentally characterized in a gas phase very recently, we strongly recommend that the unprecedented non-Wade-Mingos alane Al(8)H(12) can be effectively formed via the direct dimerization between two T(d)-Al(4)H(6), with the reaction energy (-39.65 kcal/mol) very similar to that of the known dialane (2AlH(3) --> Al(2)H(6), -35.27 kcal/mol).

  8. Proton-transfer and H2-elimination reactions of trimethylamine alane: role of dihydrogen bonding and Lewis acid-base interactions.

    PubMed

    Filippov, Oleg A; Tsupreva, Victoria N; Golubinskaya, Lyudmila M; Krylova, Antonina I; Bregadze, Vladimir I; Lledos, Agusti; Epstein, Lina M; Shubina, Elena S

    2009-04-20

    Proton-transfer and H(2)-elimination reactions of aluminum hydride AlH(3)(NMe(3)) (TMAA) with XH acids were studied by means of IR and NMR spectroscopy and DFT calculations. The dihydrogen-bonded (DHB) intermediates in the interaction of the TMAA with XH acids (CH(3)OH, (i)PrOH, CF(3)CH(2)OH, adamantyl acetylene, indole, 2,3,4,5,6-pentafluoroaniline, and 2,3,5,6-tetrachloroaniline) were examined experimentally at low temperatures, and the spectroscopic characteristics, dihydrogen bond strength and structures, and the electronic and energetic characteristics of these complexes were determined by combining experimental and theoretical approaches. The possibility of two different types of DHB complexes with polydentate proton donors (typical monodentate and bidentate coordination with the formation of a symmetrical chelate structure) was shown by DFT calculations and was experimentally proven in solution. The DHB complexes are intermediates of proton-transfer and H(2)-elimination reactions. The extent of this reaction is very dependent on the acid strength and temperature. With temperature increases the elimination of H(2) was observed for OH and NH acids, yielding the reaction products with Al-O and Al-N bonds. The reaction mechanism was computationally studied. Besides the DHB pathway for proton transfer, another pathway starting from a Lewis complex was discovered. Preference for one of the pathways is related to the acid strength and the nucleophilicity of the proton donor. As a consequence of the dual Lewis acid-base nature of neutral aluminum hydride, participation of a second ROH molecule acting as a bifunctional catalyst forming a six-member cycle connecting aluminum and hydride sites notably reduces the reaction barrier. This mechanism could operate for proton transfer from weak OH acids to TMAA in the presence of an excess of proton donor.

  9. Aryl(silyl)amino group stabilized hydridosilanediols: synthesis and characterization and use for preparation of alumino(hydrido)siloxanes.

    PubMed

    Wang, Xiaoping; Li, Jiancheng; Chen, Shimin; Liu, Weiping; Ye, Qingsong; Zhu, Hongping

    2016-04-21

    Aryl(silyl)amino group stabilized hydridosilanediols RSiH(OH)2 (R = N(SiMe2Ph)-2,6-iPr2C6H3 (), N(SiMe3)-2,6-iPr2C6H3 (), and N(SiMe2Ph)-2,4,6-Me3C6H2 ()) were prepared from the controlled hydrolysis of the related RSiHCl2 () each in the presence of aniline as the HCl acceptor. Reactions of with AlMe3, AliBu3, AlH(iBu)2, and AlH3·NMe3, respectively, yielded alumino(hydrido)siloxanes [2,6-iPr2C6H3N(SiMe2Ph)Si(H)OAlMe(THF)]2 (), [2,6-iPr2C6H3N(SiMe2Ph)Si(H)OAliBu(THF)]2 (), [2,6-iPr2C6H3N(SiMe2Ph)Si(H)O2]3[Al(THF)]2 (), and [2,6-iPr2C6H3N(SiMe2Ph)Si(H)OAlH(THF)]2 (). The reaction of with AlMe3 gave [2,6-iPr2C6H3N(SiMe3)Si(H)OAlMe(THF)]2 (), a compound similar to . Compounds are characterized by NMR ((1)H, (13)C, and (29)Si) and IR spectroscopy and CHN elemental analysis, of which and are further studied by X-ray crystallography. Compounds and feature cyclic structures all with the skeleton core of Si2O4Al2 while compound exhibits a bicyclic structure having a core of Si3O6Al2. Melting point measurements indicated that are thermally stable bearing the geminal SiH and SiOH groups. Compounds and are thermally stable as well with the O atom-bridged SiH and AlR (R = Me, iBu, or H) groups.

  10. Understanding atomistic phenomenon for hydrogen storage in complex metal hydrides

    NASA Astrophysics Data System (ADS)

    Chopra, Irinder Singh

    The storage of hydrogen into metals in the form of complex metal hydrides is one of the most promising methods. However, the incorporation and release of hydrogen requires very high temperatures. The discovery that the addition of Ti compounds lowers NaAlH4 decomposition barriers closer to ambient conditions, has re-ignited the field, and it is believed that surface processes are responsible for H2 dissociation and mass transport required to form the hydrogenated materials. Such surface reactions mechanisms are however difficult to study with typical spectroscopic and imaging surface science tools. Alanes lack contrast under electron microscopes and can modify the Scanning Tunneling Microscopy (STM) tips. Infrared spectroscopy would be a sensitive probe to investigate the adsorption of hydrogen providing, but has so far failed to detect chemisorbed hydrogen on Ti-doped Al surfaces due to the weak Al-H dynamic dipole moment. Thus despite extensive investigations, the fundamental mechanisms of the role of Ti and alane formation have remained elusive. In this study combining surface infrared (IR) spectroscopy and density functional theory (DFT), we provide atomistic details about the role of Ti as a catalyst for hydrogen uptake and alane formation and evolution on single crystal Al(111) and Al(100) surfaces. We are able to detect H indirectly by using CO as a probe molecule of the weak Al-H species. We demonstrate that aluminum doped with very small amounts of titanium (in a specific configuration) can activate molecular hydrogen at temperatures as low as 90K. Once dissociated, hydrogen spills over from these catalytic sites on to the Al surface and protects the surface from further reactions. We also show that, on Ti-doped Al surfaces, the diffusion dynamics are severely altered by Ti doping (Atomic hydrogen and AlH3 are trapped at the Ti sites) as indicated by a marked decrease of higher alane concentrations, which is deleterious for hydrogen storage for which mass transport is required. These results provide an understanding of the reaction mechanisms for hydrogen storage in the alanates (NaAlH4) that can help in identifying and realizing other complex metal hydrides for an effective hydrogen based economy.

  11. Surface investigations of the atomic layer growth mechanism in aluminum nitride thin film deposition using dimethylethylamine alane and ammonia

    NASA Astrophysics Data System (ADS)

    Kuo, Jason Se-Yung

    Aluminum Nitride (AlN), a wide-bandgap semiconductor, has been shown to be an extremely versatile material in semiconductor applications. Our previous efforts in formulating a Metalorganic Chemical Vapor Deposition (MOCVD) processing strategy to deposit AN using Dimethylethylamine Alane (DMEAA; AlH3:N(CH3)2CH2CH3) and ammonia resulted in high quality film growth at low temperatures (˜600 K). Understanding the surface reactions involved is a key step in successfully optimizing a MOCVD process. In this research, we investigated the surface interactions between DMEAA and ammonia leading to the Atomic Layer Growth (ALG) mode on a Si(100) surface using a combination of surface analysis techniques, including Secondary-Ion Mass Spectrometry (SIMS), Temperature-Programmed SIMS (TPSIMS), X-ray Photoelectron Spectroscopy (XPS), and Temperature-Programmed Desorption (TPD). The exposure of Si(100) to DMEAA at 310 K resulted in self-limiting adsorption of molecular DMEAA and Dimethylethylamine (DMEA). Based on the stoichiometric information from XPS, the molecularly adsorbed DMEA most likely originated from the exposure of a mixed DMEAA-DMEA gas phase rather than a dissociative adsorption process. The DMEAA molecule is susceptible to thermal decomposition, as the aminealane adduct configuration was no longer observed above 490 K. This can impose an upper temperature limit in developing a processing strategy. The chemical interaction between ammonia and DMEAA resulted in a displacement of DMEA by ammonia. A new surface intermediate (AlHND2) was detected with both SIMS and XPS. This displacement mechanism was rationalized using Hard-Soft-Acid-Base (HSAB) theory. We were able to observe, in a step-by-step fashion, the atomic layer growth process by monitoring the C:N ratios using XPS. The resulting AlN film contained substantial hydrogen but the hydrogen content may be removed thermally. Atomic layer growth mechanism provides an effective means to grow high quality thin films by specific chemical interactions. Employing this approach, we have shown that the carbon contamination from the organic ligands may be controlled stringently.

  12. Neutral and cationic aluminium complexes of a sterically demanding N-imidoylamidine ligand.

    PubMed

    Masuda, Jason D; Stephan, Douglas W

    2006-05-07

    The N-imidoylamidine ligand i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2 2 was prepared. Direct reactions with AlI3 or AlMe3 afforded [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlI2][AlI4] 3 and [i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlMe2][AlMe4].AlMe3, 4 respectively. Thermolysis of 4 gave (i-Pr2C6H3NC(=CH2)(NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlMe2 6. Subsequent reaction with B(C6F5)3 gave the zwitterionic species [(i-Pr2C6H3)N(C(=CH2)NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlMe(mu-MeB(C6F5)3)] 7. In a related reactions of 2, [Ph3C][B(C6F5)4] and AlMe3, AlH3.NEtMe2 or AlD3.NMe3, the complexes [(i-Pr2C6H3N(C(Me)NC6H3i-Pr2)2)AlR2][B(C6F5)4] (R = Me 5, H 8, D 9) and [(i-Pr2C6H3)N(C(=CH2)NC6H3i-Pr2)(C(Me)NC6H3i-Pr2)AlH][B(C6F5)4] 10 are formed. Single-crystal X-ray data for 2, 3, 5 and 10 are reported.

  13. Structural Characterization of Metal Hydrides for Energy Applications

    NASA Astrophysics Data System (ADS)

    George, Lyci

    Hydrogen can be an unlimited source of clean energy for future because of its very high energy density compared to the conventional fuels like gasoline. An efficient and safer way of storing hydrogen is in metals and alloys as hydrides. Light metal hydrides, alanates and borohydrides have very good hydrogen storage capacity, but high operation temperatures hinder their application. Improvement of thermodynamic properties of these hydrides is important for their commercial use as a source of energy. Application of pressure on materials can have influence on their properties favoring hydrogen storage. Hydrogen desorption in many complex hydrides occurs above the transition temperature. Therefore, it is important to study the physical properties of the hydride compounds at ambient and high pressure and/or high temperature conditions, which can assist in the design of suitable storage materials with desired thermodynamic properties. The high pressure-temperature phase diagram, thermal expansion and compressibility have only been evaluated for a limited number of hydrides so far. This situation serves as a main motivation for studying such properties of a number of technologically important hydrides. Focus of this dissertation was on X-ray diffraction and Raman spectroscopy studies of Mg2FeH6, Ca(BH4) 2, Mg(BH4)2, NaBH4, NaAlH4, LiAlH4, LiNH2BH3 and mixture of MgH 2 with AlH3 or Si, at different conditions of pressure and temperature, to obtain their bulk modulus and thermal expansion coefficient. These data are potential source of information regarding inter-atomic forces and also serve as a basis for developing theoretical models. Some high pressure phases were identified for the complex hydrides in this study which may have better hydrogen storage properties than the ambient phase. The results showed that the highly compressible B-H or Al-H bonds and the associated bond disordering under pressure is responsible for phase transitions observed in brorohydrides or alanates. Complex hydrides exhibited very high compressibility suggesting possibility to destabilize them with pressure. With high capacity and favorable thermodynamics, complex hydrides are suitable for reversible storage. Further studies are required to overcome the kinetic barriers in complex hydrides by catalytic addition. A comparative study of the hydride properties with that of the constituting metal, and their inter relationships were carried out with many interesting features.

  14. Crack Propagation During Sustained-Load Cracking of Al-Zn-Mg-Cu Aluminum Alloys Exposed to Moist Air or Distilled Water

    NASA Astrophysics Data System (ADS)

    Holroyd, N. J. Henry; Scamans, G. M.

    2011-12-01

    Intergranular sustained-load cracking of Al-Zn-Mg-Cu (AA7xxx series) aluminum alloys exposed to moist air or distilled water at temperatures in the range 283 K to 353 K (10 °C to 80 °C) has been reviewed in detail, paying particular attention to local processes occurring in the crack-tip region during crack propagation. Distinct crack-arrest markings formed on intergranular fracture faces generated under fixed-displacement loading conditions are not generated under monotonic rising-load conditions, but can form under cyclic-loading conditions if loading frequencies are sufficiently low. The observed crack-arrest markings are insensitive to applied stress intensity factor, alloy copper content and temper, but are temperature sensitive, increasing from ~150 nm at room temperature to ~400 nm at 313 K (40 °C). A re-evaluation of published data reveals the apparent activation energy, E a for crack propagation in Al-Zn-Mg(-Cu) alloys is consistently ~35 kJ/mol for temperatures above ~313 K (40 °C), independent of copper content or the applied stress intensity factor, unless the alloy contains a significant volume fraction of S-phase, Al2CuMg where E a is ~80 kJ/mol. For temperatures below ~313 K (40 °C) E a is independent of copper content for stress intensity factors below ~14 MNm-3/2, with a value ~80 kJ/mol but is sensitive to copper content for stress intensity factors above ~14 MNm-3/2, with E a , ranging from ~35 kJ/mol for copper-free alloys to ~80 kJ/mol for alloys containing 1.5 pct Cu. The apparent activation energy for intergranular sustained-load crack initiation is consistently ~110 kJ/mol for both notched and un-notched samples. Mechanistic implications are discussed and processes controlling crack growth, as a function of temperature, alloy copper content, and loading conditions are proposed that are consistent with the calculated apparent activation energies and known characteristics of intergranular sustained-load cracking. It is suggested, depending on the circumstances, that intergranular crack propagation in humid air and distilled water can be enhanced by the generation of aluminum hydride, AlH3, ahead of a propagating crack and/or its decomposition after formation within the confines of the nanoscale volumes available after increments of crack growth, defined by the crack arrest markings on intergranular fracture surfaces.

  15. Computational study of pristine and titanium-doped sodium alanates for hydrogen storage applications

    NASA Astrophysics Data System (ADS)

    Dathar, Gopi Krishna Phani

    The emphasis of this research is to study and elucidate the underlying mechanisms of reversible hydrogen storage in pristine and Ti-doped sodium aluminum hydrides using molecular modeling techniques. An early breakthrough in using complex metal hydrides as hydrogen storage materials is from the research on sodium alanates by Bogdanovic et al., in 1997 reporting reversible hydrogen storage is possible at moderate temperatures and pressures in transition metal doped sodium alanates. Anton reported titanium salts as the best catalysts compared to all other transition metal salts from his further research on transition metal doped sodium alanates. However, a few questions remained unanswered regarding the role of Ti in reversible hydrogen storage of sodium alanates with improved thermodynamics and kinetics of hydrogen desorption. The first question is about the position of transition metal dopants in the sodium aluminum hydride lattice. The position is investigated by identifying the possible sites for titanium dopants in NaAlH4 lattice and studying the structure and dynamics of possible compounds resulting from titanium doping in sodium alanates. The second question is the role of titanium dopants in improved thermodynamics of hydrogen desorption in Ti-doped NaAlH4. Though it is accepted in the literature that formation of TiAl alloys (Ti-Al and TiAl3) is favorable, reaction pathways are not clearly established. Furthermore, the source of aluminum for Ti-Al alloy formation is not clearly understood. The third question in this area is the role of titanium dopants in improved kinetics of hydrogen absorption and desorption in Ti-doped sodium alanates. This study is directed towards addressing the three longstanding questions in this area. Thermodynamic and kinetic pathways for hydrogen desorption in pristine NaAlH4 and formation of Ti-Al alloys in Ti-doped NaAlH 4, are elucidated to understand the underlying mechanisms of hydrogen desorption. Density functional theory formalism as implemented in CASTEP (Cambridge Serial Total Energy Package) is used to study the structure and energetics of pristine and Ti-doped sodium alanates. From investigations of various models of sodium alanates with Ti dopants, it is shown that the difference between the energy required for Ti→SNa (Ti-substituted Na at the lattice site on the surface) and Ti→TI (Ti placed on top of the surface interstitial SI site) is 0.003 eV atom-1, and is minimal compared to other models. Since less energy is required for Ti→S Na and Ti→TI, these two sites (SNa and T I) would be preferred by the Ti dopants. In Ti→SNa model, Ti is coordinated to two aluminum and seven hydrogen atoms resulting in the possible formation of a TiAl2H7 complex. At elevated temperatures (423 and 448 K), the number of aluminum atoms coordinating with titanium in the complex increase from two (at distances in the 2.6-2.7 A range) to five (at distances in the 2.6-2.7 A range). Besides the formation of a Ti-Al-H complex, Al-Al association (with a 2.97 A bond length) is also seen from the DFT-MD results. In the case of Ti→TI, Ti is coordinated to two aluminum and two hydrogen atoms resulting in the possible formation of a TiAl2H2 complex. TiAl2 H2 complex becomes TiAl3H6 and TiAl 3H7 at elevated temperatures of 423 and 448 K, respectively. The investigation of thermodynamics pathways in Ti-doped sodium alanates illustrates a three step reaction pathway to the formation of TiAl3 (Ti and AlH3 after the first reaction, TiAl after the second and finally TiAl3). This investigation also suggests aluminum in its +3 oxidation state present in aluminum hydride species is responsible in the formation of Ti-Al alloys. From kinetics studies, the proposed mechanism is related to transition from AlH4- to AlH6 3-. The rate limiting step is determined to be associated with hydrogen evolution from association of AlH3 species nucleating aluminum phase. This step is 15 kJ/mol higher than the nearest highest barrier in the reaction path related to transition from AlH52- to AlH63-. From the DFT-MD simulations, it is observed that the titanium dopants are present on the surface during the entire simulation time and exhibit the role in catalytic splitting of hydrogen from surrounding AlH4 groups. Besides the catalytic role, Ti dopants also form bonds with Al, and we also see that the AlH4 groups on the surface and that are present in the sub-surface layers are drawn towards the Ti dopants. This association of Al around titanium indicates the initiation of Al nucleation site facilitated by Ti dopants residing on the surface.

  16. Metal hydride and pyrophoric fuel additives for dicyclopentadiene based hybrid propellants

    NASA Astrophysics Data System (ADS)

    Shark, Steven C.

    The purpose of this study is to investigate the use of reactive energetic fuel additives that have the potential to increase the combustion performance of hybrid rocket propellants in terms of solid fuel regression rate and combustion efficiency. Additives that can augment the combustion flame zone in a hybrid rocket motor by means of increased energy feedback to the fuel grain surface are of great interest. Metal hydrides have large volumetric hydrogen densities, which gives these materials high performance potential as fuel additives in terms of specifc impulse. The excess hydrogen and corresponding base metal may also cause an increase in the hybrid rocket solid fuel regression rate. Pyrophoric additives also have potential to increase the solid fuel regression rate by reacting more readily near the burning fuel surface providing rapid energy feedback. An experimental performance evaluation of metal hydride fuel additives for hybrid rocket motor propulsion systems is examined in this study. Hypergolic ignition droplet tests and an accelerated aging study revealed the protection capabilities of Dicyclopentadiene (DCPD) as a fuel binder, and the ability for unaided ignition. Static hybrid rocket motor experiments were conducted using DCPD as the fuel. Sodium borohydride (NabH4) and aluminum hydride (AlH3) were examined as fuel additives. Ninety percent rocket grade hydrogen peroxide (RGHP) was used as the oxidizer. In this study, the sensitivity of solid fuel regression rate and characteristic velocity (C*) efficiency to total fuel grain port mass flux and particle loading is examined. These results were compared to HTPB combustion performance as a baseline. Chamber pressure histories revealed steady motor operation in most tests, with reduced ignition delays when using NabH4 as a fuel additive. The addition of NabH4 and AlH3 produced up to a 47% and 85% increase in regression rate over neat DCPD, respectively. For all test conditions examined C* efficiency ranges between 80% and 90%. The regression rate and C* efficiency mass flux dependence indicate a shift towards a more diffusion controlled system with metal hydride particle addition. Although these types of energetic particles have potential as high performing fuel additives, they can be in low supply and expensive. An opposed flow burner was investigated as a means to screen and characterize hybrid rocket fuels prior to full scale rocket motor testing. Although this type of configuration has been investigated in the past, no comparison has been made to hybrid rocket motor operation in terms of mass flux. Polymeric fuels and low melt temperature fuels with and without additives were investigated via an opposed flow burner. The effects of laminar and turbulent flow regimes on the convective heat transfer in the opposed flow system was depicted in the regression rate trends of these fuels. Regression rate trends similar to hybrid rocket motor operation were depicted, including the entrainment mechanism for paran fuel. However, there was a shift in overall magnitude of these results. A decrease in regression rate occurred for HTPB loaded with passivated nano-aluminum, due to low resonance time in the reaction zone. Previous results have shown that pyrophoric additives can cause an increase in regression rate in the opposed flow burner configuration. It is proposed that the opposed burner is useful as a screening and characterization tool for some propellant combinations. Gaseous oxygen (GOX) was investigated as an oxidizer for similar fuels evaluated with RGHP. Specifically, combustion performance sensitivity to mass flux and MH particle size was investigated. Similar results to the RGHP experiments were observed for the regression rate tends of HTPB, DPCD, and NabH 4 addition. Kinetically limited regression rate dependence on mass flux was observed at the higher mass flux levels. No major increase in C* efficiency was observed for MH addition. The C* efficiency varied with equivalence ratio by approximately 10 percentage points, which was not observed in the RGHP experiments. A 10 percentage point decrease in C* efficiency was observed with increasing mass flux in the system. This was most likely due to poorly mixed fuel and oxidizer in center of the combustion chamber at the higher mass flux levels. Detailed measurements of the hybrid rocket combustion zone is useful for understanding the mechanisms governing performance, but can be difficult to obtain. Traditional slab burner configurations have proven useful but are operationally limited in pressure and mass flux ranges. A new optical cylindrical combustor (OCC) design is presented that allows surface and flame zone imaging and tracking during hybrid rocket motor operation at appreciable mass flux and pressure levels, > 100 kg/s/m2 and > 0.69 MPa. The flame height and regression rate sensitivity to mass flux and chamber pressure was examined for the same fuels examined in the GOX hybrid rocket motor, with the addition of DCPD fuel loaded with Al and unpassivated mechanically activated Al-PTFE. The regression rate trends were on the same order of magnitude of traditional hybrid rocket motor results. A flame height decrease was observed for increased mass flux. The flame height increased with NabH 4 addition, which is most likely a function of increased blowing at the surface. There was no appreciable flame height sensitivity to NabH4 particle size. There was no relative change in flame height or regression rate between the Al and AL-PTFE addition. The OCC allowed visualization of the hybrid rocket fuel flame zone at mass flux and pressure levels that are not known to be report for traditional slab burner configurations in literature. The OCC proved to be a new useful tool for investigated hybrid rocket propellant combustion characteristics.

  17. Aqueous speciation studies of europium(III) phosphotungstate.

    PubMed

    Zhang, Cheng; Howell, Robertha C; Scotland, Kymora B; Perez, Frances G; Todaro, Louis; Francesconi, Lynn C

    2004-11-29

    The incorporation of lanthanide ions into polyoxometalates may be a unique approach to generate new luminescent, magnetic, and catalytic functional materials. To realize these new applications of lanthanide polyoxometalates, it is imperative to understand the solution speciation chemistry and its impact on solid-state materials. In this study we find that the aqueous speciation of europium(III) and the trivacant polyoxometalate, PW9O34 9-, is a function of pH, countercation, and stoichiometry. For example, at low pH, the lacunary (PW11O39)7- predominates and the 1:1 Eu(PW11O39)4-, 2, forms. As the pH is increased, the 1:2 complex, Eu(PW11O39)2 11- species, 3, and (NH4)22[(Eu2PW10O38)4(W3O8(H2O)2(OH)4].44H2O, a Eu8 hydroxo/oxo cluster, 1, form. Countercations modulate this effect; large countercations, such as K+ and Cs+, promote the formation of species 3 and 1. Addition of Al(III) as a counterion results in low pH and formation of [Eu(H2O)3(alpha-2-P2W17O61)]2, 4, with Al(III) counterions bound to terminal W-O bonds. The four species observed in these speciation studies have been isolated, crystallized, and characterized by X-ray crystallography, solution multinuclear NMR spectroscopy, and other appropriate tech-niques. These species are 1, (NH4)22[(Eu2PW10O38)4(W3O8(H2O)2(OH)4].44H2O (P; a=20.2000(0), b=22.6951(6), c=25.3200(7) A; alpha=65.6760(10), beta=88.5240(10), gamma=86.0369(10) degrees; V=10550.0(5) A3; Z=2), 2, Al(H3O)[Eu(H2O)2PW11O34].20H2O (P, a=11.4280(23), b=11.5930(23), c=19.754(4) A; alpha=103.66(3), beta=95.29(3), gamma=102.31(3) degrees; V =2456.4(9) A3; Z=2), 3, Cs11Eu(PW11O34)2.28H2O (P; a=12.8663(14), b=19.8235(22), c=21.7060(23) A; alpha=114.57(0), beta=91.86(0), gamma=102.91(0) degrees ; V=4858.3(9) A3; Z=2), 4, Al2(H3O)8[Eu(H2O)3(alpha-2-P2W17O61)]2.29H2O (P; a=12.649(6), b=16.230(8), c=21.518(9) A; alpha=111.223(16), beta=94.182(18), gamma=107.581(17) degrees ; V=3842(3) A3; Z=1).

  18. Boron and aluminum complexes of sterically demanding phosphinimines and phosphinimides.

    PubMed

    Courtenay, Silke; Walsh, Denise; Hawkeswood, Sarah; Wei, Pingrong; Das, Anjan Kumar; Stephan, Douglas W

    2007-04-30

    Reactions of sterically demanding phosphinimines R3PNH [R=i-Pr (1), t-Bu (2)] were examined. Reactions with B(C6F5)3 formed the adducts (R3PNH)B(C6F5)3 [R=i-Pr (3), t-Bu (4)] in high yield. On the other hand, 2 reacts with HB(OBu)2, evolving H2 to give t-Bu3PNB(OBu)2 (5). The reaction of 2 equiv of 2 with BH3.SMe2 affords the species (t-Bu3PN)2BH (6). In contrast, the reaction of n-Bu(t-Bu)2PNH with BH3.SMe2 results in the formation of the robust adduct n-Bu(t-Bu)2PNH.BH3 (8). An alternative route to borane-phosphinimide complexes involves Me3SiCl elimination, as exemplified by the reaction of BCl2Ph with n-Bu3PNSiMe3, which gives the product n-Bu3PNBCl(Ph) (9). The corresponding reactions of the parent phosphinimines 1 and 2 with AlH3.NMe2Et give the dimers [(mu-i-Pr3PN)AlH2]2 (10) and [(mu-t-Bu3PN)AlH2]2 (11). Species 11 reacts further with Me3SiO3SCF3 to provide [(mu-t-Bu3PN)AlH(OSO2CF3)]2 (12). The reaction of the lithium salt [t-Bu3PNLi]4 (13) with BCl3 proceeds smoothly to give t-Bu3PNBCl2 (14), which is readily alkylated to give t-Bu3PNBMe2 (15). Subsequent reaction of 15 with B(C6F5)3 results in methyl abstraction and the formation of [(mu-t-Bu3PN)BMe]2[MeB(C6F5)3]2 (16). The reaction of 13 in a 2:1 ratio with BCl3 gives the salt [(t-Bu3PN)2B]Cl (17). This species can be methylated to give (t-Bu3PN)2BMe (18), which undergoes subsequent reaction with [Ph3C][X] (X=[B(C6F5)4], [PF6]) to form the related salts [(t-Bu3PN)2B][B(C6F5)4] (19) and [(t-Bu3PN)2B][PF6] (20), respectively. Analogous reactions with [Ph3C][BF4] afforded [t-Bu3PNBF2]2 (21). Compounds 3, 4, 6, 8, 11, 12, 17, 19, and 21 were characterized by X-ray crystallography.

  19. Search for nitrates on Mars by the Sample Analysis at Mars (SAM) Instrument

    NASA Astrophysics Data System (ADS)

    Navarro-Gonzalez, Rafael

    One of the main goals of the Mars Science Laboratory is to determine whether the planet ever had environmental conditions capable of supporting microbial life. Nitrogen is a fundamental element for life, and is present in structural (e.g., proteins), catalytic (e.g., enzymes and ribozymes), energy transfer (e.g., ATP) and information storage (RNA and DNA) bio-molecules. Planetary models suggest that nitrogen was abundant in the early Martian atmosphere as dinitrogen (N _{2}). However, a fraction of N _{2} has been lost to space by sputtering and photochemical processes [1, 2], impact erosion [3], and chemical oxidation to nitrates [4, 5]. Nitrates produced early in Mars’ history by photochemistry may later decompose back into N _{2} by the current impact flux [6]. It is estimated that the Martian surface could contain soil nitrates at levels of 0.3 wt.% N, if mixed homogenously [6], or a layer of pure NaNO _{3} of about 3 m thickness [5] distributed globally. Nitrates are a fundamental source for nitrogen for terrestrial microorganisms. Therefore, the detection of soil nitrates is important to assess habitability in the Martian environment. The only previous attempt to search for soil nitrates was by TEGA and the MECA WCL on the Phoenix mission but no evolved N-containing species were detected [7]. Nitrates have been tentatively identified in two Martian meteorites: Nakhla [8] and EETA79001 [9]. SAM is capable of detecting nitrates by their thermal decomposition into nitric oxide, NO. SAM analyzed samples from Rocknest soil and two drill holes located at John Klein (JK) and Cumberland (CB) mudstones in the Sheepbed member of the Yellowknife Bay formation in Gale Crater. There appear to be several peaks associated with the release of m/z 30 in the temperature range from 150(°) °C to 600(°) °C. M/z 30 can be attributed to nitric oxide; however, other possible chemical interferences may be present, such as ethane (C _{2}H _{6}), formaldehyde (HCHO), diazene (N _{2}H _{2}), aluminum trihydride (AlH _{3}), and silylene (SiH _{2}), and they are assessed. The origin of nitric oxide is discussed and its thermal evolution is compared with analog studies of mixtures of nitrates and perchlorates [10]. [1] Luhmann, J.G., Johnson E. And Zhang, M.H.G.: 1992, Evolutionary impact of sputtering of the Martian atmosphere by O (+) pickup ions. Geophys. Res. Lett. 19, 2151-2154. [2] Jakosky, B.M. Pepin, R.O., Johnsom, R.E. and Fox, J.L: 1994, Mars atmospheric loss and isotopic fractionation by solar-wind-induced sputtering and photochemical escape. Icarus 111, 271-288. [3] Melosh, H.J. and Vickery, A.M.: 1989, Impact erosion of the primordial atmosphere of Mars. Nature 338, 487-489. [4] Mancinelli, R.L. and McKay, C.P. :1988, The evolution of nitrogen cycling. Origins Life 18, 311-325. [5] Manning, C.V., McKay, C.P., and Zahnle, K.J.: 2008, The nitrogen cycle on Mars: Impact decomposition of near-surface nitrates as a source for a nitrogen steady state. Icarus 197, 60-64. [6] Smith, M.L., Claire, M.W., Catling, D.C., and Zahnle, K.J.: 2014, The formation of sulfate, nitrate and perchlorate salts in the martian atmosphere. Icarus 231, 51-64. [7] Hecht, M. H., Kounaves, S.P., Quinn, R.C., West, S.J., Young, S.M.M., Ming, D.W.,Catling, D.C., Clark, B.C., Boynton, W.V.,Hoffman, J., DeFlores, L.P., Gospodinova, K., Kapit, J., and Smith,P.H.: 2009, Detection of Perchlorate and the Soluble Chemistry of Martian Soil at the Phoenix Lander Site. Science, 325, 64-67. [8] Grady, M.M., Wright, I. P., and Pillinger C. T.: 1995, Search for nitrates in Martian meteorite. J. Geophys. Res. 100, 5449. [9] Kounaves, S.P., Carrier, B.L., O’Neil, G.D., Stroble, S.T., Claire, M.W.: 2013, Evidence of martian perchlorate, chlorate, and nitrate in Mars meteorite EETA79001: implications for oxidants and organics, Icarus 229, 206. [10] Support from the following grants is acknowledged: IN106013 and CONACYT 98466.

  20. Complex Hydride Compounds with Enhanced Hydrogen Storage Capacity

    SciTech Connect

    Mosher, Daniel A.; Opalka, Susanne M.; Tang, Xia; Laube, Bruce L.; Brown, Ronald J.; Vanderspurt, Thomas H.; Arsenault, Sarah; Wu, Robert; Strickler, Jamie; Anton, Donald L.; Zidan, Ragaiy; Berseth, Polly

    2008-02-18

    The United Technologies Research Center (UTRC), in collaboration with major partners Albemarle Corporation (Albemarle) and the Savannah River National Laboratory (SRNL), conducted research to discover new hydride materials for the storage of hydrogen having on-board reversibility and a target gravimetric capacity of ≥ 7.5 weight percent (wt %). When integrated into a system with a reasonable efficiency of 60% (mass of hydride / total mass), this target material would produce a system gravimetric capacity of ≥ 4.5 wt %, consistent with the DOE 2007 target. The approach established for the project combined first principles modeling (FPM - UTRC) with multiple synthesis methods: Solid State Processing (SSP - UTRC), Solution Based Processing (SBP - Albemarle) and Molten State Processing (MSP - SRNL). In the search for novel compounds, each of these methods has advantages and disadvantages; by combining them, the potential for success was increased. During the project, UTRC refined its FPM framework which includes ground state (0 Kelvin) structural determinations, elevated temperature thermodynamic predictions and thermodynamic / phase diagram calculations. This modeling was used both to precede synthesis in a virtual search for new compounds and after initial synthesis to examine reaction details and options for modifications including co-reactant additions. The SSP synthesis method involved high energy ball milling which was simple, efficient for small batches and has proven effective for other storage material compositions. The SBP method produced very homogeneous chemical reactions, some of which cannot be performed via solid state routes, and would be the preferred approach for large scale production. The MSP technique is similar to the SSP method, but involves higher temperature and hydrogen pressure conditions to achieve greater species mobility. During the initial phases of the project, the focus was on higher order alanate complexes in the phase space between alkaline metal hydrides (AmH), Alkaline earth metal hydrides (AeH2), alane (AlH3), transition metal (Tm) hydrides (TmHz, where z=1-3) and molecular hydrogen (H2). The effort started first with variations of known alanates and subsequently extended the search to unknown compounds. In this stage, the FPM techniques were developed and validated on known alanate materials such as NaAlH4 and Na2LiAlH6. The coupled predictive methodologies were used to survey over 200 proposed phases in six quaternary spaces, formed from various combinations of Na, Li Mg and/or Ti with Al and H. A wide range of alanate compounds was examined using SSP having additions of Ti, Cr, Co, Ni and Fe. A number of compositions and reaction paths were identified having H weight fractions up to 5.6 wt %, but none meeting the 7.5 wt%H reversible goal. Similarly, MSP of alanates produced a number of interesting compounds and general conclusions regarding reaction behavior of mixtures during processing, but no alanate based candidates meeting the 7.5 wt% goal. A novel alanate, LiMg(AlH4)3, was synthesized using SBP that demonstrated a 7.0 wt% capacity with a desorption temperature of 150°C. The deuteride form was synthesized and characterized by the Institute for Energy (IFE) in Norway to determine its crystalline structure for related FPM studies. However, the reaction exhibited exothermicity and therefore was not reversible under acceptable hydrogen gas pressures for on-board recharging. After the extensive studies of alanates, the material class of emphasis was shifted to borohydrides. Through SBP, several ligand-stabilized Mg(BH4)2 complexes were synthesized. The Mg(BH4)2*2NH3 complex was found to change behavior with slightly different synthesis conditions and/or aging. One of the two mechanisms was an amine-borane (NH3BH3) like dissociation reaction which released up to 16 wt %H and more conservatively 9 wt%H when not including H2 released from the NH3. From FPM, the stability of the Mg(BH4)2*2NH3 compound was found to increase with the inclusion of NH3 groups in the inner-Mg coordination sphere, which in turn correlated with lowering the dimensionality of the Mg(BH4)2 network. Development of various Ak Tm-B-H compounds using SSP produced up to 12 wt% of H2 desorbed at temperatures of 400°C. However, the most active material can only be partially recharged to 2 wt% H2 at 220-300°C and 195 bar H2 pressure due to stable product formation. While gravimetric & volumetric targets are feasible, reversibility remains a persistent challenge.

  1. The development of reactive fuel grains for pyrophoric relight of in-space hybrid rocket thrusters

    NASA Astrophysics Data System (ADS)

    Steiner, Matthew Wellington

    This study presents and investigates a novel hybrid fuel grain that reacts pyrophorically with gaseous oxidizer to achieve restart of a hybrid rocket motor propulsion system while reducing cost and handling concerns. This reactive fuel grain (RFG) relies on the pyrophoric nature of finely divided metal particles dispersed in a solid dicyclopentadiene (DCPD) binder, which has been shown to encapsulate air-sensitive additives until they are exposed to combustion gases. An RFG is thus effectively inert in open air in the absence of an ignition source, though the particles encapsulated within remain pyrophoric. In practice, this means that an RFG that is ignited in the vacuum of space and then extinguished will expose unoxidized pyrophoric particles, which can be used to generate sufficient heat to relight the propellant when oxidizer is flowed. The experiments outlined in this work aim to develop a suitable pyrophoric material for use in an RFG, demonstrate pyrophoric relight, and characterize performance under conditions relevant to a hybrid rocket thruster. Magnesium, lithium, calcium, and an alloy of titanium, chromium, and manganese (TiCrMn) were investigated to determine suitability of pure metals as RFG additives. Additionally, aluminum hydride (AlH3), lithium aluminum hydride (LiAlH4), lithium borohydride (LiBH4), and magnesium hydride (MgH2) were investigated to determine suitability of metals hydrides as RFG additives or as precursors for pure-metal RFG additives. Pyrophoric metals have been previously investigated as additives for increasing the regression rate of hybrid fuels, but to the author's knowledge, these materials have not been specifically investigated for their ability to ignite a propellant pyrophorically. Commercial research-grade metals were obtained as coarse powders, then ball-milled to attempt to reduce particle size below a critical diameter needed for pyrophoricity. Magnesium hydride was ball-milled and then cycled in a hydride cycling apparatus to attempt to fracture the particles through hydrogen sorption and thermal stresses. These powders were then tested for pyrophoricity with atmospheric and pure concentrations of oxygen. The TiCrMn powder was chosen as the material for evaluation of propellant performance, and was mixed with DCPD in various weight ratios to determine the required additive loading needed for pyrophoricity of the bulk propellant. Weight percentages of 10, 20, 30, and 50 wt.% TiCrMn were used to evaluate relight capability and propellant performance, and weight loadings of 50, 70, and 90 wt.% TiCrMn were used to evaluate approximate maximum loading possible without rendering the propellant structurally unsound. Propellant tests were conducted in an opposed flow burner apparatus for sub-scale regression rate and relight experiments, and an optically accessible cylindrical combustion chamber (OCC) that allows high speed cameras to record the regressing propellant surface during combustion. Gaseous oxygen (GOX) was used as an oxidizer for all tests due to its ready availability and common use as a hybrid rocket oxidizer. Opposed flow burner experiments are an inexpensive means of rapidly testing various propellant formulations at different conditions, whereas OCC tests are useful for obtaining realistic data on how an RFG would likely operate as part of a propulsion system. Relight in the opposed flow burner was attempted by cycling oxygen and nitrogen flows with carefully timed solenoid valves to initiate and extinguish combustion, and to control the slow diffusion of oxygen to the surface of the propellant, which would render the TiCrMn non-pyrophoric. The opposed flow burner experiments did not conclusively demonstrate the pyrophoric relight capability of the RFG propellant due in part to the persistence of hot spots between oxygen and purge nitrogen cycles, as determined by high-speed imaging in the near infrared range. An opposed flow burner apparatus was then constructed within a vacuum chamber assembly thus preventing atmospheric oxygen from diffusing to the propellant surface, but these tests did not demonstrate pyrophoric relight. Future work is proposed to evaluate the effect of pyrophoric particle size in order to determine the role ignition delay of each particle has in the relight capability of RFGs. OCC experiments were conducted at a low and high GOX mass flux of approximately 150 and 300 kg/s/m2, respectively, at a nominal chamber pressure of 150 psia. Four strand compositions were used: pure DCPD, 30 wt.% pyrophoric TiCrMn powder with average particle diameters of approximately 1-10 microns, 30 wt.% oxidized TiCrMn powder with average particle diameters of approximately 1-10 microns, and 30 wt.% TiCrMn powder with average particle diameters of approximately 1-4 mm. Regression rate was measure by weight loss, average web thickness change at three axial locations on the strand, and through time-resolved tracking of the regressing propellant surface via high speed video. While visual observations suggest that the addition of TiCrMn significantly increases regression rate, initial data do not show a significant trend. Additionally, it is observed that the oxidized TiCrMn strands regress at the same rate as those loaded with pyrophoric TiCrMn, suggesting that erosive burning and heat addition of the added metal may be the cause of the observed increase in regression rate. The data are too sparse to make conclusions about the effect of particle size on regression rate, so further tests are recommended to develop a significant data set for the effect of pyrophoricity and particle size on regression rate. The test article was damaged at the end of the regression rate experimental campaign, which precluded the collection of relight data that was planned for strands loaded with 50 wt.% TiCrMn particles with an average diameter of approximately 1-4 mm. Though further tests are needed to demonstrate pyrophoric relight of an RFG, the current work establishes a baseline for RFG performance and suggests that pyrophoric relight is possible by tailoring the particle size of the pyrophoric metal additive to control heat release and ignition delay.