| 1. |
- Alcantara, K. Suarez, et al.
(författare)
-
3CaH(2)+4MgB(2) + CaF2 Reactive Hydride Composite as a Potential Hydrogen Storage Material: Hydrogenation and Dehydrogenation Pathway
- 2012
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 116:12, s. 7207-7212
-
Tidskriftsartikel (refereegranskat)abstract
- A reactive hydride composite (RHC) with initial composition 3CaH(2) + 4MgB(2) + CaF2 was studied by in situ synchrotron radiation powder X-ray diffraction (SR-PXD) and X-ray absorption near edge structure (XANES) at the B K-edge and at the Ca K-edge. The hydrogenation reaction proceeds by an unknown intermediate. No evidence of intermediates was observed during the dehydrogenation reaction. B and Ca K-edge XANES results hint to a closed interaction of CaF2 and Ca(BH4)(2). The main function of CaF2 in the 3CaH(2) + 4MgB(2) + CaF2 RHC is as a dopant for the hydrogenation and dehydrogenation reactions.
|
|
| 2. |
- Arnbjerg, Lene M., et al.
(författare)
-
Structure and Dynamics for LiBH4-LiCl Solid Solutions
- 2009
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 21:24, s. 5772-5782
-
Tidskriftsartikel (refereegranskat)abstract
- A Surprisingly high degree of structural and compositional dynamics is observed in the system LiBH4-LiCl as a function of temperature and time. Rietveld refinement of synchrotron radiation powder X-ray diffraction (SR-PXD) data reveals that Cl- readily substitutes for BH4- in the Structure of LiBH4. Prolonged heating a sample of LiBH4-LiCl (1:1 molar ratio) above the phase transition temperature and below the melting point (108 < T < 275 degrees C) can produce highly chloride substituted hexagonal lithium borohydride, h-Li(BH4)(l-x)Cl-x, e.g., x similar to 0.42, after heating from room temperature (RT) to 224 degrees C at 2.5 degrees C/min. LiCl has a higher solubility in h-LiBH4 its compared to orthorhombic lithium borohydride, o-LiBH4, which is illustrated by a LiBH4-LiCl (1:1) sample equilibrated at 245 degrees C for 24 days and left at RT for another 13 months. Rietveld refinement reveals that this sample contains o-Li(BH4)(0.91)Cl-0.09 and LiCl. This illustrates a significantly faster dissolution of LiCl in h-LiBH4 its compared to a slower segregation of LiCl from o-LiBH4, which is also demonstrated by in situ SR-PXD from three cycles of heating and cooling of the same Li(BH4)(0.91)Cl-0.09 sample. The substitution of the smaller Cl- for the larger BH4- ion is clearly observed as a reduction in the unit cell volume as a function of time and temperature. A significant stabilization of h-LiBH4 is found to depend on the degree of anion substitution. Variable temperature solid-state magic-angle spinning (MAS) Li-7 and B-13 NMR experiments oil pure LiBH4 show an increase in full width at half maximum (fwhm) when approaching the phase transition from o- to h-LiBH4, which indicates an increase of the relaxation rate (i.e. T-2 decreases). A less pronounced effect is observed for ion-substituted Li(BH4)(1-x)Cl-x, 0.09 < x < 0.42. The MAS NMR experiments also demonstrate a higher degree of motion in the hexagonal phase, i.e., fwhm is reduced by more than a Factor of 10 at the o- to h-LiBH4 phase transition.
|
|
| 3. |
- Barkhordarian, Gagik, et al.
(författare)
-
Formation of Ca(BH4)(2) from hydrogenation of CaH2+MgB2 composite
- 2008
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:7, s. 2743-2749
-
Tidskriftsartikel (refereegranskat)abstract
- The hydrogenation of the CaH2+MgB2 Composite and the dehydrogenation of the resulting products are investigated in detail by in situ time-resolved synchrotron radiation powder X-ray diffraction, high-pressure differential scanning calorimetry, infrared, and thermovolumetric measurements. It is demonstrated that a Ca(BH4)(2)+MgH2 composite is formed by hydrogenating a CaH2+MgB2 composite, at 350 degrees C and 140 bar of hydrogen. Two phases of Ca(BH4)(2) were characterized: alpha- and beta-Ca(BH4)(2). alpha-Ca(BH4)(2) transforms to beta-Ca(BH4)(2) at about 130 degrees C. Under the conditions used in the present study, beta-Ca(BH4)(2) decomposes first to CaH2, Ca3Mg4H14, Mg, B (or MgB2 depending on experimental conditions), and hydrogen at 360 degrees C, before complete decomposition to CaH2, Mg, B (or MgB2), and hydrogen at 400 degrees C. During hydrogenation under 140 bar of hydrogen, beta-Ca(BH4)(2) is formed at 250 degrees C, and alpha-Ca(BH4)(2) is formed when the sample is cooled to less than 130 degrees C. Ti isopropoxide improves the kinetics of the reactions, during both hydrogenation and dehydrogenation. The dehydrogenation temperature decreases to 250 degrees C, with 1 wt % of this additive, and hydrogenation starts already at 200 degrees C. We propose that the improved kinetics of the above reactions with MgB2 (compared to pure boron) can be explained by the different boron bonding within the crystal structure of MgB2 and pure boron.
|
|
| 4. |
- Boesenberg, Ulrike, et al.
(författare)
-
Hydrogen sorption properties of MgH2-LiBH4 composites
- 2007
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1873-2453 .- 1359-6454. ; 55:11, s. 3951-3958
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed analysis of the reaction mechanism of the reactive hydride composite (RHC) MgH2 + 2LiBH(4) <-> MgB2 + 2LiH + 4H(2) was performed using high-pressure differential scanning calorimetry (HP-DSC) measurements and in situ synchrotron powder X-ray diffraction (XRD) measurements along with kinetic investigations using a Sievert-type apparatus. For the desorption the following two-step reaction has been observed: MgH2 + 2LiBH(4) <-> Mg + 2LiBH(4) + H-2 <-> MgB2 + 2LiH + 4H(2). However, this reaction is kinetically restricted and proceeds only at elevated temperatures. In contrast to the desorption reaction, LiBH4 and MgH2 are found to form simultaneously under fairly moderate conditions of 50 bar hydrogen pressure in the temperature range of 250-300 degrees C. As found in pure light metal hydrides, significant improvement of sorption kinetics is possible if suitable additives are used. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
|
|
| 5. |
|
|
| 6. |
- Cerenius, Yngve, et al.
(författare)
-
Crystallography at MAX-lab
- 2004
-
Ingår i: Synchrotron Radiation in Natural Science. - 1644-7190. ; 3:1-2, s. 13-16
-
Tidskriftsartikel (refereegranskat)
|
|
| 7. |
- Cerenius, Yngve, et al.
(författare)
-
Preliminary tests on the use of an acoustic levitator for liquid X-ray diffraction experiments.
- 2003
-
Ingår i: Journal of Applied Crystallography. - 1600-5767. ; 36:1, s. 163-164
-
Tidskriftsartikel (refereegranskat)abstract
- Some preliminary tests at the crystallography beamline I711 at the MAX II synchrotron in Lund, Sweden, have shown that it is possible to use acoustical levitation to keep a droplet of liquid and solid (powder) samples in an X-ray beam for a sufficient time for collection of the X-ray diffraction pattern.
|
|
| 8. |
- Cerenius, Yngve, et al.
(författare)
-
Status of the MAX IV Laboratory
- 2016
-
Ingår i: Synchrotron Radiation News. - : Informa UK Limited. - 0894-0886 .- 1931-7344. ; 29:1, s. 34-38
-
Tidskriftsartikel (refereegranskat)abstract
- On the day of the 2016 summer solstice, June 21, MAX IV, the new synchrotron radiation facility in Lund, Sweden, will be inaugurated. MAX IV is setting a new standard in terms of emittance, thereby providing beamlines with the best possible brilliance and coherence. At the same time, MAX IV continues a more than three-decades-long successful history of Swedish synchrotron-radiation-based research. The activities at the present MAX-lab, which officially started when the MAX I storage ring opened for users in 1986, have been concluded with a “last beamdump” ceremony for the MAX II and MAX III storage rings on December 13, 2015, Saint Lucy's Day. In Sweden, the winter solstice is celebrated with a festival of light.
|
|
| 9. |
- Christensen, Axel Norlund, et al.
(författare)
-
Thermally induced phase transitions of barium oxalates
- 2011
-
Ingår i: Solid State Sciences. - : Elsevier BV. - 1873-3085 .- 1293-2558. ; 13:7, s. 1407-1413
-
Tidskriftsartikel (refereegranskat)abstract
- The thermal decomposition of BaC2O4 center dot 3.5H(2)O and BaC2O4 center dot 0.5H(2)O was investigated using in situ synchrotron X-ray and neutron powder diffraction. The decomposition routes for the barium oxalate hydrates were observed to depend on the applied heating rate. Thermal decomposition of BaC2O4 center dot 0.5H(2)O showed transformation to alpha-BaC2O4 and to beta-BaC2O4 prior to the formation of BaCO3. The decomposition of BaC2O4 center dot 3.5H(2)O showed formation of BaC2O4 center dot 0.5H(2)O at 58 degrees C and the hemi hydrate transforms to alpha-BaC2O4 at 187 degrees C using a relatively fast heating rate of 6.25 degrees C/min. The phase transitions were more complicated using lower heating rate, which also reveal formation of beta-BaC2O4 coexisting with alpha-BaC2O4 along with an unidentified compound. Heating alpha- and beta-BaC2O4 to higher temperatures (T > 400 degrees C) produced BaCO3. A sample of alpha-BaC2O4 was prepared in situ by thermal decomposition of BaC2O4 center dot 3.5H(2)O on a powder neutron diffractometer. The neutron diffraction data has broad diffraction peaks due to small crystallite sizes and overlapping Bragg reflections. [A structural model for alpha-BaC2O4 was derived from the neutron pattern, triclinic, space group P-1, a = 5.127(7), b = 8.905(12), c = 9.068(12) angstrom, alpha = 82.74(1), beta = 99.46(2), gamma = 100.10(1)degrees measured at T= 300 degrees C. The average Ba-O distances are 2.84(3) angstrom and 2.66(3) angstrom for Ba 1 and Ba2 respectively, C-O atom distances in the oxalate ions were found in the range 1.25(3)-1.26(4) angstrom, and C-C distances were 1.60(1)-1.61(1) angstrom]. (C) 2011 Elsevier Masson SAS. All rights reserved.
|
|
| 10. |
- Eigen, N., et al.
(författare)
-
Reversible hydrogen storage in NaF-Al composites
- 2009
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 477:1-2, s. 76-80
-
Tidskriftsartikel (refereegranskat)abstract
- This work demonstrates that hydrogen can be reversibly stored in a composite of NaF and Al. NaF and Al reacts to a mixture of Na3AlF6 and NaAlH4 via hydridofluoride phases of the form Na3AlH6-xFx. The analysis of thermodynamics based on literature standard enthalpies of formation yields the technically favourable enthalpy of reaction of roughly 35 kJ/mol H-2 for a theoretical gravimetric hydrogen storage capacity of 3.3 wt%. Reaction mechanisms are discussed with respect to substitution of hydrogen by fluorine in complex hydrides. (C) 2008 Elsevier B.V. All rights reserved.
|
|
| 11. |
- Gaponov, Yury, et al.
(författare)
-
Some aspects of SR beamline alignment
- 2011
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002. ; 649:1, s. 231-233
-
Konferensbidrag (refereegranskat)abstract
- Based on the Synchrotron Radiation (SR) beamline optical element-by-element alignment with analysis of the alignment results an optimized beamline alignment algorithm has been designed and developed. The alignment procedures have been designed and developed for the MAX-lab 1911-4 fixed energy beamline. It has been shown that the intermediate information received during the monochromator alignment stage can be used for the correction of both monochromator and mirror without the next stages of alignment of mirror, slits, sample holder, etc. Such an optimization of the beamline alignment procedures decreases the time necessary for the alignment and becomes useful and helpful in the case of any instability of the beamline optical elements, storage ring electron orbit or the wiggler insertion device. which could result in the instability of angular and positional parameters of the SR beam. A general purpose software package for manual, semi-automatic and automatic SR beamline alignment has been designed and developed using the developed algorithm. The TANGO control system is used as the middle-ware between the stand-alone beamline control applications BLTools, BPMonitor and the beamline equipment. (C) 2010 Elsevier B.V. All rights reserved.
|
|
| 12. |
- Gosalawit-Utke, Rapee, et al.
(författare)
-
Ca(BH4)(2)-MgF2 Reversible Hydrogen Storage: Reaction Mechanisms and Kinetic Properties
- 2011
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:9, s. 3762-3768
-
Tidskriftsartikel (refereegranskat)abstract
- A composite of Ca(BH4)(2)-MgF2 is proposed as a reversible hydrogen storage system. The dehydrogenation and rehydrogenation reaction mechanisms are investigated by in situ time-resolved synchrotron radiation powder X-ray diffraction (SR-PXD) and Raman spectroscopy. The formation of an intermediate phase (CaF2-xHx) is observed during rehydrogenation. The hydrogen content of 4.3 wt % is obtained within 4 h during the first dehydrogenation at isothermal and isobaric conditions of 330 degrees C and 0.5 bar H-2, respectively. The cycling efficiency is evaluated by three release and uptake cycles together with absorbed hydrogen content in the range 5.1-5.8 wt % after 2.5 h (T = 330 degrees C and p(H-2) = 130 bar). The kinetic properties on the basis of hydrogen absorption are comparable for all cycles. As compared to pure Ca(BH4)(2) and Ca(BH4)(2)-MgH2 composite, Ca(BH4)(2)-MgF2 composite reveals the kinetic destabilization and the reproducibility of hydrogen storage capacities during cycling, respectively.
|
|
| 13. |
- Gosalawit-Utke, R., et al.
(författare)
-
LiF-MgB2 System for Reversible Hydrogen Storage
- 2010
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:22, s. 10291-10296
-
Tidskriftsartikel (refereegranskat)abstract
- LiF-MgB2 composites are proposed for reversible hydrogen storage. With respect to pure LiBH4, a significantly kinetic destabilization regarding hydrogenation and dehydrogenation is accomplished. The reversible hydrogen storage capacity is up to 6.4 wt %. The kinetic properties are improved significantly during cycling. The formations of the hydridofluoride phases (LiBa4-yFy and LiH1-xFx) are observed by in situ synchrotron X-ray diffraction (XRD) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Hydrogenation and dehydrogenation mechanisms are described on the basis of the formation and decomposition of the hydridofluoride phases, respectively.
|
|
| 14. |
- Gosalawit-Utke, Rapee, et al.
(författare)
-
Nanoconfined 2LiBH(4)-MgH2 Prepared by Direct Melt Infiltration into Nanoporous Materials
- 2011
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:21, s. 10903-10910
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoconfined 2LiBH(4)-MgH2 is prepared by direct melt infiltration of bulk 2LiBH(4)-MgH2 into an inert nanoporous resorcinol-formaldehyde carbon aerogel scaffold material. Scanning electron microscopy (SEM) micrographs and energy dispersive X-ray spectroscopy (EDS) mapping reveal homogeneous dispersion of Mg (from MgH2) and B (from LiBH4) inside the carbon aerogel scaffold. Moreover, nanoconfinement of LiBH4 in the carbon aerogel scaffold is confirmed by differential scanning calorimetry (DSC). The hydrogen desorption kinetics of the nanoconfined 2LiBH(4)-MgH2 is significantly improved as compared to bulk 2LiBH(4)-MgH2. For instance, the nanoconfined 2LiBH(4)-MgH2 releases 90% of the total hydrogen storage capacity within 90 mm, whereas the bulk material releases only 34% (at T = 425 degrees C and p(H-2) = 3.4 bar). A reversible gravimetric hydrogen storage capacity of 10.8 wt % H-2, calculated with respect to the metal hydride content, is preserved over four hydrogen release and uptake cycles.
|
|
| 15. |
- Jensen, Torben R., et al.
(författare)
-
Versatile in situ powder X-ray diffraction cells for solid-gas investigations
- 2010
-
Ingår i: Journal of Applied Crystallography. - 1600-5767. ; 43, s. 1456-1463
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes new sample cells and techniques for in situ powder X-ray diffraction specifically designed for gas absorption studies up to ca 300 bar (1 bar = 100 000 Pa) gas pressure. The cells are for multipurpose use, in particular the study of solid-gas reactions in dosing or flow mode, but can also handle samples involved in solid-liquid-gas studies. The sample can be loaded into a single-crystal sapphire (Al2O3) capillary, or a quartz (SiO2) capillary closed at one end. The advantages of a sapphire single-crystal cell with regard to rapid pressure cycling are discussed, and burst pressures are calculated and measured to be similar to 300 bar. An alternative and simpler cell based on a thin-walled silicate or quartz glass capillary, connected to a gas source via a VCR fitting, enables studies up to similar to 100 bar. Advantages of the two cell types are compared and their applications are illustrated by case studies.
|
|
| 16. |
- Knaapila, Matti, et al.
(författare)
-
A new small-angle X-ray scattering set-up on the crystallography beamline I711 at MAX-lab.
- 2009
-
Ingår i: Journal of Synchrotron Radiation. - 1600-5775. ; 16:Pt 4, s. 498-504
-
Tidskriftsartikel (refereegranskat)abstract
- A small-angle X-ray scattering (SAXS) set-up has recently been developed at beamline I711 at the MAX II storage ring in Lund (Sweden). An overview of the required modifications is presented here together with a number of application examples. The accessible q range in a SAXS experiment is 0.009-0.3 A(-1) for the standard set-up but depends on the sample-to-detector distance, detector offset, beamstop size and wavelength. The SAXS camera has been designed to have a low background and has three collinear slit sets for collimating the incident beam. The standard beam size is about 0.37 mm x 0.37 mm (full width at half-maximum) at the sample position, with a flux of 4 x 10(10) photons s(-1) and lambda = 1.1 A. The vacuum is of the order of 0.05 mbar in the unbroken beam path from the first slits until the exit window in front of the detector. A large sample chamber with a number of lead-throughs allows different sample environments to be mounted. This station is used for measurements on weakly scattering proteins in solutions and also for colloids, polymers and other nanoscale structures. A special application supported by the beamline is the effort to establish a micro-fluidic sample environment for structural analysis of samples that are only available in limited quantities. Overall, this work demonstrates how a cost-effective SAXS station can be constructed on a multipurpose beamline.
|
|
| 17. |
|
|
| 18. |
|
|
| 19. |
- Kuktaite, Ramune, et al.
(författare)
-
Structure and Morphology of Wheat Gluten Films : From Polymeric Protein Aggregates toward Superstructure Arrangements
- 2011
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 12:5, s. 1438-1448
-
Tidskriftsartikel (refereegranskat)abstract
- Evaluation of structure and morphology of extruded wheat gluten (WG) films showed WG protein assemblies elucidated on a range of length scales from nano (4.4 angstrom and 9 to 10 angstrom, up to 70 angstrom) to micro (10 mu m). The presence of NaOH in WG films induced a tetragonal structure with unit cell parameters, a = 51.85 angstrom and c = 40.65 angstrom, whereas NH4OH resulted in a bidimensional hexagonal close-packed (HCP) structure with a lattice parameter of 70 angstrom. In the WG films with NH4OH, a highly polymerized protein pattern with intimately mixed glutenins and gliadins bounded through SH/SS interchange reactions was found. A large content of beta-sheet structures was also found in these films, and the film structure was oriented in the extrusion direction. In conclusion, this study highlights complexities of the supramolecular structures and conformations of wheat gluten polymeric proteins in biofilms not previously reported for biobased materials.
|
|
| 20. |
- Labrador, Ana, et al.
(författare)
-
The yellow mini-hutch for SAXS experiments at MAX IV Laboratory
- 2013
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 425:Part 7, s. 1-4
-
Tidskriftsartikel (refereegranskat)abstract
- I911-SAXS is the new SAXS (Small-Angle-X-ray-Scattering) beamline at the MAX IV Laboratory in Lund, Sweden. It is one of the 5 stations of the hard X-ray Cassiopeia beamline (I911) at the 1.5 GeV ring MAX II. I911-4 was converted into a multipurpose SAXS station which opened to the scientific community in May 2011. The SAXS users community at this laboratory comes from diverse fields of research with different needs and requirements at the end-station. This results in different set-ups routinely being installed in the easy-accessible experimental mini-hutch. The beam can be focused at sample-to-detector distances between a few hundred millimeters and more than two meters. This versatility permits a selection of q-ranges between 0.006 1/Å and 2 1/Å. The recent acquisition of a fast readout, low noise pixel detector (PILATUS 1M) and the implementation of a high-throughput solution SAXS are the latest beamline upgrades.
|
|
| 21. |
- Lee, Ji Youn, et al.
(författare)
-
Decomposition Reactions and Reversibility of the LiBH4-Ca(BH4)(2) Composite
- 2009
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:33, s. 15080-15086
-
Tidskriftsartikel (refereegranskat)abstract
- LiBH4 is one of the promising candidates for hydrogen storage materials because of its high gravimetric and volumetric hydrogen capacity. However, its high dehydrogenation temperature and limited reversibility has been a hurdle for its use in real applications. In an effort to overcome this barrier and to adjust the thermal stability, we make a composite system LiBH4-Ca(BH4)(2). In order to fully characterize this composite system we study xLiBH(4) + (1 - x)Ca(BH4)(2) for several x values between 0 and 1, using differential scanning calorimetry, in situ synchrotron X-ray diffraction, thermogravimetric analysis, and mass spectrometry. Interestingly, this composite undergoes a eutectic melting at ca. 200 degrees C in a wide composition range, and the eutectic composition lies between x = 0.6 and 0.8. The decomposition characteristics and the hydrogen capacity of this composite vary with x, and the decomposition temperature is lower than both the pure LiBH4 and Ca(BH4)(2) at intermediate conpositions, for example, for x approximate to 0.4, decomposition is finished below 400 degrees C releasing about 10 wt % of hydrogen. Partial reversibility of this system was also confirmed for the first time for the case of if mixed borohydride composite.
|
|
| 22. |
- Mammen, C B, et al.
(författare)
-
Design of a 5-station macromolecular crystallography beamline at MAX-Lab
- 2002
-
Ingår i: Acta Physica Polonica. Series A: General Physics, Physics of Condensed Matter, Optics and Quantum Electronics, Atomic and Molecular Physics, Applied Physics. - 0587-4246. ; 101:5, s. 595-602
-
Tidskriftsartikel (refereegranskat)abstract
- A beamline for macromolecular crystallography is under construction at the Swedish synchrotron light source MAX-lab at Lund University in a collaborative effort between Denmark and Sweden. Of the 7 mrad horizontal wiggler fan emitted from the new superconducting multipole wiggler, the central 2 mrad will be used and split in three parts. The central 1 mrad will be used for a tunable station optimised for multi-wavelength anomalous diffraction experiments and on each side of the central fan there will be two fixed wavelength stations using different energies of the same part of the beam. These in total five stations can be used simultaneously and independently for collecting diffraction data.
|
|
| 23. |
- Minella, Christian Bonatto, et al.
(författare)
-
Effect of Transition Metal Fluorides on the Sorption Properties and Reversible Formation of Ca(BH4)(2)
- 2011
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:5, s. 2497-2504
-
Tidskriftsartikel (refereegranskat)abstract
- Light metal borohydrides are considered as promising materials for solid state hydrogen storage. Because of the high hydrogen content of 11.5 wt % and the rather low dehydrogenation enthalpy of 32 kJ mol(-1)H(2), Ca(BH4)(2) is considered to be one of the most interesting compounds in this class of materials. In the present work, the effect of selected TM-fluoride (TM = transition metal) additives on the reversible formation of Ca(BH4)(2) was investigated by means of thermovolumetric, calorimetric, Fourier transform infrared spectroscopy, and ex situ, and in situ synchrotron radiation powder X-ray diffraction (SR-PXD) measurements. Furthermore, selected desorbed samples were analyzed by B-11{H-1} solid state magic angle spinning nuclear magnetic resonance (MAS NMR). Under the conditions used in this study (145 bar H-2 pressure and 350 degrees C), TiF4 and NbF5 were the only additives causing partial reversibility. In these two cases, B-11{H-1} MAS NMR analyses detected CaB6 and likely CaB12H12 in the dehydrogenation products. Elemental boron was found in the decomposition products of Ca(BH4)(2) samples with VF4, TiF3, and VF3. The results indicate an important role of CaB6 for the reversible formation of Ca(BH4)(2).
|
|
| 24. |
- Mosegaard, Lene, et al.
(författare)
-
Intermediate phases observed during decomposition of LiBH4
- 2007
-
Ingår i: Journal of Alloys and Compounds. - 0925-8388. ; 446-447, s. 301-305
-
Konferensbidrag (refereegranskat)abstract
- Lithium tetrahydridoboranate is among the materials with the highest hydrogen content and has great potential as a possible H-2-storage material, although, the release and uptake of H-2 is not fully understood. In this work, LiBH4 was studied by in situ synchrotron radiation powder X-ray diffraction (PXD) and solid state CP/MAS NNIR both at variable temperatures. This study revealed two new phases observed during dehydrogenation of LiBH4. Phase I is hexagonal, a = 4.93(2) and c = 13.47(3) angstrom and is observed in the temperature range -200-300 degrees C, and phase II is orthorhombic, a = 8.70(1), b = 5.44(1) and c = 4.44](8) angstrom and is observed in the temperature range similar to 300-400 degrees C applying a constant heating rate of 5 degrees C/min. Apparently, I transforms into II, e.g. at a constant temperature of T= 265 degrees C after 5 h. Furthermore, a third phase, III, is observed in the temperature range RT to 70 degrees C, and is caused by a reaction between LiBH4 and water vapor from the atmosphere. Hydrogen release is associated with the decomposition of III at ca. 65 degrees C. (C) 2007 Elsevier B.V. All rights reserved.
|
|
| 25. |
- Mosegaard, Lene, et al.
(författare)
-
Reactivity of LiBH4: In situ synchrotron radiation powder X-ray diffraction study
- 2008
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:4, s. 1299-1303
-
Tidskriftsartikel (refereegranskat)abstract
- Lithium tetrahydridoboranate (LiBH4) may be a potentially interesting material for hydrogen storage, but in order to absorb and desorb hydrogen routinely and reversibly, the kinetics and thermodynamics need to be improved significantly. A priori, this material has one of the highest theoretical gravimetric hydrogen contents, 18.5 wt%, but unfortunately for practical applications, hydrogen release occurs at too high temperature in a non-reversible way. By means of in situ synchrotron radiation powder X-ray diffraction (SR-PXD), the interaction between LiBH4 and different additives-SiO2, TiCl3, LiCl, and Au - is investigated. It is found that silicon dioxide reacts with molten LiBH4 and forms Li2SiO3 or Li4SiO4 at relatively low amounts of SiO2, e.g., with 5.0 and 9.9 mol % SiO2 in LiBH4, Whereas, for higher amounts of SiO2 (e.g., 25.5 mol %), only the Li2SiO3 phase is observed. Furthermore, we demonstrate that a solid-state reaction occurs between LiBH4 and TiCl3 to form LiCl at room temperature. At elevated temperatures, more LiCl is formed simultaneously with a decrease in the diffracted intensity from TiCl3. Lithium chloride shows some solubility in solid LiBH4 at T > 100 degrees C. This is the first report of substituents that accommodate the structure of LiBH4 by a solid/solid dissolution reaction. Gold is found to react with molten LiBH4 forming a Li-Au alloy with CuAu3-type structure. These studies demonstrate that molten LiBH4 has a high reactivity, and finding a catalyst for this H-rich system may be a challenge.
|
|
