| 1. |
- 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.
|
|
| 2. |
- 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.
|
|
| 3. |
- 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.
|
|
| 4. |
- Nielsen, Thomas K., et al.
(författare)
-
A Reversible Nanoconfined Chemical Reaction
- 2010
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 4:7, s. 3903-3908
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrogen is recognized as a potential, extremely interesting energy carrier system, which can facilitate efficient utilization of unevenly distributed renewable energy. A major challenge in a future "hydrogen economy" is the development of a safe, compact, robust, and efficient means of hydrogen storage, in particular, for mobile applications. Here we report on a new concept for hydrogen storage using nanoconfined reversible chemical reactions. LiBH4 and MgH2 nanoparticles are embedded in a nanoporous carbon aerogel scaffold with pore size D-max similar to 21 nm and react during release of hydrogen and form MgB2. The hydrogen desorption kinetics is significantly improved compared to bulk conditions, and the nanoconfined system has a high degree of reversibility and stability and possibly also improved thermodynamic properties. This new scheme of nanoconfined chemistry may have a wide range of interesting applications in the future, for example, within the merging area of chemical storage of renewable energy.
|
|
| 5. |
- Pistidda, Claudio, et al.
(författare)
-
Pressure Effect on the 2NaH+MgB2 Hydrogen Absorption Reaction
- 2010
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:49, s. 21816-21823
-
Tidskriftsartikel (refereegranskat)abstract
- The hydrogen absorption mechanism of the 2NaH + MgB2 system has been investigated in detail. Depending on the applied hydrogen pressure, different intermediate phases are observed. In the case of absorption measurements performed under 50 bar of hydrogen pressure, NaBH4 is found not to be formed directly. Instead, first an unknown phase is formed, followed upon further heating by the formation of NaMgH3 and a NaH-NaBH4 molten salt mixture; only at the end after heating to 380 degrees C do the reflections of the crystalline NaBH4 appear. In contrast, measurements performed at lower hydrogen pressure (5 bar of H-2), but under the same temperature conditions, demonstrate that the synthesis of NaBH4 is possible without occurrence of the unknown phase and of NaMgH3. This indicates that the reaction path can be tuned by the applied hydrogen pressure. The formation of a NaH-NaBH4 molten salt mixture is observed also for the measurement performed under 5 bar of hydrogen pressure with the formation of free Mg. However, under this pressure condition the formation of crystalline NaBH4 is observed only during cooling at 367 degrees C. For none of the applied experimental conditions has it been possible to achieve the theoretical gravimetric hydrogen capacity of 7.8 wt %.
|
|
| 6. |
- Pranzas, P. Klaus, et al.
(författare)
-
Characterization of Hydrogen Storage Materials and Systems with Photons and Neutrons
- 2011
-
Ingår i: Advanced Engineering Materials. - : Wiley. - 1527-2648 .- 1438-1656. ; 13:8, s. 730-736
-
Tidskriftsartikel (refereegranskat)abstract
- Complex hydrides are very promising candidates for future light-weight solid state hydrogen storage materials. The present work illustrates detailed characterization of such novel hydride materials on different size scales by the use of synchrotron radiation and neutrons. The comprehensive analysis of such data leads to a deep understanding of the ongoing processes and mechanisms. The reaction pathways during hydrogen desorption and absorption are identified by in situ X-ray diffraction (XRD). Function and size of additive phases are estimated using X-ray absorption spectroscopy (XAS) and anomalous small-angle X-ray scattering (ASAXS). The structure of the metal hydride matrix is characterized using (ultra) small-angle neutron scattering (SANS/USANS). The hydrogen distribution in tanks filled with metal hydride material is studied with neutron computerized tomography (NCT). The results obtained by the different analysis methods are summarized in a final structural model. The complementary information obtained by these different methods is essential for the understanding of the various sorption processes in light metal hydrides and hydrogen storage tanks.
|
|
| 7. |
- Prasciolu, Mauro, et al.
(författare)
-
On the use of multilayer Laue lenses with X-ray free electron lasers
- 2021
-
Ingår i: International Conference on X-Ray Lasers 2020. - : SPIE. - 1996-756X .- 0277-786X. - 9781510646186 ; 11886
-
Konferensbidrag (refereegranskat)abstract
- We report on the use of multilayer Laue lenses to focus the intense X-ray Free Electron Laser (XFEL) beam at the European XFEL to a spot size of a few tens of nanometers. We present the procedure to align and characterize these lenses and discuss challenges working with the pulse trains from this unique X-ray source.
|
|
| 8. |
- Reiser, Mario, et al.
(författare)
-
Resolving molecular diffusion and aggregation of antibody proteins with megahertz X-ray free-electron laser pulses
- 2022
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron lasers (XFELs) with megahertz repetition rate can provide novel insights into structural dynamics of biological macromolecule solutions. However, very high dose rates can lead to beam-induced dynamics and structural changes due to radiation damage. Here, we probe the dynamics of dense antibody protein (Ig-PEG) solutions using megahertz X-ray photon correlation spectroscopy (MHz-XPCS) at the European XFEL. By varying the total dose and dose rate, we identify a regime for measuring the motion of proteins in their first coordination shell, quantify XFEL-induced effects such as driven motion, and map out the extent of agglomeration dynamics. The results indicate that for average dose rates below 1.06 kGy μs−1 in a time window up to 10 μs, it is possible to capture the protein dynamics before the onset of beam induced aggregation. We refer to this approach as correlation before aggregation and demonstrate that MHz-XPCS bridges an important spatio-temporal gap in measurement techniques for biological samples.
|
|
| 9. |
- Seiboth, Frank, et al.
(författare)
-
Aberration Correction for Hard X-ray Focusing at the Nanoscale
- 2017
-
Ingår i: Advances in X-Ray/EUV Optics and Components XII. - : SPIE - International Society for Optical Engineering. - 9781510612303 - 9781510612297
-
Konferensbidrag (refereegranskat)abstract
- We developed a corrective phase plate that enables the correction of residual aberration in reflective, diffractive, and refractive X-ray optics. The principle is demonstrated on a stack of beryllium compound refractive lenses with a numerical aperture of 0.49 x 10(-3) at three different synchrotron radiation and x-ray free-electron laser facilities. By introducing this phase plate into the beam path, we were able to correct the spherical aberration of the optical system and improve the Strehl ratio of the optics from 0.29(7) to 0.87(5), creating a diffraction-limited, large aperture, nanofocusing optics that is radiation resistant and very compact.
|
|
| 10. |
- Seiboth, Frank, et al.
(författare)
-
Perfect X-ray focusing via fitting corrective glasses to aberrated optics
- 2017
-
Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Due to their short wavelength, X-rays can in principle be focused down to a few nanometres and below. At the same time, it is this short wavelength that puts stringent requirements on X-ray optics and their metrology. Both are limited by today’s technology. In this work, we present accurate at wavelength measurements of residual aberrations of a refractive X-ray lens using ptychography to manufacture a corrective phase plate. Together with the fitted phase plate the optics shows diffraction-limited performance, generating a nearly Gaussian beam profile with a Strehl ratio above 0.8. This scheme can be applied to any other focusing optics, thus solving the X-ray optical problem at synchrotron radiation sources and X-ray free-electron lasers.
|
|
