|
|
Catalysis of Hydrogen De-sorption from MgH2
Čermák, Jiří ; David, Bohumil
Hydrogen is considered to be clean fuel for various energy sources in the near future. One of technical problems in this area is its effective storage. MgH2 is very perspective material whose main advantage is high hydrogen storage capacity (theoretically 7.6 wt. % H2). However, there are negative features of this material as a hydrogen storage medium: before all, it is its poor hydrogen de-sorption kinetics. Therefore, much effort has been devoted in the past to find out possible ways how to enhance the MgH2 de-sorption rate and how to shift this material close to technical applications. It is known that nickel and Mg2Ni enhance hydrogen de-sorption from MgH2. This paper continues our previous works on hydrogen de-sorption from Mg-Ni –based materials. It is devoted to the investigation of separate catalytic effect of Mg2NiH4 and Mg2Ni upon the hydrogen de-sorption from the principal component of the material - MgH2. It was found that catalytic efficiency of Mg2NiH4 is much higher than that of Mg2Ni.
|
|
|
Nanokrystalické částice oxidů železa, karbidů železa a alfa-Fe připravené z ferihydritu
Schneeweiss, Oldřich ; Grygar, Tomáš ; David, Bohumil ; Pizúrová, Naděžda ; Žák, Tomáš ; Zbořil, R. ; Mašláň, M.
Preparation of nanocrystalline iron oxides (hematite alpha-Fe2O3, magnetite Fe3O4), Haag carbide (Fe5C2), and alpha-Fe by thermal treatment of ferrihydrite in various atmospheres is reported. The phase composition and size of nanoparticles was controlled using the annealing temperature and atmosphere (vacuum, hydrogen, or ethylene).
|
|
| |
|
|
Strukturní vlastnosti nanometrických železných částic
David, Bohumil ; Schneeweiss, Oldřich ; Pizúrová, Naděžda ; Klementová, Mariana ; Morjan, I.
Fe-based nanoparticles were prepared by the laser pyrolysis method using a cross-flow reactor in which the laser orthogonally irradiates the gas mixture of Fe(CO)5, C2H2, and C2H4. Ethylene serves as the CO2 laser radiation absorber. The as-synthesized powder was characterised by HRTEM, XRD, Raman spectroscopy, Mössbauer spectroscopy, and magnetic measurements. As observed under TEM, the as-synthesized powder consisted of nanoparticles smaller then 10 nm embedded in a pyrolytic carbon matrix. The XRD pattern exhibited three broad peaks: the first peak is assigned to pyrolytic carbon, the second peak is assigned to maghemite/magnetite, and the third peak belongs to α-Fe particles. The particle size d 2 nm was obtained for α-Fe from the Scherrer formula. The presence of α-Fe and maghemite/magnetite phases was also observed in the Mössbauer spectrum measured at 4 K.
|
|
|
α-Fe nanočástice připravené rozkladem pentakarbonylu železa v mikrovlnném výboji
David, Bohumil ; Pizúrová, Naděžda ; Schneeweiss, Oldřich ; Hoder, T. ; Kudrle, V. ; Janča, J.
The nanocrystalline iron powder has been prepared by the introducing of Fe(CO)5 vapor into the microwave induced argon discharge. A microwave 2.45 GHz source was operated at 430 W. The reaction was performed in a quartz tube passing through the microwave waveguide. The in-situ passivation using air was applied after synthesis. The powder was characterised by TEM, XRD, and Mössbauer spectroscopy. According to our TEM investigation, the produced passivated powder included aggregated core-shell nanoparticles. The cores consist of α-Fe and the shell is supposed to be iron oxide (indicated by TEM). The presence of α-Fe and iron oxides was confirmed by XRD and Mössbauer spectroscopy. The mean coherence domain size of α-Fe cores was estimated to be 30 nm. The synthesized nanopowder exhibits ferromagnetic behaviour.
|
|
| |
|
|
Použití mikrovlnného plazmatu pro syntézu alfa-Fe nanočástic
Hoder, T. ; Kudrle, V. ; Frgala, Z. ; Janča, J. ; David, Bohumil
Microwave induced plasma decomposition of iron pentacarbonyl has been used to prepare iron nanosized particles. Vapours of iron pantacarbonyl have been introduced into argon surfaguide discharge, optical mission spectra have been taken and rotational and vibrational temperatures obtained. The temperatures were plotted as a functions of axial and radial distance and of iron pentacarbonyl concentration. Iron nanoparticles have been produced, XRD results and TEM images were obtained. The core-shell nanoparticles were observed, with alpha phase iron as a core and Fe(x)O(y)/C shell.
|
|
|
Nanocompositní materiál s železnými nanočásticemi obalenými grafitem připravený dvoustupňovou procedurou
David, Bohumil ; Pizúrová, Naděžda ; Schneeweiss, Oldřich ; Bezdička, Petr ; Alexandrescu, R. ; Morjan, I. ; Cruneteanu, A. ; Voicu, I.
We describe the phase composition and magnetic properties of the nanocomposite based on iron/graphite core-shell structured nanoparticles. This nanocomposite was prepared by a two-step procedure: in the first step, the original Fe-C-N based nanopowder was synthesized by the method of laser pyrolysis of gas phase reactants, and subsequently in the second step, it was heated up to 800°C in vacuum. Annealing in vacuum induced the formation and growth of iron/graphite core-shell structured nanoparticles. Both the originally synthesized Fe-C-N based nanopowder and the annealed nanopowder were characterized by TEM, XRD and magnetic measurements. The presence of iron nanoparticles with the mean diameter of 40 nm in the annealed state of the nanopowder was proved by XRD and TEM analysis. Mössbauer spectroscopy was used to observe a qualitative change in phase composition.
|
|
| |
guest ::
