Ne (1019)
Ano (4)
Počet nalezených dokumentů:
1023
Publikováno od
do
INFLUENCE OF GRAPHITE UPON THE KINETICS OF HYDROGEN SORPTION IN Mg@Mg17Al12
Čermák, Jiří; Král, Lubomír; Roupcová, Pavla
2018 - anglický
Influence of graphite addition to the ball-milling charge composed of Mg splinters and Mg17Al12 particles upon the hydrogen sorption was investigated at sorption temperature 623 K. Measurements were carried out by Sieverts method. Graphite facilitates the ball-milling: It prevents re-agglomeration of crushed particles into large secondary particles. It also suppresses sticking the milled material to the balls and walls of the milling jar. It was found that an increase of carbon concentration up to a certain limit c(L) lying between 14 and 23 wt. % C, carbon increases both the absorption and the desorption rates and hydrogen storage capacity. Above c(L), carbon causes a considerable decrease in HS capacity, which spoils the application potential of Mg@Mg17Al12/C. Crystallite size of the material under study, obtained by XRD, is in the order of tens of nm.
Klíčová slova:
storage; Hydrogen storage; Mg alloys; graphite
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
INFLUENCE OF GRAPHITE UPON THE KINETICS OF HYDROGEN SORPTION IN Mg@Mg17Al12
Influence of graphite addition to the ball-milling charge composed of Mg splinters and Mg17Al12 particles upon the hydrogen sorption was investigated at sorption temperature 623 K. Measurements were ...
ESTIMATION OF EQUILIBRIUM HYDROGEN PRESSURE - A NEW METHOD
Čermák, Jiří; Král, Lubomír
2018 - anglický
A new method is proposed to estimation of hydrogen pressure in equilibrium with hydride phase in a hydrogen\nstorage material. It is applicable both for hydrogen absorption and desorption in cases where the hydride phase\nis formed by nucleation and growth mechanism. The proposed method saves considerably the experimental\ntime replacing the conventional time consuming measurement of pressure-composition isotherms, the so\ncalled PCT curves. The proposed evaluation procedure is illustrated using hydrogen chemi-sorption at\ntemperatures 623 K, 573 K and 523 K in chosen hydrogen storage alloys Mg-Si-C, Mg-Li-C and Mg-Na-C.
Klíčová slova:
Hydrogen storage; magnesium; new method
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
ESTIMATION OF EQUILIBRIUM HYDROGEN PRESSURE - A NEW METHOD
A new method is proposed to estimation of hydrogen pressure in equilibrium with hydride phase in a hydrogen\nstorage material. It is applicable both for hydrogen absorption and desorption in cases ...
MICROSTRUCTURE AND COMPOSITION OF FINE PARTICLES RELEASED BY CAR BRAKING
Švábenská, Eva; Roupcová, Pavla; Pizúrová, Naděžda; Schneeweiss, Oldřich
2018 - anglický
Vehicular traffic is connected with large volume of fine particles released during brake processes of cars. Our research is focused on the phase, structure and chemical analysis of the fine particles taken from some car brake parts by their services. The information on structure and phase composition was obtained by X-Ray Powder Diffraction, Mossbauer Spectroscopy, scanning electron microscopy with EDX and transmission electron microscopy. The results of the wear debris analysis are compared with original brake materials components. Most of recognized particles are based mainly on iron oxides. Wear brake particles are discussed in the relation to the potential risk to the environment and human health.
Klíčová slova:
wear; Nanoparticles; wear debris; environment
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
MICROSTRUCTURE AND COMPOSITION OF FINE PARTICLES RELEASED BY CAR BRAKING
Vehicular traffic is connected with large volume of fine particles released during brake processes of cars. Our research is focused on the phase, structure and chemical analysis of the fine particles ...
HYDROGEN STORAGE PROPERTIES OF GRAPHENE OXIDE MATERIALS PREPARED BY DIFFERENT WAYS
Král, Lubomír; Čermák, Jiří; Bytesnikova, Z.
2018 - anglický
Graphene-based materials show unique properties. These single layered materials consist of 2D structure of carbon atoms, belong to the strongest known materials, that are very mechanically flexible, optically transparent and that are excellent electrical and thermal conductors. Recently, several studies on these types of materials have highlighted the potential of this material for hydrogen storage (HS) and raised new hopes for the development of an effective solid-state HS media. In the present paper, the structure and HS properties of graphene oxide (GO) and chemically reduced graphene oxide (rGO) produced by different procedures were studied. Hydrogen sorption characteristics of GO and rGO were measured using the Sieverts-type gas sorption analyzer PCT-Pro Setaram Instrumentation. The study of HS was carried out at temperature range from 198 K to 423 K under hydrogen pressure from 1x10(-4) to 4 MPa.
Klíčová slova:
adsorption; reduction; graphite; Graphene oxide; hydrogen storage; adsorption; desorption
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
HYDROGEN STORAGE PROPERTIES OF GRAPHENE OXIDE MATERIALS PREPARED BY DIFFERENT WAYS
Graphene-based materials show unique properties. These single layered materials consist of 2D structure of carbon atoms, belong to the strongest known materials, that are very mechanically flexible, ...
Quantum-mechanical study of magnetic properties of superalloy nanocomposite phase Fe2AlTi
Slávik, Anton; Miháliková, Ivana; Friák, Martin; Všianská, Monika; Šob, Mojmír
2018 - anglický
The L21-structure Fe2AlTi intermetallic compound is one of the two phases identified in Fe-Al-Ti superalloy nanocomposites. Experimental data related to low-temperature magnetic properties of this Heusler compound indicate that magnetic moment is about 0.1 Bohr magneton per formula unit. In contrast, previous quantum-mechanical calculations predicted Fe2AlTi to have much higher magnetic moment, 0.9 Bohr magneton per formula unit. In order to solve this discrepancy between the theory and experiment we have performed a series of quantum-mechanical fix-spin-moment calculations and compared our results with those for non-magnetic state. It turns out that the total energy of the non-magnetic state is only by 10.73 meV/atom higher than that of the magnetic state. When applying Boltzmann statistics to this very small energy difference we predict that the non-magnetic state appears at non-zero temperatures with significant probabilities (for instance, 22.36 % at T = 100 K) and reduces the overall magnetic moment. As another mechanism lowering the magnetization we studied selected shape deformations, in particular trigonal shearing. Fe2AlTi exhibits a compression-tension asymmetry with respect to these strains and, for example, the strain 0.08 destabilizes the spin-polarized state, leaving the non-magnetic state as the only stable one.
Klíčová slova:
Ab initio calculations; Fe-Al based superalloys; Fixed-spin-moment; Nanocomposites
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Quantum-mechanical study of magnetic properties of superalloy nanocomposite phase Fe2AlTi
The L21-structure Fe2AlTi intermetallic compound is one of the two phases identified in Fe-Al-Ti superalloy nanocomposites. Experimental data related to low-temperature magnetic properties of this ...
DISPLACEMENT FIELD ANALYSIS IN WEDGE SPLITTING TEST\nSPECIMEN BY ODM METHOD
Seitl, S.; Miarka, P.; Růžička, V.; Malíková, Lucie; Merta, I.
2018 - anglický
Multi-parameter fracture mechanics is nowadays quite extensively applied when cracked\nstructures/specimens are investigated. The reason is that it has been shown that it can be\nhelpful and bring more accurate results when fracture processes happen in a larger\nregion around the crack tip, what can be typical for material like concrete or other\nmaterials with quasi-brittle behaviour. Various relative crack length configurations have\nbeen chosen in order to investigate the importance of the higher-order terms of the\nWilliams power expansion on the crack-tip stress field distribution in Wedge splitting\ntest specimen. The higher-order terms are calculated by means of the over-deterministic\nmethod from displacements of nodes around the crack tip obtained by a finite element\nanalysis in different radial distances from the crack tip. The effect of the constraint level\nis investigated. Although the third and higher terms of the Williams series are very often\nneglected, their influence on the opening stress values is investigated.
Klíčová slova:
ODM, WST; WST; constraint; Williams series; FEM; stress intensity factor; displacement
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
DISPLACEMENT FIELD ANALYSIS IN WEDGE SPLITTING TEST\nSPECIMEN BY ODM METHOD
Multi-parameter fracture mechanics is nowadays quite extensively applied when cracked\nstructures/specimens are investigated. The reason is that it has been shown that it can be\nhelpful and bring ...
MICROSTRUCTURE AND COMPOSITION OF FINE PARTICLES RELEASED BY CAR BRAKING
Švábenská, Eva; Roupcová, Pavla; Pizúrová, Naděžda; Schneeweiss, Oldřich
2018 - anglický
Vehicular traffic is connected with large volume of fine particles released during brake processes of cars. Our research is focused on the phase, structure and chemical analysis of the fine particles taken from some car brake parts by their services. The information on structure and phase composition was obtained by X-Ray Powder Diffraction, Mossbauer Spectroscopy, scanning electron microscopy with EDX and transmission electron microscopy. The results of the wear debris analysis are compared with original brake materials components. Most of recognized particles are based mainly on iron oxides. Wear brake particles are discussed in the relation to the potential risk to the environment and human health.
Klíčová slova:
Nanoparticles; wear debris; environment
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
MICROSTRUCTURE AND COMPOSITION OF FINE PARTICLES RELEASED BY CAR BRAKING
Vehicular traffic is connected with large volume of fine particles released during brake processes of cars. Our research is focused on the phase, structure and chemical analysis of the fine particles ...
First-principles study of interface energies in Fe-Al-based superalloy nanocomposites
Miháliková, Ivana; Slávik, Anton; Friák, Martin; Všianská, Monika; Koutná, N.; Holec, David; Šob, Mojmír
2018 - anglický
Fe-Al-based nanocomposites with a superalloy-type of microstructure constitute a very promising class of materials. They possess a great potential as an alternative to the currently used steel grades in high temperature applications. Intermetallics-containing nanocomposites, such as those with the Fe3Al compound being one of the phases, may open a way towards future automotive and energy-conversion technologies with lower fuel consumption and reduced environmental impact. We employ quantum-mechanical calculations to analyze relations between ordering tendencies of Al atoms in the disordered Fe-18.75at.%Al phase on one hand and thermodynamic, structural and magnetic properties of Fe-Al-based nanocomposites on the other. When comparing supercells modeling disordered Fe-Al phase with different atomic distribution of atoms we find out that the supercell without 1st and 2nd nearest neighbor Al-Al pairs has a lower energy than that mimicking a perfect disorder (a special quasi-random structure, SQS). Further, coherent interfaces with (001), (110) and (1-10) crystallographic orientations between Fe3Al compound and SQS Fe-Al phase have higher energies than those exhibiting atomic distribution without 1st and 2nd nearest neighbor Al-Al pairs.
Klíčová slova:
Ab initio calculations; Fe-Al based superalloys; Interface energies; Nanocomposites
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
First-principles study of interface energies in Fe-Al-based superalloy nanocomposites
Fe-Al-based nanocomposites with a superalloy-type of microstructure constitute a very promising class of materials. They possess a great potential as an alternative to the currently used steel grades ...
Estimation of equilibrium hydrogen pressure - A new method
Čermák, Jiří; Král, Lubomír
2018 - anglický
A new method is proposed to estimation of hydrogen pressure in equilibrium with hydride phase in a hydrogen\nstorage material. It is applicable both for hydrogen absorption and desorption in cases where the hydride phase\nis formed by nucleation and growth mechanism. The proposed method saves considerably the experimental\ntime replacing the conventional time consuming measurement of pressure-composition isotherms, the so\ncalled PCT curves. The proposed evaluation procedure is illustrated using hydrogen chemi-sorption at\ntemperatures 623 K, 573 K and 523 K in chosen hydrogen storage alloys Mg-Si-C, Mg-Li-C and Mg-Na-C.
Klíčová slova:
hydrogen storage; magnesium; new method
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Estimation of equilibrium hydrogen pressure - A new method
A new method is proposed to estimation of hydrogen pressure in equilibrium with hydride phase in a hydrogen\nstorage material. It is applicable both for hydrogen absorption and desorption in cases ...
Měření velmi pomalých creepových deformací materiálů pro pokrytí jaderného paliva technikou helikoidních vzorků.
Kloc, Luboš
2018 - český
Metodika umožňuje přímé experimentální stanovení creepových vlastností povlakových trubek jaderného paliva za podmínek, při kterých probíhá creepová deformace velmi pomalu, takže není standardními metodami creepových zkoušek měřitelná. Takto získané údaje jsou potřebné ve výpočtových kódech pro modelování chování paliva v reaktoru i mimo\nněj při skladování paliva a dosud chybí, popřípadě jsou získávany nespolehlivou extrapolací. Presented technique enables experimental determination of the creep properties of the nuclear fuel cladding tubes under conditions leading to very low strain rates, which are not measurable by conventional creep tests. The data are necessary for the numerical modeling of the nuclear fuel behavior inside the reactor or during the fuel storage and are not available or used to be replaced by the data obtained by unreliable extrapolation.
Klíčová slova:
measurement of slow creep deformation; helicoid specimen test; creep rate measurement
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Měření velmi pomalých creepových deformací materiálů pro pokrytí jaderného paliva technikou helikoidních vzorků.
Metodika umožňuje přímé experimentální stanovení creepových vlastností povlakových trubek jaderného paliva za podmínek, při kterých probíhá creepová deformace velmi pomalu, takže není standardními ...
NUŠL poskytuje centrální přístup k informacím o šedé literatuře vznikající v ČR v oblastech vědy, výzkumu a vzdělávání. Více informací o šedé literatuře a NUŠL najdete na webu služby.
Vaše náměty a připomínky posílejte na email nusl@techlib.cz
Provozovatel
Zahraniční báze