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85 results on '"Černý R"'

27. Hydrogenation of LaNi5 studied by in situ synchrotron powder diffraction

Author

Joubert, J.-M., Černý, R., Latroche, M., Percheron-Guégan, A., and Schmitt, Bernd

Subjects
*HYDROGENATION, *COAL liquefaction, *THERMAL desorption, *SYNCHROTRONS, *TEMPERATURE
Abstract

Abstract: Hydrogen absorption in LaNi5 intermetallic compound has been studied by in situ synchrotron powder diffraction. Fast data acquisition allows the measurement to be performed under dynamical conditions, i.e., while the full reaction proceeds. The major finding of this study is evidence of a non-equilibrium transient γ phase never reported at room temperature without prior high-temperature cycling. Other findings are the variations of the extent of the line broadening and changes in the line shape during the absorption and desorption processes. They are explained by a reorganization of the hydrogen-induced dislocations in α and β phases. [Copyright &y& Elsevier]

Published
2006
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28. Compressibility and thermal expansion of LaNi5 and its substitutional derivatives (LaNi5-xMx; M=Mn, Al, Co)

Author

Joubert, J.-M., Černý, R., Latroche, M., Percheron-Guégan, A., and Yvon, K.

Subjects
*COMPRESSIBILITY, *ANISOTROPY, *CRYSTALLOGRAPHY, *THERMAL expansion, *HYDRIDES, *OPTICAL diffraction
Abstract

Abstract: The elastic properties of LaNi5 and related substitutional derivatives (LaNi4.6Mn0.4, LaNi4.7Al0.3, LaNi4.25Co0.75 and LaNi3.55Mn0.4Al0.3Co0.75) are investigated by means of room temperature compressibility and low-temperature thermal expansion (both studied by powder diffraction methods). Anisotropy of the compressibility and thermal expansion coefficients has been evidenced. The extent of this anisotropy changes, depending on the substituting element. A softening of the lattice accompanies also the substitution. These findings have been tentatively related to the nature and the quantity of the defects generated during hydride formation by those compounds. [Copyright &y& Elsevier]

Published
2005
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29. Thermal and hygric properties of Portland cement mortar after high-temperature exposure combined with compressive stress

Author

Černý, R., Totová, M., Poděbradská, J., Toman, J., Drchalová, J., and Rovnaníková, P.

Subjects
*ATMOSPHERIC water vapor, *MORTAR, *PORTLAND cement
Abstract

Thermal conductivity λ, water vapor permeability δ, and liquid moisture diffusivity κ of cement mortar are measured on specimens subjected to four types of pretreatment, namely, unloaded, mechanically loaded to 90% of compressive strength, thermally loaded by subjecting to a temperature of 800 °C for 2 h, and loaded both mechanically and thermally. The values of λ and κ are found to depend very significantly on the loading mode. The maximum differences observed compared to the unloaded samples are almost one order of magnitude for λ and as much as three orders of magnitude for κ. In contrast, the values of δ are found to increase by only about 40% compared to the basic unloaded material. It is proposed that the observed large differences in λ and κ are due to the formation of cracks and the increase of total pore volume, which were shown by visual analysis and mercury porosimetry. [Copyright &y& Elsevier]

Published
2003
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30. Mg6Ir2H11, a new metal hydride containing saddle-like [IrH4]5− and square-pyramidal [IrH5]4− hydrido complexes

Author

Černý, R., Joubert, J.-M., Kohlmann, H., and Yvon, K.

Subjects
*INTERMETALLIC compounds, *OPTICAL diffraction, *DEUTERIUM
Abstract

Mg6Ir2H11 has been synthesised by both hydrogenation of the intermetallic compound Mg3Ir at 20 bar and ∼300 °C, and sintering of the elements at ∼500 °C under 50 bar hydrogen pressure. Neutron powder diffraction on the deuteride indicates a monoclinic structure (space group P21/c, Mg6Ir2D11: a=10.226(1), b=19.234(2), c=8.3345(9) A˚, β=91.00(1)°, T=20 °C) that is closely related to orthorhombic Mg6Co2H11. It contains a square-pyramidal [IrH5]4− complex and three saddle-like [IrH4]5− complexes of which one is ordered and two are disordered. Five hydride anions H− are exclusively bonded to magnesium. The compound has a red colour, is presumably non-metallic and decomposes under 3 bar argon at 500 °C into Mg3Ir, iridium and a previously unreported intermetallic compound of composition Mg5Ir2. [Copyright &y& Elsevier]

Published
2002

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