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    Wyświetlanie 1-23 z 23
    Tytuł:
    Use of Energy Summing for Selection of Coincidence Events in Positron-Lifetime Spectroscopy
    Autorzy:
    Bec̆vár̆, F.
    C̆iz̆ek, J.
    Procházka, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/2007883.pdf
    Data publikacji:
    1999-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    Opis:
    A BaF$\text{}_{2}$ positron-lifetime spectrometer equipped with a coincidence system that represents a compromise between the traditional fast-fast and fast-slow arrangements is described. The main difference of the present configuration from both the fast-slow and fast-fast ones consists in use of a sum of the energy signals from the start and stop detectors to select the coincidence events. Quality of the spectrometer response function (≈ 150 ps FWHM for $\text{}^{22}$Na) is very close to that observed for our fast-slow configuration with the equivalent detectors but throughput of the present apparatus is increased almost by a factor of two. Moreover, the electronic scheme becomes less complicated, which has also a positive impact on its cost.
    Źródło:
    Acta Physica Polonica A; 1999, 95, 4; 448-454
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Hydrogen-Induced Defects in Palladium
    Autorzy:
    Melikhova, O.
    Čížek, J.
    Procházka, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1338026.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    61.72.-y
    Opis:
    In the present work positron annihilation spectroscopy was employed for investigation of hydrogen-induced defects in Pd. Well annealed Pd samples were electrochemically charged with hydrogen and development of defects with increasing hydrogen concentration $x_{H}$ was investigated. At low concentrations (α-phase, $x_{H}$ < 0.017 H/Pd) hydrogen loading introduced vacancies, since absorbed hydrogen segregating at vacancies lowers remarkably the vacancy formation energy. When hydrogen concentration exceeds 0.017 H/Pd, particles of palladium hydride (PdH) are formed. Stress induced by growing PdH particles leads to plastic deformation which generates dislocations and vacancies in the sample.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 752-755
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Performance of a High-Resolution Digital Positron-Lifetime Spectrometer
    Autorzy:
    Bečvář, F.
    Čížek, J.
    Procházka, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1812465.pdf
    Data publikacji:
    2008-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    Opis:
    This work describes a digital positron-lifetime spectrometer based on two ultrafast digitizers. Performance of the digital spectrometer in conditions of a routine measurement is compared with an analogue setup connected to the same detectors. It was found that engagement of the digital setup leads to an improvement of timing resolution (FWHM for $\text{}^{22}Na$) from 169 ps for the traditional analogue setup to 146 ps for the digital setup. The coincidence count rate for 1.2 MBq $\text{}^{22}Na$ source is 75-80 coinc./s for both configurations. These results clearly demonstrate the advantages of the digital timing over the traditional analogue setup.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 5; 1279-1284
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Vickers Hardness and Positron Annihilation Study of Eurofer97 and ODS Eurofer
    Autorzy:
    Bartošová, I.
    Čížek, J.
    Lukáč, F.
    Slugeň, V.
    Powiązania:
    https://bibliotekanauki.pl/articles/1196045.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    28.52.Fa
    Opis:
    This paper describes investigations of Eurofer97 and oxide dispersion strengthened version of this steel, in as received state and after annealing. Vickers hardness test was performed on the as received specimens and after annealing at various temperatures to obtain information about development of the strength of studied materials. After identifying the temperature region where significant changes of the strength take place we applied positron annihilation spectroscopy to probe the microstructural changes in ferritic/martensitic steels. An observation of phase transformation was observed in both steels at various temperatures indicating different behaviour of the base material and its strengthened version. All applied methods proved the importance of strengthening by oxides to improve properties of steels.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 702-705
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Thermal Development of Free Volumes in Nafion Membrane
    Autorzy:
    Melikhova, O.
    Čížek, J.
    Košinová, L.
    Hruška, P.
    Powiązania:
    https://bibliotekanauki.pl/articles/1033913.pdf
    Data publikacji:
    2017-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    61.66.Hq
    82.35.Lr
    Opis:
    In this work we employed positron lifetime spectroscopy for investigation of the thermal development of free volumes in H⁺ Nafion membrane over a broad range of temperatures from -150 to 150°C. Positron lifetime studies were combined with differential scanning calorimetry. Size distribution of free volumes was determined from ortho-positronium contribution to positron lifetime spectra. Our investigations revealed that the mean size of free volume holes strongly increases with temperature. On the other hand, the width of the size distribution and the positronium yield decreases with temperature. Transition temperatures corresponding to a change in the slope of the temperature dependence of ortho-positronium lifetime were identified. Results of positron lifetime spectroscopy agree well with the curve obtained by differential scanning calorimetry.
    Źródło:
    Acta Physica Polonica A; 2017, 132, 5; 1538-1542
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Precipitation Effects in Mg-Zn Alloys Studied by Positron Annihilation and Hardness Testing
    Autorzy:
    Hruška, P.
    Čížek, J.
    Vlček, M.
    Melikhova, O.
    Procházka, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1196079.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    61.72.J-
    Opis:
    In the present work positron annihilation spectroscopy combined with Vickers hardness testing were employed in order to investigate precipitation effects in Mg-Zn alloys. It was found that incoherent precipitates of a metastable Zn-rich phase formed in the samples isochronally annealed above 200C cause hardening of the alloy.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 718-721
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Investigation of Precipitation Effects in Mg-Tb and Mg-Tb-Nd Alloys
    Autorzy:
    Vlček, M.
    Čížek, J.
    Melikhova, O.
    Hruška, P.
    Procházka, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1196115.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    61.72.J-
    Opis:
    Investigation of precipitation effects in solution treated Mg-Tb and Mg-Tb-Nd alloy was performed. Solution treated alloys were compared with samples deformed by high pressure torsion to examine influence of deformation on precipitation effects. Dislocations present in samples processed by high pressure torsion can serve as diffusion channels for atoms and also as nucleation sites for precipitates. Therefore precipitation of some phases in high pressure torsion deformed samples was observed at lower temperatures than in solution treated ones.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 744-747
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Influence of Ceramic Nanoparticles on Thermal Stability of Ultra Fine Grained Copper
    Autorzy:
    Čížek, J.
    Procházka, I.
    Cieslar, M.
    Islamgaliev, R.
    Kulyasova, O.
    Powiązania:
    https://bibliotekanauki.pl/articles/1812477.pdf
    Data publikacji:
    2008-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    79.60.Jv
    Opis:
    A detailed study of the bulk ultra fine grained pure copper and copper with $Al_2O_3$ particles was carried out in the present work. The specimens were prepared by the high-pressure torsion and their microstructure was investigated by positron lifetime spectroscopy combined with transmission electron microscopy and microhardness tests. Defects in the as-deformed materials were characterized and the thermal stability of the ultra fine grained microstructure was subsequently examined in annealing experiments. An addition of $Al_2O_3$ nanoparticles was found to improve significantly the thermal stability of the ultra fine grained structure, the optimum content of $Al_2O_3$ being ≈0.5 wt.%.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 5; 1285-1292
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Defects in Zirconia Nanomaterials Doped with Rare-Earth Oxides
    Autorzy:
    Prochazka, I.
    Cizek, J.
    Melikhova, O.
    Konstantinova, T.
    Danilenko, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1338541.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.07.Wx
    61.46.Hk
    78.70.Bj
    Opis:
    Positron lifetime and coincidence Doppler broadening measurements on $ZrO_2$+3 mol.% $RE_2O_3$ (RE = Eu, Gd, Lu) nanopowders and ceramics obtained by sintering these nanopowders are reported. The initial nanopowders were prepared by a co-precipitation technique and exhibited a mean particle size of ≈ 15 nm. The nanopowders were calcined and pressure-compacted. All compacted nanopowders exhibited the prevailing tetragonal phase with at most 15% of the monoclinic admixture. Positrons in compacted nanopowders were found to annihilate almost exclusively at grain boundaries: (i) vacancy-like misfit defects along grain boundaries and (ii) larger defects situated at intersections of grain boundaries (triple points). In nanopowders, a small portion of positrons formed positronium in pores between crystallites. Sintering of nanopowders at 1500C caused a substantial grain growth and formation of ceramics. Sintering-induced grain growth led to a disappearance of the triple points and pores. The ceramics containing Eu and Gd dopants consist of mixture of the monoclinic and the tetragonal phase, while the ceramics with Lu dopant exhibits almost exclusively the tetragonal phase.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 760-763
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positron Lifetime Spectroscopy of Nanocrystalline Copper
    Autorzy:
    C̆ížek, J.
    Procházka, I.
    Vostrý, P.
    Chmelík, F.
    Islamgaliev, R. K.
    Powiązania:
    https://bibliotekanauki.pl/articles/2007957.pdf
    Data publikacji:
    1999-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    79.60.Jv
    Opis:
    Positron lifetime spectroscopy was applied to investigate the thermal stability of nanocrystalline copper prepared by severe plastic torsion deformation. Positrons annihilating in as prepared specimens exhibited free positron component τ$\text{}_{1}$ and two defect components τ$\text{}_{2}$=164 ps and τ$\text{}_{3}$=255 ps. Evolution of the lifetimes and relative intensities of all the three components with increasing annealing temperature during step-by-step isochronal annealing up to 630°C was studied. Behaviour of positrons in nanocrystalline copper could not be interpreted in the frame of conventional 3-state trapping model due to highly inhomogeneous defect distribution. Therefore a modified trapping model was developed and applied to explain the experimental results.
    Źródło:
    Acta Physica Polonica A; 1999, 95, 4; 487-495
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positron Lifetimes in Zirconia-Based Nanomaterials
    Autorzy:
    Procházka, I.
    Čížek, J.
    Kuriplach, J.
    Melikhova, O.
    Konstantinova, T.
    Danilenko, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1812546.pdf
    Data publikacji:
    2008-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    61.46.Hk
    81.05.Je
    81.07.Wx
    Opis:
    Positron lifetime spectroscopy is employed in a comparative study of several zirconia-based materials: (i) the pressure-compacted nanopowders of the three zirconia polymorphs - pure $ZrO_2$ (monoclinic), yttria-stabilized $ZrO_2$+3 mol.% $Y_2O_3$ (tetragonal) and yttria-stabilized $ZrO_2$+8 mol.% $Y_2O_3$ (cubic), (ii) ceramic materials obtained by sintering of the above two yttria-stabilized zirconia nanopowders and (iii) the tetragonal and cubic yttria-stabilized zirconia monocrystals. Positron lifetime data observed on the nanopowders suggest that the two shortest components, exhibiting lifetimes of ≈180 and ≈370 ps, arise from the annihilation of positrons trapped in defects associated with grain boundaries, presumably the vacancy-like defects and tripple points, respectively. Positron lifetime spectra observed on the ceramic materials resemble those found for the corresponding monocrystals, giving thus an additional support to the above interpretation of the nanopowders results.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 5; 1495-1499
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Defects Studies of ZnO Single Crystals Prepared by Various Techniques
    Autorzy:
    Lukáč, F.
    Čížek, J.
    Procházka, I.
    Melikhova, O.
    Anwand, W.
    Brauer, G.
    Powiązania:
    https://bibliotekanauki.pl/articles/1196118.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    61.72.J-
    Opis:
    The aim of the present work was a comparison of defects in ZnO crystals grown by various techniques available nowadays, namely hydrothermal growth, pressurized melt, Bridgman method growth and vapor phase growth. Positron annihilation spectroscopy was employed as a principal tool for characterization of defects in ZnO crystals grown by above mentioned various techniques. ZnO crystals can be divided into two groups: (i) hydrothermal grown crystals, which exhibit positron lifetime of 179-182 ps and (ii) ZnO crystals grown by the other techniques (pressurized melt, Bridgman method, vapor phase growth) which are characterized by the lower lifetimes falling in the range of 160-173 ps. Comparison of experimental data with ab initio theoretical calculations revealed that HT grown ZnO crystals contains Zn vacancies associated with hydrogen atom in a bond-centered site. On the other hand, ZnO crystals prepared by other techniques contain most probably stacking faults created by stresses induced by temperature gradients in the melt.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 748-751
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Simulation of Positron Annihilation Response to Mechanical Deformation of Nanostructured AgCo
    Autorzy:
    Melikhova, O.
    Kuriplach, J.
    Čížek, J.
    Procházka, I.
    Hou, M.
    Pisov, S.
    Zhurkin, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/1812541.pdf
    Data publikacji:
    2008-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    71.15.Pd
    61.46.Hk
    Opis:
    Nanostructured materials attract nowadays a broad attention due to their specific properties. Defects play an essential role in material properties so their characterisation is very important. The evolution of the various open volume defects in AgCo nanowire modelled samples obtained using molecular dynamics was studied. Isothermal and isoenergetic deformation mechanisms are considered. General analyses of open volume defects concerning their size and their chemical environment were performed. Positron lifetimes, binding energies, and high momentum parts of the momentum distribution of annihilationγ-quanta were calculated for selected defects.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 5; 1455-1464
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Characterization of Defects in Titanium Created by Hydrogen Charging
    Autorzy:
    Hruška, P.
    Čížek, J.
    Knapp, J.
    Melikhova, O.
    Havela, L.
    Mašková, S.
    Lukáč, F.
    Powiązania:
    https://bibliotekanauki.pl/articles/1033958.pdf
    Data publikacji:
    2017-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    61.72.-y
    Opis:
    Hydrogen interaction with vacancies in α-Ti was investigated employing positron lifetime spectroscopy combined with ab initio theoretical modeling of vacancy-hydrogen complexes. Ab initio modeling revealed that multiple hydrogen atoms up to 7 can be trapped at vacancies in the α-Ti lattice. Trapped H atoms are located close to the nearest neighbor tetrahedral sites around the centre of vacancy. Lifetimes of positrons trapped at vacancies associated with various numbers of hydrogen atoms were calculated. Positron lifetime measurement of H-loaded α-Ti samples revealed that phase transition into the hydride phase introduced dislocations. Vacancies were created by H loading as well and agglomerated into small vacancy clusters.
    Źródło:
    Acta Physica Polonica A; 2017, 132, 5; 1606-1610
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positronium Formation in Nanostructured Metals
    Autorzy:
    Čížek, J.
    Melikhova, O.
    Hruška, P.
    Vlček, M.
    Anwand, W.
    Liedke, M.
    Novotný, M.
    Bulíř, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1033937.pdf
    Data publikacji:
    2017-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    41.75.Fr
    36.10.Dr
    Opis:
    Positronium formation in Au films was studied using a magnetically guided continuous slow positron beam with variable energy. Black Au film with porous morphology was compared with conventional smooth Au film. In the smooth Au film positronium is formed on the film surface only. The black Au film exhibits porous sub-surface region containing micro-cavities interconnected with surface. Positronium is formed on inner surfaces of micro-cavities in the sub-surface region and travels through interconnected cavities towards the surface. 3-γ annihilation of ortho-positronium leaves a clear signature in two-dimensional coincidence Doppler broadening spectra. Measures of 3-γ annihilation contribution calculated from single γ-ray and coincidence Doppler broadening spectra were calculated and compared.
    Źródło:
    Acta Physica Polonica A; 2017, 132, 5; 1579-1584
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Hydrogen Interaction with Vacancies in Electron Irradiated Niobium
    Autorzy:
    Čižek, J.
    Procházka, I.
    Brauer, G.
    Anwand, W.
    Gemma, R.
    Nikitin, E.
    Kirchheim, R.
    Pundt, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1812478.pdf
    Data publikacji:
    2008-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    61.72.-y
    Opis:
    Defect studies of Nb irradiated with 10 MeV electrons were performed in the present work by means of positron annihilation spectroscopy. The lattice defects were characterized by positron lifetime spectroscopy. Moreover, defect depth profiles were studied by slow positron implantation spectroscopy. The experimental investigations were accompanied by first principles theoretical calculations of positron parameters. It was found that irradiation-induced vacancies in Nb specimens are surrounded by H, which causes a shortening of the lifetime of trapped positrons. The influence of a Pd and Cr over-layer on the H concentration in the Nb specimens was examined.
    Źródło:
    Acta Physica Polonica A; 2008, 113, 5; 1293-1299
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positronium Probing of Pores in Zirconia Nanopowders
    Autorzy:
    Prochazka, I.
    Cizek, J.
    Lukac, F.
    Melikhova, O.
    Hruska, P.
    Anwand, W.
    Liedke, M.
    Konstantinova, T.
    Danilenko, I.
    Powiązania:
    https://bibliotekanauki.pl/articles/1033930.pdf
    Data publikacji:
    2017-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.07.Wx
    61.46.Hk
    78.70.Bj
    Opis:
    In the present paper, conventional positron lifetime measurements on selected zirconia-based nanopowders are reported. The nanopowders were doped with various metal cations (Y³⁺, Eu³⁺, Gd³⁺, Lu³⁺ and Mg²⁺). Lifetime experiments were conducted in air and supplemented with mass density measurements. In a range of lifetimes, from a few ns to ≈70 ns, up to two individual lifetime components could be identified. Such observations confirmed positronium (Ps) formation with subsequent ortho-Ps pick-off annihilation as well as the occurrence of pores of different size. Pore sizes were estimated using a shape-free model of the correlation between pore size and ortho-Ps lifetime. The origins of pores are discussed on the basis of the ortho-Ps data in combination with the results of mass density measurements.
    Źródło:
    Acta Physica Polonica A; 2017, 132, 5; 1564-1567
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Defects in Ultra-Fine Grained Mg and Mg-Based Alloys Prepared by High Pressure Torsion Studied by Positron Annihilation
    Autorzy:
    Čížek, J.
    Procházka, I.
    Smola, B.
    Stulíková, I.
    Kužel, R.
    Matěj, Z.
    Cherkaska, V.
    Islamgaliev, R.
    Kulyasova, O.
    Powiązania:
    https://bibliotekanauki.pl/articles/2043304.pdf
    Data publikacji:
    2005-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    79.60.Jv
    61.72.-y
    Opis:
    Despite the favourable strength and thermal stability, a disadvantage of the Mg-based alloys consists in a low ductility. Recently it has been demonstrated that ultra fine grained metals with grain size around 100 nm can be produced by high pressure torsion. A number of ultra fine grained metals exhibit favourable mechanical properties consisting in a combination of a very high strength and a significant ductility. For this reason, it is highly interesting to examine microstructure and physical properties of ultra fine grained Mg-based light alloys. Following this purpose, microstructure investigations and defect studies of ultra fine grained pure Mg and ultra fine grained Mg-10%Gd alloy prepared by high pressure torsion were performed in the present work using positron annihilation spectroscopy combined with X-ray diffraction, TEM observations, and microhardness measurements. Positrons are trapped at dislocations in Mg and Mg-10%Gd alloy deformed by high pressure torsion. A number of dislocations increases with the radial distance r from the centre to the margin of the sample. No microvoids (small vacancy clusters) were detected. Mg-10%Gd alloy deformed by high pressure torsion exhibits a homogeneous ultra fine grained structure with a grain size around 100 nm and high dislocations density. On the other hand, pure Mg deformed by high pressure torsion exhibits a binomial type of structure which consists of "deformed regions" with ultra fine grained structure and a high dislocation density and dislocation-free "recovered regions" with large grains. It indicates a dynamic recovery of microstructure during high pressure torsion processing.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 5; 738-744
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ultra Fine-Grained Metals Prepared by Severe Plastic Deformation: A Positron Annihilation Study
    Autorzy:
    Čížek, J.
    Procházka, I.
    Kužel, R.
    Matĕj, Z.
    Cherkaska, V.
    Cieslar, M.
    Smola, B.
    Stulíková, I.
    Brauer, G.
    Anwand, W.
    Islamgaliev, R. K.
    Kulyasova, O.
    Powiązania:
    https://bibliotekanauki.pl/articles/2043303.pdf
    Data publikacji:
    2005-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    79.60.Jv
    Opis:
    Recent investigations of ultra fine-grained metals (Cu, Fe, Ni) performed within a Prague-Rossendorf-Ufa collaboration will be reviewed. The specimens were prepared by severe plastic deformation: the high-pressure torsion and equal channel angular pressing. Positron annihilation spectroscopy was used as the main method including (i) the conventional lifetime and the Doppler broadening measurements with $\text{}^{22}$Na and (ii) the slow-positron implantation spectroscopy with the Doppler broadening measurement. Other methods were also involved: transmission electron microscopy, X-ray diffraction, and microhardness. First, the mean grain size was determined and defects were identified in the as-deformed materials. Defects concentration and spatial distribution were studied in detail. Dislocations situated in distorted regions along grain boundaries, and a few-vacancy clusters distributed homogeneously inside dislocations-free grains, were observed in the ultra fine-grained Cu, Fe, and Ni. Subsequently, the thermal evolution of the ultra fine-grained structures during isochronal annealing was studied.
    Źródło:
    Acta Physica Polonica A; 2005, 107, 5; 745-752
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    New thoughts on the prospects of petroleum potential in the Eger rift (Czech Republic)
    Rozważania o nowych możliwościach przemysłu naftowego na obszarze rowu tektonicznego w okolicy miasta Eger (Czechy)
    Autorzy:
    Sidorova, M.
    Cizek, P.
    Galant, Y.
    Pinka, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/219164.pdf
    Data publikacji:
    2017
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    rów tektoniczny
    policykliczne węglowodory aromatyczne
    rift structures
    polycyclic aromatic hydrocarbons
    correlation analysis
    sources of hydrocarbons
    Opis:
    The present paper highlights the problem related to the source of hydrocarbons in the Eger Rift in Czech Republic. The authors discuss the existence of polygenetic deep sources of hydrocarbons. The investigations are based on direct indicators of Polycyclic Aromatic Hydrocarbons (abbr. PAHs). Among the diverse components of PAHs has been recognized typomorphic oil association – videlicet: phenanthrene, chrysene, pyrene and benzo(a)pyrene. On the basis of new geochemical, geological and mathematical data the oil and gas potential of Eger Rift is also discussed.
    W pracy omówiono problemy związane z obecnością źródeł węglowodorów na obszarze rowu tektonicznego w okolicy miasta Eger (Czechy). Autorzy dyskutują o możliwej obecności w regionie głębokich złożach węglowodorów. Analizy prowadzone są w oparciu o bezpośrednie wskaźniki obecności policyklicznych węglowodorów aromatycznych (PAH). Spośród węglowodorów wyodrębniono typomorficzne produkty ropopochodne: fenantren, chrysen, piren oraz benzoalfapireny. Na podstawie nowo uzyskanych wyników badań geochemicznych, geologicznych oraz w oparciu o dane matematyczne analizowano potencjalne zasoby gazu i ropy naftowego na obszarze rowu tektonicznego w okolicy miasta Eger.
    Źródło:
    Archives of Mining Sciences; 2017, 62, 1; 203-214
    0860-7001
    Pojawia się w:
    Archives of Mining Sciences
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Resonance contributions to low-energy electron collisions with molecular hydrogen
    Autorzy:
    Horácek, J.
    Cížek, M.
    Houfek, K.
    Kolorenc, P.
    Pichl, L.
    Powiązania:
    https://bibliotekanauki.pl/articles/148461.pdf
    Data publikacji:
    2003
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    electron scattering
    molecules
    attachment
    vibrational excitation
    Opis:
    Calculations of electron dissociative attachment and vibrational excitation of molecular hydrogen by low-energy electrons based on an improved nonlocal resonance model are reported. The role of the rotational excitation of the target molecules is discussed.
    Źródło:
    Nukleonika; 2003, 48, 2; 109-112
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Rozdrobnienie ziarna stopu AlMn1Cu przez duże odkształcenie plastyczne (SPD)
    Grain Refinement of AlMn1Cu Alloy by Severe Plastic Deformation
    Autorzy:
    Rusz, S.
    Čížek, L.
    Dutkiewicz, J.
    Tylšar, S.
    Salajka, M.
    Divin, V.
    Kedroň, J.
    Klos, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/211914.pdf
    Data publikacji:
    2014
    Wydawca:
    Sieć Badawcza Łukasiewicz - Instytut Obróbki Plastycznej
    Tematy:
    powtarzalna obróbka plastyczna
    metoda ECAP
    twardość
    analiza metalograficzna
    SPD process
    severe plastic deformation
    ECAP method
    hardness
    metallographic analysis
    Opis:
    Duże odkształcenie plastyczne SPD to technika stosowana w produkcji materiałów o ultradrobnej strukturze (UFG), oparta o intensywne rozdrobnienie ziarna. Dla procesu tego bezwzględnie najważniejsza jest sprawność. Najbardziej znanymi technologiami, które są aktualnie najintensywniej rozwijane są: ECAP, C2S2, CONFORM, HPT, CCDC, ARB oraz CGP. W opracowaniu dokonano analizy technologii ECAP, gdzie istotna poprawa sprawności procesu osiągana jest przez zmianę technologii narzędzia, a przez to zmianę ścieżki deformacji, co znacznie przybliża wizję wdrożenia tej technologii do przemysłu. Wpływ zmiany geometrii wkładki narzędzi ECAP na osiągnięcie wysokiego stopnia odkształcenia, z czym wiąże się wzrost sprawności procesu (tzn. osiągnięcie wymaganej średniej wielkości ziarna przy mniejszej ilości przejść przez narzędzie formujące) przedstawiono na przykładzie stopu AlMn1Cu wyprodukowane przez firmę AL Invest Bridlicna a.s. Dokonano zarówno matematycznej symulacji, jak i fizycznego przeciśnięcia próbek przez narzędzie ECAP. Badanie zostało skoncentrowane na podwyższeniu twardości i średniej wielkości ziarna w klasycznej geometrii kanałów ECAP w porównaniu z narzędziem ECAP o zmodyfikowanej geometrii, gdzie kanał poziomy został odchylony o 20° względem osi „x”, oraz w porównaniu z geometrią, gdzie w kanale poziomym utworzona została linia śrubowa (elektroerozyjnie). Dodatkowo, dla poszczególnych rodzajów geometrii ECAP wykonana została analiza metalograficzna struktury z wykorzystaniem transmisyjnej mikroskopii elektronowej (TEM) oraz przez pozyskanie obrazów dyfrakcyjnych w wybranych obszarach próbki (SAED). Sprawność nowego projektu została jednoznacznie potwierdzona.
    Severe plastic deformation is basic process used in technologies for production of ultra-fine grained materials (UFG), using the principle of high disintegration of grain. Efficiency of the given process is therefore of utmost importance. The best known technologies that are currently being intensively developed are the following ones: ECAP, C2S2, CONFORM, HPT, CCDC, ARB and CGP. The paper analyses the ECAP technology, where substantial enhancement of the process efficiency is achieved by change of tool geometry and therefore by change of deformation route, which significantly approaches implementation of this technology into industrial practice. Influence of change of geometry of the ECAP tool insert on achievement of high degree of deformation and thus on the increased efficiency of the process (i.e. achievement of the required mean grain size at significantly lower number of passes through the forming tool) has been demonstrated on the alloy AlMn1Cu manufactured by the company AL Invest Bridlicna a.s. Both mathematical simulation and practical extrusion of samples through the ECAP tool have been performed. Research was focused on the resulting magnitude of hardness and mean grain size in classical geometry of ECAP channels in comparison with modified geometry of the ECAP tool, where horizontal channel was deflected in respect to the axis “x“ by 20°, and in comparison with geometry, when helical line was created (by sparking) into part of horizontal channel. Moreover, metallographic analysis of structure realised on TEM and SAED was applied to individual types of ECAP channel geometry. Efficiency of new design has been confirmed unequivocally.
    Źródło:
    Obróbka Plastyczna Metali; 2014, 25, 2; 87-98
    0867-2628
    Pojawia się w:
    Obróbka Plastyczna Metali
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Ultrafine Grain Refinement of AlMn1Cu and AZ 31 Alloys by SPD Process
    Rozdrobnienie ziarn stopów AlMn1Cu i AZ 31 do rozmiarów ultrametrycznych z zastosowaniem procesu SPD
    Autorzy:
    Rusz, S.
    Cizek, L.
    Salajka, M.
    Tylsar, S.
    Kedron, J.
    Michenka, V.
    Donic, T.
    Hadasik, E.
    Klos, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/352152.pdf
    Data publikacji:
    2014
    Wydawca:
    Polska Akademia Nauk. Czytelnia Czasopism PAN
    Tematy:
    severe plastic deformation
    ECAP method
    hardness
    microstructure
    duże odkształcenia plastyczne
    metoda ECAP
    twardość
    mikrostruktura
    Opis:
    One of the ways to the more effective use of metallic materials is their processing by forming. At present in this the area the use of the process of severe plastic deformation (SPD process), leading to a refinement of the structure (materials with UFG structure) and thus to achievement of higher level of their utility value, is expanding. AlMn1Cu alloy is commercially produced aluminum alloy by the company Al Invest Bridlicna (the cast strip with a mild reduction by rolling up to 10% to the thickness of 10 and 15 mm, which has its uses especially in engineering. AZ31 alloy is commercially produced aluminum alloy after casting and extrusion at 400°C on final rod with 20 mm diameter. For experimental purposes from the belts of alloys the test samples of the underlying dimensions of 10x10 mm length 40 mm (geometry with channel deflection 20°) and 15x15 mm length 60 mm (geometry with helix matrix) in the direction of rolling were made. All three instruments are made of high tool steel - HOTVAR. For compare the influence of geometry ECAP tool on structure refining was used AlMn1Cu and AZ31 alloys were used three specially made tools ECAP, differing mainly in the construction design.
    Jednym ze sposobów bardziej efektywnego kształtowania plastycznego metali jest metoda dużych odkształceń plastycznych Aktualnie do tego celu wykorzystywany jest proces SPD. w wyniku którego osiąga się wysokie wartości odkształcenia materiału z ultra drobnoziarnistą strukturą. Prowadzi to do wzrostu właściwości wytrzymałościowych, przy nieznacznym obniże- niu plastyczności. W artykule przedstawiono wyniki badań dwóch stopów - stop aluminium AlMnlCu, który jest produkowany w formie blachy grubości 10 lub 15 mm z zastosowaniem w przemyśle maszynowym oraz stop magnezu AZ31. który po odlaniu jest wyciskany w temperaturze 400°C z pręta o średnicy 60 mm na średnicę 20 mm. Do eksperymentów użyto próbek o rozmiarach 10x10-40 mm z odchyleniem kanału narzędzia ECAP o 20° od kierunku poziomego oraz próbki o rozmiarach 15x15-60 mm z nową geometrią kanału narzędzia ECAP (część kanału w kształcie śruby) dla zwiększenia odkształcenia w poszczególnych przejściach próbki narzędziem ECAP. Uzyskane wyniki twardości oraz struktury, przy użyciu wyżej podanych geometrii narzędzia ECAP. były porównywane oddzielnie u obu stopów.
    Źródło:
    Archives of Metallurgy and Materials; 2014, 59, 1; 359-364
    1733-3490
    Pojawia się w:
    Archives of Metallurgy and Materials
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-23 z 23

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