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    Wyświetlanie 1-4 z 4
    Tytuł:
    Positron Annihilation in $MnFe_2O_4$/MCM-41 Nanocomposite
    Autorzy:
    Wiertel, M.
    Surowiec, Z.
    Gac, W.
    Budzyński, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1339369.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    78.70.Bj
    34.80.Lx
    78.67.Bf
    62.23.Pq
    68.43.-h
    75.50.Gg
    78.47.D-
    Opis:
    In the paper results of studies of $MnFe_2O_4$/MCM-41 nanocomposites have been presented. The influence of manganese ferrite loading on changes of porous properties of mesoporous MCM-41 structure was studied by means of $N_2$ sorption/desorption method and positron annihilation lifetime spectroscopy. Disappearance of the longest-lived ortho-positronium component ($τ_5$) of pure MCM-41 mesoporous material in the positron annihilation lifetime spectra of $MnFe_2O_4$/MCM-41 measured in vacuum is a result of either o-Ps quenching or the Ps inhibition mechanism. Filling of pores in the studied nanocomposites by air at ambient pressure causes partial reappearance of the ($τ_5$) component except for the sample with maximum ferrite content. Both the ($τ_5$) component lifetime and intensity are suppressed together with increasing $MnFe_2O_4$ content by chemical quenching and inhibition of Ps formation occur. Observed anti-quenching effect of air is a result of two processes: neutralization of some surface active centres acting as inhibitors and considerably weaker paramagnetic quenching by $O_2$ molecules.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 793-797
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Influence of Reduction Process on the Iron-Molybdenum Nanoparticles in Modified MCM-41 Silica
    Autorzy:
    Surowiec, Z.
    Wiertel, M.
    Gac, W.
    Budzyński, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1381974.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    76.80.+y
    78.67.Bf
    78.67.Rb
    75.20.-g
    Opis:
    Iron-molybdenum silica mesoporous materials were obtained by the application of direct hydrothermal method. The influence of high temperature samples reduction in the $H_2$ flow on their structural and magnetic properties was studied. Four samples with different metal contents relative to silica were investigated. The study was carried out by means of X-ray diffraction, $\text{}^{57}Fe$ Mössbauer spectroscopy and the temperature programmed reduction method. With an increasing metals content, primary pores of MCM-41 transformed into the bottle-like pores, and then into the slit-like ones. Reduction and heat treatment caused the α-Fe, $Fe_2Mo$, and Fe-Mo alloy formation. Iron and molybdenum atoms after being released into the silica matrix, where they were embedded, create clusters or crystallites. It was observed that the high temperature reduction caused partial transformation of highly dispersed Fe-Mo oxides species initially embedded in silica walls into crystallites big enough to give magnetic sextet component in the Mössbauer spectra.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 846-849
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    The Synthesis and Properties of High Surface Area $Fe_{2}O_{3}$ Materials
    Autorzy:
    Surowiec, Z.
    Gac, W.
    Wiertel, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1506442.pdf
    Data publikacji:
    2011-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    76.80.+y
    78.67.Bf
    78.67.Rb
    75.20.-g
    Opis:
    Two types of the silica materials were used for the preparation of iron oxides. The MCM-48 type silica support and wide-pore silica gel were impregnated with iron nitrates. The samples were investigated by the nitrogen adsorption/desorption method, X-ray diffraction, scanning electron microscopy, and $\text{}^{57}Fe$ Mössbauer spectroscopy. Redox properties were studied by the temperature programmed reduction method. Strongly dispersed hematite was evidenced on the supports. An application of the MCM-48 silica mesoporous materials led to the development of the oxide phases within the ordered porous structure. The detailed temperature programmed reduction studies evidenced slight differences of the redox properties of the species located within the silica templates and after their removal. Magnetic properties of iron oxides were related to the porous structure of the silica supports. The Mössbauer study of high surface area materials Fe/$SiO_{2}$ and Fe/MCM-48 type silicate templates revealed existence of ferro- and superparamagnetic phases. The relative contribution of the superparamagnetic doublet component in Mössbauer spectra is 15% and 80% for Fe/$SiO_{2}$/c and Fe/MCM-48/c samples, respectively.
    Źródło:
    Acta Physica Polonica A; 2011, 119, 1; 18-20
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positron Annihilation Studies of Mesoporous Iron-Molybdenum Modified MCM-41 Silica
    Autorzy:
    Surowiec, Z.
    Wiertel, M.
    Gac, W.
    Budzyński, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1339204.pdf
    Data publikacji:
    2014-03
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    34.80.Lx
    78.67.Bf
    78.70.Bj
    62.23.Pq
    78.67.Sc
    Opis:
    Iron-molybdenum modified MCM-41 mesoporous materials were obtained by the application of direct hydrothermal method. An incorporation of iron and molybdenum ions in the synthesis stage led to structural changes of the MCM-41 support. With an increasing metals content, cylindrical pores of silica are destroyed. X-ray diffraction investigations indicated that both iron and molybdenum ions were first embedded in the silica walls and then formed highly dispersed species in the pores. The porous structure of the studied samples was examined by means of $N_2$ adsorption/desorption and PALS methods. The longest-lived o-Ps lifetime component remains constant but its intensity monotonically decreases, except for the sample with the highest metals content. These results indicate that an effect of o-Ps formation inhibition occurs.
    Źródło:
    Acta Physica Polonica A; 2014, 125, 3; 789-792
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-4 z 4

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