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    Wyświetlanie 1-9 z 9
    Tytuł:
    Influence of annealing temperature on structural and magnetic properties of MnFe2O4 nanoparticles
    Autorzy:
    Surowiec, Z.
    Wiertel, M.
    Gac, W.
    Budzyński, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/146127.pdf
    Data publikacji:
    2015
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    manganese ferrite
    MCM-41 porous silica
    Mössbauer effect
    superparamagnetic nanoparticles
    Opis:
    Nanoparticles of manganese ferrite were obtained by the impregnation of highly ordered mesoporous MCM-41 silica support. The investigated sample contained 20% wt. Fe. The obtained nanocrystallites were strongly dispersed in silica matrix and their size was about 2 nm. The sample annealing at 500°C led to increase of particle size to about 5 nm. The Mössbauer spectroscopy investigations performed at room temperature show on occurrence of MnFe2O4 nanoparticle in superparamagnetic state for the sample annealed in all temperatures. The coexistence of superparamagnetic and ferromagnetic phase was observed at liquid nitrogen temperature. The sample annealed at 400°C and 500 °C has bigger manganese ferrite particle and better crystallized structure. One can assign them the discrete hyperfi ne magnetic field components.
    Źródło:
    Nukleonika; 2015, 60, 1; 137-141
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Study on the effect of atmospheric gases adsorbed in MnFe2O4/MCM-41 nanocomposite on ortho-positronium annihilation
    Autorzy:
    Wiertel, M.
    Surowiec, Z.
    Budzyński, M.
    Gac, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/146949.pdf
    Data publikacji:
    2015
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    manganese ferrite
    MCM-41 silica
    nanocomposite
    o-Ps quenching
    positronium annihilation
    Opis:
    In this paper, results of positron annihilation lifetime spectroscopy (PALS) studies of MnFe2O4/MCM- -41 nanocomposites in N2 and O2 atmosphere have been presented. In particular, the influence of manganese ferrite loading and gas filling on pick-off ortho-positronium (o-Ps) annihilation processes in the investigated samples was a point of interest. Disappearance of the longest-lived o-Ps component with τ5 present in the PAL spectrum of initial MCM-41 mesoporous material in the PAL spectra of MnFe2O4-impregnated MCM-41 measured in vacuum is a result of either a strong chemical o-Ps quenching or the Ps inhibition effects. The intensity I4 of the medium-lived component initially increases, reaching a maximum value for the sample with minimum manganese ferrite content, and then decreases monotonically. Analogous dependence for the intensity I3 of the shortest-lived component shows a maximum at higher MnFe2O4 content. Filling of open pores present in the studied nanocomposites by N2 or O2 at ambient pressure causes partial reappearance of the τ4 and τ5 components, except a sample with maximum ferrite content. The lifetimes of these components measured in O2 are shortened in comparison to that observed in N2 because of paramagnetic quenching. Anti-inhibition and anti-quenching effects of atmospheric gases observed in the MnFe2O4/MCM-41 samples are a result of neutralization of some surface active centers acting as inhibitors and weakening of pick-off annihilation mechanism, respectively.
    Źródło:
    Nukleonika; 2015, 60, No. 4, part 1; 783-787
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    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:
    Synthesis and characterization of iron - cobalt nanoparticles embedded in mesoporous silica MCM - 41
    Autorzy:
    Surowiec, Z.
    Wiertel, M.
    Budzyński, M.
    Gac, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/147878.pdf
    Data publikacji:
    2013
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    cobalt
    iron
    MCM-41 porous silica
    Mössbauer effect
    superparamagnetic nanoparticles
    Opis:
    Fe1.xCox/MCM-41 nanocomposite materials were prepared by wet impregnation of the silica mesoporous support with aqueous solution of iron and cobalt salt mixtures. Samples, after calcination, were reduced at 573 K in order to obtain homogeneous distribution of (Fe-Co)3O4 oxide species over the MCM-41 support. Bimetallic systems were achieved through high temperature reduction, carried out at 1073 K. The temperature-programmed reduction studies indicated complex nature of the oxide species. The phase analysis of the obtained samples after low temperature reduction process carried out by means of X-ray diffraction method and using 57Fe Mossbauer spectroscopy revealed the presence of nanostructured magnetite- and maghemite-like phases. The samples with higher cobalt contents (x . 0.2) contained additionally bimetallic phases. The complete transformation of oxide phases to bimetallic Fe-Co systems occurred during reduction process in hydrogen at 1073 K. It was observed that high temperature processing caused partial transformation of highly dispersed iron oxide nanocrystallites into fayalite species embedded in the silica walls.
    Źródło:
    Nukleonika; 2013, 58, 1; 87-92
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Positron annihilation studies of mesoporous iron modified MCM-41 silica
    Autorzy:
    Wiertel, M.
    Surowiec, Z.
    Budzyński, M.
    Gac, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/147950.pdf
    Data publikacji:
    2013
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    iron
    MCM-41 silica mesoporous materials
    N2 sorption
    positron annihilation
    positron lifetime spectra
    Opis:
    MCM-41 silica materials modified by iron incorporation in the stage of its synthesis were investigated. The aim of the studies was determination of the nature of iron species and the influence of its content on the structural changes of materials and following the changes of their properties. For this purpose, the N2 sorption/desorption method and positron annihilation lifetime spectroscopy (PALS) were used. Disappearance of the longest-lived ortho-positronium (o-Ps) component (tau5) present in the PALS spectra of the initial MCM-41 material in the spectra of Fe-modified MCM-41 measured in vacuum is a result of a strong chemical o-Ps quenching and/or the Ps inhibition mechanism. Filling of pores by air or N2 at ambient pressure causes reappearance of the (tau5) component with lifetime shortened in comparison to that observed in vacuum for pure MCM-41 to the extent which can be explained by usual paramagnetic quenching in air. In contrary to the tendency observed for (tau5) lifetime which is practically independent of Fe content, the relevant intensity I5 monotonically decreases. This fact suggests that only inhibition of Ps formation occurs for the samples in air. Observed anti-quenching effect of air seems to be a result of competition of two processes : neutralization of surface active centres acting as inhibitors and considerably weaker paramagnetic quenching by O2 molecules.
    Źródło:
    Nukleonika; 2013, 58, 1; 245-250
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    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
    Tytuł:
    An application of Mössbauer spectroscopy in the studies of iron - molybdenum silica mesoporous materials
    Autorzy:
    Surowiec, Z.
    Wiertel, M.
    Marynowska, A.
    Gac, W.
    Zawadzki, W.
    Powiązania:
    https://bibliotekanauki.pl/articles/147814.pdf
    Data publikacji:
    2013
    Wydawca:
    Instytut Chemii i Techniki Jądrowej
    Tematy:
    iron
    MCM-41 porous silica
    molybdenum
    Mössbauer effect
    superparamagnetic nanoparticles
    Opis:
    Iron-molybdenum silica mesoporous materials were obtained by the application of direct hydrothermal method. Four samples with different metal contents relative to silica were investigated. 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 initially transformed into bottle-ink type pores, and then into the slit-like ones. Mössbauer spectroscopy investigations indicated that Fe ions were embedded in the silica walls and then formed nanosized crystallites in the pores. Superparamagnetic phase was observed at liquid nitrogen temperature.
    Źródło:
    Nukleonika; 2013, 58, 1; 137-141
    0029-5922
    1508-5791
    Pojawia się w:
    Nukleonika
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-9 z 9

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