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  • 2000-2004  (14)
Material
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Bingley : Emerald
    Environmental management and health 12 (2001), S. 67-78 
    ISSN: 0956-6163
    Source: Emerald Fulltext Archive Database 1994-2005
    Topics: Medicine , Economics
    Notes: The continent of Antarctica consists of 14 million km2, roughly equivalent to the whole of South America, and is of immense interest to humanity, in particular to the countries of the Antarctic Treaty. The Antarctic continent is the continent of superlatives: it is almost isolated from the rest of the continents, and is severely cold, windy, and dry. In winter, the Antarctic area increases to nearly 32 million km2, because of formation of a 1,000km wide ice-belt. The average depth of ice on the continent is in the order of 2,000m, and in the transantarctic region this depth is 4,800 meters. Antarctica is the biggest sweet water reservoir of the planet earth. Icebergs are common and huge ones (190km in length and 130km wide) have also been observed. The minimum temperature recorded (–89.2°C) at Vostok (Russian base) on 21 July 1983 is also the minimum recorded environmental temperature on the planet earth. Because of extreme temperature variations the Antarctic winds have high velocity. The environment is very dry and at the center of the continent the dryness is of the same magnitude as in the driest desert anywhere on the planet. This is the only uninhabited continent of the planet, except for some 50 research bases which cover an insignificant area located on the continent and the Antarctica Peninsula. Because of its economic, strategic, geopolitical, scientific, meteorological, and oceanographic importance and possible exploitation in the future, Antarctica has been attracting greater attention every day. Antarctica is basically concentrated around the South Pole and it touches the Atlantic, Pacific, and Indian Oceans. Brazil, in common with many other nations, has geopolitical interests and in untapped mineral deposits (considerable deposits of coal, petroleum, gas). In the south, where the Atlantic, Pacific and Indian Oceans meet, the cold water of Antarctica is the habitat housing hundreds of species of sea life. Unrestricted and unbalanced exploitation of Antarctica could cause changes in the meteorological and oceanographic balance. In the present paper, the Brazilian Antarctic Program, and summarized results of studies of Antarctic soil, rocks, and sediments are reported.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1662-9779
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of radioanalytical and nuclear chemistry 246 (2000), S. 57-60 
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract 151Eu Mössbauer spectrum of IR-transmitting calcium aluminate glass, 60CaO·32Al2O3·5Fe2O3·3Eu2O3, consists of a broad peak due to distorted Eu(III) with δ and Δ values of 0.91 and −2.02 mm·s−1, respectively. Debye temperatures (θD) of 360 and 320 K were obtained from the temperature dependence of absorption area (A) and that of δ, respectively. These θD values indicate that Eu(III) atoms occupy substitutional sites of distorted Al(III)O4 tetrahedra in calcium aluminate glass. The δ value of 0.62 mm/s obtained from the heat-treated sample (glass ceramic) indicates that Eu(III)-O bonds became less covalent. A smaller Δ value of −1.20 mm·s−1 was obtained for Eu(III) in the glass ceramic, indicating less distorted Eu(III)O4 tetrahedra.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract 119Sn conversion electron Mössbauer spectroscopy, X-ray diffractometry and energy dispersive X-ray analysis (EDAX) were employed to investigate microstructure, composition and phases present in as-electroplated Sn-Cr and Sn-Cr-Zn alloys deposited on copper substrates. In the Sn-Cr deposits Cu, β-Sn, Cr-Sn phases can be identified by X-ray diffractometry. The phase composition is significantly different between the samples prepared with relatively higher and lower current densities. In the diffractograms of Sn-Cr-Zn deposits Cu, β-Sn, Zn phases can be well identified. A small intensity amorphous peak is also present, which can perhaps be associated with the presence of some amorphous Zn and Sn alloy. 119Sn Mössbauer spectra of Sn-Cr deposits exhibit an asymmetric broad main line centered near the isomer shift characteristic of β-Sn as well as they contain a small component near the zero velocity which can be attributed to a SnO2 phase based upon its characteristic. 119Sn Mössbauer spectra of Sn-Cr-Zn deposits are roughly similar to those of Sn-Cr deposits although the Mössbauer parameters of the third phase are different and vary with the Zn content. The presence of SnO2 on the surface mainly in the Sn-Cr samples can be attributed to the corrosion process in the air.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of radioanalytical and nuclear chemistry 246 (2000), S. 107-112 
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Introduction of the Mössbauer nuclei 57Fe into Hg-1223 phase and that of 57Fe and 151Eu into Tl-1212 and Tl-1223 superconductors were investigated. Samples of high phase purity were obtained. Scanning electron microscopy and optical microscopy in normal and polarized light were employed to study the microstructure of the specimens. Energy dispersive X-ray analysis showed that 57Fe in the Hg-based samples and 57Fe as well as 151Eu in the Tl-based compounds, entered superconducting phases. Incorporation of Eu3+ into the superconducting phase favored the formation of the Tl-1212 phase. Mössbauer spectroscopy showed that Eu3+ entered the Ca-site. Two doublets found in the 57Fe Mössbauer spectra in both the Hg-1223 and the Tl-1223 phase referred to two different micro-environments of Fe3+. The assignment of the 57Fe Mössbauer spectra was made under the assumption that Fe favored the 1223 phase. Fe3+ may replace Cu in both the square pyramidal, five-fold oxygen coordinated Cu sites between the Ca and Ba-(Sr)-O layers, and in the square planar, four-fold oxygen coordinated Cu sites the Ca layers in the superconducting phases in both the Hg- and the Tl-based materials. From the relative areas of the two doublets, we concluded that the Fe3+ preferred the square planar Cu site.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of radioanalytical and nuclear chemistry 246 (2000), S. 117-121 
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract 57Fe Mössbauer spectroscopy measurements were performed on the perovskite compounds Eu0.7Pr0.3Ba2(Cu0.99 57Fe0.01)3O7-δ, EuBa1.5Pr0.5(Cu0.99 57Fe0.01)3O7-δ and EuBa1.3Pr0.7(Cu0.99 57Fe0.01)3O7-δ. The observed 57Fe Mössbauer spectra provided an evidence for the correct site assignment of subspectra originating from 57Fe in different microenvironments. Apart from a minor component which was assigned to the 57Fe in the Cu(2) site of the copper oxide plane, all the subspectra could be attributed to the 57Fe in the Cu(1) copper oxide chain site with a fourfold (doublet D1), fivefold (doublet D2) or sixfold (doublet D3) oxygen coordination. In contrast, in the compound EuBa2(Cu0.99 57Fe0.01)3O7-δ the 6-coordinated (D3) species has not been observed. The substitution of Pr for Eu or for Ba resulted in an increased occupancy of the O(5) antichain oxygen sites, which was explained by the charge neutrality criterion. Especially, the replacement of Ba2+ with Pr3+ led to an unusually high degree of occupancy of O(5) sites. In the 57Fe Mössbauer spectra the relative area of the 6-coordinated species (D3) increased, and that of the 4-coordinated one (D1) vanished completely in the case when Pr was substituted for Ba. Furthermore, the proportion of the 6-coordinated (D3) species increased at the expense of the 5-coordinated (D2) one with an increasing concentration of Pr at the Ba site. These experimental results are consistent with the variety of Mössbauer results reported so far.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A real specimen originating from the primary circuit of a VVER-440 type pressurized water cooled nuclear reactor has been studied by Conversion Electron Mössbauer Spectroscopy (CEMS) in order to find out how the AP-CITROX decontamination procedure modifies the structure and composition of the surface oxide layer of stainless steel which is used in the steam generator. Other methods like voltammetry, gravimetry, and SEM-EDAX were also applied to characterize the samples and to help the interpretation of CEMS results. It was found that, in contradiction with expectations, the presence of the surface magnetite layer could not be convincingly identified even on the non-decontaminated sample. This finding together with the relatively weak Mössbauer signals indicated that the surface oxide layer is strongly Fe-depleted. It was also concluded that the upper layer of the bulk steel (under the oxide layer) has an altered composition probably due to irradiation-enhanced diffusion of the metallic constituents. It was established that the AP-CITROX decontamination procedure does not exert detrimental effects on the thickness and composition of the surface oxide layer.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract 57Fe and 151Eu Mössbauer spectroscopy as well as RF susceptibility measurements were applied to study the effects of Pr substitution either into the rare earth or into the Ba site in Eu1−x Pr x Ba2Cu3O7−δ and EuBa2−x Pr x Cu3O7−δ, respectively. Site mixing of Pr between the rare earth and Ba sites could be excluded by the utilization of 57Fe Mössbauer spectroscopy. It was found that there exists a correlation between the 151Eu isomer shift and the onset temperature of the superconducting transition independent of the location of Pr. RF susceptibility measurements provide an evidence for a difference in the magnetic moment of Pr substituted for the Eu or Ba sites. The obtained results can be explained by hole filling as the dominant effect of Pr substitution.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of radioanalytical and nuclear chemistry 246 (2000), S. 379-384 
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract 57Fe transmission Mössbauer spectroscopy and X-ray diffractometry were used to study clay mineral samples originated from two different regions (Um-arrazm and Alkawasim) of Libya in order to get information about their mineralogical composition to assess their potential for use in the Libyan oil industry. In the samples originated from Um-arrazm calcite, akaganeite and nontronite while in the samples originated from Alkawasim quartz, akaganeite, montmorillonite, kaolinite, illite, mica and hematite were identified with different ratios by using diffraction method. The differences in the phase composition of iron-containing phases of samples from different localities have reflected in the complex Mössbauer spectra at both 300 K and 80 K. For the samples originated from Um-arrazm the Mössbauer parameters of subspectra were identified as nontronite and akaganeite.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract 151Eu and 141Pr Mössbauer spectroscopy was applied to study the effects of Pr substitution for Eu or Ba atoms in Eu1-x Pr x Ba2Cu3O7-δ and EuBa2-x Pr x Cu3O7-δ, respectively. It was found that there exists a correlation between the 151Eu isomer shift and the onset temperature of the superconducting transition, independent of the location of Pr. This shows that the extra electrons provided by the Pr increase the electronic density in the copper oxide planes and in the 4f orbitals of Eu31, simultaneously. The polycrystalline compound EuBa1.3Pr0.7Cu3O7-δ has been investigated by 141Pr Mössbauer spectroscopy. The observed 141Pr isomer shift, δ(4.2 K) = 0.10(15) mm/s relative to PrF3, reflects a valence state of 3+ for the Pr located at the Ba site in EuBa1.3Pr0.7Cu3O7-δ, being in contrast to the valence state of 3.4+ found earlier for Pr which was situated at the rare earth site. This means that the valence state of Pr substituted for Eu is different from that of Pr substituted for Ba. These results suggest that the suppression of superconductivity by Pr substituted for the rare earth atoms is a consequence of the hole filling effect.
    Type of Medium: Electronic Resource
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