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The quality of drinking water is a major public concern, but the detection of most potential pathogens is not always included in drinking water hygienic monitoring or is only assessed with highly biased cultivation-based methods. In this study, the occurrence of Pseudomonas aeruginosa and Legionella spp. was examined with taxon-specific PCRs in samples taken at ten points of a municipal drinking water supply system in three months. Sequence analysis confirmed the positivity of samples and revealed a diverse community of legionellae. The results showed that chlorination was an important and effective disinfection method against pathogenic bacteria in drinking water, but pathogenic bacteria could reoccur in the system farther away from the chlorination point. No strong correlation was found between the presence of the investigated potentially pathogenic bacteria and the measured abiotic and biotic parameters within the investigated range. It is hypothesized that instead of physicochemical parameters, the main factors influencing the presence of pathogens in the drinking water were rather the composition of the microbial community, the biotic interactions between individual non-pathogenic and pathogenic microorganisms (competition or promotion of growth) and the structure of biofilm grown on the inner surface of the supply system.

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Abstract  

Perovskite oxides of composition (Sr1-x Ca x )(Fe0.5Co0.5)O3- were investigated for CO2 absorption properties and were proved to be useful as materials for CO2 absorption in the temperature range from 550 to 850 °C. The absorption rate of CO2 increased with Ca doping. The mechanical treatment of perovskite oxides for several minutes, especially for the oxides containing a small amount of Ca, was found to be effective for activating the oxides for CO2 absorption and for reducing the starting temperature of CO2 absorption by about 80 °C. However, it was not less effective to treat the oxides for a long time. The site distortion due to Sr and Ca ions at site A and the mixed valence states at site B were confirmed to be effective for CO2 absorption at high temperatures. During the absorption of CO2, a spinel compound was formed according to the following reaction: 2(Sr,Ca)(Fe,Co)O2.5 + CO2 (Sr,Ca)CO3 + (Sr,Ca)(Fe,Co)2O4.

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Abstract  

Perovskite type oxides of Ba x Ca1−x Fe0.8Co0.2O3−δ withx=0.95, 0.8, 0.6 and 0.4 have been studied by57Fe transmission Mössbauer spectroscopy. The microenvironment of Fe was found to be sensitively dependent on the Ba to Ca ratio and, more importantly, on the oxygen content. At high Ba concentration, magnetic relaxation is indicated by the Mössbauer spectra. Identification of the various sextets and doublets in the Mössbauer spectra is attempted by the help of thermal treatments of the samples in air and methane as well as by quenching experiments and low temperature measurements.

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Abstract  

Iron was diffused into aluminium along grain boundaries and studied by Mössbauer spectroscopy. The Mössbauer spectrum of the investigated sample contained one doublet with isomer shift =0.360/5/ mm s–1 /relative to -iron/ and quadrupole splitting =0.84/l/ mm s–1. These results suggest that the iron atoms in the grain boundaries of aluminium have environment very similar to that which is present in amorphous iron /III/ oxides.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
A. Vértes
,
Z. Klenesár
,
Gy. Vankó
,
T. Marek
,
K. Süvegh
,
Z. Homonnay
, and
E. Kuzmann

Abstract  

The paper offers three applications of nuclear methods in the research of chemical structure. First, progress in positron annihilation spectroscopy is illustrated by a positron beamline study, which obtained results that are not available through conventional experiments. The positron beam was used for the study of Langmuir-Blodgett (LB) films containing 4-58 layers of arachidic acid and its salts. These measurements have shown that this emerging technique is capable of characterizing even such elusive systems. Second, the potential of Mössbauer spectroscopy to answer current challenges of solid state chemistry are shown in a study on perovskites of recent interest. 151Eu Mössbauer spectroscopy was used to study the effect of Pr substitution in EuBa2Cu3O7- . It was shown that the introduction of Pr into the rare earth site as well as into the Ba site results in the appearance of extra electrons both in the copper oxide planes and at the 4f shell of Eu cations. The observed effects were explained by the hole filling effect of Pr. Finally, a survey is presented on the recently developed techniques for nuclear resonant scattering of synchrotron radiation, an exciting and very rapidly developing extension to conventional Mössbauer spectroscopy. An interesting new result is that nuclear inelastic scattering experiments performed on solutions of 57Fe complexes show contribution from vibrations rather than from diffusion to the inelastic spectra.

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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.

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Abstract  

57Fe Mössbauer spectroscopy measurements were performed on the perovskite compounds Eu0.7Pr0.3Ba2(Cu0.99 57Fe0.01)3O7- , EuBa1.5Pr0.5(Cu0.99 57Fe0.01)3O7- and EuBa1.3Pr0.7(Cu0.99 57Fe0.01)3O7- . 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- 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.

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Summary  

The double perovskites, AFe0.5Mo0.5O3with A=(Ba,Sr) or (Sr,Ca), were prepared by a sol-gel method, and the substitution effect at site A was studied by Mössbauer spectrometry. In the Mössbauer spectra of the double perovskite (Ba, Sr)Fe0.5Mo0.5O3, the isomer shifts decreased fromδ=0.72 mm/s to δ=0.4 mm/s and the internal magnetic fields increased with the increase of the Sr content. The Ba-rich samples were shown to contain superparamagnetic components under the same preparation conditions. Better crystallinity and larger hyperfine fields were obtained when 5% of the Sr-content of SrFe0.5Mo0.5O3was substituted by Ca as compared with substitution by Ba. Phonon density of states (DOS) of SrFe0.5Mo0.5O3substituted with Ca or Ba were obtained by nuclear inelastic scattering. The peaks of phonon DOS were shifted, depending on chemical compression/expansion of the lattice. The chemical pressure effect could be observed in the Mössbauer spectra and the phonon DOS spectra.

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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.

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Abstract  

Sr0.95Ca0.05Fe0.5Co0.5O3- and Sr0.5Ca0.5Fe0.5Co0.5O3- perovskites were studied by 57Fe emission Mössbauer spectroscopy. It was found that Co prefers lower valence and lower coordination number than Fe in both compounds. The comparison of the emission and transmission Mössbauer spectra of the CO2 treated materials revealed a preferred formation of Fe-containing products in reaction with CO2 in Sr0.5Ca0.5Fe0.5Co0.5O3- , and it is proposed that such a reaction can be responsible for phase separation in Sr0.95Ca0.05Fe0.5Co0.5O3– after absorption and partial desorption of CO2 at 950 °C.

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