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Formation of crystalline phases is detected at different depths of the surface regions in (FeCo)MoCuB ( x = 0, 0.25) alloy by CEMS and CXMS techniques. Magnetite is predominantly present on the wheel sides of the ribbons while the alloy is amorphous. During annealing, formation of bcc-Fe and bcc-Fe,Co starts earlier on the air sides of the x = 0 and x = 0.25, respectively. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles have promising applications in many areas, for example optics, electronics, biology, medicine, etc. The primary goal of this study was to synthesize nanoparticles of magnetic ɛ-Fe2O3 embedded in amorphous SiO2. The structure and properties of the final product have been found to depend strongly on the initial conditions of preparation. The Mössbauer spectroscopy analysis of the samples was complemented by the study of X-ray powder diffraction, magnetic measurements, and high-resolution transmission electron microscopy. [ABSTRACT FROM AUTHOR]

A heat treatment was performed on selected epidote and clinozoisite crystals to establish the nature of any changes in the optical and crystal-chemical properties and to identify a breakdown product using a wide spectrum of analytical methods. Natural samples were heated from 900 to 1200 °C under atmospheric pressure in ambient oxidation conditions for 12 h. Epidote and clinozoisite were stable at 900 °C; those heated at 1000 °C, 1100 °C, and 1200 °C exhibited signs of breakdown, with the development of cracks and fissures. The average chemical composition of epidote is Ca2.000Al2.211Fe0.742Si2.994O12(OH), while that of clinozoisite is Ca2.017A12.626Fe0.319Si3.002O12(OH). The breakdown products identified by electron microanalysis, powder X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy were anorthite, pyroxene compositionally close to esseneite, and wollastonite. The decomposition of the epidote-clinozoisite solid solution is controlled by the following reaction: 4 epidote/clinozoisite → 2 pyroxene + 2 wollastonite + 4 anorthite + 2 H2O. Pyroxene likely contains a significant proportion of tetrahedral Fe3+ as documented by the Mössbauer spectroscopy. Moreover, the presence of hematite in the Mössbauer spectrum of the clinozoisite sample heated at 1200 °C can result from the following reaction: 4 epidote → pyroxene + 3 wollastonite + 4 anorthite + hematite + 2 H2O. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, we have investigated progress of crystallization in the Fe91− x Mo8Cu1B x (x =12, 15, 17, 20) alloy as a function of annealing temperature. This material belongs to the family of the Fe–M–B–(Cu) alloys (transition metal M=Zr, Nb, Hf, Mo, …) called also NANOPERM. The alloy was found to contain small amounts (<5%) of bcc Fe(Mo) and Mo2FeB2 nanocrystallites (<2nm) located on the surface of the ribbon-shaped samples already in the as-quenched state. Depending upon composition, the nanocrystallites are formed on the air and/or wheel side of the ribbon. They are characterized by atomic force microscopy, conversion electron Mössbauer spectroscopy, and by X-ray diffraction of synchrotron radiation. Fast detection (every 10s) of the latter during continuous heating of as-quenched specimens enabled an in situ observation of the evolution of the crystallization. For x =12, the crystallization starts earlier at the wheel side of the ribbon but its progress is more rapid at the opposite, i.e. air side. [Copyright &y& Elsevier]

Abstract: Rapidly quenched amorphous Fe80Zr4Ti3Cu1B12 (numbers indicate at.%) alloy was exposed to heat treatments in vacuum resulting in formation of a nanocrystalline structure with varying amounts of bcc-Fe grains. Mössbauer effect measurements were performed at 300 and 77K. An onset of crystallization was observed after annealing at 435°C for 1h. Analyses of Mössbauer spectra corresponding to nanocrystalline specimens revealed a presence of three structurally distinct regions: amorphous residual phase, crystalline phase, and interface zone. Evolution of these components and their hyperfine interactions which correlate with magnetic microstructure are studied by distributions of hyperfine magnetic fields. Magnetic regions develop in the retained amorphous phase with rising temperature of annealing. They are undergoing notable changes due to segregation of Fe atoms into bcc nanograins. Consequently, variations in the chemical short-range order are observed as a function of: (a) varying number of nanograins in the samples studied, and (b) temperature of measurement. Measurements of magnetic properties evidenced that partially crystallized samples exhibit high saturation magnetic flux density as well as high permeability. Moreover, low core losses and good frequency stability is observed. [Copyright &y& Elsevier]

An ancient axe from Early Medieval Age which was unearthed on a territory of the archaeological excavation site near the village Borovce (Slovakia) is investigated. The surface of the axe was supposed to be covered with a sort of glassy system. Mössbauer effect measurements performed in backscattering and transmission geometry upon original as well as powdered pieces of the axe confirmed that the surface layers of the axe consist of goethite, lepidocrite, akageneite, and/or magnetite. After temperature treatment at 400°C/100 min hematite and maghemite were found; these are products of thermal decomposition of the above mentioned iron phases. These findings ruled out the hypothesis that the surface covering substance was put on the axe by intention. [ABSTRACT FROM AUTHOR]

Iron-based nanomaterials have high technological impacts on various pro-environmental applications, including wastewater treatment using the co-precipitation method. The purpose of this research was to identify the changes of iron nanomaterial's structure caused by the presence of selenium, a typical water contaminant, which might affect the removal when the iron co-precipitation method is used. Therefore, we have investigated the maturation of co-precipitated nanosized ferric oxyhydroxides under alkaline conditions and their thermal transformation into hematite in the presence of selenite and selenate with high concentrations. Since the association of selenium with precipitates surfaces has been proven to be weak, the mineralogy of the system was affected insignificantly, and the goethite was identified as an only ferric phase in all treatments. However, the morphology and the crystallinity of ferric oxyhydroxides was slightly altered. Selenium affected the structural order of precipitates, especially at the initial phase of co-precipitation. Still, the crystal integrity and homogeneity increased with time almost constantly, regardless of the treatment. The thermal transformation into well crystalized hematite was more pronounced in the presence of selenite, while selenate-treated and selenium-free samples indicated the presence of highly disordered fraction. This highlights that the aftermath of selenium release does not result in destabilization of ferric phases; however, since weak interactions of selenium are dominant at alkaline conditions with goethite's surfaces, it still poses a high risk for the environment. The findings of this study should be applicable in waters affected by mining and metallurgical operations. [ABSTRACT FROM AUTHOR]

Due to their excellent magnetic properties, amorphous metallic alloys (AMAs) are considered for the construction of magnetic cores of radio-frequency cavities in accelerators. Here, they might be exposed to ion bombardment. The influence of irradiation by both light and heavy ions featuring low and high energies, respectively, is followed by the techniques of 57Fe Mössbauer spectrometry. Modifications of surface layers in selected Fe-containing AMAs after ion irradiation are unveiled by detection of conversion electrons and photons of characteristic radiation whereas those in their bulk are derived from standard transmission spectra. Rearrangement of microstructure which favors the formation of magnetically active regions, is observed in surface regions bombarded by light ions. Heavy ions caused pronounced effects in the orientation of net magnetization of the irradiated samples. No measurable impact upon short-range order arrangement was observed. Part I of this paper is devoted to radiation effects in Fe-based AMAs induced by neutron irradiation. [ABSTRACT FROM AUTHOR]

Amorphous and nanocrystalline Fe80M7Cu1B12 (M = Mo, Nb, Ti) alloys are investigated at room and liquid nitrogen temperatures. 57Fe Mössbauer spectrometry is employed because its local probe behaviour is able to elucidate the nature of hyperfine interactions at different resonating iron nuclei and to distinguish their immediate atomic surroundings. Using two independent distributions of hyperfine fields in addition to a crystalline sextet, the contributions to hyperfine interactions stemming from the amorphous residual phase and from the interfacial regions can be distinguished. The role of different constituent elements is also discussed. [ABSTRACT FROM AUTHOR]

57Fe Mössbauer spectroscopy is used to elucidate the nature of the hyperfine interactions present in amorphous and nanocrystalline forms of Fe80Ti7Cu1B12 alloy. Two mutually independent distributions of hyperfine fields and one sextet of Lorentzian lines are employed to reproduce the broad (atoms in amorphous rest and interface zone) and narrow (ordered) parts of the spectra, respectively. The presented conclusions are derived from three-dimensional mapping of the hyperfine field distributions corresponding to both amorphous and interfacial spectral components. The individual distributions are decomposed into Gaussian components which characterize different types of hyperfine interactions. [ABSTRACT FROM AUTHOR]

A fitting model based on the use of two independent blocks resulting from distributions of hyperfine fields and one sextuplet of Lorentzian lines is introduced to simulate Mössbauer spectra of FeMCuB type nanocrystals. It is discussed for the spectra of M = Mo, Nb, and Ti alloys in the first stage of crystallization. One distribution is ascribed to the amorphous residual matrix, while the other is attributed to Fe atoms located in the interface zone. The sextuplet of Lorentzian lines identifies α-Fe crystalline phase. Three dimensional mappings of hyperfine field distributions and models of structural arrangement and topography of hyperfine interactions are briefly reported. [ABSTRACT FROM AUTHOR]

Iron-based amorphous metallic alloys (AMAs) of several compositions were exposed to neutron irradiation with fluences of up to 1019 n/cm2. These materials exhibit excellent magnetic properties which predetermine them for use in electronic devices operated also in radiation-exposed environments. Response of the studied AMAs to neutron irradiation is followed by Mössbauer spectrometry which probes the local microstructure. Neutron irradiation leads to rearrangement of constituent atoms, their clustering, and formation of stress centers. The observed modifications of topological short-range order result in changes of spectral parameters including average hyperfine magnetic field, 〈 B 〉 , standard deviation of the distribution of hyperfine fields, and position of the net magnetic moment. After irradiation, especially differences in 〈 B 〉 -values develop in two opposite directions. This apparent controversy can be explained by formation of specific atomic pairs with different exchange interactions, which depend on the composition of the samples. Part II of this paper will be devoted to radiation effects caused in Fe-based AMAs by ion irradiation. [ABSTRACT FROM AUTHOR]