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57Fe Mössbauer spectroscopic studies of iron ludwigite Fe3O2BO3 performed between 4 and 450 K allow the discussion of magnetic spin arrangements and the dynamics of electronic configurations of iron. The observed magnetic transitions are related to charge ordering. [ABSTRACT FROM AUTHOR]

Low temperature Mössbauer experiments were performed in Fe-doped and in C-deficiency MgCNi3. No magnetic moment was found for Fe in MgC(Ni0.99Fe0.01)3 sample and no magnetic hf field was observed at any temperature for all the samples. These results shown no evidence of magnetic fluctuation or magnetic ordering influencing the depress of superconductivity in hole-doped MgCNi3. [ABSTRACT FROM AUTHOR]

In this work a study on gold mineral samples is reported, using optical microscopy, X-ray diffraction (XRD) and Mössbauer spectroscopy (MS). The auriferous samples are from the El Diamante mine, located in Guachavez-Narinño (Colombia) and were prepared by means of polished thin sections. The petrography analysis registered the presence, in different percentages that depend on the sample, of pyrite, quartz, arsenopyirite, sphalerite, chalcopyrite and galena. The XRD analysis confirmed these findings through the calculated cell parameters. One typical Rietveld analysis showed the following weight percent of phases: 85.0% quartz, 14.5% pyrite and 0.5% sphalerite. In this sample, MS demonstrated the presence of two types of pyrite whose hyperfine parameters are δ1 = 0.280 ± 0.002 mm/s and δ1 = 0.642 ± 0.002 mm/s, Δ2 = 0.379 ± 0.002 mm/s and Δ2 = 0.613 ± 0.002 mm/s. [ABSTRACT FROM AUTHOR]

The results of a Mössbauer spectroscopy (MS) and a neutron diffraction (ND) study carried out on a set of Fe-Mn alloys quenched from high temperatures are reported. Upon quenching the high temperature stable phase FCC (γ) together with metastably retained HCP-(ɛ) phase are formed. The lattice parameters obtained using ND are in excellent agreement with previous results of the literature. The phase fractions obtained from MS are coincident, within experimental errors, with those extracted from ND, with exception of the case of an alloy with the lowest Mn content (16.8 at.% Mn). That situation can be associated with the occurrence of a high density of stacking faults (SF) in the γ phase or to the presence of a paramagnetic γ phase. ɛ phase fractions obtained from MS and ND decrease smoothly with Mn content but are always larger than the values reported in literature resulting from dilatometry. [ABSTRACT FROM AUTHOR]

We have investigated the mechanosynthesis of gadolinium and yttrium iron garnets by high-energy ball-milling of α-Fe2O3 and Gd2O3 or α-Fe2O3 and Y2O3, respectively, followed by short thermal annealings conducted at moderate temperatures. The samples were characterized by X-ray diffraction and Mössbauer spectroscopy, in order to determine the influence of the milling time and annealing conditions on the final products. For as-milled samples of each rare-earth system, the results revealed the formation of perovskite phases, in relative amounts that depend on the milling time. The formation of garnet phases was observed in as-annealed samples treated at 1000°C for 2 h or 1100°C for 3 h, i.e., at very modest annealing requirements when compared with ordinary solid-state-reaction processes performed without previous high-energy milling. Also, the occurrence was verified of a milling time for which the relative amount of garnet phases formed by annealing was maximized. This time depends on the rare-earth composing the garnet phase and on the annealing temperature. [ABSTRACT FROM AUTHOR]

In this work we report the magnetic and structural properties obtained by Mössbauer spectrometry, Vibrating Sample Magnetometer and X-ray diffraction of milled powders with initial composition Nd2(Fe100−xNbx)14B with x = 0 and x = 4. The mixtures were ball milled for different times up to 240 h. Structural and microstructural parameters were derived from high statistics X-ray patterns and discussed as a function of milling time. The Mössbauer spectra of the samples were fitted by means of a sextet and an hyperfine field distribution, associated to a pure iron phase (α-Fe) and a disordered iron-based phase, respectively. The α-Fe grain size decreases from 50 nm for 6 h up to 5 nm for 240 h milling time. The Vibrating Sample Magnetometer results allow to conclude that these samples behave as soft ferromagnets. [ABSTRACT FROM AUTHOR]

In order to investigate some of the fundamental physical properties of the fcc-FeX (X=C, N) austenite solid solutions, we compare the hyperfine parameters obtained by Mössbauer 57Fe spectrometry and those obtained by the full-potential linear augmented-plane wave (FLAPW) method. We have focused the study on isomer shifts and quadrupole splittings at Fe sites obtained by FLAPW assuming an Fe8X structure to sketch the austenite. In the present work, we will discuss this point and compare the results of the calculations with experimental data. [ABSTRACT FROM AUTHOR]

In this work we report a comparative study of the magnetic and structural properties of Fe50Al50 alloys produced by mechanical alloying using two different planetary ball mills with the same ball mass to powder mass relation. The Fe50Al50 sample milled during 48 h using the Fritsch planetary ball mill pulverisette 5 and balls of 20 mm, presents only a bcc alloy phase with a majority of paramagnetic sites, whereas that sample milled during the same time using the Fritsch planetary ball mill pulverisette 7 with balls of 15 mm, presents a bcc alloy phase with paramagnetic site (doublet) and a majority of ferromagnetic sites which include pure Fe. However for 72 h of milling this sample presents a bcc paramagnetic phase, very similar to that prepared with the first system during 48 h. These results show that the conditions used in the first ball mill equipment make more efficient the milling process. [ABSTRACT FROM AUTHOR]

Anelastic behavior of crystalline solids is generated by several microstructural processes. Its experimental study yields valuable information about materials, namely: modulus, dissipation mechanisms and activation enthalpies. However, conventional techniques to evaluate it are complicated, expensive, time consuming and not easily replicated. As a new approach, in this work a Mössbauer spectrum of an iron specimen is obtained with the specimen at repose being its parameters the "base parameters." After that, the same specimen is subjected to an alternated stress-relaxation cycle at frequency ω1 and a new Mössbauer spectrum is obtained under this excited condition; doing the same at several increasing frequencies ωn in order to scan a wide frequencies spectrum. The differences between the Mössbauer parameters obtained at each excitation frequency and the base parameters are plotted against frequency, yielding an "anelastic spectrum" that reveals the different dissipation mechanisms involved, its characteristic frequency and activation energy. Results are in good agreement with the obtained with other techniques. [ABSTRACT FROM AUTHOR]

We have studied the Morin transition in nanostructured pseudocubic α-Fe2O3 particles of about 1.8 mm side. The preparation was carefully chosen to obtain a system with a very narrow crystallite size distribution and particles of homogeneous morphology. Two samples were studied: one without thermal treatment (α-Fe2O3(ap)) and another annealed at 673 K in air for 12 h (α-Fe2O3(an)). Both were characterized by XRD, SEM, TGA and Mössbauer spectroscopy. The results indicate that the Morin transition is suppressed for α-Fe2O3(ap), however, a-Fe2O3(an) has a TM ≈ 230 K and the transition is completed over a very narrow temperature range. These results are discussed in connection with the crystallite size, the cell parameters, and the presence of OH− groups (hydrohematite) or incorporated water (protohematite). [ABSTRACT FROM AUTHOR]

Fe79Mn21, (Fe79Mn21)90Cu10, and (Fe79Mn21)80Cu20, alloys, prepared by high energy ball milling were characterized by Mössbauer spectroscopy, X-ray diffraction and ac-susceptibility. Results indicate that the Cu addition favors the formation of a FCC phase with two different magnetic states at room temperature, i.e., an antiferromagnetic and a paramagnetic one. Thermal evolution of the Mössbauer spectra revealed the occurrence of a magnetic ordering along a wide temperature range. This behavior is probably related to Fe atoms in FCC-Fe(Mn,Cu) phase having different environments and grain size distribution. Thermal dependence of in-phase acsusceptibility shows that a long range ordering starts at 240 K for the Fe79Mn21 alloy and shifts towards lower temperatures with the Cu content. These results would reflect a long-range magnetic ordering transition with a distribution of ordering temperatures rather than a blocking process of particle single-domains. [ABSTRACT FROM AUTHOR]

Powder magnetite was analyzed in situ via Mössbauer with temperatures ranging from 170 K up to 900 K. Hyperfine fields of the tetrahedral and octahedral sites of magnetite as well as the corresponding average field were followed as a function of temperature in order to elucidate the critical behavior of magnetite at around the Curie temperature. Results evidence a progressive collapse of the Mössbauer spectra onto a singlet-type line at a critical temperature of around 870 K characterized by a critical exponent β=0.28(2) for the hyperfine field. In order to describe such temperature dependence of the hyperfine field, a Monte Carlo-Metropolis simulation based on a stoichiometric magnetite and an Ising model with nearest magnetic neighbor interactions was also carried out. In the model, we have taken into account antiferromagnetic and ferromagnetic interactions depending on the involved ions. A discussion about the critical behavior of magnetite and a comparison between the hyperfine field obtained via Mössbauer and the magnetization obtained via Monte Carlo is finally presented. [ABSTRACT FROM AUTHOR]

ILEEMS is the acronym for Integral Low-energy Electron Mössbauer Spectroscopy. In this variant of Mössbauer spectroscopy the low-energy electrons, E < ∼15 eV, emitted by the probe nuclei in the absorber are counted as a function of source velocity. As a consequence of their low energy, the detected electrons' origin lies within a very thin surface layer with thickness of a few nanometers and consequently, ILEEMS is a useful technique to examine surfaces of Fecontaining substances. In a first part of this paper the authors briefly describe the design of a homemade ILEEMS equipment allowing the temperature of the investigated sample to be varied between 77 K and room temperature. The second part of this contribution deals with a selection of results obtained from ILEEMS spectra for various Fe oxides. In particular, the following items are covered: (1) surface versus bulk Morin transition in small-particle and near-bulk hematite, α-Fe2O3; (2) bulk and thin-film magnetite, Fe3O4; (3) ferrihydrite, 5Fe2O3 · 9H20, goethite, α-FeOOH, and lepidocrocite, γ-FeOOH, all to some extent in relation to their morphology. Interesting and intriguing findings concerning the surface properties of these oxides were obtained and it is argued that the results encourage more systematic research in this and related fields using the surface-sensitive ILEEMS technique. [ABSTRACT FROM AUTHOR]

An autonomous control system for Mössbauer spectrometry based on two modules has been designed and built. The first module operates as a multichannel analyzer for the acquisition and storage of spectra, and the second one is a driver unit which controls and supplies the power for the velocity transducer. A microcontroller executes the digital control algorithm for the velocity transducer motion and manages the data acquisition and storage tasks. The user can monitor the system from an external PC through the serial port. A graphic interface made with the LabVIEW software allows the user to adjust digitally the control parameters for the velocity transducer motion, the channels number, to visualize as well as save spectra in a file. The microcontroller can be reprogrammed from the PC through the same serial port without intervention of a universal programmer, which allows the user to make proper software for different applications of the system. The system has been tested for linearity with several standard absorbers yielding satisfactory results. The low cost of its design, construction and maintenance make this equipment to be an attractive choice when assembling a Mössbauer spectrometer. [ABSTRACT FROM AUTHOR]

The rust products formed on weathering and carbon steels exposed to dry-wet cyclical processes in different chloride-rich solutions are carefully examined by means of different techniques. Special emphasis is given to the methodology of analysis of the data using 300 K and 77 K Mössbauer spectrometry and X-ray diffraction. The rust that is loosely bound to the metal surface and that it is lost during the corrosion process, for both types of steel, was found to be composed of lepidocrocite, superparamagnetic goethite, hematite, and traces of akaganeite. On the other hand, the adherent rust, which is differentiated as scraped and hit according to the way it is obtained, from both steels was found to be composed of akaganeite, spinel phase, goethite exhibiting broad distribution of particle sizes and lepidocrocite. The relative abundances of rust components for both steels were very similar, suggesting similar corrosion processes. Mass loss measurements show that the corrosion rates increases with increasing the chloride concentration. The presence of large quantities of spinel phase and akaganeite are a consequence of a corrosion process under the influence of very high chloride concentrations. Our results are useful for assessing the behavior of weathering steels where the levels of chlorides are high or in contact with sea water. [ABSTRACT FROM AUTHOR]

In this work the synthesis of calcium telluride has been carried out by two methods using enriched 128Te in both cases. The X-ray diffraction results of both samples correspond to the orthorhombic tricalcic telluride. Once the two samples of calcium telluride were identified, they were irradiated with thermal neutrons in a Nuclear Reactor. The results of both samples of iodine correspond to the 27.72 keV photo peak of 129I reported in 1962. The calcium telluride obtained by the two methods resulted in a possible Mössbauer 129I source. [ABSTRACT FROM AUTHOR]

We have synthesized by sol-gel method the following polycrystalline double perovskite samples: Sr2Fe1−xScxReO6 (x = 0, 0.05, 0.1). The results of the Rietveld refinements presented single double perovskite phases with orthorhombic symmetry for the system Sr2Fe1−xScxReO6, the differences in atomic radii between Fe3+ and Sc3+ cause a lowering in symmetry with respect to the parent Sr2FeReO6 tetragonal compound. The Curie temperatures are found at about 426 and 436 (±5) K for Sr2Fe0.9Sc0.1ReO6 and Sr2Fe0.9Sc0.05ReO6, respectively. The Mössbauer spectra measured at 77 K show complex hyperfine structures resulting from different magnetic contributions at Fe3+ sites; the average hyperfine field is estimated 50 T and the isomer shift at 0.5 mm/s. At room temperature an intermediate valence state for Fe is also observed. [ABSTRACT FROM AUTHOR]

We have measured 121Sb Mössbauer spectra at 20 K for 52 compounds of antimony(III). An Sb(III) atom with the electron configuration [Kr] 4d105s2 has a lone pair electrons. The stereochemical property of the lone pair has been found to depend very much on the kinds of atoms surrounding the antimony atom and the configurations of the coordinating atoms. [ABSTRACT FROM AUTHOR]

Calcium tin silicate, CaSnSiO5, called Malayaite is synthesized with equimolecular quantities of calcium oxide, silica and stannic oxide followed by a thermic process. In this work, the synthesis of Malayaite and the structure of a Malayaite-based pigment, Sn/Co pink, is investigated by X-ray diffraction and Mossbauer spectroscopy. The results indicate Malayaite and Cassiterite formation, but the ion cobalt incorporated in the Malayaite structure, diminishes the Cassiterite proportion and causes larger asymmetry in the environment of the tin atom. [ABSTRACT FROM AUTHOR]

X-ray diffraction and 57Fe Mössbauer spectroscopy are used to characterize the influence of borate on two-line ferrihydrite's structure and develop likely models for its attachment. Particle sizes were in the 2-4 nm range, and as borate sorption increased, the ferrihydrite particle size decreased. The d-spacings of two-line ferrihydrite increased with increased borate adsorption. Isomer shift and quadrupole splitting exhibit slight increasing trends as well. Also, the phase transformation temperature of ferrihydrite to hematite is significantly raised due to borate coating of the surface. We suggest borate is sorbed onto the surface by attachment to the oxygen corners of the iron octahedra that are on the surface of the nanoparticles, placing boron in a tetrahedral molecular geometry. [ABSTRACT FROM AUTHOR]

Amorphous Fe78Si9B13 alloy ribbons were heat treated between 296 and 763 K, using heating rates between 1 and 4.5 K/min. Whereas one ribbon partially crystallized at Tx = 722 K, the other one partially crystallized at Tx = 763 K. The partially crystallized ribbon at 722 K, heat treated using a triangular form for the heating and cooling rates, was substantially less fragile than the partially crystallized at 763 K where a tooth saw form for the heating and cooling rates was used. Vickers microhardness and hyperfine magnetic field values behaved almost concomitantly between 296 and 673 K. The Mössbauer spectral line widths of the heat-treated ribbons decreased continuously from 296 to 500 K, suggesting stress relief in this temperature range where the Vickers microhardness did not increase. At 523 K the line width decreased further but the microhardness increased substantially. After 523 K the line width behave in an oscillating form as well as the microhardness, indicating other structural changes in addition to the stress relief. Finally, positron lifetime data showed that both inner part and surface of Fe78Si9B13 alloy ribbons were affected distinctly. Variations on the surface may be the cause of some of the high Vickers microhardness values measured in the amorphous state. [ABSTRACT FROM AUTHOR]

This paper is a review of the current status about the remaining problems that are found in the investigation of the Quaternary Argentine soils and loessic sediments, and the way that Mössbauer studies can assist in solving them. There are two main types of investigations that make use of the magnetic response of the samples to correlate them with information gathered by other methods. On the one hand, there is the stratigraphic and chronological research, which is of importance from the geological and paleontological points of view. On the other hand, the paleoclimatic records, of significance toward a possible model of the past climate, are also studied because of their close relation to the sediments history. However, there is not yet a model that can tell the difference between the modifications due to the climatic conditions at the time when the soils were buried from processes that occurred after burial. Some examples are given that show that Mössbauer studies can be applied with a certain degree of success when cross-checked with magnetic measurements toward understanding the processes that occurred in alluvial B (paleosols) and C horizons (loess) from the eastern part of Buenos Aires Province. Although the application of Mössbauer studies to hydromorphic processes in soils is not straightforward, there are cases in which Mössbauer spectroscopy, if applied properly and correlated with other techniques, is able to characterize the type of iron oxides existing in the materials and thus assist theories about its origin and history. [ABSTRACT FROM AUTHOR]

The diamond-bearing gravels found along South Africa's West Coast are being beneficiated by means of dense medium separation (DMS) to reclaim the alluvial diamonds. Granular ferrosilicon (Fe-Si) is used as the DMS material and at the end of each operation the Fe-Si is reclaimed from the process stream using a magnetic separator and is then recycled but losses of Fe-Si due to attrition, adhesion to the separation products, density changes and changes to the magnetic properties can occur. The gravel obtained from the mining operation is washed and screened before heavy mineral separation. The concentrate, tailings and Fe-Si samples were investigated by means of SEM and Mössbauer spectroscopy to determine where changes to the Fe-Si, or contamination could occur. The composition of the Fe-Si was determined to be Fe (76.1 at%), Si (20.3 at%), Mn (1.5 at%), Al (1.5 at%) and Cr (0.6 at%) resulting in a more or less ordered DO3 phase with a calculated composition of Fe3Si for this Fe-Si, consistent with the Mössbauer results where two sextets with hyperfine magnetic fields of 18.6 T and 28.4 T were observed. After DMS, magnetite and ilmenite, the minerals found in the gravel, were still present in the concentrate. In the tailings virtually no magnetite or ilmenite was found and only a doublet, identified as an oxihydroxide, due to the abrasion of the Fe-Si, was found. After magnetic separation, to wash and clean the Fe-Si for re-use, it was found that magnetite and ilmenite were still present in the Fe-Si, which results in a change in density of the Fe-Si, resulting in a higher density and loss of valuable diamonds. [ABSTRACT FROM AUTHOR]

The most commonly used route in the hydrometallurgical extraction of zinc and copper from a sulphide ore is the concentrate-roast-leach-electro winning process. In the present investigation a zinc-copper ore from the Maranda mine, located in the Murchison Greenstone Belt, South Africa, containing sphalerite (ZnS) and chalcopyrite (CuFeS2), was studied. The 57Fe-Mössbauer spectrum of the concentrate yielded pyrite, chalcopyrite and clinochlore, consistent with XRD data. Optimal roasting conditions were found to be 900°C for 3 h and the calcine produced contained according to X-ray diffractometry equal amounts of franklinite (ZnFe2O4) and zinc oxide (ZnO) and half the amount of willemite (Zn2SiO4). The Mössbauer spectrum showed predominantly franklinite (59%), hematite (6%) and other Zn- or Cu-depleted ferrites (35%). The latter could not be detected by XRD analyses as peak overlapping with other species occurred. Leaching was done with HCl, H2SO4 and HNO3, to determine which process would result in maximum recovery of Zn and Cu. More than 80% of both were recovered by using either one of the three techniques. From the residue of the leaching, the Fe-compounds were precipitated and <1% of the Zn and Cu was not recovered. [ABSTRACT FROM AUTHOR]

The Vredefort Impact Structure in South Africa is the biggest and oldest remnant meteorite impact crater in the world where various ancient cultures thrived. In this paper some light will be shed on the Iron Age, iron smelting aspects of the people that inhabited the area and the results of a laboratory study of iron artefacts and a possible source of iron ore in the region is given. A sectional piece from a hoe manufactured in a small bloomery furnace was polished and etched and subsequently analyses with SEM and Mössbauer techniques were obtained. The hoe has a typical cast iron composition (2.9% C, 0.1% Mn, 0.4% Si, 0.4% P and 96.2% Fe, all wt.%) and contains many slag inclusions with wustite dendrites. The Mössbauer spectrum consisted of iron (86%), wustite (5%) and oxihydroxide (9%) and the thin (200 mm) corrosion layer consisted of hematite (55%) and oxihydroxides (45%). At a furnace site, various slag clumps (26.3% C, 24.8% SiO2, 11.3% Al2O3, 1.3% P2O5, 1.0% K2O, 0.4% CaO and 30.2 FeO, all wt.%, average of four samples) and iron nodules (7.6% C, 6.0% Mn, 4.3% Si, 1.4% Al, 80.7% Fe, all wt.%) were found. The Mössbauer spectrum of the slag consisted of iron (7%), magnetite (56%), fayalite (2%) and oxihydroxides (35%) and that of the iron nodules yielded iron (28%), wustite (12%), magnetite (20%) and oxihydroxides (40%). A possible ore source containing 84% FeO, 7% of Al2O3 and SiO2 (all in wt.%) and minor impurities is located a few kilometers from the furnace site, yielding a Mössbauer spectrum consisting of hematite (70%) and oxihydroxides (30%). [ABSTRACT FROM AUTHOR]

Alumina-europia mixed oxides with 5 and 10 wt.% Eu2O3 were studied by Mössbauer spectroscopy, 27Al MAS-NMR and X-ray diffraction (XRD). The samples were prepared by the sol-gel technique. The XRD patterns for the calcined samples show a broad peak around 2θ = 30° which is assigned to the Eu2O3; after treatment with hydrogen at 1073 K no reduction to Eu+2 or Eu0 was observed. The NMR spectra show three peaks, which are assigned to the octahedral, pentahedral and tetrahedral aluminum sites; the intensity of each peak depends on the concentration of europium ions. The Mössbauer spectra of the calcined samples show a single peak near zero velocity which is attributed to the Eu+3; after H2 treatment at 1073 K similar spectra were obtained, suggesting Eu+3 is not reducibly at this temperature. [ABSTRACT FROM AUTHOR]

Iron supported systems are frequently used as catalysts in the Fischer-Tropsch synthesis being the Fe0 the active phase for the reaction. We have studied the influence of the calcination atmosphere (air or nitrogen) on the iron oxide reducibility and the metallic iron particle size obtained in Fe/SiO2 system. We have impregnated a silicagel with Fe(NO3)3 · 9H2O aqueous solution and the solid obtained was calcinated in air or N2 stream. These precursors, with 5% (wt/wt) of Fe, were characterized by Müssbauer Spectroscopy at 298 and 15 K. Amorphous Fe2O3 species with 3 nm diameter in the former, and α-Fe2O3 crystals of 48 nm diameter were detected in the last one. Both precursors were reduced in H2 stream. Two catalysts were obtained and characterized by Mössbauer spectroscopy in controlled atmosphere at 298 and 15 K, CO chemisorption and volumetric oxidation. α-Fe0, Fe3 O4 and Fe2+ were identified in the catalyst calcined in air. Instead, only α-Fe0 was detected in the catalyst calcined in N2. The iron metallic crystal sizes were estimated as ≈2 nm for the former and ≈29 nm for the last one. The different oxide crystal sizes, obtained from the diverse calcination atmospheres, have led to different structural properties of the reduced solids. It has been possible to reduce totally the existing iron in an Fe/SiO2 system with iron loading lower than 10% (wt/wt). [ABSTRACT FROM AUTHOR]