Mössbauer study of rapidly solidified Al-Fe based amorphous alloys

Mössbauer spetroscopy and X-ray diffraction were used to study the structure of rapidly quenched Al₈₈Fe₅Y₇, Al₈₈Fe₄Y₇Sb₁ and Al₉₃Fe₅Sb₂ alloys. Sb addition diminishes the glass forming ability and results in precipitation of the stable AlSb compound. The X-ray amorphous Al₈₈Fe₅Y₇ alloy shows a short range order resembling to the Al₆Fe compound as it can be judged from the Mössbauer data.     

Mössbauer and X-ray studies of Fe-powder mechanically alloyed with C using power ultrasonics

The M?ssbauer and X-rays analysis of as-received Fe-powder and Fe-powder mechanically alloyed with C using high power ultrasonics were carried out. The powder blend of Fe-powder and graphite was processed in He environment during 5 to 50 h. The dissolution of carbon in iron particles and inhomogeneous distribution of C atoms in crystallites was revealed. The ultrasonic milling of the f.c.c. Fe-Ni-powder with graphite was carried out. As established, the saturation of iron particles with carbon under ultrasonic milling occurs for much shorter time as compared to the high-energy ball milling.     

A Mössbauer study of rapidly quenchedCuFe alloys — Antiferromagnetic γ-Fe

A series ofCuFe alloys containing 5, 10 and 16 at% Fe has been prepared using standard ribbon spinning techniques. It is found that samples containing significant fractions ( 5%) of Fe in the form of r-Fe can be obtained readily on quenching from the (r + liquid) phase, applied field spectra (0–5.2 T) on antiferromagnetic r-Fe at 4. 2 K indicate that the anisotropy energy is small and that spins tilt from the minimum energy configuration (spin axes perpendicular to B_appl) for B_appl 2.5T.     

Microstructure of supersaturated fcc Al–Fe alloys: A comparison of rapidly quenched and mechanically alloyed Al98Fe2

Alloys of the composition Al₉₈Fe₂ have been prepared by rapid quenching from the melt and mechanical alloying methods and have been studied by Xray diffraction techniques and room temperature ⁵⁷Fe Mössbauer effect methods. Results may be summarized as follows: The rapidly quenched sample is a single phase supersaturated fcc Al–Fe alloy. Mössbauer effect spectra indicate the presence of a substantially greater degree of Fe clustering than is expected for a random distribution of atoms on the lattice sites. Mechanically alloyed samples have been studied as a function of milling time and show the initial formation of a supersaturated fcc phase with microstructural properties which are quite similar to those of the rapidly quenched sample. Further milling results in the reduction of the average grain size and the formation of an amorphous phase. Mössbauer studies and previously reported phase diagrams suggest that a substantial fraction of the Fe resides in this phase.     

Mössbauer study of internally oxidized silver-tin alloys

A Mössbauer study of internally formed oxides as a function of oxidation temperatures between 200 C and 850 C was performed on previously annealed 1 at%AgSn alloys. The oxide formed at high temperatures (t 500 C) consists in agglomerates of tin dioxide = 0.00 ± 0.01 mm/s, Q=0.50 ± 0.03 mm/s). The low temperature oxide (t 300 C) is characterized by = 0.29 ± 0.02 mm/s and Q=0.32 ± 0.03 mm/s, and could be in the form of one-Sn-atom oxide complexes in the silver matrix. From the measured isomer shifts in the range 400 t 550 C, the maximum contribution of the silver matrix to the effective number of electrons per Sn atom in oxide agglomerates has been estimated have a value of about 0.06. The effect of the cold work on the hyperfine parameters of the oxidized tin has also been investigated. As rolled samples were found to attain the same values of isomer shifts and quadrupole splittings as annealed specimens, but at lower temperatures.     

A Mössbauer and X-ray diffraction study of nonstoichiometry in magnetite

The paper deals with the applicability of Mössbauer spectroscopy and X-ray diffraction methods for the determination of the deviation of magnetite from stoichiometry. The results show that among the data obtainable by both methods, the ratio of intensities of two partial spectra composing the Mössbauer spectrum of magnetite enables to evaluate the deviation of magnetite from stoichiometry quantitatively.The authors express their gratitude to Prof. Dr. Ing. J.Cirák who enabled them to perform all measurements of Mössbauer spectra at the Department of Nuclear Physics and Technics, Slovak Technical University, Bratislava. The authors are also indebted to Ing. P.Holba (Institute of Solid State Physics, Czechoslovak Academy of Sciences) and to Ing. Z.Drbálek (Research Institute of Sound and Picture) for the preparation of magnetite samples, and to Mr. P.Chaloupek (Faculty of Mathematics and Physics, Charles University, Praha) for computer calculation of lattice constants. The aid provided by members of the G. V. Akimov State Research Institute for the Protection of Materials, Dipl. Chem. K.Jendelová who carried out chemical analysis of the samples and Ing. K.Turecká who took part in X-ray diffraction measurements, is gratefully acknowledged.     

Mössbauer study of isothermally annealed amorphous Fe-Nb-Cu-Si-B alloys

Amorphous ribbons of Fe_73.5Nb₃Cu₁Si_13.5B₉ have been annealed above the crystallization temperature. Annealed samples consisted of crystalline and amorphous phases in a wide temperature range. Two samples of different thicknesses of 33 µm and 27 µm were isothermally annealed at a temperature of 545°C from 0.5 to 5 h in a vacuum furnace. The amount of crystalline phase increases rapidly in the ticker sample. The crystalline part of the Mössbauer spectrum consists of four sharp sextets which can be assigned to a DO₃-structure FeSi alloy. After 700°C annealing the amorphous phase was not observed and the crystalline phase consisted of the DO₃-structure FeSi alloy, paramagnetic FeNbB and presumably Fe₂₃B₆ and Fe₃SiB₂.     

Mössbauer spectroscopy of zirconium alloys

Mössbauer investigations of zirconium alloys were examined. Data about the chemical state of iron atoms in the zirconium alloys of different composition has been provided. Mössbauer spectroscopy revealed that small quantities of iron in binary zirconium alloy are in the solid solution α-Zr (up to 0.02 wt.%). Different iron atoms concentration and thermo-mechanical treatments may lead to formation the intermetallic compounds Zr₃Fe, Zr₂Fe, ZrFe₂. Adding tin atoms does not affect the formation and shape of Mössbauer spectra of these compounds. Adding Cr and Nb atoms makes significant changes in the shape of Mössbauer spectra and leads to the formation of complex intermetallic compounds. Adding Cu and W atoms, the shape of the binary alloys spectra (Zr-Fe) remains unchanged, but a change in the temperature dependence behavior of the spectral parameters occurs and also, changes to the properties of the alloys.     

Mössbauer study of Fe-Re alloys prepared by mechanical alloying

The room temperature Mössbauer spectra of ⁵⁷Fe were measured for nanocrystalline iron-based solid solutions Fe _1?x Re _x , prepared by mechanical alloying with x in the range 0.01 ≤ x ≤ 0.04. The obtained data were analysed in terms of the binding energy E _b between two rhenium atoms in the Fe-Re system. The extrapolated value of E _b for x = 0 was used for computation of enthalpy of solution of rhenium in iron. The result was compared with that resulting from the cellular atomic model of alloys by Miedema as well as with value, derived from proper data for Fe-Re solid solutions obtained by melting in an arc furnace. From the comparison it follows that our findings are in agreement with the Miedema’s model predictions and previous Mössbauer studies.     

Mössbauer and X-ray phase analysis of carburized steel

⁵⁷Fe backscattering Mössbauer phase analysis of the ASTM A295-70 type chromium bearing steel gas was performed for samples with varying phase composition achieved by gas carburization up to 3 wt% C followed by standard hardening, i.e. austenitizing and quenching procedures. Variations of contents of principal metallographic phases (alloyed martensite, austenite, magnetic and non-magnetic carbides) were determined and compared with reported X-ray data. Results are discussed in connection with the composition and heat treatment. Good mutual agreement of results was found, the Mössbauer phase analysis being superior for distinguishing magnetic and non-magnetic carbides, for finding the dependence on composition and also for detecting alloying element segregation. On the other hand, the Mössbauer method of determination of a small content of alloyed retained austenite suffers from the small difference between its satellites and non-magnetic carbides.     

Mössbauer study of tektites

Room temperature ⁵⁷Fe Mössbauer spectroscopy has been used to investigate the structural and oxidation state of Fe in tektites from different strewn fields. Spectra have been analyzed in terms of two quadrupole splitting distributions corresponding to Fe^3?+? and Fe^2?+?. All tektites show similar distribution of quadrupole splitting. Each distribution has one peak. The Fe^2?+? sites show a narrow region of Mössbauer line shift (δ) and quadrupole splitting (ε), δ?= 1.02–1.10 mm/s and ε?= 0.85–1.00 mm/s relative to α-Fe. These values have been assigned to intermediate coordination between tetrahedral and octahedral. The Fe^3?+? sites show wider regions of hyperfine parameters: δ?= 0.25–0.45 mm/s and ε?= 0.65–0.90 mm/s. The Fe^3?+?/Fe^2?+? ratio was found to be 0.05–0.15.     

Mössbauer study of the annealing effect on low‐alloyed steels

Structural analyses of Fe-Cr and Fe-Cr-Ni low‐alloyed steels before and after annealing at 600^○C using Mössbauer spectrometry, X‐ray diffraction and scanning electron microscopy are reported. At the received state, the two steels present a fine bainitic microstructure with equal hardness. From Mössbauer analysis, two iron sites are identified as substitutional by Cr, Mo, Ni atoms and as insertional by carbon in bainitic ferrite. Both sites are locally deformed by residual stresses. The presence of small quantities of retained austenite and ε carbide has been observed. Annealing for one hour at 600^○C causes a decrease in hardness for both steels with a decrease of retained austenite. After longer time of annealing, precipitation of (Fe,Ni)₂₃C₆ occurs in the Fe-Cr-Ni steel and increases hardness.     

Mössbauer and EPR study of nitrosyl hemoglobin

Nitrosyl hemoglobin was prepared by bubbling fresh⁵⁷Fe-enriched rat hemoglobin with NO. S- and X-band EPR spectra at 77 K are typical for anS=1/2 system with an anisotropicg-tensor and exhibit hyperfine interactions of¹⁴N with the electronic spin. Mössbauer spectra at 4.2 and 100 K consist of a superposition of spectra from high- and low-spin Fe(III), deoxygenated hemoglobin and a component corresponding toS=1/2,g=2, hyperfine constantsA _xx /g _{n n} =A _yy /g _{n n} =–19.6 T,A _zz /g _{n n} =6.8 T, quadrupole splitting E _Q=1.5 mm s^–1, isomer shiftI _s=0.42 mm s^–1 and linewidth 0.4 mm s^–1. The spin-lattice relaxation rate at 100 K is <2×10⁶ s^–1.     

Mössbauer and X-ray study of the firing process for production of improved roofing tiles

The effects of firing atmosphere parameters on the microstructural characteristics and physical properties of clay roofing tiles were studied. For these investigations, ⁵⁷Fe Mössbauer spectroscopy, X-ray diffractometry and dilatometry were used. XRD of the raw material exploited from the clay pit belonging to the roofing tile factory “Potisje-Kanjiza”, revealed the presence of montmorillonite, kaolinite, illite and some chlorite clay minerals, as well as, quartz, albite, calcite and dolomite. Gradual changes were observed both in the ⁵⁷Fe Mössbauer spectra and X-ray diffractograms with samples fired in reducing CO/N₂ gas atmosphere at temperatures between 700 and 1060 °C. These changes reflect the dehydroxylation processes, oxide (Fe₃O₄) formation, carbonate decomposition, densification and new silicate (plagioclase) formation. The firing conditions in reducing atmosphere were determined to produce roofing tiles with improved properties.     

Mössbauer spectroscopy study of the disordering process of Fe-rich FeAlSi alloys

In this work we study systematically the influence of different Al/Si ratios on the magnetic and structural properties of mechanically disordered powder Fe₇₅Al_25?x Si _x , Fe₇₀Al_30?x Si _x and Fe₆₀Al_40?x Si _x alloys by means of Mössbauer spectroscopy and X-ray diffraction measurements. In order to obtain different stages of disorder the alloys were deformed by ball milling annealed (ordered) alloys during different number of hours. X-ray and Mössbauer data show that mechanical deformation induces the disordered A2 structure in these alloys. The results indicate that addition of Si to binary Fe–Al alloys makes the disordering more difficult. The study of the hyperfine fields indicates that depending on the Fe content the magnetic behaviour of these ternary alloys varies. For Fe₇₅Al_25?x Si _x series, the alloys have different magnetic behaviours with deformation depending on the Si content. The magnetization of the alloys with high Si content decreases with deformation, as it happens to binary Fe₇₅Si₂₅ and the magnetization of the alloys with low Si content increases with deformation, as it happens to binary Fe₇₅Al₂₅. For Fe₇₀Al_30?x Si _x series the mean hyperfine fields show that there are two different stages with the disordering, in a first stage the mean hyperfine fields decrease and in the second stage they increase. Finally, for Fe₆₀Al_40?x Si _x alloys there is a magnetic transition, from a paramagnetic ordered state to a magneticdisordered state.     

Mössbauer study of Fe-Al disordered alloys near the critical concentration

Disordered bcc Fe_1–q Al _q alloys in the composition range 0.5q0.6 were studied by Mössbauer effect measurements. The Mössbauer spectra at 300 K of all the samples consist of two paramagnetic sites, one is a singlet and the other a doublet with quadrupole splitting. The results can be interpreted by considering that the sites of this disordered system are arranged near the configurations of the Fe and Al sites of the Fe-Al ordered system.     

Mössbauer and XRD study of pulse plated Sn-Fe,Sn-Ni and Sn-Ni-Fe electrodeposited alloys

Effect of pulse plating on novel electrodeposited binary and ternary amorphous alloys was studied by ⁵⁷Fe and ¹¹⁹Sn conversion electron Mössbauer spectroscopy and X-ray diffraction. Our results show that by adjusting the parameters of pulse plating a fine tuning of the composition and current efficiency can be achieved within these systems. On the contrary to direct current deposition, where the crystalline FeSn₂ phase dominates, pulse plating technique produces amorphous Sn-Fe alloy phases, of which the ferromagnetic phase is the dominant one. Both, direct current and pulse plated Sn-Ni deposits consist of paramagnetic alloy phases and minor amounts of β-Sn, the occurrence of which correlates with the tin content of the samples. Pulse plated Sn-Ni-Fe coatings are amorphous and in a dominantly ferromagnetic state, however at long on- and off-pulse times and high peak current density the paramagnetic state dominates and β-Sn segregation also occurs.     

Mössbauer and X-ray studies of an iron meteorite sample

Detailed analysis of the room temperature Mössbauer spectrum of an Fe-Ni ( 91.9% Fe, 7.5% Ni) meteorite from the Henbury crater region of northern Australia shows that it behaves identically to an Fe-Ni alloy. The enhanced resonance absorption is due to thickness effects, with the line broadening reflecting a range of atomic environments. The isotope ratio⁵⁶Fe/⁵⁷Fe for the meteorite agrees with the earth bound values.     

A study of amorphous,quasi crystalline and crystalline Al-Fe alloys by Mössbauer-effect and diffraction techniques

Amorphous Al₆Fe, icosahedral Al-Fe and crystalline Al_mFe have been investigated by X-ray diffraction, electron diffraction and Mössbauer-effect measurements. The results show that the type and number of iron nearest neighbors is very similar in all three alloys. It is suggested that one possible explanation for the spread in Electric Field Gradient magnitudes can be the existence of holes in the aluminum network.     

Mössbauer study of Slovak meteorites

⁵⁷Fe Mössbauer spectroscopy was used as an analytical tool in the investigation of iron containing compounds of two meteorites (Rumanová and Ko?ice) out of total of six which had fallen on Slovak territory. In the magnetic fraction of the iron bearing compounds in the Rumanová meteorite, maghemite, troilite and Fe-Ni alloy were identified. In the non-magnetic fraction silicate phases were found, such as olivine and pyroxene. The paramagnetic component containing Fe^3?+? ions corresponds probably to small superparamagnetic particles. The Ko?ice meteorite was found near the town of Ko?ice in February 2010. Its magnetic fraction consists of a Fe-Ni alloy with the Mössbauer parameters of the magnetic field corresponding to kamacite α-Fe(Ni, Co) and troilite. The non-magnetic part consists of Fe^2?+? phases such as olivine and pyroxene and traces of a Fe^3?+? phase. The main difference between these meteorites is their iron oxide content. These kinds of analyses can bring important knowledge about phases and compounds formed in extraterrestrial conditions, which have other features than their terrestrial analogues.