Characterization of converted tin phosphate coating on iron and steel by conversion electron Mössbauer spectrometry (CEMS)

The chemical states of tin in converted tin phosphate coatings on iron and steel and in tin phosphate powders were analysed by conversion electron Mössbauer spectrometry and transmission Mössbauer spectrometry. The tin species in stannous phosphate, stannic oxide and metallic tin were recognized in the converted tin phosphate coatings. Mössbauer parameters of Sn(II) included in the phosphate coatings were slightly different from those of Sn(II) incorporated in powders of zinc and manganese phosphate compounds. The tin atoms mainly occupied two different sites in three sites of stannous phosphate structure, depending on the preparations.     

Solid state amorphization transformation in the mechanically alloyed Fe27.9Nb2.2B69.9 powders

Mössbauer spectrometry and Rietveld analysis of X-ray diffraction patterns were used to follow the solid state amorphization transformation during the milling process of the Fe_27.9Nb_2.2B_69.9 powders. The reaction between elemental Fe, Nb and B powders leads to the formation of the Nb(B) and Fe(B) solid solutions after 1 and 10 h of milling, respectively. A mixture of α-Fe, Nb(B) and highly disordered Fe(Nb, B) solid solution is found after 25 h of milling. An amorphous structure is obtained on further milling time (100 h). From the Mössbauer spectrometry results, it is observed that the total mixing of the elemental powders, at the atomic level, is achieved after 50 h of milling and a stationary state corresponding to a full paramagnetic amorphous phase is reached after 100 h of milling. The amorphization process can be described by an Avrami parameter close to n = 1.     

Mössbauer spectroscopy and X-ray diffraction of oxide precipitates formed from FeSO4 solution

Chemical and structural properties of oxide precipitates formed from FeSO₄ solution were investigated using X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy. The hydrolysis of urea at elevated temperature was used for the generation of OH^– ions during the precipitation process. The formation of particular oxide phase in the precipitate is strongly dependent on the concentrations of FeSO₄ and urea, as well as on the rate of oxygenation. The phase analysis of precipitates showed the presence of different oxide phases, such as goethite, lepidocrocite, hematite and magnetite, and in one sample of a small amount of siderite. Only substoichiometric magnetite, Fe_3–x O₄, was detected. Significant differences in the Mössbauer spectrum of goethite were observed, due to a very small particle size, the degree of crystallinity and/or different content of structurally bonded water. The correlation between the Mössbauer spectra of precipitated goethite and goethite formed during the atmospheric corrosion of steel is discussed.     

Laser remelting of cast iron: a Mössbauer study

The Mössbauer spectroscopy in backscattering technique (CXMS) was used to analyse cw-CO₂ laser-treated samples of cast iron. The depth profile as revealed by Mössbauer phase analysis is discussed in connection with the initial microstructure.     

Effect of nanocrystallization on the electrical conductivity enhancement and Mössbauer hyperfine parameters of iron based glasses

Selected glasses of Fe₂O₃-PbO₂-Bi₂O₃ system have been transformed into nanomaterials by annealing at temperature close to crystallization temperature (T_c) for 1 h. The effects of the annealing of the present samples on its structural and electrical properties were studied by Mössbauer spectroscopy, transmission electron micrograph (TEM), differential scanning calorimeter (DSC) and dc conductivity (σ). Mössbauer spectroscopy was used in order to determine the states of iron and its hyperfine structure. The effect of nanocrystalization on the Mössbauer hyperfine parameters did not exhibit significant modifications in present glasses. However, in case of glass ceramic nanocrystals show a distinct decrease in the quadrupole splitting (Δ) is observed, reflecting an evident decrease in the distortion of structural units like FeO₄ units. In general, the Mössbauer parameters of the nano-crystalline phase exhibit tendency to increase with PbO₂ content. TEM of as-quenched glasses confirm the homogeneous and essentially featureless morphology. TEM of the corresponding glass ceramic nanocrystals indicates nanocrystals embedded in the glassy matrix with average particle size of about 32 nm. The crystallization temperature (T_c) was observed to decrease with PbO₂ content. The glass ceramic nanocrystals obtained by annealing at T_c exhibit improvement of electrical conductivity up to four orders of magnitude than the starting glasses. This considerable improvement of electrical conductivity after nanocrystallization is attributed to formation of defective, well-conducting phases “easy conduction paths” along the glass-crystallites interfaces.     

Supermonochromatization of synchrotron radiation by Mössbauer filtration with total reflection from the isotope interface

Mössbauer filtration (supermonochromatization) of synchrotron radiation at the isotope interface of Mössbauer and non-Mössbauer isotopes of the same chemical element (e.g., Fe⁵⁶ and Fe⁵⁷) is theoretically investigated in conditions of total internal reflection of quanta in resonant interaction with the nuclei of the Mössbauer isotope. The merits of experiment geometry in which the isotope interface is not parallel to other boundaries, inevitably occurring in real experiments are shown. The discussed scheme is attractive for the implementation of standard of length in x-ray frequency range of electromagnetic radiation.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 55–57, January, 1994.The author V. M. Belyakov thanks the International Science Foundation for partial financial support of this work.     

Microstructural analysis of Fe-Si-Al alloy powders and films by Mössbauer spectrometry

The powder, plate and films of Fe-Si-Al alloy were prepared by gas atomizer, extrusion, sputtering, and quenching. The characteristics of these alloy materials were studied by Mössbauer spectrometry, and estimated on the base of iron configuration. The magnetic hyperfine fields were dependent on each preparation process. Quenched ribbon gave a perfect DO₃ structure.     

One-step aqueous synthesis of stoichiometric Fe-Cu nanoalloy

Fe_50 − xCu_50 − xB_2x alloy was obtained by an aqueous chemical reduction at pH = 7.0, using fast and slow NaBH₄ solution addition methods. According to X-ray diffraction patterns, TEM and HRTEM observations, smaller than 10 nm nanocrystals of fcc-FeCuB were formed when the fast method was employed. The room temperature Mössbauer spectrum of this FeCuB nanoalloy shows a quadrupole doublet with an isomer shift of 0.355(1) mm/s and a quadrupole splitting of 0.772(2) mm/s, and a broadened magnetic sextet with a quadrupole splitting of 0.020(3) mm/s and an isomer shift of 0.436(5) mm/s, exhibiting a distinctive high average magnetic field of 40.57(5) T. Grains with a size larger than 10 nm were obtained for a slow method nanoalloy, and its Mössbauer spectrum consisted only of a broadened sextuplet characteristic of an fcc-FeCuB alloy.     

Analysis of black layers on steel using conversion electron Mössbauer spectrometry

Iron and steel were treated in alkaline solutions at boiling point, and the black layers produced on their surfaces were analysed using conversion electron Mössbauer spectrometry (CEMS). The CEM spectra, measured at room temperature, consisted of distorted magnetically split peaks or broad doublet peaks due to ferrimagnetic and superparamagnetic magnetite, respectively. The refined and black surface of steel consisted of fine particles of magnetite with many cations' vacancies at the octahedral structure (B site).     

Local magnetization of Fe in Mo from Mössbauer experiments

From Mössbauer experiments on dilute sources of⁵⁷Co in Mo the local moment behavior of the Kondo system Fe in Mo is obtained. In addition, impurity-impurity interactions are clearly seen from line broadening of the Mössbauer spectra, which depend on the preparation of the samples. The local magnetization deduced from the splitting of the Mössbauer spectra in external fields is identical for samples with differing impurity concentrations, indicating that it is characteristic of isolated Fe in Mo. The initial local susceptibility is in good agreement with earlier bulk magnetization data. The low-temperature susceptibility yields a Kondo temperature of about 0.2 K. On the other hand, the overall temperature dependence of the susceptibility is more complex than the simple Curie-Weiss law with saturation to a constant value at low temperatures known for typical Kondo systems such asCuFe.     

Spectroscopic behaviour and internal friction of glasses containing iron having different redox ratios

The Mössbauer and ESR spectra and internal friction behaviour of Na₂O-3SiO₂ glasses having different redox ratios have been studied. As the redox ratio changes over a considerable range, there is a significant structural change associated with both the Fe³⁺ and Fe²⁺ ions, as evidenced from the analysis of the molar volume and Mössbauer data. The ESR data qualitatively supports the Mössbauer data on the Fe³⁺ ions. The change of internal friction behaviour of these glasses around 50% Fe³⁺ is described in terms of the structural changes associated with the Fe ions, which is thought to influence the oxygen structure of these glasses. The importance of this structural change on the electronic conductivity behaviour of these types of glasses is mentioned.     

Magnetic structure of the modulated martensite phase in Ni-Mn-Ga ferromagnetic shape memory alloys

The magnetic structure of the seven layered (7 M) modulated martensite phases in Mn-rich Ni-Mn-Ga alloys was studied using Mössbauer spectroscopy. The Mössbauer results clearly demonstrate that in contrast to the non-modulated tetragonal structure two new magnetic sublattices exists for the 7 M orthorhombic martensite phase. Based on the unit cell symmetry and atomic coordination, the additional magnetic sublattices have been assigned to the Ni site. The variation in the magnetic properties of the martensite phases has been related to the underlying magnetic structure.     

Mössbauer studies and magnetic properties of SnO2 doped with Fe

Transparent conducting SnO₂ powders doped with 10% Fe content were prepared by a polymerized complex method under acidic solutions, and annealed finally at 550 °C, and at 600 °C. These samples were characterized by X-ray diffraction, magnetization, and Mössbauer spectrometry at room temperature. Rutile SnO₂ phase was obtained for both samples, and the crystallite sizes were in the range of 13-14 nm. Both samples exhibit magnetization and the saturation magnetization was smaller for the sample annealed at 600 °C than for sample annealed at 550 °C. Room temperature Mössbauer spectra for both samples showed the presence of two different paramagnetic iron sites but no magnetic sextets. These results suggest that ferromagnetism originates from magnetic defects and not directly from iron ions.     

Study of LaFe12O19 from Mössbauer spectra

A study of lanthanum ferrite, LaFe₁₂O₁₉, by use of the Mössbauer effect has contributed experimental data on the temperature dependence of the internal magnetic field on the sites of the⁵⁷Fe nuclei, on isomer shift and on quadrupole splitting in the region from 90 to 820K. The Curie temperature was determined at 697K. The Mössbauer spectra of lanthanum and thallium lanthanum ferrite suggest that a special Fe²⁺ sublattice is not present.     

Mössbauer Study of Nanoscale Crystallization in Amorphous Fe–P–Si Alloys during Annealing

The crystallization behavior of amorphous Fe–P–Si alloys is studied by Mössbauer spectroscopy and physicochemical analysis. The resulting materials are found to contain nanocrystalline particles of complex composition, characterized by a doublet and several sextets in the Mössbauer spectrum. In the alloys containing 6 or 10 at. % Si, crystallization leads to the precipitation of pure Fe, which increases Si mobility and, accordingly, the rate of particle growth.     

Mössbauer Studies in the Mechanochemistry of Spinel Ferrites

Mössbauer spectroscopy can provide information on a large variety of mechanochemical processes in solids. In this overview, selected examples are presented of Mössbauer studies of homogeneous and heterogeneous mechanochemical reactions in spinel ferrites. Several interesting features are involved in the work, e.g., mechanically induced cation redistributions, changes of nearest-neighbor configurations, superparamagnetic relaxation, spin-canting effects, as well as formation and redox reactions. The considerable literature on mechanically treated spinel ferrites is reviewed. Despite numerous efforts, the understanding of the nonequilibrium mechanochemical processes in spinel ferrites is considered to be far from complete.     

Study of structural and magnetic properties of (Co–Cu)Fe2O4/PANI composites

The nanocomposites of the polyaniline and Co_1−xCu_xFe₂O₄ (PANI/CoCuFe) were prepared by in-situ oxidative polymerization of aniline. Prepared nanocomposites samples were characterized by using various experimental techniques like X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), vibrating sample magnetometer (VSM), Mössbauer spectroscopy and ultraviolet–visible spectrophotometry (UV–VIS). The elemental analysis as obtained from the energy dispersive X-ray spectroscopy (EDAX) measurement is in close agreement with the expected composition from the stoichiometry of the reactant solutions. XRD result confirms that all the samples have the single phase cubic spinel structure. Unit cell parameter ‘a’ is found to decrease with the increase in copper ion substitution. The crystallite size was investigated by using the Debye–Scherer formula and it was found in the range of ∼28–37 nm. FE-SEM confirmed the homogeneous and well defined surface morphology of the synthesized samples. FT-IR study showed the main absorption bands corresponding to the spinel structure those arose due to the tetrahedral and octahedral stretching vibrations. Cation distribution was estimated using XRD data. Hysteresis measurements revealed that the saturation magnetization decreased with increase in Cu²⁺ substitution. Magnetic environment of ⁵⁷Fe in Cu-doped cobalt ferrite was investigated by using Mössbauer spectroscopy. Mössbauer study evidenced the ferrimagnetic behavior of the synthesized samples.     

Structural and magnetic properties of a mechanochemically activated Ti-Fe2O3 solid mixture

The mechanochemical effects on the reactivity and properties of a titanium/hematite powder mixture with molar ratio of 1/2 are investigated. Crystalline-phase structure, composition, hyperfine and magnetic behaviors were analyzed as a function of activation time by means of X-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy and vibrating sample magnetometry. The results showed that at relatively short activation times metallic Ti reduces part of the ferric ions, yielding a complex product formed mainly by a mix of two solid solutions Fe_3−xTi_xO₄ (titanomagnetites), both with very different x values (0 < x < 1). Also metallic iron and superparamagnetic hematite particles were detected by Mössbauer spectroscopy. As the mechanical treatment extends the composition of the reactive mixture changes, prevailing in the end the solid solution with higher x value. In contrast, when these activated samples are thermally treated the fraction of the solid solution which is richer in Ti diminishes. This fact produces a significant variation of the saturation magnetization of the obtained material.     

Studies on the formation and thermal properties of manganese phosphate coatings and hureaulite by means of conversion electron and transmission Mössbauer spectrometry

The chemical states of iron species, produced in manganese phosphate coatings by the immersion of steel in a manganese phosphate bath, were analysed with the help of conversion electron and conventional transmission Mössbauer spectrometry (CEMS and TMS). The modifications of hureaulite by the variation of iron to manganese ratio are discussed with regard to the growth of manganese phosphate coatings. The thermal properties of manganese phosphate coatings and synthetic hureaulite were also investigated by means of differential thermal analysis and the composition analysis of thermal products.     

Electronic and magnetic properties of ultra-thin epitaxial magnetite films on MgO(001)

The electronic and magnetic properties of epitaxial Fe₃O₄ (001) films on MgO(100) substrates were studied throughout the 2.5- to 30-nm thickness range using conversion electron Mössbauer spectroscopy. Despite the superparamagnetism that was observed for film thickness below 5 nm, the Verwey transition persisted even for the thinnest film. Temperature-dependent Mössbauer measurements between 80 K and 400 K revealed that the activation energy for the magnetic moment fluctuations in the 3-nm magnetite film is higher than the magnetic anisotropy energy by an order of magnitude.