Studying the properties of Fe and Fe–Co nanotubes in polymer ion-track membranes

Iron and iron–cobalt nanostructures are probed by means of Mössbauer spectroscopy combined with scanning electron microscopy, energy-dispersion analysis, and X-ray diffraction. The obtained nanostructures are single-phase Fe_{1 ? x}Co _x (0 ≤ x ≤ 1) nanotubes that have high degrees of polycrystallinity and a bcc lattice 12 μm long and 110 ± 3 nm in diameter, with walls 21 ± 2 nm thick. A random distribution of the orientations of the magnetic momenta of Fe atoms are observed for Fe nanotubes, while Fe–Co nanotubes are characterized by a magnetic texture along their axes.     

Mössbauer study of iron removal in a montmorillonite

⁵⁷Fe Mössbauer spectroscopy in conjunction with atomic absorption spectrometry and X-ray powder differaction analyses have been used to study the iron present in a montmorillonite prior to and after different successive stages of two deferration processes. Fe³⁺ ions occupy mainly octahedrical M(2) sites in the mineral structure; no impurities of iron oxides were detected. The quite efficient deferration by HCl refluxing produced a substantial alteration of lamellar structure of montmorillonite, whilst dithionite/citrate treatment did not induce severe structural changes but had low iron removal efficiency.     

Mössbauer and magnetic study of silicon substituted cobalt ferrite

Silicon substituted cobalt ferrites have been investigated for improved performance as stress sensing materials. A series of samples with the formulae CoSi _x Fe_2???x O₄ were prepared using conventional powder ceramic technique. X-ray diffraction patterns were taken to examine spinel crystal structures and energy dispersive spectrometry was done to confirm Si segregations at the grain boundaries. Magnetic and magneto-strictive measurements were carried out to evaluate the material performance. Mössbauer spectra were taken on selective samples to understand the cationic distribution responsible for the modification of properties. The variations are explained on the basis of the strength of the exchange interactions between cations, and anisotropy contributions of cobalt ions. The results demonstrate the possibility of controlling magnetic and magneto-mechanical properties such as Curie temperature and strain derivative through Co and Si substitutions.     

Mössbauer study of ancient iron smelting slag in Japan

For an investigation of the ancient iron manufacturing technique, a reproducing experiment was carried out by archaeologists, where ancient type of iron smelting furnace was built and iron sand with high titanium contents was used as the raw material. During the operation of furnace, a large amount of slag flowed away from the furnace. In order to investigate the possibility for the estimation about the operative condition of furnace and the raw material, ⁵⁷Fe Mössbauer spectroscopy was applied for characterizing these slags and it was found that these slags mainly consisted of ferropseudobrookite (FeTi₂O₅).     

Mössbauer study of CO-precipitated Fischer-Tropsch iron catalysts

Mössbauer spectroscopy studies of precipitated Fischer-Tropsch (FT) iron catalysts, viz. 100 Fe/5 Cu/4.2 K/x SiO₂, wherex=0,8, 16, 24, 25, 40, or 100, have shown that reduction of the oxide precursor in CO gives rise to -carbide Fe₅C₂ whose amount decreases with an increase of SiO₂ content. The -carbide is converted into magnetite Fe₃O₄ while catalyzing the FT synthesis reaction. A correlation between FT activity and the content of -carbide in the catalysts was found, which indicated that -carbide is active for FT synthesis reaction.     

Fe57 Mössbauer study in cobalt substituted magnetite

The Mössbauer effect has been studied in the mixed ferrites Co _x Fe_3–x O₄ (forx=0.8, 0.9 and 1) with the spinel structure in the temperature range between 78 and 380 K. The composition withx=1, showed an expected Zeeman spectrum with two overlapping magnetic hyperfine patterns related to the Fe³⁺ ions in tetrahedral and octahedral sites. While for samples withx=0.8 and 0.9 the Mössbauer spectrum for each compound was successfully analysed into three different patterns corresponding to the ferric ions placed at the tetrahedral and octahedral sites and ferrous ions at the octahedral sites, indicating no electron transfer between Fe³⁺ and Fe²⁺, where the quantity of cobalt is sufficiently large to be located at the six nearest neighbours to ferrous ions. The Mössbauer effect parameters were calculated for these observed sites and their variation with temperature reported. The reduced hyperfine magnetic fields of the Fe³⁺ (B) ions were found to follow the Brillouin curve forS=5/2 and one third power law. The magnetic ordering temperature was determined to be 815 K and the possible magnetic interactions were discussed.     

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 Al and Cr co-substituted Yttrium iron garnets

The Mössbauer spectra of Y₃Al _x Cr _X Fe_5???2x O₁₂ (x?=?0.0 to 0.6) measured at 300 K have been fitted with two sextets in the ferrimagnetic state corresponding to Fe³⁺ at the octahedral (a) and the tetrahedral (d) sites for x?≤ 0.6. The isomer shifts (δ) and quadrupole splitting (ΔE_Q) indicate the presence of high spin Fe³⁺ ions in the tetrahedral (d) and octahedral (a) sites, typical of yttrium of yttrium iron garnet structure. Mössbauer results have shown that Al³⁺, enters a-sites only but Cr³⁺ enters both a-and d-sites.     

A Mössbauer spectroscopy study of the corrosion of nodular cast iron in mine waters

The corrosion of ductile cast iron in water containing different amounts of chloride ions was investigated under both static and dynamic conditions. Corrosion/time relationships were established for exposure times of up to 30 days. Post-corrosion investigations were performed, employing Mössbauer spectroscopy, optical microscopy and electrochemical techniques. It was found that the nature of the surface corrosion product formed under static conditions differed morphologically and chemically from that formed under dynamic conditions. The latter was a hard layer consisting of a mixture of - and -FeOOH (situated on an underlying cementite layer), whereas the static tests resulted in a soft, spongy corrosion product, identified as -FeOOH.     

Mössbauer spectroscopic study of iron fluoride surface layers

The reaction products formed during exposure of iron foils to hydrogen fluoride in the presence of atmospheric oxygen and water have been examined with conversion electron Mössbauer spectroscopy (CEMS) [1]. After exposure for several hours the product in the corrosion layer was found to consist mainly of the mixed-valence iron fluoride, Fe₂F₅·7H₂O. Although the products formed during the initial steps of the reaction could not be completely characterized, a model for the reaction process is suggested.     

Lattice dynamics of iron complexes embeddings in PMAA hydrogel Mössbauer study

The interaction of cross-linked poly(methacrylic acid) (PMAA) hydrogel and ferroine(iron - phenantroline complex) resulted in gel collapse because additional cross-links have been formed. To find out the mechanism of metal-polymer bonding and defining parameters of these bonds the lattice dynamics of frozen samples was studied by means of Mössbauer spectroscopy. Lattice dynamics parameters, such as Mössbauer lattice temperature θ _M and effective mass M_eff were calculated for PMAA gel-ferroine system. These calculations allowed us to estimate the ferroine complexes embedded in the PMAA hydrogel bonds strength.     

Mössbauer study of the iron atom state in modified chromium dioxide

Powders of modified chromium dioxide produced by the hydrothermal method were studied using ⁵⁷Fe Mössbauer spectroscopy at a temperature of 298 K. The content of the modifier, i.e., ⁵⁷Fe compound, was varied from 2 to 10 mmol/mol Cr at a Sb content of 2.2 and 10 mmol/mol Cr. It was shown that, independently of concentrations, Fe³⁺ ions are distributed between three magnetic solid solutions (sextets): based on CrO₂ (bulk material and iron-enriched surface layer), based on Cr₂O₃, and surface β-CrOOH (doublet). In this case, chromium atoms were not substituted in the CrSbO₄ nucleation (12 nm in size) phase with an accuracy up to the Mössbauer factor. It was assumed that the powder coercivity, in addition to the size factor, is controlled by the iron concentration in the CrO₂ surface layer.     

Mössbauer spectroscopy study of iron corrosion underneath painting system

The effect of pigments on the development of corrosion products between the painting system and metal surface when exposed to marine environments has been discussed. The pigments studied were; Red Mud Zinc chromate, Zinc chromate, Red oxide Zinc Phosphate, Manganese Phosphate Barium chromate and Basic Lead Silico Chromate. Mossbauer Spectroscopy revealed that the upper rust layer in all the cases consisted of-Fe203,-FeOOH and-FeOOH. The lower rust layer immediately in contact with the metal surface consisted of an asymmetrical doublet due to -FeOOH.     

Mössbauer study of iron hydride produced under high pressure

The hexagonal iron hydride formed at a hydrogen pressure of about 7 GPa was studied by⁵⁷Fe Mössbauer spectroscopy. At 80 K its spectrum consists of two magnetic patterns with hyperfine fields of 33.6 and 29.0T, respectively. Both have an isomer shift of +0.50mm/s with respect to-iron. A tentative explanation for these results is that iron hydride is stoichiometric FeH with a dhcp crystal structure.     

A 57Fe Mössbauer spectroscopy study of iron nanoparticles obtained in situ in conversion ferrite electrodes

Transmission Mössbauer spectroscopy and CEMS are powerful tools to study the changes in which iron-containing active materials of conversion electrodes are involved during lithium cell charge and discharge. The usual spectrum of pristine CoFe₂O₄ spinel with two sextets ascribable to Fe^3?+? ions in both tetrahedral and octahedral environments, changes dramatically after cell discharge to 0 V vs. Li, and can be interpreted as the result of iron reduction to the metallic state in the form of superparamagnetic metal nanoparticles dispersed in a Li₂O matrix. After cell charge to 3 V, the MS of the pristine sample is not recovered. Instead, two new doublets are visible with IS ascribable to Fe^3?+? ions. ⁵⁷Fe CEMS evidences the different environment of iron atoms in the surface of the nanodispersed material found in the used electrodes.     

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 and magnetization studies of iron oxide nanocrystals

Monodisperse iron oxide nanocrystals have been produced following non-hydrolytic, thermal decomposition routes. Spherically shaped particles with diameter of 4 and 12 nm and cubic shaped particles with an edge length of 9 nm have been studied. The particles have been shown to consist of mainly maghemite. A reduction of the saturation magnetic hyperfine field is observed for the 4 nm particles as compared to the corresponding bulk value. The anisotropy energy determined from the temperature variation of the magnetic hyperfine field was strongly enhanced for the 4 nm particles.     

Mössbauer study of iron carbide nanoparticles produced by laser ablation in alcohols

Iron carbide nanoparticles were synthesized by laser ablation of iron in alcohols (methanol and ethanol). A new cell, designed to allow the ablation to be conducted in a flowing solvent, enabled separation and collection of the nanoparticles immediately after production, thus preventing further photochemical reactions of the colloids. The nanoparticles were investigated using Mössbauer spectroscopy, X-ray diffraction, and transmission electron microscopy. In methanol, they consisted of α-iron, γ-iron, iron carbide, and amorphous paramagnetic iron carbides, whereas in ethanol they consisted of iron carbides and amorphous paramagnetic iron carbides. The difference in products depending on the alcohol was attributed to the different carbon supplies for methanol and ethanol. For both solvents, the average particle size was found to be 16 nm, and the nanoparticles were dispersed in amorphous carbon. We also examined the effect of further laser irradiation of the colloids using stagnant solvent, and the particle size was found to increase and a very small amount of carbonization was observed.     

A Mössbauer spectroscopic study of cobalt-iron molybdates

Fe _x Co_1–x MoO₄ compounds prepared by coprecipitation were studied by XRD, electrical conductivity and mainly by absorption and emission Mössbauer spectroscopy. FeMoO₄ and CoMoO₄ samples were shown to contain Fe³⁺ and Co³⁺, respectively, in solid solution. Three kinds of Fe _x Co_1–x MoO₄ solids can be described. Forx0.16: one has a -Co(Fe²⁺, Fe³⁺)MoO₄ solid solution. For 0.17x0.25: one has the same solid solution with its surface rich in Fe³⁺. Forx0.26: one has the same solid solution with only bulk Fe³⁺, and ferric molybdate. Studies of reduction by hydrogen and of catalytic reaction of mechanical mixtures of CoMoO₄ and ferric molybdate support these statements.     

Mössbauer study of the dynamics of iron ions in bipyramidal positions of strontium hexaferrite

The dynamics of Fe³⁺ ions in bipyramidal 2b positions of a type M hexaferrite are studied on single-crystal and polycrystalline SrFe₆Ga₆O₁₉ samples in the paramagnetic temperature range. We show that when the angle between the c axis of the crystal and the direction of -ray emission varies from 0 to 32 the area under the resonance lines corresponding to Fe³⁺ ions in 2b positions increases by a factor of roughly 1.5. The effect is more pronounced upon passing from a single-crystal sample (=0) to a polycrystalline sample. A comparison of the line intensities under different experimental conditions served as a basis for an evaluation of the difference between the mean-square displacements of the Fe³⁺ ions in 2b positions along the c axis in the perpendicular plane.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 5–8, January, 1991.