Industrial applications of Mössbauer Spectroscopy

A review of the industrial applications of Mössbauer Spectroscopy is presented underlining the powerfulness and usefulness of the technique in the control and optimization of the production processes. A few examples are reported concerning the developments of thin protective coatings for structural parts and media for the magnetic recording field.     

Mössbauer Spectroscopy Study of Iron Nickel Alloys

Three samples of Fe_100–x Ni _x (with x=30, 35 and 40) were prepared by arc melting technique. The Mössbauer spectra of the three samples were collected and analyzed. The spectrum of the sample with x=30 consists of a singlet and a sextet. The singlet component which has isomer shift (IS=–0.08 mm/s) is attributed to a superparamagnetic phase. The value of the magnetic hyperfine field associated with the sextet component, 34.0 T, is consistent with that of -Fe–Ni alloy. In the spectra of the other samples the central line disappears. The magnetic component, used in fitting the spectrum of the sample with x=40 has a hyperfine magnetic field B _hf=30.0 T. This component is assigned to the high-spin -FCC Fe–Ni phase. Two magnetic components of 16.3 T and 27.3 T are used to fit the spectrum of the sample with x=35. The 27.3 T component is associated with the typical high-spin -FCC Fe–Ni phase while the 16.3 T component is associated with a -FCC Fe–Ni phase with magnetic relaxation.     

A Mössbauer experiment on Mars

A Mössbauer spectrometer for the mineralogical analysis of the Mars surface is under development. This instrument will be installed on a Mars-Rover, which is part of the Russian Mars'96 mission. Due to power and mass restrictions, the electromechanical drive and the electronic components have been extremely miniaturized, and for the rude conditions during take-off and landing, very much ruggedized in comparison to standard systems. Solid-state detectors (PIN-diodes) are used for - and X-ray detection in backward geometry and will also give information on the elemental composition by X-ray fluorescence spectroscopy. The different operations of the spectrometer are controlled autonomously by a microprocessor.     

Magnetic Properties of Neutron-Irradiated RPV Steel by Mössbauer Spectroscopy

The neutron irradiated reactor pressure vessel (RPV) steels at various doses of 010¹⁸ n/cm² have been studied with Mössbauer, X-ray diffraction, and VSM. The Mössbauer data show that the value of a magnetic hyperfine field of Fe atom that exists at the martensite is 330 kOe at site 1, and 305 kOe, at site 2. At room temperature, the total absorption area of Mössbauer spectra with respect to irradiation of neutron is constant for the dose of 010¹⁶ n/cm², while over the dose of 10¹⁷ cm² the absorption area decreases rapidly. But the doublet area for the dose of 010¹⁶ n/cm² is constant, while over the dose of 10¹⁷ cm² it increases with an increase in the fluence level of neutron. The value of IS and QS at site 1,2 varied slightly with an increase in the fluence level of neutron. However, at a doublet site existing Fe³⁺ state, over the dose of 10¹⁷ cm², the values of IS and QS increase with an increase in the fluence level of neutron. Note that over the dose of 10¹⁷ n/cm² the neutron irradiated sample loses crystal structure slowly. The coercivity and remanence of the neutron irradiated samples do not change significantly. But the maximum induction decreases by 5% at 10¹⁸ n/cm², us compared with that of the as-received sample.     

Characterization of Argentine Loess and Paleosols by Mössbauer Spectroscopy

Hyperfine Interactions - We have used Mössbauer spectroscopy to investigate iron-bearing mineral samples of loess and paleosols from a geologic section at La Plata, Argentina, 34°...     

Mössbauer study on iron-polygalacturonate coordination compounds

⁵⁷Fe Mössbauer spectroscopy was used to determine the oxidation state and microenvironments of iron in the Fe-polygalacturonate compound prepared by a novel method from pectin. ICP analysis was applied to study the iron content of the coordination compounds. It was found that there are two ferrous and one ferric microenvironments in the compound. In the iron- polygalacturonate compound the ferrous forms occur dominantly. A model for the bonding of Fe in the polygalacturonate chains is proposed.     

A Fitting Procedure for Magnetic Multiphase Materials Mössbauer Spectra

In this work a practical method of fitting complex multiphase Mössbauer effect spectra is proposed. The task is simplified imposing specific restrictions to the analysing functions, which are appropriate for cases where the component phases spectra do not change substantially during the process under study. The ME spectra can be analysed using the phases subspectra, by defining only a reduced number of parameters. The constraints are equivalent to assume a Doppler velocity transformation v=(v–_m)B _m0/B _m+_m0 for each phase, where _m and B _m are fitting parameters containing information on the phase mean isomer shift and hyperfine field and _m0 and B _m0 their reference values. In this manner physically meaningful results are easy to obtain. The idea was applied to partially nitrogenated R₂Fe₁₇N _x (R= Sm and Y) and partially hydrogen-decomposed Nd–Fe–B materials.     

Application of Mössbauer Spectroscopy to the Carbon Oxides Hydrogenation Reactions

Iron-based catalysts have favorable activity and selectivity properties for the CO and CO₂ hydrogenation reactions. Several Fe phases (oxides and carbides) can be present in these catalysts. The interaction of Fe with the other components of the catalyst (support, promoters) can affect the ease of reduction and also its transformation during the reactions. In this work, the relationship between catalytic behavior in the CO and CO₂ hydrogenation reactions and the Fe phase composition of fresh and reacted catalysts was studied. Two types of catalysts were tested: a laterite and the other one made of iron supported on alumina, both unpromoted and promoted with K and Mn. Only those Fe species which can be reduced-carburized, by means of a pretreatment or by an in situ transformation under the reaction, seem to be able to perform the CO or CO₂ hydrogenation. The reoxidation of the Fe carbide to magnetite was not associated to deactivation. The selectivity seems to be more affected by Fe species difficult to reduce than by magnetite produced by reoxidation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of Ni-Containing Goethites by Mössbauer Spectroscopy and Other Techniques

A set of goethite samples from the oxidized level of Vermelho Ni-lateritic deposit was investigated by TEM, XRD, TGA-DTA, FTIR and Mössbauer spectroscopy and compared to a series of synthetic goethite samples, with similar Ni content. Natural Ni-containing goethite presents poor crystallinity and does not incorporate more than about 4 mol% Ni. Natural goethite particles also contain significant amounts of Al and Cr (1.6 and 0.7 mol%, in average, respectively). The wavenumbers of the OH deformation vibration bands -OH (in-plane vibration) and lengthening -OH (out of plane vibration) are coarsely negatively correlated with Ni content. The weight loss during the thermal analysis of synthetic samples shows a good linear relationship with Ni content, pointing to a proton uptake in order to compensate a possible charge imbalance due to a Ni²⁺ for Fe³⁺ substitution. The Mössbauer spectra of Ni-goethite present one sextet whose parameters are in agreement with those usually reported for goethite. The magnitude of the hyperfine field slightly decreases with increasing Ni, while the other parameters remain unchanged. These variations may be explained by Ni incorporation, but also by differences in the crystallinity. The effect of the low Ni concentration in our samples was a weak to medium correlation of the analytical signals with the Ni content in goethite, but when considered together, the results indicate that isomorphic substitution is occurring.     

Magnetic field effects on Mössbauer spectra ofAuFe

Zero and applied field Mössbauer spectra onAuFe alloys with 5, 10 and 20 at % Fe have provided information on the spin glass, cluster glass and long range ferromagnetic phases which are present in this system. The mean hyperfine parameters for these phases are presented.     

Mössbauer Spectroscopy Study of FeSe0.91S0.09 Superconductor Single Crystals

JETP Letters - Mössbauer spectra of single crystals of sulfur-doped iron selenide FeSe0.91S0.09 are studied in a wide temperature range, including the vicinity of structural and...     

Synchrotron Mössbauer reflectometry

Grazing incidence nuclear resonant scattering of synchrotron radiation can be applied to perform depth-selective phase analysis and to determine the isotopic and magnetic structure of thin films and multilayers. Principles and recent experiments of this new kind of reflectometry are briefly reviewed. Methodological aspects are discussed. Model calculations demonstrate how the orientations of the sublattice magnetisation in ferro- and antiferromagnetic multilayers affect time-integral and time-differential spectra. Experimental examples show the efficiency of the method in investigating finite-stacking, in-plane and out-of-plane anisotropy and spin-flop effects in magnetic multilayers. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mössbauer spectroscopy on57Fe: NaCl crystals

Mössbauer absorbtion spectra of⁵⁷Fe-doped NaCl crystal were measured and correlated with an adequate electric field gradient computation to describe the dipolar complexes occuring at the decay of Suzuki-phase under thermal treatment and X-ray irradiation. An electrostatic potential of the type was taken into account in the evaluation of EFG tensor.     

The influence of pressure on the Mössbauer effect

A study was made of the pressure dependence of the intensity of the Mössbauer line, and the dependence of this quantity on the specific volume of the crystal, which has the same form for all these crystals in the first approximation, was derived for regular atomic crystals in the Grüneisen approximation. The change in intensity of the Mössbauer line due to pressure can be converted, except for a multiplication factor, to a change in intensity of this line caused by a change in temperature.     

Study on chemical reactions of isolated Mössbauer probes in solid gas matrices using in-beam Mössbauer spectroscopy

In-beam Mössbauer spectra of ⁵⁷Fe after ⁵⁷Mn (T _1/2= 1.45 min) implantation into a CH ₄ matrix and mixture matrices of CH ₄ and Ar at 18 K were measured. The spectrum obtained in the CH ₄ matrix was analyzed well with a doublet and a singlet peaks. These components were assigned to two constitutional isomers of Fe(CH ₄)\(_{\mathrm {2}}^{\mathrm {+}}\) as derived from density functional theory calculations and the Mössbauer parameters. In the case of the low concentration of CH ₄ with an Ar matrix, the Fe ⁺ (3d ⁷4s) in the excited state atomic configuration and Fe ⁺ (3d ⁶4s ¹) in the ground state were observed, as observed in our previous implantation experiment into Ar and Xe matrices. The formation yields of Fe(CH ₄)\(_{\mathrm {2}}^{\mathrm {+}}\) are discussed in term of the number of first-nearest-neighbor CH ₄ molecules around an Fe ⁺ ion.     

Oxidation of Pyrite Grains: A Mössbauer Spectroscopy and Mineral Magnetism Study

Fe²⁺ in pyrite is found in a low-spin d⁶ configuration, a necessary condition for diamagnetic and semi-conducting properties of material. The semi-conducting property of pyrite has been studied since the time when pyrite was used as a rectifier in early radios. Pyrite posses the highest possible crystal field stabilisation energy and offers a better altemative as solar material compared to Si-based materials. Unfortunately, pyrite is difficult to study due to its inherent deviation from stoichiometry and its ease of oxidation. Since pyrite and its oxidation products are all Fe-bearing phases, combining Mössbauer spectroscopy with mineral magnetic methods provides enough information to monitor the oxidation of pyrite in air and identify the different phases produced and their relation to different experimental parameters. For mm-sized grain samples, heating FeS₂ at temperatures between 450 °C and 650 °C five different mineral assemblages are identified. FeS₂ is oxidized to α-Fe₂O₃ along two separate routes: $${\text{FeS}}_{2} \to {\text{FeSO}}_{4} \to \varepsilon {\text{ - Fe}}_{2} {\text{O}}_{3} \to \alpha {\text{ - Fe}}_{2} {\text{O}}_{3} ;\;{\text{and}}$$ $${\text{FeS}}_{2} \to {\text{FeSO}}_{4} \to {\text{Fe}}_{2} {\left( {{\text{SO}}4} \right)}_{3} \to \beta {\text{ - Fe}}_{2} {\text{O}}_{3} \to \alpha {\text{ - Fe}}_{2} {\text{O}}_{3} $$      

A Comparative Study of Iron Concentrates by Mössbauer Spectroscopy and Optical Microscopy

Five samples of iron-ore concentrates used for the production of pellets were heated at different temperatures under air atmosphere and characterised by chemical analysis, optical microscopy and Mössbauer spectroscopy. In all samples it was observed the presence of specular hematite, martite, and goethite in different proportions, whereas one sample also contains 15% (w/w) of magnetite. The presence of residual goethite was observed in the samples heated at 300°C, whereas the magnetite was only converted to hematite after heating at 900°C. However, the results of the optical microscopy pointed to the existence of large amounts of goethite even in the samples heated at 900°C, which is obviously incorrect. Therefore, it can be concluded that the reflectance of hematite derived from goethite is similar to that of the original goethite, limiting the use of optical microscopy for these types of samples.     

Austempering Transformation Kinetics of Compacted Graphite Cast Irons Obtained by Mössbauer Spectroscopy

Mössbauer spectroscopy has been applied systematically to study the processes occurring during the Stage I of the austempering transformation of compacted graphite cast irons at temperatures from 573 to 673 K for two Mn concentrations. The kinetics of transformation (γ→α _Fe +γ _hc ) was followed determining the dependence of the high-carbon austenite percentage on austempering time for different austempering temperatures and Mn contents. The evolution of the C concentration and the total amount of C incorporated into high-carbon austenite were also monitored. The results are compared with those of other morphologies and discussed in the frame of Johnson-Mehl's and diffusion models.