Application of 57Fe Mössbauer spectroscopy as a tool for mining exploration of bornite (Cu5FeS4) copper ore

Nuclear resonance methods, including Mössbauer spectroscopy,are considered as unique techniques suitable for remote on-line mineralogical analysis. The employment of these methods provides potentially significant commercial benefits for mining industry. As applied to copper sulfide ores, Mössbauer spectroscopy method is suitable for the analysis noted. Bornite (formally Cu₅FeS₄) is a significant part of copper ore and identification of its properties is important for economic exploitation of commercial copper ore deposits. A series of natural bornite samples was studied by ⁵⁷Fe Mössbauer spectroscopy. Two aspects were considered: reexamination of ⁵⁷Fe Mössbauer properties of natural bornite samples and their stability irrespective of origin and potential use of miniaturized Mössbauer spectrometers MIMOS II for in-situ bornite identification. The results obtained show a number of potential benefits of introducing the available portative Mössbauer equipment into the mining industry for express mineralogical analysis. In addition, results of some preliminary ^63,65Cu nuclear quadrupole resonance (NQR) studies of bornite are reported and their merits with Mössbauer techniques for bornite detection discussed.     

Depth resolved structural study of heavy ion induced phase formation in Si/Fe/Si trilayer

Intermixing in Si/Fe/Si trilayer induced by 120 MeV Au ions has been studied. X-ray fluorescence provides information about the depth distribution of Fe atoms, while Mössbauer spectroscopy and XAFS provide information about the changes in the local structure. In the as-deposited film Fe layer is amorphous in nature with a significant Si content in it. Irradiation to a fluence of 1 ×10¹³ ions/cm² results in formation of non-magnetic intermixed layer with its hyperfine parameter close to those of Fe_0.5Si with CsCl structure. XAFS measurements under X-ray standing wave condition provide depth resolved structural information.     

Simultaneous Triple Radiation Mössbauer Spectroscopy (STRMS)

The setup for Simultaneous Triple Radiation Mössbauer Spectroscopy (STRMS) is described. The arrangement allows an independent and simultaneous recording of conversion electron Mössbauer spectra (CEMS) and of conversion X-ray Mössbauer spectra (CXMS), both in backscattering geometry, and-in addition-of γ-ray absorption spectra in transmission (TMS). Due to the different escape or penetration ranges of the three radiations involved, the spectra give information on phases, depth and orientation. From a practical point of view the counter for γ-rays, X-rays and electrons must be separated and shielded to minimize the mutual perturbation.     

Clays and clay minerals: What can Mössbauer spectroscopy do to help understand them?

Mössbauer spectroscopy is a powerful technique for the characterization of materials formed in the weathering environment. Mössbauer studies of clay-sized phyllosilicates, however, are burdened with several problems: the samples are rarely monomineralic, they may be poor in iron, and only few iron-rich species order magnetically above 4.2 K. Site occupancies are difficult to determine, and cis and trans octahedral-OH site assignments are normally not possible. Unequivocal information that can be gained from such work thus is often restricted to the determination of the oxidation state of iron and average structural site distortions. Mössbauer data on iron oxides are generally more straightforward to interpret because these can be studied in the magnetically ordered state. A further asset of Mössbauer spectroscopy when studying iron oxides lies in its high sensitivity for magnetically ordered phases. Adverse effects ensuing from small particle size, interparticle interactions, non-stoichiometry and foreign-element substitution that often affect the Mössbauer parameters of iron oxides occurring in clays and soils can be at least partly offset by taking spectra at low temperatures.     

Nuclear quadrupole resonance in the gamma-resonance spectra of soft matter

It is shown that the harmonic librations (oscillations) of the principal axis of the electric field gradient tensor in “cages” of liquids, glasses, ferroliquids, and other “soft” systems qualitatively change the shape of the Mössbauer spectra of the quadrupole hyperfine structure. In addition to an effective decrease in the quadrupole coupling constant in the fast-libration limit, nuclear quadrupole resonance is predicted, which must be manifested in the Mössbauer spectra at the libration frequency that is approximately equal to the quadrupole splitting of spectral lines. By analogy with nuclear magnetic resonance, simple analytical expressions are derived, which describe resonance Mössbauer spectra in terms of the effective quadrupole coupling constant and the resonance splitting constant for the main lines. The observed features of the formation of quadrupole hyperfine structure spectra can be manifested in the Mössbauer spectra of soft matter and must be taken into account in analysis of experimental data.     

Magnetic insulator glasses

An outline is given of the use of Mössbauer spectroscopy as a probe of the amorphous structure and magnetic coordination in magnetic insulator glasses. Using the⁵⁷Fe Mössbauer resonance as an example in the context of amorphous ferric oxides and fluorides, the manner in which both paramagnetic and hyperfine-field-split spectra can be analyzed is presented. Emphasis is given to the information contained in Mössbauer lineshapes and linewidths in addition to the more obvious line-position data. A number of general findings are set out for ferric speromagnetics with particular references to Mössbauer studies of amorphous Fe₂O₃, Y₃Fe₅O₁₂ (YIG), FeF₃ and NaFeF₄.     

Mössbauer study of new functional metal/polymer nanocomposites with spatially oriented FeGa particles

Mössbauer spectroscopy has been applied to study the structure and magnetostriction interdependence of metall/polymer composites with spatially oriented FeGa particles in a polymer matrix. Composites were synthesized combining modified polyurethane with nanocrystalline mechanosynthesized particles of magnetostrictive FeGa composition through polymerization to achieve a considerable magnetostrictive response. To increase magnetoelastic effects a spatial particle arrangement in the polymer matrix was generated. The magnetostrictive composition of the mechanosynthesized particles has been determined by Mössbauer spectroscopy, X-ray diffraction and TEM at different stages of ball milling. The microstructure of the composites via the particle orientation in the polymer has been researched by SEM and Conversion Mössbauer spectroscopy with the registration of resonant X-rays. The spatial particle inhomogeneity and magnetic anisotropy have been analyzed in order to reveal the factors determining the functional properties of the manufactured composites. Three-fold enhancement of the magnetostrictive response for FeGa/polyurethane composites with non-standard magnetic anisotropy has been demonstrated.     

Study of nano-scale diffusion in thin films and multilayers

It is shown that x-ray reflectivity and x-ray fluorescence under standing wave conditions can be used to study atomic diffusion with an accuracy of a fraction of a nanometer. Both the techniques can be made isotope selective by making use of nuclear resonance scattering from a Mössbauer active isotope. The techniques have been used to study self-diffusion of Fe in amorphous and nano-crystalline alloys of FeZr and FeN. The observed correlation of the activation energy E with pre-exponent factor D₀ confirms that in amorphous FeZr alloy diffusion takes place via collective motion of a group of atoms. Even in nanocrystalline alloys it is found that atomic diffusion occurs mainly through grain boundaries which are amorphous or highly disordered in nature.     

Artificial neural networks in Mössbauer material science

Mössbauer spectroscopy is a useful technique for characterizing the valencies, electronic and magnetic states, coordination symmetries and site occupancies of the cation. The Mössbauer parameters of isomer shift and quadrupole splitting are useful to distinguish paramagnetic ferrous and ferric iron in several substances, while the internal magnetic field provides information on the crystallinity. In recent years artificial neural networks have shown to be a powerful technique to solve problems of pattern recognition of a mineral from its Mössbauer spectrum, Mössbauer parameters data bank, crystalline structure and magnetic phases of soil from Mössbauer parameters. A computer software named Mössbauer Effect Assistant has been developed. It uses learning vector quantization neural network linked to a Mössbauer data bank that contains Mössbauer parameters of isomer shift, quadrupole spliting, internal magnetic field and the references of the substances. The program identifies the substance under study and/or its crystalline structure when fed with experimental Mössbauer parameters. It can also list the references from the literature by feeding the name of the substance or the author of the publication. Typical application of Mössbauer Effect Assistant in iron-bearing materials Mössbauer spectroscopy is present in user friendly Microsoft Windows environment.     

Interface study of Ag/57Fe/Ag trilayer using Mössbauer and X-ray standing wave analysis

Interface of Ag/⁵⁷Fe/Ag trilayer has been studied with a depth resolution of a fraction of a nanometer using x-ray standing waves generated by a W/Si multilayer mirror used as a substrate. Two interfaces of 38 Å thick Fe layer in Ag/⁵⁷Fe/Ag trilayer are clearly resolved. It is found that the rms roughness of the two interfaces Fe-on-Ag and Ag-on-Fe are 10 ± 1.0 and 6 ± 1.0 Å, respectively. Conversion electron Mössbauer spectroscopy (CEMS) has been used to get information about the volume fraction of the intermixed region and the estimated roughness from the relative area of the two sextets of CEMS spectra is found to be 7.0 Å which is consistent with the average roughness obtained by X-ray fluorescence measurements. However, the asymmetry of the interfaces can not be inferred from CEMS measurements.     

Study of the magnetic properties of GdZn compound using PAC spectroscopy with 140Ce and 111Cd as probe nuclei

Nanocrystalline Al₆₄Cu₂₃Fe₁₃ icosahedral quasicrystal has been obtained by milling of solid quasicrystal precursors prepared by arc-melt. The local structure around Fe atoms was studied by Mössbauer spectroscopy using a quadrupole splitting distribution method. Mössbauer results of annealed and milled samples show the existence of a broadened distribution of Fe sites which is associated to intrinsic disorder. The structural characterization was determined using x-ray diffraction. The average grain-size of the nanostructured quasicrystal, obtained from the line broadening of the X-ray diffraction peaks, was estimated to be of the order of 10 nm for a sample milled by 5 h.     

Lattice Dynamics and Inelastic Nuclear Resonant X-Ray Scattering

Measurement of thermal and elastic properties of materials, like phonon density of states, specific heat or speed of sound, by a new X-ray scattering technique is presented. Inelastic nuclear resonant scattering of X-rays produced from new electron storage rings, coupled with advances in high-energy-resolution crystal optics and fast detectors has enabled the development of a new method of analyzing the energy loss in a scattering process with a resolution of 10⁷ or better in the X-ray region of 6–30 keV. Some unique aspects like element (isotope) selectivity, the amount of material needed for analysis (nanograms) and physical size that X-rays can be focused (5 micrometer or better) favors this approach over more established techniques of neutron scattering, Mössbauer, and Raman spectroscopy. Applications to several unique cases (e.g., multilayers and high pressure) are discussed.     

Laser Investigations of Stored Metal Cluster Ions

The Mössbauer characterization of nanosized iron oxides is based on the dependence of the magnetic relaxation time on several parameters. Because the contributions of the magnetic anisotropy and of the particle volume cannot be separated, the knowledge of properties other than hyperfine by the use of several techniques is needed to achieve a full understanding of the studied system. In this work, after a brief review of the difference between bulk and nanostuctured magnetism, we show how Mössbauer spectroscopy, complemented by other techniques, applied to nanosized systems of maghemite and hematite, yields a good characterization of the solids and of the interparticle interactions. In the case of hematite we also show that more work is needed to identify in depth the parameters that determine the Morin transition.

     

Mössbauer spectroscopy of metals from birth to death

In today's metallurgy, precision techniques, such as X-ray and electron diffraction, electron microscopy, infrared spectroscopy and electron probe micro-analyzer, are being indispensably used, and, comparing to them, Mössbauer spectroscopy is not inferior at all in usefulness, convenience and cost benefit. Actually, however, it is not yet popular among the metallurgists probably because people believe that the Mössbauer effect is a difficult physics, radioactive sources are difficult to handle, and spectral analyses are complicated. These beliefs are in fact groundless and must be dissolved for further diffusion of this useful Mössbauer technique in metals and other industries. The present introductory talk intends to help people's better understanding and no anxiety for using the Mössbauer spectroscopy by showing how it can be applied to various problems of metals and alloys from their birth to the end, that is, from the study of minerals and ores before smelting to that of corrosion and other failures. Firstly, the principle of Mössbauer spectroscopy will be explained with simplest illustrations together with simple pictures of apparatuses including the high temperature furnace and the high pressure cell. In the second will be shown typical examples of Mössbauer patterns of magnetite, carbon steel and other alloys, with indications of how to analyze the seemingly complicated spectra. Some other examples will be shown with special apparatuses easy to measure. The usefulness and convenience of Mössbauer spectroscopy will be understood again from these examples. More examples will be on amorphous alloys and other advanced materials.     

Characterization and pH stability of insoluble products of the reaction between cyanide and ferrous sulphate

X-ray diffraction (XRD), infrared (IR) spectroscopy and⁵⁷Fe Mössbauer effect spectroscopy were used to characterize and monitor the pH stability of cyanide and ferrous sulphate reaction mixtures. Limited information was obtained from the XRD and IR measurements because of the amorphous nature of the samples. The Mössbauer studies show that considerable changes occur when there is an increase in pH at which the sample is prepared. Prussian-blue type compounds and iron oxide in the form of small particles crystallize out at low and high pH values, while additional complexes are formed at intermediate pH values of 6 to 9.⁵⁷Fe Mössbauer effect spectroscopy is thus a powerful technique for monitoring the environmental stability of cyanide waste streams that result when modern methods of extractive metallurgy of gold are employed on mineral ores.     

Mössbauer,X-rays and SEM analysis of meteorites from the mineralogy museum of the University of Parma (Italy)

Five meteorites, belonging to the private collection of the Mineralogy Museum of the University of Parma have been analyzed by Mössbauer spectroscopy, X-rays diffraction X-rays fluorescence and by scanning electron microscope. Following standard classification they have been assigned to the ordinary chondrites class, L type, with different minor compositions.     

Dynamics of iron in Fe-porphyrin aggregates studied by X-ray absorption and Mössbauer spectroscopy

The iron-porphyrin aggregates were studied by optical absorption and fluorescence method, infrared spectroscopy, X-ray absorption and Mössbauer spectroscopy. The aggregation of porphyrin molecules strengthens the Fe-ligands bonds and accelerates the spin-spin relaxations. A significant speeding-up of relaxation was observed with lowering the temperature down to 25 K. The comparison of the EXAFS (Extended X-ray Absorption Fine Structure) and Mössbauer spectroscopy results enabled some separation of the individual Fe vibration from its collective movement with ligands.     

In-situ identification of iron--zinc intermetallics in galvannealed steel coatings and iron oxides on exposed steel

Identification of all the compounds present in various coatings on steels is particularly difficult. Non-destructive, in-situ analysis is necessary if the fraction of each compound as well as its probable layering within the coating, is to be determined. Mössbauer spectroscopy is one valuable probe capable of uniquely identifying all iron compounds which form as coatings on steel and other iron alloy surfaces. To investigate a complete coating several criteria need to be considered. Removing the coating inevitably leaves a small and perhaps important component intact on the substrate. Therefore investigating the coating as it remains intact on the steel is important if complete identification of the iron compounds is to be made. This also preserves crystalline texture or preferred growth orientation within the coating to which the Mössbauer effect is sensitive. Mössbauer spectroscopy is a non-destructive technique which allows the integrity of the coating to be maintained during analysis. The combined transmission and scattering Mössbauer geometries generally result in accurate analysis of the coating composition. For the scattering geometry added information on compound layering is obtained if separate Mössbauer spectra are recorded using the re-emitted gamma rays as well as the conversion electrons and subsequently emitted X-rays. In-situ scattering Mössbauer spectroscopy has been used to characterize the iron--zinc alloys which form in the coatings of commercially produced corrosion resistant galvannealed sheet steel, a product of great interest to automotive producers. The results show that different amounts of four iron--zinc phases are present depending on the production conditions of the coating. The different phases are also distinctly layered. Mössbauer analyses of corrosion coatings formed on the surface of steels which have been exposed to different environments has also been undertaken. Materials include structural steels exposed for up to 25 years in marine, rural and industrial environments, and the interior surfaces of boiler pipes subjected to adverse chemical and temperature environments.     

Aspects of thermal martensite in a FeNiMnCo alloy

Thermal martensite characteristics in Fe–29%Ni–2%Mn–2%Co alloy were investigated with scanning electron microscopy (SEM) and Mössbauer spectroscopy characterization techniques. SEM observations obviously revealed the lath martensite morphology in the prior austenite phase of examined alloy. As well, the martensitic transformation kinetics was found to be as athermal type. On the other hand, Mössbauer spectroscopy offered the paramagnetic austenite phase and ferromagnetic martensite phase with their volume fractions. Also, the internal magnetic field of the martensite was measured as 32.9 T from the Mössbauer spectrometer.