Mössbauer study of mechanically alloyed powders

Using the⁵⁷Fe Mössbauer spectroscopy, the microscopic behavior of Fe powders has been investigated during and after the mechanical alloying (MA) process for Al?Fe and Ag?Fe systems. A repeated rolling method as well as a conventional ball-milling method are employed in order to understand the microscopic process of the kneading of Al and Fe powders during their MA and the resultant powders show quite similar Mössbauer spectra suggesting that the kneading by an impact between colliding balls is the same process as that of the thickness reduction by cold rolling. Mössbauer spectra show clearly the occurrence of the mutual atomic dispersion for the thermodynamically immiscible Ag?Fe system.     

CXMS study of mild steel laser alloyed with CrB2

Laser alloying of surfaces has attracted a great deal of attention for technical applications. By laser alloying of materials it is possible to improve hardness as well as wear and corrosion resistance of the surface without affecting the bulk material. The surface of a mild steel (C45) substrate was laser-alloyed with chromium-boride CrB₂. The chromium-boride was added to the substrate surface by powder injection during laser surface melting with a high power continuous-wave CO₂-laser. The resulting surface layers were studied by surface Mössbauer measurements. The backscattering geometry of Conversion X-ray Mössbauer Spectroscopy (CXMS) was used to study the phase formation in the laser alloyed surface. The results for the treated surfaces are discussed for different samples.     

A study of laser surface alloyed steel

Coatings composed of Ni and Co based alloys were prepared by surface alloying of steel substrate. In the study of composition and structure of the coatings, Mössbauer spectroscopy in scattering geometry, X-ray diffraction and energy dispersive X-ray microanalysis were applied. The results, in addition to phase composition data, showed the effect of the thermal history of samples. The contribution of Mössbauer spectroscopy consists in revealing the structure details resulting from rapid cooling of the remelted surface layer.     

The Mössbauer community in the USA

Scientists in the United States assumed major roles in developing the Mössbauer community during its early years. However, since the termination of the Mössbauer Effect Methodology meetings in 1976, there has been little in the way of regular Mössbauer meetings in the United States. Nevertheless, there is an active United States Mössbauer community, as noted by the number of annual publications – 156 in 2004. In recent decades, attendance of Mössbauer researchers from the United States at the International Conferences on the Applications of the Mössbauer Effect (ICAME) has been far below what would be expected from the number of contributions in the Mössbauer literature. Attempts have been made, unsuccessfully, to arrange for regular Mössbauer meetings. Models for possible future Mössbauer meetings of US scientists are discussed, including a regular biannual meeting, and another being a virtual Mössbauer conference. Also discussed are other models to maintaining an active Mössbauer community in the United States, making use of information technologies that are available to us along with other resources we can use.     

Mössbauer diffraction and interference studies of polycrystalline metals and alloys

After a review of previous work on Mössbauer diffraction and interference phenomena, the principles of the kinematical theory of Mössbauer diffraction are presented. The emphasis is on how the spectroscopic capabilities of the Mössbauer effect can be used to advantage in diffraction studies on materials and condensed matter. Experimental results from Mössbauer powder diffractometry experiments are presented. These results identify the difficulties of Mössbauer powder diffraction experiments, but also demonstrate that a unique chemical environment selectivity is possible for Mössbauer diffraction. Future experiments with Mössbauer powder diffraction require the development of efficient detectors, and some possibilities are suggested.     

Mössbauer study of incompletely alloyed nanocrystalline Fe100 − x Al x prepared by high energy ball milling

Mechanically alloyed Fe_100???x Al _x powders, with 20≤?x?≤90, have been studied by X-ray diffraction and room temperature ⁵⁷Fe Mössbauer spectroscopy. The milling time was chosen such that complete alloying does not take place. For a fixed milling time of 10 h, the rate of alloying was seen to increase exponentially with increase in Fe content. Mössbauer spectra of all the samples consist of a broad magnetic sextet and a quadrupole doublet. The isomer shifts and quadrupole splitting of the doublets are typical of Al-rich, Fe–Al alloys. The area under the quadrupole doublet is a maximum for x?=?66. Analysis of the Mössbauer spectra indicates the formation off- stoichiometric Fe₃Al phase for x?<?66, while the formation of Fe clusters is largely responsible for the magnetic hyperfine component in x?≥?66 compositions.     

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.     

Phase transformations of the FePO4 catalyst in the oxidative dehydrogenation to form an alkyl methacrylate

A phase specific iron orthophosphate catalyst, FePO₄, was synthesized and subjected to oxidative dehydrogenation reactions to form an alkyl methacrylate. The phases of the catalyst, before and after the reactions, were characterized by Mössbauer spectroscopy. The Mössbauer spectra show the change of the catalyst precursor FePO₄, tridymite-like phase (tdm), to the reduced form, iron(II) pyrophosphate, Fe₂P₂O_7, and thereafter the phase change is governed by the temperatures of oxidation. X-ray diffraction and Mössbauer measurements on the spent catalyst, after using organic and water co-feeds, show a transformation of the catalyst to a mixture of phases which are condition specific.     

Structural-Phase Transformations and Short-Range Order Evolution in the Fe–Cr System during Mechanical Alloying

Physics of the Solid State - Using Mössbauer spectroscopy on 57Fe nuclei and X-ray diffraction, the mechanism of mechanical alloying in a planetary ball mill of the Fe–Cr nanocrystalline...     

X-Ray Diffraction,Mössbauer and Magnetization Studies of Nanocrystalline Fe33Ge67 Alloy Prepared by Mechanical Alloying

Hyperfine Interactions - The nanocrystalline Fe33Ge67 alloy was prepared by mechanical alloying and its formation was followed by X-ray diffraction, 57Fe Mössbauer spectroscopy and...     

Mechanical alloying of Fe and Cr: Structural and magnetic studies

Mechanical milling of a mixture of pure iron and chromium powders with a nominal composition of 28 at. % of Fe and 72 at. % of Cr was performed using two kinds of tools. The alloying process was followed by X ray diffraction and⁵⁷Fe Mössbauer spectroscopy. The room temperature Mössbauer spectra revealed the formation of a broad single line at the expense of the area of α-Fe sextet. At 4.2 °K most of the singlet still remains unsplit. This behavior may be due to some metastable structure induced by the preparation method.     

The Mössbauer research community: A report

The Mössbauer research community has gone through various stages of development in its 30⁺ year history. Signs of maturity of the Mössbauer effect is shown in the number of experimental applications, the number of Mössbauer transitions that are available and the large number of scientists that have been and are involved with Mössbauer research. In recent years, there has been a significant increase in the number of publications using Mössbauer Spectroscopy to investigate both amorphous and high temperature superconductor materials. This overall growth in the Mössbauer scientific literature has been 6–7% per year since 1984, while during the preceding period there was no increase in the number of publications per year. The Mössbauer Effect Data Center continues to make use of the various developing technologies in the area of computers and communications. The Center recently completed a ten-year project of bringing together all its databases into one computer system. Also, the Center has recently completed the development of a new approach to the dissemination of information by making available subsets of the Mössbauer database on PC computer disks. The future of the Data Center will focus significant attention on networking strategies with the Mössbauer research community.     

Influence of Cu and Ni on the morphology and composition of the rust layer of steels exposed to industrial environment

Four samples of steels with alloying elements were exposed to an industrial environment during 1,955 days, aiming to elucidate the effect of the alloying elements Cu and Ni on the resistance of weathering steels to corrosion processes. The samples were characterized with optical microscopy, scanning electron microscopy (SEM), powder X-ray diffraction (XRD), saturation magnetization measurements and with energy dispersive (EDS), infrared, Mössbauer and Raman spectroscopies. All the steels originated orange and dark corrosion layers; their thicknesses were determined from the SEM images. EDS data of such rust layers showed that the alloying element content decreases from the steel core towards the outer part of the rust layer. Moreover, in the dark rust layer some light-gray regions were identified in the W and Cu-alloy steel, where relatively higher Cr and Cu contents were found. XRD patterns, infrared, Raman and Mössbauer spectra (298, 110 and 4 K) indicated that the corrosion products are qualitatively the same, containing lepidocrocite (γFeOOH; hereinafter, it may be referred to as simply L), goethite (αFeOOH; G), feroxyhite (δ′FeOOH; F), hematite (αFe₂O₃; H) and magnetite (Fe₃O₄; M) in all samples; this composition does not depend upon the steel type, but their relative concentrations is related to the alloying element. Mössbauer data reveal the presence of (super)paramagnetic iron oxides in the corrosion products. Saturation magnetization measurements suggest that feroxyhite may be an occurring ferrimagnetic phase in the rust layer.     

Hyperfine and Structural Properties of the Mechanically Alloyed (FeMn)30Cu70 System

Hyperfine Interactions - Nanostructured Fe15Mn15Cu70 alloys were prepared by high-energy ball milling. The alloying process spans grinding times from 15 minutes to 114 hours. The Mössbauer...     

Structure and Dynamics of High-Z Ions Studied at the ESR Storage Ring

Hyperfine Interactions - The magnetic order and crystallization of the amorphous Fe75Si15B10 alloy prepared by mechanical alloying was studied in situ by 57Fe Mössbauer spectroscopy. These...     

Small-angle neutron scattering and the Mössbauer effect in nitrogen austenite

Small-angle neutron scattering (SANS) in Fe-19%Cr-19%Mn-0.9%N and Fe-18%Cr-10%Mn-16%Ni-0.5%N (wt %) high-nitrogen austenites is investigated. The neutron diffraction patterns and Mössbauer spectra are measured and analyzed. The SANS curves are approximated in the framework of the Guinier and Porod models. The nature of small-angle neutron scattering in nitrogen austenite is explained in terms of microinhomogeneities whose structure depends on the alloying with nickel. The mean size and shape of inhomogeneities are evaluated. The effect of low-temperature annealing of the Fe-19%Cr-19%Mn-0.9%N austenite on small-angle neutron scattering and the parameters of the Mössbauer spectra is analyzed.     

Hyperfine Interactions in Amorphous Fe–Nb Alloys Prepared by Mechanical Alloying

Hyperfine Interactions - Single-phase amorphous Fe52Nb48 and Fe36Nb64 alloys were synthesized during mechanical alloying (MA) processes. X-ray diffraction and Mössbauer spectroscopy were used...     

On the role of alloying elements in nitrogen implanted iron

The role of alloying elements such as Cr and Al in the stability of the nitride phases formed due to nitrogen implantation in metallic iron was studied by using conversion electron Mössbauer spectroscopy (CEMS). The thermal stability of nitride phases was greatly increased by alloying elements as compared to pure α-Fe implanted with nitrogen.     

Mössbauer study of mechanical alloying in a Mo<Subscript>80</Subscript>Fe<Subscript>20</Subscript> system

The sequence of solid state reactions upon the mechanical alloying of Mo and Fe powders with an 80: 20 atomic ratio was established by means of Mössbauer spectroscopy and X-ray diffraction. At the first stage, a nanostructure and Mo₆₃Fe₃₇ hexagonal close packed (HCP) phase are formed in Mo body-centered cubic lattice (BCC) particles. At the second stage, a body-centered cubic lattice of Mo-Fe solid solution is formed. The process is accompanied by the formation of a minor amount (about 20%) of X-ray amorphous phase.     

Mössbauer investigation of magnetite nanoparticles incorporated in a mesoporous polymeric template

Mössbauer spectroscopy was used in this study to investigate magnetite-based nanocomposites, using mesoporous styrene-divinylbenzene (Sty-DVB) microspheres as the hosting template. The magnetite content was increased in the polymeric template by performing several in situ chemical reactions (one to six cycles) in the hosting material. We found the Mössbauer linewidth associated to site-A increasing with the relative increase of iron in site-A. The Mössbauer linewidth associated to site-B decreases with the relative decrease of iron in site-B. We explain our findings by assuming local change in the homogeneity associated to changes in the relative iron population in sites A and B.