Papers by Keyword: Mössbauer Spectroscopy CEMS

Abstract: The systematic studies of non-stoichiometric phases from Fe-Al system obtained by selfpropagating high-temperature synthesis (SHS) were the aim of the present work. Investigations were performed using 57Fe transmission Mössbauer spectroscopy. The presence of nonsteichiomertic FeAl, FeAl2 and Fe2Al5 phases was found. It is can be concluded that the studied powder material is in non-equilibrium state. As the result of milling process the contents of FeAl phase increase whereas of FeAl2 and Fe2Al5 ones decrease. The determined crystal structure parameters and the hyperfine interaction parameters are presented and discussed.

Abstract: The Fe-Al-X and Fe-Al-Ni-X (X = Fe,Ni,Cu,Cr) metallic powders obtained by the selfdecomposition method and next intensive grinding in an electro-magneto-mechanical mill were examined by X-ray powder diffraction (XRD). Morphology of powders was determined by scanning electron microscopy (SEM) whereas energy dispersive spectroscopy (EDS) was applied to identify the composition of phases. The FeAlX and FeAlNiX phases both of B2 type structure were found besides small amounts of Al(OH)3 and rest of metallic additions.

Abstract: The temperature dependence of the magnetization (ac and dc) indicate that Sm1/3Sr2/3FeO3-d undergoes an antiferromagnetic transition at TN = 150 K. In low applied fields, the zero field cooled (ZFC) and field cooled (FC) magnetization below TN exhibit a hysteretic behavior. This behavior is suppressed by high applied field. The ac susceptibility for Sm1/3Sr2/3FeO2.95 shows that there is a clear frequency dependence developing below TN. The relusts of both ac and dc measurements suggest that the antiferromagnetic long-range order coexist with ferromagnetic correlations. Field-dependent resistivity versus temperature measurements reveal the existence of a magnetoresistance (MR) in the temperature below TN. The appearance of some ferromagnetic component within an antiferromagnetically ordered state may be responsible for the MR at low temperature.

Abstract: Magnetic oxide-coated iron nanoparticles with the mean size ranging from 6 to 75 nm were synthesized by aerosol method using iron carbonyl as a precursor under the flowing inert gas atmosphere. Oxide shells were formed by passivation of as-prepared iron particles. The influence of experimental parameters on the nanoparticles’ microstructure, phase composition and growth behavior as well as magnetic properties were investigated and discussed in this study.

Abstract: In this paper, a review of recent 57Fe Mössbauer spectroscopy (MS) studies of external influence on the properties of amorphous and nanocrystalline Fe- and Co-based alloys is submitted. Different types of alloys (FeCuNbZr, FeCuNbSiB, FeCoCuNbB, CoFeZrB and CoFeSiB) in the form of original amorphous and nanocrystalline ribbons were subjected to different external factors: different annealing atmospheres, mechanical stress (for example influence of ball-milling) and tensile stress. It will be shown that the Mössbauer spectrometry is a suitable tool for such studies because the measured spectral parameters are very sensitive to the changes in the vicinity of the probe 57Fe-nuclei and thus, this technique provides a wide variety of information about structural and magnetic behavior of Fe-containing materials.

Abstract: As the critical constructive analysis, with using the thermodynamic and crystal-chemical approaches, of the related experimental data is shown, the anomalous (with respect to the Al selfdiffusion characteristics (DAl - the self-diffusion coefficient, D0Al - the entropy (frequency) factor of the self-diffusion coefficient, QAl – the self-diffusion activation energy (enthalpy)) quantities of D*, D0*, Q* of the transition impurity Fickian diffusion in Al in many cases can be of the apparent character (related to the known Oriani model), whereas the normal quantities of D, D0, Q (i.e., close to DAl, D0Al, QAl), and the anomalously low quantities of D⊥, Q⊥, D0⊥ can be as the true characteristics of the impurity Fickian diffusion in the normal Al lattice (bulk) and in the compound-like nanosegregation (CLNS) structures at dislocations, respectively.

Abstract: We present magnetic and morphological characterization of iron- and iron-carbide- based nanopowder obtained by the laser synthesis from sensitized gas phase mixture containing acetylene and iron pentacarbonyl vapors. The analysis was performed on the as-prepared material and the annealed material. The results of TEM, XRD, Mössbauer and magnetic measurements are reported. Phase transformations taking place during annealing of the nanopowder when core-shell nanoparticles appear are discussed.

Abstract: The tool carbon steel powder, containing 1.1 % C, was subjected to heavy cold working by ball milling in a Fritsch P5 planetary ball mill. XRD studies showed that ball milling results in a dissolution of cementite and formation of nanoferrite. The crystallite size and lattice strain of ferrite, calculated by applying Williamson-Hall method, were 10 nm and 1%, respectively. Mössbauer spectroscopy measurements confirmed the formation of a phase called “distorted ferrite”, characterized by the values of hyperfine field of 28.5 T and isomer shift of 0.15 mm/s, different from ones of ferrite (32.9 T and 0.00 mm/s, respectively). DSC investigations revealed two heat effects recorded during heating the sample after 100 h of ball milling: exothermic effect at 360oC and endothermic one at 580oC. The first one was attributed to the dramatic decreasing of lattice strain (from 1% after milling down to 0.1%, as showed XRD studies) and slightly increasing of crystallite size (from 10 to 25 nm).The formation of Fe3C was not observed in this temperature and the structure of nanoferrite was preserved. The second observed heat effect was reversible and probably related to the eutectoid transformation, shifted by ball milling to lower temperature range, comparing to equilibrium conditions.