Papers by Keyword: Mössbauer Spectroscopy

Abstract: Mössbauer spectroscopy (MS), was used to characterize the synthesized materials prepared from the elemental powders by hydrothermal method which are binary iron-based nanoparticles (NPs) Fe₁₅Co₈₅ and Fe₁₀Co₉₀ alloys. The transmission ⁵⁷Fe Mössbauer spectra were measured at room temperature RT (T~300K), using ⁵⁷Co γ-ray source with an Activity ~ 1.85 GBq (50 mCi). The analysis of Mössbauer spectra curves was by using WinNormos with two subspectra with the “Site” option and then with the “Dist” option in order to learn more about hyperfine interactions and parameters such as isomer shifts IS, quadruple splitting QS and hyperfine magnetic field B_hf. MS results observe only one Zeeman sextet with a relative area of ~77.125% with parameter B_hf = 32.727 T and line width Γ=0.693 mm/s for Fe₁₀Co₉₀, and a relative area of ~84.719% with parameter B_hf = 34.354 T and line width Γ=1.043 mm/s for Fe₁₅Co₈₅ and one broad singlet which confirms the body-centered cubic structure BCC. The main contribution to the spectra comes from the magnetic sextet which is assigned to ferromagnetic FeCo phase which is the dominant one while the singlet is assigned to paramagnetic phase. As a result of the analysis of the distributions hyperfine magnetic field the average values of the hyperfine parameters of the Mössbauer spectra were obtained <B_hf>Fe₁₀Co₉₀ = 28.3363 T and <B_hf>Fe₁₅Co₈₅ = 31.4657 T. Therefore, it is observed that the increasing of the cobalt concentration decreases the hyperfine field. The results observe indicates Co concentration dependence, where for Co-rich alloys (Fe₁₀Co₉₀) the FCC (face-centered cubic structure) contributing to the decrease in B_hf due to the absence of BCC. the obtained NPs most likely to be in disordered structure A2.

Abstract: This study describes the sol-gel method's synthesis of ferrites [MFe₂O₄, M(II) = Co, Cu, Mg, Ni, and Zn]. The structure was studied by X-ray diffraction analysis. The surface morphology was studied using scanning electron microscopy (SEM), and the magnetic properties were studied using Mössbauer spectroscopy. The diffraction peaks at 30.1^◦, 35.6^◦, 43.2^◦, 53.6^◦, 57^◦, and 62.6◦ can be attributed to Bragg reflections (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1), and (4 4 0) planes confirm the formation of a cubic spinel structure of ferrite nanocrystals. The average size of magnesium ferrite crystallites calculated from the half-width of the most intense peak (3 1 1) was 25.96 ± 4.32 nm. Magnesium ferrite is a magnetically soft ferromagnetic powder with a predominance of the magnetite phase and relatively high magnetisation values. The magnitude of the hyperfine magnetic field for the studied nanoparticles is in the range of 440-490 kOe, which confirms the hypothesis that the analysed samples are particles of an iron-containing oxide with a disordered structure.

Abstract: Fe(Ni, Si) solid solutions were elaborated by high energy mechanical alloying from elemental Fe, Ni and Si powdersfor a milling time of 72 h. From X-ray diffraction (XRD) analysis, it has been shown that the Fe(Ni, Si) samples present a single phase in the whole range of Si content and exhibit a solid solution of disordered bcc α-Fe. The lattice parameter a (Å) of the new structures and the mean crystallitessize <D> (nm) were found to decrease with increasing Si contents. In contrast, the microstrain behaviour presents two different stages as the Si contents are increased. Scanning Electron Microscopy (SEM) images confirmed the behaviour of the mean crystallites size, where it can be seen that the addition of Si promotes the reduction of the size of powder particles. The saturation magnetization Ms was found to decrease by a factor of almost 1.4 and the coercively was found to increase by a factor of almost 2.4, when the Si content was increased from x= 0 % to x= 20 %. The Mössbauer spectroscopy confirmed the local in site crystal locations of Si and Ni as they diffuse into the matrix of the bcc α-Fe structure to form a solid solution.

Abstract: Magnetic nanoparticles (MNPs) have many uses for biomedical applications including drug delivery, magnetic resonance imaging (MRI) contrast agents, theranostics and hyperthermia. MNPs photo-thermally heated by laser light could be used to treat the typically difficult to access tumors such as glioblastomas. Due to their high magnetic saturation, monometallic iron nanoparticles would have an edge over iron oxide nanoparticles currently being investigated for hyperthermia. The goal of this study was to synthesize spherical iron nanoparticles less than 10 nm in diameter by thermal decomposition. The ability of various biocompatible coatings to protect the metallic iron nanoparticles from oxidation was investigated. Coatings studied included Brij, polyethylene glycol and iron oxide. Transmission electron microscopy and Mössbauer spectroscopy were utilized to characterize the coated and uncoated iron nanoparticles’ size and oxidation state to evaluate the effectiveness of the coatings and the procedures in which the coatings were applied. A ferrite shell was found to provide the best stabilization; however, its longer synthesis time increased particle size distribution. Polymer coatings provided biocompatibility but did not prevent oxidation.

Abstract: Nanocrystalline Ni₇₅Fe₂₅ (Ni₃Fe) powders were prepared by mechanical alloying process using a vario-planetary high-energy ball mill. The intermetallic Ni₃Fe formation and different physical properties were investigated, as a function of milling time, t, (in the range 6 to 96 h range), using X-Ray Diffraction (XRD) and Mössbauer Spectroscopy techniques. X-ray diffraction were performed on the samples to understand the structural characteristics and get information about elements and phases present in the powder after different time of milling. The refinement of XRD spectra revealed the complete formation of fcc Ni (Fe) disordered solid solution after 24 h of milling time, the Fe and Ni elemental distributions are closely correlated. With increasing the milling time, the lattice parameter increases and the grains size decreases. The Mössbauer experiments were performed on the powders in order to follow the formation of Ni₃Fe compound as a function of milling time. From the adjustment of Mössbauer spectra, we extracted the hyperfine parameters. The evolution of hyperfine magnetic field shows that the magnetic disordered Ni₃Fe phase starts to form from 6 h of milling time and grow in intensity with milling time. For the milling time more than 24 h, only the Ni₃Fe disordered phase is present with a mean hyperfine magnetic field of about 29.5 T. The interpretation of the Mossbauer spectra confirmed the results obtained by XRD.

Abstract: Mechanical alloying has recently attracted considerable attention as researchers try to improve materials properties. The process can be performed at room temperature and homogeneous alloys can be produced. In this work Fe–28 wt. % Al; Fe–26 wt. % Al–2 wt. % Sn and Fe–26 wt. % Al–2 wt. % V alloys were synthesized by mechanical alloying to investigate the effects of tin and vanadium additions on the structural and microstructural properties of Nanocrystalline FeAl Alloy. Fe₇₂Al₂₈, Fe₇₂Al₂₆Sn₂ and Fe₇₂Al₂₆Sn₂ were ball milled for 30 h under argon atmosphere using a rotating speed of 200 rpm with 15 min pause time after every 15 min running time. The structural and microstructural properties of the ball milled powders were analyzed using X-ray diffraction (DRX) and Mössbauer spectroscopy techniques. The final powders are characterized by an average crystallite size of 10 nm for the Fe₇₂Al₂₈ alloy, 6 nm for the Fe₇₂Al₂₆Sn₂ alloy and 19 nm for the Fe₇₂Al₂₆V₂, accompanied by the introduction of a lattice strain of order of 1.55 %, 0.78 % and 0.80% respectively. The Mossbauer study of the Fe₇₂Al₂₆V₂ samples showed doublet with isomer shift IS= 0.17 mm/s and three magnetically split sextet.

Abstract: Nanostructured (Fe_0.6Al_0.4)_100-xSi_x powders with x= 0, 5, 10, 15 and 20 at.% were elaborated by means of mechanical alloying for a fixed milling time of 72 h. We have investigated the effect of silicon addition on the microstructure and magnetic properties of these ternary alloys. X-ray diffraction experiments reveal that these powders are single-phase disordered solid solutions with body centered cubic crystal structure. The lattice parameter diminishesalmost linearly as the Si content increases. The mean crystallite size,<D(nm)>, is around three times smaller for the samples with higher amount of Si (≈ 10 nm) compared with that of the binary alloy (27 nm). Moreover, the volume fraction of grain boundaries (fgb) seems to be higher with increasing the Si content, as well as both dislocation density (ρ) and lattice microstrain (<ε>),that follow alinear trend. The SEM images show that the Si helps in refining the shape and size of the powder particles, leading to a nearly homogeneous small particles.The addition of Si strongly affects the value of the saturation magnetization, Ms, that falls nearly an order of magnitude for the sample with 20 at.% Si, while the coercivity remains almost unchanged. The Mössbauer spectra show the presence of a sextet (ferromagnetic phase) and a singlet or a doublet (non ferromagnetic phase), except for the sample corresponding to x = 10, where only one singlet is observed in the spectrum.

Abstract: Capabilities of application of Mössbauer spectroscopy for determination of grain-boundary diffusion parameters in coarse-grained and ultrafine-grained materials have been analyzed. Application of this method for revealing of non-equilibrium state of grain boundaries in ultrafine-grained materials obtained by severe plastic deformation is demonstrated.

Abstract: It is shown that the value of the equilibrium oxygen partial pressure, Po₂ as a value available for measurements is possible to be taken as a measure of slag redox potential of, taking into account its electronic system performance. Application of the electromotive force method (EMF) allowed establishing the character of a change in the average oxidation state of iron ν_Fe depending on Po₂, the temperature and slag composition. The study of Mössbauer absorption spectra of quenched slag samples confirmed the possibility of simultaneous presence of iron in the flux in oxidation states from 0 to +3.

Abstract: In the present study, flat specimens from polycrystalline α-iron were monotonically and cyclically loaded at ambient temperature for the investigation of magneto-mechanical behavior. The magnetic flux density was measured by a Hall-sensor in in-situ and ex-situ experiments. For the characterization of the magnetic microstructure of α-iron Kerr microscopy was used. Additionally, Moessbauer spectroscopy of specimens in initial state and after failure was performed.