A. Umićević

Hydrogen diffusion in MgH2 doped with Ti, Mn and Fe

Incorporation of suitable dopants in MgH2 is widely investigated as the way of improving hydrogen storage characteristics of this material. The catalytic role of transition metal dopants on hydrogen desorption from MgH2 is very promising, but further attention is required in order to optimize the experimental methods and design materials with desired properties. In this paper we investigate the role of Ti, Fe, and Mn on the transport properties of hydrogen in MgH2, which are marked as limiting factor in the effort to lower the hydrogen desorption temperature. Taking into account the lattice relaxation around the impurities, we consider a number of different diffusion paths in the pure and doped system. Using PAW DFT calculations in combination with the NEB method, we demonstrate that the diffusion of the most relevant positively charged hydrogen vacancy and negatively charged interstitial hydrogen atom is locally hindered by the presence of the impurity atoms.

SEM and XRD Characterization of Ni-Hf Alloys at Low Hf Concentration

The alloying and phase formation in Ni-Hf samples with 0.2-, 2-, and 5-at.% Hf were studied by X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). Both characterization methods, XRD and SEM, reveal the presence of the HfNi5 phase (fcc structure) where the excess Ni atoms are present in the form of Ni or Ni-rich segregations in the sample containing 5-at.% Hf. The sample with 2-at.% Hf is characterized by the presence of the two phases present in the 5-at.% sample and by Hf atoms, which occupy substitutional lattice positions in the Ni lattice. Finally, in the third sample with 0.2-at.% Hf, the Hf atoms mainly substitute the Ni atoms in the lattice. This analysis is being complemented with additional information on the local structure around Hf by extended X-ray absorption fine structure spectroscopy (EXAFS).

Site preference and lattice relaxation around 4d and 5d refractory elements in Ni3Al

X-ray absorption spectroscopy is employed to investigate site preference and lattice relaxation around Mo, Ru, Hf, W and Re dopants in Ni3Al. The site occupation preference and the measured distances between the refractory elements as dopants and the nearest host atoms are compared with the results of ab initio calculations within the density functional theory. Combined experimental and theoretical results indicate that Mo, Hf, W and Re atoms reside on the Al sublattice in Ni3Al, while Ru atoms occupy the Ni sublattice. A more pronounced lattice relaxation was detected in the case of Hf and Ru doping, with a strong outward relaxation of the nearest Ni and Al atoms.

Mineral characterization of soil type ranker formed on serpentines occurring in southern Belgrade environs Bubanj Potok

The paper addresses the issue of health risk associated with the presence of chrysotile in the soil type ranker formed on massive serpentines occurring in the area of Bubanj Potok, a settlement located in the southern Belgrade environs, Serbia. Characterization of the ranker soil was conducted by scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy and transmission 57Fe Mossbauer spectroscopy. Scanning electron microscopy figures showed regular shaped smectite (montmorillonite) particles, aggregates of chlorite, and elongated sheets of serpentines minerals antigorite. X-ray diffraction analysis confirmed the presence of detrital mineral quartz polymorph as well as minor amounts of other mineral species. Micro-Raman spectroscopy identified the presence of dominant minerals, such as montmorillonite, kaolinite, muscovite, gypsum, calcite, albite, amphiboles (hornblende/kaersutite) and orthoclase. Important polymorph silica modifications of quartz, olivine (forsterite), pyroxene (enstatite/ferrosilite, diopside/hedenbergite), and serpentine (antigorite/lizardite/chrysotile) were identified.

Mössbauer Spectroscopic Analysis of Nd2Fe14B/α-Fe Hard Magnetic Nanocomposites

Among novel magnetic intermetallics based on rare earth-transition compounds, the Nd2Fe14B/α-Fe isotropic nanocomposites have been obtained by recrystallization from an amorphous phase, prepared by melt spinning. For variable 5 wt.% Fe and 10 wt.% Fe contents we recorded transmission 57Fe Mössbauer spectra at the room temperature, hardened of the α-Fe phase by exchange interactions. The spectra have been analyzed in terms of ten Zeeman sextets and one paramagnetic doublet related to the Nd1.1Fe4B4 phase. One sextet corresponds to the α-Fe phase, whereas others are attributed to six non-equivalent Fe sites in the Nd2Fe14B structure, namely 16k1, 16k2, 8j1, 8j2, 4c, and 4e. The three remaining sextets belong to the Fe3B structure with three inequivalent Fe sites FeI(8g), FeII(8g) and FeIII(8g). All relevant parameters for both nanocomposites: the magnetic hyperfine field, the isomer shift and the quadrupole splitting are determined for each of these sites.