Structural Transformations in Fe/Zr Bi- and Multilayers Induced by Ion-Beam Mixing

The Ar-ion-beam mixing of Fe/Zr bi- and multilayers is studied by conversion electron Mössbauer spectroscopy as a function of ion dose ranging from 1×10¹⁴ to 1×10¹⁷ at./cm². The mixing leads to amorphization of the Fe/Zr system. It was shown that the mixing process in bilayers depends strongly on the thickness of the Zr substrate. The amorphization is much more effective and occurs at lower ion doses in multilayers as compared to corresponding bilayers.     

Dependence of Magnetic Properties on Composition of Nanocrystalline Fe–M–B–Cu (M: Zr,Nb, Mo,Ti, Ta) Alloys

The specialized rf-Mössbauer technique is used to elucidate the magnetic properties of NANOPERM-type nanocrystalline alloys. The influence of alloy composition on the soft magnetic properties is studied for the Fe₈₀M₇B₁₂Cu₁ (M: Ti, Ta, Nb, Mo, Zr) alloys. The rf-Mössbauer experiments allowed us to distinguish magnetically soft nanoclusters from magnetically harder microcrystalline phases. The measurements performed as a function of the rf field intensity allowed the determination of the distribution of anisotropy fields related to the size distribution of bcc nanoclusters. Smaller anisotropy fields in the nanocrystalline phase were found in Nb-, Zr-, and Mo-containing alloys as compared with the alloys which contain Ti and Ta. The Mössbauer measurements were supplemented by X-ray diffraction determination of the size of nanocrystalline grains.     

The proton relaxation timesT 1 in binuclear copper complexes

Proton spin-lattice relaxation times as a function of temperature for two kinds of binuclear copper complexes with antiferromagnetic exchange interactionJS₁S₂ have been measured in order to understand the relaxation effects in exchange clusters. It is shown that the results reflect the coupling of the nuclear and electron subsystems; in the rangekT<J the coupling of the subsystems is modulated by temperature independent processes, in the rangekT≥J the temperature dependence of the dynamics of the electron subsystem is manifested. The response of the nuclear subsystem to the change in the nature of magnetic excitations is discovered.     

On the formation of the nanostructure in Fe80M7B12Cu1 (M: Ti, Ta, Nb, Mo) alloys

The dependence of the formation of the nanocrystalline bcc-Fe phase on the alloy composition is studied for Fe₈₀M₇B₁₂Cu₁ (M: Ti, Ta, Nb, Mo) alloys. The rf-Mössbauer technique is used to determine the optimal soft magnetic properties. This technique allowed us to compare anisotropy fields in each phase present in the composite alloys. The smallest anisotropy field was found in the bcc-Fe nanograins formed in Nb- and Mo-containing alloys.     

57Fe Mössbauer spectroscopy and X-ray diffraction study of complex metamict minerals. Part II

The magnetic behaviour of the nanocrystalline Ni_0.5Cu_0.5Fe₂O₄, synthesized by the co-precipitation method has been studied. The X-ray diffraction patterns confirm the formation of cubic spinel structure. The dc magnetization measurements show that the samples are superparamagnetic above the blocking temperatures and the blocking temperature increases with particle size. The reduction in saturation magnetization in the case of nanoparticles as compared to their bulk counterpart has been explained on the basis that the magnetic moments in the surface layers of a nanoparticle are in a state of frozen disorder. The hump in ZFC curve progressively shift to a lower temperature with increasing field and broader curves at higher field, suggests the spin-glass nature of the system.     

Adsorption of La,Eu and Lu on raw and modified red clay

Adsorption of La, Eu, and Lu on red clay was studied in an initial concentration range of 10^?4–10^?3 mol/dm³ and a pH range of 2–10. Among the different forms of red clay: T-clay (thermally modified), R-clay (raw, unmodified), Na-clay (sodium form), H-clay (acid form), and HDTMA-clay (surfactant-modified form), T-clay was found to be the most effective adsorbent of the lanthanides studied. The adsorption/desorption isotherms, i.e. log K _d versus log c _eq dependencies, had a linear character. Among the investigated lanthanides, Eu was most strongly bound by the clay surface and, therefore, parameters a (slopes of the lines log K _d = alog c _eq + b) of Eu were the highest compared to those for La and Lu. Desorption isotherms were located above adsorption isotherms, which resulted from chemiadsorption of the investigated lanthanides. Changes in lanthanide adsorption with pH were successfully modelled based on the molar fractions of Ln³⁺, LnOH²⁺, LnCO₃ ⁺, and Ln(CO₃) ₂ ^? species in the aqueous phase [Ln—lanthanide(III)].     

Study of effect of phosphate and uranium ions on the thermal properties of surfactant-modified natural red clay using TG–FTIR–MS techniques

Products of sorption of uranyl ions on HDTMA-red clay in the presence of phosphates were characterized by thermal analysis. It was established on the basis of DTG curves of the sorption products and FTIR spectra of the gaseous phase of sorption products decomposition that the thermal stability of the mineral increased when P(V) ions were sorbed along with U(VI) ions, i.e., the temperature of defragmentation/oxidation of surfactant increased when going from U(VI)–HDTMA-clay to U(VI)–P(V)–HDTMA-clay to P(V)–HDTMA-clay. The DSC curves of the sorption products showed that defragmentation/oxidation was an exothermic process and dehydration and dehydroxylation had an endothermic character. The investigated sorption system has practical importance, since an evident increase in U(VI) sorption over the entire pH range is observed when going from U(VI)–HDTMA-clay to U(VI)–P(V)–HDTMA-clay.

     

Structure and magnetic properties of bulk amorphous Fe60Co10Ni10Zr7B13 alloy formed by mechanical synthesis and hot pressing

Formation and magnetic properties of the bulk amorphous Fe₆₀Co₁₀Ni₁₀Zr₇B₁₃ alloy are described. The amorphous powder was prepared by high-energy ball milling of the amorphous ribbon and then was pressed under high pressure and temperature to obtain a bulk alloy in the form of a disc 5 mm in diameter and 2.5 mm thick. The compacted discs are fully amorphous as confirmed by X-ray diffraction and Mössbauer spectroscopy measurements. Differential scanning calorimetry curve recorded for the amorphous ribbon shows two exothermal peaks related to two stages of crystallization. Similar thermal behavior is observed for the powder samples. Hysteresis loops obtained for the amorphous ribbon, as-milled and compacted powders reveal their soft magnetic properties.     

A thermal,sorptive and spectral study of HDTMA-bentonite loaded with uranyl phosphate

The influence of phosphate ions on the thermal stability of complexes obtained by adsorption of uranium(VI) on organobentonite was determined. Organoclay samples were prepared by the reaction of hexadecyltrimethylammonium bromide with bentonite. The isotherms of sorption/desorption of U(VI) from aqueous solutions containing phosphate ions onto different forms of bentonite were measured using the batch method. The highest amount of uranium was absorbed on HDTMA-bentonite in the presence of phosphates. This may have been associated with the complexing of U(VI) ions by phosphate ions, which interacted with surfactant cations probably via electrostatic forces. A TG–DSC–MS study showed that the thermal decomposition of the surfactant sorbed on bentonite proceeded in two stages: at 200–400 and at 600–800 °C. The first stage involved defragmentation and oxidation of surfactant cations present in the interior and on the surface of the mineral. The second stage involved oxidation of charcoal and simultaneous dehydroxylation of the sorbent. The oxidation of surfactant cations and the dehydroxylation of the mineral were suppressed in the presence of phosphates.     

A DFT study of uranyl hydroxyl complexes: structure and stability of trimers and tetramers

A DFT study of U(VI) hydroxy complexes was performed with special attention paid to the [(UO₂)₃(OH)₅(H₂O)_4–7]⁺ and [(UO₂)₄(OH)₇(H₂O)_5–8]⁺ species. It was established that the ionicity of the U=O bond increased when moving from [(UO₂)(H₂O)₅]²⁺, [(UO₂)₂(OH)(H₂O)₈]³⁺, [(UO₂)₂(OH)₂(H₂O)₆]²⁺, [(UO₂)₃(OH)₅(H₂O)_4–6]⁺ to [(UO₂)₄(OH)₇(H₂O)_5–8]⁺ species. In both [(UO₂)₃(OH)₅(H₂O)_4–6]⁺ and [(UO₂)₄(OH)₇(H₂O)_5–8]⁺ complexes, the U=O bond was observed to have a range of different lengths which depended on the composition of the first coordination sphere of UO₂ ²⁺. The cyclic structures of trimeric complexes were somewhat more stable than their linear structures, which was probably due to the steric effect.