T. Yu. Kiseleva

Low temperature formation of nanocrystalline Fe–W and Fe–Mo compounds

Abstract Nanocrystalline Fe–W and Fe–Mo compounds obtained by coupled reduction of fine dispersed FeOOH with H 2 WO 4 (or with H 2 MoO 4 ) in continuous H 2 flow at the temperature range 700–740°C were studied by means of Mossbauer spectroscopy and X-ray diffraction. The formation of partially disordered and even amorphous intermetallic phases and solid solutions with extended concentrations was observed. Hydrogen incorporation in the structure of disordered intermetallic phases during the reduction process was revealed.

Study of the products of interaction between iron and gallium during mechanical activation

Mechanochemical interaction between iron and gallium has been investigated. The multistage character and the dynamics of mechanochemical formation of the gallium solid solution in iron have been established. X-ray diffraction, electron microscopy, and atomic force microscopy have been used for studying structural and morphological peculiarities of products formed at various stages of mechanical activation. Mössbauer spectroscopy has been used for the investigation of local variations in the nearest surroundings of iron atoms during phase transformations.

Mechanochemically synthesized powder precursors local structure influence on the microstructure of SHS Fe2O3/Fe/Zr/ZrO2 composites

Composite powder materials containing zirconia and iron oxide nanoparticles, as well as iron-zirconium intermetallic compounds, are of great interest for use as high-temperature functional coatings, in catalysis, and for medical and biotechnological purposes. In this work the influence of the forming local structure of particles during the mechanical activation of Fe/Zr and Fe2O3/(Fe/Zr) powder precursors on the microstructure of Fe2O3/Fe/Zr/ZrO2 nanocomposites, synthesized in a SHS combustion mode, is investigated.

Step-by-step powder composite mechanosynthesis for functional nanoceramics

To study the possibility of Fe2O3 mechanochemical reduction by preliminary mechanically alloyed Fe+20%Al compound their powder mixture was subjected to high-energy ball-milling in Ar atmosphere, with the milling time varying between 2 and 12 minutes. The milled samples obtained at various times of milling were characterized by X-ray diffraction and Mossbauer spectroscopy. As a result gradual α-Fe2O3 reduction via formation of intermediate Fe-Al-O oxides was observed. The presence of the intermediate Fe2AlO4 spinel phases stable over long milling time is stated. Mechanocomposite Fe+20%Al transformation to α-Fe(Al) solid solutions which evolve peculiarly with the milling time, was observed also. The kinetics of α-Fe2O3 reduction process was analyzed in comparison with the same processes in the systems: α-Fe2O3 + Al and α-Fe2O3 + Al + Fe.

Mechanochemical production of nanocomposites of metal/oxide and intermetallic/oxide systems

Addition of nanosized intermetallic or metallic phases into corundum considerably raises mechanical behavior of the material. In this work, the nanocomposites of α-Al2O3/intermetallic and α-Al2O3/metal systems were obtained by mechanochemical reduction of α-Fe2O3 by Al (and by solid solution of Al in Fe). The mechanochemical reduction process of hematite by various amount of metal-reducer was studied by IR and Mossbauer spectroscopies, and by X-ray synchrotron radiation diffraction technique.

Anisotropic magnetostrictive metal-polymer composites for functional devices

New metal-polymer composites based on mechanochemically synthesized magnetostrictive Fe-Ga phase particles with dimensions of up to 2 μm dispersed and spatially oriented in a polymer matrix have been studied. The polymer matrix for spatial anisotropic stabilization of particles was represented by modified polyurethane (PU). An increase in the magnetostrictive effect was achieved by directed orientation of particles in a magnetic field applied during polymerization of the PU matrix. The spatial anisotropy of the composite has been studied by the methods of conversion Mössbauer spectroscopy with resonant X-ray detection and scanning electron microscopy. It is shown that the mechanochemical synthesis is an effective method of obtaining particles with microstress-enhanced magnetostriction. The use of these particles for the formation of a functional elastomer composite provides a material with significant magnetostrictive effect, which can be several-fold increased due to orientation of particles in an applied magnetic field. The obtained anisotropic magnetostrictive composite is a promising material for the creation of smart functional components of positioning systems, attenuators, and sensors.

Mössbauer spectrocopy in the technology of nanocomposite functional materials

Research results obtained to date by applying Mössbauer spectroscopy to iron-containing nanosized structures and the revealed patterns of how the nanoscale state impacts hyperfine interaction parameters in simple, multicomponent, and hybrid systems lay the groundwork for developing algorithms for the targeted synthesis of multifunctional nanoscale materials. This work discusses the contribution Mössbauer spectroscopy is making to the development of technologies for synthesizing new functional nanocomposites containing mechanically activated nanoparticles.

UV luminescence of commercial YAG:Ce phosphors

It is established that the emission spectrum of synthesized YAG:Ce phosphors excited at a wave-length of 290 nm contains, in addition to a yellow-green band, two intense UV bands with maxima at ∼320 and ∼360 nm. The observed separation of these emission bands is related to the partial absorption of radiation by Ce3+ ions. Nonreabsorbed UV luminescence spectra have been measured and characterized.

Obtainment of the Fe0.70−xCrxAl0.3/Al2O3 nanocomposite by the method of SHS of mechanoactivated Cr2O3 + Fe + Al mixtures

Applying Mössbauer spectroscopy methods, we have studied the structure of nanocomposites obtained by a technique combining the preliminary mechanical activation of an 8.1 wt % Cr2O3 + 65.9 wt % Fe + 25 wt % Al mixture and self-propagating high-temperature synthesis (SHS). It has been found that, at the stage of mechanical activation, an Fe/Al/Cr2O3 composite with a low impurity of the Fe2Al5 intermetallide is formed. At the stage of SHS, the interaction between activated components of the mixture leads to the formation of the Fe0.7 − xCrxAl0.3 (x = 0 − 0.2)/Al2O3 composite.

Study of the crystallization stages for amorphous system Fe84−xWxB16 (x = 0−5)

Abstract The crystallization process of this ternary amorphous system was studied by Mossbauer spectroscopy, X-ray diffraction and DTA. We examined the sequence of crystalline metastable and stable phases emergence and the particulars of their compositions. The Mossbauer parameters for the stable crystalline phase FeWB the quadrupole splitting Δ = 0.30 mm s and the isomer shift δ = − 0.20 mm s were first determined in our research.