Naděžda Pizúrová

Fe3Si surface coating on SiFe steel

Abstract Fe3Si layers were prepared using chemical vapor deposition of Si on the surface of GO steel and its subsequent heat treatment. The changes in the structure and phase composition after different heat treatment conditions have been analyzed. The coating is characterized by high hardness, good corrosion resistance, high electrical resistivity, and the spin texture which differs from the steel substrate.

α-Fe nanopowder synthesised in low-pressure microwave plasma and studied by Mössbauer spectroscopy

An iron-based nanocomposite has been prepared by the microwave plasma method: Fe(CO)5 vapour was introduced into an argon discharge at ~1 kPa. The synthesised nanopowder was passivated in situ with a mixture of Ar and air. The as-prepared nanopowder was characterised by XRD, TEM, Raman and M?ssbauer spectroscopies. In the XRD pattern of the nanopowder the ?-Fe (dXRD = 14 nm, 76 wt.%) and Fe3O4 (dXRD = 3 nm, 24 wt.%) phases were identified only. ?-Fe cores covered with oxide shells were observed under TEM. A huge increase of M?ssbauer absorption was observed after the sample was cooled down to 5 K. The results of magnetic and thermal properties studies at low and high temperature are presented. The heat capacity of the sample exhibited an unexpectedly high value of 599 J/kg/K.

Iron-Based Nanopowders Containing α-Fe, Fe3C, and γ-Fe Particles Synthesised in Microwave Torch Plasma and Investigated with Mössbauer Spectroscopy

Two Fe-based nanopowders were synthesised using microwave torch discharge at 1 bar. The main channel of the discharge was operating in Ar, which flowed through the central nozzle of an electrode, whereas the reactive mixture H(2)/Fe(CO)(5) was added through a concentric outer nozzle. Besides rarely observed gamma-Fe particles (for the first sample: d(XRD) = 30 nm, 35 wt %; for the second sample: d(XRD) = 9 nm, 33wt %) samples also included alpha-Fe, Fe(3)C, and Fe(3)O(4)/gamma-Fe(2)O(3) particles. The presence of gamma-Fe phase was proved by the interpretation of the XRD patterns and the Mossbauer spectra taken at 293 and 5 K.

Versatile low-pressure plasma-enhanced process for synthesis of iron and iron-based magnetic nanopowders

Using microwave low-pressure discharge, we synthesised magnetic iron-oxide nanopowder from the iron pentacarbonyl precursor. We were able to vary the size and chemical composition (especially the ratio between various iron oxides) by careful control of the process parameters. The nanoparticulate product was analysed by X-ray diffraction (XRD) and Raman spectroscopy. However, the XRD cannot reliably distinguish between the size-broadened peaks of γ-Fe2O3 (maghemite) and Fe3O4 (magnetite) due to their nearly identical crystalline structure. Hence we used a chemical method to determine the presence of Fe(II) and Fe(III) ions in the nanopowder samples. The results agree with those from the Raman spectroscopy.

Nanocrystal Growth in Thermally Treated Fe75Ni2Si8B13C2 Amorphous Alloy

Thermal treatment of amorphous Fe75Ni2Si8B13C2 alloy leads to crystallization of the stable α-Fe(Si) and Fe2B as well as to the metastable Fe3B phase. The study of the mechanism of crystal growth of the α-Fe(Si) phase revealed that the mechanism of α-Fe(Si) growth changes from two dimensional in the early stage to one dimensional in the later stage of crystallization. The Fe2B phase was found to crystallize through two independent routes: from the amorphous phase and from the metastable Fe3B phase, which leads to a different mechanism of crystal growth for each route. Both routes exhibit a change in the mechanism of crystal growth: from two dimensional to one dimensional and from three dimensional to two dimensional, respectively. The respective mechanisms of crystal growth correlate well with the observed changes in preferential orientation of the crystallites of the Fe2B phase.

Thermally Induced Structural Transformations of Fe40Ni40P14B6 Amorphous Alloy

Thermal stability and thermally induced structural transformations of Fe40Ni40P14B6 amorphous alloy were examined under non-isothermal and isothermal conditions. Formation of metastable α-(Fe,Ni), and stable γ-(Fe,Ni) and (Fe,Ni)3(P,B) crystalline phases as the main crystallization products was observed, while the presence of small amounts of other crystalline phases like Fe23B6 and Fe2NiB was indicated by electron diffraction in HRTEM. Thermomagnetic curve indicated that Fe content in different crystalline phases is very different, resulting in markedly different Curie temperatures after crystallization. Transmission electron microscopy and atomic force microscopy study suggested multiple-layered platelet-shaped morphology, both on the surface and in the bulk of the crystallized alloy sample. The thermal treatment heating rate and maximum temperature affected surface roughness and grain size inhomogeneity.

Iron-Based Nanocomposite Synthesised by Microwave Plasma Decomposition of Iron Pentacarbonyl

A nanocrystalline iron-based powder has been prepared by microwave plasma method: Fe(CO)5 vapor was introduced into an argon discharge at ~1 kPa. A microwave 2.45 GHz generator was operated at 430 W. The reaction took place inside a quartz tube passing through a microwave waveguide. The microwave discharge (without and with Fe(CO)5) was characterized by optical emission spectroscopy. The synthesized nanopowder was passivated in situ with air. The asprepared nanopowder was characterized by TEM, XRD, Raman and Mössbauer spectroscopies. The nanopowder included α-Fe, α-Fe2O3, and Fe3O4 phases. The core-shell nanoparticles were observed under TEM: α-Fe cores had shells formed of Fe3O4 or carbon. The mean crystallite size of α-Fe was 36 nm (Scherrer formula). The synthesized nanopowder exhibited ferromagnetic behavior.