Synthesis and physicochemical properties of composites for electromagnetic shielding applications: a polymeric matrix impregnated with iron- or cobalt-containing nanoparticles G.Yu. Yurkov; A.S. Fionov; A.V. Kozinkin; Yu.A. Koksharov; Y.A. Ovtchenkov; D.A. Pankratov; O.V. Popkov; V.G. Vlasenko; Yu.A. Kozinkin; M.I. Biryukova; V.V. Kolesov; S.V. Kondrashov; N.A. Taratanov; V.M. Bouznik //Journal of Nanophotonics. 2012. V.6, Iss.1, 061717 (December 05, 2012)
Magnetic, magnetic resonance, and structural properties of iron and cobalt nanoparticles embedded in a polyethylene matrix were studied. The materials were prepared by thermal decomposition of cobalt or iron formate in a polyethylene melt in mineral oil and contained from 2 to 40% wt. of metal. Transmission electron microscopy data indicate that the average diameter of particles is up to 8.0 nm. According to extended x-ray absorption fine structure and Mössbauer spectroscopy studies, the particles comprise a metallic core and nonmetallic shell which is chemically bound to the surrounding matrix. Electrophysical and magnetic properties of the materials prepared were studied along with their reflection and attenuation factors in the super high frequency band. The materials were found to be suitable for use in electromagnetic shielding.
The possibility of combination of properties specific for metals and polymers in a single material, as well as control of these properties by means of concentration variations, has been studied for a while. Different polymers can be used as the matrix in such a material, e.g., polyethylene, polypropylene, polytetrafluoroethylene, and others. These polymers exert relatively high thermal resistance, unique rheological properties and high dielectric strength and they are chemically inert and easily processable, which allows one to form items of any desired shape and size from them. It is also important that these polymers are produced using well-studied methods.
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Mössbauer study of oxo derivatives of iron in the Fe2O3-Na2O2 system. Pankratov D.A. //Inorganic Materials. 2014. V. 50. № 1. P. 82-89
Various compositions of oxo derivatives of iron reacting with sodium peroxide have been studied by Mössbauer spectroscopy. We have examined several mathematical models of the measured spectra. The results obtained are inconsistent with hypotheses made previously that such conditions may lead to the formation of compounds of iron in oxidation states above (+6). We demonstrate that a large excess of an alkali peroxide leads, most likely, to the formation of at least two iron(V) derivatives in tetrahedral coordination. In their Mössbauer spectra, they have isomer shifts of −0.45 and −0.51 mm/s and unusually large quadrupole splittings: 1.32 and 1.94 mm/s (at room temperature).
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