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Synthesis and physicochemical properties of composites for electromagnetic shielding applications: a polymeric matrix impregnated with iron- or cobalt-containing nanoparticles

Mössbauer spectra of the iron-containing samples: sample 4; sample 4 after annealed in argon; and sample 4 after annealed in air

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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Structural Features of Green Cobalt(III) Hydroxide

Deconvolution of emission Mossbauer spectra for green cobalt(III) hydroxide at 78 K and 298 K according to model 2
Structural Features of Green Cobalt(III) Hydroxide. D. A. Pankratov, A. A. Veligzhanin, Y. V. Zubavichus //Russian Journal of Inorganic Chemistry, 2013, Vol. 58, No. 1, pp. 67–73Search the full text below. Ищи полный текст ниже.

Emission Mössbauer and X-ray absorption XANES/EXAFS spectroscopic techniques are applied to elucidate the structural features of green cobalt(III) hydroxide. A comparative analysis of structurally characterized cobalt(II) and cobalt(III) oxo-compounds shows that the parameters of the local environment of cobalt atoms in green cobalt(III) hydroxide differ substantially from those of its analogues.

According to several reports of the late 50's of the twentieth century, the low-temperature reaction of cobalt(II) chloride with hydrogen peroxide in alcoholic media in the presence of sodium hydroxide affords dark green cobalt(II) peroxide. Although this synthesis protocol is broadly recited (in particular, it is described in all editions of the classical manual on inorganic synthesis by N.G. Klyuchnikov starting from 1965), the formation of such a simple cobalt(II) peroxide compound seems hardly possible. 


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Mössbauer study of oxo derivatives of iron in the Fe2O3-Na2O2 system

Possible models for describing of sum Mössbauer spectra at different temperaturesMössbauer study of oxo derivatives of iron in the Fe2O3-Na2O2 system. Pankratov D.A. //Inorganic Materials. 2014. V. 50. № 1. P. 82-89Search the full text below. Ищи полный текст ниже.

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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Formation Of Iron(VI) In Ozonalysis Of Iron(III) In Alkaline Solution

Mossbauer spectrum of Fe(VI) frozen solution in 5M NaOH (77 K)Formation of iron(VI) in ozonalysis of iron(III) in alkaline solution. Perfiliev Y.D., Benko E.M., Pankratov D.A., Sharma V.K., Dedushenko S.K. //Inorganica Chimica Acta. 2007. V.360. №8. P.2789-2791.Search the full text below. Ищи полный текст ниже.

Here we report the formation of iron in hexavalent state, FeVIO42- in ozonalysis of iron(III) in alkaline medium. The formation of tetrahedral FeVIO42- ion is confirmed by UV–Visible and Mössbauer spectroscopic techniques. The value of isomer shift - δ, of the tetraoxyanion is consistent with known δ values for various salts of iron(VI) ion.

Iron is the most abundant transition element on Earth and commonly exists in compounds of its +2 and +3 oxidation states. Iron ions in these two oxidation states are generally used in biological electron transfer processes. Iron in higher oxidation states such as +4, +5, and +6 are involved in iron enzymes, organic synthesis, and Fenton chemistry. Examples include capability of Fe(IV) and Fe(V) at enzymatic sites to abstract H and/or to break C–C bond, participation of high-valent nonheme ironoxo species in biometric oxidations, and involvement of aqua oxoiron(IV) in environmental and catalytic chemistry.


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Mössbauer Diagnostics of the Isomorphic Substitution of Iron for Aluminum in Triclinic Iron Vanadate

Dependence on the fraction of iron atoms in the i-th position in respective surrounding j on the degree of substituting x in AlxFe3 – xV3O12Mössbauer Diagnostics of the Isomorphic Substitution of Iron for Aluminum in Triclinic Iron Vanadate. Pankratov D.A., Yur’ev A.I. //Bulletin of the Russian Academy of Sciences. Physics. 2013. V.77. №6. P.759-764.Search the full text below. Ищи полный текст ниже.

Mössbauer spectroscopy and X-ray powder diffractometry (XRD) phase analysis are used to study mixed vanadates with the composition AlxFe3– xV3O12, where x is 0, 0.3, 1.0, 1.5, 2.0, 2.7 and 3.0. Mössbauer spectroscopy is used to study the distribution of trivalent cations over different crystallographic positions. It is shown that the distribution of aluminum atoms differs from those expected from statistic and thermodynamic models.

Materials based on iron and vanadium compounds, which include material doped by transition or nontransition metals, are widely used as catalysts and sensor materials. Apart from solid solutions, two individual compounds form in the iron(III) oxide–vanadium(V) oxide system in particular: Fe2V4O13 and FeVO4. In turn, iron ortovanadate FeVO4 crystallizes depending on the conditions in an orthorhombic or triclinic system. In addition to its use in catalysis, triclinic iron vanadate has recently attracted attention due to its interesting magnetic properties. The type of iron vanadate formed at normal pressures is a multiferroic, and antiferromagnetic ordering is observed in it at temperatures below 22 K.


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