Yu. D. Perfil’ev

Identification of Iron Oxidation States in the Products of Interaction of Na 2 O 2 and Fe 2 O 3 by Mössbauer Absorption Spectroscopy

The first stage of the solid-phase reaction of Na2O2 and Fe2O3 yields a tetravalent iron derivative. The product is unstable and disproportionates to form compounds with different oxidation states of iron. Analysis of their Mössbauer spectra was performed with the DISCVER program based on the Afanas’ev-Chuev method. At the early stage of analysis, the program identifies the maximal possible number of well-defined lines in the spectrum with a specified statistical quality and, thus, discerns a large number of known and unknown iron derivatives (phases) in samples of complex composition. Previously unknown highest oxidation states of iron from +5 to +8 were identified.

Resemblance of Intratrack Processes as a Common Starting Point of Radiation Chemistry and Positron, Muon, and Mössbauer Spectroscopies

A comparison of the yields of final products (57Fe2+, 119Sn2+) of the transformation of Mössbauer nuclei (57Co, 119Sn) in frozen aqueous and alcoholic glassy solutions with the Ps, Ms, and radiolytic-hydrogen formation probabilities in the same liquid media subjected to irradiation with positrons, muons, and fast electrons, respectively shows that the yields of 57Fe2+, 119Sn2+, Ps, Mu, and H2 vary in similar manners with a change in the concentration of electron scavengers or the temperature of the medium. These correlations are a manifestation of a profound similarity between the primary processes occurring in ionizing-particle tracks. Obviously, the recombination of ion-electron pairs inside large swarms (blobs) involving H2O+, e+, μ+, Fe3+, and 119Sn3+, respectively, is the most important process for understanding the formation of H2, Ps, Mu, 57Fe2+, and 119Sn2+.

Time-space evolution of the cloud of ion-electron pairs formed by Auger electrons around Mossbauer ion 57Fen+

It is shown that the emission of energetic Auger electrons during formation of the Mossbauer nucleus 57Fe leads not only to the formation of multicharged ion 57Fen+, but also to the formation of a cloud of several hundred (200–300) ion-electron pairs (H2O+, e−) around the Fe ion. This cloud is called an Auger blob. Its size (radius) is approximately ∼100 Å. Fast radiation-chemical reactions in an Auger blob determine the experimentally observable ratio of yields of final chemically stable states (Fe3+ and Fe2+) of the Mossbauer ion. Knowledge of this ratio is important for an adequate interpretation of the results of Mossbauer emission spectroscopy. Although our assessments relate to iron nuclei in frozen aqueous solutions, they can be easily adjusted for media of other chemical composition.

Magnetic porous composite material: Synthesis and properties

A new method of obtaining magnetic porous composite materials is described, which is based on the self-propagating high-temperature synthesis (SHS) in the form of solid-phase combustion. The SHS process involves transformation of the nonmagnetic α-Fe2O3 particles (contained in the initial mixture) into magnetic Fe3O4 particles. The synthesized material comprises a porous carbonaceous matrix with immobilized Fe3O4 particles. The obtained composite has been characterized by electron microscopy, X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. The sorption capacity of the porous material has been studied.

Interaction of Sr(II) and Np(V) with potassium ferrate(VI) reduction products in aqueous solution

The interaction of Sr(II) and Np(V) with potassium ferrate(VI) reduction products in aqueous solution at pH 4–8 was studied by liquid scintillation spectrometry. The ferrihydrite precipitate formed by reduction of ferrate ions quantitatively sorbs Sr(II) and Np(V) from 0.1 M NaClO4. The precipitate particle size determined by scanning electron microscopy is in the nanometer range. The degree of recovery of the radionuclides from simulated liquid radioactive wastes containing such complexing agents as acetate, citrate, and nitrate ions is 70 ± 5 and 84 ± 2%, respectively.

Emission Mössbauer study of “Cobalt Peroxide”

The product of the reaction of cooled alcohol solutions of cobalt(II) chloride with hydrogen peroxide, described in the literature as CoO2, was studied by emission Mössbauer spectroscopy. It was shown that the dark green product obtained was actually cobalt(III) oxide.

Mössbauer study of matrix effects in formation of high oxidation states of iron and cobalt

To fix unstable states of pentavalent iron and cobalt, a matrix containing (according to the preparation conditions) potassium manganates (V) was simultaneously doped with iron and radioactive cobalt. The absorption and emission spectra of this matrix, with allowance for the reversal of the source and absorber functions, are similar, which is indicative of the identity of the oxidation states (IV, V, and VI) of iron and cobalt in it. Stabilization of 57Fe and 57Co in the β-MnO2 matrix is also investigated by Mössbauer absorption and emission spectroscopy.

Primary Chemical Reactions Induced by Radioactive Nuclear Transformations

A series of chemical reactions is suggested to describe primary chemical transformations induced by Auger electrons from radioactive nuclear decay in glassy and crystalline frozen aqueous media. The mechanism is based on Mössbauer emission spectroscopy data supplemented by data on reactions in the tracks of fast positrons and electrons in an aqueous medium. It is shown that variation of temperature, the degree of crystallinity, the concentration of electron acceptors, etc., results in correlated changes in the yields of the final reaction products—Fe2+, Fe3+ or Sn2+, Sn4+ ions, positronium atoms, and molecular radiolytic hydrogen. These correlations indicate the similarity of chemical processes in the nanometer vicinity of decayed 57Co and 119mSn nuclei and in the tracks of fast positrons and electrons. This similarity is caused by the same behavior of secondary intratrack electrons produced due to ionization losses of fast positrons, electrons, and Auger electrons.

Self-oscillations of an ordered magnetic structure

The first observation of self-oscillations of an ordered magnetic structure is reported. They were detected by the Mössbauer effect in the Tb0.8Y0.2Fe2 ferrimagnetic compound and occur with a period of several days. The oscillations were initiated by a single electric-field pulse (∼108 kV cm−1 s−1). A phenomenological model of the phenomenon is proposed.

Mechanism of crystal modification of ferrihydrite by polymer hydrogels according to data of Mössbauer spectroscopy

The effect of a polymer hydrogel matrix and an ultrasonic field on the formation of a phase of iron(III) hydroxide is studied by means of Mössbauer spectroscopy. Polyacryl amide (PAA) and gelatin are chosen as polymer matrices for hydrogels. The transformation of iron hydroxide is interpreted as the formation of ferrihydrite with two different forms of iron relative to imperfect and relatively perfect fragments of the structure of crystallites. It is shown that the ultrasonic field and (in some cases) the polymer matrix have a substantial effect on the processes of crystallization of the dispersed phase.