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The development of chemical sensor devices operating in non-contact mode is of primary interest due to the demand from various industries for a fast, simple and inexpensive determination of chemical composition in different media in a non-invasive way. One of the promising directions for the development of analytical devices with such characteristics is the use of high-frequency electrical signals. The paper discusses the evolution of high-frequency contactless conductometry method, likewise other methods and devices operating on similar physical principles (dielectric spectroscopy, microwave sensors, C4D detectors). [ABSTRACT FROM AUTHOR]

Terbium orthoferrite (TbFeO3) perovskite demonstrates specific magnetic properties which are object of interest. Aggregated granular nanopowder of TbFeO3 particles of 85.6 nm were obtained by direct solution combustion method. The orthorhombic perovskite structure (space group Pbnm) of the terbium orthoferrite was confirmed by powder X-ray diffraction, Raman spectroscopy and 57Fe Mössbauer spectroscopy. The unusual granular morphology and mesoporous structure of the nanopowder were investigated by scanning electron microscopy and adsorption-structural analysis via low-temperature (77 K) adsorption-desorption of nitrogen with a total porosity of 0.0145 cm³/g and average pore width of 12 nm. The magnetic properties of TbFeO3 nanoparticles were thoughtfully studied, M = 34.2 emu/g at T = 10 K, Hc = 300 Oe. The onset of reorientation of the Fe3+ spin system at T ~ 18 K and the antiferromagnetic ordering of Tb3+ ions at T ~ 4 K were observed by vibrational magnetometry. Obtained results confirm the flexible paramagnetic to antiferromagnetic behavior of granular TbFeO3 nanopowder. Highlight: Granular nanopowder of TbFeO3 was obtain by direct solution combustion method. Aggregated granular morphology of perovskite TbFeO3 was confirmed. Magnetization of TbFeO3 granules is in pronounced dependence of temperature. [ABSTRACT FROM AUTHOR]

The experience of developing methods of magnetic filtration (MF) for the purification of various aqueous media from impurities of iron oxides has been studied. An analysis of the reasons for the successes and failures of previous researchers in the development of methods and means of magnetic filtration has been carried out. Theoretical prerequisites for new technical solutions for high-gradient magnetic filters (HGMF) are considered. Laboratory experiments were performed on a high-gradient filter with a superconducting magnetic system using model solutions to determine the basic characteristics of the method. It has been established that it is sufficient to use permanent magnets based on rare earth elements (NdFeB, SmCo) as a magnetic field source to calculate the required magnetic field strength gradient. Designs of high-gradient filters with systems based on permanent magnets, as well as a program for numerical simulation of the process of processing particles of corrosion products of various phase and dispersed composition in a high-gradient magnetic field for these filters, have been developed. The tests results of VGMF of various designs for water treatment of spent fuel assemblies' (SFA) storage pools on a full-scale test bench—a prototype of a transport nuclear power plant (NPP) and a VVER-440 reactor plant—are presented. The efficiency of purification of the coolant of the first circuit from activated corrosion products by ion-exchange and high-gradient magnetic filters was compared when performing reagent-free decontamination of equipment. Certification of the innovative design of the VGMF with a system based on permanent magnets, which can be used to purify the water of heat supply systems of urban utilities from corrosion products, was carried out. [ABSTRACT FROM AUTHOR]

The results of the investigation into the morphology and phase and chemical composition of protective films and corrosion products deposits that form spontaneously on the steel surface during operation of the heat-exchange equipment with the oxidizing water chemistry in the tertiary coolant circuit of a BN-800 reactor unit are reported. A comparison is made of the phase composition of protective oxide films on the working surfaces in the tertiary coolant circuit of steam generators at BN-600 and BN-800 reactor units operating with different water chemistries. It has been demonstrated that, unlike type PGV horizontal steam generators employed at power units with pressurized water power reactors, where oxide films and deposits of corrosion products in the secondary circuit are determined only by magnetite (Fe3O4), films and deposits in the N-272 steam generator contain three phases: magnetite (Fe3O4), hematite (α-Fe2O3), and lepidocrocite (γ-FeOOH). A protective oxide film of magnetite (100%) is formed directly on the metal. On the film surface are formed a layer of deposits tightly bound to it and consisting of 70% of magnetite, 25–30% of hematite, 1–5% of lepidocrocite, and loose surface corrosion products deposits of corrosion products. The phase compositions of the dense layer (hematite) and loose corrosion products' deposits (hematite + lepidocrocite) on the working surfaces of the heat-transfer tubes in the N-272 steam generator correspond to the weakly alkaline oxidizing water chemistry for the tertiary circuit of the BN-800 reactor unit. It has been established that, irrespective of the type of water chemistry (oxidizing for the BN-800 reactor or reducing for the BN-600 reactor), an oxide layer of magnetite with protective properties is formed spontaneously on the surface of pearlitic steel during operation. [ABSTRACT FROM AUTHOR]

Nanocrystals of Bim+ 1Fem– 3Ti3O3m+ 3 (m = 4–9) Aurivillius phases were synthesized by thermal decomposition of a coprecipitated mixture of bismuth, iron, and titanium hydroxides. The average crystallite size in nanopowders depends on m and is 50–100 nm. The samples were characterized by simultaneous thermal analysis, elemental analysis, X-ray diffraction, and Mössbauer spectroscopy. It was shown that the onset of Bim+ 1Fem– 3Ti3O3m+ 3 crystallization is near the melting point of the bismuth oxide-based non-autonomous (surface) phase (450°C). The Bim+ 1Fem– 3Ti3O3m+ 3 compounds where m ≤ 5 crystallize in one stage. The compounds where m > 5 are formed in two stages. First, Aurivillius phases with m ≈ 5 and an amorphous phase are formed. Then, the components of the amorphous phase are incorporated into the perovskite-like blocks of the Aurivillius (m ≈ 5) phases, most likely through their outer perovskite-like layers. Then, the components are redistributed between the outer and inner layers of the perovskite-like blocks. The elucidated dependence of the formation mechanism of Bim+ 1Fem– 3Ti3O3m+ 3 nanocrystals on their composition can be used in the technology of directed synthesis of nanocrystalline multiferroics. [ABSTRACT FROM AUTHOR]

Nanocrystalline BiFeO3-based powder materials with an average crystallite size near 40 nm have been prepared by solution combustion synthesis from bismuth and iron nitrates using sucrose and tartaric acid as fuel. The materials have been characterized by X-ray diffraction, helium pycnometry, scanning electron microscopy, energy dispersive X-ray microanalysis, and Mössbauer spectroscopy. Magnetometry results demonstrate that the magnetic response of the materials varies over several orders of magnitude, depending on the synthesis procedure. [ABSTRACT FROM AUTHOR]

BiFeO3 with 50–70 nm crystallites was obtained by glycine–nitrate combustion under varying conditions. These nanopowders demonstrated magnetic ordering at temperatures up to 400 K. The results were compared with the data known from other works, and it was shown that at the sizes lower than 70 nm the predominant contribution to the magnetization belongs to the crystallite surface. The effect of the increased magnetization, associated with the spin cycloid distortion, can also occur which, however, is less essential for crystallites of sizes ∼10 nm. For the first time, it was shown that the value of magnetization can be controlled technologically within several orders. [ABSTRACT FROM AUTHOR]

Layered perovskite-like oxides Bi5–xCaxFeTi3O15–δ with the structure of the four-layer Aurivillius phase were synthesized in the Bi2O3–CaO–TiO2–Fe2O3 system by the solid-state reaction method. The features of the formation and thermal behavior of the solid solution synthesized were studied. [ABSTRACT FROM AUTHOR]

The features of the formation of nanocrystals in the BiFeO3–CaFeO3 system via glycine-nitrate combustion were studied. The crystallite size of the bismuth orthoferrite-based solid solutions (20–45 nm), as well as their particle size, were found to depend on the calcium content. The formation processes were activated in the temperature range corresponding to the melting of the surface (nonautonomous) phase. [ABSTRACT FROM AUTHOR]

The paper describes magnetic core-shell nanoparticles (Fe3O4/SiO2) synthesis that is an important stage of the manufacturing of smart material for targeted drug delivery based on the construction of the composite system mesoporous silica (MCM-41) - magnetite nanoparticles (Fe3O4) - immune cells (macrophages) for targeted drug delivery. The synthetic procedure for the fabrication of core-shell nanoparticles is modified in order to produce core-shell nanoparticles of the composition Fe3O4@SiO2 in the superparamagnetic state. This is confirmed by the studies of phase composition and magnetic properties of this material. The dependence of the particles size of magnetite sol on initial concentration of iron chlorides is established. The conditions for the fabrication of core-shell Fe3O4@SiO2 particles that are aggregatively stable in water are determined. Structural investigations of the samples demonstrate that the sizes of Fe3O4@SiO2 particles lie in the range 30 - 50 nm. [ABSTRACT FROM AUTHOR]

A series of tellurides FexTi1− x Te1.65 ( x = 0, 0.1, 0.2 ..., 1.0) synthesized at 850°C were studied by X-ray phase and X-ray fluorescent analysis and Møssbauer spectroscopy on 57Fe. In this series two solid solutions are formed: phases I and II with homogeneity regions within the limits of 0 ≤ x ≤ 0.3 and 0.9 ≤ x ≤ 1.0, respectively. Iron in this series exists in two various states: Fe2+ sym and Fe2+ asym as differentiated from the series of tellurides FexTi1− x Te1.45 where three states of iron Fe2+ sym, Fe2+ asym, and Fe0 were found. On passing from FexTi1− x Te1.45 to FexTi1− x Te1.65 the number of formed phases decreases, and phase relations become simpler. The absence of Fe0 from phase I of tellurides FexTi1− x Te1.65 can point to the fact that TiTe1.45 and TiTe1.65 belong to different homogeneity regions. [ABSTRACT FROM AUTHOR]

The multipurpose spectrometer for nondestructive, depth selective investigation of physical and chemical properties of a surface and bulk is described. It realizes opportunities of Mössbauer and X-ray Fluorescence Spectroscopy in normal and TER-conditions, Mössbauer and X-ray diffractometry and also Mössbauer and X-ray Reflectometry. Some analytical characteristics and capabilities of a spectrometer are illustrated as an example of research with a model sample. [ABSTRACT FROM AUTHOR]