Mechanochemical synthesis and thermal stability of phases in the Y2O3–Yb2O3 system

Substitutional, continuous solid solution of the general formula Y_2–xYb_xO₃ was obtained from the mixture of Y₂O₃ and Yb₂O₃ oxides, for the first time by the mechanochemical method in a high-energy ball milling. The monophasic samples of nanocrystalline solid solution for x?>?0.00 and x?<?2.00 were examined by the methods: XRD, DTA, SEM, IR and UV–Vis–DR. As follows from the results, the solid solution crystallizes in cubic system and is isostructural with Y₂O₃ and Yb₂O₃. The solution is stable in the air atmosphere up to at least 900°C, and its decomposition temperature decreases with the increase in x, that is, with decreasing number of Yb³⁺ ions replacing Y³⁺ ions in the crystal lattice of Y₂O₃. The energy band gap estimated for the solid solution varies from?~?5.30 eV for x?=?0.50 to?~?4.90 eV for x?=?1.50, which means that it is an insulator.

     

Reactivity of T-Nb2O5 or H-Nb2O5 towards V2O5. Synthesis in the solid state and properties of V4Nb18O55

The IR spectrum of V₄Nb₁₈O₅₅ has been compared with the IR spectra of selected niobates of known structures to show structural relations between these compounds. This comparison shows that V₄Nb₁₈O₅₅ has crystal structure related to T-Nb₂O₅, W16Nb18O94 and Ba₂NaNb₅O₁₅. On the other hand, reaction between V₂O₅ and H-Nb₂O₅ yields a solid solution of V₂O₅ in VNb₉O₂₅. It has been proposed two models of synthesized solid solution with formulas V_1+xNb_9-xO₂₅ or V_1+xNb₉O_25+5x/2.Independently of Nb₂O₅ polymorph, used for synthesis, the metastable compound VNbO5 cannot be synthesized in the solid state below 650°C      

Phase Composition and Properties of Iron Nanocrystals and Clusters Embedded in MgO Matrix

Formation and stability of highly dispersed iron particles in crazed porous polymer matrices were studied. The iron–polymer composites obtained were characterized by different morphologies and dimensions of iron particles. The phase content of the iron constituent in a composite studied by Mössbauer spectroscopy was shown to depend on the type of the iron salt and the method of introduction of the initial reagents into a polymer.     

The reactivity of SbVO<Subscript>5</Subscript> with T-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> in solid state in air

The reactivity of SbVO₅, a compound known since a short time, with T-Nb₂O₅ in solid state in air has been investigated over the whole component concentration range of a system built by these two reacting substances. The investigation results have shown that an equimolar mixture of SbVO₅ and T-Nb₂O₅ reacts with a subsequent formation of a hitherto unknown compound of the formula Nb₂VSbO₁₀. This compound has been characterized by the methods XRD, DTA/TG, and SEM. Its orthorhombic unit cell parameters have been calculated, and its stability in air up to 880 ± 10 °C has been proved. At this temperature, the compound melts incongruently with an accompanying deposition of solid Nb₉VO₂₅, i.e., of a compound that crystallizes in the binary oxide system V₂O₅–Nb₂O₅.     

Synthesis and properties of Fe-W powder

This paper deals with the study of Fe-W powders, which were prepared by electrolyzing, and their stabilized properties. The synthesized Fe-W powders were studied using X-ray diffraction, thermal analysis, Mössbauer spectroscopy and thermomagnetic measurement. A poor hydrogen absorption occurred. After the heat treatment at 800°C, the amorphous and α-Fe(W) phases were decomposed into prevailing α-Fe with approx. 3 at.% W accompanied by the W(Fe), λ-Fe₂W, and Fe²⁺ in oxide phases.     

Magnetic Properties of Iron/Graphite Core-shell Structured Nanoparticles Prepared by Annealing of Fe-C-N Nanocomposite

We are reporting the core-shell structured iron/graphite nanoparticles formed during annealing of a nanopowder prepared by laser pyrolysis of gas phase reactants. The originally synthesized Fe-C-N nanocomposite powder has been characterized by TEM, XRD and magnetic measurements. Nanopowder was heated up to 800 °C at ～ 1 Pa vacuum. Presence of iron nanoparticles with mean diameter 40 nm in the annealed state of nanopowder was proved by XRD and TEM analyses. Mössbauer spectroscopy was used for characterization of synthesized/annealed nanopowder to confirm the qualitative change in phase composition.     

Multi-walled carbon nanotubes formed by condensed-phase conversions of Fe-C-based nanopowder in vacuum

We describe the formation of multi-walled carbon nanotubes (MWCNTs) which have grown during annealing at 800 °C of Fe-C-based nanopowder in vacuum. The Fe-C-based nanopowder was produced by a laser pyrolysis of gas-phase reactants. The as-synthesized and annealed samples were characterised by TEM, XRD, Mössbauer spectroscopy, Raman spectroscopy, and magnetic measurements. Under the TEM, MWCNTs were observed in the annealed sample. In addition, larger particles with the graphitic shells and various graphitic structures were found. XRD and Mössbauer analysis confirmed that only two iron phases were present in the annealed sample: α-Fe and Fe₃C. Phase transformations taking place during the thermal treatment of the sample are discussed.     

Silver colloid nanoparticles: synthesis, characterization, and their antibacterial activity

A one-step simple synthesis of silver colloid nanoparticles with controllable sizes is presented. In this synthesis, reduction of [Ag(NH(3))(2)](+) complex cation by four saccharides was performed. Four saccharides were used: two monosaccharides (glucose and galactose) and two disaccharides (maltose and lactose). The syntheses performed at various ammonia concentrations (0.005-0.20 mol L(-1)) and pH conditions (11.5-13.0) produced a wide range of particle sizes (25-450 nm) with narrow size distributions, especially at the lowest ammonia concentrations. The average size, size distribution, morphology, and structure of particles were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), and UV/Visible absorption spectrophotometry. The influence of the saccharide structure (monosacharides versus disaccharides) on the size of silver particles is briefly discussed. The reduction of [Ag(NH(3))(2)](+) by maltose produced silver particles with a narrow size distribution with an average size of 25 nm, which showed high antimicrobial and bactericidal activity against Gram-positive and Gram-negative bacteria, including highly multiresistant strains such as methicillin-resistant Staphylococcus aureus. Antibacterial activity of silver nanoparticles was found to be dependent on the size of silver particles. A very low concentration of silver (as low as 1.69 mug/mL Ag) gave antibacterial performance.