Recent Developments in Advanced Materials and Processes

Volume 518

doi: 10.4028/

Paper Title Page

Authors: Maxim V. Kuznetsov, Ivan P. Parkin, A. Kvick, S.M. Busurin, I.V. Shishkovskiy, Yuri G. Morozov
Abstract: New experimental methods for investigations of phase formation during SHS have been established. First experiments using penetrating synchrotron radiation and energy dispersive detectors for different classes of complex inorganic materials were carried out at ESRF (Grenoble, France) and Daresbury (UK). A new and very sensitive thermal imaging method (Thermal Imaging Technique (TIT)) based on continuous registration of the whole combustion process by using highly sensitive IR-camera and software developed by MIKRON Instruments Co. (USA) was used for precise registration of the combustion parameters. SHS was performed on different types of pure and doped complex inorganic materials in pellet and powder form in a range of dc magnetic fields up to 20 T and in electrical field strengths up to ±220 kV/m. The dc magnetic field was applied during the reaction, supplied either by a permanent magnet (transverse, up to 1.1 T) or by an electromagnet (longitudinal, up to 20 T). The dc electrical field was applied along the direction of the combustion wave front propagation. The combined processes of SHS and SLS (Selective Laser Sintering) of 3D articles for different powdered compositions were optimized with laser irradiation power.
Authors: A. Bykov, G. Oleynik, A. Ragulya, I. Timofeeva, L. Klochkov, A. Kovalev
Abstract: The high pressure sintering process of nanocrystalline diamond powder was studied. The influence of the liquid phase on the base of boron oxide was analyzed. The mechanism of cooperative-diffusive coalescence, which acts during sintering of ultradisperse diamond powders, is proposed.
Authors: Jarmila Degmová, J. Sitek, J. Bednarčík
Abstract: In this paper, a review of recent 57Fe Mössbauer spectroscopy (MS) studies of external influence on the properties of amorphous and nanocrystalline Fe- and Co-based alloys is submitted. Different types of alloys (FeCuNbZr, FeCuNbSiB, FeCoCuNbB, CoFeZrB and CoFeSiB) in the form of original amorphous and nanocrystalline ribbons were subjected to different external factors: different annealing atmospheres, mechanical stress (for example influence of ball-milling) and tensile stress. It will be shown that the Mössbauer spectrometry is a suitable tool for such studies because the measured spectral parameters are very sensitive to the changes in the vicinity of the probe 57Fe-nuclei and thus, this technique provides a wide variety of information about structural and magnetic behavior of Fe-containing materials.
Authors: G. Postole, A. Gervasini, A. Auroux, B. Bonnetot
Abstract: In this study we report on the preparation and characterization of boron nitride supported noble metal catalysts with potential applications as catalysts for oxidation reactions. The deposition and the dispersion of the active phase were strongly influenced by the preparation process and in particular by the solvent used as the dispersing phase. Techniques such as BET, XRD and TEM were used to study the role played by the phase used as solvent (benzene, glyme, water, THF, diglyme, isopropanol, glycol) in particles size and dispersion of metals deposed on the BN support. Different palladium depositions under various conditions and different noble metal coatings under the same deposition condition are presented. The catalytic performances were tested in methane traces oxidation in excess oxygen and in the presence of water. The light-off temperature (50 % methane conversion) increased in the following order: Ag/BN < Pt/BN < Au/BN < Pd /BN.
Authors: B. Todorović-Marković, Z. Marković, I. Mohai, Z.M. Nikolić, Z. Farkas, J. Szépvölgyi
Abstract: In this paper, report on fullerene formation in a radio-frequency (RF) thermal plasma reactor has been presented. In order to determine the degree of evaporation of the graphite precursor used, analysis of SEM micrographs of deposited soot in different parts of RF reactor has been made. It was found that the degree of graphite evaporation and fullerene yield varied depending on the distance from the plasma torch nozzle. Carbon concentration and rotational temperature of C2 radicals in plasma flame have been calculated as well. The concentration of C2 radicals in plasma flame, which participated in fullerene formation, was in the range of (1.75-3.88)×1020 m-3.
Authors: M. Baćić-Vukčević, A. Udovičić, Z. Laušević, A. Perić-Grujić, M. Laušević
Abstract: In this work, surface characteristics of different carbon materials were investigated. The materials under consideration were: activated carbon, carbon monolith, carbon felt and glassy carbon (powder, plate and broken plate). The surface functional groups of the studied carbon materials were determined by Boehm’s method and point of zero charge by mass titration. The specific surface area was studied by BET method with N2 adsorption. As a specific test for surface activity, cementation of silver from aqueous solution of silver salts was used. The rate of silver deposition on the carbon materials was studied as a function of immersion time (AgNO3 concentration 75 mg/dm3), as well as a function of concentration of AgNO3 solution (25, 50, 75, 100, 125 mg/dm3) by atomic absorption spectrometry (AAS) to determine the concentration of Ag in the solution. The morphology of silver coatings was characterized by scanning electron microscopy (SEM) and structural characteristics by X-ray diffraction. The results obtained show that metallic silver deposits were formed at the surface of all examined samples. Oxygen complexes at the surface of glassy carbon samples were analysed by temperature programmed desorption (TPD) before and after silver deposition in order to establish the mechanism of silver deposition.
Authors: V. Jovanović, V. Dondur, Lj. Damjanović, J. Zakrzewska, M. Tomašević-Čanović
Abstract: The surface properties of zeolites A, X, Y and natural zeolite clinoptilolite (CLI) functionalized by cationic surfactants were investigated. The quaternary ammonium type surfactants, such as hexadecyltrimethylammonium (HDTMA) chloride, stearildimethylbenzylammonium (SDMBA) chloride and distearildimethylammonium (DSDMA) chloride, replaced inorganic cations like Na+ and Ca2+ on the external surface of zeolites. The adsorption capacities of all organic cations followed the order of CLI>CaY>CaX>CaA>NaY>NaX>NaA and increased with the increase of Si/Al molar ratio in zeolite structure. This modification resulted in an alteration in the surface property of zeolites - it changed from hydrophilic to hydrophobic. The adsorption of selected pesticides with different hydrophobicity on surfactant-modified zeolites was studied. It is shown that surfactant-modified zeolites can be used for removal of pesticides from the environment. The increase in hydrophobicity of pesticides resulted in an increase in pesticide adsorption on SDMBA and DSDMA modified zeolites.
Authors: Ljiljana Živković, V. Paunović, M. Miljković, Momcilo M. Ristić
Abstract: Nb/Mn and Dy/Mn codoped BaTiO3 specimens, prepared by conventional solid-state procedure, were investigated regarding their microstructural and dielectric properties. The powders were doped with Nb2O5 and Dy2O3 with an amount of 0.1, 0.5 and 1.0 at% of dopants ions. The MnO content of 0.05 at% Mn was the same in both types of samples. The specimens were sintered in air at 1320 and 1350 °C for two hours. Microstructural and compositional studies were done by SEM equipped with EDS. In low doped BaTiO3 the grain size is around 1-3 μm, while in ceramics with high dopant content (1.0 at%) the grain size distribution was in the range of 3-10 μm. High dielectric constant is associated with small-grained microstructure, being 5000 for Dy-doped and 6500 for Nb-doped BaTiO3 sintered at 1350 °C. The specimens with low dopant content demonstrate the Curie-Weiss behavior in a paraelectric regime. A nearly flat permittivity response with temperature was obtained for specimens with 0.5 and 1.0 at% Dy content. Loss tangents were in the range of 0.03 - 0.32.
Authors: M. Žunić, Z. Branković, G. Branković, D. Poleti
Abstract: The effect of Co, Cr and Nb on the electrical properties of the grain boundaries of SnO2-based varistors was investigated. The powders were prepared by the method of evaporation and decomposition of solutions and suspensions. Varistor samples were obtained by uniaxial pressing followed by sintering at 1300 °C for 1h. The electrical properties of the grain-boundary region, such as resistance (R) and capacitance (C), were determined using ac impedance spectroscopy in the 27-330 °C temperature interval. Activation energies for conduction (EA) were calculated from the Arrhenius equation. The non-linear coefficients (α) and the breakdown electric fields (Eb) of the samples were determined from the current-voltage characteristics. The potential barrier height (Φb) was calculated using the Schottky-type conducting model. After a comparison of the characteristic parameters for different varistor compositions it was found that the Cr/Nb ratio has a crucial influence on the grain-boundary properties in SnO2 varistors.
Authors: S. Marković, M. Mitrić, N. Cvjetićanin, Dragan P. Uskokovic
Abstract: BaTi1-xSnxO3 (BTS) powders, with x ranging from 0 to 1, were synthesized by solid-state reaction technique. The powders were pressed into pellets and sintered at 1370 and 1420 oC. The structural characterization of sintered BTS samples was made at room temperature using X-ray diffraction and Raman spectroscopy measurements. The BTS samples were found to be singlephase solid solutions. Dielectric properties of sintered BTS samples were studied as a function of sintering temperatures and tin contents, too. For samples with x ranging from 0 up to 0.15, it has been found that the Curie temperature decreases while the maximum of the dielectric constant increases with increasing tin content. These samples have relatively high dielectric constants, contrary to x > 0.2 samples with very low dielectric constants. It is noticed that BTS ceramics sintered at 1420 oC exhibit better dielectric properties than those sintered at 1370 oC.

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