Research Trends in Contemporary Materials Science

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Authors: J. Radić-Perić
Abstract: The formation of gas phase boron and carbon containing molecular species at high temperatures (thermal plasma) is investigated theoretically, by computing the equilibrium composition of the gas mixture containing boron, carbon, hydrogen and argon. The calculations are performed for the temperature range between 500 and 6000 K, B/C=1 and 2 and for the total pressure in the system of 1 bar. Use is made of the fact that the thermal plasma is plasma in local thermodynamic equilibrium, which makes possible theoretical determination (by employing the Gibbs free energy data for the compounds present in the system) of its equilibrium composition. From the calculated compositions of the investigated gas systems, presented in this paper, it was concluded that the initial molecule for cluster formation, as a connection between individual molecules and the solid state, in the case of the synthesis of solid boron carbide by means of thermal plasma should be the B2C molecule.
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Authors: Snezana Pašalić, P.B. Jovanić, B. Bugarski
Abstract: There are many developed strategies for evaluating emulsion stability, aimed at determining the life circle of emulsions. Most of them are based on rheological properties of emulsions. There are, however, very few based on direct emulsion observations. In this paper we present a developed method for the emulsion stability evaluation by direct observation of optical emulsion properties. We propose the fractal dimension approach as a stability quantification measure. The method is based on the measure of emulsion transmittance properties, which are directly dependent on the emulsion stability at the moment of measurement. The oil in water emulsion was used as a test emulsion. The system is classified as stable emulsion and our intention was to find the moment when it starts to break. Emulsion transmittance properties were measure applying a system for acquisition of visual information, which is based on a CCD camera and a fast PC configuration equipped with the capturing software. The acquired sets of visual information were analyzed by the OZARIA software package. The fractal dimensions were determined by the box counting method. For these experiments, 100 boxes of different sizes were used. Experimental emulsions were measured after 7, 14, 21 and 28 days from the moment of creation. A slight increase in fractal dimensions was observed, which indicates that the emulsions are still in the stable region, or from the fractal point of view emulsion are still regular and no significant irregularities were observed. From the first experiments the applied methodology proved to be sensitive enough to be used for emulsions stability evaluation.
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Authors: Miha Drofenik, M. Kristl, Andrej Žnidaršić, Darja Lisjak
Abstract: Nanoparticles of barium hexaferrite were prepared by controlled hydrothermal synthesis at 280oC. During the synthesis, the composition of the precursor and the suspension concentration were controlled. The as-synthesized crystalline barium hexaferrite platelets of about 50 nm in length and 5 nm in thickness exhibited a saturation magnetization of 40 emu/g.
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Authors: D. Djurović, Matvei Zinkevich, Snezana Bošković, V. Srot, Fritz Aldinger
Abstract: A nano-sized CeO2 powder was synthesized by a modified glycine nitrate process (MGNP). The synthesized powder was characterized by X-ray diffraction (XRD), the Brunauer Emmett Teller (BET) method, and transmission electron microscopy (TEM). The lattice parameter and crystallite size were determined by the Rietveld refinement of X-ray diffraction patterns. The shrinkage kinetics of the green body was continuously monitored in air and in oxygen atmospheres using a high temperature dilatometer up to 1500°C. During the high temperature sintering in air a redox reaction occurred (Ce4+ was partially reduced to Ce3+, and oxygen gas was released). The redox reaction influenced the sintering behaviour of CeO2, resulting in a decrease in density. On the basis of shrinkage kinetics data in oxygen atmosphere a master sintering curve for CeO2 was constructed. Using the concept of the master sintering curve, the densification behaviour in oxygen atmosphere was successfully predicted from early to final stages of sintering. During sintering of CeO2 at lower temperature in air atmosphere a significant contribution of the surface diffusion was observed.
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Authors: S.K. Milonjić, L.K. Zhigunova, V.Lj. Pavasović
Abstract: The adsorption of organic electrolytes from aqueous solutions on various adsorbents has been frequently investigated because of its importance in water purification. Phenol and substituted phenols are very common contaminants of water. In this paper, the adsorption results of some weak organic electrolytes (hydrochinon, phloroglucin and acidum gallicum) from aqueous solutions on silica are presented. The adsorption of the organics was investigated by the batch method. Effects of solution pHs (in the 2-10 range) and concentrations of these compounds on the adsorption were investigated. In the case of acidum gallicum, adsorption isotherms (in the 2-6 pH range) were determined. The obtained results indicate that the amount of adsorbed acidum gallicum increases with its increasing concentration. The maximum adsorption was recorded at pH=2-3 (pH equal to pHpzc of SiO2) with acidum gallicum molecule being undissociated (pKa= 4.41). The experimental data were fitted with different adsorption isotherms models. The maximum amount of acidum gallicum adsorbed as well as the Freundlich constants of adsorption were calculated. The adsorption of hydrochinon and phloroglucin from aqueous solutions (in the investigated pH range) on silica was negligible.
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Authors: S. Uskoković-Marković, Philippe Colomban, U.B. Mioč, M.R. Todorović
Abstract: On the basis of previously recorded Raman and IR spectral data on different crystallohydrates of alkaline-earth 12-tungstophosphoric acid salts (obtained from mother solution and those kept under constant relative humidity (RH) of 35%), an effort was made to determine the position of cations in the Keggin unit. Shifts or band splitting in vibrational spectra of the salts, as well as the changes in band intensities were found to be connected to the cation properties. The spectral data also demonstrated a great influence of cation properties on the secondary structure of Keggin anions and dynamics of protonic species.
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Authors: M.R. Todorović, I. Holclajtner-Antunović, U.B. Mioč, D. Bajuk-Bogdanović
Abstract: The K3PW12O40, K2.5H0.5PW12O40, K2HPW12O40, KH2PW12O40, Ag3PW12O40 and Tl3PW12O40 salts were synthesized and characterized by thermal analysis, IR and impedance spectroscopy, and SEM. The physicochemical characterization of acid alkaline salts revealed the presence of biphasic mixtures of unreacted heteropoly acid and its neutral salt. The unreacted heteroply acid could be washed away by treating the acid salt with water.
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Authors: Maja Milojević, V. Dondur, Lj. Damjanović, Vesna Rakić, Nena Rajić, Alenka Ristić
Abstract: In this work, a series of iron-containing zeolitic materials has been tested as heterogeneous catalysts for decomposition of H2O2 and for oxidation of the cationic dye Methylene Blue with H2O2 in aqueous solutions. FeAPO and FeBEA zeolites, synthesized through hydrothermal crystallization of basic hydrogels, and FeY and FeZSM-5 zeolites, prepared by ionexchange procedures, have been studied. The ion exchange with Fe(III) cations was performed from different salt solutions. Fe-exchange procedure carried out in Fe-citrate solution has been identified as an attractive option for the preparation of highly effective FeZSM-5 catalysts in wet oxidation processes. It has been shown that both tetrahedral, framework Fe, and octahedral, extra-framework Fe species incorporated into zeolite structure are catalytically active in wet oxidation reactions.
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Authors: B. Nedić, V. Dondur, A. Kremenović, R. Dimitrijević
Abstract: Ceramic materials, barium and strontium diphyllosilicates doped with ytterbium ions, were obtained by thermal treatment from Ba–LTA and Sr–LTA zeolites. The samples were characterized with Differential Scanning Calorimetry, Infra–Red Spectroscopy and Scanning Electron Microscopy. The crystal structures of diphyllosilacetes have been refined.
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Authors: D. Jugović, N. Cvjetićanin, M. Mitrić, S. Mentus
Abstract: Olivine-type lithium iron phosphate (LiFePO4) powders were synthesized applying three different methods: solid state reaction at high temperature, ultrasonic spray pyrolysis, and sonochemical treatment. The samples were characterized by X-ray powder diffraction (XRPD). Particle morphologies of the obtained powders were determined by scanning electron microscopy (SEM). It was found that structural and microstructural parameters of this material were strongly dependent on the synthesis conditions. We present here the results obtained upon optimization of each procedure for designing this cathode material.
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