Research Trends in Contemporary Materials Science

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Authors: Jelena Dukić, Snezana Bošković, B. Matović, B. Dimčić, Lj. Karanović
Abstract: Two nanopowders with nominal compositions (Ca0.7La0.3)MnO3 (CLM) and (Ca0.7La0.3)(Mn0.8Ce0.2)O3 (CLMC) were synthesized by a modified glycine/nitrate procedure. XRD analysis revealed binary phase mixture in both samples. The influence of La and Ce on unit cell parameters, atom positions, and average bond distances were analyzed. According to these results and refined occupation factors of La and Ca, as well as quantitative phase analysis it was found that the CLM sample consists of 85 mass.% of Ca0.62La0.38MnO3 and 15 mass.% of Ca0.99La0.01MnO3, while the CLMC sample consists of 70 mass.% of Ca0.58La0.42MnO3 and 30 mass.% of CeO2. Microstructure size-strain analysis was performed and the Rietveld refinement gave crystallites of about 100 Å. TEM images showed particle sizes of about 100-500 Å.
Authors: Katarina Djuriš, G. Branković, Z. Branković, Slavko Bernik, M. Počuča, D. Poleti, B. Antić
Abstract: In this work pure and doped LMO were prepared using modified Pechini method from lanthanum and manganese citrates. Lanthanum citrate was prepared starting from La2O3, while manganese citrate was prepared from Mn(NO3)2. Valence state of the manganese was controlled by adjusting pH value of the solution and confirmed by EPR and UV/VIS analysis. Thermal treatment conditions for preparation of LMO powders were determined from TG/DTA of dried precursors. XRD results confirmed that pure perovskite phase was successfully prepared in single LMO and Cadoped LMO. SEM and measurements of specific surface area of the powders showed the existence of large agglomerates consisting of submicronic primary particles.
Authors: Z.Ž. Lazarević, N.Ž Romčević, M.J. Romčević, B.D. Stojanović
Abstract: Bismuth titanate is a typical layer-structured ferroelectric material and belongs to the Aurivilius type-structure compounds family. A bismuth titanate ceramic material could be obtained by mechanically activated synthesis after thermal treatment at a temperature slightly lower than in conventional solid-state reaction. In this case bismuth titanate was prepared through mechanochemical synthesis starting from bismuth oxide and titanium oxide in rutile form. The mixture of oxides was milled in a zirconium oxide jar in a planetary ball-mill in intervals from 1 to 12 hours. The ratio of powders to zirconium oxide balls during milling was 1:20. Bismuth titanate was formed after 1 h. The Raman spectroscopy analysis was performed.
Authors: S. Marković, M. Mitrić, Č. Jovalekić, M. Miljković
Abstract: Multilayered BaTi1-xSnxO3 (BTS) ceramics with different Ti/Sn ratios were produced by pressing and sintering at 1420 oC for 2 hours. X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy were used for structural, microstructural and elemental analysis, respectively. The dielectric and ferroelectric behavior of sintered samples was studied, too. It is found that in ingredient materials, with increasing Sn content, the tetragonality decreases; Curie temperature moves towards room temperature, while the maximum of the dielectric constant increases, and also, they becomes less hysteretic. It is noticed that multilayered BTS ceramics with different Ti/Sn contents have a broad transition temperature and show a relatively high dielectric constant in a wide temperature range. It is shown that dielectric properties of these materials may be modified by a combination of different BTS powders as well as layers number.
Authors: Dj. Kosanović, Lj. Milovanović, S. Milovanović, A. Šaponjić
Abstract: Boron carbide powder was synthesized by sol-gel polycondensation of boric acid with citric acid. The starting materials of Serbian origin were dissolved in water and mixed homogeneously until a precomposite gel was formed, which was converted into cryogels after freeze-drying. Pyrolysing and subsequent heat treatment of these cryogels resulted in boron carbide materials. Characterization by nitrogen adsorption showed that the precomposite cryogels and the composite powders were micro and mesoporous materials with large surface areas. Materials have been analyzed by means of X-ray diffraction and scanning electron microscopy. The Rietveld refinement was employed to get the structural information of the synthesized powder. The results show that the obtained carbide powder is composed of nearly equiaxed particles of narrow size distribution.
Authors: A. Devečerski, A. Radosavljević-Mihajlović, A. Egelja, M. Pošarac, B. Matović
Abstract: The objective of this manuscript was to investigate the synthesis of SiC by carbothermal– reduction reactions of sepiolite. Sepiolite of Serbian origin and carbon (from various precursors) as a reducing agent were used. The green bodies with various C/SiO2 ratios were carbonized at 1073 K and heattreated at 1673 K in a controlled Ar flow atmosphere. Phase evolution and phase content were followed as a function of C/SiO2 ratio and carbon origin. The starting materials and products were characterized by means of XRD and SEM. The results show that sepiolite can be very effective source for obtaining silicon carbide powders.
Authors: Lj. Vulićević, N. Ivanović, N. Popović, V. Kusigerski, Milesa Srećković, Ž. Tomić, S. Vardić
Abstract: The investigated nanometric magnetite powders were synthesized electrochemically, and examined by XRD and SEM techniques. Their reduction was conducted through the isothermal heating in hydrogen in the temperature range from 600 to 860 K. Kinetics of the hydrogen recovery process during oxidation of freshly formed Fe powders in a water vapor stream was also studied. It was assumed that the solid-gas reaction is diffusion controlled, and Jander’s model was applied to describe it. The experimental data suggest that the reoxidation process proceeds in two stages, at various activation energies. By changing the conditions of the electrochemical (EC) process we were able to produce the iron oxide powders with optimal particle size and activity, for pure hydrogen production through appropriate reduction/oxidation processes.
Authors: Ana Čeliković, Ljiljana Kandić, M. Zdujić, Dragan P. Uskokovic
Abstract: The ZnO and ZrO2 powders were prepared by mechanochemical processing and subsequent heat treatment of the starting powder of precursors mixture of ZnCl2 and Ca(OH)2, and ZrOCl2·8H2O and NaOH, respectively. Inert salt matrix, ether CaCl2 or NaCl, which prevents particle agglomeration was formed during mechanochemical solid state reaction. After mechanochemical treatment, samples were calcined at various temperatures. Selective removal of the matrix phase by washing the resulting powder with appropriate solvent yields almost pure ZnO and ZrO2 powders. Characterization of the powders was performed by X-ray diffraction (XRD), differential thermal and thermo gravimetric analysis (DTA−TG) and scanning electron microscopy (SEM).
Authors: Marija Jevtić, Dragan P. Uskokovic
Abstract: The main purpose of the present work was to investigate the influence of urea concentration on hydroxyapatite (HAp) synthesis. Calcium nitrate and ammoniumdihydrogenphosphate were used as Ca and P sources. A homogeneous precipitation agent – urea - was applied in the field of ultrasonic irradiation. Different Ca : P : urea molar ratios were applied and the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR). The results reveal the influence of the urea concentration on the phase composition of the system, crystallite size and the particle morphology. Different Ca : P : urea molar ratios led to various system formation: from biphasic OCP and HAp to monophasic HAp. The estimated HAp crystallite size was 24.4 nm. An explanation of the mechanism of the HAp synthesis is given, regarding the formation of the intermediate and final product during ultrasonic irradiation.

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