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Tadic M.,University of Belgrade | Citakovic N.,Military Academy | Panjan M.,Jozef Stefan Institute | Stojanovic Z.,Serbian Institute of Technical Sciences | And 2 more authors.
Journal of Alloys and Compounds | Year: 2011

We report on hydrothermal synthesis, plate-like morphology, microstructure and magnetic properties of hematite (α-Fe 2O 3) plate-like particles. The sample is obtained immediately after the hydrothermal process without using any template and without further heat treatment. The so-obtained sample is characterized by X-ray powder diffraction (XRPD), energy-dispersive X-ray spectroscopy (EDX), field-emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and superconducting quantum interference device (SQUID) magnetometer. XRPD confirms the formation of a single-phase hematite sample whereas EDX reveals that iron and oxygen are the only components of the sample. SEM, FE-SEM, TEM and HRTEM show that the sample is composed of plate-like particles. The width of the particles is ∼500 nm whereas thickness is ∼100 nm (aspect ratio 5:1). The HRTEM images exhibit well defined lattice fringes of α-Fe 2O 3 particles that confirm their high crystallinity. Moreover, the HRTEM analysis indicates the plate-like particles preferring crystal growth along [0 1 2] direction. Magnetic measurements display significant hysteretic behavior at room temperature with coercivity H C = 1140 Oe, remanent magnetization M r = 0.125 emu/g and saturation magnetization M S = 2.15 emu/g as well as the Morin transition at T M ∼ 250 K. The magnetic properties are discussed with respect to morphology and microstructure of the particles. The results and comparison with urchin-like, rods, spherical, hexagonal, star-like, dendrites, platelets, irregular, nanoplatelets, nanocolumns and nanospheres hematites reveal that the plate-like particles possess good magnetic properties. One may conjecture that the shape anisotropy plays an important role in the magnetic properties of the sample. © 2011 Elsevier B.V. All rights reserved.


Lukic M.J.,Serbian Institute of Technical Sciences | Skapin S.D.,Jozef Stefan Institute | Markovic S.,Serbian Institute of Technical Sciences | Uskokovic D.,Serbian Institute of Technical Sciences
Journal of the American Ceramic Society | Year: 2012

The study is devoted to the processing of hydroxyapatite (HAp) nanopowder to develop fully dense nanostructured bioceramics by pressureless sintering. The sintering behavior of stoichiometric HAp prepared by hydrothermal processing was investigated by nonisothermal, two-step, and conventional sintering. By low-temperature two-step sintering (TSS), at 900°C and 850°C, with appropriate dwell time, dense bioceramics without final-stage grain growth and average grain size of 75 nm was obtained. A concept of master sintering curve was applied, enabling control of sintering process, estimation of effective activation energy for sintering of HAp nanopowder, and qualitative understanding of sintering mechanisms. According to estimated activation energy of 412.6 kJ/mol, low sintering temperature and particles' microstructure as the dominant sintering mechanism we proposed diffuse-viscous flow controlled by grain boundary diffusion. HAp nanoparticles comprising of different interior and boundary regions as ordered/disordered microstructure are found to be of an advantage for low-temperature sintering. © 2012 The American Ceramic Society.


Vujkovic M.,University of Belgrade | Jugovic D.,Serbian Institute of Technical Sciences | Mitric M.,Vinča Institute of Nuclear Sciences | Stojkovic I.,University of Belgrade | And 2 more authors.
Electrochimica Acta | Year: 2013

The nitrate-(glycine + malonic acid)-assisted gel-combustion process, followed by a heat treatment at 750°C under reductive atmosphere, was used as a fast and effective way to synthesize vanadium dopedolivine incorporated in carbon matrix, of general formula LiFe(1-x)VxPO 4/C. The two-phased Rietveldrefinement confirmed that vanadium incorporation into olivine structure was complete. The heatingunder reduction atmosphere caused the formation of iron phosphide to some extent, the concentrationwas determined by Rietveld analysis. The capacity and rate capability of these composites were testedby both cyclic voltammetry and galvanostatic cycling. Specifically, the average discharging capacities ofthe composite with x = 0.055, determined in an saturated aqueous LiNO3 solution equilibrated with air,at the rates of 1, 10 and 100 C, amounted to 91, 73 and 35 mAh g-1, respectively, with no perceivablecapacity fade. © 2013 Elsevier Ltd. All rights reserved.


Krstajic N.V.,University of Belgrade | Gajic-Krstajic Lj.,Serbian Institute of Technical Sciences | Lacnjevac U.,Serbian Institute for Multidisciplinary Research | Jovic B.M.,Serbian Institute for Multidisciplinary Research | And 2 more authors.
International Journal of Hydrogen Energy | Year: 2011

In this work the Ni-MoOx coatings have been prepared and characterized in view of their possible application as electrocatalysts for hydrogen evolution reaction (HER) in alkaline solution. The procedure of deposition of Ni-MoOx coatings from the Watt's type bath containing MoO3 powder particles onto Ni mesh, under the conditions of simulated industrial deposition conditions for commercial cathodes, has been presented. The morphology of the obtained coatings was investigated by SEM, the composition by EDS and the phase composition by XRD techniques. The polarization characteristics for hydrogen evolution on the obtained Ni-MoOx coatings were investigated in the 32 wt.% NaOH at 90 °C and compared with the one recorded for the commercial De Nora's coating (DN). It was shown that the best Ni-MoOx coating exhibits almost identical polarization characteristics as the commercial one. By the cross section and XRD analysis of deposited samples it was confirmed that MoO3 powder particles were not occluded by the Ni deposit and that molybdenum species were deposited from the molybdate ions formed by dissolution of MoO3, following the mechanism of induced co-deposition. The reaction mechanism for MoO3 phase deposition has also been proposed. Copyright © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Elezovic N.R.,Serbian Institute for Multidisciplinary Research | Babic B.M.,Vinča Institute of Nuclear Sciences | Gajic-Krstajic Lj.,Serbian Institute of Technical Sciences | Radmilovic V.,University of California at Berkeley | And 2 more authors.
Journal of Power Sources | Year: 2010

In order to point out the effect of the support to the catalyst for oxygen reduction reaction nano-crystalline Nb-doped TiO2 was synthesized through a modified sol-gel route procedure. The specific surface area of the support, SBET, and pore size distribution, were calculated from the adsorption isotherms using the gravimetric McBain method. The support was characterized by X-ray diffraction (XRD) technique. The borohydride reduction method was used to prepare Nb-TiO2 supported Pt (20 wt.%) catalyst. The synthesized catalyst was analyzed by TEM technique. Finally, the catalytic activity of this new catalyst for oxygen reduction reaction was investigated in acid solution, in the absence and the presence of methanol, and its activity was compared towards the results on C/Pt catalysts. Kinetic analysis reveals that the oxygen reduction reaction on Nb-TiO2/Pt catalyst follows four-electron process leading to water, as in the case of C/Pt electrode, but the Tafel plots normalized to the electrochemically active surface area show very remarkable enhancement in activity of Nb-TiO2/Pt expressed through the value of the current density at the constant potential. Moreover, Nb-TiO2/Pt catalyst exhibits higher methanol tolerance during the oxygen reduction reaction than the C/Pt catalyst. The enhancement in the activity of Nb-TiO2/Pt is consequence of both: the interactions of Pt nanoparticles with the support and the energy shift of the surface d-states with respect to the Fermi level what changes the surface reactivity. © 2010 Elsevier B.V.


Terzic A.,Serbian Institute for Materials Testing | Andric L.,Serbian Institute of Technical Sciences | Mitic V.,Serbian Institute for Technology of Nuclear and other Raw Mineral Materials
Ceramics International | Year: 2014

A growing demand for refractory castables with advanced properties has given rise to a continuous technological evolution and highlighted the necessity for secondary raw materials reapplication even in refractory industry. For the experiment, refractory shotcretes with the same matrix composition were prepared from 30 wt% of high aluminate cement, 40 wt% of bauxite aggregate and 30 wt% of chamotte filler. The request for obtaining a low-cement castable is fulfilled by application of mechanically activated coal ash as microfiller in one of the bauxite shotcretes. The fly ash was activated by means of vibratory disc mill and ultra-centrifugal mill, and results were compared. The shotcrete samples were dried at 110 °C during 24 h to create specimens for investigation of mechanical and thermal properties. The properties have been studied at temperatures ranging from room temperature to adopted maximal temperature 1400 °C. At maximal 1400 °C, the bauxite shotcretes were mainly composed of anorthite, corundum, mullite and cristobalite. Mechanisms of hydration and sintering were investigated by means of differential thermal analysis (DTA) at three different heating rates. DTA measurements showed different activation energies for ordinary bauxite shotcrete and shotcrete with microfiller. The evolution of the refractory shotcretes properties was investigated and correlated with microstructural changes induced by temperature and microfiller addition. The combination of advantages in investigated refractory shotcretes makes them suitable for use in severe conditions at high temperature applications especially in refractory industries. © 2014 Elsevier Ltd and Techna Group S.r.l.


Mancic L.,Serbian Institute of Technical Sciences | Lojpur V.,Vinča Institute of Nuclear Sciences | Marinkovic B.A.,Pontifical Catholic University of Rio de Janeiro | Dramicanin M.D.,Vinča Institute of Nuclear Sciences | Milosevic O.,Serbian Institute of Technical Sciences
Optical Materials | Year: 2013

Examples of (Y2O3-Gd2O3): Eu3+ and Y2O3:(Yb3+/Er3+) rare earth oxide-based phosphors are presented to highlight the controlled synthesis of 1D and 2D nanostructures through simple hydrothermal method. Conversion of the starting nitrates mixture into carbonate hydrate phase is performed with the help of ammonium hydrogen carbonate solution during hydrothermal treatment at 200 C/3 h. Morphological architectures of rare earth oxides obtained after subsequent powders thermal treatment at 600 and 1100 C for 3 and 12 h and their correlation with the optical characteristics are discussed based on X-ray powder diffractometry, field emission scanning electron microscopy, infrared spectroscopy and photoluminescence measurements. Strong red and green emission followed by the superior decay times are attributed to the high powders purity and homogeneous dopants distribution over the host lattice matrix. © 2013 Elsevier B.V. All rights reserved.


Lojpur V.,Serbian Institute of Technical Sciences | Nikolic M.,Vinča Institute of Nuclear Sciences | Mancic L.,Serbian Institute of Technical Sciences | Milosevic O.,Serbian Institute of Technical Sciences | Dramicanin M.D.,Vinča Institute of Nuclear Sciences
Ceramics International | Year: 2013

Recently, trivalent rare earth doped materials have received significant attention due to the strong temperature dependence of the fluorescence emission of these materials, which can be useful in temperature sensing. Here, we investigated Y2O3 ceramic powders doped with Yb 3+ and co-doped with either Tm3+ or Ho3+. The powders were obtained via spray pyrolysis at 900 °C and additionally thermally treated at 1100 °C for 24 h. Structural characterization using X-ray powder diffraction confirmed the cubic bixbyte structure. Scanning electron microscopy (SEM) revealed that the particles exhibit a uniform spherical morphology. The up-conversion emissions were measured using laser excitation at 978 nm, resulting in the following transitions: blue emission in the range of 450-500 nm, weak red emission in the range of 650-680 nm and near infrared emission in the range of 765-840 nm for Tm3+, as well as green emission centered at 550 nm and weak near infrared emission at 755 nm for the Ho3+ ions. In addition, the temperature dependence of the fluorescence intensity ratios of different Stark components was analyzed in the range of 10-300 K. Significant temperature sensitivity was detected for several components, with the largest value of 0.097 K-1 related to the intensity ratio of I536 and I772 emissions observed for the Y2O3:Yb,Ho powder. © 2012 Elsevier Ltd and Techna Group S.r.l.


Paunovic V.,University of Niš | Mitic V.V.,University of Niš | Mitic V.V.,Serbian Institute of Technical Sciences | Prijic Z.,University of Niš | Zivkovic L.,University of Niš
Ceramics International | Year: 2014

Dy/Mn doped BaTiO3 with different Dy2O3 contents, ranging from 0.1 to 5.0 at% Dy, were investigated regarding their microstructural and dielectric characteristics. The content of 0.05 at% Mn was constant in all the investigated samples. The samples were prepared by the conventional solid state reaction and sintered at 1290, and 1350 C in air atmosphere for 2 h. The low doped samples (0.1 and 0.5 at% Dy) exhibit mainly fairly uniform and homogeneous microstructure with average grain sizes ranged from 0.3 μm to 3.0 μm. At 1350 C, the appearance of secondary, abnormal, grains in the fine grain matrix and core-shell structure were observed in highly doped Dy/BaTiO3. Dielectric measurements were carried out as a function of temperature up to 180 C. The low doped samples sintered at 1350 C, display the high value of dielectric permittivity at room temperature, 5600 for 0.1Dy/BaTiO3. A nearly flat permittivity-temperature response was obtained in specimens with 2.0 and 5.0 at% additive content. Using a Curie-Weiss and modified Curie-Weiss low, the Curie constant (C), Curie like constant (C′), Curie temperature (TC) and a critical exponent (γ) were calculated. The obtained values of γ pointed out the diffuse phase transformation in highly doped BaTiO3 samples. © 2013 Elsevier Ltd and Techna Group S.r.l.


Karan B.,Serbian Institute of Technical Sciences
21st International Conference in Central Europe on Computer Graphics, Visualization and Computer Vision, WSCG 2013 - Poster Proceedings | Year: 2013

Accuracy of depth measurement with Microsoft Kinect and similar 3D vision sensors depends on variations in sensor production. Sensor reading may show significant systematic errors that can be compensated in software by using an adequate depth calibration model. This paper presents one such model and a procedure for identification of its parameters. An example calibration is given to illustrate the procedure and the attained improvements.

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