Papers by Author: Momcilo M. Ristić

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Authors: N. Obradović, Nebojsa Labus, Tatjana Srećković, Momcilo M. Ristić
Abstract: Starting powder mixtures of ZnO and TiO2, at the molar ratio that is in accordance with the stoichiometry of zinc titanate Zn2TiO4, were mechanically activated using a planetary ball mill in different time intervals from 0 to 90 minutes. X-ray diffraction analysis, scanning electron microscopy and non-isothermal dilatometric measurements were performed in order to investigate zinc titanate formation. Processes occurring during mechanical activation led to the formation of a specific structure of obtained powders that promoted and accelerated solid-state reactions and densification during sintering. The main conclusion based on analysis is that mechanical activation enables better compaction of activated powders, i.e. possibility of achieving higher densities of green bodies without binders, but first of all that Zn2TiO4 ceramics can be obtained by mechanical activation after a certain time with appropriate thermal treatment, i.e. heating rate and sintering time, at temperatures lower than those when non-activated mixtures were used.
Authors: R. Agatonovic, V. Blank, I. Gridnjeva, A. Radakovic, V. Mikijelj, Ju. Solpan, Momcilo M. Ristić
Authors: B.A. Marinković, Z. Žakula, S. Đurić, N. Nikolić, O. Milošević, Momcilo M. Ristić
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: V. Mitic, Z.S. Nikolić, Momcilo M. Ristić, D.C. Stefanovic
Authors: P. Kostic, Tatjana Srećković, M. Kovacevic, L.S. Lukić, V. Mikijelj, Momcilo M. Ristić
Authors: Momcilo M. Ristić, L.F. Pryadko, D.C. Stefanovic
Authors: V.V. Mitié, Lj.M. Kocié, Momcilo M. Ristić
Authors: Vera P. Pavlović, Maria V. Nikolić, V. Spasojević, Jovan Blanuša, Ljiljana Živković, B.D. Stojanović, Vladimir B. Pavlović, Momcilo M. Ristić
Abstract: In this paper the influence of tribophysical activation on non-isothermal sintering of barium titanate has been investigated. BaTiO3 powders were tribophysically activated in a planetary ball mill for 0, 60 and 120 min., pressed and non-isothermally sintered up to 1380oC. Dilatometric analysis was performed in air in the temperature range from room temperature to 1380oC with heating rates of 10, 20 and 30oC/min. The samples were analyzed by the X-ray powder diffraction method. Investigation of the morphology of microstructure constituents was performed using the scanning electron microsocopy method. With the purpose of optimizing technological parameters the results obtained by microstructure analysis were correlated with the results of quantitative dilatometric analysis.
Authors: N. Obradović, Nebojsa Labus, Tatjana Srećković, Momcilo M. Ristić
Abstract: The influence of tribophysical activation on Zn2TiO4 synthesis along with the changes in powders during tribophysical treatment was observed. Mixtures of ZnO and TiO2 powders were mechanically activated using a high-energy ball mill at different time intervals from 0 to 300 minutes. XRD was performed in order to obtain information about phase composition variations. Microstructure parameters were revealed from an approximation method. Particle size distribution along with scanning electron microscopy gave very useful information about powder morphology.
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