Ivana Veljkovic (Ивана Вељковић)

Publications

• 0.49

  Impact points

  Solid State Synthesis of Extra Phase-Pure Li4Ti5O12 Spinel

  I. Veljkovic, D. Poleti, Lj. Karanovic, M. Zdujic, G. Brankovic

  Science of Sintering. 12/2011; 43(43):343.

  Extra phase-pure Li4Ti5O12 spinel with particle sizes less than 500 nm was synthesized by solid state reaction of mechanochemicaly activated mixture of nano anatase and Li2CO3 for a very short annealing time, 4 h at 800 °C. Structural and microstructural properties, the mechanism of solid state reac... [more] Extra phase-pure Li4Ti5O12 spinel with particle sizes less than 500 nm was synthesized by solid state reaction of mechanochemicaly activated mixture of nano anatase and Li2CO3 for a very short annealing time, 4 h at 800 °C. Structural and microstructural properties, the mechanism of solid state reaction between anatase and Li2CO3 as well as thermal stability of prepared spinel were investigated using XRPD, SEM and TG/DSC analysis. The mechanism of reaction implies decomposition of Li2CO3 below 250 ºC, formation of monoclinic Li2TiO3 as intermediate product between 400 and 600 °C and its transformation to Li4Ti5O12 between 600–800 ºC. The spinel structure is stable up to 1000 ºC when it is decomposed due to Li2O evaporation.

• EBONEX® BASED PLASTIC-BONDED MATERIAL FOR BIPOLAR PLATE IN Pb-ACID BATTERY

  Ivana Veljković, Dejan Poleti, Miloš Simičić, Miodrag Zdujić

  First Conference of the Serbian Ceramic Society, Belgrade; 01/2011

  Several samples of oxygen deficient titanium oxides (TiO, Ti4O7, Ti5O9, Ti6O11) or their mixtures were prepared using mechanochemical procedure followed, in some cases, by thermal treatment. The prepared oxides, mixtures identical or similar to Ebonex powder, and original Ebonex powder have procee... [more] Several samples of oxygen deficient titanium oxides (TiO, Ti4O7, Ti5O9, Ti6O11) or their mixtures were prepared using mechanochemical procedure followed, in some cases, by thermal treatment. The prepared oxides, mixtures identical or similar to Ebonex powder, and original Ebonex powder have proceeded into plastic–bonded foil electrodes using a low density polyethylene. The electrodes were tested for corrosion stability in real Pb-acid battery conditions and their conductivities were compared. If contact resistance to cathode and anode active mass can be overcome, some investigated samples are very promising for application as current collector in extremely aggressive H2SO4 surrounding.

• Structural Transformations of Hydrothermaly Synthesized alpha-Li2-xTiO3-0,5x•(H2O)y

  I. Veljković, D. Poleti, Lj. Karanović, J. Rogan

  Conference of the Serbian Crystallographic Society; 01/2011

  https://www.facebook.com/media/set/?set=a.10150211482258610.329694.51465243609

• Self-assembled Flower-like Lithium Titanium Oxide

  Ivana Z. Veljković, Dejan D. Poleti, Ljiljana Č. Karanović, Jelena R. Rogan

  International Workshop - Procesing of nanostructured ceramics, Polymers and Composites, Belgrade; 01/2010

  3D nanostructures have attracted much attention because of their unique properties and potential applications. The simplest synthetic route to make 3D nanostructures is probably self-assembling, in which ordered aggregates are formed in a spontaneous process. Due to their safety and compatibility wi... [more] 3D nanostructures have attracted much attention because of their unique properties and potential applications. The simplest synthetic route to make 3D nanostructures is probably self-assembling, in which ordered aggregates are formed in a spontaneous process. Due to their safety and compatibility with the electrolyte, lithium titanium oxides (LTO) and titania are of great interest for anode materials in Li-ion batteries. Performances of Li-ion batteries extremely depend on electrodes properties, especially on electrode/electrolyte contact area, because of reduced Li+ transport distances. Reduction into nano-scale is the best solution for increasing the contact area to enabling batteries to work at higher power. We report the synthesis of self-organizing LTO nanopetals, less than 10 nm thick, that spontaneously make 3D flower-like nanoarchitectures, providing high surface to volume ratio of material. LTO nanostructure was prepared by a heterogeneous reaction of anatase, TiO2, nanopowder and aqueous LiOH solution under mild hydrothermal conditions (autogenous pressure at 200 ºC). Crystal structure and Li placing were investigated in detail by XRPD and SAED analysis. Additionally, structural evolution and phase transitions with increasing temperature up to 800 ºC were studied. The chemical compositions of as-prepared and treated samples were estimated by ICP-OES or EDS analysis.

• Titanium Oxide Materials for Greener Environment

  I. Veljković

  Restca_ A course in X-ray Application, Serbia, Belgrade; 01/2010

  http://www.rgf.bg.ac.rs/restca/events.html

• NANOSIZED ANATASE OBTAINED BY HYDROTHERMAL SYNTHESIS

  I. Veljković, D. Poleti, J. Rogan, M. Zdujić, Lj. Karanović

  XVI Conference of the Serbian Crystallographic Society, Divčibare, Serbia; 10/2009

• Titanium Oxides

  Ivana Veljković, Dejan Poleti, Miodrag Zdujić, Ljiljana Karanović

  11th International Conference and Exibition of the Europian Ceramic Society, Krakow, Poland; 06/2009

• Nonstoichiometric titanium oxides (Nestehiometrijski oksidi titana)

  Ivana Veljković, Dejan Poleti, Miodrag Zdujić, Ljiljana Karanović

  XLVII Meeting of the Serbian Chemical Society, Belgrade; 03/2009

• Mechanochemistry of Titanium Oxides (Mehanohemija oksida titana)

  Ivana Veljković, Dejan Poleti, Miodrag Zdujić, Ljiljana Karanović

  Hemijska Industrija. 01/2009; 63:247.

  Mechanochemistry represents an alternative route in synthesis of nanomaterials. Mechanochemical routes are attractive because of their simplicity, flexibility, and ability to prepare materials by solid state reactions at room temperature. The aim of this work is the mechanochemical synthesis of nano... [more] Mechanochemistry represents an alternative route in synthesis of nanomaterials. Mechanochemical routes are attractive because of their simplicity, flexibility, and ability to prepare materials by solid state reactions at room temperature. The aim of this work is the mechanochemical synthesis of nanostructured titanium oxides of different composition starting from mixtures of Ti and TiO2, TiO and TiO2 or Ti2O3 and TiO2. Emphasis is on the Magneli phases Ti4O7 and Ti5O9 because their mixture is commercially known as EBONEX material. The materials prepared were characterized by XRPD, TG/DTA analysis, SEM and optical microscopy. Titanium monoxide and several Magneli oxides, Ti4O7, Ti5O9 and Ti6O11, are successsfully prepared. The results are very interesting because the EBONEX materials were prepared at lower than usual temperature, which would decrease the effective cost of production.

• Mechanochemically induced amorphous/crystalline phase transition in the Bi4Ti3O12 compound

  M. Zdujic, C. Jovalekic, D. Poleti, I. Veljkovic, L. Karanovic

  Materials Letters. 01/2009; 63:2542.

  Concurrent milling of Bi4Ti3O12 was carried out in a planetary ball mill with hardened-steel 13 or 6 mm diameter balls with a goal to investigate how the system responds to the constrains imposed by milling. Milling intensity for various milling parameters was derived from the electrical power measu... [more] Concurrent milling of Bi4Ti3O12 was carried out in a planetary ball mill with hardened-steel 13 or 6 mm diameter balls with a goal to investigate how the system responds to the constrains imposed by milling. Milling intensity for various milling parameters was derived from the electrical power measurement. The reverse amorphous - crystalline phase transition induced by milling is governed by impact energy and frequency. Below a certain threshold value of impact energy crystallization does not occur, whereas a higher impact frequency accelerates amorphization. Mechanochemical reactions are predominantly discrete processes, which occur at the moment of impact.

• Mechanochemistry of titanium oxides

  Ivana Veljkovic, Dejan Poleti, Miodrag Zdujic

  7th Young Researchers Conference, Belgrade; 12/2008

  Mechanochemistry represents an alternative route in synthesis of nanomaterials. Mechanochemical routes are attractive because of their simplicity, flexibility, and ability to prepare materials by solid state reactions at room temperature. First part of this work is review of nanomaterials prepared b... [more] Mechanochemistry represents an alternative route in synthesis of nanomaterials. Mechanochemical routes are attractive because of their simplicity, flexibility, and ability to prepare materials by solid state reactions at room temperature. First part of this work is review of nanomaterials prepared by mechanochemical treathment. The aim of the work is the mechanochemical synthesis of nanostructured titanium oxides of different composition beginning from mixtures of Ti and TiO2, TiO and TiO2 or Ti2O3 and TiO2. Accent is on the Magneli’s phases Ti4O7 and Ti5O9 because their mixture is commercially known as EBONEX material. The materials prepared were characterized by XRPD, TG/DTA analysis, SEM and optical microscopy. Titanium monoxide and several Magneli’s oxides, Ti4O7, Ti5O9 and Ti6O11, are sucesfully prepared.

• Mechanochemical synthesis of nanocrystalline titanium monoxide

  Ivana Veljkovic, Dejan Poleti, Miodrag Zdujic, Ljiljana Karanovic, Cedomir Jovalekic

  Materials Letters. 06/2008; 62:2769-2771.

  Nanocrystalline cubic titanium monoxide, TiOx (0.92 < x < 1.19), with mean crystallite size of ≈ 6 nm, was synthesized by mechanochemical treatment of Ti and TiO2 (rutile) powder mixtures with molar ratios of 1:1, 1.10:1 and 1.25:1. The mechanochemical solid state reaction in a high-energy pla... [more] Nanocrystalline cubic titanium monoxide, TiOx (0.92 < x < 1.19), with mean crystallite size of ≈ 6 nm, was synthesized by mechanochemical treatment of Ti and TiO2 (rutile) powder mixtures with molar ratios of 1:1, 1.10:1 and 1.25:1. The mechanochemical solid state reaction in a high-energy planetary ball mill was completed for 2 h in either air or argon atmosphere. During heating in vacuum at 900 and 1000 °C for 24 h, nanocrystalline TiOx transforms to a well-crystallized, cubic or monoclinic TiOx. The materials prepared were characterized by XRPD, TGA/DSC and SEM/EDS analysis.

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• Structural characterization of mechanochemically prepared TiO

  I. Veljkovic, D. Poleti, Lj. Karanovic, M. Zdujic, C. Jovalekic

  XIV Conference of the Serbian Crystallographic Society, Vrsac; 07/2007

  Titanium monoxide belongs to the class of highly nonstoichiometric interstitial phases and exists in a wide composition range, from TiO0.80 to TiO1.25. Even among highly nonstoichiometric compounds TiOy is unique in the sense that it contains a large amount of both, metal and non-metal vacancies. To... [more] Titanium monoxide belongs to the class of highly nonstoichiometric interstitial phases and exists in a wide composition range, from TiO0.80 to TiO1.25. Even among highly nonstoichiometric compounds TiOy is unique in the sense that it contains a large amount of both, metal and non-metal vacancies. To adequately describe the defect structure of titanium monoxide, its formula should take into account Ti and O vacancies: TixOz = TiOy, or Tix■1-xOz□1-z = TiOy, where y = z/x, while □ and ■ designate O and Ti vacancies, respectively. The distribution of atoms and vacancies over the crystal lattice of titanium monoxide can be disordered and ordered, depending on the oxygen content and thermal treatment. In a disordered phase, with the cubic NaCl structure, atoms and structural vacancies are randomly distributed over the crystal lattice sites. Ordering is accompanied by the reduction to the monoclinic symmetry, but the effect of ordering on thermodynamic properties of titanium monoxide has not been studied in detail yet. In conventional synthetic procedures, TiOy samples usually consist of two phases and contains both, ordered and disordered phase. Also, the colour of conventionally synthesized materials vary from yellowish silvery over golden yellow to dark golden yellow. In this work TiOy samples were prepared from Ti metal and TiO2 (rutile) powders by solid state reaction in a planetary ball mill. The mixtures of reactants, with Ti:TiO2 molar ratios equal to 1:1, 1.10:1 and 1.25:1, were milled for 2 hours using hardened-steel vials and balls in an air or argon atmosphere. The synthesized samples were further annealed (sealed quartz ampoules) in a vacuum or argon atmosphere for 24 hours at temperature range 600–1100 °C. The products were characterized by X-ray powder diffraction (XRPD) and TG/DT/DSC analysis, optical and scanning electron microscopy. The approximate average crystallite size of milled samples was calculated using the Scherrer formula. After milling, XRPD analysis confirmed formation of disordered cubic titanium monoxide of low crystallinity and nanometer crystallite size in all cases. After annealing at different temperatures the crystallinity increased and disordered structure remained, except in the case of the 1.25:1 reactants ratio, where the maxima of an ordered monoclinic titanium monoxide were observed at 900 °C. Optical microscopy showed a wide range of colours (intensive blue, violet, golden yellow, brown and silver grey) what probably can be attributed to the nonstoichiometry and iron contamination, because the EDS analysis revealed an average iron content of about 2.5 wt.%. The cubic to monoclinic and vice versa TiOy phase transitions were investigated by DSC analysis in an argon atmosphere. No expected phase transitions were observed up to 1300 ºC.

• Mechanochemical Synthesis of TiOx with x<2

  I. Veljkovic, D. Poleti, Lj. Karanovic, M. Zdujic, C. Jovalekic

  XIII Conference of the Serbian Crystallographic Society, Novi Sad; 06/2006