854 results on '"Obradović, Nina"'
Search Results
2. Effect of mechanical activation on carbothermal synthesis and densification of ZrC
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Obradović, Nina, Feng, Lun, Filipović, Suzana, Mirković, Miljana, Kosanović, Darko, Rogan, Jelena, and Fahrenholtz, William G.
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- 2023
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3. Electronic properties of BZT nano-ceramic grades at low frequency region
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Kosanović Darko, Blagojević Vladimir A., Aleksić Stanko O., Živojinović Jelena, Peleš-Tadić Adriana, Pavlović Vladimir B., and Obradović Nina
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bzt ceramics ,sintering ,dielectric properties ,Chemical technology ,TP1-1185 - Abstract
BZT ceramics was prepared by using fine powder mixture of BaCO3, TiO2 and ZrO2 in the respective molar ratio to form Ba(Zr0.10Ti0.90)O3 via solid state reaction at elevated temperature. The prepared BZT was milled in the planetary ball mill from 0-120 min to achieve different powder grades from micron to nano-sized particles. After the powder characterization by XRD and SEM the samples were pressed in disc shape and sintered at different temperatures from 1100-1350°C in the air. The sintered samples were characterized by SEM and their density and average grain size was determined and presented vs. sintering temperature and powder grades (milling time). After that the silver epoxy electrodes were deposited on sintered disc samples. The disc samples capacity and resistivity were measured at low frequency region from 1 Hz to 200 kHz using low frequency impedance analyzer. The sintering temperatures and powder grades were used as parameters. Finally the specific resistance ρ, dielectric constant (ε' + jε") and tgδ where determined from the impedance measurements. The behavior of electronic properties where analyzed e.g. the relaxation effect of the space charge (inter-granular electric charges) vs. sintering temperature and ceramic grades. The results obtained were compared with best literature data for the losses in BZT ceramics at low frequencies.
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- 2023
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4. Influence of mechanical activation on SrTiO3 mixture with Fe2O3 as aditive
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Živojinović Jelena A., Peleš-Tadić Adriana P., Kosanović Darko A., Filipović Suzana Ž., Stanković Ana V., and Obradović Nina N.
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mechanical activation ,xrd ,srtio3 ,fe2o3 ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
The authors investigated the influence of mechanical activation on the structure of SrTiO3 mixture with 6 wt.% Fe2O3. Powders were mechanically activated in a planetary ball mill with WC balls in time intervals from 0 to 120 minutes. XRD method was used for the identification of phase structure, while SEM and PSA were employed for monitoring of changes in morphology and particle size distribution. Structural changes were followed by Raman spectroscopy, and band gap values were calculated as well. The purpose of mechanical activation is lowering the temperature and time of sintering in the process of obtaining the final product.
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- 2023
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5. Morphological and structural characterization of MgAl2O4 spinel
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Obradović Nina, Filipović Suzana, Fahrenholtz William G., Marinković Bojan A., Rogan Jelena, Lević Steva, Đorđević Antonije, and Pavlović Vladimir B.
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spinel ,mechanical activation ,sintering ,structure ,Chemical technology ,TP1-1185 - Abstract
Magnesium aluminate has the spinel structure along with good mechanical, chemical, and thermal properties. Magnesium aluminate has a wide range of applications including refractory ceramics, optically transparent ceramic windows, and armors. Its low dielectric permeability and low loss tangent enable its applications for integrated electronic devices, as well. In this paper, MgO and Al2O3 powders were mixed in a one-to-one molar ratio and calcined at temperatures ranging from 1500 to 1800oC to produce phase pure spinel. Thereafter, pellets were crushed and treated in a planetary ball mill for 60 min to obtain a fine powder. All powders were examined for phase composition, crystal structure, and morphology. The obtained results showed that by increasing the temperature, samples with higher density were synthesized. Milling for 1 h led to formation of larger particles, but finer powders after milling. XRPD and Raman spectroscopy showed disorder in the crystal structure after milling.
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- 2023
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6. Removal of the As(V) and Sr(VI) from the water using magnetite/3D-printed wollastonite hybrid adsorbent
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Popović Mina, Veličković Zlate S., Bogdanov Jovica, Marinković Aleksandar D., Casas-Luna Mariano, Trajković Isaak, Obradović Nina, and Pavlović Vladimir
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arsenic ,chromium ,adsorption ,magnetite ,3d-printed wollastonite ,Chemical technology ,TP1-1185 - Abstract
In this study, the structure, morphology and composition of the synthesized magnetite/3D-printed wollastonite (3D_W/M) composite were characterized, and its adsorption performance with respect to As(V) and Cr(VI) were studied. Magnetite (MG) modified 3D printed wollastonite was obtained by two step procedure: modification of 3D_W with 3-aminoproylsilane (APTES) followed by controlled magnetite (MG) deposition to obtain 3D_W/M adsorbent. The structure/properties of 3D_W/M were confirmed by applying FTIR, XRD, TGD/DTA, and SEM analysis. The adsorption properties of hybrid adsorbents were carried out for As(V) and Cr(VI) removal - one relative to the initial pH value, the adsorbent mass, the temperature, and the adsorption time. Time-dependent adsorption study was best described by pseudo-second order equation, while Weber Morris analysis showed that intraparticle diffusion controled diffusional transport. Similar activation energy, 17.44 and 14.49 kJ•mol-1 for adsorption As(V) and Cr(VI) on 3D_W/M, respectively, indicated main contribution of physical adsorption. Determination of adsorption parameters was performed by applying different adsorption isotherm models, and the best fit was obtained using Freundlich model. The adsorption capacity of 24.16 and 29.6 mg g-1 for As(V) and Cr(VI) at 2ºC, Co = 5.5 and 5.3 mg L-1, respectively, were obtained. Thermodynamic study indicated favourable process at a higher temperature. Preliminary fixed-bed column study and results fitting with Bohart-Adams, Yoon-Nelson, Thomas, and Modified dose-response model showed good agreement with results from the batch study.
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- 2022
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7. Synthesis and Properties of (Hf,Mo,Ti,W,Zr)B2-(Hf,Mo,Ti,W,Z)C Dual Phase Ceramics
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Filipović, Suzana, Filipović, Suzana, Hilmas, Gregory E., Fahrenholtz, William G., Obradović, Nina, Curtarolo, Stefano, Filipović, Suzana, Filipović, Suzana, Hilmas, Gregory E., Fahrenholtz, William G., Obradović, Nina, and Curtarolo, Stefano
- Abstract
Dual phase high entropy ceramics are attractive due to potential synergetic effects of the constituents on mechanical properties and thermal stability. In this research, dense, dual phase (Hf,Mo,Ti,W,Z) B2-(Hf.Mo.Ti.W,Zr)C powder was synthesized by varying the contents of the transition metals in the final product. The co-synthesis method was used to obtain boride and carbide constituents by boro/ carbothermal reduction of mixtures of oxides and appropriate amounts of carbon black and B4C. Solid solution formation and densification of the reacted powders were done utilizing two step spark plasma sintering or hot pressing processes. Phase compositions of the produced ceramics were identified by x-ray diffraction while chemical compositions were measured using energy dispersive spectroscopy. The final microstructures showed submicron grains due to pining effect of the two phases. Investigation of the mechanical properties showed increasing in Vickers hardness values s up to 48.6 2.2 GPa for applied load of 0.49N for compositions with optimized elemental contents. Room temperature strength was also measured.
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- 2024
8. Robocasting of controlled porous CaSiO3–SiO2 structures: Architecture – Strength relationship and material catalytic behavior
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Casas-Luna, Mariano, Torres-Rodríguez, Jorge Alberto, Valdés-Martínez, Omar Uriel, Obradović, Nina, Slámečka, Karel, Maca, Karel, Kaiser, Jozef, Montúfar, Edgar B., and Čelko, Ladislav
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- 2020
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9. Formation kinetics and cation inversion in mechanically activated MgAl2O4 spinel ceramics
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Obradović, Nina, Fahrenholtz, William G., Filipović, Suzana, Marković, Smilja, Blagojević, Vladimir, Lević, Steva, Savić, Slobodan, Đorđević, Antonije, and Pavlović, Vladimir
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- 2020
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10. Carbothermal reaction of mechanically activated ZrC powders followed by DSC-TGA
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Obradović, Nina, Obradović, Nina, Filipović, Suzana, Bohannan, Eric W., Fahrenholtz, William G., Obradović, Nina, Obradović, Nina, Filipović, Suzana, Bohannan, Eric W., and Fahrenholtz, William G.
- Abstract
Mixtures of ZrO2 and C were prepared by high-energy ball milling. Powders were milled for times from 0 to 120 minutes in air atmosphere. As milling time increased, surface area of powders increased, indicating significant particle size reduction. The thermal treatment cycle included heating at 10 °C/min to 1600 °C followed by an isothermal hold for 2 hours under the vacuum (~20 Pa) in a resistance-heated graphite element furnace. This first step of the process promoted carbothermal reaction of the starting materials. DSC-TGA was used to follow the carbothermal reaction. The onset temperature does not seem to change for non-activated and activated powders. The change in peak area may be related to the amount of the powder that reacts at this temperature. The catbothermal reaction was split into two parts for powders activated 60 and 120 minutes. Only part of the powder reacts at the initial reaction, and then higher temperatures are required for full reaction.
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- 2023
11. Characterization of mechanically activated ZrO2-C powder mixtures
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Obradović, Nina, Obradović, Nina, Feng, Lun, Filipović, Suzana, Mirković, M., Kosanović, Darko, Živojinović, Jelena, Rogan, Jelena, Fahrenholtz, William G., Obradović, Nina, Obradović, Nina, Feng, Lun, Filipović, Suzana, Mirković, M., Kosanović, Darko, Živojinović, Jelena, Rogan, Jelena, and Fahrenholtz, William G.
- Abstract
Mechanical activation represents a very useful technique for powder processing prior to sintering process. First of all, it makes powders homogenized, leads to attrition of powder particles, and makes powder mixtures more reactive. Secondly, it can lead to mechano-chemical reaction, and finally, lowering of sintering time and temperature. Mixtures of ZrO2 and C were mechanically activated by high-energy ball milling. Powders were milled for times from 0 to 120 minutes in air atmosphere. Mechanically activated powder mixtures were characterized by various techniques, such as particle size analysis (PSA), X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, and diffraction scanning calorimetry along with thermo gravimetry (DSC-TGA). As milling time increased, surface area of powders increased, indicating significant particle size reduction. Mechanical activation for 15 minutes provides the best balance between particle size reduction and reactivity for the powders.
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- 2023
12. Kinetics of thermally activated processes in cordierite-based ceramics
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Obradović, Nina, Blagojević, Vladimir, Filipović, Suzana, Đorđević, Nataša, Kosanović, Darko, Marković, Smilja, Kachlik, Martin, Maca, Karel, and Pavlović, Vladimir
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- 2019
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13. Effects of mechanical-activation and TiO2 addition on the behavior of two-step sintered steatite ceramics
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Terzić, Anja, Obradović, Nina, Kosanović, Darko, Stojanović, Jovica, Đorđević, Antonije, Andrić, Ljubiša, and Pavlović, Vladimir B.
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- 2019
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14. Sintering of Zinc-Titanate
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Obradović, Nina, Lee, William E., editor, Gadow, Rainer, editor, Mitic, Vojislav, editor, and Obradovic, Nina, editor
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- 2016
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15. Effect of the filler morphology on the crystallization behavior and dielectric properties of the polyvinylidene fluoride‐based composite.
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Filipović, Suzana, Obradović, Nina, Corlett, Cole, Fahrenholtz, William G., Rosenschon, Martin, Füglein, Ekkehard, Dojčilović, Radovan, Tošić, Dragana, Petrović, Jovana, Đorđević, Antonije, Vlahović, Branislav, and Pavlović, Vladimir B.
- Abstract
Ceramic/polymer composites can be chemically stable, mechanically strong, and flexible, which make them candidates for electric devices, such as pressure or temperature sensors, energy storage or harvesting devices, actuators, and so forth. Depending on the application, various electrical properties are of importance. Polymers usually have low dielectric permittivity, but increased dielectric permittivity can be achieved by the addition of the ceramic fillers with high dielectric constant. With the aim to enhance dielectric properties of the composite without loss of flexibility, 5 wt% of BaTiO3‐Fe2O3 powder was added into a polyvinylidene fluoride matrix. The powder was prepared by different synthesis conditions to produce core/shell structures. The effect of the phase composition and morphology of the BaTiO3‐Fe2O3 core/shell filler on the structure and lattice dynamics of the polymer composites was investigated. Based on the results of the thermal analysis, various parameters of ceramic/polymer composites were determined. Differences in the phase composition and morphology of the filler have an influence on the formation of various polyvinylidene fluoride allomorphs and the degree of crystallinity. Furthermore, the dielectric performances of pure polyvinylidene fluoride and the polymer/ceramic composites were measured. [ABSTRACT FROM AUTHOR]
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- 2024
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16. Characterization of MgAl2O4 sintered ceramics
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Obradović Nina, Fahrenholtz William G., Filipović Suzana, Corlett Cole, Đorđević Pavle, Rogan Jelena, Vulić Predrag J., Buljak Vladimir, and Pavlović Vladimir
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mechanical activation ,sintering ,xrd ,sem ,spinel ,Chemical technology ,TP1-1185 - Abstract
Single phase MgAl2O4 was made from a one-to-one molar ratio of MgO and Al2O3 powders mixed using ball-milling. Mixtures of MgO and Al2O3 were subsequently treated in planetary ball mill for 30, 60, 90 and 120 minutes in air. The aim of this study was to examine phase composition, microstructure, and densification behavior of sintered specimens. After sintering in dilatometer at 1500°C, the powder was converted to single phase MgAl2O4. The results show that mechanical activation improved the densification behavior of MgAl2O4 sintered specimens, and it reduced the onset temperature for sintering by approx. 100°C. Based on dilatometer data, powders were subsequently densified at 1450°C by hot pressing. Almost аll specimens exhibited full density, while sample activated for 30 minutes showed the fastest densification rate. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. OI 172057, and Grant no. III 45007]
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- 2019
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17. Properties of 3Y-TZP zirconia ceramics with graphene addition obtained by spark plasma sintering
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Obradović, Nina and Kern, Frank
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- 2018
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18. Controllable synthesis of Fe3O4-wollastonite adsorbents for efficient heavy metal ions/oxyanions removal
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Rusmirović, Jelena D., Obradović, Nina, Perendija, Jovana, Umićević, Ana, Kapidžić, Ana, Vlahović, Branislav, Pavlović, Vera, Marinković, Aleksandar D., and Pavlović, Vladimir B.
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- 2019
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19. Physical properties of sintered alumina doped with different oxides
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Filipović Suzana, Obradović Nina, Marković Smilja, Đorđević Antonije, Balać Igor, Dapčević Aleksandra, Rogan Jelena, and Pavlović Vladimir
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mechanical activation ,densities ,SEM ,sintering ,alumina ,Chemical technology ,TP1-1185 - Abstract
Corundum (α-alumina) is a suiTab. material for usage in various industry fields owing to its chemical stability, electrical and mechanical features. It is known that properties of ceramics could be modified by addition of different oxides, as well as by changing the consolidation parameters. In this respect, alumina was doped with 1 wt.% of Cr2O3, Mn2O3 and NiO, followed by 1 hour of mechanical activation in a high-energy planetary ball mill. A sensitive dilatometer was used for sintering of powder mixtures up to 1400 oC and recording the obtained dilatation. The final density varied between cca. 1.9 and 3.3 g/cm3. Microstructural changes were detected by SEM measurements. Changes in electrical permittivity and loss tangent were associated with the preparation conditions (types of additives, duration of mechanical activation). For a given mixture, the sintering increases the relative permittivity and decreases losses, exhibiting the optimal values of 8.32 and 0.027, respectively, for the sample activated 60 minutes and sintered, with the addition of MnO2. Mechanical measurements indicate significant differences in strength with the addition of different transition metal oxides. Samples with Mn and Ni, activated and sintered, with strength of 121 and 86 MPa, respectively, have a significantly higher tensile strength than the other tested samples, due to their more compact microstructures. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. OI 172057, Grant no. III 45007 and Grant no. III 45019]
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- 2018
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20. Application of thick film segmented thermistors for measurement and analysis of ground top layer temperature profile
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Aleksić Stanko O., Mitrović Nebojša S., Luković Miloljub D., Luković Snežana G., and Obradović Nina N.
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temperature measurement ,thick film thermistors ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
A new sensor for measuring ground top layer temperature profile was formed as a row of 40 thermistor segments connected in series, with which the change of temperature in the soil is mesaured and placed on 550 mm depth. The temperature sensor is multiple protected of humidity, calibrated on room temperature and placed vertically in the hole drilled on the lawn. The main electrical properties of the new sensor based on NTC thick film segmented thermistors are given in brief. The ground top layer temperature profile measurements were done in 40 points at 7am and 2 pm each day from the beginning of November 2017 to the end of February 2018.At the same time and in the same period of time the air temperature were measured and recorded. The results of measurements of ground top layer temperatureT(t,z) were given in daily and monthly diagrams as a function of time t and ground deepness d on z-axis. The correlation between ground top layer temperature profile and air temperature was analyzed: changes of ground temperature gradient and effect of precipitations on ground temperature profile. The results obtained enable study of temperature regime of ground top layer.
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- 2018
21. Final stage densification kinetics of direct current sintered ZrB 2
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Stanfield, Austin D., primary, Smith, Steven M., additional, Filipović, Suzana, additional, Obradović, Nina, additional, Buljak, Vladimir, additional, Hilmas, Gregory E., additional, and Fahrenholtz, William G., additional
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- 2023
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22. Characterization of FeCoV alloy processed by PIM/MIM route
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Nedeljković Borivoje, Mitrović Nebojša, Orelj Jelena, Obradović Nina, and Pavlović Vladimir
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powder injection moulding technology ,FeCoV alloy ,structural properties ,mechanical properties ,magnetic properties ,Chemical technology ,TP1-1185 - Abstract
In this study the characterization of FeCo-2V alloys toroidal samples produced by PIM/MIM technology was presented. The feedstock for metal injection molding (MIM) was prepared by mixing starting FeCoV powder with a low viscosity binder. Green samples were subjected to solvent debinding and subsequent thermal debinding followed by sintering. Sintering was performed during 3.5 hours from 1370°C to 1460°C in hydrogen atmosphere in order to attain the appropriate mechanical and magnetic properties. Microstructure, hardness HV10 and magnetic hysteresis B(H) were investigated as a function of sintering temperature. Optimum combination of functional properties was observed after sintering at temperature of 1370°C. In addition, magnetic properties were analyzed as frequency dependent and successfully simulated in operating frequency range from 5 Hz to 60 Hz. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. OI 172057]
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- 2017
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23. Electrical properties of magnesium titanate ceramics post-sintered by hot isostatic pressing
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Đorđević Antonije R., Olćan Dragan I., Obradović Nina, Paunović Vesna, Filipović Suzana, and Pavlović Vladimir B.
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magnesium titanate ,hot isostatic pressing ,complex permittivity ,thermistors ,varistors ,Chemical technology ,TP1-1185 - Abstract
Post-sintering of magnesium titanate ceramics by hot isostatic pressing (HIP) in an oxygen-free atmosphere significantly alters various electrical properties of the product. In particular, the sintered material becomes a semiconductor. The aims of this paper are: to extend our investigations of the electrical properties of this material by expanding the frequency range of measurements, to design interpolation formulas for the frequency dependence of the complex relative permittivity, and to propose HIP-sintered magnesium titanate as a material for thermistors that have a negative-temperature-coefficient resistance (NTCR), as well as for varistors. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. TR 32005 and Grant no. ON 172057]
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- 2017
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24. Formation of porous wollastonite-based ceramics after sintering with yeast as the pore-forming agent
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Obradović Nina, Filipović Suzana, Rusmirović Jelena, Postole Georgeta, Marinković Aleksandar, Radić Danka, Rakić Vesna, Pavlović Vladimir, and Auroux Aline
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Yeast ,Sintering ,Porous wollastonite ceramics ,Chemical technology ,TP1-1185 - Abstract
In this paper, synthesis of porous wollastonite-based ceramics was reported. Ceramic precursor, methylhydrocyclosiloxane, together with micro-sized CaCO3, was used as starting material. After 20 min of ultrasound treatment, and calcination at 250 oC for 30 min, yeast as a pore-forming agent was added to the as-obtained powders. Sintering regime was set up based on the results obtained by differential thermal analysis. Prepared mixture was pressed into pallets and sintered at 900 oC for 1 h. After the sintering regime, porous wollastonite-based ceramics was obtained. The phase composition of the sintered samples as well as microstructures was analyzed by X-ray diffraction method and SEM. In a batch test, the influence of pH, contact time and initial ion concentration on adsorption efficiency of As+5, Cr+6, and phosphate ions on synthesized wollastonite-based ceramics were studied. Time-dependent adsorption was best described by pseudo-second-order kinetic model and Weber-Morris model that predicted intra-particle diffusion as a rate-controlling step of overall process. High adsorption capacities 39.97, 21.87, and 15.29 mgg-1 were obtained for As+5, Cr+6, and phosphate ions, respectively.
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- 2017
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25. Multi-phase (Zr,Ti,Cr)B 2 solid solutions: Preparation, multi-scale microstructure, and local properties
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Silvestroni, Laura, primary, Gilli, Nicola, additional, Sangiorgi, Alex, additional, Corozzi, Alessandro, additional, Filipović, Suzana, additional, Obradović, Nina, additional, Ortiz-Membrado, Laia, additional, Jiménez-Piqué, Emilio, additional, and Fahrenholtz, William G., additional
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- 2023
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26. Optimization of processing parameters for high entropy dual phase ceramics
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Filipović, Suzana, Filipović, Suzana, Smith, Steven, Obradović, Nina, Hilmas, Gregory E., Fahrenholtz, William G., Filipović, Suzana, Filipović, Suzana, Smith, Steven, Obradović, Nina, Hilmas, Gregory E., and Fahrenholtz, William G.
- Abstract
High entropy carbide/boride (HEC/HEB) ceramics are materials with a wide range of possible applications in harsh environments due to their good mechanical properties, oxidation resistance, and thermal stability. They are usually formed by the solid solutioning of four or more transition metals (TM) in the boride and carbide lattice. In this research, boro/carbothermal reduction was used to form an individual diboride and carbide phases from oxide mixtures. The stoichiometry of the reaction was varied in order to synthesize pure dual phase ceramics. The reacted powders were spark plasma sintered (SPS) or hot pressed (HP), using a two-step process, to produce dense ceramics and to develop the solid solutions. Ceramics processed by SPS still contained residual oxides, while ceramics produced by HP were nominally phase-pure high entropy dual phase materials. Preferential segregation of the TMs was detected by energy dispersive spectroscopy. Vickers hardness measurements confirmed that the highest hardness was obtained for specimens densified by HP at 1950°C that contained no residual oxides and had the smallest grain size. The hardness increased from 25.7 ± 0.2 GPa to 33.6 ± 2.2 GPa with decrease applied load from 9.81N to 0.49N, respectively.
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- 2023
27. Radio-frequency electrical characterization of viable-cell suspensions
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Dinkić, J., Dinkić, J., Lević, S. M., Nedović, Viktor, Obradović, Nina, Đorđević, Antonije, Dinkić, J., Dinkić, J., Lević, S. M., Nedović, Viktor, Obradović, Nina, and Đorđević, Antonije
- Abstract
Suspended viable cells significantly influence the relative complex permittivity (dielectric constant) of the suspension. This influence depends on the concentration, viability, size, and even the cell shape. Hence, by measuring the permittivity, various fermentation processes can be monitored (e.g., in wine making and preparation of milk products). Thereby, the complex impedance (or admittance) between electrodes immersed into the suspension is measured and the permittivity is obtained by a suitable de-embedding procedure. There exist various data in the literature on this influence, but they do not provide sufficient information for wide implementation of the technique. The aim of the paper was to experimentally investigate various aspects of the measurement procedures and establish practical guidelines and limitations. Measurements were performed using an LCR meter, a classical vector network analyzer, and a nanoVNA analyzer, in the frequency range from 10 Hz to 100 MHz. Various suspension containers and systems of electrodes were designed and manufactured. Bipolar systems of electrodes were found to be more suitable for higher frequencies than tetrapolar ones. Open electrode systems were found to be more prone to the influence of the environment than shielded systems (e.g., coaxial). Good results were obtained for simple yeast suspensions. However, the presence of other cells and dispersed solids (e.g., in pressed grape juice) was found to completely overshadow the yeast cells. Electrochemical effects on the electrodes were found to be insignificant above around 200 kHz. Bubbles on electrodes, delamination, high concentrations of ions, and even temperature variations significantly hindered measurements in many cases.
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- 2023
28. Fractal analysis and microstructure development PVDF based multifunctional material
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Peleš Tadić, Adriana, Peleš Tadić, Adriana, Vuković, George, Kojović, Aleksandar, Stojanović, Dušica, Vlahović, Branislav, Obradović, Nina, Pavlović, Vladimir, Peleš Tadić, Adriana, Peleš Tadić, Adriana, Vuković, George, Kojović, Aleksandar, Stojanović, Dušica, Vlahović, Branislav, Obradović, Nina, and Pavlović, Vladimir
- Abstract
Polyvinylidene fluoride (PVDF) is a novel gel polymer electrolyte alternative which can reduce the risk of irreversible failure in lithium-ion batteries (LIB) [1]. PVDF matrix structures which exhibit inter-crosslinking networks have previously demonstrated favorable thermal and mechanical properties for LIB applications [2]. PVDF based multifunctional material is attracting a great scientific interest due to its excellent piezoelectric, pyroelectric and ferroelectric properties. Such as, its properties strongly depend on synthesis procedures and obtained microstructures. In this research, porous structure and cross-linking patterns of PVDF were prepared by electrospinning method and it has been found that these microstructures can have fractal structure. Fractal analysis can be used as a powerful tool for describing structural and functional properties of these this material. Because of that, in this research we have used different fractal methods for the reconstructions of various PVDF microstructure morphologies. Fractal analysis has been performed by using scanning electron microscope micrographs and computational modeling tools. Theory of Iterated Function Systems and Voronoi tessellation, have been used for modeling PVDF porous structures. A Python algorithm was created to determine the distribution of pore areas in SEM micrographs. Algorithm’s distribution of calculated pore surface areas were compared with measured pore surface areas and fractal reconstructions of different morphologies and their connection with functional properties were analyzed.
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- 2023
29. Effect of the filler morphology on the crystallization behavior and dielectric properties of the polyvinylidene fluoride‐based composite
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Filipović, Suzana, Obradović, Nina, Corlett, Cole, Fahrenholtz, William G., Rosenschon, Martin, Füglein, Ekkehard, Dojčilović, Radovan, Tošić, Dragana, Petrović, Jovana, Đorđević, Antonije, Vlahović, Branislav, Pavlović, Vladimir B., Filipović, Suzana, Obradović, Nina, Corlett, Cole, Fahrenholtz, William G., Rosenschon, Martin, Füglein, Ekkehard, Dojčilović, Radovan, Tošić, Dragana, Petrović, Jovana, Đorđević, Antonije, Vlahović, Branislav, and Pavlović, Vladimir B.
- Abstract
Ceramic/polymer composites can be chemically stable, mechanically strong, and flexible, which make them candidates for electric devices, such as pressure or temperature sensors, energy storage or harvesting devices, actuators, and so forth. Depending on the application, various electrical properties are of importance. Polymers usually have low dielectric permittivity, but increased dielectric permittivity can be achieved by the addition of the ceramic fillers with high dielectric constant. With the aim to enhance dielectric properties of the composite without loss of flexibility, 5 wt% of BaTiO3-Fe2O3 powder was added into a polyvinylidene fluoride matrix. The powder was prepared by different synthesis conditions to produce core/shell structures. The effect of the phase composition and morphology of the BaTiO3-Fe2O3 core/shell filler on the structure and lattice dynamics of the polymer composites was investigated. Based on the results of the thermal analysis, various parameters of ceramic/polymer composites were determined. Differences in the phase composition and morphology of the filler have an influence on the formation of various polyvinylidene fluoride allomorphs and the degree of crystallinity. Furthermore, the dielectric performances of pure polyvinylidene fluoride and the polymer/ceramic composites were measured.
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- 2023
30. Structural characteristics of MgAl2O4 spinel
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Peleš Tadić, Adriana, Peleš Tadić, Adriana, Živojinović, Jelena, Tadić, Nenad, Lević, Steva, Marković, Smilja, Pavlović, Vladimir B., Filipović, Suzana, Obradović, Nina, Peleš Tadić, Adriana, Peleš Tadić, Adriana, Živojinović, Jelena, Tadić, Nenad, Lević, Steva, Marković, Smilja, Pavlović, Vladimir B., Filipović, Suzana, and Obradović, Nina
- Abstract
Magnesium aluminate spinel (MgAl2O4) is a material with good mechanical, chemical, and thermal properties, low dielectric permeability and loss tangent. Based on those properties, MgAl2O4 has found a significant application in refractory ceramics, ceramics windows, integrated electronic devices, etc. Also, it possesses a high chemical and radiation resistance. In this research, MgO was calcined at 1000ºC for an hour, with a step of 10ºC/min to avoid presence of hydroxide or carbonate. MgO and Al2O3 powders were mixed in a one-to-one molar ratio afterwards. The powders were mechanically activated for 15, 30, and 60 minutes. The mass ratio of powder and balls was 1:40. The mechanically activated powders are pressed in the tablets, under the pressure of 0.5 t. The pressed powders were heated up to 1300 ºC with a step of 10 ºC/min and held for 1 h for the reaction. Reacted pellets were crushed and sieved. Obtained spinel powders were sintered at 1450 ºC for 2 h. Both sintered and non-sintered samples were investigated by XRD and SEM. The particle size distribution of the reacted powders was investigated by laser diffraction analysis. Raman spectroscopy was used to determine the lattice vibration in the sintered samples. All results are in accordance with our previous results, and the pure dense spinel phase is obtained.
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- 2023
31. Characterization of NTC thick film thermistor paste Cu0.2 Ni0.5 Zn1.0 Mn1.3O4
- Author
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Aleksić, Stanko, Aleksić, Stanko, Obradović, Nina, Mitrović, Nebojša S., Luković, Miloljub D., Aleksić, Stanko, Aleksić, Stanko, Obradović, Nina, Mitrović, Nebojša S., and Luković, Miloljub D.
- Abstract
A powder of Cu0.2Ni0.5Zn1.0 Mn1.3O4 composition for custom thermistor was prepared by using a certain mixture of metal oxides and solid state reaction at 1000 °C/4h in air. The obtained thermistor powder was milled in the planetary ball mill and agate mill for a prolonged time to achieve submicron powder. The prepared thermistor powder was further characterized by using XRD and SEM techniques. After that, the thermistor powder was pressed into small disc-shaped samples and sintered at 1150 °C/2h. The sintered samples were also characterized by using XRD and SEM. The main electrical properties such as nominal resistance R and thermistor exponential factor B were measured in the climatic test chamber. After that, the thick film paste was prepared using the same powder, an organic vehicle and a glass frit. The paste was printed on alumina substrate, dried at 150 °C / 30 min and sintered in air at 850 °C / 10 min in the hybrid conveyor furnace. The planar electrodes were printed on the sintered NTC thermistor layer using the PdAg thick film paste. The electric properties of sintered thick film thermistor were also measured in the climatic test chamber. The obtained results were used for development of novel self-heating thermistor applications.
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- 2023
32. Mechanical properties of zirconium diboride ceramics
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Kosanović, Darko, Kosanović, Darko, Filipović, Suzana, Trajković, Isaak, Obradović, Nina, Brune, Paul M., Hilmas, Gregory E., Fahrenholtz, William G., Kosanović, Darko, Kosanović, Darko, Filipović, Suzana, Trajković, Isaak, Obradović, Nina, Brune, Paul M., Hilmas, Gregory E., and Fahrenholtz, William G.
- Abstract
Zirconium diboride(ZrB2) belongs to the group of ultrahigh temperature ceramics (UHTCs) because of its high melting point (3250°C). Due to its excellent properties, such as the melting temperature, high strength and hardness, high thermal and electrical conductivities relative to other ceramics and good corrosion resistance to molten metals, it has attracted great interest from materials scientists. Fully dense ZrB2 ceramics were successfully obtained by hot pressing at 2150oC for 10 minutes. Prior to hot pressing, commercially available ZrB2 powder was ball milled for 24hr with ZrB2 media. Carbon was added as a densification aid in the amount of 0.5 wt.% using phenolic resin. For mechanical testing, three different methods were compared. Three point bending was performed in air at room temperature and the obtained strength was 546±55 MPa. Four-point bend strengths were measured under same conditions resulting in strengths of 476±112 MPa. Finally, the fracture toughness of pure ZrB2 ceramics was determined by the chevron notched beam method to be 4.1 ± 0.5 MPa•m1/2. The obtained results of mechanical testing make this ceramic material applicable as cutting tools, and parts for hypersonic aerospace vehicles.
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- 2023
33. Influence of Fe Doping on the Crystal Structure and Optical Properties of Mechanically Activated SrTiO3 Powders
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Živojinović, Jelena, Živojinović, Jelena, Peleš Tadić, Adriana, Kosanović, Darko, Tadić, Nenad, Vasiljević, Zorka Ž., Lević, Steva, Obradović, Nina, Živojinović, Jelena, Živojinović, Jelena, Peleš Tadić, Adriana, Kosanović, Darko, Tadić, Nenad, Vasiljević, Zorka Ž., Lević, Steva, and Obradović, Nina
- Abstract
Iron-doped strontium-titanate (SrTiO3) powders with various iron(III) oxide (Fe2O3) weight percentages (1.5, 3 and 6 wt%) were prepared by a solid-state method in the presence of mechanical activation (10, 30 and 120 min). A systematic investigation by XRD, SEM and Raman spectroscopy has been undertaken to evaluate the role of dopant on the microstructural and morphological study of the perovskite oxide obtained. The optical properties of the different iron-doped and activated Fe-SrTiO3 powders have been also evaluated. The results demonstrated that Fe has been substituted into the lattice and surface layers of particles of SrTiO3 powders and the absorption edge shifted to higher wavelength values with increasing activation time and dopant weight percentage. The lowest value of the band gap (Eg=3.20 eV) was registered for the longest activation (120 min) and the highest weight percentage of dopant (6 wt%). Combining doping with mechanical activation, led to lower values of Eg and that fact could be used in subsequent studies to make Fe-SrTiO3 more suitable photocatalysts.
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- 2023
34. Fractal analysis and microstructure development of BaTiO3 and PVDF based multifunctional materials
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Peleš Tadić, Adriana, Peleš Tadić, Adriana, Vuković, George, Kojović, Aleksandar, Stojanović, Dušica, Vlahović, Branislav, Milosavljević, Nataša, Obradović, Nina, Pavlović, Vladimir B., Peleš Tadić, Adriana, Peleš Tadić, Adriana, Vuković, George, Kojović, Aleksandar, Stojanović, Dušica, Vlahović, Branislav, Milosavljević, Nataša, Obradović, Nina, and Pavlović, Vladimir B.
- Abstract
Barium titanate (BaTiO3) and polyvinylidene fluoride (PVDF) based multifunctional materials are attracting a great scientific interest due to their excellent piezoelectric, pyroelectric and ferroelectric properties. These materials undergo controlled transformations through physical interactions and respond to environmental stimuli, such as temperature, pressure, electric and magnetic fields. Their properties strongly depend on synthesis procedures and obtained microstructures. This include intergranular contact surfaces of BaTiO3 based materials, as well as, porous structure and cross-linking patterns of PVDF prepared by electrospinning. It has been found that these microstructures can have fractal structure and that the fractal analysis can be used as a powerful tool for describing structural and functional properties of these materials. Having this in mind, in this research we have used different fractal methods for the reconstructions of various BaTiO3 and PVDF microstructure morphologies. Fractal analysis has been performed by using scanning electron microscope micrographs and computational modeling tools. Fractal dimension of irregular morphologies which exhibit fractal regularity were determined by using box-counting method. This method enables the analysis of self-similar microstructure morphologies by quantifying the rate at which an object's geometrical details develop at increasingly fine scales. Theory of Iterated Function Systems and Voronoi tessellation, have been used for modeling BaTiO3 random microstructures and PVDF porous structures. A python algorithm was created to determine the distribution of pore areas in SEM micrographs. Algorithm’s distribution of calculated pore surface areas was compared with measured pore surface areas and fractal reconstructions of different morphologies and their connection with functional properties were analyzed.
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- 2023
35. Elevated Temperature Thermal Properties of ZrB2 with Tungsten Additions
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Kosanović, Darko, Kosanović, Darko, Fahrenholtz, William G., Obradović, Nina, Filipović, Suzana, Watts, Jeremy L., Hilmas, G. E., Kosanović, Darko, Kosanović, Darko, Fahrenholtz, William G., Obradović, Nina, Filipović, Suzana, Watts, Jeremy L., and Hilmas, G. E.
- Abstract
The thermal properties of zirconium diboride (ZrB2) ceramics with tungsten additions of up to 5 wt% were characterized up to 2000°C. Densification was promoted by the addition of 0.5 wt% carbon. ZrB2 ceramics were prepared from commercially available powder by hot pressing. The crystalline phases present were determined by x-ray diffraction. The microstructure and density change as a result of the addition of tungsten, but this does not affect much the thermal behavior of ZrB2 at room and elevated temperatures. Thermal diffusivity at 200°C decreased from 0.158 cm2/s for nominally pure ZrB2 to 0.149 cm2/s for ZrB2 with 5 wt% Tungsten carbide (WC). The thermal diffusivity decreased with increasing temperature, reaching a value of 0.145 cm2/s at 2000°C for ZrB2 with 5 wt% Tungsten carbide (WC). Heat capacity, unlike thermal diffusivity, did not change during thermal cycling. Thermal conductivity, which was calculated from thermal diffusivity, heat capacity, and density, was as high as 77.9 W/(m·K) at 2000°C for ZrB2 with 5 wt% Tungsten carbide (WC). Any level of Tungsten carbide (WC) contamination reduces thermal conductivity. Properties, including hardness, oxygen content, elastic modulus, strength were measured and will be discussed.
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- 2023
36. Synthesis, densification, and cation inversion in high entropy (Co,Cu,Mg,Ni,Zn)Al2O4 spinel
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Corlett, Cole A., Corlett, Cole A., Obradović, Nina, Watts, Jeremy L., Bohannan, Eric W., Fahrenholtz, William G., Corlett, Cole A., Corlett, Cole A., Obradović, Nina, Watts, Jeremy L., Bohannan, Eric W., and Fahrenholtz, William G.
- Abstract
The synthesis, densification behavior, and crystallographic site occupancy were investigated for four different spinel-based ceramics, including a high-entropy spinel (Co0.2Cu0.2Mg0.2Ni0.2 Zn0.2)Al2O4. Each composition was reacted to form a single phase, but analysis of X-ray diffraction patterns revealed differences in cation site occupancy with the high-entropy spinel being nearly fully normal. Densification behavior was investigated and showed that fully dense ceramics could be produced by hot pressing at temperatures as low as 1375°C for all compositions. Vickers’ hardness values were at least 10 GPa for all compositions. The cations present in the high-entropy spinel appear to have a stabilizing effect that led to nearly normal site occupancy compared to full cation inversion behavior of nickel aluminate spinel. This is the first report that compares cation site occupancy of a high-entropy spinel to conventional spinel ceramics.
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- 2023
37. Multi-phase (Zr,Ti,Cr)B2solid solutions: Preparation, multi-scale microstructure, and local properties
- Author
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Silvestroni, Laura, Silvestroni, Laura, Gilli, Nicola, Sangiorgi, Alex, Corozzi, Alessandro, Filipović, Suzana, Obradović, Nina, Ortiz-Membrado, Laia, Jiménez-Piqué, Emilio, Fahrenholtz, William G., Silvestroni, Laura, Silvestroni, Laura, Gilli, Nicola, Sangiorgi, Alex, Corozzi, Alessandro, Filipović, Suzana, Obradović, Nina, Ortiz-Membrado, Laia, Jiménez-Piqué, Emilio, and Fahrenholtz, William G.
- Abstract
Multi-phase ceramics based on ZrB2, TiB2 and doped with CrB2 and SiC were prepared by powder metallurgy and hot pressing to explore the possibility of obtaining multi-scale microstructures by super-saturation of complex (Zr,Ti,Cr)B2 solid solutions. Core–shell structures formed in TiB2 grains, whereas ZrB2 appeared to form a homogeneous solid solution with the other metals. Precipitation of nano-inclusions within both micron-sized borides was assessed by transmission electron microscopy and thermodynamics elucidated the preferential formation of boride inclusions due to the specific sintering atmosphere. In addition, atomic size factors explicated the precipitation of CrB2 nano-particles into ZrB2-rich grains and of ZrB2 nano-particles into TiB2-rich grains. The hardness of the constituent phases measured by nanoindentation ranged from 36 to 43 GPa.
- Published
- 2023
38. Effects of mechanical activation and two-step sintering on the structure and electrical properties of cordierite-based ceramics
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Obradović, Nina, Filipović, Suzana, Đorđević, Nataša, Kosanović, Darko, Marković, Smilja, Pavlović, Vladimir, Olćan, Dragan, Djordjević, Antonije, Kachlik, Martin, and Maca, Karel
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- 2016
- Full Text
- View/download PDF
39. Final‐stage densification kinetics of direct current–sintered ZrB2.
- Author
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Stanfield, Austin D., Smith, Steven M., Filipović, Suzana, Obradović, Nina, Buljak, Vladimir, Hilmas, Gregory E., and Fahrenholtz, William G.
- Subjects
SPECIFIC gravity ,ACTIVATION energy ,DIFFUSION coefficients ,GRAIN size ,SINTERING ,CERAMICS - Abstract
Final‐stage sintering was analyzed for nominally phase pure zirconium diboride synthesized by borothermal reduction of high‐purity ZrO2. Analysis was conducted on ZrB2 ceramics with relative densities greater than 90% using the Nabarro–Herring stress–directed vacancy diffusion model. Temperatures of 1900°C or above and an applied uniaxial pressure of 50 MPa were required to fully densify ZrB2 ceramics by direct current sintering. Ram travel data were collected and used to determine the relative density of the specimens during sintering. Specimens sintered between 1900 and 2100°C achieved relative densities greater than 97%, whereas specimens sintered below 1900°C failed to reach the final stage of sintering. The average grain size ranged from 1.0 to 14.7 μm. The activation energy was calculated from the slope of an Arrhenius plot that used the Kalish equation. The activation energy was 162 ± 34 kJ/mol, which is consistent with the activation energy for dislocation movement in ZrB2. The diffusion coefficients for dislocation motion that controls densification were 5.1 × 10−6 cm2/s at 1900°C and 5.1 × 10−5 cm2/s at 2100°C, as calculated from activation energy and average grain sizes. This study provides evidence that the dominant mechanism for final‐stage sintering of ZrB2 ceramics is dislocation motion. [ABSTRACT FROM AUTHOR]
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- 2023
- Full Text
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40. Influence of mechanical activation on MgO-Al2O3-SiO2 system in the presence of TeO2 additive
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Filipović Suzana Ž., Obradović Nina N., Đorđević Nataša G., Kosanović Darko A., Marković Smilja B., Mitrić Miodrag N., and Pavlović Vladimir B.
- Subjects
mechanical activation ,PSA ,XRD ,SEM ,cordierite ,TeO2 ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
Cordierite 2MgO+2Al2O3+5SiO2 is frequently used ceramic material, that is commonly used as a carrier of electrical components due to its low dielectric constant (~ 5), and low temperature thermal expansion coefficient (20·10-7 oC-1). In order to accelerate the process of sintering, 5.00 mass% TeO2 was added to the starting mixtures. System was tested in two parallel mixtures, one with no additives, and the other one with TeO2. The mechanical activation of the both mixtures was performed in a highenergy ball mill in time intervals from 0 to 40 min with ball to powder mass ratio 1:40. The particle size analysis (PSA) was employed in order to determine the changes in the particle size of the mechanically treated powders. The phase composition of the starting powders as well as microstructures was analyzed by the means of X-ray diffraction method and SEM.
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- 2016
- Full Text
- View/download PDF
41. Microstructural and electrical properties of cordierite-based ceramics obtained after two-step sintering technique
- Author
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Obradović Nina, Filipović Suzana, Đorđević Nataša, Kosanović Darko, Pavlović Vladimir, Olćan Dragan, Đorđević Antonije, Kachlik Martin, and Maca Karel
- Subjects
mechanical activation ,two-step sintering ,microstructure ,electrical properties ,cordierite ,Chemical technology ,TP1-1185 - Abstract
Cordierite-based ceramic materials are attracting much interest for their various applications in industry, for manufacturing multilayer circuit boards, catalytic converters, filters, thermal insulation, kiln furniture, components of portable electronic devices, etc. In order to reduce production costs and modify cordierite-based materials, mechanical activation can be used. In this study, microstructural and electrical properties of mechanically activated MgO-Al2O3-SiO2 system have been analyzed. The mixtures of MgO-Al2O3-SiO2 powders were mechanically activated in a planetary ball mill for the time periods from 0 to 160 min. Morphological investigations have been performed on the obtained powders. The effects of activation and two-step sintering process on microstructure were investigated by scanning electron microscopy (SEM). Electrical measurements showed variations of the dielectric constant (εr) and loss tangent (tan δ) as a function of time of mechanical treatment.
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- 2016
- Full Text
- View/download PDF
42. Microstructural and optical properties of MgAl2O4 Spinel: Effect of Mechanical Activation, Yttrium and Graphene addition
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Obradović, Nina, Obradović, Nina, Fahrenholtz, William G., Corlett, Cole, Filipović, Suzana, Nikolić, Marko G., Marinković, Bojan A., Failla, Simone, Sciti, Diletta, Sani, Elisa, Obradović, Nina, Obradović, Nina, Fahrenholtz, William G., Corlett, Cole, Filipović, Suzana, Nikolić, Marko G., Marinković, Bojan A., Failla, Simone, Sciti, Diletta, and Sani, Elisa
- Abstract
Magnesium aluminate and other alumina-based spinels attract attention due to their high hardness, high mechanical strength, and low dielectric constant. MgAl2O4 was produced by solid-state reaction between MgO and α-Al2O3 powders. Mechanical activation of 30 minutes in a planetary ball mill was used to increase the reactivity of powders. Yttrium oxide and graphene were added to prevent abnormal grain growth during sintering. Samples were sintered by hot-pressing under vacuum at 1450 °C. Phase composition and microstructure of sintered specimens were characterized by X-ray diffraction analysis and scanning electron microscopy. Rietveld analysis revealed 100 % pure spinel phase in all sintered specimens, and decrease in crystallite size with the addition of yttria or graphene. Density measurements indicated that the mechanically activated specimen reached 99.6 % relative density, while other specimens were above 96.5 % relative density. Furthermore, the highest solar absorbance and highest spectral selectivity as a function of temperature were detected for the mechanically activated specimen with graphene addition. Mechanical activation is an efficient method to improve the densification behaviour of MgAl2O4 produced from mixed oxide powders, while additives improve microstructure and optical properties.
- Published
- 2021
43. Preparation and characterization of ZrB2-TiB2 based composites for hypersonic systems
- Author
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Obradović, Nina, Obradović, Nina, Filipović, Suzana, Gilli, N., Silvestroni, L., Obradović, Nina, Obradović, Nina, Filipović, Suzana, Gilli, N., and Silvestroni, L.
- Abstract
ZrB2 ceramics are considered potential materials for hypersonic systems in view of the melting point exceeding 3000 °C and excellent ablation resistance. Second phases, including SiC or CrB2, further improve the oxidation behavior, whereas a lighter phase, like TiB2 can decrease the overall weight. In this work, a powder mixture containing ZrB2, TiB2, CrB2 and SiC was mechanically activated using high energy ball-milling. Sintering was performed by hot pressing following different thermal cycles, and subsequent annealing to remove oxide phases and reduce micro-cracking. The microstructure and hardness of the dense ceramics are compared in relationship to the thermal history. Fully dense ceramics were obtained with different oxide-phases amount depending on the sintering cycle and hardness approaching 24 GPa were achieved. Future works will explore the strength and oxidation resistance of this multi-phase system to check its suitability for hypersonic systems.
- Published
- 2021
44. Influence of BaTiO3/Fe2O3 addition on crystallization and polymorphism of PDVF polymer matrix followed by DSC-TG
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Obradović, Nina, Obradović, Nina, Filipović, Suzana, Rosenschon, Martin, Füglein, Ekkehard, Obradović, Nina, Obradović, Nina, Filipović, Suzana, Rosenschon, Martin, and Füglein, Ekkehard
- Abstract
Ceramic/polymer dielectric composites are widely used as components for electric devices, mainly because of their high chemical stability, mechanical strength, and flexibility. In order to increase dielectric permittivity, ceramic fillers with high dielectric constant have been usually incorporated in the polymer matrix in large amounts. With the aim to enhance dielectric properties of matrix, 5 wt.% of BaTiO3/Fe2O3 core/shell composite was added into the PVDF matrix. Prior to addition, five BaTiO3/Fe2O3 powders were prepared by different synthesis conditions. The changes in crystal structure and lattice dynamics of the obtained ceramic/polymer composite were correlated with changes in the phase composition and morphology of BaTiO3/Fe2O3 core/shell filler. Thermal analysis such as DTA/TG/DSC are useful methods to determine various parameters in ceramic/polymer composites. We were able to corroborate that differences in phase composition and morphology of BaTiO3/Fe2O3 core/shell filler have influence on formation of various PVDF allomorph modification, as well as a level of crystallinity.
- Published
- 2021
45. Reaction kinetics of mechanically activated cordierite-based ceramics studied via DTA
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Obradović, Nina, Đorđević, Nataša, Filipović, Suzana, Marković, Smilja, Kosanović, Darko, Mitrić, Miodrag, and Pavlović, Vladimir
- Published
- 2016
- Full Text
- View/download PDF
46. Cesium removal from aqueous solution by natural mineral clinoptilolite
- Author
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Nenadović Snežana S., Kljajević Ljiljana M., Šešlak Bojan Ž., Obradović Nina N., Vukanac Ivana S., and Pavlović Vladimir B.
- Subjects
clinoptilolite ,adsorption ,cesium ,natural radioactivity ,phase transformation ,differential thermal analysis ,Nuclear and particle physics. Atomic energy. Radioactivity ,QC770-798 - Abstract
The aim of this study was to investigate the Cs+ ions sorption on natural minerals clinoptilolite. The analysis of clinoptilolite and clinoptilolite with adsorbed Cs+ ion was con- ducted by X-ray diffraction, scanning electron microscopy, X-ray fluorescence, and gamma spectrometry. The specific activity of naturally occurring radionuclides in clinoptilolite was determined by gamma spectrometry by using the HPGe semiconductor detector. Obtained activity concentrations ranged from 49 Bq/kg to 810 Bq/kg for 40K, 5.7 Bq/kg to 10 Bq/kg for 238U, 5.8 Bq/kg to 70 Bq/kg for 232Th(228Ac), and the presence of artificial radionuclides was not detected (137Cs < 0.02 Bq/kg). The study of the thermal decomposition of raw clinoptilolite and Cs adsorbed clinoptilolite by differential thermal analysis is presented in this paper. The activation energy of the reaction phase transformation of raw clinoptilolite is 156.7 kJ/mol, while Cs adsorbed clinoptilolite is 121.7 kJ/mol. The lower value of activation energy reaction of the phase transformation Cs adsorbed clinoptilolite indicates that Cs which is adsorbed destabilizes the crystal structure of clinoptilolite and thus facilitates the transition to the amorphous state. [Projekat Ministarstva nauke Republike Srbije, br. 45012]
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- 2014
- Full Text
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47. Synthesis of magnesium titanates by mechanochemical method
- Author
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Filipović Suzana Ž., Obradović Nina N., Pavlović Vladimir B., Marković Smilja B., Mitrić Miodrag N., and Mitrović Nebojša S.
- Subjects
mechanochemistry ,magnesium titanates ,XRD ,SEM ,Engineering (General). Civil engineering (General) ,TA1-2040 - Abstract
The aim of this paper was mechanochemical preparation of magnesium titanates. Powder mixtures of starting oxides MgO and TiO2 were mechanically activated in a planetary ball mill for the time interval from 0 to 160 minutes. Structural, stereological, thermal characterizations were performed on produced powders. The effects of activation on morphology were investigated by scanning electron microscopy and particle size analyses, while the changes in the phase composition were determined by X-ray diffraction. It is determined that the first traces of MgTiO3 became detectable after 40 minutes of milling, while after 160 minutes the pure magnesium titanates were noticed. The differential thermal analyses and thermo gravimetric analysis, in temperatures range from 25 oC to 1100 oC, has been performed in order to investigate thermal behavior of the mixtures.
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- 2014
- Full Text
- View/download PDF
48. Porous cordierite-supported polyethyleneimine composites for nickel(II) and cadmium(II) ions removal
- Author
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Obradović, Nina, Obradović, Nina, Rusmirović, Jelena D., Filipović, Suzana, Kosanović, Darko, Marinković, Aleksandar, Radić, Danka, Pavlović, Vladimir, Obradović, Nina, Obradović, Nina, Rusmirović, Jelena D., Filipović, Suzana, Kosanović, Darko, Marinković, Aleksandar, Radić, Danka, and Pavlović, Vladimir
- Abstract
Industrial/technological growth is directly connected with environmental pollution, but its influence can be minimized through pollution abatement approaches such as the treatment of industrial wastewater. In this study, novel porous amine-functionalized silicate minerals, specifically, cordierite was investigated for the removal of toxic heavy metals from industrial wastewaters. Cordierite supports were synthesized by mixing MgO, Al2O3, and SiO2 powders in 2:2:5 molar ratios, and mechanically activated via ball milling in ethanol for 10, 40, or 80 min. Pellets were sintered by heating in air at 20 degrees C min(-1) to 1,350 degrees C, for 2 h. Porous supports were produced by coarsely crushing the sintered pellets and mixing the crushed and sieved cordierite powder with 20 wt.% of a pore-forming agent, either nanocellulose or yeast. The resulting pellets were sintered by heating at 5 degrees C min(-1) to 700 degrees C in air. The synthetic cordierite support was modified by treatment in poly-ethylenimine. Activated supports were then tested for the removal of Ni2+ and Cd2+ ions. The phase composition of the cordierite supports was analyzed by the X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Analysis of adsorption isotherms, kinetics, and thermodynamic parameters indicated that adsorption was a spontaneous, endothermic process with a maximum adsorption capacity of 36 mg g(-1) for Cd2+ and 43 mg g(-1) for Ni2+. This work has shed light on the mechanism of heavy metal removal from the aquatic medium using the novel hybrid functionalized cordierite-based ceramic.
- Published
- 2020
49. Removal of the As(V) and Cr(VI) from the Water Using Magnetite/3D-Printed Wollastonite Hybrid Adsorbent
- Author
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Popović, Mina, Popović, Mina, Veličković, Zlate S., Bogdanov, Jovica, Marinković, Aleksandar D., Luna, Mariano Casas, Trajković, Isaak, Obradović, Nina, Pavlović, Vladimir B., Popović, Mina, Popović, Mina, Veličković, Zlate S., Bogdanov, Jovica, Marinković, Aleksandar D., Luna, Mariano Casas, Trajković, Isaak, Obradović, Nina, and Pavlović, Vladimir B.
- Abstract
In this study, the structure, morphology and composition of the synthesized magnetite/3D-printed wollastonite (3D_W/M) composite were characterized, and its adsorption performance with respect to As(V) and Cr(VI) were studied. Magnetite (MG) modified 3D printed wollastonite was obtained by two step procedure: modification of 3D_W with 3-aminoproylsilane (APTES) followed by controlled magnetite (MG) deposition to obtain 3D_W/M adsorbent. The structure/properties of 3D_W/M were confirmed by applying FTIR, XRD, TGD/DTA, and SEM analysis. The adsorption properties of hybrid adsorbents were carried out for As(V) and Cr(VI) removal-one relative to the initial pH value, the adsorbent mass, the temperature, and the adsorption time. Time-dependent adsorption study was best described by pseudo-second order equation, while Weber Morris analysis showed that intraparticle diffusion controled diffusional transport. Similar activation energy, 17.44 and 14.49 kJ•mol-1 for adsorption As(V) and Cr(VI) on 3D_W/M, respectively, indicated main contribution of physical adsorption. Determination of adsorption parameters was performed by applying different adsorption isotherm models, and the best fit was obtained using Freundlich model. The adsorption capacity of 24.16 and 29.6 mg g-1 for As(V) and Cr(VI) at 2o C, Co = 5.5 and 5.3 mg L-1, respectively, were obtained. Thermodynamic study indicated favourable process at a higher temperature. Preliminary fixed-bed column study and results fitting with Bohart-Adams, Yoon-Nelson, Thomas, and Modified dose-response model showed good agreement with results from the batch study.
- Published
- 2022
50. Spark plasma sintering of mechanically activated MGO-TiO2 system
- Author
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Filipović, Suzana, Filipović, Suzana, Obradović, Nina, Fahrenholtz, William G., Smith, Steven, Mirković, Miljana M., Peleš, Adriana, Đorđević, Antonije, Filipović, Suzana, Filipović, Suzana, Obradović, Nina, Fahrenholtz, William G., Smith, Steven, Mirković, Miljana M., Peleš, Adriana, and Đorđević, Antonije
- Abstract
MgTiO3 is a material often used in different types of high-frequency capacitors, temperature compensating capacitors, and chip capacitors, so the enhancement of this material is still the focus of many research groups due to its remarkable dielectric properties. Outstanding features can only be achieved when the ceramics are highly dense. Densification of magnesium titanate by Spark Plasma Sintering (SPS) was the aim of this work. Magnesium titanate ceramics were prepared by applying mechanical activation as the first step. Powders prepared in this way were SPS sintered, at 1200 °C with a heating rate of 100 °C/min. After reaching the desired temperature, a uniaxial pressure of 50 MPa was applied. The dwell time at this condition was 5 min, followed by cooling to room temperature at 5°C/min. X-ray diffraction was performed in order to establish the phase composition of milled powders and obtained ceramics. Differences between samples milled in various times intervals, as well as sintered ceramics were examined by means of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The presence of MgTiz0s phase was detected in XRD and was confirmed by EDS analysis for the non-milled ceramics. In the samples obtained from milled powders, no MgTi2O5 was detected in XRD patterns, but this phase was detected in EDS spectra in a lower amount. Dielectric measurements were performed at a wide range of frequencies, while the hardness of the SPS samples was measured at loads up to 10 N. The highest value of the hardness was obtained from powder milled for 15 min before SPS.
- Published
- 2022
Catalog
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