Papers by Zorka Vasiljevic
Social Science Research Network, 2022
Metastable nanopowder ZnTiO 3 was pressed into cylindrical compacts at 200 MPa. Compacts were tre... more Metastable nanopowder ZnTiO 3 was pressed into cylindrical compacts at 200 MPa. Compacts were treated by conventional heating with isothermal holding at 931 o C for 10 minutes, 25 minutes and 40 minutes. ZnTiO 3 compacts were also heated with a two-step sintering schedule with maximal 913 o C and isothermal holding at 896 o C, for approximately the same holding times as the isothermal schedule. Shrinkage during heating was monitored with a dilatometric device, while microstructure was determined with atomic force microscopy. XRD patterns were collected for the most interesting samples. Microstructures of sintered specimens showed differences introduced during the last sintering stage by the two different heating schedules. Goal of the presented work was to discuss the possible sintering mechanisms for the two step sintering schedulle according to the presented results.
Royal Society Open Science, Sep 1, 2020
This article has been edited by the Royal Society of Chemistry, including the commissioning, peer... more This article has been edited by the Royal Society of Chemistry, including the commissioning, peer review process and editorial aspects up to the point of acceptance.
Two pseudobrookite (PSB) containing pastes were composed of a mixture of starting nanopowders of ... more Two pseudobrookite (PSB) containing pastes were composed of a mixture of starting nanopowders of hematite (a-Fe2O3) and anatase (TiO2) in the molar ratios 1:1 (referred to as PSB-1) and 1:1.5 (referred to as PSB-1.5), respectively, organic vehicle and glass frit. The pastes were screen printed on alumina (Al2O3) substrates and sintered in a hybrid conveyor furnace at 850 °C/10 min in air. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis showed that the resulting thick film samples were composed of pseudobrookite (Fe2TiO5) and also excess rutile (TiO2) in the case of PSB-1.5 samples with a small grained and relatively homogenous microstructure. An electric resistivity with negative temperature coefficient (NTC) was observed. An interdigitated electrode geometry was designed and different electrode spacing (0.2 and 0.25 mm) was analyzed. The electrode structure was printed of PdAg paste. The resistivity of pseudobrookite was measured and analyzed in view of possible applications as a sensor of environmental gases with sufficiently high sensitivity at operating temperatures lower than conventional gas sensor systems.
IEEE Sensors Journal, Jul 15, 2020
Nanocomposite Zn2SnO4/SnO2 powder was obtained by solid state synthesis from homogenized starting... more Nanocomposite Zn2SnO4/SnO2 powder was obtained by solid state synthesis from homogenized starting nanopowders of ZnO and SnO2, mixed in the 1:1 molar ratio, structurally and morphologically characterized using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Thick film paste was made by adding organic vehicles to the obtained powder. Three to five layers (layer thickness approx. 12 µm) were screen printed on alumina substrate with small test PdAg electrodes and fired at 600 o C for 30 minutes. SEM analysis confirmed formation of a porous structure suitable for humidity sensing. Impedance response was studied at the working temperatures of 25 and 50 o C in a humidity chamber where the relative humidity (RH) was 30-90% and measured frequency 42 Hz-1 MHz. With increase in film thickness the overall sensor impedance increased. It reduced at 100 Hz from 36 to 0.25 MΩ (60 µm), from 23.4 to 0.25 MΩ (48 µm) and from 6.8 to 0.02 MΩ (36 µm) at 25 o C, while at 50 o C and also 100 Hz it reduced from 14 MΩ to 0.72 MΩ (48 µm) for RH 30 and 90%, respectively. The response (8 s) and recovery (10 s) was fast, showing that this nanocomposite has potential for application in humidity sensing.
Journal of Materials Science: Materials in Electronics, Nov 25, 2016
In this work we have investigated changes in dielectric properties, electrical conductivity and c... more In this work we have investigated changes in dielectric properties, electrical conductivity and complex impedance of Fe 2 TiO 5 nanopowder compacts and bulk samples as a function of elevated temperature (room to 423 K compacts, to 443 K bulk samples), frequency (100 Hz-1 MHz) and composition (starting molar ratio of Fe 2 O 3 and TiO 2 1:1-PSB11 and 1:1.5-PSB115). XRD, SEM and TEM analysis of PSB11 and PSB115 powders obtained by a simple solid state process from starting hematite and anatase nanopowders confirmed the formation of nanostructured orthorhombic pseudobrookite with small amounts of excess hematite and rutile. The dielectric constant decreased with frequency and temperature for both compacts and bulk samples. Higher values were determined for bulk samples also reflecting the influence of sample composition. Change in the dielectric loss also reflected the influence of sample composition showing one maximum at high frequencies for compacts, and two maxima at room temperature for bulk samples. Complex impedance was analyzed using equivalent circuits and showed in the case of compacts the influence of both grain and grain boundary components, while in the case of bulk samples the dominant influence of grain boundaries. The temperature dependence of the determined grain and grain boundary resistance for compacts and grain boundary resistance for bulk samples was analyzed using the adiabatic small polaron hopping model enabling determination of activation energies for conduction, while the temperature dependence of relaxation times enabled determination of activation energies for relaxation. Changes in electrical conductivity for compacts and bulk samples followed Jonscher's power law. The change of the determined frequency constant with temperature showed that at elevated temperatures the quantum mechanical-tunneling model for the case of small polaron hopping explains the conduction mechanism occurring in both compacts and bulk samples.
Универзитет у Београду, Jul 5, 2019
Pseudobrookite thick films were obtained by screen printing paste composed of a 1:1.5 molar ratio... more Pseudobrookite thick films were obtained by screen printing paste composed of a 1:1.5 molar ratio mixture of starting nanopowders of hematite and anatase, glass frit and organic binder. The films were deposited on alumina substrates with interdigitated electrode geometry. Sintering at 850 °C resulted in the formation of pseudobrookite. X-Ray Diffraction (XRD) analysis showed pseudobrookite with a mixed orthorhombic and monoclinic structure and a small amount of excess rutile. Gas sensing measurements with low NO gas concentrations in air were performed using an in-house gas sensor testing setup in the temperature range 100–300 °C. On the example of one particular gas concentration, results showed that pseudobrookite exhibited a distinct response to NO already at 150 °C that further improved with increased sample temperature.
Nanocrystalline nickel manganite (NiMn $_{2} O_{4}$) was obtained by sol-gel combustion using gly... more Nanocrystalline nickel manganite (NiMn $_{2} O_{4}$) was obtained by sol-gel combustion using glycine as fuel, followed by calcination at 800°C. X-ray diffraction (XRD) analysis confirmed the formation of a pure cubic spinel structure with a crystallite size of 54.5 nm. Scanning electron microscopy (SEM) of the obtained nickel manganite powder showed porous nanocrystalline morphology. The material constant (B) of the obtained nickel manganite powder applied as paste and dried at 100°C was determined as 4812 K in the temperature range 20-50°C, confirming potential application in flexible temperature sensors.
Food Chemistry, Oct 1, 2022
Sensors and Actuators B-chemical, Dec 1, 2018
Pseudobrookite based nanopowder was obtained by solid state synthesis of starting hematite and an... more Pseudobrookite based nanopowder was obtained by solid state synthesis of starting hematite and anatase nanopowders in the weight ratio 55:45. Structural and morphological properties were analyzed using X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV/Vis diffuse reflectance spectroscopy, Field emission scanning electron microscopy (FESEM) and Transmission electron microscopy (TEM) confirming the formation of nanocrystalline pseudobrookite. The obtained powder was mixed with a binder (ethyl cellulose), dispersant (α-terpinol) and adhesion agents (acetic acid and distilled water) to obtain a thick film paste. It was screen printed on alumina substrate with interdigitated PdAg electrodes and fired at 600 o C for 30 minutes. Formation of a porous nanocrystalline thick film structure was shown using Scanning electron microscopy (SEM), while Hall measurements enabled determination of carrier mobility. Change of impedance response in the frequency range 42 Hz-1 MHz with humidity was analyzed at room temperature (25 o C) and 50 o C in the relative humidity range 30-90% and 40-90%, respectively. At 42 Hz, and room temperature the impedance reduced 28 times, while at 50 o C it reduced 147 times in the relative humidity range 40-90%. The sensor showed rapid response (16 s) and relatively low hysteresis (8.39% at 25 o C and 2.64% at 50 o C) showing that this is a promising material for application in humidity sensing.
Journal of Materials Science: Materials in Electronics, Mar 19, 2018
Bulk samples of pseudobrookite with an orthorhombic crystal structure were prepared by sintering ... more Bulk samples of pseudobrookite with an orthorhombic crystal structure were prepared by sintering a mixture of starting hematite and anatase nano powders in the weight ratio 60:40 at three different sintering temperatures (950, 1050 and 1150 °C) resulting in different microstructures determined by SEM analysis. Humidity sensing properties of pseudobrookite were investigated by measuring changes in electrical properties at operating temperatures of 20, 40 and 60 °C in the frequency range 100 Hz-100 kHz in the relative humidity range 30-90% in a climatic chamber. At 100 Hz, and 20 °C the impedance of pseudobrookite sintered at 1150 °C reduced over 5 times in the humidity range 40-90%, and 7 times at 60 °C for pseudobrookite sintered at 950 °C. Detailed analysis of dielectric properties showed that the dielectric constant increased noticeably with increase in humidity at low frequencies. Electrical conductivity change with frequency followed the Jonscher power law, and increased with increase in relative humidity. The determined frequency constant reduced with increase in sample temperature and increase in relative humidity. The conduction mechanism can be explained using the correlated barrier hopping model. Analysis of complex impedance using an equivalent circuit showed the dominant influence of grain boundaries. Low hysteresis (3.6 and 2.99%) was obtained in the 40-90% humidity range at room temperature (25 °C) for pseudobrookite sintered at 950 and 1150 °C.
Journal of Alloys and Compounds
Chemosensors
Temperature- and humidity-sensing properties were evaluated of NixMg1-x spinel ferrites (0 ≤ x ≤ ... more Temperature- and humidity-sensing properties were evaluated of NixMg1-x spinel ferrites (0 ≤ x ≤ 1) synthesized by a sol-gel combustion method using citric acid as fuel and nitrate ions as oxidizing agents. After the exothermic reaction, amorphous powders were calcined at 700 °C followed by characterization with XRD, FTIR, XPS, EDS and Raman spectroscopy and FESEM microscopy. Synthesized powders were tested as humidity- and temperature-sensing materials in the form of thick films on interdigitated electrodes on alumina substrate in a climatic chamber. The physicochemical investigation of synthesized materials revealed a cubic spinel Fd3¯m phase, nanosized but agglomerated particles with a partially to completely inverse spinel structure with increasing Ni content. Ni0.1Mg0.9Fe2O4 showed the highest material constant (B30,90) value of 3747 K and temperature sensitivity (α) of −4.08%/K compared to pure magnesium ferrite (B30,90 value of 3426 K and α of −3.73%/K) and the highest averag...
Food Chemistry
An emerging technology of active packaging enables prolongation of food shelf life by limiting th... more An emerging technology of active packaging enables prolongation of food shelf life by limiting the oxygen transfer and the reactivity of free radicals, which both destruct food freshness. In this work, Fe 2 TiO 5 nanoparticles were synthesized using a modified sol-gel method and evaluated as an enforcement of alginate food packaging film. Pure phase Fe 2 TiO 5 nanoparticles had an average particle size of 44 nm and rhombohedral morphology. Fe 2 TiO 5 nanoparticles induce no cell damage of human Caco-2 epithelial cells and show no inhibitory effect towards growth of a panel of bacterial strains, suggesting good biocompatibility. Films obtained by incorporation of Fe 2 TiO 5 nanoparticles into alginate using the solvent casting method show no migration of iron or titanium ions from films to food simulants again suggesting their safety as a packaging material. Fe 2 TiO 5 nanoparticles also showed strong antioxidant efficiency as determined using the DPPH˙assay, and confirmed further in a preservation test on fresh fruit.
Uploads
Papers by Zorka Vasiljevic