Aleksandra Saponjic - Academia.edu (original) (raw)
Uploads
Papers by Aleksandra Saponjic
Science of Sintering
Effect of methyl methacrylate (MMA) as a binder and heating treatment were investigated to improv... more Effect of methyl methacrylate (MMA) as a binder and heating treatment were investigated to improve green alumina compacts machinability. Properties of green compacts and their corresponding sintered samples prepared with and without MMA were compared. Investigation of green and sintered properties was performed on samples compacted at applied pressures up to 150 MPa. After pressing, samples with MMA were thermally treated at 115oC. The intention was to enhance the polymerization of MMA at a temperature a little higher than the glass transition temperature (Tg = 103oC) of poly (methyl methacrylate). Green compacts with MMA had higher green density values than those without MMA. Sintered samples with MMA had lower values of sintered density and higher values of total porosity; after sintering, relative linear shrinkage was around 15 % for the whole range of applied pressures. The possibility of easily machining the green compacts with MMA produces great possibilities for application i...
Journal of Cleaner Production
Journal of the Australian Ceramic Society
Materials Science and Engineering: B, 2020
Materials Research Bulletin, 2018
Ceramics International, 2016
Ceramics International, 2016
The most promising method for obtaining a large variety of non-oxide products having important te... more The most promising method for obtaining a large variety of non-oxide products having important technical uses is carbothermal-reduction reaction (CRR). By using this procedure, SiC and ZrC/SiC powders are obtained from diatomaceous earth and zircon powder. In this way the synthesized powders are obtained at a relatively low temperature due to good homogenization. Starting C/ZrSiO 4 admixtures having different molar ratios (3:1, 4:1, 5:1 and 7:1) and C/SiO 2 having ratios 1:1, 3:1, 4:1, and 7:1 were heated at temperatures between 1300 and 1600 °C in a controlled Ar flow atmosphere. The phase evolution was a function of the raw materials molar ratios and sintering temperature. The optimal parameters for the synthesis of SiC and ZrC/SiC powders were obtained. The results obtained by EDS analysis are in good agreement with those obtained by XRD analysis for the synthesized carbide powders.
Ceramics International, 2015
Journal of Optoelectronics and Advanced Materials, 2008
The possibility of using Mg-exchanged zeolite as additive for densification of Si 3 N 4 ceramic w... more The possibility of using Mg-exchanged zeolite as additive for densification of Si 3 N 4 ceramic was studied. The zeolitic precursor was previously heated at 800 °C to obtain an amorphous powder with a composition corresponding to MgO.Al 2 O 3 .nSiO 2 . The powder was mixed with Si 3 N 4 and the sintering additive was homogenized by attrition milling in the presence of isopropanol and finally compacted by cold isostatic pressure. Pushrod dilatometry was used to measure the shrinkage behaviour of green bodies under a nitrogen atmosphere from room temperature to 1500°C. The chemical reactions and phase evolution during pressureless sintering were also followed by means of X-ray and dilatometric analysis. Results show that the first liquid forms as low as 1070 °C, sharing in a significant reduction of sintering temperature. The final phase composition obtained at 1500°C consist of crystalline α-SiN 4 phase which is emended in oxynitride glassy phase The results show that the Mg-exchange...
Science of Sintering, 2018
Science of Sintering, 2020
Macroporous silica ceramic was obtained using clay and diatomite. Boric acid as a low-cost additi... more Macroporous silica ceramic was obtained using clay and diatomite. Boric acid as a low-cost additive in the amount of 1 wt% was used. These porous materials were obtained at low forming pressure (40-80 MPa) and lower sintering temperature (850-1300 oC) for 4h in air. The influence of boric acid, forming pressure, and sintering temperature on the microstructure, porosity parameters, and mechanical properties of obtained porous monoliths were investigated. As-received and the modified samples were characterized by X-ray diffraction, FTIR, SEM, and mercury porosimetry measurements. As for modified clay and diatomite, they were pressed at 60 MPa and then sintered at 1150 oC, obtaining porosities of about 10 % and 60 %, respectively. Both of the analyzed samples had the pore diameter in the range of macroporous materials. The pore diameters of clay samples are ranging from 0.1-10 μm, whereas the pore diameter of diatomite samples was slightly lower with values ranging from 0.05-5 μm. Modi...
Science of Sintering
Data on thermally induced transformations of Mn exchanged zeolites LTA and FAU topology are prese... more Data on thermally induced transformations of Mn exchanged zeolites LTA and FAU topology are presented in this paper. Thermally induced phase transformation of Mn-exchange zeolites are followed in the range from 700 to 1300?C. Both frameworks collapse into amorphous intermediate products after heating between 600 and 650?C. Prolonged heating of the intermediate product above 1100?C results directly in formation of a disorder Mn-anorthiteLTA and Mn-anorthiteFAU. The parameter of unit cell of Mn-anorthiteLTA and Mn-anorthiteFAU, in temperature range between 700 and 1300?C, was observed in space group C-1. The phase conversions in the temperature range investigated were followed by thermal, X-ray powder diffraction and FT-IR analyses
Materials and Manufacturing Processes
International Journal of Hydrogen Energy, 2013
ABSTRACT In this contribution, we present results of electrochemical characterization of prepared... more ABSTRACT In this contribution, we present results of electrochemical characterization of prepared tungsten carbide supported palladium and platinum and Vulcan XC-72 supported palladium. These catalysts were employed as anode catalysts in PEMFC and results are compared to commercial platinum catalyst. Platinum seems to be irreplaceable as a proton exchange membrane fuel cell (PEMFC) catalyst for both the anode and the cathode, yet the high price and limited natural resources are holding back the commercialization of the PEMFCs. Tungsten carbide is recognized as promising catalyst support having the best conductivity among interstitial carbides. Higher natural resources and significantly lower price make palladium good candidate for replacement of the platinum catalyst. The presented results show that all prepared catalysts are very active for the hydrogen oxidation reaction. Linear sweep voltammetry curves of Pd/C and Pd/WC show existence of peaks at 0.07 V vs. RHE, which is assigned to absorbed hydrogen. H-2 vertical bar Pd/WC vertical bar Nafion117 vertical bar Pt/C vertical bar O-2 fuel cell has almost the same efficiency and similar power output as commercial platinum catalyst. Copyright
Ceramics International, 2014
ABSTRACT Intention of this work was to obtain porous silicon dioxide ceramics by using boric acid... more ABSTRACT Intention of this work was to obtain porous silicon dioxide ceramics by using boric acid as an inexpensive additive at low forming pressure and low sintering temperature. Starting raw material, smectite clay from surface coal mine Kolubara, Serbia, was purified from organic and inorganic impurities by using heat and chemical treatment. Boric acid was used as binding and sintering aid in amount of 0.5, 1 and 2 wt%. Powder was compacted by using different pressures: 40, 60 and 80 MPa. Pressed samples were sintered at 850, 1000, 1150, and 1300 degrees C for 4 h in air. A relatively high porosity of nearly 40% is obtained for the samples pressed at 40, 60 and 80 MPa and sintered at 1000 degrees C. Median pore size diameters are in the range of macroporous up to 0.2 mu m and 10 mu m in the samples sintered at 1150 and 1300 degrees C, respectively. X-ray diffraction (XRD), scaning electron microscopy (SEM), and porosimetry measurements were employed to characterize the phases and microstructure of the obtained ceramics. The relations between mechanical characteristics of samples (Young modulus and Poisson ratio) and content of boric acid were studied.
International Journal of Hydrogen Energy
Science of Sintering
Effect of methyl methacrylate (MMA) as a binder and heating treatment were investigated to improv... more Effect of methyl methacrylate (MMA) as a binder and heating treatment were investigated to improve green alumina compacts machinability. Properties of green compacts and their corresponding sintered samples prepared with and without MMA were compared. Investigation of green and sintered properties was performed on samples compacted at applied pressures up to 150 MPa. After pressing, samples with MMA were thermally treated at 115oC. The intention was to enhance the polymerization of MMA at a temperature a little higher than the glass transition temperature (Tg = 103oC) of poly (methyl methacrylate). Green compacts with MMA had higher green density values than those without MMA. Sintered samples with MMA had lower values of sintered density and higher values of total porosity; after sintering, relative linear shrinkage was around 15 % for the whole range of applied pressures. The possibility of easily machining the green compacts with MMA produces great possibilities for application i...
Journal of Cleaner Production
Journal of the Australian Ceramic Society
Materials Science and Engineering: B, 2020
Materials Research Bulletin, 2018
Ceramics International, 2016
Ceramics International, 2016
The most promising method for obtaining a large variety of non-oxide products having important te... more The most promising method for obtaining a large variety of non-oxide products having important technical uses is carbothermal-reduction reaction (CRR). By using this procedure, SiC and ZrC/SiC powders are obtained from diatomaceous earth and zircon powder. In this way the synthesized powders are obtained at a relatively low temperature due to good homogenization. Starting C/ZrSiO 4 admixtures having different molar ratios (3:1, 4:1, 5:1 and 7:1) and C/SiO 2 having ratios 1:1, 3:1, 4:1, and 7:1 were heated at temperatures between 1300 and 1600 °C in a controlled Ar flow atmosphere. The phase evolution was a function of the raw materials molar ratios and sintering temperature. The optimal parameters for the synthesis of SiC and ZrC/SiC powders were obtained. The results obtained by EDS analysis are in good agreement with those obtained by XRD analysis for the synthesized carbide powders.
Ceramics International, 2015
Journal of Optoelectronics and Advanced Materials, 2008
The possibility of using Mg-exchanged zeolite as additive for densification of Si 3 N 4 ceramic w... more The possibility of using Mg-exchanged zeolite as additive for densification of Si 3 N 4 ceramic was studied. The zeolitic precursor was previously heated at 800 °C to obtain an amorphous powder with a composition corresponding to MgO.Al 2 O 3 .nSiO 2 . The powder was mixed with Si 3 N 4 and the sintering additive was homogenized by attrition milling in the presence of isopropanol and finally compacted by cold isostatic pressure. Pushrod dilatometry was used to measure the shrinkage behaviour of green bodies under a nitrogen atmosphere from room temperature to 1500°C. The chemical reactions and phase evolution during pressureless sintering were also followed by means of X-ray and dilatometric analysis. Results show that the first liquid forms as low as 1070 °C, sharing in a significant reduction of sintering temperature. The final phase composition obtained at 1500°C consist of crystalline α-SiN 4 phase which is emended in oxynitride glassy phase The results show that the Mg-exchange...
Science of Sintering, 2018
Science of Sintering, 2020
Macroporous silica ceramic was obtained using clay and diatomite. Boric acid as a low-cost additi... more Macroporous silica ceramic was obtained using clay and diatomite. Boric acid as a low-cost additive in the amount of 1 wt% was used. These porous materials were obtained at low forming pressure (40-80 MPa) and lower sintering temperature (850-1300 oC) for 4h in air. The influence of boric acid, forming pressure, and sintering temperature on the microstructure, porosity parameters, and mechanical properties of obtained porous monoliths were investigated. As-received and the modified samples were characterized by X-ray diffraction, FTIR, SEM, and mercury porosimetry measurements. As for modified clay and diatomite, they were pressed at 60 MPa and then sintered at 1150 oC, obtaining porosities of about 10 % and 60 %, respectively. Both of the analyzed samples had the pore diameter in the range of macroporous materials. The pore diameters of clay samples are ranging from 0.1-10 μm, whereas the pore diameter of diatomite samples was slightly lower with values ranging from 0.05-5 μm. Modi...
Science of Sintering
Data on thermally induced transformations of Mn exchanged zeolites LTA and FAU topology are prese... more Data on thermally induced transformations of Mn exchanged zeolites LTA and FAU topology are presented in this paper. Thermally induced phase transformation of Mn-exchange zeolites are followed in the range from 700 to 1300?C. Both frameworks collapse into amorphous intermediate products after heating between 600 and 650?C. Prolonged heating of the intermediate product above 1100?C results directly in formation of a disorder Mn-anorthiteLTA and Mn-anorthiteFAU. The parameter of unit cell of Mn-anorthiteLTA and Mn-anorthiteFAU, in temperature range between 700 and 1300?C, was observed in space group C-1. The phase conversions in the temperature range investigated were followed by thermal, X-ray powder diffraction and FT-IR analyses
Materials and Manufacturing Processes
International Journal of Hydrogen Energy, 2013
ABSTRACT In this contribution, we present results of electrochemical characterization of prepared... more ABSTRACT In this contribution, we present results of electrochemical characterization of prepared tungsten carbide supported palladium and platinum and Vulcan XC-72 supported palladium. These catalysts were employed as anode catalysts in PEMFC and results are compared to commercial platinum catalyst. Platinum seems to be irreplaceable as a proton exchange membrane fuel cell (PEMFC) catalyst for both the anode and the cathode, yet the high price and limited natural resources are holding back the commercialization of the PEMFCs. Tungsten carbide is recognized as promising catalyst support having the best conductivity among interstitial carbides. Higher natural resources and significantly lower price make palladium good candidate for replacement of the platinum catalyst. The presented results show that all prepared catalysts are very active for the hydrogen oxidation reaction. Linear sweep voltammetry curves of Pd/C and Pd/WC show existence of peaks at 0.07 V vs. RHE, which is assigned to absorbed hydrogen. H-2 vertical bar Pd/WC vertical bar Nafion117 vertical bar Pt/C vertical bar O-2 fuel cell has almost the same efficiency and similar power output as commercial platinum catalyst. Copyright
Ceramics International, 2014
ABSTRACT Intention of this work was to obtain porous silicon dioxide ceramics by using boric acid... more ABSTRACT Intention of this work was to obtain porous silicon dioxide ceramics by using boric acid as an inexpensive additive at low forming pressure and low sintering temperature. Starting raw material, smectite clay from surface coal mine Kolubara, Serbia, was purified from organic and inorganic impurities by using heat and chemical treatment. Boric acid was used as binding and sintering aid in amount of 0.5, 1 and 2 wt%. Powder was compacted by using different pressures: 40, 60 and 80 MPa. Pressed samples were sintered at 850, 1000, 1150, and 1300 degrees C for 4 h in air. A relatively high porosity of nearly 40% is obtained for the samples pressed at 40, 60 and 80 MPa and sintered at 1000 degrees C. Median pore size diameters are in the range of macroporous up to 0.2 mu m and 10 mu m in the samples sintered at 1150 and 1300 degrees C, respectively. X-ray diffraction (XRD), scaning electron microscopy (SEM), and porosimetry measurements were employed to characterize the phases and microstructure of the obtained ceramics. The relations between mechanical characteristics of samples (Young modulus and Poisson ratio) and content of boric acid were studied.
International Journal of Hydrogen Energy