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Photocatalytic Activity of TiO_2 Powders Synthesized by Supercritical Gas Antisolvent Method

100%
Tuncer M., Ozdemir B.
Acta Physica Polonica A
|
2014
|
vol. 125
|
issue 2
608-610
EN
Synthesis of nanocrystalline, spherical, and anatase type TiO_2 photocatalyst were performed by supercritical gas antisolvent process in the range of 50-150C and 100-150 bar. As-prepared samples were calcined at 500C and characterized by X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller method, differential thermal analysis/thermal gravimetry. In X-ray diffraction analysis, the anatase crystalline phase of titanium dioxide has been detected. The mean crystalline size of powders is about 13 nm. The photoactivity test of the powders was evaluated by the photodegradation of aqueous RR 180 (reactive red 180) solution under UV light. While the photocatalytic performance of TiO_2 powders (Brunauer-Emmett-Teller surface area of 69.2 m^2/g) produced at 150 bar and 150C was found to be 98%, only 25% degradation was observed with powder produced at 150 bar and 100°C. Results showed that the powder properties and photocatalytic activity can be tuned by controlling the supercritical conditions such as temperature and pressure.
2
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Mechanical Properties of Nanocrystalline Tetragonal Zirconia Stabilized with CaO, MgO and Y_2O_3

52%
Sahin O., Demirkol İ., Göcmez H., Tuncer M., Ali Cetinkara H., Salih Güder H., Sahin E., Rıza Tuncdemir A.
Acta Physica Polonica A
|
2013
|
vol. 123
|
issue 2
296-298
EN
The citrate gel method, similar to the polymerized complex method, was used to synthesize homogeneous tetragonal zirconia at 1000°C. Nanocrystalline tetragonal phase has been fully stabilized at wide temperature range with 10 mol.% CaO, MgO, and Y_2O_3 addition. Scanning electron microscopy, X-ray diffraction, and microhardness tests are used to characterize synthesized materials. The grain size and dislocation density were calculated from X-ray diffraction data. The examined material exhibits indentation size effect behavior. Results revealed that the Vickers and Knoop microhardness are dependent on indentation test load. Geometrically necessary dislocation model and modified proportional resistance model are used to analyze the load dependence of the microhardness. The highest hardness values were obtained for the samples with CaO addition; however the lowest values were acquired for sample stabilized with Y_2O_3 by using both Knoop and Vickers techniques. This situation might be explained using the Hall-Petch relation.
3
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Hardness Behavior of Alumina-Zirconia Nanocomposites Synthesized by Gel Process

52%
Sahin O., Hasde A., Göcmez H., Tuncer M., Ali Cetinkara H., Salih Güder H., Sahin E., Rıza Tuncdemir A.
Acta Physica Polonica A
|
2013
|
vol. 123
|
issue 2
299-301
EN
The alumina-zirconia composites are one of the relatively good and promising candidates for biomaterials application, due to biocompatibility and their mechanical properties that combines high flexural strength with a high toughness. The aim of the present work is to analyze the mechanical properties of these composites, where zirconia content was varied from 5 to 50 wt%. The citrate gel method, similar to the polymerized complex method, was used to synthesize these ceramics. Scanning electron microscopy, X-ray diffraction and microhardness tests are used to characterize synthesized materials. The examined material exhibits the behaviour of indentation size effect. Modified proportional resistance model are used to analyze the load dependence of the microhardness. X-ray diffraction analysis was used to calculation of the grain size and dislocation density. It is found that hardness is decreased when the zirconia content increases with enlargement of grain size.
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