Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Citation - WoS: 10Citation - Scopus: 11Novel High-Pressure Phase of ZrO2: An ab initio Prediction(Academic Press inc Elsevier Science, 2015-10) Durandurdu, MuratThe high-pressure behavior of the orthorhombic cotunnite type ZrO2 is explored using an ab initio constant pressure technique. For the first time, a novel hexagonal phase (Ni2In type) within P6(3)/mmc symmetry is predicted through the simulation. The Ni2In type crystal is the densest high-pressure phase of ZrO2 proposed so far and has not been observed in other metal dioxides at high pressure before. The phase transformation is accompanied by a small volume drop and likely to occur around 380 GPa in experiment. (C) 2015 Elsevier Inc. All rights reserved.Article Citation - WoS: 5Citation - Scopus: 5Modification of Surface Charge Characteristics for Unsupported Nanostructured Titania-Zirconia UF/NF Membrane Top Layers With Calcination Temperature(Springer, 2019-04-18) Erdem, Ilker; Ciftcioglu, MuhsinCeramic membranes are more advantageous alternatives especially for harsh working conditions when compared with the polymeric membranes. The porous multilayer structure of the ceramic membranes (composed of support, intermediate, and top layers) can be prepared via different oxides. Titania and zirconia, having superior properties, are mainly preferred for the top layer formation. The separation properties of the membrane are both dependent on pore morphology and surface charge of the oxide(s) forming the top layer. The effect of surface charge in separation may be very significant in case of filtration of charged species with relatively lower mass as in the ultrafiltration (UF) and nanofiltration (NF). In this study, unsupported membrane top layers were prepared with varying titania/zirconia ratios by sol-gel technique. Their surface charges at different pH conditions after calcination at varying temperatures (400 degrees, 500 degrees, and 600 degrees C) were determined. The surface charge of the pure titania (full Ti) top layer was decreasing with the increasing calcination temperature. The highest magnitudes of zeta potential for both acidic and basic conditions were measured via Zr rich top layer (TiZr2575) at calcination temperatures >= 500 degrees C, which was composed of anatase, rutile (titania), and tetragonal (zirconia) phases after calcination. The tailor-made top layer can be prepared with modifications during membrane preparation.Article Citation - WoS: 6Citation - Scopus: 8Influence of Calcination Temperature on Microstructure and Surface Charge of Membrane Top Layers Composed of Zirconia Nanoparticles(Australian Ceramic Society, 2015) Erdem, I.; Ciftcioglu, M.; Ciftҫioğlu, M.; Çiftçioğlu, M.The purpose of the research is to investigate the changes in microstructure and physicochemical characteristics, mainly surface charge (i.e. zeta potential) of zirconia membrane top layer during calcination. Zirconia is one of the most commonly preferred materials for ceramic membrane top layers due to its superior durability. The physicochemical properties of the top layer composed of submicron / nano particles is necessary not only for Donnan exclusion but also for dynamics of membrane fouling. In the present research the possibility of preparation of zirconia top layers with varying surface charge with changing calcination temperature was shown and a correlation between phase transformation and surface charge was determined.Article Citation - WoS: 1Citation - Scopus: 1Amorphous Zirconia at High Pressure(Wiley, 2018-06-08) Durandurdu, MuratWe show, by means of ab initio calculations, that amorphous zirconia progressively transforms to a high-density amorphous phase with the application of pressure. The average coordination number of Zr and O atoms under pressure rises gradually to 8 and 4, respectively. The main building unit of the dense noncrystalline state is the eightfold-coordinated Zr atoms (62.5%). When the coordinated modification of Zr atoms in the zirconia crystal at high pressure and temperature conditions is considered, it can be perceived that amorphous zirconia follows a transformation mechanism similar to the one observed at high temperature but different than the one detected at high pressure. The dense disordered phase is indeed found to be locally comparable with the high-temperature tetragonal crystal. Upon decompression, some high-pressure arrangements are persevered in the model and a transformation into another amorphous state whose structure is intermediate between uncompressed and dense amorphous phases is observed in the simulations. The high-pressure amorphous structures are found to be semiconductors with a band gap smaller than that of the original model.