25 results
Search Results
Now showing 1 - 10 of 25
Article Citation - WoS: 11Citation - Scopus: 10Synthesis and Characterization of Hydrothermally Grown Potassium Titanate Nanowires(Korean Assoc Crystal Growth, inc, 2015) Kapusuz, Derya; Kalay, Y. Eren; Park, Jongee; Ozturk, Abdullah; Eren Kalay, Y.; Metallurgical and Materials EngineeringPotassium titanate (KT) nanowires were synthesized by a one-step hydrothermal reaction between TiO2 and aqueous KOH solution. The effects of KOH concentration and reaction time on hydrothermal formation and KT nanowire growth were investigated. The nanowire growth mechanism was elucidated using a combined study of powder X-ray diffraction, and scanning and transmission electron microscopy. The results revealed that hydrothermal growth was initiated by the formation of amorphous-like Ti-O-K sheets in anatase. Increasing hydrothermal reaction time caused the transformation of anatase to Ti-O-K sheets, from which potassium hexa-titanate (K2Ti6O13) nuclei formed and grew to establish one-dimensional morphology through preferential growth along the b-axis. It was revealed that the hydrothermal reactions followed a quite different mechanism than the well-known calcination route. Potassium tetra-titanate (K2Ti4O9) crystals formed in the amorphous region using the hexa-titanate phase as a nucleation site for heterogeneous crystallization. Increasing the KOH concentration in the solution accelerated the hydrothermal reaction rate.Article Citation - WoS: 31Citation - Scopus: 37Effect of Initial Water Content and Calcination Temperature on Photocatalytic Properties of Tio2 Nanopowders Synthesized by the Sol-Gel Process(Elsevier Sci Ltd, 2015) Agartan, Lutfi; Kapusuz, Derya; Park, Jongee; Ozturk, AbdullahThe effects of initial water content and calcination temperature on sol gel synthesized TiO2 powders were studied. Mother solutions had water/Ti-precursor mole ratios (R ratio) of 1, 5, 10, and 50. Dried aerogels were calcined for 3 h at temperatures of 300, 400, and 500 degrees C to obtain crystallized TiO2 nanopowders in the range of 15-30 nm. PE-scanning electron microscopy and X-ray diffraction techniques were employed to investigate the morphological and structural properties of the nanopowders synthesized. Profound effect of gel viscosity was observed on the formation mechanism and extent of crystallinity in the powders. Methylene blue degradation test results suggest, photocatalytic performance is enhanced as initial water content and calcination temperature increased. Band-gap energy of the powders ranged from 3.09 to 3.27 eV. Overall, this study shows that initial water content and calcination regime have a profound effect on the phase assembly, crystallite size, band-gap energy, and photocatalytic performance of sol gel synthesized TiO2 nanopowders. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.Conference Object Citation - WoS: 2Citation - Scopus: 4Influence of Boron And/Or Zirconium Doping on Morphology and Optical Properties of Titania(Tanger Ltd, 2011) Kapusuz, Derya; Park, Jongee; Ozturk, Abdullah; Metallurgical and Materials EngineeringSol-gel derived B (boron) and Zr (zirconium) doped TiO2 (Titania) nanoparticles were synthesized. Microstructural, photocatalytic and crystallographic properties of the doped particles were investigated. Highest photocatalytic activity was achieved by 10 wt% Zr doping. 5 wt% doping was the optimum value for effective B doping. B ions were found to form oxygen vacancies behaving as interstitial defects whereas Zr ions substituted Ti4+ ions in the lattice.Article Citation - WoS: 23Citation - Scopus: 27Facile synthesis of CsPbBr3/PbSe composite clusters(Taylor & Francis Ltd, 2018) Thang Phan Nguyen; Ozturk, Abdullah; Park, Jongee; Sohn, Woonbae; Tae Hyung Lee; Jang, Ho Won; Kim, Soo Young; Nguyen, Thang Phan; Lee, Tae HyungIn this work, CsPbBr3 and PbSe nanocomposites were synthesized to protect perovskite material from self-enlargement during reaction. UV absorption and photoluminescence (PL) spectra indicate that the addition of Se into CsPbBr3 quantum dots modified the electronic structure of CsPbBr3, increasing the band gap from 2.38 to 2.48 eV as the Cs:Se ratio increased to 1:3. Thus, the emission color of CsPbBr3 perovskite quantum dots was modified from green to blue by increasing the Se ratio in composites. According to X-ray diffraction patterns, the structure of CsPbBr3 quantum dots changed from cubic to orthorhombic due to the introduction of PbSe at the surface. Transmission electron microscopy and X-ray photoemission spectroscopy confirmed that the atomic distribution in CsPbBr3/PbSe composite clusters is uniform and the composite materials were well formed. The PL intensity of a CsPbBr3/PbSe sample with a 1:1 Cs: Se ratio maintained 50% of its initial intensity after keeping the sample for 81 h in air, while the PL intensity of CsPbBr3 reduced to 20% of its initial intensity. Therefore, it is considered that low amounts of Se could improve the stability of CsPbBr3 quantum dots.Article Citation - WoS: 12Citation - Scopus: 11Enhanced Bioactivity and Low Temperature Degradation Resistance of Yttria Stabilized Zirconia/Clay Composites for Dental Applications(Elsevier Sci Ltd, 2022) Tufan, Yigithan; Park, Jongee; Ozturk, Abdullah; Ercan, BaturYttria stabilized zirconia (YSZ)/clay composites were produced to improve osseointegration and undesired tetragonal-to-monoclinic phase transformation (low temperature degradation, LTD) of YSZ ceramics so that long-term clinical success of YSZ implants is achieved. Various amounts (0.5,1,2, and 4 wt%) of clay was incorporated to YSZ. Predetermined amounts of clay and YSZ were mixed and pressed uniaxially at 15 MPa into compacts that were subsequently pressureless sintered at 1450 degrees C. Density, compressive strength, hardness and indentation crack resistance of 4 wt% clay incorporated YSZ/clay composite were 5.77 +/- 0.01 g/cm3, 1188 +/- 121 MPa, 1223 +/- 9 HV, and 4.4 +/- 0.1 MPa root m, respectively. Additionally, biological properties of YSZ/clay composites were assessed in vitro using bone cells. Incorporation of 4 wt% clay significantly enhanced bone cell prolifer-ation, spreading, and functions. Moreover, a significant increase in the LTD resistance of YSZ was achieved upon 4 wt% clay incorporation. The findings collectively suggest that YSZ/clay composites have a potential to be used as an alternative material for dental applications.Article Effects of Graphene Transfer and Thermal Annealing on Anticorrosive Properties of Stainless Steel(Amer Scientific Publishers, 2017) Oh, Jeong Hyeon; Han, Sangmok; Kim, Tae-Yoon; Park, Jongee; Ozturk, Abdullah; Kim, Soo YoungStainless steel (STS) films were annealed in a thermal quartz tube and covered with graphene to improve their anticorrosive properties. Graphene was synthesized via the chemical vapor deposition method and transferred onto the surface of the STS film by the layer-by-layer approach. The structure of the STS film changed from alpha-Fe to gamma-Fe after annealing at 700 C for 1 h, resulting in an increase of 82.72% in the inhibition efficiency. However, one-layer graphene acted as a conductive pathway and therefore deteriorated the anticorrosive properties of the STS film. To overcome this problem, graphene was transferred layer by layer onto the STS film. It was found that transfer of three layers of graphene onto the STS film resulted in a 91.57% increase in the inhibition efficiency. Therefore, thermal annealing and transfer of multilayer graphene are considered to be effective in enhancing the anticorrosive properties of STS films.Article Citation - WoS: 44Citation - Scopus: 43Sol-Gel Synthesis and Photocatalytic Activity of B and Zr Co-Doped Tio2(Pergamon-elsevier Science Ltd, 2013) Kapusuz, Derya; Park, Jongee; Ozturk, AbdullahEffects of boron (B) and/or zirconium (Zr) doping on photocatalytic activity of sol-gel derived titania (TiO2) powders were investigated. A conventional, non-hydrous sol-gel technique was applied to synthesize the B, Zr doped/co-doped TiO2 powders. Doping was made at molar ratios of Ti/B=1 and Ti/Zr=10. Sol-gel derived xero-gels were calcined at 500 degrees C for 3 h. The crystal chemistry and the morphology of the undoped and B, Zr doped/co-doped TiO2 nanoparticles were investigated using X-ray diffractometer and scanning electron microscope. Nano-scale (9-46 nm) TiO2 crystallites were obtained after calcination. Doping and co-doping decreased the crystallite size. Photocatalytic activity was measured through the degradation of methylene blue (MB) under 1 h UV-irradiation using a UV-vis spectrophotometer. Results revealed that B doping into anatase caused the formation of oxygen vacancies, whereas Zr addition caused Ti substitution. Both B and Zr ions had a profound effect on the particle morphology and photocatalytic activity of TiO2. The photocatalytic activity of B and Zr doped TiO2 particles increased from 27% to 77% and 57%, respectively. The best activity (88.5%) was achieved by co-doping. (C) 2013 Elsevier Ltd. All rights reserved.Conference Object Citation - WoS: 1PRODUCTION OF SILVER LOADED PHOTOCATALYTIC TIO2 POWDERS BY BALL MILLING(Tanger Ltd, 2011) Aysin, Basak; Park, Jongee; Ozturk, AbdullahThe present study was undertaken to improve photocatalytic efficiency of TiO2 powder by silver doping and/or particle size reduction through mechanical ball milling. A planetary ball mill was employed to reduce the particle size of TiO2 powders to nanoscale and silver loading to TiO2 powders. Silver nitrate was used as silver source to obtain about 1% Ag load. Slurry taken from ball mill was separated by centrifugal separator into nano and micro sols. Separated nanosol was taken into the furnace to be dried at 103 degrees C and calcined at 400 degrees C for 1 hour to assist silver loading. X-Ray powder diffraction (XRD) was employed to identify the crystalline phases present in the powders produced. XRD results revealed that doped TiO2 powders were consisted of only anatase phase of TiO2. Changes in lattice parameters of TiO2 structure after doping were determined also by XRD. Scanning Electron Microscope (SEM) and particle size analyzer were used for examining the size reduction effect of ball milling process. Photocatalytic performance of the powders was evaluated by Methylene Orange (MO) test under UV light illumination using UV-Spectrophotometer.Article Citation - WoS: 4Citation - Scopus: 4Bioactivity of Apatite-Wollastonite Glass-Ceramics Produced by Melting Casting(World Scientific Publ Co Pte Ltd, 2013) Park, Jongee; Ozturk, AbdullahGlass-ceramics containing only apatite and wollastonite crystals were produced in the system MgO-CaO-SiO2-P2O5-F by the melt casting process. The bioactivity of the glass-ceramics was determined by immersing the glass-ceramics in a simulated body fluid (SBF) and by assessing the resulting apatite formation on the free surface after various immersion durations. A 12-mu m-thick apatite layer formed on the surface of the glass-ceramic containing only apatite crystals after 20 days immersion in SBF. However, the thickness of the apatite layer formed on the surface of the glass-ceramic containing apatite and wollastonite crystals was 1 mu m. Results have shown that the bioactivity of glass-ceramic depends strongly on the type of crystal(s) developed during the glass-ceramic process and their proportion in the glassy matrix.Article Citation - WoS: 11Citation - Scopus: 14Tribological Behavior of Alumina-Added Apatite-Wollastonite Glass-Ceramics in Simulated Body Fluid(Elsevier Science Sa, 2010) Park, Jongee; You, Sang-Hee; Shin, Dong-Woo; Ozturk, AbdullahTribological properties of an alumina-added apatite-wollastonite glass-ceramic produced by controlled heat treatment of a glass in the system MgO-CaO-SiO(2)-P(2)O(5)-Al(2)O(3) have been evaluated and compared with those of selected commercial dental ceramics, Duceragold and IPS Empress. Tribological tests were performed in dry condition and in simulated body fluid (SBF) using a pin-on-disk apparatus. The friction coefficient and specific wear rate of the tested materials were measured in dry and in artificial saliva (simulated body fluid: SBF) in order to elucidate the appropriateness of the alumina-added apatite-wollastonite (A-W) glass-ceramic for dental applications. Wear rate of the materials investigated varied from 0.96 x 10(-4) mm(3) N(-1) m to 41.37 x 10(-4) mm(3) N(-1) m depending on the bioenvironmental test conditions. The results of this study revealed that the alumina-added A-W glass-ceramic becomes more wear resistant as sintering temperature is increased and exhibits tribological properties similar to those of the commercial dental materials investigated. (C) 2010 Elsevier B.V. All rights reserved.
- «
- 1 (current)
- 2
- 3
- »