Person: TAV, CUMALİ
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TAV
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CUMALİ
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Publication Metadata only Investigation of Nd3+:Y2Si2O7Phosphors Using Photoluminescence and Positron Annihilation Lifetime Spectroscopy(2023-08-01) TAV, CUMALİ; YAHŞİ, UĞUR; Akay L. N., Kuzeci S., Akti N., Erdem M., TAV C., YAHŞİ U., Eryürek G., Di Bartolo B.Neodymium-doped Y2Si2O7 nanopowders were synthesized by sol-gel and annealed under varying annealing temperature conditions. The phase transformation of Y2Si2O7 and the crystalline size change were observed with annealing temperature. Photoluminescence and the decay patterns of the 4F3/2→ 4I9/2,4I11/2, and 4I13/2 transitions were examined to reveal the spectroscopic characteristics of the powders. The spectral outputs of Nd3+:Y2Si2O7 phosphors remain strongly connected to the phase properties of Y2Si2O7. The positron lifetimes (τ 2, τ 3, and τ 4) and intensities (I 2, I 3, and I 4) obtained by positron annihilation lifetime spectroscopy were discussed for neodymium-doped Y2Si2O7 phosphors to relate the structural and boundary changes in terms of the phases and molar contents of the Nd3+ ions. The τ 2 and I 2 components were related to the structural open space in the grain, the τ 3 and I 3 components were correlated with vacancy-like defects in the grain boundaries, and the τ 4 and I 4 components were associated with vacancy defects in the grain, together with the effect of the increasing content of the Nd3+ ions.Publication Metadata only FİZİK, Fen ve Mühendislik için Teknoloji Güncellemeli, Serway, Jewett,, CİLT 2, Elektrik ve Manyetizma, Optik(Palme Yayın Dağıtım, 2022-07-01) KESKİN, SIDDIK SİNAN; DUMLUDAĞ, FATİH; TAV, CUMALİ; YUMAK YAHŞİ, AYŞE; YAHŞİ, UĞUR; Yahşi U., Saçlı Ö. A., Keskin S. S., Tav C., Dumludağ F., Altındal A., Yumak Yahşi A., Avgın İ., Atav Ü., Ulutaş D., et al.Publication Metadata only A detailed survey for determination of the grafted semifluorinated acrylic compound effect on thermal, microstructural, free volume, mechanical and morphological features of HDPE(ELSEVIER SCIENCE SA, 2020) TAV, CUMALİ; Soykan, Ugur; Sen, Behiye Ozturk; Cetin, Sedat; Yahsi, Ugur; Tav, CumaliThis study mainly aims to investigate the role of grafted semifluorinated acrylic compound in the crucial characteristic properties of high density polyethylene (HDPE). Graft copolymerization of the semifluorinated acrylic compound, 3,3,4,4,5,5,6,6,7,7,8,8,8-dodecafluoro-5-methyloctyl-4-(acryloyloxy) benzoate (ABCF13) onto HDPE within the different content levels of ABCF13 (5, 10, 15, 20, 30 and 40 %) was performed by bulk-melt polymerization method. The changes in the thermal, microstructural and free volume characteristics of graft coproducts with extent of grafting were investigated in detail by means of DSC, powder X-ray diffraction and PALS techniques, respectively. The experimental findings showed that the melting temperature of crystalline domains and crystallinity ofHDPE reached the maxima at the 15 % and 40 % ABCF13 contents, respectively. The grafting of ABCF13 onto HDPE also gave rise to significant expansion and contraction in lateral dimensions of orthorhombic unit cell parameters in the crystalline domains of HDPE. Moreover, PALS analyses depicted that the size of the free volumes increased almost linearly with the grafting percentage. As for mechanical behaviours of the graft products, remarkable improvements were achieved in especially tensile strength (from 18.75 MPa to 43.75 MPa) and impact strength (from 19.30 Mpa to 38.72 MPa). The morphological properties of the fractured surfaces obtained from tensile and impact tests of products were also examined by SEM analysis. The samples possessed completely homogeneous structure without any phase separation. A gradual transition from ductile behaviour to brittle nature was observed as the grafting level increased in the products.Publication Open Access Effects of sintering and zirconmullite doping on nanostructural vacancies of bovine hydroxyapatite by positron techniques(2023-01-01) TAV, CUMALİ; YAHŞİ, UĞUR; ERKMEN, ZİYA ENGİN; Akay L. N., Kalkandelen C., Akti N., Sengul M. S., TAV C., YAHŞİ U., ERKMEN Z. E.In this study, the nanostructural vacancy behavior of bovine derived hydroxyapatite (BHA) doped with powder zirconmullite (ZM) contents of 5, 7.5, 10 and 12.5 wt.% were presented at sintering temperatures of 1000, 1100, 1200 and 1300 degrees C. ZM-doped BHA (ZM-BHA) was characterized by X-ray diffraction and positron annihilation lifetime spectroscopy (PALS). Density and hardness behavior were measured with respect to increasing sintering temperature. PALS results indicate that the longest lifetime component tau(3) of ortho-positronium (o-Ps) localized at open spaces is attributed to the vacancy site and almost constant with the ZM contents and the sintering temperatures to have a mean value of 0.680 ns (corresponding to the radius of 0.997 nm). This average value is ascribed to the OH group defects along the main crystalline line. On the other hand, the o-Ps intensity attributed to the number of vacancy sites increases almost linearly with ZM additives and sintering temperatures. The intensity is also related to the density and hardness of ZM-BHA in terms of ZM contents.Publication Metadata only Optical and photoluminescence spectroscopy analysis and Doppler broadening annihilation radiation studies of perovskites based on La1-XNiXMnO2.75 thin layers(ELSEVIER GMBH, 2020) YUMAK YAHŞİ, AYŞE; Arrar, A.; Benhaliliba, M.; Boukhachem, A.; Yahsi, U.; Tav, C.; Yumak, A.; Amlouk, M.In this work, perovskite La1-xNixMnO2.75 (with x = 0, 0.1, 0.2, 0.3 and 0.4) is synthesized by spray pyrolysis route at 460 degrees C. X-ray pattern analysis showed orthorhombic structure of the pure and Ni-doped. Based on X-ray analysis interesting parameters are then extracted such as crystallite size, micro-strain (epsilon) and dislocation density (delta). A high transmittance coefficient at 76 % and the optical band gap varies from 2.33 to 2.85 eV are revealed by the spectroscopy analysis. The Urbach energy varies from 273 to 381.7 meV. Furthermore, refractive index, extinction coefficient, and dielectric constants versus photon wavelength are plotted for pure and Ni-doped LaMnO2.75 layers. PL measurements analysis describe peaks within violet, blue, and green emission ranges. Finally, Doppler-broadening energy studies have been performed to investigate the defect structural evolution in polycrystalline La1-xNixMnO2.75. The studies derived S, R and W parameters are used to perovskite samples.Publication Metadata only Heavy ion irradiation induced defects in Zircaloy-4(IOP PUBLISHING LTD, 2021) TAV, CUMALİ; Izerrouken, M.; Hazem, R.; Yahsi, U.; Naceri, S. E.; Tav, C.; Kuzeci, S.; Sari, A.; Haid, F.; Ishaq, A.; Menchi, O.; Ghamnia, M.Radiation damage induced in Zircaloy-4 by 20 MeV Au ions was investigated using Grazing x-ray diffraction (GIXRD), positron annihilation techniques, micro-and nano-hardness techniques. The irradiations were performed at room temperature in the fluence range 1 x 10(13)-5 x 10(14) ions cm(-2) corresponding to 0.07-3.63 displacements per atom (dpa). The grazing incidence angle x-ray diffraction (GIXRD) revealed the presence of the hydride precipitates in the analyzed zircaloy-4. According to our experimental data it is found that the amount of these precipitates decreases after irradiation as emphasized by GIXRD and Positron Annihilation Lifetime Spectroscopy (PALS) results. The same data revealed also a zircaloy-4 swelling above a certain dose. From the combination of domain size/microstrain with the micro- and nano-hardness results, we conclude that the Zircaloy hardening is mainly due to the dislocation formation indicating the effect of the microstructure on the mechanical properties. Moreover, from the dose dependence of irradiation hardening we conclude that the transition point from low-dose to high-dose regime is observed around 0.07 dpa.Publication Metadata only Investigation of the relation between free volume and physico-mechanical performance in rigid polyurethane foam containing turkey feather fibers: Part 2(2022-11-01) YAHŞİ, UĞUR; TAV, CUMALİ; Soykan U., Khaleel M., Cetin S., YAHŞİ U., TAV C.© The Author(s) 2022.Rigid polyurethane foams (RPUFs) were modified with 0–15 wt.% turkey feather fibers (TFFs) produced from waste turkey feathers. One-shut free rising method was used for the production of TFFs-filled-RPUFs in a closed mold. The dependence of mechanical performance and water vapor permeability (WVP) feature of the final foams on TFFs loading was evaluated with free volume change. The free volume analysis was performed via Positron Annihilation Lifetime Spectroscopy (PALS), while the mechanical and WVP characteristics were determined with the use of the universal tester machines. PALS findings showed that the incorporation of TFFs with RPUF matrix caused the considerable diminishment in the free volume due to TFFs serving as a filling material and formation of strong secondary bonds between components. Moreover, tensile strength and extension of the foams decreased with the increasing of TFFs, which caused by the occurrence of noteworthy restriction on the spatial alignment and orientation capability of polyurethane chains due to the lack of sufficient free volume allowing the chains to move freely. As for the compression tests, all the TFFs-loaded RPUFs depicted substantially lower performance due to TFFs interfering with the ordered organization of isocyanate domains. Moreover, impact test results showed that the addition of TFFs into RPUF matrix brought about the insufficient impact energy delocalization throughout the matrix due to the restriction on the mobility of polymer chains. Additionally, the remarkable diminishment in WVP was recorded due to the reduction in the number of vacancies and constitution of keratin composed of roundly 60% of hydrophilic protein (especially cystine). All in all, this study established a strong links between free volume and characteristics of TFFs-loaded RPUFs.Publication Open Access Effect of Free Volume on Curcumin Release from Various Polymer-Based Composite Films Analyzed Using Positron Annihilation Lifetime Spectroscopy(MDPI, 2021-09-29) TAV, CUMALİ; Rhim, Jong-Whan; Kuzeci, Saygin; Roy, Swarup; Akti, Necmettin; Tav, Cumali; Yahsi, UgurThis work reports the effects of free volume on curcumin release in various polymer-based composite films. Curcumin-reinforced biocomposite films were fabricated with natural biopolymers (carrageenan and chitosan) and bioplastics (poly(lactide) (PLA) and poly (butylene adipate-co-terephthalate) (PBAT)) via the solvent casting method. The curcumin release test was performed using an aqueous medium, and it was found that it was released the fastest in the carrageenan film, followed by the chitosan, PLA, and PBAT films, presumably owing to the dissimilarity of the polymer matrix. The free volume of the polymer films was determined using positron annihilation lifetime spectroscopy (PALS) to understand the release phenomena of curcumin. The free volume fraction was varied and reliant on the type of polymer, with the highest in the PBAT-based film followed by the PLA-, chitosan-, and carrageenan-based films. The free volume method helps analyze the release of bioactive compounds in a polymer matrix and may help to achieve a better understanding of the release of bioactive compounds.Publication Open Access Decoding Polymer Architecture Effect on Ion Clustering, Chain Dynamics, and Ionic Conductivity in Polymer Electrolytes(2023-01-01) YAHŞİ, UĞUR; TAV, CUMALİ; Bakar R., Darvishi S., Aydemir U., YAHŞİ U., TAV C., Menceloglu Y. Z., Senses E.Poly(ethylene oxide) (PEO)-based polymer electrolytes are a promising class of materials for use in lithium-ion batteries due to their high ionic conductivity and flexibility. In this study, the effects of polymer architecture including linear, star, and hyperbranched and salt (lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI)) concentration on the glass transition (Tg), microstructure, phase diagram, free volume, and bulk viscosity, all of which play a significant role in determining the ionic conductivity of the electrolyte, have been systematically studied for PEO-based polymer electrolytes. The branching of PEO widens the liquid phase toward lower salt concentrations, suggesting decreased crystallization and improved ion coordination. At high salt loadings, ion clustering is common for all electrolytes, yet the cluster size and distribution appear to be strongly architecture-dependent. Also, the ionic conductivity is maximized at a salt concentration of [Li/EO ≈ 0.085] for all architectures, and the highly branched polymers displayed as much as three times higher ionic conductivity (with respect to the linear analogue) for the same total molar mass. The architecture-dependent ionic conductivity is attributed to the enhanced free volume measured by positron annihilation lifetime spectroscopy. Interestingly, despite the strong architecture dependence of ionic conductivity, the salt addition in the highly branched architectures results in accelerated yet similar monomeric friction coefficients for these polymers, offering significant potential toward decoupling of conductivity from segmental dynamics of polymer electrolytes, leading to outstanding battery performance.Publication Metadata only The role of defects in the structural and photocatalytic properties of Mg/B co-doped ZnO nanoparticles(2023-03-01) ŞENGÜL, MUSTAFA TAYLAN; TAV, CUMALİ; YAHŞİ, UĞUR; ŞENTÜRK K., Yalcin B., Yalcin I., Alphan M., ŞENGÜL M. T., TAV C., YAHŞİ U., Arda L.Mg/B co-doped ZnO nanoparticles were synthesized by using the sol–gel technique to investigate the role of the defects on the structural, biological and photocatalytic properties. Single phases with ZnO wurtzite hexagonal structures were observed in the X-ray diffraction measurements. Scanning electron microscopy and transmission electron microscopy were used to determine the surface, particle size, and shapes of the nanoparticles. Electron dispersive spectroscopy was used to determine the elemental compositions of the nanoparticles. Photoluminescence spectrophotometry and positron annihilation lifetime spectroscopy were used to study the defect type, density and crystal quality of Mg/B co-doped ZnO nanoparticles. A broad visible emission band (including violet–blue-orange and red emissions) was observed. The violet–blue-orange and red emissions could be attributed to the O vacancies (VO), interstitial Zn (Zni), Zn vacancies (VZn), and the double charged oxygen vacancy (VO(++)), which were strongly dependent on the synthesis conditions and doping ratio. SEM images revealed that Mg/B-co-doped ZnO nanoparticle magnifications were dense, quasispherical, and agglomerating. The photocatalytic activities and blood compatibilities of Mg/B co-doped ZnO nanoparticles were studied by the photocatalytic degradation tests of crystal violet (CV) and hemolysis tests, respectively.