Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Enhanced Oxidation and Thermal Shock Resistance of N-Type Mg2Si0.89(Sn0.1,Sb0.01) Thermoelectric Material Via Cr0.9Si0.1 Coating(Wiley-VCH Verlag GmbH, 2025) Gurtaran, Mikdat; Zhang, Zhenxue; Li, Xiaoying; Dong, HanshanIn this study, Cr0.9Si0.1 coatings are deposited onto Mg2Si0.89(Sn0.1Sb0.01) thermoelectric (TE) materials using a closed-field unbalanced magnetron sputtering system. The cyclic oxidation behavior of uncoated and Cr0.9Si0.1-coated TE materials is thoroughly investigated at 500 degrees C for 10 and 50 cycles, with each cycle lasting 1 h. Surface morphology, phase constitution, cross-sectional layer structure, and elemental distribution are analyzed using scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. Oxidation kinetics are assessed by measuring the mass gain of samples after cyclic oxidation testing. The uncoated TE material exhibits significant surface degradation after cyclic oxidation, initially forming MgO particles, followed by the development of SiO2 and Mg2SiO4 phases in later stages. Encouragingly, the Cr0.9Si0.1 coating demonstrates excellent thermal stability on the n-type Mg2Si0.89(Sn0.1Sb0.01) substrate. Although some oxygen diffusion occurs along grain boundaries within the coating, it is effectively trapped, thereby preventing further penetration into the underlying substrate. The high oxygen affinity of Cr and/or Si atoms plays a critical role in blocking oxidation, offering robust protection. These findings strongly support the use of Cr0.9Si0.1 coatings as an effective antioxidant barrier for TE materials under harsh operational conditions, ensuring the long-term operation of TE modules at elevated temperatures.Article Citation - WoS: 1Citation - Scopus: 1Effect of Compaction and Fluoride Content on the Remelting Efficiency of Pure Magnesium Chips(Taylor & Francis, 2023) Yörük, Pınar; Gökelma, Mertol; Derin, BoraMagnesium is widely used in industries, such as automotive, aerospace, and medical fields. The demand on magnesium has been growing, although the production and melt treatment is complex due to strong oxidation tendency. Recycling of magnesium scraps is crucial due to the criticality of magnesium-containing raw materials in Europe as well as increasing environmental concerns. Remelting of magnesium is typically conducted under a salt flux which absorbs the impurities and protects the melt against oxidation. This study investigates the effect of compaction, fused salt flux, and salt composition on remelting behavior of magnesium chips. Metal yield and coagulation efficiency were calculated after remelting, and samples were characterized by using Scanning Electron Microscope and X-ray Diffraction. The liquidus temperature and density of fluxes were analyzed by FactSage software. Remelting of compacted chips under a fused salt flux with 5 wt.% CaF2 showed the highest magnesium recovery with a yield of 97.7%. Le magnesium est largement utilise dans une variete d'industries, telles que les domaines de l'automobile, de l'aerospatiale et de la medecine. La demande en magnesium s'est accrue, bien que la production et le traitement du bain soient complexes en raison de sa forte tendance a l'oxydation. Le recyclage des dechets de magnesium est crucial en raison de la criticite des matieres premieres contenant du magnesium en Europe ainsi que des preoccupations environnementales croissantes. La refusion du magnesium est effectuee typiquement sous un flux de sel qui absorbe les impuretes et protege le bain contre l'oxydation. Cette etude examine l'effet du compactage, du flux de sel fondu et de la composition du sel sur le comportement a la refusion des copeaux de magnesium. On a calcule le rendement en metal et l'efficacite de la coagulation apres des experiences de refusion, et l'on a caracterise les echantillons a l'aide d'un microscope electronique a balayage et de la diffraction des rayons X. On a analyse la temperature du liquidus (Tliq) et la densite des flux de sel avec le logiciel FactSage. La refusion des copeaux compactes sous un flux de sel fondu avec 5% en poids de CaF2 a montre la recuperation de magnesium la plus elevee avec un rendement de 97.7%Article Citation - WoS: 11Citation - Scopus: 12Treatment of Sugar Industry Wastewater by Using Subcritical Water as a Reaction Media(Wiley, 2023) Orak, Ceren; Öcal, Bulutcem; Yüksel, AslıThe sugar industry is one of the most wastewater-producing industries and it contains high content of organic and inorganic substances. Treating and reusing wastewater has significant importance because sugar industry needs to use a high volume of water. In this study, sugar industry wastewater was treated under subcritical conditions and the impacts of reaction temperature and duration over TOC removal percentage were investigated. Additionally, the impact of NaOH concentration over TOC removal percentage was examined. The highest TOC removal was obtained almost 95 % in the presence of 0.1 M of NaOH at 240 degrees C for 90 min of reaction duration. Treatment of sugar industry wastewater by subcritical water oxidation followed the second-order reaction kinetic model and the activation energy was found as 11.41 kJ/mol. Furthermore, the intermediate products were identified via GC-MS.Article Citation - WoS: 3Citation - Scopus: 3Atomic-Scale Investigation of the Effect of Surface Carbon Coatings on the Oxidation and Mechanical Properties of Iron Nanowires(Royal Society of Chemistry, 2021) Aral, Gürcan; Islam, Md MahbubulThe understanding of the complex atomistic-scale mechanisms of the oxidation process of carbon (C) coated iron nanowires (Fe NW) and also the resulting modulation of mechanical properties is a highly challenging task. We perform reactive molecular dynamics (RMD) simulations based on the ReaxFF force field to investigate the mechanisms of the oxidation process of [001]-oriented pristine cylindrical Fe NWs with and without a C coating in an O2 environment in order to obtain detailed insights into the influences of the surface C coating on the oxidation process at room temperature. Here, we show that the C-coated shell layer on the free surface of pristine Fe NWs partially controls the spontaneous oxidation when exposed to O2 molecules by hindering the absorption-dissociation of O2 molecules and diffusion of O ions into the shell layer. In particular, the surface modification of the pristine Fe NW with the C-coated shell layer has pronounced effects on the improvement of oxidation resistance by lowering the surface reactivity, which limits the formation of an oxide shell layer on the free surface of the NW. The formation of strong Fe-C bonds in the C-coated shell layer largely restrains the oxidation process. Furthermore, to examine the influence of the C-coated shell layer on the resulting modulation of mechanical properties of the pristine Fe NW, we systematically investigate the mechanical deformation processes and related properties of Fe NW with and without a C coating including their oxidized counterparts subjected to both uniaxial tensile and compressive loads at room temperature. The yield stress and strain (the elastic limit) of Fe NWs including the elastic and plastic deformation phase of the stress-strain relationship are found to be sensitive to the loading modes, the existence of the C-coated shell layer and the resulting formation of an oxide shell layer on the surface of the C-coated Fe NW.Article Citation - WoS: 37Citation - Scopus: 39Reaction of Methyl Radicals With Metal Powders Immersed in Aqueous Solutions(Wiley-VCH Verlag, 2003) Rusonik,I.; Polat,H.; Cohen,H.; Meyerstein,D.Methyl radicals radiolytically produced in aqueous solutions react efficiently with Cr0, Mn0, Fe0, Ni 0, Cu0 and Zn0 powders immersed in the solution. The Cr0, Mn0, Fe0, Ni0 and Zn0 powders reduce the radicals to form methane. On the other hand the Cu0 powder seems to oxidize the radicals. Surprisingly a part of the energy absorbed by the Cr0, Fe0, Ni 0 and Zn0 powders is transferred to the aqueous solution, thus increasing the radical yield. CH4, C2H4, C2H6, C3H6 and C3H 8 are formed when an aqueous deaerated buffer solution, pH 4-5, is added to powders of analytical iron, zinc, manganese and chromium. The source of these gases is carbon traces present, as atoms or atom clusters, in the "analytical" metal powders. These carbon atoms, when present on the surface of the metals, are reduced by the metal particles in aqueous solutions. This mechanism might be the source of light alkanes and alkenes in the prebiotic era. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.Article Citation - WoS: 24Citation - Scopus: 26Role of Surface Oxidation on the Size Dependent Mechanical Properties of Nickel Nanowires: a Reaxff Molecular Dynamics Study(Royal Society of Chemistry, 2017) Aral, Gürcan; Islam, Md Mahbubul; Van Duin, Adri C. T.Highly reactive metallic nickel (Ni) is readily oxidized by oxygen (O2) molecules even at low temperatures. The presence of the naturally resulting pre-oxide shell layer on metallic Ni nano materials such as Ni nanowires (NW) is responsible for degrading the deformation mechanisms and related mechanical properties. However, the role of the pre-oxide shell layer on the metallic Ni NW coupled with the complicated mechanical deformation mechanism and related properties have not yet been fully and independently understood. For this reason, the ReaxFF reactive force field for Ni/O interactions was used to investigate the effect of surface oxide layers and the size-dependent mechanical properties of Ni NWs under precisely controlled tensile loading conditions. To directly quantify the size dependent surface oxidation effect on the tensile mechanical deformation behaviour and related properties for Ni NWs, first, ReaxFF-molecular dynamics (MD) simulations were carried out to study the oxidation kinetics on the free surface of Ni NWs in a molecular O2 environment as a function of various diameters (D = 5.0, 6.5, and 8.0 nm) of the NWs, but at the same length. Single crystalline, pure metallic Ni NWs were also studied as a reference. The results of the oxidation simulations indicate that a surface oxide shell layer with limiting thickness of ∼1.0 nm was formed on the free surface of the bare Ni NW, typically via dissociation of the O-O bonds and the subsequent formation of Ni-O bonds. Furthermore, we investigated the evolution of the size-dependent intrinsic mechanical elastic properties of the core-oxide shell (Ni/NixOy) NWs by comparing them with their un-oxidized counterparts under constant uniaxial tensile loading. We found that the oxide shell layer significantly decreases the mechanical properties of metallic Ni NW as well as facilitates the initiation of plastic deformation as a function of decreasing diameter. The disordered oxide shell layer on the Ni NW's surface remarkably reduces the yield stress and Young's modulus, due to the increased softening effects with the decreasing NW diameter, compared to un-oxidized counterparts. Moreover, the onset of plastic deformation occurs at a relatively low yielding strain and stress level for the smaller diameter of oxide-coated Ni NWs in comparison to their pure counterparts. Furthermore, for pure Ni NWs, Young's modulus, the yielding stress and strain slightly decrease with the decrease in the diameter size of Ni NWs.Article Citation - WoS: 32Citation - Scopus: 34Effects of Oxidation on Tensile Deformation of Iron Nanowires: Insights From Reactive Molecular Dynamics Simulations(American Institute of Physics, 2016) Aral, Gürcan; Wang, Yun-Jiang; Ogata, Shigenobu; Van Duin, Adri C.T.The influence of oxidation on the mechanical properties of nanostructured metals is rarely explored and remains poorly understood. To address this knowledge gap, in this work, we systematically investigate the mechanical properties and changes in the metallic iron (Fe) nanowires (NWs) under various atmospheric conditions of ambient dry O2 and in a vacuum. More specifically, we focus on the effect of oxide shell layer thickness over Fe NW surfaces at room temperature. We use molecular dynamics (MD) simulations with the variable charge ReaxFF force field potential model that dynamically handles charge variation among atoms as well as breaking and forming of the chemical bonds associated with the oxidation reaction. The ReaxFF potential model allows us to study large length scale mechanical atomistic deformation processes under the tensile strain deformation process, coupled with quantum mechanically accurate descriptions of chemical reactions. To study the influence of an oxide layer, three oxide shell layer thicknesses of ∼4.81 Å, ∼5.33 Å, and ∼6.57 Å are formed on the pure Fe NW free surfaces. It is observed that the increase in the oxide layer thickness on the Fe NW surface reduces both the yield stress and the critical strain. We further note that the tensile mechanical deformation behaviors of Fe NWs are dependent on the presence of surface oxidation, which lowers the onset of plastic deformation. Our MD simulations show that twinning is of significant importance in the mechanical behavior of the pure and oxide-coated Fe NWs; however, twin nucleation occurs at a lower strain level when Fe NWs are coated with thicker oxide layers. The increase in the oxide shell layer thickness also reduces the external stress required to initiate plastic deformation.Article Citation - WoS: 48Citation - Scopus: 64Active Packaging of Ground Beef Patties by Edible Zein Films Incorporated With Partially Purified Lysozyme and Na 2edta(John Wiley and Sons Inc., 2011) Uysal Ünalan, İlke; Korel, Figen; Yemencioğlu, AhmetIn this study, antimicrobial activity of zein films incorporated with partially purified lysozyme and disodium ethylenediaminetetraacetic acid (Na 2EDTA) has been tested on selected pathogenic bacteria and refrigerated ground beef patties. The developed films containing 700μgcm -2 lysozyme and 300μgcm -2 Na 2EDTA showed antimicrobial activity on Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella typhimurium. The application of lysozyme and Na 2EDTA incorporated zein films on beef patties significantly decreased total viable counts (TVC) and total coliform counts after 5days of storage compared to those of control patties (P<0.05). Zein films incorporated with lysozyme and Na 2EDTA or Na 2EDTA alone significantly slowed down the oxidative changes in patties during storage (P<0.05). Redness indices of patties coated with zein films were significantly lower than those of uncoated control patties during storage (P<0.05). This study demonstrated the potential usage of zein films containing lysozyme and Na 2EDTA for active packaging of refrigerated meat products. © 2011 The Authors. International Journal of Food Science and Technology.Article Citation - WoS: 7Citation - Scopus: 7The Roles of Thiol Oxidoreductases in Yeast Replicative Aging(Elsevier Ltd., 2010) Hacıoğlu, Elise; Esmer, Işıl; Fomenko, Dmitri E.; Gladyshev, Vadim N.; Koç, AhmetThiol-based redox reactions are involved in the regulation of a variety of biological functions, such as protection against oxidative stress, signal transduction and protein folding. Some proteins involved in redox regulation have been shown to modulate life span in organisms from yeast to mammals. To assess the role of thiol oxidoreductases in aging on a genome-wide scale, we analyzed the replicative life span of yeast cells lacking known and candidate thiol oxidoreductases. The data suggest the role of several pathways in controlling yeast replicative life span, including thioredoxin reduction, protein folding and degradation, peroxide reduction, PIP3 signaling, and ATP synthesis. © 2010 Elsevier Ireland Ltd.Article Citation - WoS: 11Citation - Scopus: 13Liquid-Phase Oxidation of Carvacrol Using Zeolite-Encapsulated Metal Complexes(American Chemical Society, 2006) Güneş, Alev; Bayraktar, Oğuz; Yılmaz, SelahattinWe report here the use of zeolite-encapsulated metal (salpn) complexes as catalysts in the oxidation reaction of the natural compound carvacrol in acetonitrile with hydrogen peroxide as the oxidant. No previous studies on the oxidation of carvacrol in the presence of metal salpn complexes have been reported. By using a general flexible ligand method, Cr(III), Fe(III), Bi(III), Ni(II), and Zn(II) complexes of N,N′-bis(salicylidene)propane1,3-diamine (H2salpn) encapsulated in NaY zeolite were prepared. All catalysts were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM) analyses to confirm the complex encapsulation. The activities of all prepared catalysts for the oxidation of carvacrol and hydrogen peroxide were tested. The performances of all catalysts were compared on the basis of the leaching test results and carvacrol conversions. Thymohydroquinone and benzoquinones were observed as byproducts at high conversions of carvacrol. No product was formed in the absence of a catalyst. Fe(salpn)-NaY catalyst exhibited the highest carvacrol conversion of 27.6% with a yield of 22.0%, followed by Cr(salpn)-NaY catalyst with 23.5% carvacrol conversion and a yield of 17.6%. Other catalysts have shown relatively lower performances in terms of carvacrol conversion and leaching. The Cr(salpn)-NaY catalyst was found to be a more efficient catalyst than others on the basis of leaching and activity tests. With the selected catalyst Cr (salpn)-NaY, the effects of temperature and carvacrol/hydrogen peroxide molar ratio on carvacrol oxidation reactions were investigated. Increasing the temperature from 40 to 60 °C caused an increase in the thymoquinone yield from 6.2% to 16.0%. An increase in carvacrol/hydrogen peroxide molar ratio from 1 to 3 resulted in a decrease in the thymoquinone yield.