Mühendislik ve Doğa Bilimleri Fakültesi Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.13091/1624

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Bakır Anot Çamurundan Bakırın Liçinde Düşük Ötektik Noktalı Çözücü Kullanımının Araştırılması
(2021) Topçu, Mehmet Ali; Rüşen, Aydın; Kalem, Volkan
Bu çalışmada, pirometalurjik yöntemle metalik bakır üretiminin elektrokazanım aşamasında ortaya çıkan anot çamurundan bakır geri kazanımı üzerine çevre ve insan sağlığına duyarlı düşük ötektik noktalı çözücü (DES) kullanımı araştırılmıştır. Taguchi optimizasyon yöntemi kullanılarak liç sıcaklığı, liç süresi ve katı/sıvı oranı deneysel parametrelerin bakır geri kazanımı üzerine etkisi incelenmiştir. Kolin klorür (ChCl) ve ürenin 1:2 molar oranda karıştırılmasıyla hazırlanan DES çözücüsü ile yapılan liç işlemleri sonunda optimum şartlar; 95 oC’liç sıcaklığı, 2 saat liç süresi ve 1/20 katı/sıvı oranı olarak belirlenmiş ve bu şartlarda %98 bakır geri kazanımı elde edilmiştir. Yapılan bu çalışma ile ChCl-üre karışımıyla hazırlanan DES çözücüsünün anot çamurundan bakır geri kazanımı için çevreci bir çözücü adayı olabileceği ortaya konulmuştur.
Citation - WoS: 22
Citation - Scopus: 22
Boriding of Laser-Clad Inconel 718 Coatings for Enhanced Wear Resistance
(Mdpi, 2021) Lindner, Thomas; Günen, Ali; Toeberling, Gerd; Vogt, Sabrina; Karakaş, Mustafa Serdar; Loebel, Martin; Lampke, Thomas
Nickel-based superalloys are particularly suitable for applications under corrosive conditions. Economic advantages can be achieved by limiting the use of materials to the surface region. Furthermore, the tribological property profile can be significantly improved by surface hardening. In the present study, the possibility of a process combination comprising a coating and a surface hardening technology was investigated. For this purpose, Inconel 718 coatings were applied to austenitic stainless steel by laser cladding. Subsequently, a thermochemical surface hardening by boriding was carried out. Scanning electron microscopic (SEM) examinations were performed to evaluate the microstructure. The phase composition was determined by means of X-ray diffraction (XRD) for the different states of the coating system. The influence of thermochemical hardening was investigated for different wear conditions. The increase in microhardness and wear resistance clearly demonstrates the utilization potential of the presented process combination.
Citation - WoS: 37
Citation - Scopus: 38
Characteristics and High Temperature Wear Behavior of Chrome Vanadium Carbide Composite Coatings Produced by Thermo-Reactive Diffusion
(ELSEVIER SCIENCE SA, 2020) Günen, Ali; Kalkandelen, Müge; Gök, Mustafa Sabri; Kanca, Erdoğan; Kurt, Bülent; Karakaş, Mustafa Serdar; Çetin, Melik
In this study, Cr-V-C composite carbide layers were grown on the surface of a GGG-80 ductile iron using thermoreactive diffusion (TRD). The TRD process was carried out at temperatures of 900, 1000, and 1100 degrees C for 1 h using nano-sized Fe-V and Fe-Cr powders. The coatings were characterized by X-ray diffractometry (XRD), 2D profilometry, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), microhardness measurements, nanoindentation, and wear tests. The wear tests were performed on untreated and coated samples using a ball-on-disc type wear tester under 10 N load at four different temperatures (25 degrees C, 250 degrees C, 500 degrees C and 750 degrees C) against a 6-mm WC ball. Metallographic investigations revealed that the graphite nodules near the surface were dissolved as a result of the TRD process. Depending on the TRD process temperature, a coating with a thickness of 12-36 mu m, hardness of 24.14-31.38 GPa, and elastic modulus of 198-233 GPa was obtained. An increase in process temperature increased the thickness, hardness, and elastic modulus of the obtained Cr-V-C layers, which resulted in low friction coefficient values and decreased wear rates. Although all coated samples showed improved wear resistance in all wear test conditions, the wear rates were significantly increased at 750 degrees C due to flaking.
Citation - WoS: 2
Citation - Scopus: 1
A Combinatorial Study on Zno-In2o3 System: the Effects of Different Postgrowth Annealing Conditions on Optical and Electrical Properties
(Elsevier Science Sa, 2022) Can, Hilal Aybike; Öztürk, Tayfur; Akyıldız, Hasan
ZnO-In2O3-SnO2 (ZITO) thin film library was produced via the combinatorial approach. The films were deposited using a magnetron sputtering system. Varying ZITO compositions were obtained in a single deposition run by employing a custom-made triangular type of substrate carrier magazine. The effect of various postgrowth annealing atmospheres on the electrical and optical properties of the films were ex-amined. Air, Ar, forming gas (Ar+4 vol% H-2), and successive annealing under forming gas + argon atmo-spheres were studied. Room temperature (RT) deposited films were identified either crystalline or amorphous depending on the location of the substrate on the holder. All these samples exhibited average visible transmittance (T-vis) below 75 % and sheet resistance (R-S) higher than 50 S2/? . Annealing under air atmosphere improved the optical and electrical properties of the films significantly, but not simultaneously for the same composition. Although better optical improvement was achieved by annealing under Ar and increase in electrical conductivity after annealing under forming gas, optimum properties have been ob-tained with the latter condition. T-vis values above 85 % and R-S values below 50 S2/? were attained. On the other hand, successive annealing did not provide any advantage in reaching optimal samples when com-pared to single gas atmosphere annealings. Further, increasing the annealing temperature were found to be beneficial particularly for the conductivity of many compositions. Finally, this study has introduced a systematic approach to produce transparent conductive oxide thin films with reduced indium content that can be suitable for many optoelectronic applications. (C) 2022 Published by Elsevier B.V.
Compression and Interlaminar Shear Properties of Nanoparticle Doped Hybrid Nanofiber Interleaved Glass/Epoxy Composites
(2021) Metin, Fatih; Avcı, Ahmet
The effects of SiC-Fe3O4 nanoparticles doped electrospun Polysulfone (PSF) nanofibers on compressive and interlaminar shear strength of glass/epoxy composite laminates were investigated in this study. Pure PSF and hybrid PSF nanofibers were produced by the electrospinning process. Nanofiber interleaved glass/epoxy composite laminates were manufactured by using a vacuum-assisted hand-lay-up method. The addition of SiC-Fe3O4 nanoparticles into PSF nanofibers improved the tensile properties of nanofiber mats. The results revealed that PSF hybrid nanofiber interleaving increased the compressive and interlaminar shear strengths of composite laminates up to 26% and 12.4%, respectively.
Citation - WoS: 45
Citation - Scopus: 44
A Correlative Four-Dimensional Study of Phase-Separation at the Subnanoscale To Nanoscale of a Ni-Al Alloy
(PERGAMON-ELSEVIER SCIENCE LTD, 2019) Plotnikov, Elizaveta Y.; Mao, Zugang; Baik, Sung-Il; Yıldırım, Mehmet; Li, Yongsheng; Cecchetti, Daniel; Seidman, David N.
The temporal evolution of ordered gamma'(L1(2))-precipitates precipitating in a disordered gamma(f.c.c.) matrix is studied in extensive detail for a Ni-12.5 Al at.% alloy aged at 823 K (550 degrees C), for times ranging from 0.08 to 4096 h. Three-dimensional atom-probe tomography (3-D APT) results are compared to monovacancy-mediated lattice-kinetic Monte Carlo (LKMC1) simulations on a rigid lattice, which include monovacancy-solute binding energies through 4th nearest-neighbor distances, for the same mean composition and aging temperature. The temporal evolution of the measured values of the mean radius, (R(t)>, number density, aluminum supersaturations, and volume fraction of the gamma'(L1(2))-precipitates are compared to the predictions of a modified version of the Lifshitz-Slyozov diffusion-limited coarsening model due to Calderon, Voorhees et al. The resulting experimental rate constants are used to calculate the Gibbs interfacial free-energy between the gamma(f.c.c.)- and gamma'(L1(2))-phases, which enter the model, using data from two thermodynamic databases, and its value is compared to all exiting values. The diffusion coefficient for coarsening is calculated utilizing the same rate-constants and compared to all archival diffusivities, not determined from coarsening experiments, and it is demonstrated to be the inter-diffusivity, (D) over tilde, of Ni and Al. The monovacancy-mediated LKMC1 simulation results are in good agreement with our 3-D APT data. The compositional interfacial width, for the (100)-interface, between the gamma(f.c.c.)- and gamma'(L1(2))-phases, decreases continuously with increasing aging time and < R(t)>, both for the 3-D APT results and the monovacancy-mediated LKMC1 simulations, in disagreement with an ansatz intrinsic to the trans-interface diffusion-controlled coarsening model, which assumes the exact opposite trend for binary alloys. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Çözücü ve Isıl İşlem Sürecinin Mos2 İnce Filmlerinin Yapısal Özelliklerine Etkisinin İncelenmesi
(2022) Akyol, Mustafa; Kıvrak, Burak
Son yıllarda, geçiş metali kalkojenleri (GMK) kendilerine özgü fiziksel ve kimyasal özelliklerinden dolayı çokça çalışılan malzeme gruplarından biri olmuştur. GMK’ler, optoelektronik uygulamalarda, hidrojen evrim reaksiyonları, enerji depolama sistemleri, güneş pili uygulamalarında ve radar emici sistemlerde sıkça kullanılmaktadır. Bu çalışmada, farklı çözücüler ve ısıl işlem süreçleri kullanılarak üretilen GMK grubundan olan MoS2 ince filmlerinin yapısal özellikleri araştırılmıştır. İnce filmler sol-gel spin kaplama yöntemi ile üretilmiştir. Filmlerin kristalizasyonu farklı sıcaklık değerlerinde vakum altında tutulan ve azot gazı (N2) akışı sağlanan fırın sisteminde sağlanmıştır. Isıl işlem sıcaklığı ve çözücü kimyasalın etkisi yapısal analiz metotları ile değerlendirilmiştir. Bu kapsamda, X-ışını kırınım metodu (XRD) ve Raman saçınım ve taramalı elektron mikroskop (SEM) metodu filmlerin yapısal analizlerinin yapılmasında kullanılmıştır.
Citation - WoS: 33
Citation - Scopus: 34
Crystal Reorientation and Amorphization Induced by Stressing Efficient and Stable P-I Vacuum-Processed Mapbi(3) Perovskite Solar Cells
(Wiley, 2021) Kaya, İsmail C.; Zanoni, Kassio P. S.; Palazon, Francisco; Sessolo, Michele; Akyıldız, Hasan; Sönmezoğlu, Savaş; Bolink, Henk J.
Herein, the long-term stability of vacuum-deposited methylammonium lead iodide (MAPbI(3)) perovskite solar cells (PSCs) with power conversion efficiencies (PCEs) of around 19% is evaluated. A low-temperature atomic layer deposition (ALD) Al2O3 coating is developed and used to protect the MAPbI(3) layers and the solar cells from environmental agents. The ALD encapsulation enables the MAPbI(3) to be exposed to temperatures as high as 150 degrees C for several hours without change in color. It also improves the thermal stability of the solar cells, which maintain 80% of the initial PCEs after aging for approximate to 40 and 37days at 65 and 85 degrees C, respectively. However, room-temperature operation of the solar cells under 1sun illumination leads to a loss of 20% of their initial PCE in 230h. Due to the very thin ALD Al2O3 encapsulation, X-ray diffraction can be performed on the MAPbI(3) films and completed solar cells before and after the different stress conditions. Surprisingly, it is found that the main effect of light soaking and thermal stress is a crystal reorientation with respect to the substrate from (002) to (202) of the perovskite layer, and that this reorientation is accelerated under illumination.
Cucoo2 Parçacıkları ile Yeni Metal Oksit Kompozitlerin Üretimi ve Kirleticilerin Uzaklaştırılmasında Kullanılması
(2022) Dursun, Sami
Elektro-eğirme metodu ile sentezlenen metal oksit nanofiberleri üzerine hidrotermal yöntem ile sentezlenen delafosit parçacıkları ağırlıkça farklı oranlarda dekore edilerek heteroyapılı fotokatalizörler elde edilmiştir. Kalay kaynaklı metal oksitin, bakır kaynaklı delafositin ve oluşturdukları heteroyapılı malzemelerin mikroyapısal, morfolojik, optik ve elektrokimyasal özellikleri karakterize edilmiş ve bu malzemelerin başarılı bir şekilde üretildiği tespit edilmiştir. Ayrıca farklı ağırlık yüzdelerinde delafosit dekore edilen heteroyapıların aktiviteler sistematik olarak incelenmiş, en iyi sonucu veren numunenin Ağ.%0,40 delafosit içeren metal oksit nanofiberi olduğu görülmüştür. Bu fotokatalizör kullanılarak görünür ışık ışıması altında 90 dk’da metilen mavisi (MM) boyasının neredeyse tamamına yakınının (%95,8) bozunduğu tespit edilmiştir. Metal oksit nanofiber fotokatalizörüne kıyasla delafosit dekore edilmiş metal oksit fotokatalizörü MM boyasının bozunma hızında %58,5’lik bir artış sağlamıştır. Fotokatalitik aktivitedeki bu gelişme; metal oksit nanofiberinin dar bant aralığına sahip delafosit parçacıkları ile oluşturduğu heteroyapının daha fazla ışığı soğurumu sayesinde daha fazla e--h+ çifti oluşturması ile ilişkilendirilebilir.
Derin Öğrenme Teknikleri Kullanılarak Yüz Tanıma Tabanlı Müşteri Doğrulama ile Bankamatiklerde Sahtekârlık Tespiti
(Konya Teknik Üniversitesi, 2019) Yıldırım, Mehmet; Uymaz, Sait Ali
Günümüzde bankamatikler banka müşterilerinin finansal işlerini yerine getirmeleri için çok yaygın olarak kullanılmaktadır. Bankamatikler manyetik bir kart ve dört haneli bir PIN ile müşteri doğrulama sağladıktan sonra kullanıma açılmaktadır. Bu durum, sahtekârlara bankamatik donanımlarını kullanarak para çalmak için fırsat oluşturmaktadır. Dijital bankacılık platformlarının sayısı arttıkça banka müşterileri banka şubelerini fiziki olarak ziyaret etmek zorunda kalmadan hesap açabilir hale gelmiştir. Benzer şekilde banka kartları müşterilere kurye aracılığı ile şubeye gelmeye gerek kalmadan ulaştırılabilmektedir. Bu durum, kötü niyetli kurye çalışanlarına kart bilgilerini çalmak için fırsat vermektedir. Buna ek olarak banka müşterileri genellikle dört haneli PIN kodunu; doğum tarihi, yaşadıkları şehirlerin plakaları ve ulusal kimlik numaraları gibi hatırlanması kolay şifrelerden seçmektedir. Sahtekârlar bu kodu tahmin edebilmekte veya kendilerini banka çalışanı gibi tanıtıp bu kodları kolayca elde edebilmektedir. Banka kartı ve bankamatiklerdeki buna benzer dezavantajlar nedeniyle dolandırıcılar banka müşterilerinden kolayca para çalma potansiyeline sahiptir. Bu çalışmada, bankamatiklerde ilgili sahtekârlıkların önüne geçmek için bankaların standart şifre esaslı kimlik doğrulama yöntemine ek olarak yüz tanıma teknolojilerini kullanarak bir kimlik doğrulama yöntemi ortaya konulmuştur. Müşteri bankada hesap açarken müşteriden alınan yüz örnekleri derin öğrenme modelinden geçirilerek benzersiz bir kimlik üretilip kaydedilecektir. Daha sonra müşteri bankamatikte işlem yaparken tekrar alınan yüzler derin modelden geçirilip çıkan sonuç, kaydedilen kimlik ile karşılaştırılacaktır. Bu karşılaştırma sonucu, belirlenen eşik değerinin altında kalırsa müşteri doğrulaması sağlanacaktır. Aksi takdirde, kart ve PIN bilgisiyle dahi bankamatiğe giriş sağlanamayacaktır. Böylece bankaların bankamatik aracılığıyla verdikleri hizmetlerde çok daha güvenli bir platform sunmaları sağlanacaktır.
Citation - WoS: 23
Detrimental Effects of Commonly Used Textile Dyes on the Aquatic Environment and Human Health - a Review
(Parlar Scientific Publications (P S P), 2022) Yıldırım, Özlem Altıntaş; Bahadır, Mufit; Pehlivan, Erol
Properties and hazards of various dye and pigment families used during textile manufacturing (like yarns, cloths, nonwovens, outerwear, cashmere and rugs) are already reported in the literature. Synthetic organic dyes are currently known as water pollutants. Such dyes are widely used in a variety of industries, including textiles, tanning, cosmetics, and food stuff, as well as in human and veterinary healthcare. They are classified as reactive, dispersed, indigo, azo, sulphur, and basic dyes. They are found in liquid wastes from textile washing and pose a serious risk to the receiving water environment's quality, if not purified. Because of their widespread use and large-scale production, various synthetic dyes have found their way into various parts of the water and soil ecosystems. In fact, because these dyes and pigments are not biodegradable, their presence can cause drastic changes in the ecological conditions of aquatic animals and plants. This will have a negative impact on the aquatic environment's stability, resulting in serious and significant damages (algal blooms, oxygen depletion, colour, turbidity and bad smells), long-term dangers (persistence, bioaccumulation of cancer-causing aromatic products, and emergence of chlorination side products), and carcinogenic and teratogenic effects. This overview picks up scientific information on possible application fields, toxic effects, sources, environmental presence and the eventual demise of synthetic organic dyes, as well as the ecological effects of synthetic natural dyes existence in the general environment.
Citation - WoS: 36
Citation - Scopus: 34
A Dopant-Free 2,7-Dioctyl[1]benzothieno[3,2 (c8-Btbt) Hole Transporting Layer for Highly Stable Perovskite Solar Cells With Efficiency Over 22%
(Royal Soc Chemistry, 2022) Kaya, İsmail Cihan; Özdemir, Resul; Usta, Hakan; Sönmezoğlu, Savaş
In this study, for the first time, n-i-p PSCs were fabricated using dopant-free 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) as the solution-processed hole transporting layer (HTL). The power conversion efficiency (PCE) of the optimized device with the C8-BTBT film that favored edge-on molecular alignment was 22.45% with negligible hysteresis. A thinner dopant-free C8-BTBT HTL effectively protected the perovskite layer from moisture resulting in better shelf-life stability for un-encapsulated PSCs, which maintained >80% of its initial PCE (after a period of 120 days) at a relative humidity level of 40-45%. In addition, the C8-BTBT-based PSCs kept their high performance with no obvious PCE loss at 60 degrees C for 20 days in the ambient atmosphere and retained 82% of their initial PCE at 85 degrees C for 10 days. Overall, our findings revealed that a thin solution-processed C8-BTBT HTL plays a critical role not only in hole extraction and transport but also in greatly improving the ambient and thermal stability of n-i-p PSCs.
Effect of Ho Substitution on Structural, Magnetic and Magnetocaloric Properties of Co(crfe)o-4
(SPRINGER, 2021) Kıvrak, Burak; Gülkesen, Semiramis; Ayaş, Ali Osman; Akyol, Mustafa; Ekicibil, Ahmet
In this study, structural, magnetic and magnetocaloric properties of Ho-substituted Co(CrFe)O-4 spinel compounds produced by the sol-gel method were investigated. The Ho concentration in Co(CrFe)O-4 spinel structure was changed from 0 to 20% by 5% steps. It is observed that the Ho3+ ions create a new phase HoCrO3/HoFeO3 in the host spinel lattice. SEM images of samples indicate that the average particle size increases with Ho content. The paramagnetic to ferro-/ferrimagnetic phase transition temperature increases from 312 to 344 K with Ho content. While the fluctuation in saturation magnetization of samples was detected at low temperature, it almost becomes a linear change with the Ho content. The maximum magnetic entropy change under 7 T magnetic field was found as - 1.39, - 1.50, - 1.20, - 0.98 and - 0.91 J/kgK for Ho-free, 5, 10, 15 and 20 wt% Ho content in CoCrFeO4 spinel structure, respectively.
Citation - WoS: 20
Citation - Scopus: 21
Effect of Oil Pressure Upon Filament Wound Basalt/Glass Fibers Hybrid Polymer Based Composite Pipes Subjected To Low Velocity Impact
(Elsevier Sci Ltd, 2022) Demirci, Mehmet Turan; Şahin, Ömer Sinan
In this study, low-velocity impact tests were applied to E-glass fiber (GFR) and basalt fiber reinforced (BFR) filament-wound hybrid composite pipes. The BFR/GFR hybrid pipes were subjected to low-velocity impact tests when they were oil-unfilled, oil-filled at 0 bar (unpressurized oil) and low oil pressure at 5 bar. Impact energies were applied as 15 J, 20 J and 25 J, respectively. After the experiments, the dynamic behaviors and damage formation within the samples were evaluated in terms of type and severity.
Citation - WoS: 3
Citation - Scopus: 3
Effect of Surface Finish on the Colour Anodising of Ti-6al at Various Voltages
(Taylor & Francis Ltd, 2022) Kocabaş, Mustafa
In this study, the colour anodising of a Ti-6Al-4V alloy in 0.05 M H3PO4 was investigated in the voltage range of 40-100 V. The Ti-6Al-4V substrates were anodised under two initial surface conditions: ground and unground. By means of ground samples, the native oxide layer was removed before anodising using conventional mechanical grinding techniques. After anodising, the changes in surface chemistry and topography were evaluated by performing Field Emission Scanning Electron Microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Depending on the initial surface finish (ground and unground) and the anodising voltage, different interference colours were obtained on the anodised surfaces. At low anodising voltages, the surfaces displayed relatively compact structures whereas higher voltages resulted in the formation of porosity, cracks, and blisters in both conditions. These changes also influenced the corrosion behaviour. The samples which were ground prior to anodising exhibited higher resistance to corrosion compared to the unground samples.
Citation - WoS: 54
Citation - Scopus: 59
Effect of the Boriding Environment on the Wear Response of Laser-Clad Alcocrfeni High Entropy Alloy Coatings
(Elsevier Science Sa, 2022) Günen, Ali; Lindner, T.; Karakas, M. S.; Kanca, E.; Toberling, G.; Vogt, S.; Lampke, T.
Laser-clad AlCrFeCoNi high entropy alloy (HEA) coatings, produced on the surface of AISI 316 L stainless steel, were pack-borided at 1000 ?C for 4 h in open air, high-purity Ar and vacuum environments. The HEA, which had an initial hardness of 6.14 +/- 2.06 GPa, formed a complex boride layer consisting of (CoFe)B-2, (CrFe)B(2 )and Cr(2)Ni(3)B(6 )phases on its surface, with hardness ranging from 15.95 +/- 0.7 to 20.15 +/- 4.50 GPa as a result of the boriding process. While the greatest boride layer thickness was obtained in the sample borided in vacuum, the highest surface hardness was obtained in the sample borided in air. The borided coatings showed improved wear resistance and lower friction values compared to the untreated control samples, both at 25 ?C and 650 ?C. The borided coatings also showed reduced coefficients of friction at 650 ?C. The wear losses at 650 ?C significantly exceeded those at 25 ?C.
Citation - WoS: 23
Citation - Scopus: 22
Effect of Thermal Degradation on the Properties and Wear Behavior of Cr-V Composite Coatings Grown on Ductile Iron
(ELSEVIER SCIENCE SA, 2021) Günen, Ali; Kanca, Erdoğan; Karakaş, Mustafa Serdar; Gök, Mustafa Sabri; Kalkandelen, Müge; Kurt, Bülent; Karahan, İsmail Hakkı
The thermal fatigue behavior of chromium vanadium carbide (Cr - V - C) coatings and the wear of the coatings after thermal fatigue cycling was studied. The Cr - V - C coatings were grown on the surface of a ductile iron using thermo-reactive diffusion (TRD) and subjected to thermal fatigue in the temperature range of 25 to 750 degrees C for up to 500 cycles. Characterizations were made using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, microhardness measurements and wear tests. The Cr - V - C coated samples displayed superior thermal fatigue and wear resistance compared to the untreated ductile iron, mainly due to the dissolution of graphite nodules in the vicinity of the surface during TRD. The dissolution of graphite reduced the possibility of failure initiating from graphite nodules and graphite-matrix interfaces. Increasing the number of cycles resulted in increased flaking and decreased wear resistance in both the Cr - V - C coatings as well as the untreated ductile iron. Although much of the Cr V C coating was lost (due to flaking) after thermal cycling, the absence of graphite near the surface still provided improved resistance to wear in the TRD-treated samples. The results of this study indicate that TRD coatings hold great promise for use in the industrial applications.
Citation - WoS: 4
Citation - Scopus: 4
Effect of Y Addition on the Structural Properties and Oxidation Behavior of Fe60al40-Nyn Alloys (n=1, 3, and 5 At.%)
(Taylor & Francis Ltd, 2022) Yıldırım, Mehmet; Ataş, Mehmet Şahin; Akdeniz, M. Vedat; Mekhrabov, Amdulla O.
The influence of Y addition on the microstructural features, phase relationships, hardness, magnetic behaviour and cyclic oxidation performance of Fe60Al40-nYn alloys (n = 1, 3, and 5 at.%) has been examined in detail. Al8Fe4Y phase formed even at 1 at.% Y addition because of the limited solid solubility of Y in the FeAl-based phase. For all the examined compositions, the Al8Fe4Y phase developed a eutectic with the FeAl-based phase and its volume fraction increased with increasing Y up to 5 at.%, which is near the eutectic composition. The mean microhardness values increased with increasing Y content for both as-cast and heat-treated samples. Cyclic oxidation tests revealed that the oxidation rate and scale thickness increased with increasing Y content. alpha-Al2O3 was the main surface oxide for all compositions. theta-Al2O3 was also formed with relatively low amount. An internal oxidation layer composed of mixed Al/Y oxides was observed beneath the surface layer.
Citation - WoS: 66
Citation - Scopus: 68
Efficient Vacuum-Deposited Perovskite Solar Cells With Stable Cubic Fa(1)(-X)ma(x)pbi(3)
(AMER CHEMICAL SOC, 2020) Gil-Escrig, Lidon; Dreessen, Chris; Kaya, İsmail Cihan; Kim, Beom-Soo; Palazon, Francisco; Sessolo, Michele; Bolink, Henk J.
Preparation of black formamidinium lead iodide (FAPbI(3)) requires high-temperature annealing and the incorporation of smaller A-site cations, such as methylammonium (MA(+)), cesium, or rubidium. A major advantage of vacuum processing is the possibility to deposit perovskite films at room temperature (RT), without any annealing step. Here we demonstrate stabilization of the cubic perovskite phase at RT, in a three-source co-sublimation method. We found that the MA(+) incorporation is a self-limiting process, where the amount of MA(+) which is incorporated in the perovskite is essentially unvaried with increasing MAI deposition rate. In this way a phase-pure, cubic perovskite with a bandgap of 1.53 eV can be obtained at room temperature. When used in fully vacuum-processed perovskite solar cells, PCEs up to 18.8% are obtained. Despite the presence of MA(+), the solar cells were found to be thermally stable and maintained 90% of their initial efficiency after 1 month of continuous operation.
Citation - WoS: 7
Citation - Scopus: 11
Efficient Vapor-Liquid Synthesis of Copper Doped Zinc Oxide (cu:zno) Nanonails With Highly Homogeneous Dopant Distribution
(ELSEVIER SCI LTD, 2019) Altıntaş Yıldırım, Özlem
Copper doped zinc oxide (Cu:ZnO) nanonails with uniformly distributed Cu ions through the nail structure were synthesized via a vapor-liquid-solid technique using seed Cu:ZnO nanoparticles. The seed nanoparticles were prepared with a simple precipitation method. The structure and morphology of nanonails and the distribution of Cu ions were investigated using X-ray diffraction, electron energy loss spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and elemental mapping analysis. The defect states in the Cu:ZnO nanonails were characterized by room temperature photoluminescence (PL) spectra. The obtained Cu:ZnO nanonails have single phase wurtzite structure of ZnO and incorporated copper ions are in the Cu2+ oxidation state. SEM and TEM micrographs revealed that nanostructures with well-defined nail morphology composed of a hexagonal cap (similar to 350 nm in diameter) and a prismatic shaft (similar to 550 nm in diameter) connected with cylindrical neck (similar to 250 nm in diameter). Both SEM and TEM elemental mapping analysis proved that the usage of Cu:ZnO seed nanoparticles resulted in highly homogeneous distribution of Cu ions into ZnO nanonails. High crystallinity of the Cu:ZnO nanonails was revealed with PL spectra composed of predominant second order diffraction peak and near band edge of UV emission peak and also weak defect related deep level green and violent emission peaks.

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Browsing Mühendislik ve Doğa Bilimleri Fakültesi Koleksiyonu by Department "Fakülteler, Mühendislik ve Doğa Bilimleri Fakültesi, Metalurji ve Malzeme Mühendisliği Bölümü"