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  • Öğe
    Cellular response to calcium phosphate cements
    (Elsevier, 2020) Cecen, Berivan; Kalemtaş, Ayşe; Topates, Gulsum; Kozaci, Leyla Didem
    Calcium orthophosphate (COP) ceramics have been investigated as bone repair materials for many decades. The first in vivo application of these materials was accomplished in 1920 to test tricalcium phosphate performance as a bone substitute. Since this first attempt, various COPs were investigated on animals to shed light on their effect on the healing behavior of bones. Calcium phosphate cements are currently receiving a great deal of interest especially for the hard tissue repair, augmentation, and regeneration applications due to their attractive characteristics such as biocompatibility, ease of shaping, osteoconductivity, and biodegradability.
  • Öğe
    Effect of diffusion annealing on duplex coated pure titanium produced by hot-dip aluminizing and micro-arc oxidation
    (ELSEVIER SCIENCE SA, 2022) Yürektürk, Yakup
    In the present study, an Al2O3 ceramic coating was formed on a pure titanium surface with the application of the duplex coating technology produced by combining hot-dip aluminizing (HDA) and micro-arc oxidation (MAO) processes. Due to the porous nature of MAO coating with the structural and mechanical differences between the MAO (Al2O3) and HDA layers (Al, Al3Ti), diffusion annealing treatment was applied to duplex coated (HDA + MAO) titanium samples. With the diffusion annealing treatment, a composite layer with a thickness of about 125 mu m was formed beneath the modified MAO coating, which showed a denser structure by penetrating TiO2 into the MAO. MAO coatings with and without diffusion annealing exhibited compressive residual stresses with values of-1530 and-850 MPa, respectively. Microhardness and elastic modulus of the diffusion annealing-treated MAO coating reached 1230.1 HV and 241.3 GPa, respectively. The diffusion annealing-treated MAO coating provided-29% less coefficient of friction and-8.4 times greater relative wear resistance than that of MAO coating without diffusion annealing.
  • Öğe
    Evaluation of mechanical behavior, bioactivity, and cytotoxicity of chitosan/akermanite-TiO2 3D-printed scaffolds for bone tissue applications
    (Elsevier Ltd, 2022) Bulut, Büşra; Duman, Şeyma
    This report aimed to evaluate the mechanical behavior, bioactivity, and cytotoxicity of novel chitosan/akermanite-TiO2 (CS/AK/Ti) composite scaffolds fabricated using the 3D-printing method. The morphological and structural properties of these scaffolds were characterized by Fourier transform spectroscopy (FTIR) and scanning electron microscopy (SEM). The mechanical behavior was examined by measuring the compressive strength, while the bioactivity was estimated in the simulated body fluid (SBF), and also the cytotoxicity of the scaffolds was assessed by conducting cell culturing experiments in vitro. It was found that the mechanical properties were considerably affected by the amount of TiO2. The scaffolds had the possessed bone-like apatite forming ability, which indicated high bioactivity. Furthermore, L929 cells spread well on the surface, proliferated, and had good viability regarding the cell behaviors. The outcomes confirmed that the morphological, biological, and mechanical properties of developed 3D-composite scaffolds nearly mimicked the features of natural bone tissue. In summary, these findings showed that the 3D-printed scaffolds with an interconnected pore structure and improved mechanical properties were a potential candidate for bone tissue applications.
  • Öğe
    A simple manufacturing process of the miniaturised octopus-inspired underwater soft robotic grippers
    (Taylor and Francis Ltd., 2022) Eroğlu, Murat; Şam Parmak, Ebru Devrim
    In this article, we show a new fabrication technique based on CNC machining for the miniaturised octopus-inspired underwater soft robotic grippers. This method provides practical and scale-up production of these grippers. Polydimethylsiloxane/polyethylene terephthalate (PDMS/PET) film (similar to 7 x 7 cm(2)) consisting of concave structures in two different geometries (outer and inner) with the suction-based property was produced by using our suggested manufacturing method. The highest adhesion force was obtained on the flat deformable object by the outer concave structured gripper (similar to 6 kPa) and the flat rigid object by the inner concave structured gripper (similar to 12 kPa). Moreover, both the grippers exhibit switchable adhesion by changing the retraction velocity as well as high repeatability (over 100 cycles) in underwater conditions. This method will enable practical fabrication of the miniaturised octopus-inspired underwater soft robotic grippers. The proposed manufacturing technique will facilitate the widespread use and commercialisation of the grippers.
  • Öğe
    Boron and nitrogen doping in graphene: an experimental and density functional theory (DFT) study
    (IOP Publishing, 2020) Kaykılarlı, Cantekin; Uzunsoy, Deniz; Şam Parmak, Ebru Devrim; Fellah, Mehmet Ferdi; Çakır, Özgen Çolak
    Boron (B) and Nitrogen (N) doped few layer graphene (BNG) is directly synthesized via electric arc discharge (EAD) method. NH3 and BCl3 gas mixtures are used in the synthesis atmosphere. Raman spectroscopy is used to determine graphene's purity and number of layers. The investigation of structure and morphology of pristine graphene and BNG are carried out via Transmission Electron Microscopy (TEM). The presence of B and N in the structure of graphene is detected by Energy Dispersive X-ray Spectroscopy (EDS) analysis. Elemental mapping show that N and B are distributed homogeneously in the graphene structure. It is observed that doping process did not affect the positions of the D, G and 2D bands in the Raman spectroscopy. The effect of doping on the number of layers of graphene is found negligible. TEM results exhibit that pristine graphene and BNG have 5 to 6 layers. Besides, the theoretical calculations based on Density Functional Theory (DFT) are employed to support experimental studies. Theoretical results based on DFT showed that bonding of B and N is favorable.
  • Öğe
    Modelling the quasi-static flexural behaviour of composite sandwich structures with uniform- and graded-density foam cores
    (Elsevier, 2021) Liu, Haibao; Liu, Jun; Kaboğlu, Cihan; Zhou, Jin; Kong, Xiangshao; Li, Shipeng; Blackman, Bamber R. K.; Kinloch, Anthony J.; Dear, John P.
    In-service, composite sandwich structures, which consist of fibre-composite skins (also termed face-sheets) adhesively bonded to a polymeric foam core, can encounter extreme quasi-static flexural loading that may cause serious damage to the sandwich structure. The ability to model the flexural behaviour of such structures can lead to improved designs and more efficient maintenance procedures. In the present research, a three-dimensional finite-element analysis (FEA) model is developed to predict the flexural behaviour of such sandwich structures using a commercial software package (i.e. Abaqus/Explicit). The high-fidelity FEA simulation combines an elastic-plastic (E-P) damage model of the composite skins together with a crushable foam-core damage model. The E-P damage model is implemented with a user subroutine to capture the damage, such as plastic deformation of the matrix and matrix cracking, fibre fracture and delamination cracking of the composite skins. The crushable foam model is used to predict (a) the mechanical response of the crushed foam core, (b) the induced damage from ductile fracture due to growth, coalescence and fracture of the cells and (c) the induced damage from shear fracture of the foam due to plastic shear-band localisation. Results from the modelling studies, such as the loading response and the damage mechanisms, are discussed and compared with the experimental results obtained from the sandwich structures manufactured with both uniform- and graded-density foam cores but which all have the same average core density. Good agreement is achieved between the experimental results and the predictions from the numerical modelling simulations.
  • Öğe
    Influence of Electrolyte Compositions and Electrical Parameters on Thermal Properties of Micro-Arc Oxidized AZ91 Alloy
    (Springer, 2021) Selvi, Ekin; Muhaffel, Faiz; Yürektürk, Yakup; Vanli, Ali Serdar; Baydogan, Murat
    In this study, AZ91 Mg alloy was micro-arc oxidized using different voltages in silicate- and aluminate/phosphate-based (dual) electrolytes that included K2ZrF6 or Na2ZrO3 as the Zr source for synthesizing ZrO2 in the micro-arc oxidation (MAO) coatings. Structural characterizations were done by using scanning electron microscopy and x-ray diffraction techniques. MAO coating characteristics of different samples were compared by measuring coating thickness, surface roughness, average pore size, and total pore fraction. Both hardness and pull-off tests were conducted to characterize the mechanical properties of the coatings. Thermal conductivity measurements and thermal shock tests were also carried out to evaluate the effect of the electrolyte composition and the type of Zr containing compound. It was found that the equivalent thermal conductivity of the MAOed samples can be reduced up to 30% compared to the bare AZ91 alloy. The decrease of the thermal conductivity was mainly attributed to formation of a thicker and denser MAO coating, and the incorporation of ZrO2 phase into the fabricated MAO coating. Finally, increased thermal shock resistance was strongly correlated with a lower hardness and higher cohesive strength of the MAO coating, which also leads to smaller crack formation and spallation-free surface characteristics.
  • Öğe
    Mechanical and antibacterial properties of ZnO/chitosan bio-composite films
    (WALTER DE GRUYTER, 2021) Kalemtaş, Ayşe; Koçer, Hasan Basri; Aydın, Ahmet; Terzioğlu, Pınar; Aydın, Gülsüm
    In the current study, ZnO/chitosan bio-composite films were produced via solution-casting method. Two different ZnO powders, micrometer (d(50) approximately equal to 1.5 mu m) and nanometer sized (d(50) approximately equal to 100 nm), were used to investigate the effect of ZnO particle size and concentration (0, 2, and 8% w/w of chitosan) on the mechanical and antibacterial properties of the ZnO/chitosan bio-composite films. The incorporation of the ZnO powders into the chitosan film resulted in an increase in the tensile strength (TS) and a decrease in the elongation at break (EB) values. Mechanical test results revealed that TS and EB properties were considerably affected (p < 0.05) by the concentration and particle size of the ZnO reinforcement. Disc diffusion method demonstrated good antibacterial activities of bio-composite films containing high amount of ZnO (8% w/w of chitosan) against Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, and Bacillus subtilis. The growth-limiting effect of the films was more pronounced for S. aureus and K. pneumoniae. Due to enhanced TS and imparted antibacterial activity of the produced ZnO/chitosan bio-composite films, these materials are promising candidates for applications such as food packaging, wound dressing, and antibacterial coatings for various surfaces.
  • Öğe
    Experimental and Statistical Analysis of Effect of Si Modification and Grain Refinement on Tensile Properties of A356 Alloy
    (Gazi Universitesi, 2021) Uludağ, Muhammet
    The focus point of recent research on light metal castings has been on the effect of casting quality on the material properties and maximizing the quality is the most important factor toward obtaining the best properties from an alloy. Sr additions modify Si morphology while grain refiners such as AlTixBy and Ti-free B make dendrite arms smaller in the alloy. Therefore, this study has been performed to evaluate the relationship between casting quality and tensile properties of A356 alloy. The modification and refinement treatments were carried out with three different master alloys: AlSr15, AlTi5B1, and AlB3. The tests were conducted under two conditions: with and without degassing to evaluate the effect of change in melt quality. Results obtained from experimental studies were analyzed statistically. It was concluded that there is a good relationship between bifilm index and tensile test results when the bifilm index is divided into three groups, namely: poor, medium and high quality. It was found that while Ti grain refinement addition positively affects the mechanical properties, Sr addition has a negative effect on casting quality.
  • Öğe
    Lead-based antiferroelectrics revisited for high energy density capacitors and large strain actuators
    (Taylor and Francis Ltd., 2021) Sarı, Hüseyin Alptekin; Gözüaçık, Namık Kemal; Kaya, Mustafa Yunus; Menşur, Ebru; Alkoy, Sedat
    Lead zirconate stannate titanate (PZST) ceramics with the generic composition of Pb1-0.5xNbx[(ZrySn1-y)1-zTiz]1-xO3 with x representing Nb content (x = 0 or 0.02), y representing Zr:Sn ratio (y = 0.57 or 0.60), and z representing Ti content (z = 0.06 or 0.08), and lead lanthanum zirconate titanate (PLZT) ceramics with the general composition of Pb1-xLax(ZryTi1−y)1−x/4O3 with x = 0.050 − 0.120 were synthesized using solid state reaction method and sintering. The energy density and field induced strain behavior of these compositions were investigated for capacitor and actuator applications, respectively. The focus of the study was to evaluate and discuss the change in the polar state of these ceramics from normal ferroelectric to antiferroelectric to relaxor antiferroelectric to linear dielectric with compositional modification. The highest releasable energy density (1.053 J/cm3) was obtained from the antiferroelectric Pb[(Zr0.60Sn0.40)0.94Ti0.06]O3 composition among the PZST compositions that were investigated, but the efficiencies were generally low (max. 60%) due to the large hysteresis that was observed in these compositions. The highest field induced strain level of 0.26% was also measured in the same composition. In the case of PLZT compositions, the highest releasable energy density values (0.313 J/cm3) with much higher efficiencies (76%) and highest field induced strain levels (0.23%) were obtained from the PLZT compositions with relaxor antiferroelectric character.
  • Öğe
    Modification of Cold-Sprayed Aluminum Coating on Nickel-Aluminum Bronze by Micro-Arc Oxidation
    (Springer, 2021) Yürektürk, Yakup
    This study aims to improve the wear resistance of nickel-aluminum bronze (NAB) substrates by micro-arc oxidation (MAO). As this treatment is difficult to apply to NAB surface, cold spraying (CS) was first used to deposit aluminum with a purity of 99.5% onto the NAB substrates. The aluminum-coated substrate was then treated by MAO to convert the aluminum layer into Al2O3 coating in order to enhance the wear resistance. The tribological behavior of NAB substrates with or without the alumina coating was evaluated with a dry sliding wear test using a ball-on-flat reciprocating tester with varied testing loads ranging from 1 to 5 N. The results demonstrated that the oxide layer (Al2O3) formed on the aluminum layer enhanced the wear resistance of NAB alloy against 100Cr6 steel ball. Compared to uncoated NAB alloy, the wear resistance (inverse of wear rate) of the NAB alloy with the MAO coating was at least nine times higher than that of the uncoated NAB alloy at all testing loads.
  • Öğe
    Impact performances and failure modes of glass fiber reinforced polymers in different curvatures and stacking sequences
    (SAGE Publications Ltd, 2021) Kaboğlu, Cihan; Eken, Taha Yasin; Yürektürk, Yakup
    Recently, glass fiber reinforced polymer composites have been increasingly used in applications which are exposed to impact loads due to their high strength, low weight, and corrosion resistance properties. Therefore, the effect of curvature of composite laminate on their impact resistance is important. In this study, the mechanical properties of three curvature diameters and two stacking sequences, which have not been compared before, were examined and compared. The diameter of curved composites is 760 mm, 380 mm, and 304 mm and flat designated as A, B, C, and D, respectively. The fiber stacking orders are [0/0/-45/+45/90/90]S and [90/90/-45/+45/0/0]S designated as Type 1 and Type 2, respectively. The drop-weight impact tests were performed and failure modes of composites were examined. It was observed that the impact resistance decreases with the increase of curvature, where 760 mm diameter and Type 2 composites had the highest strength in all of the composites. In addition, delamination, fiber breakage, and matrix cracking failure modes were observed in the composites after impact. The reason why the strength decreases as the curvature of the composite increases is that the curved areas create an effect that increases the external force applied. The reason why Type 2 stacking order is more durable than Type 1 stacking order is that the 90° fiber direction in the bottom layer has a damping effect on the applied force. According to the results of this study, composite materials with larger diameter and stacking order starting with 0° provides more mechanical strength. (Figure presented.)
  • Öğe
    Fabrication and characterization of in-situ Al3Ni intermetallic and CeO2 particulate-reinforced aluminum matrix composites
    (Elsevier Ltd, 2021) Akçamlı, Nazlı; Şenyurt, Berk
    Al-xNi-yCeO2 (x = 6, 10, 15, 20 and y = 0, 5, 10 wt%) composites were produced by a powder metallurgical production route. Powder mixtures of Al, Ni and CeO2 were fabricated via mechanical alloying (MA) for 4 h in a Spex-type high-energy ball mill. Both the mechanically alloyed (MAed) and non-MAed (as-blended mixtures) powders were pre-compacted in a hydraulic press under 650 MPa and then pressurelessly consolidated at 630 °C for 2 h under an inert atmosphere. The effects of MA process and the amounts of Ni and CeO2 on the microstructural, mechanical and tribological properties of the sintered composites were determined. Based on the SEM and XRD investigations, the MAed powders illustrated a homogenous structure, comprising flaky particles with smaller crystallite sizes and greater lattice strain. According to the XRD analysis, Ni formed Al–Ni intermetallic compounds in the matrix of sintered composites that act as secondary reinforcement phases. The SEM observations conducted on the MAed samples demonstrated more uniformly and finely distributed Al3Ni and CeO2 phases in the microstructure of the MAed samples, unlike the non-MAed ones. The hardness values of sintered composites increased due to the MA process and increasing Ni and CeO2 amounts, and the hardness value of the MAed Al20Ni–10CeO2 sample reached 179 HV. The ultimate compressive strength and failure strain of the MAed Al6Ni–10CeO2 sample were 441 MPa and 11.3%. In the Al20Ni–10CeO2 sample, the compressive strength and failure strain were 391 MPa and 5.5%, respectively. Additionally, the reciprocating wear test results illustrated that both wear resistance and hardness values of the composites increased as the amounts of Ni and CeO2 increased, and the Al20Ni–10CeO2 sample exhibited the highest wear resistance as 0.175 × 10-3 mm3/Nm.
  • Öğe
    Fabrication of 0.94NBT–0.06BT textured ceramics using plate-like NBT templates and their electrical properties
    (Springer, 2021) Berksoy-Yavuz A.; Kaya, Mustafa Yunus; Avcı T.; Cakırbas G.; Menşur E.
    The effect of crystallographic texture on the properties of 0.94(Na0.5Bi0.5TiO3)–0.06BaTiO3 (0.94NBT–0.06BT) ceramics were investigated in this study. The optimized rectangular plate-like Na0.5Bi0.5TiO3 (NBT) templates synthesized by a three-step molten salt method were used for the texturing. Dimensions of the major surfaces of the templates which were parallel to the (001) planes were measured as 8.4 µm × 10 µm (length × width) and 1 µm thickness on the average. The green textured ceramics were fabricated by tape casting method and then sintered. All ceramics were crystallized in pure perovskite structure and the degree of grain orientation was calculated as f = 91%. Brick wall-like microstructure for the textured NBT–BT ceramics with average grain size of ~ 12 µm was obtained by scanning electron microscopy. Depolarization temperature (Td) and temperature of maximum (Tm) of the dielectric permittivity were determined as 119 °C and 341 °C at 10 kHz for the textured ceramic, respectively. The value of maximum dielectric permittivity of textured ceramics was measured as εrmax ~ 5409 at 10 kHz. The high field (@50 kV/cm) piezoelectric d33* value was increased from 239 to 412 pm/V by texturing of the 0.94NBT–0.06BT ceramics. NBT template addition and texture development led to a decrease in AC conductivity.
  • Öğe
    Low-temperature synthesis of boron carbide nanofibers via electrospinning to reinforce composites
    (Springer Science and Business Media Deutschland GmbH, 2021) Dörtler Kesici, Aslı; Kiraz N.
    This study is to obtain low-temperature boron carbide fibers from the polymer–precursor mixture. The fibers produced by the electrospinning method from a mixture of boric acid (H3BO3) and polyvinylpyrrolidone (PVP) were analyzed by scanning electron microscopy (SEM) and thermogravimetric method to create calcination programs. After calcinations, fiber structure was examined by SEM, X-ray diffraction and Fourier transform infrared spectroscopy. According to the characterization results, the thinnest fiber belongs to 0.50% by weight H3BO3–PVP proportional solution. Subsequently, these fibers were modified with the compound [3-(Methacryloxy) propyl] trimethoxysilane to form strong cross-links in the composite. Then, the organic matrix formed by the mixture of bisphenol-A glycidyl methacrylate, diurethane dimethacrylate, triethylene glycol dimethacrylate, benzoyl peroxide and modified fibers was reinforced in different proportions. In this way, 3-point bending tests were performed on fiber-reinforced and particle-reinforced composites, and the results were compared on mechanical strength values.
  • Öğe
    Corrosion behaviour of twin-roll cast 8006 aluminium alloy foil with different thicknesses for the food packaging industry
    (Emerald Group Holdings Ltd., 2021) Eken, Taha Yasin; Sarioglu C.; Kucuk I.
    Design/methodology/approach: The 8006 aluminium alloys are mostly used for the food packaging industry, as they are corrosion resistant, lightweight and shapable materials. The present work investigates the surface and corrosion behaviours of 8006 aluminium alloys at different thicknesses. TRC aluminium alloys were cold-rolled at two different reduction rates before investigation. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDX) tests were used to examine the phase and elemental analyses. FE-SEM and 3D profilometry also used to observe surface morphology. Open circuit potential (OCP), potentiodynamic polarization and electrochemical impedance spectroscopy tests (EIS) were carried out to find out corrosion behaviours. The results show that the more cold rolling reduction (CRR), the more corrosion rate and surface affection of the TRC 8006 aluminium alloys. Findings: According to the electrochemical tests (OCP, potentiodynamic polarization test and EIS) and surface morphology results (such as SEM, 3D profilometry and XRD) the more the rolling rate the less the corrosion resistance. Originality/value: First corrosion behaviour investigation of twin-rolled 8006 Al alloys using electrochemical techniques. First investigation of CRR effects on electrochemical corrosion behaviour of 8006 Al alloys with 3.5 wt.% NaCl solution using EIS. First investigation of 8006 Al alloys as a food packaging material with electrochemical ways.
  • Öğe
    Gözenekli Kordiyerit Küre Üretim ve Karakterizasyonu
    (Afyon Kocatepe Üniversitesi, 2019) Kalemtaş, Ayşe
    Bu çalışmada milimetre boyutlarında küre formunda gözenekli kordiyerit seramiklerinin üretimi ve karakterizasyon çalışmaları gerçekleştirilmiştir. Kordiyerit küre üretiminde CC31, manyezit ve silika kullanılmıştır. Üretilen kürelere % 0, 5 ve 10 oranında nişasta ilave edilerek kürelerin farklı oranlarda gözenek içerecek şekilde üretilmesi sağlanmıştır. Tasarlanan bileşimler 1150 ve 1250C’de 1 saat süreyle atmosfer koşullarında 10C/dakika ısıtma ve soğutma hızı uygulanarak sinterlenmiştir. Sinterleme sonrası elde edilen kürelerin içyapı incelemeleri taramalı elektron mikroskobu ve faz analizleri x−ışını kırınım yöntemi ile gerçekleştirilmiştir. Taramalı elektron mikroskobu incelemeleri nişastanın yapıdan uzaklaşması sonucunda büyük gözeneklerin oluştuğunu göstermiştir. Ayrıca 1250C’de sinterlenen numunelerde kürelerin dışında ve iç kısmında oluşan içyapıların oldukça farklı olduğu gözlemlenmiştir. Ayrıca aynı sıcaklıkta sinterlenmesine rağmen nişasta ilavesinin de kürelerin dış kısmındaki içyapı gelişimine önemli ölçüde etki ettiği belirlenmiştir. Nişasta miktarı azaldıkça 1250C’de sinterlenen numunelerde kürelerin dışında oluşan kristallerin boy/en oranının arttığı ve daha ince kristallerin oluştuğu belirlenmiştir.
  • Öğe
    Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate-coated carbon nanofiber electrodes via dip-coating method for supercapacitor applications
    (Springer, 2021) Altın, Yasin; Bedeloğlu, Ayşe
    The conducting polymer poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is used to modify carbon nanofibers via the dip-coating method. The modification process is carried out by immersing the carbon nanofibers 3, 6, and 9 times in PEDOT:PSS solution. As a result, the production of flexible, homogeneous, self-standing, bead-free carbon nanofibers has been accomplished. The PEDOT:PSS coating process is carried out without negatively affecting the porosity between the nanofibers and the average diameter of the nanofibers increases linearly with the dipping number. Initially, the specific capacitance of the neat carbon nanofiber is 199 F/g in the voltage range of − 0.5 to + 0.5 V at a scan rate of 10 mV/s, while specific capacitance was measured as 278, 311, 350 F/g after the 3, 6, and 9 times PEDOT:PSS coating process, respectively. Additionally, the 9P-CNF sample shows a very high capacitance value, such as 1321 F/g, at a scanning speed of 1 mV/s in 1 M H2SO4 electrolyte. On the other hand, it has been observed that the performance of the hybrid electrode retains approximately 80% of its performance after 2500 CV cycles. The performance of the carbon nanofiber electrode is enhanced by dip-coating with PEDOT:PSS, which is simple, fast, and suitable for large-scale production. The resulting hybrid electrode is suitable for a variety of energy storage applications, most notably supercapacitors.
  • Öğe
    Performance comparison of FeNiCo, FeNiCu and FeNiCoCu alloy particles as catalyst material for polymer electrolyte membrane fuel cells
    (Springer Science and Business Media B.V., 2021) Ates S.; Tarı D; Safaltın Ş.; Küçükelyas, Burak
    Fuel cells are using for electric production via redox reactions where catalyst material are used for increasing sluggish rates of reactions. Polymer electrolyte membrane fuel cells are the most promising types for daily life usage. Platinum is the most known catalyst material and it leads to high prices of fuel cell. Thus, new materials should be innovated instead of noble catalyst materials. In this study, FeNiCo, FeNiCu, FeNiCoCu alloy particles were produced in both ultrasonic spray pyrolysis and mechanical alloying methods to innovate alternative catalyst materials. Products were characterized by XRD, SEM–EDS. Spherical particles which are very important for catalytic properties, were produced with ultrasonic spray pyrolysis method. Elemental weight percentage of particles were observed close to each other. First in the literature, gas flow test was applied to observe gas consumption rates and generate the initial parameters for simulation study which was done to compare catalytic performances of products and conventional Pt catalyst. Ultrasonic spray pyrolysis method provided more catalytic surface behaviors. FeNiCu and FeNiCoCu of this method were found as promising catalyst materials.
  • Öğe
    Effect of Cold Rolling Reduction Rate on Corrosion Behaviour of Twin-roll Cast 8006 Aluminium Alloys
    (2018) Küçük, İsrafil
    Alüminyum malzemelerin, korozyon direnci ve hafiflik gibi harika özelliklerinden dolayı, otomotiv sektöründe kullanımı son yıllarda önemli bir yer tutmaktadır. Özellikle ısı eşanjörü (heat exchanger) elemanı olarak 3003, 8006 grubu hadde alüminyum alaşımlarının kullanımı, eşanjörlerin korozif bir sıvı ortamı içermesinden dolayı ve bu malzemelerin korozyon özelliklerinden dolayı tercih edilmektedir. Bu çalışmada, ikiz merdane sürekli döküm yöntemi ile elde edilen 8006 grubu alüminyum alaşımlarının korozyon özelliklerine soğuk haddeleme ezme oranının etkisi incelenmiştir. 8006 Alüminyum alaşımı, öncelikle soğuk deformasyon haddesi olan ikiz merdanelerin arasına 8.5 mm kalınlıkta levha olarak döküldü ve ardından 550 ila 600 oC arasında homojenleştirme tavlamasına tabi tutuldu. Hemen ardından ezme oranı farklı olan iki haddeleme işlemine tabi tutularak sırasıyla, %94 ve %98 oranında bir ezme işlemi uygulandı. Nihai olarak, 400 oC ila 450 oC arasında bir sıcaklıkta normalizasyon tavlamasına maruz bırakıldı. Elde edilen numunelerin yüzeyi, 1 M NaCI + H2O2 içeren çözeltide korozyon testleri (açık devre potansiyeli ölçümü ve polarizasyon eğrileri eldesi) öncesi ve sonrası, stereo mikroskop ile yüzey görünümü analizine tabi tutuldu ardından 3B yüzey pürüzlülük ölçümü yöntemi kullanılarak, yüzey pürüzlülüğü analizi gerçekleştirildi. Elde edilen sonuçlara göre, soğuk deformasyon işlemine bağlı olarak uygulanan farklı ezme oranındaki artışın ikiz merdane sürekli döküm yöntemi ile elde edilen 8006 alüminyum alaşımlarının korozyon davranışında azalmaya bağlı olarak, korozyon direncinin arttığını göstermiştir