Metalurji ve Malzeme Mühendisliği Bölümü Makale Koleksiyonu
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Öğe Investigation of physicochemical and biological properties of boron-doped biochar(Springer, Published: 15 July 2023) Ateş, Ayten; Aydemir, Burçak; Öksüz, Kerim EmreBoron doping of biochar leads to the formation of activated oxygen species and pores and defects in the carbon structure Therefore, boron-containing biochar was prepared by treating boric acid (H3BO3) solutions in diferent concentrations of hazelnut shells before pyrolysis. DSC results showed that treatment of biomass with solutions containing a low concentration (0.1 wt. %) of H3BO3 increased the degradation of cellulose and hemicellulose, but also increased char formation. However, treatment with solutions containing 2% and 5% H3BO3 increased biochar oxidation with the formation of boron oxide (B2O3). The FT-IR and XPS results showed the presence of B–B, B–O, and B–O–B in the H3BO3 treatment, which is due to the formation of B2O3. The examination of the proliferation of L929 mouse fbroblast cells in response to diferent concentrations of boron-containing biochars using the MTT assay revealed that biochar treated with 2% H3BO3 promoted cell growth (100.32±1.93). However, above this concentration, the formation of polycrystalline B2O3 species exhibited an inhibitory efect on cell proliferation (81.98±1.26) in the samples of H3BO3-doped biochar with 5% concentration. The results of the in vitro hemolysis tests for undoped biochar and high boron-containing (% 5) biochar sample showed mild hemolytic activity, with percentages of 2.46±0.02 and 3.08±0.04, respectively, according to the reported standards. Antimicrobial studies have shown that Candida albicans (a yeast, ATCC 10231) is more sensitive to H3BO3 than Staphylococcus aureus (Gram-positive bacteria, ATCC 29213). Boron-containing biochar can be used in a variety of applications, including biosensing, drug delivery, biological scafolds, and biological imaging, as well as an adsorbent in the removal of pollutants and a catalyst in oxidation and electrochemical reactions.Öğe Silk sericin?hydroxyapatite nanoribbons toward structurally stable osteogenic scafolds(Springer, 29 June 2023) Tosun, Nazan Goksen; Özer, Ali; Bektaş, Tuğba; Öksüz, Kerim Emre; Tayhan, Seçil Erden; Özdemir, TuğbaBuilding a successful, cost-effective, and natural solution toward improving the bone-implant interface is an outstanding challenge. Silkworm sericin attracted the attention of bone researchers in the past decade due to its unexpected performance toward inherently promoting osteogenic differentiation of progenitor/stem cells. Hydroxyapatite is widely utilized in bone tissue regenerative scaffolds as the majority of bone matrix is constituted of inorganic material, primarily hydroxyapatite. Combining sericin and hydroxyapatite pledges improved mineralization performance in a bone regenerative scaffold which could increase the success of implanted bone biomaterial interfaces. Through electrospinning, we produced sericin and hydroxyapatite nanoribbons to present a high surface area and porous scaffold to culture osteoprogenitors and aimed to enhance cell adhesion and proliferation ultimately improving mineralization density. Material characterization is performed through field emission scanning electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. We showed that the addition of hydroxyapatite into sericin nanoribbons significantly enhanced cell proliferation and cytoskeletal organization in vitro and detected an overall improvement in mineral density. We propose that sericin nanoribbons reinforced with hydroxyapatite are suitable platforms for further bone regenerative interface applications.Öğe Fabrication and Characterization of High Performance PVDF-based flexible piezoelectric nanogenerators using PMN-xPT (x: 30, 32.5, and 35) particles(Elsevier, 01/06/2023) Paralı, Levent; Koç, Muhterem; Akça, ErdemFlexible piezoelectric nanogenerators based on polyvinylidene difluoride (PVDF) and lead magnesium niobate-lead titanate Pb(Mg1/3Nb2/3)O3–PbTiO3(PMN-xPT compositions for x between 30 and 35) particles with various filler ratios from 10 to 30 vol% were fabricated through the electrospinning method. The phase and microstructural characterizations revealed that the homogenous and continuous fiber-shaped composite structure with good interfacial interaction between the PMN-PT particles and the PVDF matrix was achieved. It was found that the diameter of the neat PVDF fibers was approximately 354 nm, whereas the PVDF/PMN-35PT fibers with ceramic particle concentrations of 10, 20, and 30 vol% had average diameters of 317, 249, and 163 nm, respectively. The piezoelectric performance tests indicated that the 30 vol%PVDF/PMN-35PT nanogenerator had a 3 times greater electrical power efficiency (10.59 μW) at 20 Hz compared to that of the pure PVDF nanogenerator (3.56 μW) at 15 Hz under the same resistance load of 1 MΩ. All in all, the incorporation of PMNT-PT particles into the PVDF appears to be a good approach for the fabrication of high-performance flexible piezoelectric nanogenerator applications for biomechanical energy harvesting of devices converting the mechanical movements of organs such as cardiac and lung into electrical energyÖğe Cost-Effective and Fast Fabrication of Copper–Cobalt Electrochemical Glucose Sensor(01.10.2023) ZEYNALOVA, Aydan; OSKAY, Kürşad OğuzThis study aimed to develop porous Cu and Cu-Co coatings using a rapid one-step electrodeposition technique. The coatings were characterized using scanning electron microscopy and x-ray diffraction. Pencil graphite electrodes were utilized as substrates, and the non-enzymatic glucose-sensing capabilities of the coatings were evaluated using cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The results demonstrated that the sensor exhibited a wide linear response range and could detect glucose within two concentration ranges (20 μM–1 mM and 1–7.5 mM) at a potential of 0.50 V in 0.1 M NaOH. The fabrication process of the sensing electrodes was straightforward, highlighting the efficiency of Cu-Co porous coatings as a nanocomposite for glucose detection. In summary, the study presents a promising method for the production of efficient glucose sensors with potential applications in various fields.Öğe Preparation, Characterization, and Application of Metal Oxide-Doped Zeolitic Imidazolate Framework(20.07.2023) Fulya Kümbetlioğlu; Kürşad Oğuz Oskay; Zafer Çıplak; Ayten AteşMetal−organicframeworks(MOFs)attracttheattentionof researchersdue to their uniqueproperties,such ashigh surfacearea, porosity,and stability.Therefore,in this study,the synthesisof zeoliticimidazoleframeworks(ZIF-8),a subclassof MOFs,and copperoxide (Cu2O) and manganeseoxide (MnO2)containingZIF-8was carriedout by a mixingmethodwithmethanol.The characterizationresultsshowthat the polyhedralstructureof ZIF-8was preparedwith a surfacearea of 2088 m2/gand a crystallitesize of 43.48nm. Then,each and mixtureof twometaloxideswere introducedinto the ZIF-8crystalstructure.Itwas foundthat the surfacearea and pore volumesof all metal/ZIF-8 samplesdecreasedwith metal loading,dependingon the type andratio of metal oxides.The ZIF-8containing4.0 wt % Cu2O and 1.0wt % MnO2had the highestsurfacearea (2084m2/g), whichwas closestto that of ZIF-8.The polyhedralstructurewas maintainedby the additionof both metal oxides,and the crystalsize of the materialdecreasedwith the loadingof MnO2to the ZIF-8structure.All of the synthesizedsampleswere analyzedin supercapacitorapplicationsand a relativelyhighervalue of specificcapacitancewasobtainedfor Cu−Mn/ZIF-8due to highersurfacearea and improvedconductivity.In additionto supercapacitorapplications,thepropertiesof metal/ZIF-8are also promisingfor applicationssuch as catalysts,membranes,and gas storageÖğe Enzyme-free nickel electrochemical glucose sensor fabricated on pencil graphite electrode by electrodeposition(Springer, 25.02.2023) OSKAY, Kürşad Oğuz; Özkan, BülentIn this study, the optimal conditions for the electrodeposition of nickel foam-like morphology over a pencil graphite electrode for glucose sensor application are determined. The effects of NiSO4 and NH4Cl concentrations, current density, and electrodeposition time were investigated in detail. The electrochemical performance of the nickel deposit for sensing glucose is investigated by cyclic voltammetry and chronoamperometry in alkaline solutions. Under optimized conditions, the sensitivity of the sensor toward glucose oxidation was 125.9 μA/μM.cm2 and showed a linear response in a wide range of glucose concentrations, from 2 to 8000 µM. We conclude that the nickel foam-like electrode has the potential to be used as a glucose sensor due to its superior features such as low cost and fast deposition time.Öğe Effect of Chemical Composition of Boriding Agent on the Optimization of Surface Hardness and Layer Thickness on AISI 8620 Steel by Solid and Liquid Boriding Processes(08.10.2022) KUL, Mehmet; Yılmaz, Yasin; OSKAY, Kürşad Oğuz; Kumruoğlu, Levent CenkSurfaces of cam shafts made of AISI 8620 steels were hardened by boriding processes in both solid and liquid mediums. Various chemical agents were used to achieve boride layers on the surfaces of the cam shafts in these processes. It was aimed to examine effects of the chemical agents on microhardness and thickness of the boride layers obtained. It was concluded that a bath composition of 5% B4C-90% SiC-5% KBF4 was appropriate for the hardest and thickest boride layer achieved in the solid medium, and a composition of 70% Na2B4O7-30% B4C in the liquid medium.Öğe Improving the Electrochemical Energy Storage Capacity of the Renewable Carbon Derived from Industrial Tea Waste(29.06.2022) Karamustafa, Ayşenur; Sözer, Sözer; Merve Buldu-Akturk; Emre Erdem; Akgül, Gökçen; Oskay, Kürşat OğuzEnergy storage is gaining a vital role since the usage of portable electric/electronic devices and vehicles have been growing. Capacitors, called as electrochemical double layer capacitors or supercapacitors, find application on wide scale devices from mobile vehicles to huge electric vehicles with high energy and power densities, fast charge and discharge properties. Hence, energy is stored at the electrode–electrolyte interface, the electrode material forms the heart of this energy storage system. When the decreasing reserves of fossil resources and their environmental damages are considered, renewable 3-dimentional carbon could be a solution in the capacitor as carbon electrodes. Biomass-derived renewable carbon is cost-effective, abundant, sustainable, safety and environmentally friendly material. In this work, renewable carbon material was derived from industrial tea waste and three methods of graphitization, activation and heteroatom doping were implemented alltogether to develop the energy storage capacity of material. The structural ordering, surface area growth and capacitive contribution promoted the energy storage capacity to 25 F/g and high power density to 2.6 kW/kg of biowaste derived carbonÖğe Effects of pH and Current Density on Microstructure and Hardness of the Cobalt-Tungsten Coating(Dergipark, 14.04.2022) Oskay, Kürşat OğuzEffects of pH and Current Density on Microstructure and Hardness of the Cobalt-Tungsten CoatingÖğe Synthesis and characterization of chitosan–vermiculite composite beads for removal of uranyl ions: isotherm, kinetics and thermodynamics studies(Springer, 2021) Şenol, Zeynep Mine; Şimşek, Selçuk; Özer , Ali; Şenol Arslan, DilekIn this study, a new material containing Chitosan (Ch)–Vermiculite (V) composite beads was synthesized with epichlorohydrin cross-linking agent and used to remove uranyl ions from the aqueous solution. The prepared new material was characterized by SEM, XRD, FTIR analyses and PZC measurement. The effects of significant parameters on adsorption including temperature, pH, concentration and time were investigated. The obtained results indicated that the new composites of Ch–V was revealed in different structure. The zeta potential analyses showed that electrostatic attraction existed during the adsorption process between the uranyl ions and Ch–V. The maximum adsorption capacity of material was calculated as 0.665 mol kg−1 by considering Langmuir equation. Adsorption kinetic was also explained with pseudo second order and intra particular diffusion models. Experimental studies clearly showed that the adsorption was endothermic and occurred spontaneously. The newly developed smart material has many advantages such as reusability, high adsorption capacity, selectivity and economics.Öğe An investigation of corrosive effects on zirconia with different crystal structures(Wiley, 2021) Soygun, Koray; Özer, Ali; Ulucan, Mehmet Çağatay; Bolayır, GirayThis study aimed to compare the time-related corrosive resistance in different corrosive solution environments after sintering of zirconia with different crystal structures. The zirconia samples were produced in pellet form as 12.7 × 3 mm. To determine the time-related corrosion resistance of the sintered samples in sodium carbonate (Na2 CO3 ), sodium chloride (NaCl), and citric acid (C6 H8 O7 ) solutions, the weights were measured at baseline then on the first and fifth days and the microhardness values were calculated. For the evaluation of surface appearance, images were obtained with a scanning electron microscope. The baseline microhardness values of the groups with 3 and 10 mol% yttria-stabilized zirconia samples were found to be 1,064 VHN and 1,079 VHN, respectively. The microhardness values of the groups with 3 mol% yttria-stabilized zirconia samples immersed in Na2 CO3 1d (1,010 VHN) and 5d (1,060 VHN), and NaCl (1d (1,010 VHN) and 5d (1,055 VHN) were found to be affected more. The microhardness values of the sample group (1,064 VHN) with 10 mol% yttria doped zirconia which was left for 5 days in citric acid were found to be lower than the sample group (1,120 VHN) with 3 mol% yttria added. C6 H8 O7 was seen to have a greater corrosive effect with increased yttria content and the microhardness value decreased. With longer duration of the samples of all the groups in C6 H8 O7 , NaCl, and Na2 CO3 solutions, the surface characteristics of the samples were affected negatively. With prolonged immersion in the corrosive solutions, the resistance to the corrosion causing the changes in the surface topography of the samples was seen to decrease.Öğe Novel natural spider silk embedded electrospun nanofiber mats for wound healing(Elsevier, 2021) Öksüz, Kerim Emre; Kurt Özkaya, Neşe; Şahin İnan, Zeynep DenizIn recent years, electrospun nanofiber mats based on biopolymers have been extensively investigated for tissue and biomedical engineering, mainly because of remarkable morphological similarity with the natural extracellular matrix. The current study focuses on the preparation of novel natural spider silk (SS) embedded Poly(vinyl alcohol)(PVA)/Sodium alginate (NaAlg) wound dressings with desirable properties for a wound dressing application. The nanofibers’ surface morphology and structure were observed by a field emission scanning electron microscope (FE-SEM). In-vivo evaluation of PVA/NaAlg based electrospun nanofiber mats as a wound dressing material and their comparison to commercially available wound dressings was carried out by in-vivo tests on rabbit models. Some morphometric parameters such as counting cells, blood vessels, endothelial cells, determination of the area of the wound closure, wound healing performance, speed of wound healing and collagen thickness were investigated using OM and FE-SEM post-processing. Furthermore, in-vitro biocompatibility and cellular behavior such as adhesion and proliferation of mouse fibroblast cells (L929) were studied by XTT assay on developed nanofiber mats. The results of this experimental study indicated that the natural spider silk embedded electrospun nanofiber mat (PVA/NaAlg/SS) accelerated the rate of wound healing compared to other groups by improving the collagen formation rate, proliferative cell activity as well as decreasing the inflammatory cell amount. Furthermore, the results of the in-vivo and in-vitro experiments suggest that novel PVA/ NaAlg/SS nanofiber mats might be a fascinating bioactive wound dressing for clinical applications.Öğe Optimisation of recycled moulding sand composition using the mixture design method(Taylor and Francis, 25.05.2021) KUL, Mehmet; AKGÜL, Bekir; OSKAY, Kürşad Oğuz; ALSAN, Aytuğ Eren; KARACA, BahadırIn the cast iron industry, mould sand quality and the most efficient recovery of used sand into the system are critical. For this purpose, the optimum values of the factors (humidity, active bentonite and coal dust) affecting the green strength, gas permeability and shear strength of the mould sand were determined in this study. The optimum mixture ratio, which makes the green strength, gas permeability and shear strength of the mould sand the best, was made by using the mixture design method. As a result of the studies, optimum casting sand composition; the percentage of moisture content, the percentage of coal dust, the percentage of active bentonite and the percentage of recycle sand were determined as 3.92%, 0.05%, 0.30% and 95.73%, respectively. The green compression strength(B-1) 23.5 N/cm(2), shear strength(B-2) 7.7 N/cm(2) and gas permeability (B-3) 91 mmWS of the conventional cast sand prepared in this optimum composition were measured.Öğe A Novel and Eco?friendly Approach for the Simultaneous Recovery of Copper and Diamond from Waste Cutting Segments via Electrodissolution/Deposition(2021) Kul, Mehmet; Erden, Fuat; Oskay, Kürşad O; Karasungur, Onur; Şimşir, Mehmet; Kumruoğlu, L. Cenk; Karakaya, İshakA new approach is brought to diamond recovery from waste cutting segments. Unlike the commonly used hydrometallurgical processes, this approach offers the simultaneous recovery of copper with diamond. Besides, instead of strong acids, this work involves use of a dilute acid solution, reducing the evolution of toxic vapors. Copper base segments of waste diamond tools were used as anode, which were dissolved by applying potentials above the dissociation voltage of Cu. Simultaneously, the diamond grits detached from the segments and gathered at the bottom of the cell. Then, the dissolved Cu2+ cations were reduced, and Cu powders were electrodeposited at cathode without affecting the accumulated diamond particles. Eventually, the diamond particles could be collected from the bottom of the cell, providing the simultaneous recovery. In this work, the effect of individual process parameters on the outcome of presented approach is studied. The process parameters were then optimized, and mathematical models were developed for response variables by response surface methodology. Also, a mini-prototype was designed and operated at the optimized conditions to check the possibility of converging the proposed approach to industrial applications. Prototype tests show that all detached diamond could be recovered in 3 h and simultaneously with Cu powders.Öğe A comparative study of hardness/scratch/wear properties of TiCN and TiAlN coatings on DIN 1.2842 steel by CA-PVD method(2021) Simsir, Mehmet; Palaci, Yuksel; Özer, AliIn the present study, TiCN and TiAlN were deposited on DIN 1.2842 (AISI O2) steel, and their mechanical properties was compared by investigating coating thickness, adhesion strength, microhardness, and elastic modulus. To carry out characterizations, micro-wear test, Rockwell C adhesion, microhardness test, and scratch test were applied on TiCN- and TiAlN-coated DIN 1.2842 (AISI O2) steel. Deposition of the TiCN and TiAlN coatings was carried out on the hardened steel substrates (55-57 HRc) at 450–500°C by cathodic arc physical vapor deposition (CA-PVD) method. As a result of the applied tests, adequate adhesion strength was obtained for both hard coatings. Through thickness microcrack, buckling failure mode and buckle spallation failure mode are observed at critical loads as Lc1, Lc2, and Lc3, respectively. TiAlN coating has better indentation hardness properties and elastic modulus. Wear resistance of TiAlN coating is better than that of TiCN coating due to similarity with substrate and tougher metallic character.Öğe Templated grain growth of Bi(Zn0.5Zr0.5)O3 modified BiScO3?PbTiO3 piezoelectric ceramics for high temperature applications(Taylor & Francis, 2021) Akça, Erdem; Duran, Cihangir; Kowalski, Ben; Sehirlioglu, Alp2.5Bi(Zn0.5Zr0.5)O3−37.5BiScO3−60PbTiO3 (BZZ-BS-PT) ceramics were successfully textured in the [001] by templated grain growth (TGG) process using 5 vol% <001>-oriented BaTiO3 (BT) plate-like templates. The templates were aligned in the matrix powder via tape casting and textured BZZ-BS-PT ceramics sintered at 1100°C for 3 h in air had a relative density of 98% and a Lotgering factor of 0.91. Chemically stable BT templates in Pb and Bi-rich BZZ-BS-PT system gave rise to the formation of highly oriented polycrystalline structure with larger block-like grains. A very high unipolar strain of 0.3% and low-field (<5 kV/cm) piezoelectric charge coefficient (d33) of 930 pm/V when driven at 50 kV/cm were achieved in highly textured ceramics together with a Curie temperature (TC) of 403°C. The TGG approach significantly improved piezoelectric properties of the BZ-BS-PT ceramic system without deteriorating the dielectric properties, which is a very promising high-performance candidate for high-temperature sensor, transducer and actuator applications.Öğe Characterization of diamond impregnated B4C/Fe-Co MMC(European International Powder Metallurgy Congress and Exhibition, Euro PM 2011, 2011) Öksüz K.E.; Şimşir M.; Şahin Y.In this study, impregnated diamond cutting tools (Fe-Co matrix composite sockets) are processed by powder metallurgy method using hot pressing technique. The effects of Fe and B4C additions on the characteristic of diamond impregnated Co matrix composites have been investigated. Samples reinforced with and without B4C having three different compositions (different Fe/Co ratio) were produced under 25 MPa pressure and sintered at 800 oC temperature. After sintering, hardness tests were carried out and wear tests were performed by pin-on-disc. The results showed that addition of Fe caused slightly decrease in the hardness of the matrix. However, reinforcing with B4C increased the hardness of the matrix. It is observed that wear resistance of B4C reinforced Fe-Co metal matrix composite was greater than that of composites without reinforcement (B4C) and commercial sockets. SEM and EDS techniques were used to characterize the composites.Öğe The cathodic electrolytic plasma hardening of steel and cast iron based automotive camshafts(Polish Academy of Sciences, 2017) Dayança A.; Karaca B.; Kumruo?lu L.C.Cathodic electrolytic plasma hardening is a novel thermochemical surface modification and hardening process, used to increase wear resistance and surface hardness of metallic components in a local area of interest. The heating efficiency is related with the plasma nozzle design, applied current and electrolyte. The nozzle design is also a critical factor for the hardening of complex shapes, such as gears and camshafts. In this work, lobes of camshafts, fabricated from several cast iron and steel grades were hardened by cathodic electrolytic plasma hardening in aqueous carbonate electrolyte, using a specific plasma nozzle. The camshafts were attached to CNC lathe for turning them in the horizontal axis. In order to optimise heating and to achieve the ideal flowing and wetting by the electrolyte of the lobe case, the ceramic ellipse-shaped nozzle outlet was designed. As a result of preliminary studies, external surface of lobes was heated and subsequently quenched by electrolyte. The hardness of processed surface was in the range of 50-60 HRc for the different camshafts. No distortion was observed on the surface of lobes. Hardness depth was measured to be from 0.1 mm to 5 mm for several lobes. © 2017, Polish Academy of Sciences. All rights reserved.
