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Effect of tempering conditions on the final properties of ball bearings
The primary assignment of bearing is that the machine element we can encounter in every field. It provides minimum friction between raceways of inner and outer ring with relative rotary motion and ensure smooth load transformation. The bearing must have high hardness and strength properties for resistance to external forces. The hardness of steel is dependent on carbon contents in chemical composition. For this reason, 100Cr6 bearing steel, which is defined as high carbon low alloy steel, is commonly used by bearing manufacturers. The through-hardening process consists of quenching and tempering conditions. Austenitization temperature is used at 850°C. Moreover, the quenching condition that provides high hardness, includes stress. Tempering was carried out between 150-300°C by applying 10°C intervals. Also, two different tempering durations were selected; 90 and 240 minutes. The tempering condition removes residual stress and retained austenite. Retained austenite can be decomposed into the martensite phase depending on tempering temperatures and durations. However, this case causes dimensional distortion for rings. Balls are trapped between inner and outer rings. This situation causes failure of bearing. A dimensional stabilization test should be applied to the bearing rings to observe dimensional distortion. Accordingly, tempering temperatures are determined. Since there is no international dimensional stabilization test standard, the bearing manufacturers develop their own dimensional stabilization test parameters. Three different dimensional stabilization test conditions were applied to rings according to heat classes. In this study, 6208 types of bearing rings are used. Effects of tempering conditions on the final properties of bearing rings are examined. For outer rings; hardness values were observed between 790 HV1 to 643 HV1 for 90 minutes and 775 HV1 to 658 HV1 for 240 minutes duration at 150 and 300°C tempering temperature. The amount of retained austenite was completely decomposed into martensite at 230°C for 90 minutes and 220°C for 240 minutes duration. For inner rings under the same tempering temperatures; hardness values were observed between 792 HV1 to 643 HV1 for 90 minutes and 773 HV1 and 632 HV1 for 240 minutes duration. The amount of retained austenite was completely decomposed into martensite at 230°C for 90 minutes and 210°C for 240 minutes duration. The amount of retained austenite caused the dimensional distortion on rings according to dimensional stabilization test. The 240 minutes tempering duration is more suitable than 90 minutes for the phase stabilization of rings.
Patent database analysis for carbon reinfirced nano-composites used as conductivity surfaces for aerospace industry
Research and development studies has been developing especially on critical advanced technologies of aerospace industry along with aviation and space industry. Especially carbon reinforced nano composites can provide advanced technological support to meet such properties. One of this advanced technology is the nano composite technologies because nano composite materials have low weight and high electrical, optical, physical, chemical and mechanical properties. Nano composites are novel materials technology that has been improvingly used in aerospace industry. In the course of these improvements on novel materials, patent database analysis can support the studies and their route for improvements. Patent database search and analysis are important tool to identify technological roadmap. Researchers confirm their R&D policy by checking patent databases. In this study, patent database analysis has been carried out for carbon reinforced nano composites that are used for improving electrical and thermal conductivity of metal and composite surfaces used in aviation industry. It is also aimed to gather data to guide the evaluation of the relationship between patent database and technological development of carbon reinforced nano composites.
Titanium diboride (TiB2) reinforced silver (Ag) based nanocomposite coatings by electrodeposition method
Silver is one of the most used materials in electrical industry due to its excellent electrical and thermal conductivity properties and it is frequently used as electrical contact material. However, silver's low mechanical strength has prompted researchers to produce different electrical contact materials. Many studies have been carried out by reinforcing a different material into silver (adding a second phase). In this study, titanium diboride reinforced silver based nanocomposite coatings are produced in order to obtain a new generation contact material with longer service life, economical, safer, environmentally friendly and most importantly, good contact performance. Titanium diboride is a promising material for electrical contacts with its excellent features such as high hardness, high melting temperature, low density, low electrical resistivity, good thermal conductivity. In this study, unreinforced silver and titanium diboride reinforced silver based nanocomposite coatings produced by electrodeposition technique with using direct current, pulse current and pulse reverse current methods on copper substrates. Firstly, nanocomposite coatings were produced with the addition of 0.5, 1.0, 2.0 and 4.0 gram/Liter titanium diboride into electrolyte and effects of reinforcement with different amounts in silver matrix were analyzed. 1.0 gram/Liter titanium diboride reinforced silver based nanocomposite coatings were also produced with using direct current, pulse current and pulse current methods. All coatings were analyzed by Scanning Electron Microscope, Energy Dispersive Spectroscopy, X-ray Diffraction Analysis, Vickers Microhardness Test, Electrical Resistivity Measurements, Cross-Sectional Analysis, Electrical Contact Performance Test and Corrosion Resistance Tests.
Difüzyon kaynağı ile birleştirilmiş TM bakır esaslı kompozit malzemelerin mikroyapı ve mekanik özelliklerinin incelenmesi
Bakır, üretim ve tüketimde demir/çelik ve alüminyumdan sonra üçüncü sırada yer alan, başlıca ticari metal gruplarından biridir. Bakır, yüksek termal ve elektrik iletkenliği, plastisitesi, yumuşaklığı ve şekillendirilebilirliği nedeniyle geniş uygulama alanları bulmuştur. Bununla birlikte, saf haldeki bakır, zayıf mukavemet, aşınma ve yorulma direncine sahiptir ve bu nedenle elektrik anahtarlarının kontak terminalleri ve kayar yüzeyler gibi üst düzey uygulamalar için uygun değildir. Metal veya seramik matrislerde karbürlerin kullanımı, aşınmaya dayanıklı malzemelerin üretiminde giderek daha yaygın hale gelmekte ve endüstride önemli bir kullanım payı bulunmaktadır. Bakır bazlı bir kompozit matrisler, B4C, SiC parçacıkları gibi seramiklerle güçlendirilmiştir. B4C, metal matrisli kompozitler (MMK'ler) için takviye olarak kabul edilen düşük yoğunluklu, yüksek mukavemetli, yüksek sertliğe ve yüksek Young modülüne sahip bir seramiktir. Difüzyon kaynak yöntemi (DKY), saf bakırın bu sınırlamalarını aşmıştır. Geçen yüzyılın başında, gerilme kaynaklı veya çatlak oluşumunu önlemek amacıyla konvansiyonel ultra ince taneli malzemeler için geliştirilmiş bir yenilikçi bir hatı hal işlem yöntemidir. DKY, seçici konumlarda mikro yapıyı ve diğer mekanik özellikleri değiştirmek için benzersiz bir işlemdir. Bu araştırmada bakır-borkarbür (Cu+B4C) kompozitlerinin birleştirilmesinde difüzyon kaynağı yöntemi kullanılmıştır. Kompozitler toz metalurjisi (TM) ile üretilmiştir. Cu tozları ağırlıkça %2,5; 5 ve 7,5 bor karbür (B4C) içernğınde. 45 dakika süresince turbulade karıştırılmış, 40 MPa'da ve argon atmosferinde 800°C'de 4 dakika sıcak preslenmiştir. Cu+B4C kompozitleri, 800°C' ve 900°C sıcaklıkta ve 90;120 ve 180 dakika süresince difüzyon kaynağı ile birleştirilmiştir. İçerğınelı Difüzyon kaynağı sırasında 5 ve 8 MPa tek eksenli basınç ugulanmıştır. Kaynak bağlantı bölgeleri taramalı elektron ve optik mikroskop aracıyla inclenmiştir. Elde edilen bağlantılara sertlik , kesme ve enine kopma dayanımı testleri uygulanmıştır. %2,5 ve %5 oranında B4C içeren bakır numunelerde sırasıyla 144 MPa ve 166 MPa değerinde en yüksek dayanım elde edilmiştir.
Developing high-efficiency ternary thermoelectric phosphides in the systems Ca-Ag-P and Ca-Cu-P
Since the discovery of the thermoelectric (TE) effect by Seebeck, Peltier, and Thomson in the XIXth century, thermoelectricity has attracted significant attention for both fundamental science and industrial applications. Nowadays, this interest has been rejuvenated by the ever-growing worldwide energy demand and the concomitant environmental concerns tied to the emission of pernicious greenhouse gases. Among renewable energy sources, thermoelectricity stands out for not only waste-heat harvesting but also for being replaced by commercial refrigerators. Considering that about two-thirds of the energy produced is lost as waste heat, this versatile technology is quite useful as it converts heat into electricity and vice-versa. The thermoelectric efficiency of a given material is quantified through the dimensionless thermoelectric figure of merit, zT, defined as zT= α2σT/(κl+κe) where α, σ, κl, κe and T correspond to the Seebeck coefficient, electrical conductivity, lattice thermal conductivity, electronic thermal conductivity, and temperature, respectively. The higher the zT value at a given temperature, the higher the thermoelectric efficiency of the module. The challenge to overcome in thermoelectricity is thus clearly material: a good thermoelectric material should possess low electrical resistivity to minimize heat losses through Joule effect, high thermopower to maximize the thermoelectric effect, and low thermal conductivity to maintain a temperature gradient large enough between either side of the thermocouple. Ternary phosphides (CaAgP and CaCuP) are stable and can exhibit promising thermoelectric properties. To date, these materials have remained largely unexplored, but recent theoretical studies demonstrate their high predicted thermoelectric efficiencies. In this thesis study, the electrical and thermal transport properties of p-type CaAgP and CaCuP materials were investigated through Zn, Na, Sn, nano-boron (nB), and La doping. CaAgP and CaCuP powders have been synthesized by high-energy ball milling and were sintered by spark plasma sintering technique. The dopants were introduced to the materials by applying the same synthesis processes. Additionally, annealing procedures were performed on certain samples following the sintering process. Detailed chemical characterization of these polycrystalline materials has been carried out. Thermoelectric examinations of the materials obtained in the desired purity and composition have been completed. The mechanical properties of thermoelectrically promising samples were measured. The measurements of the dielectric constant of CaAgP and CaCuP, and thermoelectric modeling were also conducted by the Korean partner. The intrinsically doped CaAg0.90P sample achieved the highest zT value of approximately 0.33 at 823 K, with additional dopants failing to further enhance zT values in the CaAgP compound. Notably, the sample doped with 0.05 at.% nano boron demonstrated the maximum hardness within the Ca-Ag-P system. In the CaCuP system, the zT value improved significantly, increasing from 0.37 to 0.45 at 823 K for the Zn-doped and annealed Ca1.05Cu0.95P-Zn0.05 sample. Additionally, the inclusion of nano boron and zinc not only enhanced zT values but also improved the mechanical properties of the CaCuP and CaAg0.90P microstructures. These findings underscore the importance of detailed experimental and computational studies on ternary phosphides, which can substantially contribute to the development of new thermoelectric materials and their applications.
Investigation of structural and magnetic properties of Fe and Cu doped MoS2 thin films
In this study, structural and magnetic properties of pure and Fe/Cu-doped Fe/Cux:MoS2 (x: 0.50%, 0.75%, and 1.00%) thin film materials were investigated. Crystallizations of films were ensured decomposing of ammonium tetrathiomolybdate (ATTM) precursor at various sintering temperatures under N2 gas flow. Structural and morphological characteristics of all produced samples were investigated by measuring X-Ray Diffraction (XRD), Raman spectroscopy and Scanning Electron Microscope (SEM). It is determined from Raman spectroscopy results that the characteristic vibration modes of 2H-MoS2 formed after performing optimization samples. SEM images of pure sample show that MoS2 crystals formed as back-to-back triangle shape. This shape of crystal was changed to nanorod by doping Fe atoms in to the main structure. Magnetic properties of samples were investigated by using vibration sample magnetometer (VSM). It is observed that magnetic transition temperature of samples decreases when Fe atom is added to the main structure. The magnetization transition temperatures are found as 247.6 and 95.5 K for pure (0.95% wt. ATTM) and 0.75% Fe-doped MoS2. According to the magnetic hysteresis curves measured at 5 K, the magnetic ordering of pure and 0.75% Fe-doped samples are ferro/ferri-magnetic. For Fe-doped samples, all samples, except 0.75% Fe-doped sample, show diamagnetic characteristic at room temperature. In addition, saturation magnetization value increases with introducing of Fe atom into the main structure. For Cu-doped samples, the diamagnetic behavior was observed at room temperature.
Investigation of advanced radar absorber composite materials having high stealth technology to use in various military vehicles
The aim of the stealth technology, which has attracted great attention in the field of defense technologies in recent years, is to reduce the radar cross-sectional area (RCS) of the target object. Reducing the RCS can prevent the potential target object from being seen in enemy radar systems. Radar absorber materials are material groups that actively exhibit the stealth technology by losing the visibility of the target object by reducing and absorbing the energy of electromagnetic waves entering the material with the magnetic and dielectric loss mechanism. In this study, NixCo1-xFe2O4 (0≤x≤1with increments 0.25) and Niy:ZnO (y=0 and 0.1) nanoparticles were synthesized using the sol-gel method. X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Energy Distributed X-Ray Spectroscopy (EDS) and Vibrating Sample Magnetometer (VSM) analyzes were performed for determining the crystal structures, particle size and morphology, elemental analysis and magnetic characteristics of the produced nanoparticles, respectively. Various radar absorbing composite structures were obtained by using the epoxy casting method with the addition of the produced nanoparticles into the epoxy resin. Microwave absorption properties of nanoparticle reinforced epoxy matrix composite structures were characterized in the 8-12 GHz (X band) frequency range using a Vector Network Analyzer. In addition to the mechanical properties of composites were evaluated by applying hardness and impact test. It has been observed that the microwave absorption and mechanical properties of the nanoparticle reinforced epoxy matrix composite samples are satisfactory and can be used in potential military land, air and sea applications.
Halloysite nanotubes reinforced polybutylene terephthalate based nanocomposites: mechanical, thermal, structural and morphological characterizations
Polybutylene terephthalate (PBT) nanocomposites were melt-blended with two types of Turkish halloysite nanotubes (HN) using a co-rotating twin-screw extruder. Naturally occurring HN samples were used to produce PBT-based composites at the HN compositions of 1%, 3%, 5%, and 10% by weight. PBT was purchased as bead form under the trade name of Advanite from Sasa polyester A.Ş., Adana, Turkey. Neat and silane-modified grade of HN was supplied by Eczacıbaşı Esan, İstanbul, Turkey with the trade names of ESH HNT and ESH HNT S, respectively. Test samples were prepared by an injection molding process. Mechanical, thermo-mechanical, thermal stability, melt-flow, structural and morphological properties of the produced nanocomposites were reported using tensile, impact and shore hardness tests, dynamic mechanical analysis (DMA), thermo-gravimetric analysis (TGA), melt flow rate and density measurements and scanning electron microscopy (SEM) methods, respectively. Results of neat and silane coated HN containing composite samples were compared in order to investigate the interfacial adhesion between polymer matrix and reinforcement material.
Jeopolimerlerin sentezlenmesi ve özellikleri
Continuous cement manufacture has increased the quantity of CO2 released into the atmosphere, increasing the level of global warming, which has a negative impact on the environment. As a result, a more sustainable strategy, as well as a comprehensive review of the existing admixtures used to replace traditional concrete, has become critical. Many studies on geopolymer binders, which has equivalent or higher durability and strength than traditional concrete, have been conducted for this purpose by many researchers. Geopolymer binders offer the advantage of using extra cementitious materials mixed with alkali-activated solutions to replace traditional cement. As a result, this study offers a comprehensive review of geopolymer material, including its ingredients, manufacturing procedures, and curing regimes, as well as a comparison of its physical and mechanical properties to traditional cement structures.
Fabrication and characterization of transition metals (Mn and Co)-doped cds-based photovoltaic cells
In this study, CdS thin films were produced via chemical bath deposition method, individually doped with Mn (0.5%, 1%, 2%) and Co (1%, 3%, 5%, 7%), on indium tin oxide (ITO) coated glass substrates. Additionally, the desired device configuration was achieved by coating N719, P3HT:PCBM, and PEDOT:PSS organic layers, respectively, using spin coating method. Comprehensive XRD, SEM, EDS, transmittance, absorbance, PL analyses were conducted on both Mn and Co-doped CdS thin films and the fabricated solar cells. Furthermore, J-V tests were performed on the fabricated devices. XRD analysis revealed that the produced CdS thin films grew in a cubic structure. Addition of Mn atoms into CdS structure was determined to deteriorate crystal quality based on dislocation density and micro-strain results. Mn doping led to a positive effect on transparency of CdS films, particularly achieving over 90% transmittance in the wavelength range of 500-650 nm for CdS sample with 2% Mn addition. Mn doping was found to increase forbidden energy band gap of CdS, causing a blue-shift in absorption edge. J-V measurements of the fabricated solar cells indicated that Mn doping improved the efficiency of CdS based hybrid solar cells. Highest power conversion efficiency was achieved with a 2% Mn-doped CdS solar cell (0.202%). On the other hand, Co doping led to a change in the unit cell volume and increase in crystalline size of CdS. Additionally, a reduction in grain size of CdS thin films was observed with Co doping. Co doping was found to enhance optical transparency of CdS films and alter the forbidden energy band gap. Photoluminescence results suggested that Co doping caused additional defect states in CdS films. Furthermore, Co doping positively influenced the efficiency of CdS-based hybrid solar cells, with highest efficiency obtained from solar cells with 1% Co doping (0.488%).
Synthesis and characterization of some physical properties of Fe3O4 doped MoS2/PANI hybrid composites
Systems for absorbing electromagnetic waves in materials are essential for stealth applications and vulnerable electronic equipment. However, the ability to absorb EMW over a large bandwidth is still limited by certain limitations in material systems and engineering. Increasing the bandwidth and reducing material system reflections are crucial advancements for the development of future stealth technologies. In this study, hybrid structures were developed using semiconducting MoS2 nanosheets, Fe3O4 magnetic nanoparticles and conductive polyaniline. A systematic approach was employed to examine the structural, magnetic, morphological, thermal, electronic, and electromagnetic properties of these hybrid structures. As a result of the analysis, Fe3O4:MoS2 and PANI@Fe3O4:MoS2 hybrid sturucture, which can effectively absorb electromagnetic waves, were found to have superior EMW absorption properties. In particular, The F10M90 sample achieved a minimum reflection loss of -54.97 dB at a thickness of 3 mm and a frequency of 7.86 GHz, with an effective absorption range of 4.0 GHz. The P50F2.5M47.5 sample achieved a minimum reflection loss of -27.58 dB at a thickness of 2 mm and a frequency of 13.18 GHz, with an effective absorption bandwidth of 8.03 GHz. Based on the experimental findings, it is concluded that hybrid nanocomposites such as PANI@Fe3O4:MoS2, which are characterized by their lightweight structure and high temperature stability, can effectively absorb almost 99% of the EMW in the broadband range.
An assessment of bioplastic applications in agriculture within a sustainable framework
The Earth's surface temperature has been exceeding normal levels since the 1950s. Global warming poses threats to human and living health. Various solutions are being explored to protect water resources. Another challenge facing humanity is the increasing demand for food due to population growth. Enhancing agricultural productivity is necessary to meet this demand. The effective use of plastic mulches in agriculture, as evidenced by numerous studies, positively impacts water efficiency, productivity, and quality. However, petroleum-based plastics contribute to global warming by increasing carbon emissions and can persist in the environment for years, even when they begin to degrade, breaking down into small particles that mix into soil, water, and food, posing risks to human, animal, and environmental health. The use of biodegradable bioplastic mulch materials, which naturally decompose without polluting soil and the environment, has become essential in agriculture. To replace petroleum-based mulches with biodegradable and eco-friendly bioplastic alternatives, it is imperative to achieve significant product quality, including water vapor permeability and mechanical properties, to meet the economic expectations of supply and demand. This study demonstrates the strong relationship between sustainability and the agricultural sector, examines research related to bioplastic mulch materials, evaluates the current state of products in the market, compares their characteristics, and also assesses research conducted to the perspectives of production, application, and characterization.
Production of multifunctional nanoparticle-reinforced polymer composite surfaces by photopolymerization method and investigation of performance characteristics
In the recent years, Stereolithography (SLA) type three-dimensional (3D) printers have gained increasing importance in the production of composite materials due to their high precision, low surface roughness, and minimal material waste. Also known as additive manufacturing (AM), 3D printing enables the fabrication of complex geometries that are difficult or impossible to achieve with conventional manufacturing techniques. This technology offers design flexibility and production efficiency, making it widely used in biomedical, automotive, aerospace, and defense sectors [1,2]. SLA technology, first introduced in the 1980s using UV lasers, is based on the principle of layer-by-layer polymerization of liquid photopolymer resins via computer-controlled ultraviolet light. During the process, semi-liquid raw materials are solidified into high-resolution and dimensionally accurate geometries. The mechanical, thermal, and electrical properties of parts produced using SLA can be precisely optimized compared to conventional production methods. With recent technological advancements, research on the fabrication of nanocomposite materials via SLA has significantly increased. The design freedom, cost-effectiveness, and production speed offered by SLA technology have accelerated investigations in this field. In this thesis, nanocomposite surfaces were fabricated by incorporating nanoparticles into a photopolymer resin with concentrations of 1%, 3%, and 5%. The specimens were produced layer-by-layer using an Anycubic SLA printer with a layer thickness of 50 microns. Surface resistivity measurements were performed in accordance with the TS EN 1149-1:2006 using an ELME Multimeg device under controlled conditions of 25°C and 50% relative humidity. The results indicated that all samples exhibited surface resistivity values exceeding 1012 ohms, confirming their high electrical insulation performance. Additionally, antibacterial activity tests, conducted in accordance with TS ISO 22196, revealed that all formulations exhibited more than 99% effectiveness against S. aureus and E. coli. Electromagnetic shielding effectiveness (EMSE) was evaluated based on scattering parameters, and the materials demonstrated a shielding effectiveness of less than 5 dB in the 8–12 GHz frequency range. Consequently, the developed nanocomposites show potential for use in applications requiring electrical insulation, antimicrobial surfaces, and partial permeability to electromagnetic waves. Keywords : SLA resin, 3D printer, photopolymer, additive manufacturing, composite materials
Titanyum diborürün bağlayıcı alaşım ile basınçsız sinterlenmesi ve karakterizasyonu
Bu çalışmada TiB2 takviyeli Ni ve Fe alaşım matrisli kompozitler nispeten düşük sıcaklıkta basınçsız sinterleme ile üretilmiştir. TiB2 yüksek sertlik ve korozyon direncine sahip olan bir yüksek sıcaklık seramiğidir. Bağ yapısı ve düşük difüzyon katsayısı nedeniyle TiB2'yi saf halde sinterlemek güçtür. Bu nedenle sinterlenmesi için 1800 oC ve üzerinde sıcaklıklar gerekmektedir. Sinteleme sıcaklığı, metal bağlayıcı eklenerek düşürülebilmektedir. Ni, Fe ve alaşımları TiB2'nin sıvı faz sinterlenmesi için faydalı katkılar olarak bilinmektedir. Bu çalışmada ağırlıkça % 10, 17,5 ve 25 oranlarında TiB2 içeren Ni, Fe ve alaşımı matrisli kompozitler argon atmosferinde basınçsız sinterleme ile 1375 oC'de üretilmiştir. %10 Ni matrisin, bu sıcaklıkta sürekli bir matris oluşturmak için yeterli olmadığı bulunmuştur. Üretilen kompozitlerde ham bağıl yoğunluklar yaklaşık %65-70 ve sinterlenmiş bağıl yoğunluklar % 88-90 olmuştur. En yüksek sertlik ve eğme dayanımı değerleri, %25 Ni matrisli kompozitte sırasıyla 1556±115 HV0.2 ve 279 MPa değerleri ile elde edilmiştir. PEG kullanımı veya ılık sıkıştırma uygulaması yoğunluğu veya mikrosertliği arttırmada etkili bulunmamıştır. TiB2 parçacıklarının 6-10 mikrometre aralığında olduğu görülmüştür. Bazı deneylerde başlangıç tozlarına WC-Co ortamında bilyeli öğütme uygulanmıştır. Öğütülmüş tozlardan üretilmiş olan kompozitlerin mekanik özellikleri diğerleri ile benzer olmuştur fakat TiB2 parçacıkları 2-4 mikrometre aralığında olarak daha küçüktür. Kompozitlerin öğütme ortamından kaynaklanan WC parçacıklarını içerdiği SEM ve EDS analizleri ile belirlenmiştir. Fe, Fe+Ni ve Fe+Ni+Co matrisli kompozitlerin özellikleri, Ni matrisli kompozitlerden daha düşük olmuştur.
Hybrid 3D bioprinting of functionalized structures for tissue engineering
Tissue engineering is an interdisciplinary field of research aiming at developing methods and technologies for regenerating damaged tissues. It relies on a combinatory platform of biomaterials with cells and bioactive molecules to resemble the human microenvironment to stimulate tissue constructs. Hence, numerous factors, including biochemical, biophysical, and mechanical aspects of the host tissue, have to be taken into account for developing a successful tissue replacement. Skin replacements caused by traumas, injuries, and burns are a burden to the healthcare system globally. The human body cannot fully regenerate the tissue with all the functionalities and features in severe wounds or skin loss. Poor mechanical properties, scarring, delayed cell and biomolecules infiltration, and non/poor vascularization are the main challenges yet to be addressed. Three-dimensional (3D) bioprinting, also known as additive manufacturing (AM), a layer-by-layer fabrication method, is regarded as a gold standard technique with the ability of controlled deposition of biomaterials in the desired geometry by using computer-aided design (CAD) models. Together with the development of biomaterials and architecture design, 3D bioprinting could ease the long and complicated journey towards functional tissue regeneration. In this context, the fabrication of small fibers mimicking natural extracellular matrix (ECM), selection of functional material with good mechanical and biochemical properties, the inclusion of bioactive molecules to enhance functionality, and printability are prerequisite factors of successful scaffold fabrication. In this work, novel hybrid 3D bioprinting approaches have been developed for functionalized structures, mainly for skin tissue engineering. Within this framework, we first optimized the effect of printing parameters on fiber diameter for Melt Electrospinning Writing (MEW), a special 3D printing process, using response surface methodology (RSM) as a predictive tool. Then we copolymerized polycaprolactone (PCL) with polypropylene succinate to improve its degradation rate and hydrophilicity and functionalized it with silver nitrate to induce antibacterial properties, and finally, it was 3Dprinted using an extrusion-based printer. For preparing hybrid 3D bioprinting, we used a composite support-bath system based on Pluronic PF127 was formulated with the inclusion of Laponite RDS and calcium chloride as rheological modifier and stabilizer, respectively. The rheological characterization of support-bath showed thixotropic behavior with a high degree of recoverability which facilitated bioprinting of complex hydrogel structures within the support-bath through an extrusion system. Then, we fabricated a polymer-hydrogel construction using MEW-casting for skin tissue substitute. In this context, we first investigated the geometrical effect of melt electrowritten scaffolds on cord-like structure formation for pre-vascularization. Mesh scaffolds with 0-90and 60-120 degree orientations and honeycomb shape were explored and cell-laden gelatin hydrogels were infiltrated inside those PCL scaffolds, and the results suggested the potential of honeycomb structure for better mechanical and invitro properties. In the final stage, a functionalized hybrid MEW-hydrogel scaffold for wound healing was fabricated. A functionalized mesh structure of PCL-bioactive glass was created via MEW, and a gelatin hydrogel comprising basic fibroblast and vascular endothelial growth factors was cast within the mesh scaffold. In vivo implantation of hybrid scaffolds showed promising results for accelerating and functionality of the healed parts according to wound closure and histological evaluation.
Microfluidic integration onto gold microelectrode and its effect on electrochemistry
Integrated microfluidic devices are used in many medical, biological, and other applications due to their characteristics such as small size, sensitivity, reduced amount of needed analyte, ease of use, and accuracy of results. However, it has been noted the results depend on many variables, the most important of which is the electroactive area of the working electrode. In this study, Square Wave Voltammetry (SWV), Cyclic Voltammetry (CV), and Differential Pulse Voltammetry (DPV) have been used for examining four devices with working electrodes with varying electroactive areas altered by changing the size of the integrated channels (50, 100, 250, and 500 µm). The dimensions of the channels are directly related to the surface area of the working electrode. This study aimed to comprehend the changes in electrochemical responses such as macroelectrode-to-microelectrode conversion, limiting currents, the effect of scan rate. Also, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy(AFM) measurements were performed to analyze the nature of the electrode surface in terms of roughness and microstructure. The performance of the electrodes was determined by estimating the working areas for each electrode and conducting electrochemical and microscopic examinations for them. It was observed that when the effective area of the electrode becomes larger, the performance of the electrodes becomes better, and gives more accurate and definite results.
Photocatalytic applications of metal-organic frameworks
Metal-Organic Frameworks (MOFs) materials are a new class of crystalline porous materials that have emerged in chemistry and materials science in recent years, in which metals are bonded with covalent bonds and organic binders. MOFs are used in the catalytic degradation of organic dyes due to their semiconductor behaviors, porous structure, pore size, functionality, and excellent mechanical stability. MOFs containing different metal ligands can be produced by adjusting the structure and properties of MOFs with the appropriate choice of building blocks. In this study, the photocatalytic activity of Zr-based MOFs under an LED light to remove methylene blue (MB) colors was investigated by using PDOP as initial templates for the production of visible light-sensitive photocatalysts. The chelate formation between Zr4+ and polydopamine (PDOP) led to the nucleation of Zr-O clusters. This cluster nucleation also facilitated the growth mechanism of MOFs on the PDOP. MOF photocatalytic performance was investigated using a LED light source. Also, MOF's physical and chemical properties were investigated using XRD, SEM, and FTIR. Thanks to the newly synthesized catalysts, remarkable rates of photodegradation have been achieved.
h-BN seramik malzemelerin yapısı, morfolojik ve optik özelliklerinin incelenmesi
Bor önemli bir elementtir ve tek başına doğada bulunmaz, başka elementler içeren bileşiklerde bulunur. Bor, savunma endüstrisinden ilaç endüstrisine, temizlik maddelerinden nükleer endüstriye kadar modern teknolojide geniş bir kullanım alanına sahiptir. Borun bu önemli ve vazgeçilmez konumu gelecekte de artarak devam edecektir. Bu çalışmada borun, dünya ve Türkiye için son derece önemli olan endüstriyel yapısı, elektriksel ve teknik özellikleri hakkında bilgi vermektedir. Ayrıca bu çalışmada bor oksidin karbon ve nitrojen ile reaksiyonu sonucunda hekzagonal bor nitrür oluşumu araştırılmıştır.
Investigation of the effect of sepiolite clay, silica aerogel fillers and cnsl content on the properties of organic brake pad composites
Friction materials have an important place in both highways and railways. Brake pads are mainly produced by a mixture of four main groups of materials: binders, reinforcements, friction modifiers and fillers. Selecting these materials in appropriate ratios and optimizing them according to the desired properties of the final product has a crucial effect on both the mechanical and tribological properties of brake pads. It is seen in the literature that many different types of materials are used to improve these properties. In this study, sepiolite clay and silica aerogel, which to our knowledge was never used for this purpose, were used as alternative fillers in organic brake pad composite materials. Composites with different amounts of these fillers were prepared and their density, porosity, friction and wear properties were characterized. The effect of the content of cashew nut shell liquid (CNSL) on the properties of the composites was also investigated. The results show that, the sepiolite clay used as filler clearly increases the hardness of the composites, while the silica aerogel filler has a decreasing effect on the hardness. While both fillers did not show a significant effect on the friction coefficient level, they have a positive effect on the wear properties as they relatively decrease the specific wear rate. An improved friction stability was also observed for some compositions. It is well known that synergistic effects between different fillers can be used in friction materials. Sepiolite clay and silica aerogel combined with an optimum CNSL content are good candidate for future researches and uses in organik brake pad composites.
Grafen nanolevha/şekil hafızalı polimer nanokompozitlerin termal ve mekanik karakterizasyonu
Şekil hafızalı polimerleri son yıllarda geliştirilen en önemli malzemelerden biri olarak adlandırabiliriz. Dış uyaranlara tepki vermesi ve malzemede oluşturulan deformasyonu malzemenin ilk haline getirebilmesi özelliğiyle teknolojik ve bilimsel açıdan büyük öneme sahiptir. Şekil hafızalı polimerlerin sahip olduğu potansiyel sayesinde gelişmiş havacılık, ticari uygulamalar ve biyomedikal alanda geniş bir kullanım alanına sahiptir. Poliüretan bazlı şekil hafızalı polimerlerin biyo uyumluluk özelliği göstermesi bu malzemeleri tıbbi ürünler için uygun hale getirmiştir. Son yıllarda grafen bazlı malzemelerin biyo uyumluluk özelliği üzerinde yapılan çalışmalarda elde edilen olumlu sonuçlar ile biyomedikal alanda yapılan çalışmaların sayısı artmıştır. Bu çalışmada, Mitsubishi Heavy Industries firmasının üretmiş olduğu SMP MP3510 poliüretan bazlı polimerinin biyo uyumluluk özelliğini kaybetmeden termal ve mekanik özelliklerini iyileştirmek hedeflendi. Yüksek hızda mekanik karıştırma yöntemi ve ultrasonik karıştırma ile yüksek hızda mekanik karıştırmayı içeren hibrit bir yöntem kullanılarak ağırlıkça %0.1, %0.3 ve %0.5 grafen nanolevhalar eklenerek elde edilen nanokompozitlerin termal özelliklerini incelemek için diferansyel taramalı kalorimetre, termogravimetrik analizleri, mekanik özelliklerini incelemek için 3 nokta eğme testi ve Shore D sertlik testi, kimyasal yapısını incelemek için fourier transform infrared spektrometresi analizi, nanokompozitlerin kesit alanından grafen nanolevhaların dağılımını incelemek için taramalı elektron mikroskobu ve grafen nanolevhaların nanokompozitlerin yüzey morfolojisine etkisini incelemek için atomsal kuvvet mikroskobu ve taramalı elektron mikroskobu analizleri yapıldı.
Investigation of structural, morphological andoptical properties of deposited cdzns semiconductor
In this study, Cadmium Zinc Sulfide thin films, which are frequently used as a buffer layer in solar cells, have been deposited in proportions and the resulting thin films have been investigated in terms of structural, morphological and optical features. Chemical bath deposition method was used in the experiments. Zinc was used in different proportions and the results were discussed. Cadmium Zinc Sulfur material has been studied as a thin film, but its effect in the solar cell has not been investigated. In the experiments, the temperature of the water bath was 70 degrees and the time took 8 minutes and 15 seconds.
Elektrokimyasal kaplama yöntemi ile Au-Ag-Cu üçlü alaşımlarının oluşturulması
Gold-Silver-Copper alloys have high electrical conductivity and high corrosion and wear resistance. They are mostly used in slip rings, which are the significant part of electromechanical systems having ability to rotate 360° such as air, naval and land defense systems, medical devices like magnetic resonance imaging or computed tomography. In the scope of the study, static potential and cyclic voltammetry measurements were done to determine the optimum potassium cyanide amount and reduction potential for gold, silver and copper metal ions from unary, binary and ternary mixtures of potassium gold cyanide, silver cyanide and copper cyanide plating baths. The effects of different potassium cyanide, potassium gold cyanide, silver cyanide and copper cyanide concentrations and reduction potentials on the deposited alloy composition were studied. Analyses by scanning electron microscopy, energy dispersive spectroscopy and x-ray fluorescence characterization devices were carried out to obtain information on surface morphology, coating thicknesses and alloy compositions from the top and cross section of samples. Moreover, hardness tests of samples having different alloy compositions were done and results were compared with electroplated pure Au. Finally, scratch test via nano-indentation device was done to observe the bonding strength between gold-silver-copper alloy and nickel coating layers.
Silicon carbide reinforcement silver metal matrix nanocomposite coatings on copper by different electrodeposition methods and amount of silicon carbide
Silver is the most preferred materials metal between others in electronic and electrical industry because it has the highest electrical conductivity at room temperature. It has some intrinsic qualities such as great electrical and thermal conductivity. So, silver can be used for coating applications for electrical and electronic conductors. However, there are some weak properties for example low mechanical properties. Therefore, silver electrical contact materials can be reinforced by the second phase such as silicon carbide and carbon nanotube. In this study, silicon carbide has chosen as second phase for nanocomposite coating because of its unique mechanical and chemical properties. Unreinforced silver and various amounts of nano-sized silicon carbide reinforced silver metal matrix nanocomposite coatings were obtained by using electrodeposition technique to improve electrical properties. Different types of current which are direct current, pulse current and pulse reverse current were used. The influences of different types of current and various amount of nano-sized silicon carbide on the morphology, crystallographic orientation, mechanical and electrical properties were investigated with Scanning Electron Microscope, X-Ray Diffraction methods, Vickers's Micro Hardness test and electrical contact test respectively. Taking into account all of these, the best mechanical property was obtained with reinforced Silver by silicon carbide which were used 1 g/L amounts by pulse reverse current electrodeposition method. Also, the best electrical contact performance was obtained with reinforced by silicon carbide which were used 1 g/L amounts by direct current electrodeposition method.
Usage of organoboron based polymeric materials at enzymatic biosensors
The application and characterization of organoboron polymers to electrochemical enzymatic biosensors, which have only been tested in a limited number, have been examined within this thesis's scope, and patent applications will be made since this is one of the pioneering studies. Therefore, contribution to the literature will be made. In this thesis, the use of biocompatible organoboron polymers as enzyme immobilization molecule is added value to the biosensor system to be prepared in many ways. Utilizing the direct electropolymerization (one-step) method, an electrochemical enzymatic biosensor system was developed with polyaniline film coated carbon screen printed electrodes, and poly 3-aminophenylboronic acid film coated gold screen printed electrodes/ glassy carbon electrode, and novel organoboron polymer film-coated platinum screen printed electrodes/glassy carbon electrode. Organoboron polymer-based enzymatic and electrochemical analysis that will be developed in this thesis will be used for the determination of catechol that is one of the mostly analyzed phenolic compounds in the chemistry and agriculture industry. Catechol analysis was developed in which the tyrosinase enzyme was used as the sample determination system. With the developed biosensor system, the phenolic components were tested in the linear range between 1 µM to 200 µM with different electrodes. After the biosensor performance conditions optimization, real sample analysis were also performed for controlled catechol added green tea samples with 3% to 10% range of standard deviation results. Finally, it should be noted that the developed biosensor system can be designed and commercialized as a portable end product that allows real-time detection. Phenolic compounds, which are determined to determine the antioxidant and antimicrobial activities of natural foods, are partly made within the scope of quality control analysis, and the developed organoboron polymer-based biosensor system will allow faster, cheaper, precise, and real-time tests.