Theses supervised by Prof. Dr. Erdal Çelik
10 theses · Dokuz Eylül University
Production of BaMeO3 doped YBCO superconducting thin films by TFA-MOD technique
High temperature superconducting materials (HTS) possess very high critical density (Jc) values at low temperature and magnetic fields. In these kinds of studies, crystalline defects, such as fine precipitates of non-superconducting phases, dislocations, vacancies, grain boundaries, twin boundaries, antiphase boundaries and insulating regions in grain boundaries are considered to act as pinning centers. However, the Jc values rapidly decrease with increasing temperature in magnetic field. The main reasons of the Jc depression are recognized to be the intrinsic crystalline anisotropy of HTS and the thermal fluctuations. Nevertheless, the lack of effective pinning centers should be noted as one of the main reasons. Depending on these reasons, a novel technology has been developed by means of a nanostructure engineering to create artificial pinning centers in HTS materials. In this respect, increasing critical current density and improvement of flux pinning properties of YBa2Cu3O6.57 (YBCO) superconducting films with BaMeO3 (Me: Zr, Hf, Ir, Sn, Mn, Mo, Nb etc.) perovskite nanodots, nanorods or nanoparticles, as pinning centers, on SrTiO3 substrate are aimed using TFA-MOD method in this study.
The fabrication and technical applications of multifunctional materials
The ability for materials to respond to the needs in a useful manner has broad technological impact. Such "smart" systems are being developed in which material properties (such as mechanical, electrical, optical or magnetic characteristics) respond to external stimuli. Composite materials are ideally suited to achieve multi functionality since the best features of different materials can be combined to form a new material that has a broad spectrum of desired properties. In this study, the aim is to further the investigations of these types of materials and to advance the molecular understanding of novel multifunctional materials for applications across different scientific disciplines. Regarding the production of multifunctional materials; 4 types of materials will be added to polymer matrix to obtain those properties to the final product; antibacterial painting/coating, radar absorbing materials, self-healing materials and flame retardant material. In this research, an epoxy dye was converted to a multifunctional material which is capable of performing multiple functions. In order to reinforce the polyurethane/epoxy dyes, Ag nanoparticles, huntite/hydromagnesite minerals, barium hex ferrite particles and chitosan were utilized for multifunction property. Adding by those materials to the polymer matrix with different loading level and coating the substrates, different types of coated samples are obtained. Subsequently the samples were characterized by antibacterial tests, flame retardant tests, radar absorbing tests and self-healing tests. It was concluded that these materials exhibited a synergetic beneficial effects.
Production and industrial application of nanostructured flame retardant reinforced composite materials
Paints used in many areas of daily life are used with the aim of creating in surface protection and decorative designs of materials. These paints contain material susceptible to fire such as polymeric binders, organic solvents. Because of this reason, paints easily burn. In this study, flame retardant properties of plastic paint material were investigated and tried to be developed. In this context, composite materials were obtained by adding different amounts of environmentally friendly (hologen-free) and nanosized flame retardant materials such as huntite/hydromagnesite, antimony (III) oxide and boric acid to paint material. And then these composite materials were characterized by XRD, XPS, FT-IR, DTA-TG, SEM, surface roughness and hardness testing machines. Candle flame test standards were also performed to examine flame retardant properties of these composite materials. After the results of the performed tests, composite materials were determined to exhibit excellent flame retardant properties. Keywords: Flame retardant, paints, polymer, nanocomposites
Production and industrial applications of heat releasing electronic nanocomposite materials for heating systems
Elektrikle ısıtma teknolojisi, günümüzde birçok cihaz ve cihaz bileşeninde kullanılmaktadır. Bu teknoloji genellikle iletken bir metal üzerinden geçen elektrik akımının metalin elektriksel direnci sebebiyle ısı üretilmesi prensibine dayanmaktadır. Disiplinler arası bir bilim olan malzeme bilimi; insanlık ihtiyaçlarını karşılayacak cihazların geliştirilmesi için uygun malzemelerin araştırılması ve geliştirilmesi olarak tanımlanabilir. Bu tez kapsamında mevcut metalik ısıtma elemanlarının yerini alabilecek nitelikte karbon içerikli katkılara sahip polimerik kompozit filmlerin üretilmesi hedeflenmiştir. Doğası gereği yalıtkan olan polimerler karbon içerikli katkılar yapılarak iletken hale getirilmiştir. Üretilen filmleri yapılarının aydınlatılabilmesi için; XRD, XPS, FT-IR, DTA-TG, SEM ve NI cihazları ile karakterize edilmiştir. Yapısal analizlere ek olarak üretilen filmlerin elektriksel özellikleri, ısıtma davranışları belirlenmiştir. Optimum filmler kullanılarak ısı yayan tekstiller, sauna, kombi ve sera ısıtma sistemleri gibi prototip uygulamalar gerçekleştirilmiştir. Polimer kompozitlerde perkolasyon eşiği kavramı ile açıklanan, kritik bir katkı kompozisyonunda yalıtkan iletken geçişi söz konusudur. Kritik iletkenlik geçişi grafit ve karbon katkıları için sırasıyla ağırlıkça yüzde 15 ve 13 olarak belirlenmiştir. Bu nedenle üretilen filmlerle eşdeğer dirence sahip ancak daha az katkı miktarına sahip filmlerin üretilmesi hedeflenmiştir. Bu doğrultuda perkolasyon eşiğinin aşağı çekilebilmesi için koperkolasyon olarak tanımlanan, karbon ve grafit katkılarının birlikte farklı oranlarda kullanıldığı filmler üretilmiştir. Bu filmler ile hedeflendiği gibi; daha az katkı ile koperkolasyon da başarı sağlanmıştır. Kütlesel üretim amacı göz önünde bulundurulursa, katkı miktarında azalma üretim maliyetlerinde önemli olacaktır. Bilimsel sonuçlara ek olarak; çalışmanın özgünlüğünün ve yenilikçiliğinin bazı kuruluşlarca onaylandığı belirtilmelidir. İlk olarak çalışma Türk Patent Estitüsü tarafından 2009/05515 patent numarası ile korumaya alınmıştır. Çalışma 2009-2011 yılları arasında Türkiye Cumhuriyeti, Bilim, Teknoloji ve Sanayi Bakanlığınca SANTEZ (00360.STZ.2009-1) kapsamında desteklenmiştir. Projenin sonlandırılmasını takiben 2013 yılı Mart ayı içerisinde en iyi SANTEZ projesi seçilmiş ve ödül bizzat bakan Nihat ERGÜN tarafından takdim edilmiştir.
Design of synthesis of new generation rare earth doped K2Ln2Ti3O10 semiconducting films and their industrial applications
In this study synthesis and characterization of K2Ln2Ti3O10 (Ln; La, Nd, Gd, Sm, Dy) thin films were investigated for photocatalyic applications. Newly developed layered perovskite structures are produced by sol-gel method. With this aim, transparent solutions were prepared from K, Ti, La, Nd , Gd, Sm and Dy based precursors, propionic acid and glacial acetic acid (GAA). The obtained solutions were dried at 200 degree celcius in air to form gel structure of KLTO mixture and heat treated at 850 degree celcius for 3 hours in air. After the sintering, the powders were dispersed in propionic acid and the obtained suspensions were deposited on Si substrates using spin coating system and then annealed at 1000 degree celcius for 5 hours in air. Thermal, structural, microstructural, mechanical properties of the coatings were characterized through differential thermal analysis-thermogravimetry (DTA-TG), Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), surface profilometer, nanoindenter and scratch test devices. Methylene blue photocatalytic performance experiments were carried out in a solar box which is simulating natural radiation and ultraviolet-visible (UV-Vis) absorption spectra. According to the measurement results of K2Ln2Ti3O10 (Ln; La, Nd, Gd, Sm, Dy) samples, K2La1.5Sm0.5Ti3O10, exhibit the highest photocatalytic activity.
Production and application of n- and p-type Si wafer using CVD method
Necessity for electricity is one of the most significant issues of present time. Rapid consume of most used underground resources made it necessary for researching the new kind of energy sources. After the increase of daily requirements and quality necessities, innovations in electric production technologies gained importance. Production of electricity from the sun is based on the principal of contacting the two sides of a semiconductor stimulated by sun and the returning of electrons which have been sent to conductivity level to their initiation locations after completing the entire circuit. Materials science which is a multidisciplinary branch could be defined as investigation and development of proper tools for providing sources for humanity. In this respect, in the scale of current thesis, production of solar cells for renewable energy obtainment using modified semiconductor silicon wafers was aimed and studied. Single crystal structured crystal wafers with semi-conductive character were modified and the stimulation of material with sun light was achieved. In order to enlighten the structures of the produced solar cells, SEM, XRD, XPS, UV-vis and profilometer calculations were carried out. In addition of structural analysis, electrical properties of the produced cells were determined. There are many remarkable factors in current study in order to benefit fully from the sunlight. By texturation, refraction of photons interacted with surface was prevented opposite to the angle they interacted. Optimum realization studies of electron-hole separation were achieved with diffusion time determination. With utilization of reflection blocker coating, absorption of rays interacted with the surface of solar cells was provided. In addition to the scientific results, with the support of İZ-KA to the current study, more attention to renewable energy in Dokuz Eylül University was gained. Thanks to the energy stations in university in scope of current project, charging the batteries of electrical devices was realized.
Processing, characterization and development of rare earth doped lead magnesium niobate ferroelectric ceramic capacitors by sol-gel technique
The present thesis demonstrates synthesis, characterization and electrical properties of relaxor ferroelectric pure Lead Magnesium Niobate (PMN) and Rare Earths (RE) (Er, Eu, Dy, Sm and Tb) doped nano scale powders and PMN thin films on n-type Si substrates using sol-gel technique for capacitor applications. With this respect, transparent solutions were prepared from Pb, Mg and Nb based precursors, methyl alcohol and glacial acetic acid (GAA). The obtained solutions were dried at 80 degree celcius for 60 minutes in air to form gel structure of PMN mixture and heat treated at 530 degree celcius for 3 hours and consequently annealed at 950 degree celcius for 2 hours in air. After the sintering, the PMN powders were milled for 12 hours at room temperature to obtain PMN based nano scale powders. Finally, the powders were dispersed in alcohol and the obtained suspensions were deposited on n-type Si substrates using drop and spin coating systems and then annealed at 730 degree celcius for 1 hour in air. Thermal, structural, microstructural, optical, mechanical and electrical properties of the powder and the coatings were characterized through differential thermal analysis-thermogravimetry (DTA-TG), Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), atomic force microscopy (AFM), dynamic ultra hardness tester (DUH), scratch tester, refractometer, spectrophotometer, high resolution dielectric analyzer machines and Keithley 2400 for current-voltage characterization. The results showed that it was possible to produce the perovskite phase PMN based thin films at 730 degree celcius using sol-gel derived powder precursor suspension method. The optimum capacitor films were successfully applied to a light emitting diode (LED) flash device for camera for very low filling and draining time (17 ms).
Titanyum dioksit esaslı fotokatalizör kullanılarak toksik madde içerikli atık suların detoksifikasyonu
Sanayi, tarımsal faaliyetler ve evsel ürünlerde kullanılan kimyasallar artan bir ivmeyle çevre kirliliğine yol açmaktadırlar. Bu kimyasallar son derece düşük konsantrasyonlarda bile zararlı olabilecek maddeleri içermektedirler. Söz konusu bu maddeler su, hava ve toprağı küresel düzeyde kirletmektedir. Özellikle son yıllarda atmosferin ve yaşadığımız çevrenin evsel ve endüstriyel atıklardan dolayı kirlenmesi, en ciddi sorunlardan biri haline gelmiştir. Çevre kirliliğinin gideriminde kimyasal arıtım ve kimyasal dezenfeksiyon yerine güneş ışığı gibi yenilenebilir enerji kaynaklarının kullanılması çevre dostu sistemlerin geliştirilmesinde büyük önem taşımaktadır. Bir fotokatalizör varlığında kirlilik giderimi çevre dostu uygulamalara örnek verilebilir.Bu çalışmada sol-jel tekniği ile cam altlıklar üzerine endüstriyel boyutlarda Vanadyum (V), Erbiyum (Er), Seryum (Ce) katkılı/katkısız TiO2 ince film kaplamaların üretilmesi ve bu altlıklar kullanılarak atık sularda bulunan siyanürün fotokatalitik parçalanması amaçlanmıştır. Üretilen filmlerin yapısal, mikroyapısal, elektriksel özellikleri incelenmiş ve cam altlıklar üzerine kaplanmış ince filmler UV/güneş ışık kaynağı altında atık sularda bulunan siyanürün fotokatalitik parçalanmasında fotokatalizör olarak kullanılmıştır. Sonuç olarak modifiye edilmiş TiO2 filmlerin kullanımıyla atık sularda bulunan siyanürün parçalanmasında 85-90% verim elde edilmiştir.
Synthesis of superconducting films and improvement of their flux pinning properties with barium zirconate nanoparticles using chemical solution deposition method
The present thesis demonstrates synthesis and characterization of BZO doped YBCO and GdBCO superconducting thin films on STO and LAO single crystal substrates using chemical solution deposition technique for high magnetic field applications. With this respect, transparent solutions were prepared both from commercially available YBCO powder and metal acetates seperately by using different types of solvents as methanol, ethanol and propionic acid. Contact angle values of these solutions on STO and LAO substrates were determined to estimate their wettability features. A detailed rheological characterization was performed to determine shear profile and scrutinize effect of temperature on viscosity. The solutions were spin coated on the substrates and heat treated according to the profile. Thermal, microstructural and electrical properties of BZO doped superconducting thin films were determined through DTA-TG, FTIR, XRD, SEM-EDS, AFM, inductive critical transition temperature, inductive critical current density and transport measurements. The results show that six mol percentage BZO doped YBCO samples on both substrates possess the highest critical current density value for all magnetic fields. Additionally, GdBCO superconducting thin films exhibit higher critical transition temperature and self-field critical current density values in comparison to the YBCO films. According to the measurement results of GdBCO samples, the twelve mol percentage BZO doped GdBCO sample on STO substrate possess the highest critical current density value for all magnetic fields. These results indicate that the BZO dopant in the structure act as artificial pinning centers and increased the current carrying capability of films in magnetic field conditions.
Yarıiletken termoelektrik malzemelerin ve jeneratörlerin yenilikçi yaklaşımlarla üretilmesi ve geliştirilmesi
Termoelektrik kelimesi, yapı itibariyle sıcaklık ve elektrik kelimelerinin bileşiminden oluşan, ortamdaki sıcaklık farkı ile çalışan ve bu çalışma sonucunda elektrik üretebilen yarıiletken malzemelerin genel ismidir. Yapılan bu çalışmanın hedefi, yüksek sıcaklıklarda da çalışabilen yarıiletken termoelektrik malzemelerin ve termoelektrik jeneratörlerin yenilikçi yaklaşımlarla üretilmesi, geliştirilmesi ve otomobil egzoz sistemine uygulanmasıdır. Bu çalışmada, otomobillerin motorlarından güç alarak çalışan ve aküyü şarj eden şarj dinamosu yerine, otomobilin egzoz sistemine yerleştirilecek termoelektrik jeneratörle elektrik üreterek aküyü şarj etmek ve dolayısı ile motor verimini artırarak yakıt tüketiminin azaltılmasını sağlayacak olan malzemelerin üretilmesi hedeflenmiştir. Bu kapsamda, termoelektrik jeneratör üretiminde kullanılacak seramik esaslı p- ve n- tipi termoelektrik yarıiletken malzemeler sol-jel yöntemi ile üretilmiştir. P- tipi tozların üretimi için kalsiyum kobalt oksite gümüş ile birlikte ilk defa nadir toprak elementleri (Lantan ve Europyum) katkılanmıştır. Diğer yandan n-tipi malzemelerin üretimi için çinko oksite alüminyum ve germanyum katkılanarak çinko alüminyum germanyum oksit tozları sentezlenmiştir. Belirtilen malzemelerin Fourier Dönüşümlü Kızılötesi Spektroskopisi(FTIR), Diferansiyel Termal Analiz ve Termogravimetrik Analiz(DTA-TG), X-Işını Difraksiyonu(XRD) ve X-Işını Fotoelektron Spektroskopisi(XPS) analizleri gerçekleştirilmiş ve yorumlanmıştır. Üretilen yarıiletken seramik malzemelerin termoelektrik jeneratör üretiminde verimli olarak kullanılabilir olduğu tespit edilmiştir.