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Titania is one of the most preferable ceramic membrane materials of superior durability (as zirconia) when compared to that of other ceramics, e.g. alumina or silica. The surface charge of the membrane top layer is an important parameter of the separation performance of the multilayer ceramic membrane due to the Donnan exclusion mechanisms. In this study, the change of the surface charge of unsupported nano-structured titania top layer is investigated with calcination temperature variation. The effect observed indicates the possibility of preparation of tailor-made top layers for multilayer ceramic membranes. © 2019, University of Chemical Technology and Metallurgy.

The purpose of the research is to investigate the changes in microstructure and physicochemical characteristics, mainly surface charge (i.e. zeta potential) of zirconia membrane top layer during calcination. Zirconia is one of the most commonly preferred materials for ceramic membrane top layers due to its superior durability. The physicochemical properties of the top layer composed of submicron / nano particles is necessary not only for Donnan exclusion but also for dynamics of membrane fouling. In the present research the possibility of preparation of zirconia top layers with varying surface charge with changing calcination temperature was shown and a correlation between phase transformation and surface charge was determined.

Aim: The aim of this study was to investigate the interaction of a high viscosity glass ionomer cement (GIC) and a composite resin with caries affected dentin and to determine the remineralization levels. Materials and methods: In a split mouth design 24 GIC and composite resin atraumatic restorative treatment restorations were made in vivo and the teeth were collected after 2 years and subsequently sectioned and examined using Vickers microhardness test; the latter was performed starting from the dentin surface adjacent to the restoration. Repeated Measure ANOVA and Bonferroni statistical methods were used for data analysis. Results: The microhardness adjacent to the GIC restorative material resulted to be significantly higher. Conclusion: GIC resulted to be a better restorative material for the remineralization of caries affected dentin, though further studies are necessary for the corroboration of this finding. The GIC restored primary molar dentin had a higher level of remineralization and GIC could be the material of choice in pediatric dentistry.

Iron and nickel doped TiO2 thin films were prepared on glass slides by using sol-geland dip coating techniques. X-Ray Diffraction (XRD) analysis showed that there may be a 164solid state solubility limit of 2% on atomic basis and Fe/Ni oxide phases may be formed onthe TiO2 grain boundaries beyond this doping level. Diffuse Reflectance Spectroscopy (UVVISDRS) analysis showed that light absorption range of TiO2 was extended to visible lightregion by Fe and Ni doping. Visible light photocatalytic activities of the prepared films weredetermined by methylene blue degradation experiments. The highest activities were obtainedwith 5% Fe and 1% Ni monodoped TiO2 films as 22% and 28%, respectively. TiO2 films codopedwith 1-5% Fe-Ni were prepared in the light of these findings and the highest activity(34%) was achieved with 2% Fe-2% Ni co-doped TiO2 film. It was concluded that anoptimum nanophase structure and optical properties were achieved at this co-doping level., Cam lamlar üzerinde demir ve nikel katkılı titanyum dioksit (TiO2) ince filmleri sol-jel ve (dip coating) daldırmalı kaplama teknikleri kullanılarak hazırlanmıştır. X-ışını kırınımı (XRay Diffraction, XRD) analizleri Fe ve Ni için atomik bazda %2 civarında bir katı hal çözünürlüğünün olabileceğini ve bu katkı düzeyinin üstünde TiO2 parçacık ara yüzeylerinde bu elementlerin oksit fazlarının çökebileceğini göstermiştir. TiO2’in ışığı soğurma aralığının Fe ve Ni katkısı ile görünür ışık bölgesine genişletilebileceği UV-VIS DRS (Diffuse Reflectance Spectroscopy) çalışmaları ile belirlenmiştir. Hazırlanan filmlerin görünür ışık fotokatalitik aktiviteleri metilen mavisinin bozundurma çalışmaları ile saptanmıştır. En yüksek fotokatalitik aktiviteler %5 Fe ve %1 Ni tekil katkısı için sırası ile %22 ve %28 olarak bulunmuştur. Bu bulgular ışığında %1-5 aralığında Fe/Ni birlikte katkılı filmler hazırlanmış ve bu filmler arasında %2 Fe-%2 Ni içeren filmle en yüksek fotokatalitik aktivite (%34) elde edilmiştir. Çalışmanın bulguları bu birlikte katkı seviyesi ile optimum nanofaz yapısına ve optik özeliklere sahip TiO2 filmin hazırlandığını göstermiştir.

In this study, rare earth (RE) doped/undoped TiO2 powders were prepared by chemical precipitation/co-precipitation method and used in photocatalytic hydrogen production through artificial photosynthesis. Relatively high hydrogen production rates were obtained at low heat treatment temparatures due to the high surface areas. RE doped TiO2 powders heat treated at 700 oC produced more hydrogen per unit area due to their higher surface reactivity compared to all the other pure TiO2 powders. Properties of the doped powders like favorable anatase-rutile ratio and high light absorption capacity enhanced the photocatalytic activity by several folds by a relatively low RE doping level of 0.1%, Bu çalışmada nadir toprak elementi (NTE) katkılı/katkısız titanya (TiO2) tozları yapay fotosentezle fotokatalitik hidrojen eldesine yönelik uygulamalarda kullanılmak üzere kimyasal çöktürme/birlikte çöktürme yöntemi ile hazırlanmıştır. Düşük ısıl işlem sıcaklıklarında yüksek yüzey alanlarından dolayı yüksek hidrojen üretim miktarları elde edilmiştir. Yüzey aktivitesi bakımından ise 700 oC’de ısıl işlem görmüş katkılı tozların diğer tüm saf tozlara göre birim alan başına daha fazla hidrojen ürettiği saptanmıştır. NTE katkısı ile TiO2’in faz yapısında değişiklikler meydana getirilmiş, optimum anataz-rutil faz oranına sahip ve ışık soğurma kapasitesi yüksek bir nanoyapı elde edilmiştir. Katkıyla tozlarda oluşturulan bu özellikler görece düşük bir miktar olan % 0,1 katkı düzeyinde bile TiO2’in fotokatalitik aktivitesinin birkaç kat artmasını sağlamıştır

Hydroxyapatite (HAp) thin film coatings were prepared on bioinert glass slides by a particulate sol method and the effects of intermediate silk fibroin and silk sericin coatings on the HAp film formation and surface topography were examined. The films prepared with smaller crushed particle sols had a higher agglomeration tendency during the drying consolidation step of the thin film formation, and contained agglomerates larger in number and size, which was demonstrated experimentally and in accordance with the DLVO theory. In the thin films prepared on intermediate sericin and fibroin films the number and size of agglomerates were decisively reduced, forming homogeneous films of predominantly primary particles, especially for the larger particle size sols. The regular surface electrostatic potential arrangements of the β-sheet structures of the sericin and fibroin, and of hydroxyapatite crystals, gave rise to the coulombic attraction driven surface energy minimization, enhancing the hydroxyapatite thin film formation process. The positive degree of cooperativity in the hydroxyapatite particle deposition on the silk protein coatings was disrupted by the particle agglomeration tendency.

Proceedings of the 8th Conference and Exhibition of the European Ceramic Society; Istanbul; Turkey; 29 June 2003 through 3 July 2003, In this study preparation of fine alpha alumina powders derived from Bayer gibbsite was studied. Preparation of the alumina powders was performed by decomposition of the gibbsite into transition alumina phase followed by controlled transformation to the alpha phase. Gibbsite was thermally treated at 350°C and 900°C to obtain a transition form of alumina. The purpose of the heat treatment at 350°C was to increase the surface area of the gibbsite particles and obtain a loosely packed structure that may reduce the size of the rather coarse precursor gibbsite during the grinding step. Mechanical treatment (by using ultrasonic forces and impact forces) was utilized to increase the transformation rate to the alpha alumina in the transition phase matrix and influence the nucleation and growth rate of the solid -solid phase transformation. These powders were calcined at 1100, 1200 and 1450°C for 1 to 8 hours. Results indicated that transformation to the alpha phase was accomplished in the powders preheated at 900°C, ultrasonically treated or ground, and then calcined at 1200°C for 2 to 8 hours or at 1450°C for 2 hours. Ultrasonic treatment accelerated the transformation rate to the alpha phase at 1100°C in 2 hours. Powders that were calcined at 1100 to 1200°C for 1 hour had a significant kappa content together with the alpha phase. Additionally the powder prepared without mechanical treatment and calcined at 1100°C was mainly in the kappa phase.

Nanokristal seramikler, ileri seramiklerin gelecekteki uygulamalannda önemli etkileri olabilecek özgün kimyasal, fiziksel ve mekanik özelliklere sahiptir. Bu çalışmada, tItanyum; izopropoksit'ten titan seramikleri hazırlanması ve karakterizasyonu incelendi. Şekillendirilmiş yapılar 650-850 C aralığında hava ortamında sinterlendi. Sol-jel prosesi ve jellerin kontrollü kurutulması ile elde edilen seramiklerin yoğunluklan teorik yoğrunluğun %79-99' u olarak bulundu. Sollar, jeller ve çökertme yöntemleriyle hazırlanan tozlardan preslenen peletlerin sinterlerne işlemi öncesi ve sonrası yoğunlukları sırasıyla teorik yoğunluğun %40-52 ve %55-83' ü olarak bulundu., Nanocrystalline ceramics possess unique chemical, physical and meehanical properties which may have a significant impact on the future applications of advanced cemmies. The preparatiion and characterization of titania ceramics from titanium isopropoxide precursor was investigated in this work. Green bodies were air gintered in the 650-850°C range for the determination of the sintering behaviour. The sintered densities of the cerainics prepared by sol-gel processing and controlled drying of the gels were in the 79-99% of theoretical density. The green and sintered densities of the pellets prepared by uniaxial pressing of powders derived from sols, gels and precipitation were in the 40-52% and 55-83% respectively.

Proceedings of the 8th Conference and Exhibition of the European Ceramic Society, The preparation of calcium phosphate based powders through chemical precipitation in order to determine the optimum conditions for the preparation of stoichiometric, thermally stable hydroxyapatite (HA) powders was investigated in this work. The effects of parameters like pH, aging time, and heat treatment temperature on the phase structure and morphology of the powders were investigated by SEM and XRD.HA was prepared at a Ca/P ratio of 1.67. The precipitation pH had a profound influence on the morphology and crystallite size of the powders in the 4-11 pH range. Relatively large 5?m prismatic particles were obtained at low pH whereas the powders were formed from agglomerates of nano sized particles at high pH. Powders had a HA dominant phase structure above a pH of 8. Phase pure HA powders were obtained with close to theoretical yields at pH = 10 and 11. The crystallite sizes of the powders varied from about 30 nm at 90°C to 50-90 nm at 1250°C with the smallest crystallite sizes obtained for pH 10 and 11 powders at 1250°C. The crystallite size increased significantly with aging temperature.

Proceedings of the 8th Conference and Exhibition of the European Ceramic Society; Istanbul; Turkey; 29 June 2003 through 3 July 2003, The preparation, characterization and pure gas permeation of sol-gel derived alumina membranes were investigated in this work. The effects of acid concentration/type and water content on the particle size in the sols and pore size distributions of the unsupported membrane were investigated by N 2 adsorption/desorption isotherms and Dynamic Light Scattering. Increasing the H +/Al 3+ mole ratio from 0.1 to 0.25 caused the hydrodynamic sol particle size and BJH pore size to decrease from 65 to 30 nm and 3.6 to 2.9 nm, respectively. The pore size increased from 2.8 nm to 3 nm upon increasing the calcination temperature from 500 to 600°C. Unsupported membranes were heat treated in the 200 to 1200 °C range for the characterization of the phase structure. Pinhole and crack free alumina membranes about 3 μm (2-layer) in thickness was observed from the SEM pictures with insignificant infiltration. The CO 2 permeability through the double layer γ-Al 2O 3 membrane calcined at 600 °C was 2.25*10 -7 mol/m 2.s.Pa, and had a slight pressure dependence indicating Knudsen Diffusion and Laminar Flow being the effective transport mechanisms. Upon the calcination of a similar 2-layer alumina membrane at 500°C, the CO 2 permeability decreased to 1.51 *10 -8 mol/m 2.s.Pa. without pressure dependence.

Artan su kıtlığı tüm dünya için bir tehdit oluşturmaktadır. Sanayide aşırı su kullanımı, yetersiz geri dönüşüm ve yüksek yağ konsantrasyonlu su atıkları çevre için tehlikeli sonuçlar doğurmaktadır. Yüksek yağ konsantrasyonlu su emilsiyonları su yaşamı, toprak, atmosfer, insan sağlığı için oldukça tehlikelidir. 20 µm ve altı boyutta küçük yağ parçacıklarını uzaklaştırmak için kullanılan geleneksel metotlar yeterince verimli olmamaktadır. Son yıllarda, yağlı su arıtımındaki avantajlarından dolayı seramik mikro/ultrafiltrasyon membranları keşfedilmiş ve geliştirilmiştir.Bu yüksek lisans tezinin amacı seramik destekli boru şeklindeki membran üretimini ve mikrofiltrasyonunu çalışmaktır. Hazırlanan metal kesme sıvısı çapraz akım filtrasyon sistemiyle beslenmiş ve transmembran basıncı, çapraz akım hızı ve yağ içeriği gibi deneysel parametreler incelenmiştir. Destek katmanı üzerindeki tek ve çift katlı kaplamalar 0,4 µm α-alumina kullanılarak hazırlanmıştır. 1 saat süreli deneyde MF membranının 1 katmanı ve 2 katmanı tıkanma ve düşük süzüntü akışı gözlenmiştir. Toplam askıda katı madde ve bulanıklığın azalması %100 olarak belirlendi. Düşükmembran tıkanıklığına sahip sabit süzüntü akımı ve konsantrasyondaki polarizasyon %1 yağ içeriğine sahip destek membranda elde edilmiştir ve ve transmembran basıncı 2 bar olarak bulunmuştur. Increasing water scarcity is an important threat to the whole world. The use of too much water during the production processes and the insufficient level of reuse of this water and the increasing quantities of oil containing waste generated in many industrial activities cause dangerous consequences for the environment. Highly concentrated oil-inwater emulsions are very harmful for aquatic life, soil, atmosphere and human health.Traditional treatment methods are not effective in the removal of emulsified oil droplets which have less than 20 µm of droplet size. Ceramic micro/ultrafiltration membranes have been explored and developed in recent years due to their superior advantages in oil containing water treatment/purification. The aim of this MSc study was to produce tubular ceramic supports and microfiltration membranes for the removal of oil from stable oil in water emulsions used as metal cutting fluids. The prepared metal cutting fluids were fed to the crossflow filtration system and the effects of experimental parameters such as transmembrane pressure (TMP), crossflow velocity (CFV) and oil content on membrane performance/permeate flux were investigated. The single/double layered coatings on the support surfaces were formed in the preparation of the microfiltration membranes by using stable 0.4 µm α-alumina suspensions. The 1 layer and 2 layers containing microfiltration membranes were heavily fouled and very low permeate fluxes wereobtained in an hour of treatment. This was attributed to the formation of a thin oil layer on the microfiltration membrane surfaces. The reduction of the total suspended solids (TSS) and turbidity were determined as ~100 %. A stable permeate flux with a lower extent of membrane fouling and concentration polarization was obtained with 1% oilcontent and the support membrane and TMP=2 bars. 98

The development of a better understanding of the low temperature nanophase evolution of high surface area titania (TiO2) based powders is essential for their use in photocatalytic applications. A series of rare earth (RE) element doped TiO2 powders were prepared by sol-gel processing. The effects of RE doping level, ionic size and heat treatment temperature on the nanophase structure evolution and the dopant ion location in TiO2 main matrix were investigated. Anatase was determined to be the main phase up to 900 °C at all doping levels for all REs. Anatase to rutile phase transformation was inhibited by RE doping. The inhibitory effect of REs increased with increasing ionic radius. Oxide phases of La, Nd, Pr, Sm were not present up to 5% and Nd4Ti9O24 phase was formed at 10% doping level at 800 °C. The formation of RE2Ti2O7 phases were determined for the REs with relatively lower ionic radii at 800 °C., Scientific and Technological Research Council of Turkey (TUBITAK 10M739)

Su kıtlığı, dünyadaki tüm canlı türlerini tehdit eden küresel sorunlardan biridir. Su kıtlığının giderilmesi için çeşitli çözümler önerilmiştir. Bu çözümlerden biri evsel ve endüstriyel atık suların arıtılmasıdır. Evsel ve endüstriyel atık suların arıtılması ve yeniden kullanılması, su kıtlığının azaltılmasına önemli katkı sağlayacaktır. Atık suların arıtılması ve tuzlu sudan su eldesi için membran teknolojisi kullanılmaktadır. Bu amaçla genellikle polimerik membranlar kullanılmaktadır. Bununla birlikte, atık su arıtımındaki seramik membranların performansını değerlendirmek için çalışmalar yapılmaktadır.Bu tezin amacı, gıda endüstrisi atıksularının arıtılması için tübüler seramik membranların hazırlanmasıdır. Çalışmada tübüler Al2O3 destekleri, MF ve UF tabakası kaplı Al2O3 destekleri hazırlanmış ve bir gıda işlemesinin atık su arıtma tesisinin farklı aşamalarından elde edilen yağlı atık suların arıtılmasında kullanılmıştır. Atıksuların toplam askıda katı madde içeriği (AKM), kimyasal oksijen ihtiyacı (KOİ), renk, bulanıklık değerleri ve yağ içerikleri filtrasyon işlemlerinden önce ve sonra belirlenmiştir. Ayrıca filtrasyon işlemleri süresince belirli zaman aralıklarında alınan süzüntü örneklerinin, akı, AKM, bulanıklık ve renk değerleri de izlenmiştir.Filtrasyon deneyleri sırasında membranların temiz su akılarına kıyasla çok daha düşük süzüntü akıları gözlenmiştir. Genel olarak membrane geçiş basıncı arttığında süzüntü akısında azalma gözlenirken çapraz akış hızı arttığında süzüntü akısının arttığı gözlenmiştir. Düşük başlangıç süzüntü akıları membranların atık suda yağ ve lipidler tarafından hızlı bir şekilde tıkandığını göstermiştir. Filtrasyon işlemleri sırasında süzüntü akılarındaki azalma da tıkayıcı bir tabakanın oluşumuna işaret etmiştir. Genel olarak, tübüler seramik destekler ve MF membranları kullanılarak yapılan filtrasyon işleminde yağlı atık suyun TSS, COD, bulanıklık ve renk değerlerinde sırasıyla % 97-99, % 91-98, % 78-99 ve % 63-99 azalma gözlenmiştir. Tüm filtrasyon deneylerinde, toplanan süzüntü numunelerinde yağ tespit edilememiş ve atıksulardan yağın % 100 verimle uzaklaştırıldığı bulunmuştur.Anahtar Kelimeler: seramik membran, gıda endüstrisi atık suları, yağ içeriği, filtrasyon, süzüntü Water scarcity is one of the global problems threatening all living species on Earth. Several solutions have been suggested for resolving the water scarcity. One of these solutions is the treatment of domestic and industrial wastewaters. Treatment and reuse of domestic and industrial wastewaters will significantly contribute to the prevention of the water scarcity. Membrane technology has been used for the treatment of wastewaters and water desalination. Membranes used are generally polymeric membranes. Studies however have been conducted to evaluate the performances of ceramic membranes in wastewater treatment.The goal of this thesis was to prepare tubular ceramic membranes for the treatment of food industry wastewaters. Tubular Al2O3 supports, MF and UF layer coated supports were prepared and used for the treatment of oil containing wastewaters obtained from the different stages in the wastewater treatment facility of the food processing plant. Total suspended solid content (TSS), chemical oxygen demand (COD), color, turbidity and oil content of the wastewaters were determined before and after filtration experiments. Permeate fluxes, TSS, turbidity and color of the permeate samples taken in certain time intervals were also monitored. Permeate fluxes much lower than clean water fluxes of the membrane were observed during the filtration of oily wastewater. In general, increasing cross flow velocity increased the permeate flux while the increase in transmembrane pressure decreased the flux. The lower initial permeate fluxes indicated the rapid membrane fouling by oil and lipids present in the wastewater. Decrease in the fluxes in the course of filtration also pointed out the formation of a fouling layer. Filtration experiments performed using tubular ceramic supports and MF membranes resulted in 97-99 %, 91-98 %, 78-99 % and 63-99 % reductions in TSS, COD, turbidity and color values of the oily wastewater, respectively. No oil could be detected in the permeate samples collected and oil removal efficiencies were found to be 100 % in all experiments.Keywords: ceramic membrane, food industry wastewaters, oil content, filtration, permeate 102

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2018, Includes bibliographical references (leaves: 80-87), Text in English; Abstract: Turkish and English, The aim of this study is to develop electrocaloric (EC) materials for alternative eco-friendly cooling technologies. Considering the dielectric and piezoelectric properties of the (1-x)BaTiO3- xBi(Li1/3Ti2/3)O3 (0≤x≤0.2), this system was selected to study electrocaloric properties due to the presence of morphotropic phase boundary (MBP). The crystal structure of the samples that were synthesized by convential solid state reaction technique were determined by the X-Ray Diffraction experiments. The electrical properties of the ceramics were characterized by temperature-dependent dielectric measurements and the phase transition temperatures of the samples were identified. Temperature-dependent electrical polarization curves were measured for all compositions and electrocaloric temperature change values were calculated with the help of Maxwell equations. Using the dielectric measurements, a phase diagram was obtained. Strain-electric field measurements were done to complement dielectric and polarization measurements. A new antiferroelectric phase was discovered at high temperatures in the samples. As Bi(Li1/3Ti2/3)O3 content is increased, phase transition from the ferroelectric to antiferroelectric phase decreases. Since in the antiferroelectric phase the net polarization is very small, a large polarization change therefore large electrocaloric temperature change is obtained. Highest electrocaloric temperature change (ΔT=0.66 K under 22 kV/cm) is obtained for x=0.03 sample., Bu çalışmanın amacı, alternatif çevre dostu soğutma teknolojileri için elektrokalorik (EC) malzemeler geliştirmektir. (1-x)BaTiO3-xBi(Li1/3Ti2/3)O3 (0≤x≤0.2) sisteminde, dielektrik ve piezoelektrik ölçümlere göre morfotropik faz sınırı bulunduğundan bu sistem elektrokalorik özellikleri çalışılmak için seçilmiştir. Geleneksel katı hal reaksiyon tekniği ile sentezlenen numunelerin kristal yapısı, X-Işını Kırınımı deneyleriyle belirlenmiştir. Seramiklerin elektriksel özellikleri sıcaklığa bağlı dielektrik ölçümleri ile karakterize edilmiştir ve örneklerin faz geçiş sıcaklıkları belirlenmiştir. Sıcaklığa bağlı elektriksel kutuplanma eğrileri ölçülmüş ve Maxwell denklemlerinin yardımıyla elektrokalorik sıcaklık değişimi değerleri hesaplanmıştır. Dielektrik ölçümler kullanılarak bir faz diyagramı elde edilmiştir. Dielektrik ve polarizasyon ölçümlerini tamamlamak amacıyla gerinim-elektrik alan ölçümleri yapılmıştır. Örneklerde yüksek sıcaklıklarda yeni bir antiferroelektrik faz keşfedilmiştir. Artan Bi(Li1/3Ti2/3)O3 oranıyla ferroelektrik fazdan antiferroelektrik faza geçiş sıcaklığı düşmektedir. Antiferroelektrik fazdaki net polarizasyonun çok küçük olması nedeniyle ferroelektrik antiferroelektrik geçiş sıcaklığında yüksek bir polarizasyon değişimi dolayısıyla yüksek elektrokalorik sıcaklık değişimi elde edilmiştir. En yüksek elektrokalorik sıcaklık değişimi (22 kv/cm altında ΔT=0.66 K) x=0.03 örneğinde elde edilmiştir., TUBITAK (315M241) and IZTECH

Thesis (Master)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2018, Includes bibliographical references (leaves: 70-73), Text in English; Abstract: Turkish and English, Increasing water scarcity is an important threat to the whole world. The use of too much water during the production processes and the insufficient level of reuse of this water and the increasing quantities of oil containing waste generated in many industrial activities cause dangerous consequences for the environment. Highly concentrated oil-in-water emulsions are very harmful for aquatic life, soil, atmosphere and human health. Traditional treatment methods are not effective in the removal of emulsified oil droplets which have less than 20 μm of droplet size. Ceramic micro/ultrafiltration membranes have been explored and developed in recent years due to their superior advantages in oil containing water treatment/purification. The aim of this MSc study was to produce tubular ceramic micro/ultrafiltration membranes for the removal of oil from stable oil in water emulsions. The prepared emulsions with about 5-6 μm of droplet sizes were fed to the crossflow filtration system and the effects of experimental parameters such as transmembrane pressure (TMP), crossflow velocity (CFV) and temperature on membrane performance/permeate flux was investigated. Titania, zirconia and neodymium doped polymeric sols were prepared and coated on the MF layer in order to investigate coating/surface modification on probable permeate flux enhancement and separation ability of the membrane. The reduction of the total suspended solid (TSS) and turbidity were determined as 100 %. A stable permeate flux with a lower extent of membrane fouling and concentration polarization was obtained with 1 m/s of CFV and 2 bar of TMP., Artan su kıtlığı tüm dünya için büyük bir tehlike haline gelmektedir. Özellikle birçok endüstriyel faaliyetlerde, üretim işlemleri sırasında çok fazla su kullanılması, bu suyun yeniden kullanılmaması ve yağ içeren atıklar içermesi çevre için tehlikeli sonuçlar doğurmaktadır. Metal, gıda ve içecek, tekstil ve çelik endüstrileri tarafından üretilen yüksek konsantrasyonlu su içerisinde yağ emülsiyonları yeryüzündeki su kaynaklarının normal oksijen transfer mekanizmasını değiştirdiği için su yaşantısı, toprak, hava ve insan sağlığı için çok zararlıdır. Yerçekimi, yüzeyden sıyırma, flotasyon ve koagulasyon gibi geleneksel arıtma yöntemleri damlacık boyutunun 20 μm’den az olan emülsiyon haline getirilmiş dağ damlacıklarını uzaklaştırmak için etkili değildir. Seramik mikro/ultrafiltrasyon membranları yağ içeren sudaki üstün avantajları nedeniyle son yıllarda araştırılmış ve geliştirilmiştir. Bu yüksek lisans çalışmasının amacı sudan kararlı yağ-su emülsiyonlarını uzaklaştırmak için seramik mikro/ultrafiltrasyon membranlarının üretilmesidir. Tübülar seramik destekler, mikrofiltrasyon (MF) katmanları elde etmek için α-Al2O3 sollerle kaplandı. Ultrafiltrasyon (UF) solleri böhmit tozuyla hazırlandı ve MF membranlar üzerine kaplandı. 5-6 μm yağ damlacıklarından oluşan emülsiyon yüksek süzüntü hızı elde etmek için transmembran basıncı, çapraz akış hızı ve sıcaklık gibi deneysel parametrelerin değiştirilerek incelenmesi için çapraz akışlı filtrasyon sistemine beslendi. Zarın seçici özelliğini değiştirmeden süzüntü hızını artırmak için titania, zirkonya ve neodmiyum katkılı polimerik soller hazırlandı ve MF tabakası üzerine kaplandı. Toplam askıda katı madde (AKM) ve bulanıklık 100% oranında azaltıldı. 1 m/s çapraz akış hızı ve 2 bar tansmembran basıncı membran tıkanıklığı ve konsantrasyon polarizasyonunun az olmasını sağlayarak yüksek ve kararlı süzüntü akısı elde etmeyi sağladı. Yüksek ve kararlı süzüntü akısı elde etmek için en uygun sıcaklık aralığı 35-40 °C olarak bulundu.

Thesis (Master)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2018, Includes bibliographical references (leaves: 62-65), Text in English; Abstract: Turkish and English, The increase in the extent of greenhouse gases in earth’s atmosphere lies behind the global warming and climate change. The extensive use of unsustainable fossil fuels have intensified the greenhouse effect, causing global warming. Hydrogen is considered as an ideal fuel for the future. Hydrogen fuel can be produced from renewable energy sources and its life cycle is clean. Artificial photosynthesis has been considered as a promising prospect for the synthesis of renewable and sustainable fuels. Photocatalysis is expected to make a great contribution to environmental problems and renewable energy generation in the very near future. Titania based photocatalytic materials are one of the widely used materials in artificial photosynthesis research due to their unique chemical and optical properties. Photocatalytic water-splitting by using TiO2 based photocatalysts for hydrogen production offers a promising alternative for clean, low-cost and environmentally friendly production of hydrogen. ZrO2 doped TiO2 photocatalyst powders were prepared by coprecipitation and characterized in this work. The photocatalytic water splitting activities of these ZrO2 doped TiO2 photocatalyst powders in hydrogen production was investigated under UVVis light. The phase structures of the powders were significantly affected by the level of dopants and the primary particle sizes increased from about 130 nm to about 500 nm during heat treatments in the 550-700°C range. Maximum hydrogen yield of about 5000 μmol/hr gcat. was obtained with the 550°C heat treated powder doped at 0.1-0.1 mol% ZrO2-Nd2O3 level. ZrO2 doping above 10 mol% decreased the hydrogen yields of the catalysts to lower than 1000 μmol/hr gcat., Küresel ısınma ve iklim değişikliğinin altında yatan ana neden atmosferdeki sera gazlarının artışıdır. Sürdürülemez fosil yakıtların geniş çaplı kullanımı sera gazı efektini arttırmakta, küresel ısınmaya sebep olmaktadır. Hidrojen gelecek için ideal yakıt olarak düşünülmektedir. Hidrojen yakıtı temiz ve yenilenebilir enerji kaynaklarından üretilebilirse temiz ve yenilenebilir bir döngüye sahiptir. Yapay fotosentez yenilenebilir ve sürdürülebilir yakıtlar için umut verici bir yaklaşım olarak düşünülmektedir. Fotokatalizin çevresel problemlere ve yenilenebilir enerji üretimine büyük katkıda bulunacağı umulmaktadır. Titanya esaslı fotokatalitik materyaller eşsiz kimyasal ve optik özelliklerinden dolayı yapay fotosentez araştırmalarında geniş çaplı olarak kullanılan materyal gruplarından biridir. Hidrojen üretimi için TiO2 kullanarak fotokatalitik su parçalama, temiz, düşük maliyetli ve çevre dostu hidrojen üretimi için umut verici bir alternatif sunmaktadır. Bu çalışmada, ZrO2 katkılı TiO2 fotokatalitik tozlar birlikte çöktürme ile hazırlandı ve karakterize edildi. Bu ZrO2 katkılı TiO2 fotokatalitik tozların UV görünür ışık altında hidrojen üretimindeki fotokatalitik su parçalama aktiviteleri belirlendi. Tozların faz yapıları, katkıların seviyeleri tarafından etkilendi ve 550-700°C aralığındaki ısıl işlem boyunca birincil parçacık boyutları yaklaşık 130 nm’den 500 nm’ye kadar arttı. Maksimum hidrojen verimi, 0.1-0.1mol% ZrO2-Nd2O3 seviyesinde katkılanan 550°C’de ısıl işlem gören tozda yaklaşık 5000 μmol/hr gcat olarak elde edildi. 10 mol%’nin üstünde ZrO2 katkılı katalizörlerin hidrojen verimleri 1000 μmol/hr gcat’den düşük bulundu.

Artan su kıtlığı tüm dünya için büyük bir tehlike haline gelmektedir. Özellikle birçok endüstriyel faaliyetlerde, üretim işlemleri sırasında çok fazla su kullanılması, bu suyun yeniden kullanılmaması ve yağ içeren atıklar içermesi çevre için tehlikeli sonuçlar doğurmaktadır. Metal, gıda ve içecek, tekstil ve çelik endüstrileri tarafından üretilen yüksek konsantrasyonlu su içerisinde yağ emülsiyonları yeryüzündeki su kaynaklarının normal oksijen transfer mekanizmasını değiştirdiği için su yaşantısı, toprak, hava ve insan sağlığı için çok zararlıdır. Yerçekimi, yüzeyden sıyırma, flotasyon ve koagulasyon gibi geleneksel arıtma yöntemleri damlacık boyutunun 20 µm'den az olan emülsiyon haline getirilmiş dağ damlacıklarını uzaklaştırmak için etkili değildir. Seramik mikro/ultrafiltrasyon membranları yağ içeren sudaki üstün avantajları nedeniyle son yıllarda araştırılmış ve geliştirilmiştir. Bu yüksek lisans çalışmasının amacı sudan kararlı yağ-su emülsiyonlarını uzaklaştırmak için seramik mikro/ultrafiltrasyon membranlarının üretilmesidir. Tübülar seramik destekler, mikrofiltrasyon (MF) katmanları elde etmek için α-Al2O3 sollerle kaplandı. Ultrafiltrasyon (UF) solleri böhmit tozuyla hazırlandı ve MF membranlar üzerine kaplandı. 5-6 µm yağ damlacıklarından oluşan emülsiyon yüksek süzüntü hızı elde etmek için transmembran basıncı, çapraz akış hızı ve sıcaklık gibi deneysel parametrelerin değiştirilerek incelenmesi için çapraz akışlı filtrasyon sistemine beslendi. Zarın seçici özelliğini değiştirmeden süzüntü hızını artırmak için titania, zirkonya ve neodmiyum katkılı polimerik soller hazırlandı ve MF tabakası üzerine kaplandı. Toplam askıda katı madde (AKM) ve bulanıklık 100% oranında azaltıldı. 1 m/s çapraz akış hızı ve 2 bar tansmembran basıncı membran tıkanıklığı ve konsantrasyon polarizasyonunun az olmasını sağlayarak yüksek ve kararlı süzüntü akısı elde etmeyi sağladı. Yüksek ve kararlı süzüntü akısı elde etmek için en uygun sıcaklık aralığı 35-40 °C olarak bulundu. Increasing water scarcity is an important threat to the whole world. The use of too much water during the production processes and the insufficient level of reuse of this water and the increasing quantities of oil containing waste generated in many industrial activities cause dangerous consequences for the environment. Highly concentrated oil-in-water emulsions are very harmful for aquatic life, soil, atmosphere and human health. Traditional treatment methods are not effective in the removal of emulsified oil droplets which have less than 20 µm of droplet size. Ceramic micro/ultrafiltration membranes have been explored and developed in recent years due to their superior advantages in oil containing water treatment/purification. The aim of this MSc study was to produce tubular ceramic micro/ultrafiltration membranes for the removal of oil from stable oil in water emulsions. The prepared emulsions with about 5-6 µm of droplet sizes were fed to the crossflow filtration system and the effects of experimental parameters such as transmembrane pressure (TMP), crossflow velocity (CFV) and temperature on membrane performance/permeate flux was investigated. Titania, zirconia and neodymium doped polymeric sols were prepared and coated on the MF layer in order to investigate coating/surface modification on probable permeate flux enhancement and separation ability of the membrane. The reduction of the total suspended solid (TSS) and turbidity were determined as 100 %. A stable permeate flux with a lower extent of membrane fouling and concentration polarization was obtained with 1 m/s of CFV and 2 bar of TMP. 83

FERROELEKTRİK (1-x)BaTiO3-xBi(Li1/3Ti2/3)O3 (0≤x≤0.2) SİSTEMİNİN ELEKTROKALORİK ÖZELLİKLERİNİN BELİRLENMESİBu çalışmanın amacı, alternatif çevre dostu soğutma teknolojileri için elektrokalorik (EC) malzemeler geliştirmektir.(1-x)BaTiO3-xBi(Li1/3Ti2/3)O3 (0≤x≤0.2) sisteminde, dielektrik ve piezoelektrik ölçümlere göre morfotropik faz sınırı bulunduğundan bu sistem elektrokalorik özellikleri çalışılmak için seçilmiştir. Geleneksel katı hal reaksiyon tekniği ile sentezlenen numunelerin kristal yapısı, X-Işını Kırınımı deneyleriyle belirlenmiştir. Seramiklerin elektriksel özellikleri sıcaklığa bağlı dielektrik ölçümleri ile karakterize edilmiştir ve örneklerin faz geçiş sıcaklıkları belirlenmiştir. Sıcaklığa bağlı elektriksel kutuplanma eğrileri ölçülmüş ve Maxwell denklemlerinin yardımıyla elektrokalorik sıcaklık değişimi değerleri hesaplanmıştır. Dielektrik ölçümler kullanılarak bir faz diyagramı elde edilmiştir. Dielektrik ve polarizasyon ölçümlerini tamamlamak amacıyla gerinim-elektrik alan ölçümleri yapılmıştır. Örneklerde yüksek sıcaklıklarda yeni bir antiferroelektrik faz keşfedilmiştir. Artan Bi(Li1/3Ti2/3)O3 oranıyla ferroelektrik fazdan antiferroelektrik faza geçiş sıcaklığı düşmektedir. Antiferroelektrik fazdaki net polarizasyonun çok küçük olması nedeniyle ferroelektrik antiferroelektrik geçiş sıcaklığında yüksek bir polarizasyon değişimi dolayısıyla yüksek elektrokalorik sıcaklık değişimi elde edilmiştir. En yüksek elektrokalorik sıcaklık değişimi (22 kv/cm altında ΔT=0.66 K) x=0.03 örneğinde elde edilmiştir. DETERMINATION OF THE ELECTROCALORIC PROPERTIES OF THE FERROELECTRIC (1-x)BaTiO3-xBi(Li1/3Ti2/3)O3 (0≤x≤0.2) SYSTEMThe aim of this study is to develop electrocaloric (EC) materials for alternative eco-friendly cooling technologies. Considering the dielectric and piezoelectric properties of the (1-x)BaTiO3-xBi(Li1/3Ti2/3)O3 (0≤x≤0.2), this system was selected to study electrocaloric properties due to the presence of morphotropic phase boundary (MBP). The crystal structure of the samples that were synthesized by convential solid state reaction technique were determined by the X-Ray Diffraction experiments. The electrical properties of the ceramics were characterized by temperature-dependent dielectric measurements and the phase transition temperatures of the samples were identified. Temperature-dependent electrical polarization curves were measured for all compositions and electrocaloric temperature change values were calculated with the help of Maxwell equations. Using the dielectric measurements, a phase diagram was obtained. Strain-electric field measurements were done to complement dielectric and polarization measurements. A new antiferroelectric phase was discovered at high temperatures in the samples. As Bi(Li1/3Ti2/3)O3 content is increased, phase transition from the ferroelectric to antiferroelectric phase decreases. Since in the antiferroelectric phase the net polarization is very small, a large polarization change therefore large electrocaloric temperature change is obtained. Highest electrocaloric temperature change (ΔT=0.66 K under 22 kV/cm) is obtained for x=0.03 sample. 100

Thesis (Master)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2017, Includes bibliographical references (leaves: 76-78), Text in English; Abstract: Turkish and English, Fresh water scarcity have been the most fundamental problem in the world and is already affecting mankind and human activities. This problem forced an increasing effort in the reuse of wastewater originating from municipal, agricultural, and industrial activities. The textile industry demands large amounts of water and produces large quantities of wastewater. Adsorption, filtration, ozonation and photocatalysis techniques are currently used for wastewater treatment and safe discharge to the environment. Although membrane filtration necessitates a high initial setup cost, it has a high potential and may cause significant cost savings through the reuse of water and salts. The membrane based technologies are widely accepted to be the best method when compared with the currently available technologies for wastewater treatment. Extruded tubular alumina supports were coated by stable colloidal sols and polymeric sols prepared by using sol-gel based techniques for the formation of selective micro/ultra/nanofiltration layers in this work. Textile wastewater treatment (with and without pre-treatment) and membrane fouling analysis was conducted. The performances of the membranes were determined through the characterization of permeates by a spectrophotometer. The reduction of colors (Pt-Co, m-1), turbidity and suspended solids content were about 99%, 100% and 100%, respectively. The incorporation of a coagulation stage by using Al2(SO4)3 followed by a successive filtration reduced the membrane/irreversible fouling levels in the MF/UF membranes significantly. The Pt-Co 455 values of permeates were determined to be in the 15-260 range which are below the discharge criteria bringing the possibility of the reuse of some of these permeates., Temiz su kıtlığı dünyadaki en önemli problemlerden biri olmuş ve insanoğlunu ve aktivitelerini etkilemektedir. Bu problem kentsel, tarımsal ve endüstriyel faaliyetlerden kaynaklanan atıksuyun tekrar kullanımına yönelik giderek artan çabaları zorunlu kılmıştır. Tekstil çok yüksek miktarlarda su kullananılan ve atıksu üreten bir endüstridir. Adsorpsiyon, filtrasyon, ozonlama ve fotokataliz gibi teknikler bugünlerde atıksu arıtımı ve arıtılan suyun çevreye güvenli bir şekilde deşarjı için kullanılmaktadır. Membran filtrasyonu yüksek kurulum maliyetine ihtiyaç duymasına ragmen yüksek bir potansiyele sahiptir ve su/tuzların tekrar kullanımıyla maaliyette önemli azalmalara neden olabilir. Atıksu arıtımı için halen kullanılmakta olan teknolojiler ile membran teknolojisi kıyaslandığında membran teknolojileri yaygın bir biçimde en iyi method olara kabul görmektedir. Bu çalışmada seçici micro/ultra/nanofiltrasyon tabakalarının oluşumları için soljel teknikleri esas alınarak hazırlanmış kararlı kolloidal ve polimerik sollerle ekstrüde alümina destekler kaplandı. Tekstil atıksu arıtımı (önarıtmalı ve önarıtmasız) ve membran tıkanma analizleri yapıldı. Membranların performansları spektrofotometre tarafından karakterize edilen süzüntüler vasıtasıyla belirlendi. Katı madde miktarı, bulanıklık ve renkteki (Pt-Co, m-1) azalışlar yaklaşık olarak sırasıyla %100, %100 ve %99'dur. MF/UF membranlarında geri dönüşümsüz/membran tıkanıklık seviyeleri koagülasyon katılımı olan Al2(SO4)3 kullanımını takip eden filtrasyonda önemli oranda azalmıştır. Süzüntülerin Pt-Co 455 değerleri deşarj kriterlerinin altında 15-215 arasında belirlenmiş olup bu süzüntülerden bazılarının tekrar kullanımı olasıllığı bulunmaktadır., The Scientific and Technological Research Council of Turkey (TUBITAK ÇAYDAG 113Y344)

Thesis (Master)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2017, Includes bibliographical references (leaves: 80-85), Text in English; Abstract: Turkish and English., Textile industry generates coloured wastewater containing a significant level of dye/inorganic salts. Environmental concerns and efficient energy use make the recovery of reusable water and salts from textile wastewater vital globally. Ceramic nanofiltration (NF) membranes are becoming increasingly important for the recovery and purification of dyes and salts (e.g., NaCl) in high salinity waste streams. They have superior chemical/mechanical/thermal properties compared to their polymeric counterparts. Desalination performances of the ceramic NF membranes depend on the concentration and chemical structure of the target ions, pH of feed and the wastewater stream along with the chemical/surface/nanostructural properties of the selective NF layer. Metal oxides are generally used as NF layer materials due to their amphoteric behaviour. Repulsive/attractive forces between the ionic species in the solution and the NF layer may make the separation of ionic species possible. In this work, zirconia doped titania based NF layers were designed. Desalination experiments were conducted with 10-3 M Na2SO4 and MgSO4 salts at different pH values. Salt retention capacities of 5 different membranes were determined. Percent retention was calculated using ion concentrations in permeate and retentate streams. The Mg2+ and SO4 -2 ion concentrations were determined by titration with 0.01 M EDTA and by spectrophotometer at 420 nm, respectively. A clear pH dependency of the salt retention was found in filtration tests. The highest SO4 -2 and Mg+2 ion retentions were obtained with using MF+disperel (boehmite)+P2 (600 0C)+TTIP hydrosol+Ti/Zr polymeric (double layer) membrane as 95% and 91%, respectively., Tekstil endüstrisi, büyük miktarda boya/inorganik tuz içeren renkli atık su üretmektedir. Çevresel kaygılar ve verimli enerji kullanımı, tekstil atıksuyundan gelen yeniden kullanılabilir su ve tuzların hayati bir önem taşımasını sağlamıştır. Seramik nanofiltrasyon (NF) membranları, yüksek derecede tuz içeren atıksularda, boyalar ve tuzların (örn., NaCl) geri kazanılması ve saflaştırılması için gittikçe önem kazanmaktadır. Seramik membranlar polimerik membranlara kıyasla üstün kimyasal/mekanik/termal özelliklere sahiptirler. Seramik NF membranlarının tuzdan arındırma performansları, hedef iyonların konsantrasyonuna ve kimyasal yapısına, beslenen atıksuyun pH’ına, atık su akışına ve seçici NF tabakasının kimyasal/yüzey/nano-yapısal özelliklerine bağlıdır. Amfoterik davranışlarından dolayı metal oksitler NF tabakası malzemesi olarak kullanılırlar. NF tabakasının yüzey yükü, büyük oranda beslenen atıksuyun pH'ına bağlıdır. Çözeltideki iyonik tuzlar ile NF tabakası arasındaki itici/çekici kuvvetler, iyonik tuzların ayrılmasını mümkün kılar. Bu çalışmada, zirkonya katkılı titanyum esaslı NF tabakaları tasarlandı. Desalinasyon deneyleri, farklı pH değerlerinde 10-3M Na2SO4 ve MgSO4 tuzları şle gerçekleştirilmiştir. 5 farklı membranın tuz tutma kapasiteleri belirlendi. Membranların tuz tutma yüzdeleri süzüntü ve kalıntı örneklerinin iyon konsantrasyonları kullanılarak hesaplanmıştır. Mg2+ iyon konsantrasyonu, 0.01 M EDTA titrasyonuyla, SO4 -2 iyon konsantrasyonu ise 420 nm dalga boyunda spektrofotometre ile tespit edilmiştir. Filtrasyon testleri sonucunda tuz tutulumunun pH’a bağlı olduğu açıkça görülmüştür. En yüksek SO4 -2 ve Mg2+ iyon tutulmaları sırasıyla % 95 ve% 91 olarak MF+disperal (böhmit)+P2 (600 0C)+TTIP hidrosol+Ti/Zr polimerik (çift katmanlı) membran kullanılarak elde edilmiştir., The Scientific and Technological Research Council of Turkey (TUBITAK- ÇAYDAG 113Y344)

Bu yüksek lisans çalışmasının amacı nanoaltı boyuttaki organik bileşiklerin tutulmasında kullanılması amaçlanan seçici titanya nanofiltrayson (NF) membran katmanlarının faz yapısı evrimine neodmiyum/zirkonyum katkılarının etkilerinin araştırılmasıdır. Farklı neodmiyum ve zirkonyum katkı düzeylerindeki polimerik sollerden hazırlanan desteksiz membranlar ile dilatometrik bir çalışma yürütülmüştür. Seçici NF katmanlarının nanoyapı evriminin kontrolü ile birlikte nanoaltı gözenek yapısı tasarımı üzerine fonksiyonel becerilerin geliştirilmesi bu çalışmanın temel amacını oluşturmuştur. Kararlı oksit molar bileşimleri baz alınarak neodmiyum katkı düzeyi 0.3-5.0% aralığında, zirkonyum karışım düzeyi ise 0-100% aralığında değiştirilmiştir.Dilatometrik karakterizasyon sonuçları katkı düzeylerinin nanoyapı evrimini ve yoğunlaşma davranışlarını önemli oranda etkilediğini göstermektedir. Dinamik ışık saçılımı sonuçları sollerdeki polimerik yapıların ağırlıklı olarak 2-4 nm boyutunda olduğunu ve oldukça dar bir boyut dağılımına sahip olduğunu göstermektedir. XRD analizi sonuçları titanya anataz kristalit boyutlarının neodmiyum katkısı veya zirkonya karışımı ile önemli ölçüde düştüğünü ve faz dönüşümlerinin yaklaşık olarak 200°C geciktiğini göstermiştir. Seçilmiş zirkonya karışık ve neodmiyum katkılı katkısız membran tozlarının HR-TEM görüntüleri XRD/dilatometre kaynaklı nanoyapı evrimi sonuçlarına yeni bilgiler eklemiştir. Bu polimerik soller kullanılarak hazırlanacak NF membranlarının molekül ağırlığı ayırma sınırlarının ve saf su akılarının yakın gelecekte belirlenmesi nanoaltı ayırma becerileri üzerine değerli bir bilgi birikimi oluşturmasını mümkün kılabilir. The purpose of this MSc work was to investigate the effects of neodymium/zirconium doping on the phase structure evolution of the selective titania nanofiltration (NF) membrane layers for the rejection of subnano sized organic compounds. A dilatometric study was carried out on unsupported membranes prepared from polymeric sols with different neodymium and zirconium levels. The development of functional abilities towards the design of the pore structure in the subnano range by controlling the nanostructural evolution of the selective NF layers was the fundamental purpose of this work. The neodymium doping level was varied in the 0.3-5.0% range and the zirconium mixing level was varied in the 0-100% range based on stable metal oxide molar compositions.Dilatometric characterization results have shown that dopant level effects the nanophase evolution and the densification behavior considerably. The dynamic light scattering results have shown that the polymeric species in the sol were predominantly 2-4 nm in size and had a very narrow size distribution. XRD analysis results indicated titania anatase crystallite sizes were reduced significantly with neodymium doping or zirconia mixing and the phase transformations were retarded by about 200°C. HR-TEM images of selected zirconia mixed or neodymium doped unsupported membrane powders also added new information to the XRD/dilatometry derived nanophase evolution results. The determination of the molecular weight cut-off values and pure water fluxes of the NF membranes which would be prepared by using these polymeric sols in the near future may generate valuable knowledge on the subnano separation abilities of these NF membranes. 68

Membranlar biyokimyasal ayırma süreçleri, tekstil, kağıt ve metal endüstrisi gibi farklı endüstrilerde saflaştırma ve ayrıştırma işlemleri için kullanılmaktadır. Seramik membranlar genel olarak seçici oksit katmanlarının tübüler seramik destekler üzerine konulmasıyla oluşturulur. Katı madde oranları yüzde 55 seviyesine kadar olan ve ana ortam sıvısı su olacak şekilde hazırlanan alumina hamurlarından, seramik tübüler membranlar hazırlanmıştır. Bağlayıcı malzeme olarak böhmit ile birlikte farklı molekül ağırlıklarınıa sahip hidroksi selülöz eterler kullanılmıştır. Hamur hazırlanışında gliserin yağlayıcı olarak kullanılmıştır. Ön çalışmalar için orifice tipi kalıpta ram extrüzyon kullanılmış ve veriler mekanik mukavemet test cihazıyla alınmıştır. Alümina hamur ekstrüzyonu farklı L/D oranlarına sahip kapileri kalıplar kullanılarak farklı ekstrüzyon hızlarında ram ekstrüderi ile gerçekleştirilmiş ve alınan veriler aynı test cihazıyla Benbow Bridgwater modeli kullanılarak analiz edilmiştir. Çeşitli hamurların reolojik özellikleri 4 ve 6 parametreli modellere bağlı olarak belirlenmiştir. 6 parametreli modelin alumina hamurlarıyla daha yakın ekstrüztyon grafiklerine sahip olduğu belirlenmiştir. Hazırlanan seramik hamurlarının viskoziteleri model parametreleri o, 1, ve n kullanılarak hesaplanmıştır.Tübüler seramik hamurlarının şekillendirilmesi piston ekstrüder kullanılarak yapılmış ve hamurunun reolejisi ve kompozisyonuna bağlı olarak piston ekstrüder basıncı 20-90 bar arasında değişiklik göstermiştir. Ekstrüde edilmiş tübüler destekler kurutulup organik bağlayıcılarından arındırılmış ve %40 poroziteye sahip mekanik olarak güçlü membran destekleri elde etmek amacıyla 1525ºC'de ısıl işlem uygulanmıştır. Membrane applications in the industry currentlyis dominated by polymeric membranes, however, in recent years the development of ceramic membranes gained significant attention because of their superior chemical/thermal stability and corrosion resistance. The separation capacities of ceramic membranes basically depend on the nature of the selective oxide layers formed on the inner surfaces of tubular ceramic supports. Ceramic tubular membrane supports were prepared from alumina pastes, with solid loadings as high as 55 vol. % and water was used as the major liquid phase. Boehmite along with hydroxypropyl cellulose ethers with different molecular weightswere used as binder materials. Glycerol was used as a lubricant in the paste formulations. Extrusion of alumina paste was conductedwith a ram extruder using capillary dies with a series of L/D ratios at different extrusion velocities and the data was analyzed by using Benbow and Bridgwater model. The rheological properties of various pastes were determined according to the 4 and 6-parameter models.The six parameter model was concluded to better represent the experimental data. The viscosities of the paste batches were also determined by using the model parameters o, 1, and exponent n. The pastes were determined to have a shear thinning behaviour Piston extruder was used for shaping of tubular ceramic supports and the pressure varied in the 20-90 bar range with paste composition and rheology. The tubular extruded supports were dried, debinded to burn out organic binders and sintered at 1525ºC for the formation of about 40% porous mechanically strong membrane supports. 109

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2016, Includes bibliographical references (leaves: 76-78), Text in English; Abstract: Turkish and English, xi, 78 leaves, The availability of fresh water is vital for life, sustainable growth and healthy ecosystems on earth. Increasing world population, a changing climate, intensive agricultural practices, economic growth and urbanization will undoubtedly continue to make the issue of water scarcity a global priority for years to come. The gap between the need and the supply of water globally is increasing steadily which necessitates significant measures to be taken towards conservation, and reuse of industrially, domestically and agriculturally used water. Textile industry is one of the leading industries in the use of fresh water and the generation of wastewaters. Technologies currently in use towards industrial and domestic water treatment like sedimentation, chemical coagulation, biological treatment etc. cannot produce reusable water but also generate significant amounts of solid waste. Membranes are now widely accepted to have the potential of supplying cost-effective solutions for water treatment and a growing range of purification and separation problems. The number and the pore structure design of the multiple selective layers on the inner surfaces of tubular α-alumina supports vary with the nature of the intended separation application. Although the nature of MF membranes is relatively well developed, current research is concentrated on the design of nanoporous phase structure in NF and UF selective layers. Selective micro/ultra/nanofiltration layers were formed on extruded tubular alumina supports by colloidal/sol-gel techniques. The performance of these selective layers were investigated by the experiments performed with textile wastewater. Permeates from ceramic tubular membranes were characterized by spectrophotometer. The suspended solids and color (Pt-Co) were reduced by 90% and 80%. respectively., Temiz suyun erişilebilirliği dünyamızdaki yaşam, sürdürülebilir büyüme, ve sağlıklı ekosistemler için hayati bir öneme sahiptir. İvmelenerek artan dünya nüfusu, değişen bir iklimin varlığı, yoğun tarımsal faaliyetler, ve şehirleşme hiç şüphesiz olarak öngörebildiğimiz yıllar boyunca suyun azlığı olgusunun küresel bir öncelik olmasına neden olmaya devam edecektir. Küresel olarak temiz su gereksinimi ve varlığı arasındaki giderek büyüyen açık, suyun korunumu, ve endüstriyel, evsel ve tarımsal amaçla kullanılan suyun geri kazanılarak kullanımı konusunda çok ciddi önlemlerin alınmasını zorunlu hale getirmektedir. Günümüzde endüstriyel ve evsel atık suyun arındırılmasında kullanılan çöktürme, kimyasal koagülasyon, biyolojik arıtma v.b. teknolojiler geri kullanılabilir özelliklerde su sağlayamadıkları gibi önemli miktarlarda katı atık da üretmektedirler. Su arıtma ve büyüyen bir kapsamdaki arıtma ve ayırma problemlerine membranların ekonomik çözümler üretme potansiyaline sahip oldukları artık yaygın bir biçimde kabul edilmiş durumdadır. Çoklu seçici katmanların sayısı ve gözenek yapısı tasarımı hedeflenen ayırım uygulamasının niteliğine göre değişir. MF membranların yapısı göreceli olarak daha iyi gelişmiş ise de güncel araştırmalar NF ve UF seçici katmanların nanogözenekli faz yapısının tasarımı konusunda yoğunlaşmış durumdadır. Ekstrüzyon yöntemi ile şekillendirilmiş seramik tübüler alümina destekler üzerine kolloidal/sol-jel teknikleri ile seçici mikro/ultra/nanofiltrasyon katmanları oluşturulmuştur. Seçici katmanların performansları tekstil atık suları ile incelenmiştir. Seramik tübüler membrandan elde edilen süzüntüler spektrofotometre ile karakterize edilmiştir. Bunun sonucunda askıda katı ve renk (Pt-Co) değerleri sırasıyla 90% ve 80% ‘e düşürülmüştür.

23rd Symposium and Annual Meeting of International Society for Ceramics in Medicine, ISCM 2011; Istanbul; Turkey; 6 November 2011 through 9 November 2011, The goal of the present work was to investigate the effects of several cement preparation parameters on setting and hardening reaction mechanisms and hydroxyapatite (HA) cement properties. A central composite experimental design (CCD) was conducted by choosing particle size, solid to liquid ratio, pH, seed concentration and buffer concentration as design parameters along with compressive strength and setting time being the responses. Tetracalcium phosphate (TTCP) powders were prepared by heat treatment of calcium and phosphate source mixtures in the 1200-1400°C temperature range followed by quenching to room temperature in a dessicator. The second phase used in the formulations (brushite) was prepared by aqueous chemical methods. A series of HA pastes/cements were prepared by changing the above mentioned design parameters. Cements were characterized by a standardized setting time test, mechanical testing machine, SEM and XRD. HA cements with the desired properties can be formulated by using CCD in which the responses were expressed by a second order polynomial equation of the parameters. Compressive strengths for the majority of HA cements were determined to be in the 100-160 MPa range which is significantly higher than those reported in the literature. © (2012) Trans Tech Publications., TÜBİTAK-TEYDEB to MGM R&D Laboratories under the Tekno Girişim Project No.8070082

Monodisperse silica sols with well-defined spherical particles ranging in size from 5 to 310 nm were prepared through Stober process. Both particulate and polymeric sol-gel routes were employed for the preparation of stable silica sols. The use of polymeric species in combination with particulate silica spheres may allow the design of predefined membrane pore structures with high thermal stability by cubic/random/close packing of monodisperse spherical particles incorporated into the polymeric network. The size and volume content of spheres were varied in order to modify the consolidation behaviour of 2-structural silica membranes which would enhance the thermal stability. The low shrinkage level for sphere loaded 2-structural systems compared to the pure polymeric counterparts might be explained by the decrease in the structural free energy of the polymeric/particulate 2-structural system. The thermal stability of the microporous membranes may thus be improved by incorporating particulates into the polymeric network through the formation of a lower extent of thermally induced microcrack formation. The N2 permeation through 90 nm silica sphere added silica membranes remained constant when they were heat treated in the 250-400 °C range indicating the stability of the pore network. © 2009 Elsevier B.V. All rights reserved.

Günümüzde insanlığın varlığını tehdit edebilecek en büyük problemlerden birinin sera gazı efektine bağlı olarak ortaya çıkan küresel ısınma olduğu kabul görmektedir. Bu durumun temel sebebi karbondioksit gazının aşırı salınımı ve sonucunda da güneş ışınlarının atmosferde daha fazla emilmesidir. Karbondioksit gazı hep vardı ve fotosentez tarafından dengeleniyordu ancak sanayi devriminden sonra bu gazın salımı öyle arttı ki bilim insanları bu konuda çözüm üretmek için çalışmaya başladılar ve ilk defa 1970 lerde yapay fotosentez kavramına temel oluşturan yayınlar yapıldı.Fotosentezin canlılara değil de aygıtlara yaptırılması fikri birçok bilim insanı tarafından kabul gördü ve bu çalışmalar özellikle son 10 yılda hız kazandı. Bu noktada, metan, metanol gibi alterneatif yakıtların üretildiği yapay fotosentezdeki aktivitenin artırılması için literatürde en yaygın kullanılan fotokatalizör olan titanyum dioksitin katkılanması ve katkı ile elde edilen yeni elektrokimyasal özelliklerin saptanması büyük bir öneme sahiptir. Bu sayede fotokatilizde büyük öneme sahip olan bant genişliği ve bant pozisyonu enerji seviyeleri net bir şekilde belirlenebilir ve bu enerji seviyelerine denk gelen UV veya görünür ışık altında fotonik indirgenme verimleri iyileştirebilir. Titanyum dioksitin elektrokimyasal özellikleri döngüsel gerilimölçer (cyclic voltammetery – CV) yöntemi ile araştırılabilir ve bu özelliklerin iyileştirilmesine yönelik kullanılabilecek bulgular bu yöntem sayesinde üretilebilir.Bu tez çalışmasında nadir toprak elementi katkısının titanyum dioksitin elektrokimyasal özellikleri üzerindeki etkisi incelenmiştir. Nadir toprak elementi katkısının titanyum dioksitin elektriksel aktifliğini önemli ölçüde artırdığı bulunmuştur. Bu bağlamda titanyum dioksitin yapay fotosentezdeki aktivitesinin nadir toprak elementi katkısı ile artırabileceğini gösterilmiştir. Global warming arising from the greenhouse effect is globally accepted as the main problem which may threaten the life on the earth. Excess emission of carbon dioxide which leads to the more absorption of solar radiation in the atmosphere is the main reason for global warming. Carbon dioxide present in the atmosphere is balanced by natural photosynthesis; however this balance was disturbed by the increasing amount of carbon dioxide emissions after industrial revolution. Intense efforts was made by many scientists to find solutions to decrease the carbon dioxide level in the atmosphere and the pioneering studies were conducted in the early 1970s which founded the basic theory of artificial photosynthesis.The conceptual idea on conducting photosynthesis by technologically feasible processes was accepted by many scientists and the research on artificial photosynthesis accelerated in the last 10 years. The enhancement of the efficieny of artificial photosynthesis, by which alternative fuels such as methane, methanol may be produced, can be realized by doping titanium dioxide which is the most widely used photocatalyst in the literature. The determination of new electrochemical properties obtained by doping titanium dioxide is crucial since the oxidation/reduction reactions are controlled by the electrochemical structure of this material. Bandgap and band position energy levels which are important properties in photocatalysis can be determined and the efficiency of photoreduction under UV or visible light corresponding to these energy levels can be improved. Cyclic voltammetry (CV) can be used to determine the electrochemical properties of titanium dioxide and these properties can be improved by using the information obtained with this method.The effects of rare earth element doping on the electrochemical properties of titanium dioxide were investigated through out this Msc study. It was found that doping of titanium dioxide is significantly increased the electrochemical activity with rare earth elements. The increase in the doping amount of elements showed that articial photosynthesis activity of titanium dioxide may be enhanced by rare earth element doping. 77

Günümüzde ağırlıklı olarak sürdürülebilir olmayan fosil yakıtlara dayanan ve artan enerji ihtiyacının neden olduğu olumsuz etkiler ve bunların yarattığı kaygılar insanlığı er ya da geç sürdürülebilir temiz enerji kaynaklarına yöneltecektir. Hem küresel CO2 miktarını azaltan ve hem de yenilenebilir yakıt üretimini sağlayan yapay fotosentez önemli bir seçenek oluşturmaktadır. Fotokatalitik süreçler çevresel sorunların çözümüne ve yenilenebilir enerji üretimine önemli katkılar yapacaktır. Titanya bazlı fotokatalitik malzemeler kimyasal ve optik özelliklerinden ötürü yapay fotosentez uygulamalarında en yaygın kullanılan malzemelerdendir. Son yıllardaki araştırmalar nadir toprak elementi (NTE) katkılarının titanya fazlarını güneş ışınlarını görünür bölgede daha verimli kullanır hale getirebileceği yönünde önemli bulgular içermektedir. Bu tezde ağırlıklı olarak sol-jel temelli teknikler kullanılarak nadir toprak elementlerinin katkı düzeyleri ve ısıl işlem sıcaklığının titanya tozlarının mikroyapısal evrimine, optik özelliklerine ve fotokatalitik su parçalama/CO2 indirgeme aktivitelerine etkisi araştırılmıştır. Bu tezin sonuçları NTE iyonlarının ayrı bir oksit fazı olarak yapıda yer aldığını veya TiO2 kafes boşluklarına yerleştiğine ve düşük iyonik çaplı NTE iyonlarının NTE2Ti2O7 fazlarını oluşturabildiğine işaret etmektedir. Fotokatalitik süreçlerde yüzey alanı, kristalinite, ışık soğurma, oksijen boşlukları ve yapısal hataların aktivitede önemli rol oynadığı bu proje kapsamında yapılan deneylerle ortaya çıkmıştır. NTE katkısının TiO2'in yapay fotosentez aktivitesini olumlu yönde etkilediği saptanmıştır. Bu tez çalışmasının sonuçları düşük katkı düzeyleri ve 700oC dolayında ısıl işleme tabi tutulan tozların H2 üretimini ve CO/CH4 üretimini önemli ölçüde artırdığını göstermektedir. Growing environmental concerns related to the extensive use of nonsustainable fossil fuels and increasing energy demand will force mankind, sooner or later, to tap into clean and sustainable sources of energy and artificial photosynthesis is being considered as a promising prospect for this concern. Photocatalysis is expected to make a great contribution to solutions for environmental problems and renewable energy generation. Titania based photocatalytic materials are one of the widely used materials in artificial photosynthesis research due to their unique chemical and optical properties. Recent research have shown that rare earth element (REE) doping improves the photocatalytic activity of TiO2 phases in the visible region. The effects of REE doping level and heat treatment temperature on the microstructure evolution, optical properties and the photocatalytic water splitting/CO2 photoreduction activities of mostly sol-gel derived titania powders were investigated in this thesis. The results of this thesis indicated that REE ions may enter the interstitial voids of TiO2 lattice or segregate on the grain boundaries of TiO2 as a separate phase and RE2Ti2O7 phases were formed for the REEs with relatively smaller ionic sizes. The experimental work conducted revealed the importance of surface area, crystallinity, light absorption, the presence of oxygen vacancies and structural defects in the efficiency of photocatalytic processes. Results have shown that REE doping improves the artificial photosynthesis activity of TiO2 at relatively low doping levels and 700oC heat treatment temperature as the production rate of H2 and CO/CH4 were significantly higher with REE doped TiO2 compared to pure TiO2. 240

The compressive mechanical response of an FP™ continuous fiber (35 vol.%) Mg composite has been determined in the transverse and longitudinal directions at quasi-static and high strain rates. It was found that the composite in the transverse direction exhibited strain rate sensitivity of the flow stress and maximum stress within the studied strain-rate range of 1.3 × 10 −4 to 1550 s −1 . The failure strain in this direction, however, decreased with increasing strain rate. Microscopic observations on the failed samples have shown that the composite failed by shear banding along the diagonal axis, 45° to the loading axis. Twinning was observed in the deformed cross-sections of the samples particularly in and near the shear band region. The strain rate sensitivity of the fracture stress of the composite in transverse direction is attributed to the matrix strain rate sensitivity. In the longitudinal direction, the composite failed by kink formation at quasi-static strain rates, while kinking and splitting were observed at the high strain rates. The maximum stress in the longitudinal direction was, however, found to be strain rate insensitive within the strain rate regime of 1.3 × 10 −4 to 500 s −1 . In this direction, similar to transverse direction, twinning was observed in the highly deformed kink region. Several different reasons are proposed for the strain rate insensitive compressive strength in this direction.

The aim of this study was to investigate the stability and dispersion behaviour of aqueous alumina suspensions in the presence of polyethylene oxide–polypropylene oxide–polyethylene oxide (PEO–PPO–PEO) type triblock copolymers. For this purpose alumina suspensions at various solids loadings were prepared using four different methods. These are: Method I: powder and water were stirred only; Method II: powder and water were stirred and ultrasonic treatment was applied; Method III: powder and water were stirred in the presence of block copolymers; Method IV: powder and water were stirred and ultrasonic treatment was applied in the presence of block copolymers. These suspensions were characterized by means of rheological measurements. Sedimentation and turbidity measurements were also conducted to support these results and to investigate the stability of these systems for longer times. Surface tension measurements were performed to investigate the adsorption behaviour of block copolymers onto alumina surface. It was found that the use of PEO–PPO–PEO type triblock copolymers improved the dispersion behaviour of aqueous alumina suspensions in the presence of ultrasonic treatment at low solids loadings. However their effect was not significant at high solids loadings and without ultrasonic treatment.

Proceedings of the 8th Conference and Exhibition of the European Ceramic Society; Istanbul; Turkey; 29 June 2003 through 3 July 2003, Ceramic supports were prepared from fine alumina and zirconia powders by dry-pressing and slip-casting. These supports were heat treated in the 1100° - 1200°C temperature range and dip-coated with ceramic sols prepared from alkoxides by using sol-gel methods. The average sol particle sizes were measured as 3-7 nm for zirconia and 30-40 nm for alumina by laser scattering technique. The optimum heat treatment temperature range was determined as 500°-600°C for dip-coated membranes by using TGA (thermo gravimetric analysis) results. The microstructure of the ceramic composite membranes was investigated by SEM (Scanning electron microscope). The clean water permeability (CWP) of the membranes was tested by using deionized water in a filtration set-up. Separation experiments were performed with bovine serum albumin (BSA, Stokes diameter: 7 nm) solution and whey to determine the protein separation capacity of the composite membranes. The CWP of the dry pressed alumina supports heat treated at 1100°C was found to be higher than the permeability of the slip-casted zirconia supports heat treated at 1200°C. The protein retention of the slip-casted zirconia support was determined as 60% by using UV-Vis spectrophotometer (Abs. at 280nm). A protein retention value of 96% was achieved for whey after the modification of the support with dip-coating. The permeate flux was 40 L/m2hour for dry-pressed alumina support dip-coated with zirconia sol calcined at 500°C.

Proceedings of the 8th Conference and Exhibition of the European Ceramic Society; Istanbul; Turkey; 29 June 2003 through 3 July 2003, The preparation of nanocrystalline titania and alumina was investigated by sol-gel methods using titanium isopropoxide, boehmite and aluminum isopropoxide. Various drying control chemical additives like oxalic acid, acetic acid and polyacrylic acid were used for modifying the drying behaviour and shrinkage of the gels. The sintered densities of the ceramics prepared by sol-gel processing and the dried gels were in the 79-99% of theoretical density for rutile. The green and sintered densities of the pellets prepared by uniaxial pressing of powders derived from sols, gels and precipitation techniques for titania were in the 40-52% and 55-83% respectively. The titania ceramics were observed to experience anatase-rutile phase transformation upon heat treatment at 650oC. The grain size of the sintered ceramics at 650oC was determined to be about 26 nm. Grain size of titania increased to 213 nm. at 850oC. The mechanical properties of these nanocrystalline ceramics were investigated by using microhardness testing.

Proceedings of the 8th Conference and Exhibition of the European Ceramic Society; Istanbul; Turkey; 29 June 2003 through 3 July 2003, Magnesia-chromite (MgO + MgO·Cr2O3) and magnesia-spinel (MgO + MgO·Al2O3) refractory bricks that are used in the high temperature zones of rotary cement kilns are investigated for their microstructural characteristics. Their microstructures are important because the size, shape and distribution of periclase grains, chromites and the quality of their bonding phases significantly affect their service performances. The purpose of this study was to characterize the microstructures of industrial brick samples to develop a protocol to compare different products e.g. for evaluation as replacement bricks. In some of the chromite containing bricks iron-rich rims were observed, while a domestic brick with similar chemistry had no such feature. These iron-rich rims were examined using SEM-EDS. It was found that the counter-diffusion of Fe+3 and Cr+3 were responsible for their formation. Exsolved chrome-spinel was widely observed in the microstructures of chromite bricks. Magnesia-spinel bricks were found to contain low melting calcium aluminates as bond phases in the microstructure, posing a threat to service performance. Portmortem microanalysis of industrially used bricks revealed alkali attack in addition to creep as main destruction mechanisms for brick. Traces of elements like Mo, S and alkalies were observed and thought to originate from the use of waste derived fuels.

In the present study, the preparation and characterization of polylactide-Hydroxyapatite(HA) composite films for biomedical applications have been studied. The effects of number of parameters such as polymer type, HA loading, surface modification and its concentration on the mechanical and microstructural properties of the composites were investigated. Poly-L-Lactide and 96/4 Poly(L-Lactide co D-Lactide) copolymer-HA composites containing 10-40 wt% HA particles have been prepared by solvent casting technique. The HA powder was synthesized by precipitation technique. Interfacial interactions between HA and polylactide polymer were modified to improve filler compatibility and mechanical properties of the composites by surface treatment of the HA with two different silane coupling agents; 3-aminopropyltriemoxysilane (AMPTES) and 3-mercaptopropyltrimethoxysilane (MPTMS) at three different concentrations(0.5-2 wt%). Silane treatment indicated improvements in the mechanical properties of the composites compared to the untreated HA loaded polylactide composites. Tensile test results showed that the maximum improvement in the mechanical properties of the composites was obtained for PLA composites containing 1 wt% aminofunctional silane treated HA and 0.5-wt% mercaptopropyltrimethoxy silane treated HA for PDLA composites. Scanning electron microscopy studies also revealed better dispersion of silane treated HA particles in the polymer matrix.

Thesis (Master)--Izmir Institute of Technology, Biotechnology, Izmir, 2014, Includes bibliographical references (leaves: 54-57), Text in English; Abstract: Turkish and English, x, 58 leaves, Calcium phosphate cements (CPCs) have been extensively investigated due to their excellent biocompatibility, osteoconductivity, potential resorbability in dentistry and orthopedics. They have numerous advantages over other calcium phosphate-based materials. The CPC precursor powders were prepared in the initial stage of this work. Tetracalcium phosphate (TTCP) powders coded as TTCP-1 (obtained from H3PO4 and CaCO3) and TTCP-2 (obtained from NH4H2PO4 and CaCO3) were prepared by heat treatment of the calcium and phosphate source mixtures at 1350°C. Brushite powders were produced by aqueous chemical methods. A series of CPCs (HA cements) were prepared by using the TTCP-1 and brushite powders which were mixed with 0.2 M and 0.3 M phosphate buffer solutions at three different solid/liquid ratios (2.4, 2.7 and 3.2 g/ml) with three different HA initial seed contents (3%, 1.5% and 0.0 wt% ). The setting times of CPCs were determined to be in the 3.5-24 minute range. The phase structure and surface morphology of the cements and precursor powders were characterized by XRD and SEM. XRD analysis of powders revealed the presence of the characteristic TTCP and brushite peaks. XRD analysis also indicated that all cement samples were composed by HA phase with different crystallinity and other phases were not detected. Rod and plate-like hydroxyapatite crystals were observed in the SEM micrographs of all CPCs. Cytotoxicity testing was performed using the MTT (3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyl tetrazolium bromide) assay to determine the number of viable cells in the presence of powders and HA cements. Cytotoxicity results indicated that brushite powder caused sharp decreases in cell viability at the end of 24, 48 and 72 hours at all powder extract concentrations. TTCP-1 and TTCP-2 powders unlike brushite had no toxic effect with cell viability values over 74 %. Almost all CPCs prepared in this work had no cytotoxic effects.

Enerji insanlığın en önemli ve vazgeçilmez bir ihtiyacıdır. Artan enerji talebi teknolojik gelişmeler ve artan nüfus ile ilişkilidir. Dünyanın en ciddi sorunlarından biri, sürdürülebilir enerjiyi sağlamaktır. Dünyadaki yenilenebilir enerji kaynaklarının yaygın bulunabilirliğinden dolayı, yeni alternatif enerji kaynakları ve/veya yenilenebilir enerji teknolojileri önemli araştırma konuları haline gelmiştir. Ancak, çoğu yenilenebilir enerji kaynakları tüketicilere kesintisiz enerji sağlayamamaktadır. Ekonomik, verimli ve güvenilir bir enerji depolama teknolojisine son derece ihtiyaç duyulmaktadır. Bu nedenle, akademik çalışmalar elektrokimyasal enerji depolama teknolojilerinin kapasite gelişimine odaklanmıştır.Bu çalışmanın asıl amacı, batarya uygulamaları için çeşitli morfolojilere sahip farklı çinko oksit tozları ve katkı malzemeleri kullanılarak çinko elektrotların hazırlanması ve incelenmesidir. Çinko oksit morfolojisi ve nikel-çinko batarya performansı üzerindeki etkilerini incelemek için farklı koşullar altındaki (öncü madde, sıcaklık ve bekleme süresi) kimyasal çöktürme metoduyla çinko oksit tozları sentezlenmiştir. Çinko oksit tozunun başlangıç morfolojisinin elektrokimyasal performans açısından bir öneminin olmadığı görülmüştür. Ticari çinko oksit tozundan hazırlanan çinko elektrotlarına sahip nikel-çinko bataryaları yaklaşık 247 mAhg-1 deşarj kapasitesine sahiptir ve kimyasal çöktürme metoduyla sentezlenen çinko oksit tozlarından hazırlanan çinko elektrotlarına sahip nikel-çinko bataryalarına kıyasla bu elektrot kısmen daha iyi bir performans göstermiştir. Ayrıca, çinko elektrot morfolojisinin batarya katkı malzemeleri (PVA ve PEG) ve şarj akım yoğunluğu tarafından büyük ölçüde etkilendiği tespit edilmiştir. Seçilen bazı elektrot katkı malzemelerinin (Ca(OH)2, PbO ve PEG) batarya performansı üzerindeki etkileri de incelenmiştir. Tüm katkı malzemelerine sahip çinko elektrotu daha yüksek deşarj kapasitesi (322 mAhg-1) ve kullanım oranı (48.86 %) gibi gelişmiş elektrokimyasal özellikler göstermiştir. Energy is the most important and inevitable requirement for humankind. The increasing energy demand has been connected with technological advances and the population growth. One of the most serious problems of the world is to provide sustainable energy. New alternative energy sources and renewable energy technologies have become notable research subjects due to wide availability of renewable energy sources in the world. However, most renewable energy sources do not provide uninterrupted energy to consumers. An economic, efficient and reliable energy storage technology is desperately needed. Therefore, academic research has focused on improving the capacity of electrochemical energy storage technologies.The main goal of this study is the preparation and characterization of zinc electrodes for battery applications using different zinc oxide powders with various morphologies and additives. Zinc oxide powders were synthesized with chemical precipitation method under different conditions (precursors, temperatures and aging times) in order to investigate their effects on ZnO morphology and on the performance of nickel-zinc battery. It was found out that the initial morphology of ZnO powder was not crucial for the electrochemical performance. Nickel-Zinc batteries with zinc electrodes prepared from commercial ZnO powder had discharge capacities around 247 mAhg-1 and showed slightly better performance compared to nickel-zinc batteries with zinc electrodes prepared from ZnO powders synthesized via chemical precipitation method. It was also determined that zinc electrode morphology was greatly affected by battery additives (PVA and PEG) and charging current density. The effects of some selected electrode additives (Ca(OH)2, PbO and PEG) on battery performance were also investigated. Zinc electrode with all additives showed improved electrochemical properties, such as higher discharge capacity (322 mAhg-1) and utilization ratio (48.86 %.). 100

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2013, Includes bibliographical references (leaves: 53-55), Text in English; Abstract: Turkish and English, x, 60 leaves, In this study, use of gelatin and carrageenan gum as gel formers in gelcasting process of alumina ceramics was aimed. The effects of each gel former on the mechanical properties of gelcasted alumina ceramics were distinctly investigated. Firstly, an experimental design was made according to pre-experimental studies and researches. In this experimental design, it was determined what the factors should be and how the levels of factors should change. Two groups of gelcasting slips were prepared with alumina powder. One of them was the group that contained gelatin with changing ratios from 3 to 6 wt%. Other was the group that contained carragenan gum with changing ratios from 1 to 2 wt%. Alumina powder amounts of the slips in also each group were the same and changing from 47 to 53 vol%. Furthermore, in order to see the direct effect of each gel former type and amount on mechanical properties and compare the methods of gelcasting and slip casting, alumina slips that contained no gelatin or carrageenan gum were also prepared. Green alumina samples in suitable shapes for mechanical tests were obtained by gelcasting method from the prepared slips. After green samples were dried, half of them were sintered at 1550 oC. Rest of them weren’t subjected to any heat treatment. Green samples in block shape were cut in suitable dimensions for 3-point bending test before they were sintered. Shrinkage and densification ratios of the alumina samples after drying and sintering were measured and calculated. At the end of the mechanical tests applied on green and sintered alumina ceramics, data about change in their bending strength, compressive strength and hardness values due to varying gel amount and sintering were obtained. These data were analyzed, then the obtained results were interpreted. While optimum gel former amount needed for maximum compressive and bending strength of gelatin-gelcasted alumina samples was 5 wt%., this amount for that of gum-gelcasted alumina samples was 1.7 wt%. The effect of alumina solid loading on mechanical properties of gelcasted alumina samples was unclear. After sintering of gelatin-gelcasted alumina samples, the densification reached to a maximum of 95.80%.

Nanocrystalline mesoporous titania powders were synthesized by hydrolyzing titanium isopropoxide in ethanol–water mixtures which were ultrasonically treated without using any templates or chemicals. Titanium isopropoxide–ethanol mixture was added dropwise to a water–ethanol mixture placed in an ultrasonic bath. The properties of the sonochemically synthesized powder were compared with those of the powders prepared without ultrasonic treatment along with Degussa P-25 titania powder. The phase structure, crystallite size, surface area, particle size, powder density were determined and sintering behavior was analyzed in this work. The nanotitania powder prepared during ultrasonic induced hydrolysis (TiO 2 -U) was determined to be formed from a mixture of anatase and brookite phases at 25 °C. The brookite phase in nanotitania powder prepared without ultrasonic treatment (TiO 2 -NoU) was detected at 70 °C. The anatase–rutile phase transformation was completed in the 500–700 °C range for both powders. The average crystallite sizes of the powders at 25 °C were determined as 10 and 5 nm for TiO 2 -NoU and TiO 2 -U, respectively. The surface area decreased from 238 to106 m 2 /g for TiO 2 -NoU and from 287 to 82 m 2 /g for TiO 2 -U when the calcination temperature was increased from 200 to 500 °C. The evolution of the N 2 adsorption–desorption behavior with calcination temperature and the corresponding pore size distributions/volumes was attributed to the formation of closely packed submicron aggregates during powder synthesis and calcination. The sintering behavior was concluded to be controlled by 7–10 nm crystallites and the submicron aggregates. The determination of the densification behavior of titania powders prepared by different methods with various levels of dopants may prove to be very useful for a better understanding of the phase/pore structure evolution which is crucial for a significant number of applications.

Thesis (Doctoral)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2012, Includes bibliographical references (leaves: 254-267), Text in English; Abstract: Turkish and English, xviii, 315 leaves, The goal of this thesis is to synthesize unique, clinically relevant macroporous calcium phosphate cement blocks to be utilized both in vivo and in vitro tissue engineering applications. Calcium phosphate cements which essentially consist of hydroxyapatite or brushite are constantly improved to overcome their inherent shortcomings such as low strength, low functional porosity, and low resorption. Recent literature on the topic points to monetite forming cements as an alternative phase. A novel method to utilize monetite that is finer and stronger with respect to brushite in load bearing scaffold applications is introduced in the results section of this thesis as a contribution to ever growing literature on this scope. In the preliminary study on the conversion extent of apatite forming cement, ionic strength of the setting liquid was determined as the prime effective factor on monetite conversion extent. Subsequently brushite forming β-tricalcium phosphate – monocalcium phosphate monohydrate cement system was modified by NaCl and citric acid so that brushite formation was selectively inhibited. Singular and synergistic monetite promoting effects of NaCl and citric acid were determined by monitoring the kinetics of cement setting in excess setting liquid. Spectrometric studies revealed the difference in brushite and monetite crystal surface site density which enabled selective inhibition of brushite and promotion of monetite by the synergistic effect of NaCl anc citric acid. Proposed phase control mechanism enables tailoring the composition of biphasic cements comprising of a predetermined monetite content and brushite or hydroxyapatite. In the final stage of the thesis, size distributed NaCl particles were introduced into the cement paste containing optimum amount of citric acid to enable complete monetite formation. Resultant macroporous monetite blocks were characterized in terms of microporosity, macroporosity, density, morphology, strength, phase composition, and surface area. Interconnectivity of the cement was optimized based on the correlation of porogen size distribution and morphological data.

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2011, Includes bibliographical references (leaves:118-121), Text in English; Abstract: Turkish and English, xix, 121 leaves, The rheology of concentrated calcium carbonate, titania, silica, alumina and zirconia suspensions of submicron/nanosized particles in non-aqueous media was investigated. Calcium carbonate and silica particles were synthesized by carbonation route and Stöber method respectively while titania, alumina and zirconia powders were obtained commercially. Suspensions of the ball milled natural calcium carbonate powders were also prepared. The dispersion of these powders especially at high solids loadings was observed to be difficult. The viscosity of the 45 vol% suspensions of precipitated CaCO3 particles increased about 21 times at a shear rate of 400 sec-1 relative to its initial value indicating shear-thickening behaviour. The onset of shear thickening was at 20, 30 and 40 vol% for three different commercial titania powder suspensions. The onset of shear thickening was at lower solids volume contents and the increase in viscosity with shear rate was far less dramatic for the titania suspensions with polydispersed particle size distributions. The critical shear rate was 187 sec-1 for silica suspensions at 47 vol% with a discontinuous jump in viscosity. Rheological data at higher shear rates was not obtained due to the torque limitations of the rheometer. The critical shear rate of the polydispersed alumina powder suspensions were higher than their relatively monodispersed counterparts. The highest solids loading achieved in alumina based suspensions was 62 vol%. The dynamic shear rheology measurements showed that the solid part of the silica suspension was becoming more dominant over the liquid part as the solid content was increased. The volume fraction dependence of the high shear viscosity was fitted to a modified Krieger-Dougherty model for titania and silica suspensions. The fit of the rheological data to the Power law and to a modified version of Cross model were analysed.

Stable polymeric and colloidal boehmite sols were prepared by sol-gel process through controlled hydrolysis/condensation reactions. The particle sizes of the colloidal sols were in the 12-25 nm range depending on the process parameters and about 2 nm for polymeric sols. The presence of a significant increase in the microporosity content of the heat treated polymeric membranes relative to the mesoporous colloidal membranes might make the design of thermally stable microporous alumina membranes with controlled pore structures possible. The phase structure evolution in the 600-800 °C range had shown that the crystallization of the gamma alumina in the amorphous matrix starts at about 800 °C. This indicated that the pore structure stability may be enhanced through processing up to this relatively high temperature in polymeric alumina derived unsupported membranes. The permeance values of the two and three layered colloidal alumina membranes were observed to be independent of pressure which implies that the dominant gas transport mechanism is Knudsen diffusion in these structures. This was also supported by the 2.8 nm BJH pore sizes of the colloidal membranes. The Knudsen diffusion equation derived permeances of the polymeric alumina membranes with thicknesses of about 300 nm were determined to be very close to the experimentally determined permeance values. © 2010 Springer Science+Business Media, LLC.