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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.

In this work, effects of compaction pressure on the structural and superconducting properties of BSCCO ceramic superconductors were investigated. The study was carried out on two systems which were, System I: Bi 1.7Pb 0.3Sr 2Ca 2Cu 3O y and System II: Bi 1.6Pb 0.3Ag 0.1Sr 2Ca 2Cu 3O y, respectively. Ceramic powders were prepared by conventional solid-state reaction method and sintered at 850°C after compaction at five different pressures in the 150-750 MPa range. Critical temperatures of samples were determined by resistivity-temperature determinations made by four-point probe method in liquid nitrogen conditions. XRD analysis was conducted by powder X-ray diffraction method. Morphology of the grains present in the samples were determined by using scanning electron microscope (SEM) photographs at 2 K× and 2.5 K× magnifications for System I and System II, respectively. Sintered densities of the superconducting ceramics were measured by Archimedes water displacement method and unit cell parameters were additionally obtained from XRD data. T c values for System I was determined to be in the 109-115 K with sample D having the highest T c of 115 K while T c varied in the 104-109 K range and sample B had the highest T c value of 109 K for System II. The transition width, which is a sign of the purity of the samples, was determined to be narrow for both systems. The data obtained from X-ray diffraction measurements have shown that 2223 high-T c phase was dominant in both systems. The determination of the optimum pellet compaction pressure for BSCCO ceramic superconductors was the main purpose of this work. The results of this work indicated that compaction at around 450 MPa improves the superconducting and structural properties of the BSCCO ceramic superconductors. © 2009 Springer Science+Business Media, LLC.

Thesis (Doctoral)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2010, Includes bibliographical references (leaves: 216-228), Text in English; Abstract: Turkish and English, xxiv, 303 leaves, The main objective of this study was to determine the behavior of hydroxyapatite powders in solutions containing major ions found in human blood plasma. Research efforts however were focused on two different fields, chemical analysis and dissolution testing of hydroxyapatite. Arsenazo III-calcium analysis method was selected and modified for the low level calcium analysis whereas malachite green phosphate assay was used for phosphate determinations. Arsenazo III reagents with different dye concentrations and pH values were tested for the analysis of low levels of calcium. The effects of ions at their blood plasma concentration levels on the modified calcium analysis method were further evaluated. Effects of these ions on the accuracy of phosphate analysis by malachite green assay were also investigated. Dissolution behavior of synthesized and commercial hydroxyapatite was investigated by immersing pellets in several solutions. Calcium and phosphate release kinetics in ultrapure water, sodium chloride and sodium bicarbonate solutions were investigated. Commercial hydroxyapatite pellets were also immersed separately in magnesium chloride, and sodium chloride/bicarbonate solutions. Calcium concentrations in solutions were found to decrease in the following order: sodium chloride > ultrapure water > bicarbonate. Phosphate concentrations in solutions were found to follow an order of sodium bicarbonate > sodium chloride > ultrapure water. Bicarbonate-phosphate ion exchange was observed in bicarbonate ion containing solutions. Magnesium-calcium ion exchange and adsorption of phosphates on hydroxyapatite surfaces were found to be effective in magnesium ion containing solution.

Thesis (Doctoral)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2010, Includes bibliographical references (leaves: 225-235), Text in English; Abstract: Turkish and English, xxviii, 248 leaves, The development of modern automobile and engine industries requires lubricants that can withstand high temperatures and pressures. Recent advances made in the chemistry provide the use of inorganic particles as lubricant additives. Therefore inorganic boron-based additives have been the focus of much attention, as they posses a good combination of properties, such as wear resistance, friction-reducing ability. In this study, the state of art in the field of inorganic particle, zinc borate synthesis and its employment in tribology were investigated. The synthesis of zinc borate was achieved not just by precipitation, but also production methods such as inverse emulsions. The products were characterized by SEM, FTIR, TGA, DSC, EDX. In lubrication part, the friction reducing and antiwear ability of the particles as an additive in the mineral oil was focused. Sorbitan monostearate was used to cover the surfaces of inorganic particles in order to provide better dispersion of additives in the oil. Friction and wear behavior of the lubricants were measured by four-ball wear test machine. The effects of dispersing agent, zinc borate type as well as surfactant concentration on the tribological properties of the lubricants were investigated. Sorbitan monostearate not only outperformed as a dispersing agent of inorganic particles, but also it proved to be an efficient antiwear agent. The lowest wear scar diameter was obtained by the lubricant containing zinc borate synthesized via coordination precipitation method. The addition of this sample with the surfactant in the oil reduced the wear scar diameter from 1.402 mm to 0.550 mm.

The effect of partial substitution of Ca by Zn in Bi1.7Pb0.3Sr2Ca2−x Zn x Cu3O y at x=0.00, 0.05, 0.10, 0.15 and 0.20 levels on the electrical and structural properties was investigated in this work. The characterization of the ceramics prepared by the conventional solid-state reaction method were done by resistance–temperature measurements, XRD, SEM and density analysis. Low levels of Zn substitution of Ca caused significant changes in the properties of the ceramics. The low-T c superconducting properties were enhanced and the fraction of the low-T c (2212) phase were found to increase at x=0.15 level of Zn substitution at 830 °C sintering temperature. Zero resistance was observed only in sample D with x=0.15 and the T c was determined as 92 K. The SEM micrographs and the density analysis have shown that this was the densest packed ceramic.

Thesis (Doctoral)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2009, Includes bibliographical references (leaves: 160-164), Text in English; Abstract: Turkish and English, xviii, 245 leaves, Several rheometric techniques were applied to submicron and nano ceramic powder dispersions systematically in this study. The rheological behavior of the dispersions was determined by steady shear and dynamic shear rheology. Dynamic shear rheological techniques are scarcely used for the characterization of ceramic powder dispersions contrary to polymers.The flow behaviors of the submicron and nano dispersions were found to be dependent on the solids content and fructose concentration. The submicron alumina, nano alumina, and nano titania dispersions in fructose solution showed shear thinning behavior and were fitted to the Herschel-Bulkley model.The dynamic shear rheology measurements showed that the solid part of the dispersions was dominant over the liquid part for both submicron and nano powder dispersions. The elastic modulus was higher than the viscous modulus in stress and frequency sweep measurements. The elastic moduli of the dispersions with solids content lower than 40 vol% were dependent on the angular frequency which indicated a gel-like behavior. However, the elastic moduli of the dispersions with 40 vol% solids were independent of angular frequency which indicated a solid like behavior. Further increase in fructose content had significant effects on both steady shear and dynamic shear rheological behavior of the dispersions regardless of particle size. The submicron and nano ceramic powder dispersions can be prepared by using fructose for the regulation of the rheological behavior of ceramic powder dispersions. The characterization of powder surfaces is essential for the effective adsorption of fructose.

Nano ve mikronaltı seramik toz dağıtımlarına çeşitli reometrik teknikler sistematik olarak uygulanmıştır. Dağıtımların reolojik davranışı, kararlı kayma ve dinamik kayma reolojisi ile belirlenmiştir. Dinamik kayma reolojik teknikler seramik toz dağıtımlarının karakterizasyonunda polimerlerin aksine kullanılmıştır.Mikronaltı ve nano dağıtımların akma davranışları katı içeriğine ve früktoz konsantrasyonuna bağlı olduğu görülmüştür. Früktoz solüsyonunda mikronaltı ve nano alüminyum oksit ve nano titan dağıtımların kayma incelen davranışı göstermiş ve Herschel-Bulkley modeline uymuştur.Dinamik kayma reolojisi ölçümleri hem mikronaltı hem de nano toz dağıtımlarında katı kısmının sıvı kısmına göre daha baskın olduğunu göstermiştir. Gerilim ve frekans tarama testlerinde, elastik modül, akma modülünden daha yüksektir. Hacimsel katı içeriği %'si 40'dan az olan dağıtımların elastik modülleri açısal frekansa bağlıdır, bu da jel gibi bir davranışa işaret etmektedir. Ancak, hacimsel katı içeriği %40 olan dağıtımların elastik modülü açısal frekanstan bağımsız olup katı gibi bir davranışa işaret etmektedir. Früktoz konsantrasyonun fazla artışı hem yatışkan hem de dinamik kayma reolojisinin parçacık boyutuna bağlı olmaksızın önemli ölçüde etkilemiştir. Mikronaltı ve nano seramik toz dağıtımlarının hazırlanmasında, seramik toz dağıtımlarının reolojik davranışının ayarlanması için früktoz kullanılabilir. Tozlarin yüzey karakterizasyonu früktozun etkili adsorpsiyonunda esastır. Several rheometric techniques were applied to submicron and nano ceramic powder dispersions systematically in this study. The rheological behavior of the dispersions was determined by steady shear and dynamic shear rheology. Dynamic shear rheological techniques are scarcely used for the characterization of ceramic powder dispersions contrary to polymers.The flow behaviors of the submicron and nano dispersions were found to be dependent on the solids content and fructose concentration. The submicron alumina, nano alumina, and nano titania dispersions in fructose solution showed shear thinning behavior and were fitted to the Herschel-Bulkley model.The dynamic shear rheology measurements showed that the solid part of the dispersions was dominant over the liquid part for both submicron and nano powder dispersions. The elastic modulus was higher than the viscous modulus in stress and frequency sweep measurements. The elastic moduli of the dispersions with solids content lower than 40 vol% were dependent on the angular frequency which indicated a gel-like behavior. However, the elastic moduli of the dispersions with 40 vol% solids were independent of angular frequency which indicated a solid like behavior. Further increase in fructose content had significant effects on both steady shear and dynamic shear rheological behavior of the dispersions regardless of particle size. The submicron and nano ceramic powder dispersions can be prepared by using fructose for the regulation of the rheological behavior of ceramic powder dispersions. The characterization of powder surfaces is essential for the effective adsorption of fructose. 264

Thesis (Doctoral)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2009, Includes bibliographical references (leaves: 201-214), Text in English; Abstract: Turkish and English, xix, 214 leaves, The scope of this thesis is to design defect-free microporous and mesoporous ceramic membranes having micro-engineered pore network that would contribute to the enhancement of pore control abilities as well as the thermal stability.In this study, mono-dispersed silica sols having well-defined silica spheres ranging in size from 5 to 700 nm were prepared through sol-gel methods and thin membrane layers were consolidated on either y-alumina support or unsupported form.The packing of 5 nm silica spheres resulted in micropores of 0.87 nm in 400 oC treatedmembranes with the porosity of 0.32 which are in well aggrement with the porosity level of random loose packing. Silica spheres with varying concentration and size were incorporated into polymeric network to complement the percolative structure of sphere packing with interpenetrated polymeric silica network in order to design well-defined thermally stable transport pathway. Low shrinkage value was obtained for sphere incorporated system providing the high thermal stability by affecting the thermally induced microcrack formation as well as the structural relaxation during consolidation.The resulting hybrid structure enabled the detailed transport properties that support to be able to control the pore structure but N2/CO2 separation properties are needed to be improved.Stable polymeric alumina sols having particle sizes smaller than 2 nm could be obtained when the hydrolysis conditions were accurately controlled. The mixture of prepared polymeric silica and alumina sols in mullite compositions (3:2) provided to the crystallization of mullite with homogeneously mixed stable oxide network upon heat treatment at 775 oC.

Thesis (Doctoral)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2009, Includes bibliographical references (leaves: 147-150), Text in English; Abstract: Turkish and English, xxii, 150 leaves, The ceramic membranes with their superior chemical, thermal, mechanical and microbiological properties and long service lives are gaining importance in pressure driven filtration processes. The diverse requirements of different applications enforce preparation of tailor-made ceramic membranes with specific characteristics. This dissertation focused on the preparation and characterization and filtration performance of asymmetric multilayer ceramic membranes. Support is the layer responsible for mechanical stability while top layer is mainly responsible for separation and intermediate layer is balancing the microstructural difference between these two layers. The permeability of alumina support could be increased over 100 L / m2 h by 15% starch addition. The intermediate layer was prepared by coating fine alumina or zirconia powders and / or colloidal sols with thicknesses between 0.2-70 .. The top layer was formed from pure or mix of zirconia or titania polymeric sols with average particle sizes in the range of 3 . 50 nm with a thickness smaller than 1.. The physicochemical properties of these mixed oxides were modified by changing the composition and calcination temperature enabling preparation of top layers with varying Donnan exclusion capacities. The membranes prepared could reject sugar, PEG 1000 and PEG 4000 up to 10, 60 and 19%, respectively, that which can be increased via further optimization of parameters in coating / heat treatment processes.

Thesis (Master)--Izmir Institute of Technology, Biotechnology, Izmir, 2008, Includes bibliographical references (leaves: 66-68), Text in English; Abstract: Turkish and English, xi, 69 leaves, The preparation and characterization of chitosan-hydroxyapatite composite scaffolds and protein adsorption chracteristics of these scaffolds have been investigated in this study. The effects of different chitosan/hydroxyapatite contents of the low density composites on the protein adsorption behaviour were experimentally examined.Bradford method at 595 nm and 280 nm UV protein absorption methods were used for the determination of adsorbed amount of bovine serum albumin (BSA) and human serum protein (HSP). In this study low molecular weight chitosan and hydroxyapatite have been used for the preparation of the scaffold composites by freeze drying and SEM was used for microstructural analysis. The thermal behaviour of the composites was investigated by DSC and TGA. Composite scaffolds were prepared by using different amounts of chitosan and hydroxyapatite (HA) and six different scaffolds were prepared and coded as C100H0, C80H20, C70H30, C50H50, C30H70, and C20H80. The porous low density scaffolds had 93.5-96.3% porosity with a slight increase in density with increasing HA content. The interconnected pore network was formed from 50-250 .m relatively uniform size pores with thin pore walls. The HA particles were fully embedded in the polymer matrix in the pore walls. The TGA curves have shown that the freeze dried phase seperation induced biopolymer sturucture degrates at lower temperatures faster than the original raw polymer. The adsorptions of BSA and HSP onto composites have been studied as a function of time, protein concentration and pH. Adsorption experiments were also conducted with commercial HA powder. The adsorption kinetics experiments have indicated that protein adsorption was almost completely achieved in the first 2-3 hours with relatively high uptake values of up to 45-60 mg/g and 40-60 mg/g for 595 nm Bradford and 280 nm methods. The adsorption behaviour did not fit to the commonly known Langmuir and Freundlich isotherms. This was attributed to the swelling/degradation tendency of the freeze-dried chitosan containing scaffolds. The HSP uptake of 30 and 50 wt% HA containing composites were in the 50-60 mg/g range which was higher than other composites and the raw unprocessed chitosan.

Natural zeolites undergo structural changes after heating which open their possible use in different fields, related to their chemical and physical properties, such as building stone, lightweight aggregate, ceramic foam, concrete bricks, tiles, porcelain stoneware and additive in puzzolonic cements. In this study, thermal behavior of zeolitic tuff quarried from Gördes-Manisa, region of Turkey was investigated. Zeolitic rocks were first reduced to 2 μm and pellets were prepared by dry-pressing. The pellets were heated for 30 min in the temperature range of 200-1200 °C. Heating the tuff up to 600 °C did not cause any structural change detectable by X-Ray powder diffraction (X-Ray), Fourier Transform Infrared Spectroscopy (FTIR) and thermal characterization methods with regard to the original sample, while further increase in the temperature caused structural breakdown of zeolitic tuff. The appearance of the broad low intensity peaks in X-Ray diffraction diagrams indicated most probably a partial transformation of crystal structure into an amorphous structure. The Scanning Electron Microscopy (SEM) micrographs showed that the crystals seen in the original rock sample were broken during grinding and pressing processes. The crystal structure disappeared above 1000 °C and the spherical pores was observed at 1200 °C. Chemical composition of the zeolitic tuff did not change significantly with respect to temperature. The highest density (2.28 g/cm3) and hardness (387 Hv) were obtained by sintering the pellets at 1000 °C for 30 min., İYTE 96K121240

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2007, Includes bibliographical references (leaves: 65-69), Text in English; Abstract: Turkish and English, xi, 69 leaves, Dense alumina and zirconia crucibles manufactured in the laboratory by slip casting were tested for their resistance to corrosive attack by opaque and transparent frits between 1400-1500oC. Interface between the crucible and the frit was investigated by Scanning Electron Microscopy (SEM, Philips XL-30S FEG) equipped with EDS (Energy Dispersive Spectroscopy) unit, X-ray diffraction (XRD, Philips X.Pert Pro), and Optical Microscope (OM, Nikon Eclipse L150). Formation of a continuous band of zinc aluminate (gahnite) crystals was observed at the interface between the alumina crucible wall and the contained opaque and/or transparent frit melt. When opaque frit was used, isolated pockets of zirconia were present adjacent to the zinc aluminate band inside the frit. Deeper inside the frit incompletely dissolved zircon were observed. On the other hand zirconia crucible failed against both of the corrosive frits, resulting in complete penetration of frit species into zirconia crucible wall. Thermodynamic predictions based on the use of phase diagrams also produced similar conclusions with the practically observed results. Crucibles with 50 wt% zirconia and 50 wt% alumina were also manufactured and tested for their corrosion resistance against the frit. It was found that the alumina crucibles could be safely used for corrosion testing with minimal aluminum contribution to the frit melt.

Presented at the 10th Aachen Membrane Colloquium, 16–17 March 2005, Aachen, Germany, Ceramic supports were prepared from alumina powder and dip-coated with zirconia sol. The ceramic composite membranes prepared were characterized with respect to their microstructure/pore structures. The supports were 40% porous of which 87% were open pores. The average particle size of the sol particles was 35 nm. The prepared membrane has good protein lactose separation properties with a relatively high protein content (PR ∼80%) and with relatively low lactose retention (LR ∼7%). The permeate flux value was around 40 l/m2h. These results indicate the possibility of the preparation of ceramic composite membranes for separation of whey components with higher yields.

Thesis (Master)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2006, Includes bibliographical references (leaves: 89-94), Text in English; Abstract: Turkish and English, xii, 94 leaves, The harbour sediment accumulated in time in the zmir Bay was investigated by a number of researchers from various aspects. These sediments called marine sludge in this thesis contain organics and heavy metals which pose an important environmental problem. Marine sludge removed from the harbor is required to be safely kept in some form. In this thesis, production of ceramic tiles by using marine sludge additives was investigated. The sludge is regarded as a suitable raw material for ceramic tile production because of its physical properties and chemical composition. After the sludge is removed from the harbor floor, it was subjected to a series of treatments such as washing, sieving, dewatering, drying and grinding. This treated marine sludge was pressed in the form of pellets and sintered in the 1000-1100 °C range. The treated, untreated and sintered marine sludge along with the separated shells present in marine sludge were characterized by a variety of techniques such as XRD, FTIR, and SEM-EDX. Marine sludge powders at different proportions (0-50 %) were blended via incorporation into a structural ceramic tile raw material. The mixtures were compressed, and then pellets were fired at temperatures in the 1000-1200 °C range with one-hour hold with a firing rate of 10 °C/min. The products were characterized for mechanical and microstructural properties. Marine sludge added tiles were observed to have higher compressive strength after firing at 1100 °C. The sludge addition caused a lower firing temperature for densification/vitrification of the pellets with higher pore content. Their densities and water absorption values were determined. The densities and water absorption of the tiles fired at 1100 °C was observed to decrease with increasing sludge addition. Leaching tests were performed by varying the leach solution pH and ground tile particle size for chemical durability of the products in the final part of the work. The leaching data have shown that heavy metals were immobilized in the vitrified ceramic structure. The results of this work indicated that blending marine sludge in to the ceramic powder mixtures in the 20-50% range was beneficial for tile production.

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2006, Includes bibliographical references (leaves: 110-113), Text in English; Abstract: Turkish and English, xiv, 113 leaves, In this study, two methods of CaP coating, dip coating and biomimetic, on porous Ti6Al4V powder compacts to be used in novel spinal cages were experimentally investigated. The powder compacts produced by sintering of compacted green powders contained 37% open porosity with an average pore size of 63 micrometers. Dip-coating solutions were prepared using sol-derived and commercially available HA powders.Biomimetic CaP coatings were performed in 1(at 37°C, Ph . 7.4) °, 5 (at 37°C, pH .6.0) and 10x (at room temperature, pH . 5.8) simulated body fluid (SBF).The porous Ti6Al4V powder compacts were successfully coated using HA dip coating solutions. The optimum soaking times were 3 and 1-minute for sol-derived and milled and unmilled comercial HA powders, respectively. Increasing soaking times further started to fill the originally open pores. The thicker deposit and cracks were observed at the sintering necks of the particles was believed to be due to capillary effects drawing the coating solution into this concave region. Milling of HA powder induced more homogenous coating layer on the Ti6Al4V particles.Increasing Ca and P concentrations in SBF increased the rate of CaP nucleation.Alkaline (NaOH) and heat-treatment (600oC for 1 hour) further accelerated CaP formation. The complete coating of treated and untreated compacts was 14 and 21 days using 1xSBF, 24 and 36 hours using 5xSBF and 4 and 6 hours using 10xSBF, respectively. When considered crack free and homegenous coating layer, dip coating using milled commercial HA powder was found to be the most appropriate method for the coating present powder compacts.

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2006, Includes bibliographical references (leaves: 73-75), Text in English; Abstract: Turkish and English, x, 75 leaves, Three component hydroxyapatite-alumina-zirconia composite presents a promising candidate material for bone replacement implants. Two methods were employed to synthesize the composite that is expected to have high bioactivity, high strength and high chemical stability in physiologic environment. Wet mixing and heterogeneous precipitation methods were used for the synthesis. Commercial hydroxyapatite, alum ina and yttria stabilized zirconia were mixed in varying proportions and obtained powders were sintered upto 1300 °C subsequent to dry pressing at 160MPa. An optimum composition of 10-20-70 volume percent zirconia, alumina and hydroxyapatite respectively was found to present the most suitable proportion in terms of sinterability and phase purity. -tricalcium phosphate formation at temperatures higher than 1150 °C was found to be the only source of impurity phase in the material.Heterogeneous precipitation method was applied to synthesize a composite material with a functionally graded structure. The three components were aimed to be coated on one another, zirconia (TZ-3Y) being the core, alumina being the intermediate layer and hydroxyapatite being the outer shell. The bulk composite was expected to have both enhanced mechanical properties and enhanced phase purity due to separation of two reactive phases, hydroxyapatite and zirconia by the alumina layer. The coating was done in two steps using urea as the precipitant, aluminum sulfate as the Al3+ source, calcium nitrate as the Ca2+ source and ammonium phosphate as the P source.Precipitation of aluminum hydroxides on TZ-3Y particulates and precipitation of calcium hydroxides as a nucleation point for hydroxyapatite on cores were facilitated through decomposition of urea above 85 °C in aqueous media. Particle size, distribution and morphology were monitored for alumina coated zirconia samples prepared with varying Al2(SO4)/Zirconia and urea/Al2(SO4) molar ratios. The sample prepared with stoichiometric Al2(SO4)/Zirconia ratio and urea/Al2(SO4) ratio 10 exhibited the most suitable composition and morphology for hydroxyapatite coating. Samples synthesized in the first step were used as cores for hydroxyapatite coating.

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2006, Includes bibliographical references (leaves: 57-59), Text in English; Abstract: Turkish and English, ix, 59 leaves, Anorthite ceramics have a great potential as a substrate material due to their low thermal expansion coefficient and low dielectric constant. For lowering the sintering temperature of anorthite ceramics several routes like employing additives, sol-gel method and the use of mechanochemical methods have been proposed.In this study, anorthite was synthesized by using mechanochemical methods and boron oxide addition. The raw materials used in this study were Sivas kaolin as a source for Al2O3 and SiO2, calcined alumina or Al(OH)3 as a source for Al2O3 and calcite powder as source for CaO. Phase characterizations of synthesized powders were performed by XRD using CuK radiation. Microstructural characterization was performed by SEM. Statistical experimental design techniques (SED) were used in order to determine and analyze the more important process variables for synthesizing anorthite ceramics. The results of screening experimental design clarified that the temperature was the most important process variable. Second most important process variable was grinding speed which was followed by additive amount and additive type. This study showed that both additive type and additive amount were important process variables because these two factors were related to each other.The effect of both additive use and grinding on anorthite synthesis helped decrease the synthesis temperature down to 900 oC.

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2005, Includes bibliographical references (leaves: 78-80), Text in English; Abstract: Turkish and English, xiii, 80 leaves, The hydroxyapatite (HA) whiskers were used as reinforcements in the HA powder/HA whisker (HAp/HAw) composites. The HAw was synthesized with molten salt synthesis method (MSS). NaCl, K2SO4 and NaCl-K2SO4 fluxes and HA powders were used for the synthesis of HA whiskers. The effects of various salt/HA ratios, heat treatment temperatures and time were investigated. In order to enhance the dispersibility and the elimination of the powder agglomerates ultrasonic treatment was applied to the HA-salt powder mixtures before heat treatment. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used for the examination of the whiskers. The synthesized whiskers by using NaCl had a broad particle size range (0.25 to 40 mm in length and 0.2 to 20 mm in diameter) and similar morphologies. They had relatively larger diameters than those suitable for use as reinforcements in the HAp/HAw composites. The use of K2SO4 resulted in the formation of relatively uniform and thinner HA whiskers. The length and diameter of the whiskers varied from 5 to 90 mm and 0.5 to 10 mm, respectively. The whiskers prepared from NaCl-K2SO4 salt mixture were 12 to 110 mm in length and 0.5 to 25 mm in diameter. The HA whiskers, synthesized from NaCl-K2SO4 salt mixture and HA powder at 850°C, were selected as reinforcements for the composites because of their uniform morphology and dimensional properties. For the preparation of HAp/HAw composites, HA powder was ball milled and mixed with HAw in aqueous medium with the application of 2 h ultrasonic treatment. Sintering was carried out at 1200-1350°C range for 2 h. Pure HA powder shrunk more than the composites at all sintering temperatures and attained to 98.5% theoretical density at 1350°C. Although the density increases with sintering temperature, the density increase relative to the green structures decreases with whisker content at each sintering temperature. This may be attributed to the low shrinkage rate due to the presence of whiskers at high temperatures. The HA whiskers could be observed as embedded in the fine HA matrix for both slip cast and dry pressed samples from the SEM images. It was observed that the whiskers generally aligned in one direction except the 50% HAw-50% HAp composites.

Ülkemizde genellikle metalik alüminyum üretiminde ara ürün olarak kullanılan yerli üretim aluminanm seramik endüstrisinde teknik seramik hammaddesi olarak kullanılması son zamanlarda önem kazanmıştır. Bu durum gözönüne alınarak tez çalışmasında yerel tozlarla birlikte ithal tozların farklı kombinasyonlarda karıştırılması sonucu yoğun seramik fayansların elde edilebileceği düşünülmüştür. Yerel alumina tozun teknik seramik olarak kullanılabilmesi için özelliMerinin iyileştirilmesi gerekmektedir. Yerel tozlar iri tanelidir ve yüksek miktarda sodyum oksit (Na2Û) içerir, ayrıca tam olarak kararlı yapıya dönüşmemiştir. Bunun için tozların bünyesindeki üretim esnasmda fiziksel ve kimyasal olarak bağlanmış olan sodanın yapıdan uzaklaştırılması gerekmektedir. Bu çalışmada sıcak yıkama işlemiyle tozların sodyum oksit içeriği uygun seviyelere (

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2004, Includes bibliographical references (leaves: 94), Text in English; Abstract: Turkish and English, xvi, 97 leaves, In this study the preparation and characterization of three-dimensional chitosan-calcium phosphate composite structures and porous hydroxyapatite bodies for biomaterial applications have been studied. The effects of chitosan calcium phosphate amount on density, porosity, microstructure, chemical composition and mechanical properties on the composites and effects of porosifier contents, hydroxyapatite content of the slurry and sintering temperature on density, porosity and microstructure of the porous ceramic samples were investigated. SEM was used for microstructural analysis, XRD and FTIR were used for chemical analysis, Archimedes method was used for investigating physical properties and compression test for investigating mechanical properties. In this study low molecular weight chitosan, -tricalciumphosphate, hydroxyapatite and hydroxyapatite whisker have been used. For composites freeze drying technique and for the porous bodies dry pressing, polymer sponge method and dough method have been used.The densities of the composites prepared by using chitosan as the matrix and hydroxyapatite, hydroxyapatite whisker, and B-tricalciumphosphate as reinforcement increased and the porosities decreased with the increase in the ceramic content. The modulus of elasticity and the yield stress generally increased with the increasing ceramic content except for the chitosan/-tricalciumphosphate composites. The densities and porosities of the composite structures varied in the range of 0.059-0.29 g/cm3 and 96-88% respectively. The elastic moduli of the composites varied in a range of 4.45-10.09 MPa and yield stress varied in a range of 0.14-0.34 Mpa due to the change in the ceramic weight%. Changing the ceramic weight% also had influence on the microstructure. Generally with increasing ceramic content the pore sizes decreased.The pore sizes varied in a range between 100-250, 100-400 and 100-200 for chitosan/hydroxapatite, Chitosan/-TCP/Hydroxyapatite and chitosan/HA whisker composites respectively. FTIR and XRD analysis showed that the composite structures contained original constituents, no new chemical compounds were formed the production process had not affected crystallinity of ceramic phases. The densities of the porous ceramic bodies decreased and the porosities increased with the increasing porosifier content at the porous ceramics prepared by dough method and dry pressing method. The porosity and density values of porous hydroxyapatite samples changed in range of 34-72% and 2.03 to 0.87 g/cm3. Pore sizes of polymeric sponge samples were found to be around 300-400 and dry pressing and dough method samples were found to be 10u.

Thesis (Master)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2004, Includes bibliographical references (leaves: 89-95), Text in English; Abstract: Turkish and English, xiii, 95 leaves, Nanocrystalline materials with grain sizes under 100 nm have been counted as a very promising class of ceramic materials. The decrease in grain size imparts superior structural properties to the ceramic materials like increased fracture toughness, wear resistance and superplastic deformation at high temperatures. So, nanocrystalline ceramics can be used as structural materials in a wide range of uses covering advanced engineering applications such as aircraft and automotive technologies as well as electronics, computation and material sciences. Nanocrystalline alumina has been a popular research subject for the last decade because of the superior structural properties of alumina besides lower cost compared to other nanocrystalline materials like zirconia and titania. The raw materials are generally transitional aluminas or aluminum hydroxides such as boehmite and gibbsite all of which are widely used in industry.The main problem in nanocrystalline alumina production is to cope with agglomeration of fine powders or nano-particles in solutions due to interaction forces. Agglomeration cause nonhomogeneous microstructure with respectively larger pores which are very hard to eliminate during sintering. In this study a nanocrystalline commercial boehmite powder is used as the starting material and a homogeneous microstructure with respectively high density is aimed. Ultrasonic treatment is applied in order to reduce particle size and the stable dispersions of boehmite powder with a solid content of 30wt% was dried by spray drying. The effect of ultrasonic treatment, spray drying and compaction conditions were investigated and compared with bodies compacted from untreated powders. To see the effect of seeding on phase transformation behavior of boehmite, alpha alumina particles produced by combustion synthesis and broken into crystallites by ultrasonic treatment were used with a seed content less than 0.5%. Even that low amount of a-alumina reduced the transformation temperature by 100C but did not improve densification of alumina compacts. The homogeneity of microstructure obtained by ultrasonic treatment and granulation by spray drying yielded the highest relative densities of 65.5 % of the theoretical density. The treatment has also led more uniform microstructures compared to untreated and seeded samples during the a-phase transition which is the most important stage for densification.

Proceedings of the 8th Conference and Exhibition of the European Ceramic Society; Istanbul; Turkey; 29 June 2003 through 3 July 2003, Low temperature synthesis of spinel powder via intense mechanical grinding was performed. A dramatic decrease in the synthesis temperatures of ground powders was achieved. We were able to produce partially crystallized spinel at room temperature via a 110 minute grinding. Characterization of the synthesized powders was performed using SEM, XRD and DTA. Each stage of synthesis was analyzed using these techniques. Mixtures of Mg(OH)2 and Al(OH) 3 were used for synthesis. Temperatures as low as 800°C were able to produce bumps in the XRD patterns of ground powders at the 2θ angles for spinel crystals.

Bu çalışma biomedikal uygulamalarda kullanılması amaçlanan kitosan/kalsiyum fosfat kompozitler ve gözenekli hidroksiapatit yapıların hazırlanması ve karakterizasyonunu içermektedir. Kompozit malzemelerin yoğunluk, gözenek yapısı, mikroyapı, kimyasal kompozisyon ve mekanik özellikleri üzerinde kitosan kalsiyum fosfat miktarının etkisi araştırılmış hazırlanan başlangıç maddelerindeki gözenek yapıcı katkı maddesinin, hidroksiapatit miktarının ve sinterlenme sıcaklığının gözenekli hidroksiapatit yapılara etkileri de incelenmiştir. Elde edilen seramik numunelerin gözenek yapıları ve mikroyapıları SEM görüntüleriyle belirlenmiştir. Kimyasal analizlerde XRD ve FTIR kullanılmıştır. Fiziksel özelliklerin belirlenmesi için Arşimed yöntemine ve mekanik özelliklerin bulgulanması için basma testine başvurulmuştur. Düşük molekül ağırlıklı kitosan, B-trikalsiyumfosfat, hidroksiapatit ve hidroksiapatit visker hammadde olarak kullanılmıştır. Kompozitlerin üretiminde dondurmah kurutma yöntemi ve gözenekli yapıların hazırlanmasnda kuru presleme, polimer süngere emdirme ve hamur metodlan kullanılmıştır. Matris olarak kitosan ve güçlendirici olarak hidroksiapatit, hidroksiapatit visker ve B-trikalsiyumfosfatın kullanılmasıyla oluşturulan kompozit malzemelerin seramik miktarı arttığında yoğunluklarının da arttığı ve gözenekliliklerinin azaldığı gözlenmiştir. Kitosan/B-trikalsiyumfosfat kompozitleri dışındaki numunelerde elastik modül değerleri ve çökme stresi de seramik miktarı arttığında yükselme götermiştir. Tüm kompozit malzemelerin yoğunlukları 0.059-0.29 g/cm3 ve gözeneklilikleri 96-88% aralıklarında değişmiştir. Kompozitlerin elastik modülleri ise seramik ağırlık yüzdesine bağlı olarak değişmiş, 4.45-10.09 MPa aralığında saptanmıştır. Çökme stres değerleri ise yine seramik ağırlık yüzdesine bağlı olarak 0.14-0.34 MPa aralığında değişim göstermiştir. Numunelerin seramik yüzdelerindeki değişim mikroyapıda da değişimlere neden olmuş,genellikle seramik miktarında artışla gözeneklerin daraldığı gözlenmiştir. Kitosan/HA, Kitosan//p-TCP/HA ve Kitosan/HA visker kompozitlerin gözenek boyutları sırasıyla 100-250 u-, 100-400 j, ve 100-200 j, aralıklarında değişmektdir. FTIR ve XRD analiz sonuçları kompozit malzemelerin yapımda kullanılan hammaddelerin orijinal yapılarını koruduğunu ve üretim sürecinin seramiklerin kristalinitesi üzerinde değişime neden olmadığını göstermiştir. VIGözenekleştirici miktarı artırıldığında hamur ve kuru pres metoduyla hazırlanan seramik yapıların yoğunlukları düşmüş, gözeneklilikleri artmıştır. Hazırlanan gözenekli hidroksiapatit numunelerin yoğunlukları 34-72% gözenek değerlerine ulaşacak şekilde 2.03 ve 0.87g/cm yoğunluk aralığında değişmiştir. Süngere emdirme metoduyla hazırlanan örneklerin gözenek boyutları ise 300-400 /ı aralığında gözlenirken kuru pres ve hamur metodlarıyla hazırlanan örneklerin gözenek boyutları 10 jx olarak belirlenmiştir. VII In this study the preparation and characterization of three-dimensional chitosan- calcium phosphate composite structures and porous hydroxyapatite bodies for biomaterial applications have been studied. The effects of chitosan calcium phosphate amount on density, porosity, microstructure, chemical composition and mechanical properties on the composites and effects of porosifier contents, hydroxyapatite content of the slurry and sintering temperature on density, porosity and microstructure of the porous ceramic samples were investigated. SEM was used for microstructural analysis, XRD and FTIR were used for chemical analysis, Archimedes method was used for investigating physical properties and compression test for investigating mechanical properties. In this study low molecular weight chitosan, P-tricalciumphosphate, hydroxyapatite and hydroxyapatite whisker have been used. For composites freeze drying technique and for the porous bodies dry pressing, polymer sponge method and dough method have been used. The densities of the composites prepared by using chitosan as the matrix and hydroxyapatite, hydroxyapatite whisker, and P-tricalciumphosphate as reinforcement increased and the porosities decreased with the increase in the ceramic content. The modulus of elasticity and the yield stress generally increased with the increasing ceramic content except for the chitosan/p-tricalciumphosphate composites. The densities and porosities of the composite structures varied in the range of 0.059-0.29 g/cm and 96-88% respectively. The elastic moduli of the composites varied in a range of 4.45-10.09 MPa and yield stress varied in a range of 0.14-0.34 Mpa due to the change in the ceramic weight%. Changing the ceramic weight% also had influence on the microstructure. Generally with increasing ceramic content the pore sizes decreased. The pore sizes varied in a range between 100-250jj,, 100-400p, and 100-200jx for chitosan/hydroxapatite, Chitosan/p-TCP/Hydroxyapatite and chitosan/HA whisker composites respectively. FTIR and XRD analysis showed that the composite structures contained original constituents, no new chemical compounds were formed the production process had not affected crystallinity of ceramic phases. IVThe densities of the porous ceramic bodies decreased and the porosities increased with the increasing porosifier content at the porous ceramics prepared by dough method and dry pressing method. The porosity and density values of porous hydroxyapatite samples changed in range of 34-72% and 2.03 to 0.87 g/cm. Pore sizes of polymeric sponge samples were found to be around 300-400u and dry pressing and dough method samples were found to be 1 Ou. 113

oz Bu çalışmada hidroksiapatit (HA) tozlarının, viskerlerinin ve HA bazlı seramiklerin hazırlanması incelenmiştir. Ticari HA tozu karşılaştırma amacı ile kullanılmıştır. Tozlar ve sinterlenmiş seramikler optik mikroskop, SEM, XRD, tane buyot analizi, dilatometri ve mekanik testler kullanılarak karakterize edilmiştir. Ca-P tozlan sulu ortamda (NH^HPC^ ve Ca(N03)2. 4H20 kullamlarak çökeltme yöntemiyle sentezlenmiştir. Ca/P oram pH=10 da 60°Cde ve 24 saat yaşlandırma koşullarında 1,5 ve 1,67 ye ayarlanmış ve sırasıyla Ca-P fazlan ve HA tozu elde edilmiştir. Ca/P oram 1,67 ye sabitlenerek ortam pH sının, yaşlanma sıcaklığı ve zamanının toz özelliklerine olan etkisi incelenmiştir. Yaşlanma zamanı ve sıcaklığı sırasıyla 24 saat ve 60 °C de sabit tutularak pH 4,6,8,9,10 and 11 ayarlanmıştır. HA tozlanmn oluşumu pH 8 den sonar gözlenmiştir. pH=4 aglomere olmuş Monetite- Brushite tozu elde edilmiştir. Prizmatik Brushite kristalleri pH=6 da elde edilmiştir. Yaşlanma zamanı incelemeleri 30-90 °C de pH=10 a ve yaşlanma zamanı 24 saate sabitlenerek gerçekleştirilmiştir. Yaşlanma sıcaklığındaki artış ısıl olarak daha kararlı HA fazı oluşumunu sağlamıştır. Çökeltiler pH=10 a ve sıcaklık 60 °C ye sabitlenerek 0, 0.5, 1, 24 ve 48 saat boyunya yaşlandınlmıştır. Isıl olarak kararlı HA fazı 24 saat yaşlandırma sonrasında elde edilmiştir. Fırında kurutulan tüm çökeltiler ısıl kararlılıklarının ve faz yapısındaki gelişmelerin incelenmesi amacıyla 400-1250 °C aralığında ısıl işleme tabi tutulmuşlardır. Isıl olarak kararlı HA tozlanmn çökertilmesi için pH=10, yaşlandırma sıcaklığı ve zamanı 60 °C, 24 saat optimum şartlar olarak belirlenmiş ve bu şartlarda eşboyutlu ve 40-60 nm tane boyutlarında HA tozlan üretilmiştir HA viskerleri hazırlamak için erimiş tuz sentezlemesi (MSS) ve hidrotermal sentezleme (HDT) yöntemleri kullamlmıştır. Her iki viskerinde XRD desenleri göstermiştir ki HA baskın fazdır ve başka fazlar bulunmamıştır. Hidrotermal viskerler mikronaltı çaptadırlar ve ortalama 20 aspect oranına sahiptirler. Çoğunlukla altıgen MSS viskerlerin çaplan 1-5 mikron aralığındadır ve 10-15 aspect oranına sahiptirler. 10, 20 and 30 vol% visker içeren kompozitler hazırlanmıştır. Sinterlenme davramşlan ve mekanik özellikleri incelenmiştir. 98% teorik yoğunluklu HA seramikleri (3.16 g/cm) 1150-1250 C aralığında elde edilmiştir. MSS visker içeren kompozitler için 80-90% teorik yoğunluk 1200°C üzerinde çok az bir küçülme ile vııeldedilmiştir. HDT visker içeren kompozitlerin yoğunlukları MSS içerenlerinkinden daha fazlaydı. En yüksek sertlik değeri 1250°C de sinterlenmiş HA seramiğinden 537 Hv olarak elde edildi. Göreceli yüksek gözeneklilik sebebiyle kompozitlerin sertlikleri saf HA seramiklerinden daha düşük olarak tespit edildi. 10vol% MSS visker eklenmesi doğal kemik dokusununkiyle (170-193 Mpa basma mukavemeti, 14-18 GPa elastik modulus) karşılaştırılabilecek basma mukavemeti (460-470 MPa) ve elastik modulus(14-17 GPa) değerlerini sağlamıştır. vııı ABSTRACT The synthesis of hydroxyapatite (HA) powders, whiskers and preparation of HA based ceramics have been investigated in this work. Commercial HA powders were used for comparion purposes. The powder and sintered ceramics were characterized by optical microscopy, SEM,XRD, particle size determination, dilatometry and mechanical testing. Ca-P powders were synthesized by using (NH^HPCU and Ca(NÛ3)2. 4H2O by a precipitation method in aqueous medium. Ca/P ratio was set to 1,5 and 1,667 that yield the mixture of Ca-P phases and HA powder respectively at pH 10, 60 °C and 24hrs aging. Ca/P ratio was set to 1,667 and the effect of pH of the medium, aging temperature and aging time on the powder characteristics was investigated. pH was set to 4,6,8,9,10 and 1 1 while aging temperature and time kept constant at 60 °C and 24 hrs. Formation of HA powder was observed over pH 8. Agglomerated Monetite-Brushite powder was obtained at pH=4. Monodispersed prismatic Brushite crystals were obtained at pH=6. Aging temperature investigation was performed at 30-90 °C at pH=10 for 24 hrs aging. Increase in the aging temperature led to formation of more thermally stable HA phase. Precipitates were aged for 0, 0.5, 1, 24 and 48 hours at constant pH=10 and temperature 60 °C. Thermally stable HA phase was obtained over 24hrs aging. All of the oven-dried precipitates were heat treated at 400-1250 °C range in order to investigate the thermal stability and phase structure development. Optimum conditions for the precipitation of thermally stable HA powder was determined as pH=10, 60 °C aging temperature and 24 hrs aging time that yields equaxed HA powder with particle size about 40-60 nm. Molten salt synthesis (MSS) and hydrothermal synthesis (HDT) were used to prepare HA whiskers. XRD patterns of both whiskers have shown that HA was the dominant phase in whiskers and no other phases were detected. Hydrothermal whiskers had submicron diameters with an average aspect ratio of 20. The diameter of the MSS whiskers were in the 1-5 micron range and were mostly hexagonal with an average aspect ratio of 10. 10, 20 and 30 vol% whisker containing composites were prepared. Sintering behavior and mechanical properties were investigated. 98% TD of HA ceramics (3.16 g/cm ) was obtained in the 1150-1250 C range. 80-90% TD was obtained at above 1200°C for the MSS whisker composites with very little shinkages. Densities of theHDT whisker containing composites were higher than those of the MS S whisker composites. The highest hardness value was determined as 537 Hv for the HA ceramics 1250°C sintered. Hardness of the composites was lower than that of pure HA powder based ceramics due to the presence of relatively high porosity. 10vol% MS S whisker addition yields comparable compressive strength (460-470 MPa) and elastic modulus values (14-17 GPa) with that of natural bone tissues (170-193 MPa compressive strength, 14-18 GPa elastic modulus). VI 73

oz Bu çalışmada alumina ve silika membranların sol-jel yöntemiyle hazırlanması, karakterizasyonu ve gaz geçirgenliği incelendi. Çeşitli parametrelerin sol parçacık boyutuna ve desteksiz membran gözenek yapısına olan etkileri lazer ışık saçınım parçacık boyut analizi ve azot adzorpsiyon-dezorpsiyon analizi ile incelendi, y-alumina membranlar zirkonya desteklerin böhmit soluna ard arda daldırılmasıyla hazırlandı. Böhmit solunun hazırlanması aşamasında asit içeriğinin artmasıyla sol parçacık boyutunda ve membran gözenek çapında orantılı azalış belirlendi. HfVAl3* mol oranının 0.1'den 0.25 'e çıkması sırasıyla hidrodinamik sol parçacık boyutunun ve BJH gözenek boyutunun 65 'den 30 nm'ye ve 3.6'dan 2.9 nm'ye düşmesine neden oldu. Gözenek boyutu ısıl işlem sıcaklığının 500'den 600 °C'ye çıkarılmasıyla 2.8 'den 3 nm'ye arttı. Desteksiz membranlar faz yapısı karakterizasyonu için 200-1200 °C aralığında ısıl işleme tabi tutuldu. 500 °C'nin altında böhmit, 900°C'ye kadar Y-AI2O3 ve 1200 °C'nin üzerinde 01-AI2O3 hakim faz olarak elde edildi. Kusursuz alumina membranların yaklaşık 3 um (iki katman) kalınlığında olduğu ve önemsiz sayılabilecek miktarda destek içine nüfuz ettiği SEM fotoğraflarıyla belirlendi. 600 °C'de ısıl işleme tabi tutulmuş iki katmanlı Y-AI2O3 membranların CO2 geçirgenliği yaklaşık 2.25*10` mol/m.s.Pa'dır ve az miktarda basınca bağlı olması etkin aktarım mekanizmalarının Knudsen difüzyon ve laminar akış olabileceğini gösterdi. 500 °C'de ısıl işlemin uygulandığı benzer iki katmanlı alumina membranlarda CO2 geçirgenliği basınçtan bağımsız olarak 1.5 1 * 1 0`8 mol/m2.s.Pa' a düşmüştür. Silica membranlar sol-jel tekniği ile hazırlandı. Bu sollar çözücü ortamında tetraetilortosilikatın asit ile katalizlenmiş hidroliz ve yoğunlaşma tepkimeleriyle hazırlandı. Sol hazırlanmasında kullanılan asit çeşidi ve miktarı, sol yaşlandırma, ısıl işlem koşullan ve daldırma zamanı gibi proses parametrelerinin membran gözenek yapısı ve gaz geçirgenliğine etkileri incelendi. Destekli membranlara 50 ile 400 °C aralığında ısıl işlem uygulandı. Sol içerisine 10 saniye daldırılmış tek katmanlı silica membranların N2 ve CO2 geçirgenlikleri sırayla 2.2 * 10`10 - 2.7 * 10`8 mol/m2.s.Pa ve 1.2*10`9-6.95*108 mol/m2.s.Pa aralığındadır. Solların 50 °C'de 16 saat yaşlandırılmasıyla akışkanlığı azaldı ve jelleşti. O2 geçirgenliği yaşlandırma zamanıyla arttı. Proses boyunca optimum daldırma zamanı 10 saniye olarak belirlendi. Bu memranların geçirgenlikleri sol asit içeriğinin artmasıyla önemli oranda arttı. Silikamembranların yaklaşık 2 um kalınlığında olduğu ve önemli sayılabilecek oranda destek içine nüfuz ettiği SEM fotoğraflarından gözlendi. ABSTRACT The preparation, characterization and pure gas permeation of sol-gel derived alumina and silica membranes were investigated in this work. The effects of various parameters on sol particle size and unsupported membranes pore structure were investigated by laser light scattering particle size and N2 adsorption-desorption analysis. y-alumina membranes were prepared on Z1O2 supports by successive dipping into boehmite sols. Almost proportional decreases in sol particle size and membrane pore diameter were determined with increasing acid content during the boehmite sol preparation. Increasing the H+/A13+ mole ratio from 0.1 to 0.25 caused the hydrodynamic 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. Boehmite was the dominant phase below 500 °C, gamma being the dominant phase up to 900 °C and pure 01-AI2O3 phase was obtained upon heat treatment at 1200°C. Pinhole and crack free alumina membranes about 3 urn (double layer) in thickness were observed from SEM pictures with insignificant infiltration. The CO2 permeability through the double layer Y-AI2O3 membrane calcined at 600 °C was about 2.25*10`7 mol/m2.s.Pa, and had a slight pressure dependence which may indicate Knudsen Diffusion and Laminar Flow as the effective transport mechanisms. Upon the calcination of a similar double layer alumina membrane at 500°C, the CO2 permeability decreased to 1.51 *10`8 mol/m2.s.Pa and was independent of pressure. Silica membranes were prepared by a sol-gel technique. These sols were prepared by acid catalysed hydrolysis and condensation of tetraethylorthosilicate in the presence of a solvent. The effects of processing parameters like the acid type and amount utilized during sol preparation, sol aging, heat treatment conditions, dipping time on the membrane pore structure and the permeation of pure gases were investigated. The supported membranes were heat treated in the 50-400 °C range. The N2 and CO2 permeabilities of silica membranes varied in the 2.2 * 10`10 - 2.7 * 10`8 mol / m2.s.Pa and 1.2*10`9 - 6.95* 10`8 mol / m2.s.Pa range for single layer membranes dipped for 10 seconds into the sol. The sols became viscous and gelled in 16 hours at 50 °C. The O2 permeability increased with aging time. The optimum dipping time duringprocessing was determined to be 10 seconds. The permeabilities of these membranes increased significantly with the sol acid content. The thickness of the silica membranes were determined to be about 2(xm and significant infiltration into the support was observed from the SEM pictures. 124

öz Bu çalışmada, polilaktid ve hidroksiapatit kompozit filmlerinin hazırlanması ve karakterizasyonu çalışılmıştır. Bir çok parametrenin; polimer tipi, hidroksisapatit yoku, yüzey modifikasyonu ve konsantrasyonun, mekanik, termal, mikroyapısal ve hidrolitik bozunma özettikleri üzerine etkisi incelenmiştir. Dört farklı tip polimer, Polilaktid (PLAı), 9674 L-Laktid,D-Laköd kopoümeri (PDLAı), Polilaktid (PLAa), ve 67 /23 Poli( L-Laktid- ko-D,L-Laktid ) kopolimeri (PDLA3) kullanılmıştır. Bu çalışmada, polilaktid ve hidroksiapatit kompozit filmleri çözücü yöntemi ite hazırlanmıştır. Hidroksiapatit (HA) tozlan kimyasal çöktürme yöntemi ile sentezlenmiştir. Polilaktid-HA kompozitlerinin mekanik özelliklerini ve dolgu maddesi ile polimer arasındaki yüzeyi geliştirmek amacıyla, HA tozlarının yüzeyi iki farklı silan bağlayıcıyla, üç farklı oranda ; 3-aminopropiltrietoksisilan ( AMPTES) ve metioksisilan (MPTES) kaplanmıştır. Şuan bağlayıcıları ile modifiye edilmiş HA tozlan ile yapılan polilaktid kompozitlerinde işlem görmemiş HA tozlan ile yapılan kompozitlere göre, HA tozlarının polimer matriksdeki dağılımı ve mekanik özelliklerinde gelişme gözlenmiştir. Çekme testi sonuçlarında, mekanik özelliklerindeki maksimum iyileşme, PLA kompozitleri için, kütlece % 1 oranında AMPTES silan ve PDL A kompozitleri için ise kütlece 0.5 % oranında MPTES sılan ile kaplanmış HA tozlarında, elde edilmiştir. Taramalı elektron mikroskopu ile yapılan çaılşmalar silan ile modifiye edilmiş HA tozlarının polimer matriks içinde daha iyi dağıldığını göstermiştir. Kompozitlerin termal bozunma kinetiği incelenmiştir ve polimer matrikse HA ilavesinin hem termal bozunma sıcaklığını düşürdüğü hem de bozunma hızını yavaşlattığı bulunmuştur. Bu çalışmada, Polilaktid (PLAı), 96/4 L-Laktid,D-Laktid kopolimeri (PDLAı) ve onların HA kompozhlerinin (kütlece % 10-50 HA yükü içeren) hidrolitik bozunma özelliği yapay vücut sıvısı ortamında 37 °C de 7.4 pH da statik test yöntemi ile araştırılmıştır. Zaman içerisinde, kompozitlerin su tutma kapasitesi, ağırlık kaybı ve kompozit yüzeyindeki morfolojik değişimlerin göztenebilmesi için taramalı elektron mikroskopunun kullanılması gibi farklı teknikler kullanılarak hidrolitik bozunma özelliği gözlenmiştir. 150 günün sonunda, saf PLAı ve PLA2 filmlerinde sırasıyla kütlece % 12.5 ve 9.5 kütle kaybı kaydedilmiştir. Kopolimerlerin bozunma hızlan homopolimerlerden daha hızlıdır. PDLAı ve PDLA2 için kütle kaybı değerleri oldukçayakın değerlerde, sırasıyla kütlece % 17.5 ve 17 olarak bulunmuştur. Bu zaman İçerinde tüm polimerlerin bulunduğu ortamın pH değeri stabilitesini yaklaşık olarak 7.4 de korumuştur. Bunun nedeni yapay vücut sıvısının tampon çözelti özelliği göstermesidir. Kütlece % 10 HA içeren PLA ve PDLA kompozitlerinde bozunma hızının yavaşladığı ve bu örneklerde su tutma kapasitesinin arttığı görülmüştür. Kütlece % 10 HA içeren PLA kompozitleri için kütle kaybı değeri %12 den % 5'e düşmüş ve su tutma kapasitesi ise %10 dan %13'e yükselmiştir. Bu kompozitlerin yapay vücut sıvısında zamanla mikro yapısal özelliklerindeki değişim incelenmiştir. Polimer kompozit filmlerin yüzeyinin kalsiyum fosfat île kaplandığı bulunmuştur. Bu kaplama, HA yükü ve bozunma zamanın artmasını sağlamıştır. ABSTRACT In the thesis, the preparation and characterization of polylactide- Hydroxyapatite(HA) composite films for biomaterial applications have been studied. The effects of number of parameters such as polymer type, HA loading, surface modification and its concentration on the mechanical, thermal microstructural and hydrolytic degradation properties of the composites were investigated. Four different types of polymers, Poly (L-lactide)(PLAi), 9674 L-lactide,D-Lactide Copolymer (PDLAt), Poly (L-LaetideXPIAa), and 67/23 Poly (L-Lactme-co-D^ LactideXPDLAi}, have been used. In this study, PolyLactide-HA composite films have been prepared by solvent-casting technique. The HA powder was synthesized by precipitation technique. Interracial interactions between HA and polylactide polymer were modified to improve filter compatibility and mechanical properties of the composites by surface treatment of the HA with two different silane coupling agents; 3-amînopropyltriethoxysilane (AMPTES) and 3-mercaptopropyhrimethoxysilane (MPTMS) at three different concentration. Silane treatment indicated better dispersion of HA particles in the polymer matrix and improvements in the mechanical properties of the composites compared to tire untreated HA loaded polylactide composites. Tensile test results showed that the maximum improvement in the mechanical properties of the composites was obtained for the PLA composites containing I 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 Thermal degradation kinetics of the composites was investigated and it was found that addition of HA into polymer matrix decreased the thermal degradation temperature and also slowed down the degradation rate. In this study, the hydrolytic degradation of poly (L-LactideXPLA), poly (L- Lactide-co-D-Lactide) (PDLA) and their hydroxyapatite (HA) loaded composites (10- 50-w/w %) were investigated in simulated body fluid (SBF) at 37 ÖC and at pH 7.4 by in vitro static testing. Using different techniques, namely weighting to quantify water absorption monitored the hydrolytic degradation and weight loss, scanning electron microscopy (SEM) to observe morphological changes occurred at the surface of the films over time. At the end of the ISO days, only 12.5 wt % and 9.5 wt % of weightPLAı and PLA2 were lost respectively. Degradation of the copolymers was faster than PLAi and PLA2 and weight loss data of PDLAi and PDLAi were found to be nearly same with 17.5 wt % and 17 wt %, respectively. The changes of pH on all polymer were stable at 7.4, because of simulated body fluid indicates buffer solution properties. Degradation rate of PLA and PDLA composites containing 10 wt % HA decreased, and also water absorption of these samples increased. Weight loss decreased approximately from 12 wt % to 5 wt % and water absorption increased from 10 wt % to 13 wt % for PLA composites containing 10 wt % HA The change of microstructural properties of obtained composites has been determined in simulated body fluid as a function of time. It was found that the surface of polymer composite films was coated with the calcium phosphate layer. This coating was increased with HA loading and ageing time. 128

Thesis (Master)--Izmir Institute of Technology, Biotechnology, Izmir, 2002, Includes bibliographical references (pages 54-58), Text in English; Abstract: Turkish and English, xi, 58 leaves, Ceramic membranes possess desirable properties for industrial separation and concentration processes where extreme conditions of heat, pH, ionic strength are present. Ceramic composite membranes consisting of a support and a thin membrane layer with finer pores were prepared in this work. Ceramic supports were prepared from fine alumina and zirconia powders by dry-pressing and slipcasting.These supports were sintered in the 1100-1200°C temperature range.These supports were dip-coated with ceramic sols prepared from zirconium propoxide and aluminium isopropoxide for the preparation of thin layers with finer pores. Average particle sizes of these sols were measured as 3-7 nm for zirconia sol and 30-40 nm for alumina sol by laser scattering technique. The dipcoated membranes were calcined in the 500-600°C temperature range. The thermal characterization of membrane layers was determined with DTA/TGA. The microstructure of the ceramic composite membranes was investigated with SEM. The clean water permeability (CWP) of membranes was tested by using deionised water in a filtration set-up. Separation experiments were performed with bovine serum albumin (BSA, Stokes diameter: 7 nm) solution and whey to determine 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-cast zirconia supports heat treated at 1200°C. The protein retention of the slip-cast zirconia support was detected as 60% with UVVIS spectrophotmeter analysis (Abs. at 280nm). After the modification of the support with dip-coating protein retention of 96% was achieved. Then the composite membranes were used in whey protein concentration experiments. Whey, which is a complex biological liquid, containing proteins, carbohydrate, minerals, was fed to the membrane without any clarification process. The retention of whey proteins with dry-pressed alumina support modified with 1/4 diluted zirconia sol (calcination temperature: 500°C) was found to be 96% with a permeate flux of 40 Lm-2hour-1.

öz Bu çalışmada, kullanılmış ve kullanılmamış manyezit-krom (MgO + MgO-Cr2O3) ve manyezit-spinel (MgO + MgO-Al2O3) refrakter tuğlaların mikroyapıları karakterize edilmiştir. Çalışmanın amacı birbirinin yerini tutabilecek farklı ürünlerin mukayesesini yapmak ve refrakter aşınmalarını en aza indirgemek için yapılması gereken çalışmalara ışık tutmaktır. Biribirinden farklı çeşitli fazların mikroyapıdaki dağılım biçimleri nihayi korozyon davranışını belirleyen esas etkendir. Bu fazların özelliklerini tanımlamak amacıyla mikroyapısal analizler uygulanmıştır. Korozif tepkimelerin izlediği yolların anlaşılması amacıyla çimento döner firınında aşınmaya uğramış tuğlalar optik mikroskop, enerji yayınımlı microanaliz sistemine bağlı taramalı electron mikroskobu ve X-ışını kırınımı cihazlarıyla incelenmiştir. Kromit içeren ithal tuğlalarda demirce zengin halkalı yapıda kromit kristalitlerine rastlanırken, yerli tuğlalarda böyle bir özelliğe rastlanamamıştır. Demirce zengin bu halkalı yapılar SEM- EDS yardımıyla incelendiğinde Fe+2 ve Mg+2 çapraz yayınımının bunların oluşumuna sebebiyet verdiği ortaya çıkmıştır. Manyezit-spinel tuğlaların mikroyapılarında bağlayıcı faz olarak yer alan ve düşük erime sıcaklığına sahip olma özelliğiyle servis performansını tehdit eden kalsiyum aluminatlara rastlanmıştır. Klinker eriyiğinin, bir manyezit-krom tuğlası içine nüfuz edebilme derinliği üzerinde zaman (0.5-2.0 saat), sıcaklık (1500-1550°C) ve klinker kimyasının (ağ. %40-60 demir cevheri ilavesi) etkilerini incelemek amacıyla istatistiksel olarak tasarlanan bir dizi deney yürütülmüştür. Bu deneyler göstermektedir ki, ham karışımdaki demir oranının artırılması ve bunun artan ortam sıcaklığıyla etkileşimi aşınmada belirgin rol oynamaktadır. En yüksek sıcaklık ve demir ilavesi değerlerinde aşınma derinliği 1200 mikrona kadar ulaşmaktadır. Çimento döner fırınlarında belirli bir süre hizmet vermiş ve aşınmaya uğramış tuğlaların mikroanalizi göstermektedir ki alkali saldırısı ve sürünme, tuğla için başlıca aşındırma mekanizmalarıdır. EDS incelemelerinde çinko ve vanadium gibi elementlerin kalıntılarına rastlanmasının da atık yakıt ve/veya uzun fırın duruşlarından sonra tavlama için gerekli alevin oluşturulmasını sağlayan sıvı yakıt kullanımından kaynaklandığı düşünülebilir. ABSTRACT Microstructures of unused and used magnesia-chromite (MgO + MgOCr203) and magnesia-spinel (MgO + MgO AI2O3) refractory bricks were characterized. The purpose was to compare different products for evaluation as replacement bricks, and to minimize refractory wear. The way in which the different phases are assembled in the microstructure significantly determines the resulting corrosion behavior. Microstructural analyses were performed to identify these phase composures. Industrially worn bricks were examined by optical reflected light microscope, electron microscope (SEM) coupled with energy dispersive X-Ray microanalysis system (EDS) and X-Ray diffraction (XRD) to understand the corrosive reaction paths. In some of the chromite containing bricks iron-rich rims were observed, while the domestic brick had no such feature. These iron-rich rims were examined using SEM-EDS. It was found that the counter-diffusion of Fe+2 and Mg+2 were responsible for their formation. Magnesia- spinel bricks contain low melting calcium aluminates as bond phases in the microstructure, forming a threat to service performance. A statistically designed set of experiments was conducted to investigate the effects of time (0.5-2.0 hours), temperature (1500-1550°C) and clinker chemistry (40-60 wt.% iron ore addition) on the depth of penetration of clinker melt into a magnesia-chromite brick. These experiments indicated that the addition of iron and its interaction with temperature factor are significant. At the highest temperatures and iron ore addition quantities the corrosion depth reaches up to 1200 um. Postmortem microanalysis of industrially used bricks revealed alkali attack in addition to creep as main destruction mechanisms for brick. Traces of elements like zinc and vanadium were observed and thought to originate from the use of waste derived fuels or fuel oil firing for obtaining the main flame after long kiln shutdowns. IV 91

öz Seramik süzekler, ısı, pH, iyonik kuvvet değerlerinin uç değerlerde bulunduğu sınai ayrıştırma ve yoğunlaştırma işlemleri için gerekli özelliklere sahiptirler. Bu çalışmada, bir destek ve daha ince gözeneklere sahip bir zar tabakasından oluşan seramik karma süzekler hazırlandı. Seramik destekler, ince alumina ve zirkonya tozlardan kuru baskılama ve alçı üzerine kalıba döküm yöntemleri kullanılarak hazırlandı. Bu destekler 1100-1200°C sıcaklık aralığında pişirildi. Pişirilen destekler daha ince gözeneklere sahip ince bir tabaka oluşumunu sağlamak için alüminyum izopropoksit ve zirkonyum propoksitten hazırlanan seramik sollerine daldırılarak kaplandı. Bu sollerin ortalama parçacık boyutları, lazer saçılımı tekniği kullanılarak, zirkonya solü için 3-7 nm ve alumina sol için 30-40 nm olarak ölçüldü. Daldırılıp kaplanan zar süzekler 500- 600°C sıcaklık aralığında ısıl işleme tabi tutuldular. Zar süzek tabakanın ısıl nitelendirilmesi DTA (Diferansiyel Isıl Analiz)/TGA (Isıl Ağırlık Analizi) ile gerçekleştirildi. Seramik karma süzeklerin mikro yapıları SEM (Taramalı Elektron Mikroskobu) ile incelendi. Süzeklerin saf su geçirgenliği (SSG) deiyonize su kullanılarak bir süzme düzeneğinde ölçüldü. Karma süzeklerin protein ayırım kapasitelerini belirlemek için sığır serum albumin (BSA, Stoke çapı = 7 nm) çözeltisi ve peynir altı suyu kullanılarak ayrıştırma denemeleri gerçekleştirildi. Kuru baskılanmış ve 1100°C' de ısıl işleme tabi tutulmuş alumina desteğin saf su geçirgenliği, alçı üzerine kalıba dökülen ve 1200°C de ısıl işleme tabi tutulan zirkonya desteğin geçirgenliğinden daha yüksek olarak ölçülmüştür. Alçı üzerinde kalıplanan zirkonya desteğin protein tutma oram UV-VIS spektrofotometre kullanılarak (280 nm dalgaboyundaki absorbanı) %60 olarak belirlendi. Desteğin daldırılıp kaplanarak değiştirilmesinden sonra %96' lık bir protein tutmaya ulaşıldı. Proteinler, karbonhidrat, mineraller içeren karmaşık bir biyolojik sıvı olan peynir altı suyu süzeğe hiçbir saflaştırma işlemi uygulanmadan beslendi. Kuru baskılanmış ve 1/4 seyreltilmiş zirkonya sol ile kaplanılarak 500°C de ısıl işleme tabii tutulup değişime uğratılmış alumina desteğin peynir altı suyundaki proteinleri %96 oranında tuttuğu bulundu. Abstract Ceramic membranes possess desirable properties for industrial separation and concentration processes where extreme conditions of heat, pH, ionic strength are present. Ceramic composite membranes consisting of a support and a thin membrane layer with finer pores were prepared in this work. Ceramic supports were prepared from fine alumina and zirconia powders by dry-pressing and slip- casting. These supports were sintered in the 1100-1200°C temperature range. These supports were dip-coated with ceramic sols prepared from zirconium propoxide and aluminium isopropoxide for the preparation of thin layers with finer pores. Average particle sizes of these sols were measured as 3-7 nm for zirconia sol and 30-40 nm for alumina sol by laser scattering technique. The dip- coated membranes were calcined in the 500-600°C temperature range. The thermal characterization of membrane layers was determined with DTA/TGA. The microstructure of the ceramic composite membranes was investigated with SEM. The clean water permeability (CWP) of membranes was tested by using deionised water in a filtration set-up. Separation experiments were performed with bovine serum albumin (BSA, Stokes diameter: 7 nm) solution and whey to determine 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-cast zirconia supports heat treated at 1200°C. The protein retention of the slip-cast zirconia support was detected as 60% with UV- VIS spectrophotmeter analysis (Abs. at 280nm). After the modification of the support with dip-coating protein retention of 96% was achieved. Then the composite membranes were used in whey protein concentration experiments. Whey, which is a complex biological liquid, containing proteins, carbohydrate, minerals, was fed to the membrane without any clarification process. The retention of whey proteins with dry-pressed alumina support modified with 1/4 diluted zirconia sol (calcination temperature: 500°C) was found to be 96% with a permeate flux of 40 Lm` hour`. IV 58

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 block copolymers. The influence of water soluble triblock copolymers with molecular weight ranging from 2900 to 12600 g/mole were tested at Φ = 0.125, 1, 10, 20 vol % solid loading alumina suspensions by rheological, turbidity, sedimentation and surface tension measurements. The results indicate that an alternative dispersant for alumina suspensions is the PEO/PPO triblock copolymers. Their stabilisation mechanism was attributed to the depletion stabilisation. Rheological measurements indicated that these block copolymers (at high EO percentages) coupled with ultrasonic treatment have a positive effect on the dispersion of the agglomerated alumina suspensions. It was not possible to create stable dispersions in the absence of ultrasonic bath treatment. Turbidity measurements at Φ = 0.025, 0.125 vol % showed that, alumina suspensions with PEO/PPO added were stable and have higher turbidity values than block copolymer free suspensions.