Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Rheological Behavior of Nanocrystalline / Submicron Ceramic Powder Dispersions(Izmir Institute of Technology, 2009) Çağlar Duvarcı, Özlem; Çiftçioğlu, MuhsinSeveral 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.Doctoral Thesis Gas Permeation Through Sol-Gel Derived Alumina and Silica Based Membranes(Izmir Institute of Technology, 2009) Topuz, Berna; Çiftçioğlu, MuhsinThe 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.Doctoral Thesis Preparation of Hydroxyapatite/Silk Protein Thin Film Implant Surfaces, Investigation of Their Microstructural Properties and Model Protein Interactions(Izmir Institute of Technology, 2009) Özcan, Selçuk; Çiftçioğlu, MuhsinBiocompatible hydroxyapatite (HAp) coatings of load bearing metallic in vivo hard tissue implants act as local scaffolds for enhanced osteoconduction, providing fast bone apposition and cementless fixation. In this study, in an attempt to exploit the potential of hydroxyapatite as a carrier of bone morphogenetic proteins for post operative accelerated healing, and implant durability, the tailored microstructural properties, and protein adsorption capabilities of thin film hydroxyapatite implant surfaces were investigated.A novel particulate sol method was used to fabricate HAp thin films on bioinert glass, and Ti6Al4V substrates by dip and spin coating. The microstructural characterization of the thin films was carried out by SEM/EDX, AFM, XRD, and FTIR, and their surface roughness, Vickers hardness and adhesion strength were determined. The effects of silk fibroin and sericin thin film layers on the HAp film microstructure, and model protein (bovine serum albumin, BSA) adsorption behavior (by the size exclusion HPLC method) were investigated. The minimum threshold solid content of the suspensions was determined as 15% by weight for a continuous HAp film structure. The silk sericin and fibroin intermediate layers drastically improved homogeneity of the HAp layer. The BSA adsorption of the glass/sericin/commercial-HAp film was 2.6 ug/cm2, more than twice of the glass/commercial-HAp, and glass/sericin/dry-milled-HAp films, evidencing the effectiveness of surface micro/nano topographical structure as well as chemical structure. The XRD patterns of spin coated commercial-HAp films on Ti6Al4V pointed out to a particular crystal orientation which increased the positive degree of cooperativity between HAp and proteins during adsorption or deposition.Doctoral Thesis Investigation of Effects of Microstructural and Surface Properties of Ultrafiltration/ Nanofiltration Ceramic Membranes on Their Performance(Izmir Institute of Technology, 2009) Erdem, İlker; Çiftçioğlu, MuhsinThe 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.