Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
Browse
11 results
Search Results
Doctoral Thesis Effect of Colloidal Interactions in the Forming of Lead Magnesium Niobate Ceramics(Izmir Institute of Technology, 2007) Deliormanlı, Aylin Müyesser; Polat, MehmetElectrokinetic properties of lead magnesium niobate (PMN) powders in liquid medium are investigated in this thesis. Isoelectric point of aqueous PMN suspensions was determined as a function of solids concentration. Dissolution character of both Pb+2 and Mg+2 cations in PMN structure were examined as a function of pH. Poly(acrylic acid)-poly(ethylene) oxide PAA/PEO comb polymers were tested as the novel dispersant in this system and their effect on the stability and flow behavior of aqueous PMN suspensions was investigated. Stability and flow behavior were mainly studied by rheological measurements and sedimentation experiments as a function of pH and polyelectrolyte concentration. Adsorption of comb polymers onto PMN surface and their effect on the powder dissolution were also investigated. Results indicated that the PAA/PEO comb polymers impart stability to PMN suspensions over a wide pH range and ionic strength where pure PAA fails. In the course of this study PMN powders were consolidated using two different wet shaping methods. First, PMN films were produced using aqueous tape casting method which is widely used in the manufacture of multilayer ceramic capacitors. Secondly, three-dimensional PMN lattices were produced using robocasting method. In the former case, the goal was to provide alternative recipes for the aqueous tape casting process to be utilized in industrial applications since the current technology is based on the organic solvent based techniques. Results showed that it was possible to produce high quality PMN films with thicknesses in the range of 10 to 250 .m using aqueous based tape casting process. In the latter case, the results showed that robocasting is a suitable technique for the preparation of three dimensional PMN ceramics. Based on these results overall conclusion and the contribution of this study can be summarized as follows: The work carried out gives new insights into the manufacturing of PMN based ceramics using aqueous based techniques. Such improvements may bring benefits in the manufacturing of smaller electronic components employed in the personal computers and mobile phones and other consumer products in the near future.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 Enhancement of Thermal, Electrical and Optical Properties of Zinc Oxide Filled Polymer Matrix Nano Composites(Izmir Institute of Technology, 2009) Özmıhçı, Filiz; Balköse, DevrimThe purpose of this study is to enhance the electrical, thermal and optical properties of polyethylene and polypropylene by the addition of zinc oxide (ZnO) filler.Embedding ZnO in a polymeric matrix could make an economic, weight saving, chemically resistive, optical, flexible and conductive materials which possesses the properties of zinc oxide.Composites with higher electrical and thermal conductivity having luminescence properties were prepared using commercial and hydrothermally synthesized ZnO powders with different particle size and conductivity. Effect of ZnO loading and surface treatment on composite properties was investigated. Luminescence effects in green and blue regions were detected in all powders due to the defects on the structure of ZnO.The powders were found to be moderately conductive materials, as well. Un-homogenously dispersed composites were prepared using rheomixer since especially nano powders tended to be agglomerated in the composite. On the other hand, different surface properties of powder and polymer caused adhesion and wetting problems. Microvoids were detected in the interphase, as well.Composites can be used as an electrostatic dissipation and moderate electrical conductive applications in the field of electrical conductivity, as a heat sink in the field of thermal conductivity and as a solid state lamp due to luminescence properties. Stiffness of the composites was very high compared to neat polymer and can be properly used as an engineering material.Doctoral Thesis Nanosized zing borate production(Izmir Institute of Technology, 2009) Gönen, Mehmet; Balköse, DevrimThe present study covers both zinc borate synthesis from boric acid-zinc oxide and borax decahydrate-zinc nitrate hexahydrate pairs; treatment of those samples by supercritical carbon dioxide drying, supercritical ethanol drying, and freeze drying techniques to obtain nanosized products. Zinc borate samples before and after supercritical drying were characterized by analytical titration, SEM, XRD, TGA, DSC, FTIR, and N2 adsorption at 77 K.The use of oleic acid as a modifying agent, ultrasonic treatment and nanosized zinc oxide in the reaction of zinc oxide and boric acid did not make significant effect in controlling the particle size. However, particle size of zinc borate produced from borax and zinc nitrate has increased with reaction time. Interaction of zinc borates with CO2 or ethanol at supercritical conditions or compression of crystals by high pressure created by the expansion of water during freezing are possible side effects of the nanoparticle producing processes. Zinc borate (2ZnO.3B2O3.7H2O) having water of crystallization in its structure reacted partially with CO2 to produce zinc carbonate, however zinc borate (2ZnO.3B2O3.3H2O) containing only hydroxyl groups did not react with CO2 in supercritical CO2 drying. While zinc borate (2ZnO.3B2O3.3H2O) decomposed partially and formed anhydrous zinc borate and zinc oxide, zinc borate (ZnO.B2O3.2H2O) decomposed completely and formed only zinc oxide in the supercritical ethanol drying that was carried out at 6.5 MPa and 250aC. Boric acid formed from the decomposition of both zinc borates was separated by ethanol extraction. If the initial particle size of zinc borate sample was at nano level, it would be possible to obtain nano particles by freeze drying.Doctoral Thesis The Effect of Microwaves on Ion Exchange in Zeolites(Izmir Institute of Technology, 2009) Akdeniz, Yelda; Ülkü, SemraRecent innovations of microwave field lead many scientists to focus on this phenomenon and it has been begun to be applied in different fields of zeolite applications. The purpose of this study is to determine the effect of microwave irradiation on ion exchange degree and on the structure of natural zeolite. The clinoptilolite rich mineral from Western Anatolia was used throughout the experiments. The ion exchange experiments were performed using AgNO3, Co.(NO3)26H2O and Cu (NO3)25/2H2O within 0.01M - 1M and 40 oC - 80 oC concentration and temperature range in conventional waterbath and microwave. Different solid and solution conditions on ion exchange degree were determined, as well. Metal exchanged minerals were characterized by using instrumental techniques. Antibacterial activity of the Agexchanged clinoptilolite against E. coli was determined by Kirby.Bauer method. The Ag +, Co2+ and Cu2+ amounts within the mineral increased with decreasing S/L while increased with increasing temperature and time. For some utilized parameters microwave treatment was effective however on the whole it did not significantly improved the degree of ion exchange compared to waterbath treatment. The inspection of XRD patterns and FTIR spectra of metal exchanged minerals confirmed that no transition of clinoptilolite phase and no shifts in peak positions occurred with exchange methods applied. The sorption processes are controlled mainly by external-phase mass transfer. Ag+, Co2+ and Cu2+ sorptions on NaCLI exhibited a good fit to Freundlich model and Langmuir models. All metal exchanged minerals showed considerable superiority against E.Coli.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 An Experimental and Theoretical Study on the Improvement of Adsorption Heat Pump Performance(Izmir Institute of Technology, 2008) Demir, Hasan; Ülkü, SemraAdsorption heat pumps, which have considerably sparked attentions in recent years, have the advantage of being environmentally friendly and operating with heat sources such as waste heat, solar and geothermal energies as well as storing the energy.The present investigation covers working principle of adsorption heat pumps, a detailed literature survey on the performed studies, information about adsorption phenomena, experimental results of two differently designed and constructed systems, numerical simulation of heat and mass transfer in an annular adsorbent bed, and microcalorimetric study for obtaining isosteric heat of adsorption for water vapor-silica gel pair. The two intermittent adsorption heat pumps can operate without any leakage. The silica gelwater was employed as the adsorbent-adsorbate pair in both of the systems. The temperature and pressure in the evaporator, condenser and adsorbent bed were measured and the coefficients of performance, total entropy generation, the second law efficiency, specific heating and cooling power values were calculated based on these measured values for all of the representative cycles. The heat transfer area of the second designed adsorption heat pump is 550% greater than the first designed adsorption heat pump and this increase resulted in 170% and 200% of improvements in specific heating power (SHP) and specific cooling power (SCP) values respectively. The silica gel granules were mixed with small size metal pieces in order to accelerate heat transfer in the bed. Experiments were performed to measure the thermal diffusivity through the adsorbent bed in which adsorbent is mixed with metal pieces. It was observed that the mixing of silica gel grains with 10wt% of small size aluminum pieces increases the SHP and SCP values of the second heat pump by 250%.Doctoral Thesis Integrated Approach To Whey Utilization Through Natural Zeolite Adsorption/ Desorption and Fermentation(Izmir Institute of Technology, 2009) Polat, Zelal; Ülkü, SemraIn this thesis, the usage of clinoptilolite rich natural zeolites in the recovery of whey proteins by adsorption/desorption, and in the bioconversion of whey, lactose source, to lactic acid were investigated. The possibility for the utilization of natural zeolite deposits of Turkey; and whey, by-product of cheese manufacturing, in the production of high value added chemicals is important from both economical and environmental concerns. Natural zeolites with a particle size range of 75-150 .m were prepared and characterized. Aqueous protein solution, whey powder solution and whey were treated with the natural zeolites and dealuminated zeolites. Batch adsorption studies were performed and uptake data were collected. Equilibrium adsorption isotherms were analysed by Langmuir and Freundlich isotherms. Langmuir isotherm fits the experimental data better. Furthermore, experiments were conducted to see the effects of temperature, initial adsorbate concentration, solid/liquid ratio, agitation speed, pH, particle size and dealumination in adsorption process. The adsorption mechanism was analysed with adsorption kinetics models; and considering the effects of particle size, agitation speed and temperature external film diffusion, surface diffusion and surface reaction were found as effective. The effects of the natural zeolite on the pH, elemental composition and the adsorption tendency of the lactose-lactic acid in the fermentation media were also investigated; and the results were compared with the sythetic ones. Natural zeolites were found as an alternative inexpensive mineral source for the fermentation.Doctoral Thesis Nitrogen Monoxide Storage and Release Properties of Local Natural Zeolite for Biological Applications(Izmir Institute of Technology, 2009) Narin, Güler; Ülkü, Semra; Ülkü, SemraIn this thesis, nitrogen monoxide (nitric oxide, NO) adsorption, storage and release properties of the local clinoptilolite-rich natural zeolite and its modified forms were investigated. The zeolite particles (75-150 .m, 150-250 .m) were prepared through treatment of the natural zeolite with NaCl and consecutively with aqueous metal (Co2+, Ag+, Cu2+, Fe3+) salt solutions under different conditions. The prepared zeolites were characterized in terms of particle size and morphology, density, mineral and elemental composition, dehydration behavior, porosity, surface area, and infrared spectroscopic characteristics. The total adsorption capacities of the zeolites for NO were calculated from the breakthrough curves obtained at 30 oC on a dynamic adsorption system and found to be in the range of 5.5-8.5 mmol/g. NO was adsorbed in the zeolites reversibly and irreversibly. The total adsorption capacity was mainly contributed from the irreversible adsorption. The irreversible adsorption capacity was related to the type and amount of metal cation in the zeolite. The temperature-programmed desorption (TPD) profiles provided information about the desorption kinetics of the NO species formed on the zeolite surface upon the adsorption. The bands detected in the DRIFTS spectra upon admission of NO were assigned to reversibly and irreversibly adsorbed NO species. The unmodified and iron-sorbed zeolites gained antibacterial activity against E. coli after NO loading. The unmodified zeolite also exhibited antibacterial activity against B. subtilis after NO loading. The NO-loaded unmodified zeolite also exhibited complete bactericidal activity upon contact with both bacteria cells. The unmodified and copper-sorbed zeolites exhibited similar NO release kinetics.