Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Formation of Srtio3[tio2] Ceramic Composites at Low Temperatures(01. Izmir Institute of Technology, 2021) Karataş, Esin; Adem, Umut; Ahmetoğlu, Çekdar VakıfStrontium titanate ceramics are materials belonging to the perovskite material group with the formula ABO3. Strontium titanate ceramics have been a preferred material in many areas, such as the electroceramics industry, due to its high dielectric constant and high chemical stability and generally produced by manufacturing processes such as solid-state synthesis, hydrothermal method, and sol-gel. SrTiO3 ceramics have been produced in the literature with different temperatures, times, and starting materials. For ceramic products, a sintering step is required after the powder production step. Traditional sintering methods, which have been used for many years, are used to densify powders with high temperatures. Recently developed low-temperature densification methods enable the sintering process to be carried out at relatively lower temperatures. For this purpose, in this thesis, SrTiO3-TiO2 ceramic composites were produced at different reaction temperatures and times using the rHLPD method, which combines powder production and sintering steps in a single process. In the studies, the reaction temperature, time, and the effect of adding mineralizer to the prepared solution for the hydrothermal reaction on the final product were investigated. The aim of the thesis is to produce SrTiO3 from TiO2 green body using the rHLPD method. In addition, the production of SrTiO3-TiO2 ceramic composites with as high mole conversion and relative density values as possible was targeted with different parameters such as reaction temperature, reaction time, and addition of NaOH to the solution. As a result of the studies carried out with different parameters, SrTiO3-TiO2 ceramic composites with a final relative density value of approximately 81 % were produced. Consequently, in the XRD and Rietveld analysis, it was seen that the main phase was SrTiO3. In addition, there was a TiO2 phase in the structure. Finally, the SrCO3 phase was not detected in the structure.Master Thesis Preparation and Characterization of Whisker and Particulate Sic-Ai2 O3 Ceramic Composites(Izmir Institute of Technology, 1999) Ünver, Özlem Ebru; Çiftçioğlu, MuhsinThis work involves the preparation and the characterization of SiC particulate-Alz03 and SiC whisker- Alz03 ceramic composites. A new technique was used in order to increase the density of composite. Fine Alz03 and SiC whiskers and particulates were used as a matrix and secondary phase, respectively. Whiskers and particulate were coated with Al-S04-OH precursor by precipitation using urea. In this method, it was important to keep the alumina hydrate in the noncrystalline state at 5.5>pH>8.6. The alumina- hydrate compound was separated from SiC whiskers and particulates when the reaction was continued at high pH (pH>8.7) causing the crystallization of alumina precursor. Alumina hydrate coated SiC whiskers and particulate were used as the starting material for the preparation of SiCw/p reinforced Alz03. Die pressing was used as the most appropriate and cheapest consolidation technique of composite materials. Upon sintering Al-S04OH on the SiC transformed into Alz03 by providing empty spaces for matrix densification in the proposed technique ( shrink- fit idea). Green bodies with SiC whisker and particulate contents in the range of 10 to 40 vol.% were sintered at 14500C for 2h under atmospheric conditions. The densities of sintered composites were measured by using Archimedes method. The density of composites containing 10%, 20%, 30% and 40 vol.% coated SiC particulate and whisker composites changed from 81% to 70% of theoretical density and from 79% to 75% of theoretical density, respectively. The density of coated composites were -22% greater than that of the uncoated composites .The thermal behavior of Al-S04-OH on the SiC was characterized by using TGA, DTA. TGA curves showed that materials are hydrated and dehydroxylization was observed between -700 and 800°C. TGA and DTA curves indicated that desulfurization then occurred at about -950°C. Chemical characterization of the coated SiC whiskers and particulates were obtained by using FTIR spectrometer.The hardness of these composites were measured by usmg Vickers Microhardness Testing Device. Vickers microhardness of the 20vol.% and 30vol.% coated SiCp ,and 20vol.% and 40 vol.% SiCw-Alz03 composites were measured as 10.71, 12.94, 10.89 and 5,96 GPa, respectively and compared with the mechanical properties of the composites manufactured by the conventional methods.Master Thesis Preparation of Ultrafiltration/ Microfiltration Ceramic Composite Membranes for Biotechnology Applications(Izmir Institute of Technology, 2002) Erdem, İlker; Çiftçioğlu, MuhsinCeramic 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.Master Thesis Development of Si-O Based Ceramic Matrix Composites Produced Via Pyrolysis of a Polysiloxane(Izmir Institute of Technology, 2004) Akkaş, Hatice Deniz; Tanoğlu, MetinThe traditional ceramic processing techniques of CMCs such as hot pressing are high-temperature, high-cost processes, and unsuitable for manufacturing complex and near-net shapes. Fabrication of ceramic matrix composites (CMCs) from pyrolytic conversion of preceramic polymers has gained considerable attention in recent years due to their unique combination of low temperature processing, applicability of versatile plastic shaping technologies and microstructural control capabilities.In the present work, phenyl (PPS) and methyl (PMS) containing polysiloxanes were pyrolyzed at elevated temperatures (900-1500oC) without filler addition under argon atmosphere to investigate the thermal conversions and phase formations in thepolymer matrix. X-Ray diffraction (XRD) and Infrared spectroscopy (FTIR) techniques were used for this purpose. It was found that pyrolysis of the polymers under inert atmosphere up to 1300oC lead to amorphous silicon oxycarbide (SiOxCy) ceramics.Conversions at higher temperatures caused the transformation into the crystalline b-SiC phases. % Weight changes of the samples without filler addition were also followed by measuring the masses before and after pyrolyzation of the samples.CMC monoliths were fabricated with the addition of 60-80 wt% active and inert fillers by hot pressing under 15 MPa pressure and pyrolysis at elevated temperatures between 900-1500 C under inert argon and reactive nitrogen atmosphere. Effects of the filler type and ratio, pyrolysis temperature and atmosphere on the phase formations were investigated by using XRD, SEM-EDX and TGA techniques. The results showed that with the incorporation of active Ti fillers, formation of TiC, TiSi, and TiO within the amorphous matrix occurred due to the reactions between the Ti and the polymer decomposition products. However, no new phase development was observed in the case of inert SiC particulate addition. SEM-EDX analysis was also performed to monitor the new phase formations. Mass loss and densification values of the CMCs were measured to investigate the effect of active filler controlled polymer pyrolysis process (AFCOP).Weight changes were considerably affected in the case of addition of the fillers into the ceramic structure due to the reduction of the polymer ratio in the composite systems and the reactions between polymer and filler particles. As an example weight loss of 27 % was measured for PPS samples without filler addition, while 17 % weight reduction was measured for PMS without filler addition after pyrolysis at 1500oC. On the other hand, it was found that for the composite systems the weight loss values were reduced to 2 %.Mechanical property characterization of samples with and without filler addition was done by Vickers Indentation tests. It was found that ceramics that is the product of the pyrolysis of the polymer without filler addition exhibited the maximum hardness values (8.88 GPa for neat PPS, 10.67 GPa for neat PMS) at 1100 C, which is the optimum temperature for crack free samples with the least amount of porosity. Also, the composite system exhibited the hardness values up to 14 GPa.Master Thesis Synthesis and Characterization of Hydroxyapatite-Alumina Biocomposites(Izmir Institute of Technology, 2006) Şahin, Erdem; Çiftçioğlu, MuhsinThree 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.