Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Institution Author: search.filters.institutionAuthor.Çağlar, Özlem

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  • Master Thesis
    The Preparation Characterization and Sintering of Nanocrystalline Ceramics
    (01. Izmir Institute of Technology, 1999) Çağlar, Özlem; Çiftçioğlu, Muhsin
    Nanocrystalline Titania was prepared by a chemical synthesis technique commonly known as sol-gel method. In the sol gel method, Titanium (IV) Isopropoxide was mixed with Isopropanol and Nitric Acid solution in predetermined ratios. A rapid hydrolysis reaction occurs between Titanium (IV) Isopropoxide and water in the Nitric Acid solution resulting in the formation of Titan oxide (Titania). The sols were clear sols and then gelled without any change in its clarity.Nanocrystalline Titania were tried to prepare by two different techniques in this work. The first technique involved the drying of the gel and subsequent sintering of the dried gel. A number of organic additives (oxalic acid, acetic acid, polyacrylic acid and stearic acid) were mixed into the sol before gelation in order to control drying (drying control chemical addives-DCCAs). Powders was prepared from sols and gels by several processes and a solid form was obtained by dry pressing and subsequently sintered in second technique. Oxalic acid was the most efficient DCCA among the others.The dried gels and powder compacts were sintered at 650, 700, 750, 800, and 850C. The sintering behaviors of them were examined. Relative densities of the dried gels were between 79-99% depending on the sintering temperature. The green body density of the pellets were varied between 41-52%. Their relative densities after sintering were varied between 55-83% depending on the sintering temperature. The pellets were pressed at different pressures to observe the pressure effect on the densification. Increase in pressure improve the densification behavior. The best route for the nanocrystalline powder preparation was the Route 4. This powder had smaller size of agglomerate most probably the agglomerates were broken during the ultrasonic radiation.The pore size analyses showed the pore structure of the gel. The pore size of the gels are about 35 nm. FTIR Spectra gave the crystal structure of the sols gels and powders. As a result, the sintering behavior of the dried gels is better than the powder compacts. The pellets can be densified to higher densities by appropriate forming technique. Although, the dried gels have significantly high densities, the shape and the weight of the gels can not be controlled.
  • Master Thesis
    Structural Investigation and Wettability of Pvd Tin Caoted Cocrmo Orthopedic Alloy
    (01. Izmir Institute of Technology, 2007) Çağlar, Özlem; Öztürk, Orhan
    Wettability, defined as the ability of any solid surface to be wetted when in contact with a liquid, is one of the most important properties of biomaterials since highly wettable surfaces are expected to disclose better adhesion of the cells.The wettability characteristics of a biomaterial.s surface can be improved by surface modification techniques.In this study, wettability characteristics of TiN coated CoCrMo orthopedic alloy materials were investigated. CoCrMo alloys were coated with TiN using physical vapor deposition (PVD) technique at 550 C for 6 h. The TiN coated layer microstructure,roughness, thickness, and composition were studied by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscope (SEM). Wetting studies involved contact angle and surface tension measurements using distilled water and simulated body fluid (SBF) as test liquids. The contact angles of the coated and uncoated CoCrMo alloys were investigated by the sessile drop method and the surface tension of the test liquids was measured by the ring method. The XRD results show the PVD coated TiN films had (111) preferred orientation, while the SEM analysis indicated quite uniform TiN coated layers (about 3 m thick) with a columnar growth mode. The AFM results indicated much higher roughness values for the TiN coated surfaces compared to the uncoated ones. The experimental results show the contact angle values for the TiN coated samples is lower than the uncoated ones suggesting better wetting for the coated layer. Based on the contact angle and the surface tension values, the work of adhesion values were estimated and it was found that the TiN coated layers has better adhesion ability compared to the uncoated CoCrMo alloy. The lower contact angles for the TiN coated samples were attributed mainly to the rougher surfaces associated with the TiN coated surfaces in comparison with the relatively smooth surface of the uncoated samples. Also, based on the EDX analysis results, the surface oxygen content on the coated surface may be another factor contributing to the better wettability characteristics of the TiN coated CoCrMo alloy compared to the uncoated alloy.