Master Degree / Yüksek Lisans Tezleri

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End date: 1999Subject: search.filters.subject.Ceramic materials

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  • Master Thesis
    Preparation and Characterization of Whisker and Particulate Sic-Ai2 O3 Ceramic Composites
    (Izmir Institute of Technology, 1999) Ünver, Özlem Ebru; Çiftçioğlu, Muhsin
    This 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
    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.