Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Production and Characterization of Ceramic Components Via Current Sintering Techniques(01. Izmir Institute of Technology, 2023) Karacasulu, Levent; Ahmetoğlu, Çekdar Vakıf; Adem, UmutThis dissertation aims to utilize contemporary advanced sintering techniques such as cold sintering, reactive hydrothermal liquid phase densification, fast firing, flash sintering, and ultrafast high-temperature sintering for sintering of various ceramic materials. The ceramics produced through these methods are compared with their traditional counterparts in terms of processing-structure-property relationships. In the first section, a brief overview of the advanced sintering techniques used is provided. Chapters 2-7 give a review study on low-temperature densification techniques, and the studies conducted using the cold sintering process and reactive hydrothermal liquid phase densification process, namely cold sintering techniques, which allow densification below 400 °C. Chapters 8&9 presents research related to ceramic materials produced via the fast-firing technique with rapid heating rates compared to conventional sintering, widely employed in the industry. Chapters 10-12 cover sintering studies conducted utilizing joule heating based sintering techniques allowing very fast heating rates such as flash sintering and ultrafast high-temperature sintering. Chapter 13 presents a comparison of current sintering techniques used in terms of applicability, equipment, materials, and so on. The pros and cons of such techniques were explained. In conclusion, there may be no guarantee that every ceramic material will yield successful results in all sintering processes. It is essential to recognize that each sintering process occurs within distinct sintering mechanisms. The selection of the appropriate advanced sintering method and conditions should be based on an assessment of the specific material's characteristics and the desired properties in the final product.Doctoral Thesis Production and Characterization of Porous Ceramics for High Temperature Applications(Izmir Institute of Technology, 2022) Semerci, Tuğçe; Ahmetoğlu, Çekdar Vakıf; Akdoğan, YaşarThis thesis focuses on the production and characterization of different porous polymer derived ceramic (PDC) components (foams, additively manufactured (AM) honeycombs, and aerogels) and demonstrates their potential for high temperature applications, including gas permeability (up to ~700 o C), molten metal filtration, and heat exchanger. The foams were produced via the replica technique and different pore sizes, ranging from 300 μm to 2 mm, silicon oxycarbide (SiOC) ceramic foams were able to be formed. The average total porosity of the foams was 96 vol% with a specific surface area (SSA) of ~80 m2 /g. AM-made honeycomb-like cellular structures with different cell sizes (578 μm, 1040 μm) were obtained via fused filament fabrication. Finally, SiOC aerogels were synthesized using siloxane resin, then dried at ambient pressure and room temperature. The produced SiOC aerogels showed a total porosity of around 80 vol% and an SSA reaching 250 m2 /g. Regarding the high temperature applications of porous PDC components, initially, the gas permeability of SiOC foams was tested, and the results showed stability up to 700 °C in the air without any loss of functionality, offering reusability even in aggressive environments. In the subsequent studies, filtration of molten aluminum alloy was tested using various porous components. PDC foams demonstrated better performance in comparison to the AM-made cellular structures and commercial SiC foams. Finally, heat exchange analysis was performed to evaluate the heat transfer of SiOC foams, and an increase in pressure drop was found to be directly proportional to the rate of increase in air velocity.Doctoral Thesis Processing Foam-Like Porous Glass Structure Using a Combined Process of Glass Powder Expansion in Aqueous Environment and Sintering Process(Izmir Institute of Technology, 2019) Zeren, Doğuş; Güden, Mustafa; Akdoğan, YaşarSoda-lime glass foams were formed by the controlled pore structure of inorganic particle-liquid suspensions at room temperature and then sintered at elevated temperatures between 650oC-800 oC. The slurries were prepared using the glass particles below 38 µm (fine), between 38 and 45 µm (medium) and between 45 and 56 µm (coarse) and with 50, 55, and 60 wt% solid content and 2, 3, and 4 wt% carboxymethyl cellulose (CMC) binder addition. The slurries were foamed using an Al-based foaming agent and a calcium hydroxide alkali activator with an amount of 1 wt%. An increase in CMC content and a decrease in particle size shifted the slurries from a Newtonian to a non-Newtonian behavior and slurry stabilization with the CMC addition. The extensively increased initial bubble pressure in high viscosity slurries resulted in higher linear expansion rate initially followed by a bursting of gas bubbles. The maximum foam linear expansion of the slurries increased with CMC addition until about ~5 Pa s and the expansions stayed almost constant over 400% expansion, while the slurries with the viscosity above 50 Pa s could not be foamed. The most effective factor on the maximum expansion was found the solid content followed by CMC content and the least effective factor was determined the particle size. Partial bonding of glass particles and excessive shrinkage of glass particles due to the melting of foam green bodies were seen at 650 and 800 oC sintering temperatures. Prepared foam glasses showed lower compressive strengths and thermal conductivities than the glass foams reported in the literature. Finally, foaming at room temperature with this technique was found to be more advantageous than conventional glass foam production techniques due to ease of pore formation controlling at room temperature.