Phd Degree / Doktora
Permanent URI for this collectionhttps://hdl.handle.net/11147/2869
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Doctoral Thesis Production and Applications of Si-Based Aerogels(01. Izmir Institute of Technology, 2025) Erdemir, Öykü İçin; Ahmetoğlu, Çekdar VakıfBu tez, Si-bazlı polimerik ve seramik aerojellerin ve kompozit yapılarının polimer türevli seramik (polymer derived ceramic, PDC) yaklaşımıyla üretimini ve uygulamalarını araştırmaktadır. Polimerik, hibrit ve seramik yapıdaki saf aerojeller ve köpük-aerojel kompozitleri, işleme-yapı-özellik ilişkileri açısından derinlemesine analiz edilmiştir. İlk bölüm aerojeller, PDC'ler, motivasyon ve hedeflere genel bir bakış sunmaktadır. 2. Bölüm, ortam basıncında kurutma (ambijeller) ve CO2 süperkritik kurutma yoluyla kolayca temin edilebilen bir polisiloksan polimeri kullanılarak üretilen SiOC ambi/aerojellerinin tasarımı ve performansına ilişkin araştırmayı sunmaktadır. Bu malzemeler, oda sıcaklığında (0,046 W·m–1·K–1) ve 500 °C'de (0,073 W·m–1·K–1) düşük ısıl iletkenlikle birlikte umut verici yağ emilimi (3,1 g·g–1'e kadar) ve su temizleme performansı sergilemiştir. Bölüm 3, ticari yalıtım panellerine kıyasla 1200 °C'ye kadar bütan meşalesi altında üstün yalıtım ve mekanik özelliklerini koruyabilen, çeşitli formlara işlenebilir, yüksek gözenekli aerojel monolitlerinin üretim fizibilitesini gösteren SiOC köpük-aerojel kompozit yaklaşımını ele almaktadır. Bölüm 4, monolitik hibrit ambi/aerojellerin geliştirilmesini inceleyerek, yağ/organik çözücü temizliği için potansiyellerini vurgulamaktadır. Bu aerojeller, yağ için 13 g·g–1'e ve çözücüler için 11 g·g–1'e kadar ulaşan yüksek sorpsiyon kapasiteleri göstermektedir ve organik çözücülerle birden fazla rejenerasyon döngüsü boyunca kararlı sorpsiyon sağlamaktadır. Bölüm 5, yüksek ve düşük sıcaklıklarda olağanüstü termal yönetim elde etmek için SiOC köpüğü ve silika aerojeli birleştiren inorganik kompozitlerin tasarımını incelemektedir. Genel olarak, Si bazlı polimerik ve seramik aerojeller, düşük termal iletkenlik, verimli termal yalıtım, yüksek sıcaklık stabilitesi ve atık su arıtımı dahil olmak üzere umut verici çok işlevli özellikler sergilemiştir.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.