Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection

Permanent URI for this collectionhttps://hdl.handle.net/11147/7148

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Author: search.filters.author.Vakifahmetoglu, CekdarSubject: search.filters.subject.Aerogels

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  • Article
    Design and Performance of SiOC Foam-Silica Aerogel Composites for Hot and Cold Thermal Management Applications
    (Elsevier Ltd, 2025) Icin, Oyku; Vakifahmetoglu, Cekdar
    This study focuses on the fabrication of monolithic preceramic polymer-derived ceramic (SiOC) foam-silica aerogel composites by filling the open cells of ceramic foam with a silica aerogel solution using the sol-gel technique. The effects of different drying techniques (ambient pressure vs CO2 supercritical drying) and surface modification agents, including trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ), are comprehensively investigated. These factors are analyzed for their influence on the composites' morphology, porosity, chemical structure, and thermal insulation performance. The drying technique and surface modification agents are found to play a critical role in achieving a high filling ratio of silica aerogel within the composites. Pure silica aerogels exhibit specific surface areas (SSAs) reaching similar to 1120 m(2).g(-1), while the SiOC foam-silica aerogel composites demonstrate SSAs of 385-440 m(2).g(-1). Nearly all samples achieve a total porosity of similar to 93 vol%. Surface modification effectively tailors the surface properties, imparting hydrophobicity with a water contact angle of 133 degrees. Thermal conductivity at room temperature ranges between 38 and 43 mW<middle dot>m(-1)<middle dot>K-1. The potential applications of these SiOC foam-silica aerogel composites as thermal insulators are assessed under extreme thermal conditions. For instance, a 14 mm thick composite has a temperature of -27 degrees C when subjected to a cold source at -78 degrees C. Instead, when exposed directly to a butane flame (similar to 1200 degrees C), the backside of the composite recorded only similar to 57 degrees C.
  • Article
    Citation - WoS: 2
    Citation - Scopus: 2
    Hybrid Preceramic Aerogels for Oil and Solvent Cleanup
    (Wiley-v C H verlag Gmbh, 2025) Icin, Oyku; Vakifahmetoglu, Cekdar
    This study presents the first synthesis and characterization of monolithic hybrid preceramic aerogels using distinct drying techniques: ambient pressure (ambigels) and CO2 supercritical drying. Polymeric ambi/aerogels, derived from polyhydromethlysiloxane (PHMS) and divinylbenzene (DVB), are processed at 200 degrees C, while hybrid ceramic-polymer (ceramer) is produced through pyrolysis at 600 degrees C. Despite variations in drying methods, polymer and ceramer ambi/aerogels exhibit comparable microstructural characteristics, bulk density, pore size and volume, and specific surface area (542-841 m(2) g(-1)). Polymeric and ceramer ambigel with 90 vol% total porosity yield a compressive strength, reaching 2.5 MPa, demonstrating a low thermal conductivity of 0.046 W m-1 K-1. Sorption tests are conducted using oil and organic solvents in aqueous media to benefit their high hydrophobicity (112 degrees < theta < 142 degrees). Aerogels exhibit high sorption capacities: 13.17 g g(-1) for sesame oil, 11.74 g g(-1) for toluene, and 9.19 g g(-1) for n-hexane. The sorption rate for the oil is nearly 10 times slower than that for toluene and n-hexane. Regarding regeneration and reusability, polymer and ceramer aerogels show consistent sorption properties cycles tested for n-hexane and toluene.