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Department: search.filters.department.Department of Chemical and Biological EngineeringSubject: search.filters.subject.Ceramics

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    Total internal reflection-based optofluidic waveguides fabricated in aerogels
    (Springer, 2017) Jona, Alexandr; Department of Physics; Department of Chemical and Biological Engineering; N/A; Kiraz, Alper; Erkey, Can; Özbakır, Yaprak; Faculty Member; Faculty Member; PhD Student; Department of Physics; Department of Chemical and Biological Engineering; College of Sciences; College of Engineering; Graduate School of Sciences and Engineering; 22542; 29633; N/A
    Liquid-core optofluidic waveguides based on total internal reflection of light were built in water-filled cylindrical microchannels fabricated in hydrophobic silica aerogels. Silica aerogels with densities ranging from 0.15 to 0.39 g/cm(3) were produced by aging of alcogels in tetraethylorthosilicate solution for various time periods, followed by supercritical extraction of the solvent from the alcogel network. Subsequently, the resulting hydrophilic aerogel samples were made hydrophobic by hexamethyldisilazane vapor treatment. The synthesized samples retained their low refractive index (below similar to 1.09) and, hence, they could serve as suitable optical cladding materials for aqueous waveguide cores (refractive index n(core) = 1.33). Hydrophobic silica aerogel samples produced by the above technique also had low absorption coefficients in the visible part of the spectrum. Fabrication of microchannels in aerogel blocks by manual drilling preserving nanoporous and monolithic structure of aerogels was demonstrated for the first time. Long channels (up to similar to 7.5 cm) with varying geometries such as straight and inclined L-shaped channels could be fabricated. Multimode optofluidic waveguides prepared by filling the channels in the drilled aerogel monoliths with water yielded high numerical aperture values (similar to 0.8). Efficient guiding of light by total internal reflection in the water-filled channels in aerogels was visually revealed and characterized by monitoring the channel output. The presented technique is expected to open up further possibilities for creating three-dimensional networks of liquid channels in aerogels for optofluidic applications.
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    Tuning structural characteristics of red mud by simple treatments
    (Elsevier Sci Ltd, 2016) Soyer-Uzun, Sezen; N/A; Department of Chemical and Biological Engineering; Öztulum, Samira Fatma Kurtoğlu; Uzun, Alper; PhD Student; Faculty Member; Department of Chemical and Biological Engineering; Koç University Tüpraş Energy Center (KUTEM) / Koç Üniversitesi Tüpraş Enerji Merkezi (KÜTEM); Graduate School of Sciences and Engineering; College of Engineering; 384798; 59917
    Red mud (RM) is a hazardous waste produced vastly by aluminum industry worldwide. Because of its rich metal oxide content, it has potential to be utilized in various applications, such as ceramics production, construction, and catalysis. Here, we investigated the structural modification of RM by simple acid treatments using HCl and H2SO4 at different molarities, and at different digestion temperatures followed by calcinations at various temperatures. Structures before and after these treatments were characterized in deep detail by combining electron microscopy, diffraction, and spectroscopy complemented by thermal analysis and mass spectrometry to elucidate any changes in morphology, structure, and chemical composition introduced by these treatments. Results showed that acid treatments tremendously affect chemical composition; for instance, amount of Fe2O3 changes from 37 to 46 wt%, while that of minor components, such as Na2O, varies from approximately 9 wt% to trace amounts. Moreover, data also illustrated that high acid digestion temperature (220 degrees C) leads to significant improvements in surface area, from 17 m(2)/g to values exceeding 200 m(2)/g. Results presented here provide a guideline for modifying RM by simple treatments to tune its structural characteristics, potentially offering opportunities for its utilization as cost effective and environmentally friendly solutions to various applications.