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- W48000720 abstract "The research work presented in this thesis is concerned with the production of porous components by using preceramic polymers as a starting precursor. During the preliminary studies on which the production of polymer derived cellular ceramics was based; various compositions have been investigated. Cellular SiOC ceramics having a complex morphology were produced using three different types of polysiloxane precursors. Pore formation was attributed to the different polymer architecture which resulted in a different behavior (larger weight loss, shrinkage and gas evolution) upon pyrolysis. In this context; polysiloxane precursors were crosslinked, crushed, sieved and pressed to form compacts yielding with porous SiOC monoliths by pyrolysis. The resulted ceramic bodies showed compressive strength values reaching to 37.4MPa (~53vol% porosity). Hot-isostatic pressing enabled the formation of SiOC(N) tablets having extremely high piezoresistivity in between 100-1700 at high temperatures (700-1000°C). By using a polysilazane precursor microcellular SiOCN and macrocellular SiCN foams were produced via sacrificial templating or a physical blowing agent. Foams had mostly interconnected porosity ranging from ~60 to 80 vol% and possessing a compressive strength in the range ~1 to 11 MPa. By following the similar strategies boron including porous (70 vol%) PDC monoliths have also been produced.In the direction to produce high specific surface area (SSA) hierarchically porous PDC components; Periodic Mesoporous Organosilica (PMO) particles were embedded into a foamed polysiloxane polymer, and by pyrolysis, permeable SiOC monoliths having SSA of 137 m2/g were obtained. In the method; catalyst assisted pyrolysis (CAP), silicon nitride, silicon oxynitride or silicon carbide nanowires were formed directly during the pyrolysis of highly porous monoliths. Increasing the pyrolysis temperature caused an increase in the length and the amount of nanostructures produced. The growth mechanisms for the nanowires depended on the pyrolysis conditions and catalyst type. The presence of the nanowires afforded high SSA values to the macro-porous ceramics, ranging from 10 to 110 m2/g. The differences were explained in terms of the morphology and amount of the nanowires that were produced using the two different catalysts (Co or Fe). High temperature etching of SiCN ceramics yielded with disordered or graphitic carbon materials possessing a hierarchical bi-modal pore structure (micro-mesopores with mean pore size, 3-11 nm) and large SSA, up to 2400 m2/g. The resulting porosity (pore size, PSD, and SSA) strongly depended on nanostructural phase evolution of the PDC material, as well as on etching conditions. The mean pore size increased with increasing pyrolysis temperature." @default.
- W48000720 created "2016-06-24" @default.
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- W48000720 date "2010-01-31" @default.
- W48000720 modified "2023-09-27" @default.
- W48000720 title "FABRICATION AND CHARACTERIZATION OF POROUS CERAMICS WITH HIERARCHICAL POROSITY" @default.
- W48000720 hasPublicationYear "2010" @default.
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