Polymer-Derived SiOC Nanotubes and Nanorods via a Template Approach

The synthesis of silicon-based ceramic nanowires and nanotubes produced by liquid infiltration of commercially available silicon-based polymers, namely polysilazane (Ceraset (TM), polyureasilazane), polysilazane VL20 (Kion Coop.) and polycarbosilane (Starfire Systems SP-Matrix (TM)) in alumina templates with defined pore channels is reported. After polymer infiltration, pyrolysis of the preceramic polymer at 1000-1100 degrees C in Ar atmosphere followed by dissolution of the alumina templates, ceramic nanowires and nanotubes were obtained. In the case of the polymeric ceramic precursor polysilazane, nanorods were formed only if an oligomeric fraction was distilled off from the polymer precursor prior to infiltration of the template. In contrast, the formation of nanotubes was found after infiltration of the untreated (crude) preceramic polymer. Despite the fact that the preceramic polymers contain silicon, carbon and nitrogen and no oxygen as constituting elements, the final ceramic nanostructures obtained were analysed consistantly by various techniques to contain oxygen and only limited amounts of carbon and nitrogen after pyrolysis consistent with a composition as silicon oxycarbide (SiOC). This behaviour strongly indicates that the porous alumina template may significantly influence the pyrolysis process of the precursors thus affecting the chemical composition of the final ceramic products. It is a central result of our study that the alumina templates are not inert under the reaction conditions employed instead acting as a reaction partner at the high temperatures employed during pyrolysis. Taking this into account, reaction of otherwise inert amorphous alumina with inorganic polymers at elevated temperatures could lead to a directed synthesis of new ceramic compositions. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)