Fabrication of porous SiC-based ceramic microchannels via pyrolysis of templated preceramic polymers
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This article reports conversion chemistry of preceramic polymer to ceramic phase during the fabrication of high-temperature stable silicon carbide and silicon carbonitride monolithic porous microchannels. The micromolding in capillaries method is used to fabricate porous channels by the initial infiltration of a solution of 1.5-m diameter silica spheres or 1-m diameter polystyrene spheres into polydimethylsiloxane channels followed by filling the void space among the spheres by using viscous commercial polymeric precursors. Subsequently, the polymer-sphere composite channel was cured and pyrolysed at 1200 °C under inert atmosphere, and final wet etching step of silica spheres with 10% hydrofluoric acid solution developed the pore structures by removing the silica spheres, whereas polystyrene sphere decomposes at the early stage of pyrolysis.
I. INTRODUCTION
An important issue in the development of microelectro-mechanical systems (MEMS) for hash chemical conditions is the selection of a material that is stable at high temperatures and can resist chemical oxidation.1 Fabrication of MEMS by using nonoxide ceramic materials such as silicon carbide (SiC),2,3 silicon carbonitride (SiCN),4 silicon nitride (Si3N4),5 and borosilicon carbonitride (SiBNC)6 is receiving lot of attention because of the chemical inertness and high thermal stability of such types of ceramic materials. Commercial availability of preceramic polymer or precursor polymer has triggered a rapid growth in the formation of nonoxide, silicon-based ceramic materials. The fabrication of dense bulk Si-based ceramics by using preceramic polymer involves crosslinking [thermal or ultraviolet (UV) radiation] of the processable liquid polymeric precursor followed by a polymerto-ceramic transformation step. The processable precursor allows formation of a variety of shapes during the initial cross-linking process such as preparation of fibers,7,8 as well as other processing techniques like infiltration of preceramic polymer,4 spin coating to prepare thin film for MEMS2,3 application, etc. Despite the extensive use of preceramic polymer or precursor polymer in the formation of nonoxide, silicon-based ceramic materials, relatively fewer articles have reported conversion
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0192 J. Mater. Res., Vol. 21, No. 6, Jun 2006
chemistry of polymer to ceramic phase, especially in the case of polyvinylsilazanes (KiON VL 20), which has been used in the present work. In our group, we are currently exploring the use of polymer precursors to prepare ceramic micro/nanostructures and tailored mesoporous monoliths for different applications in MEMS and microsystem technology.4,9,10 Among all of the micro/nanostructure for MEMS, the use of tailored porous structures as catalyst beds or microreactor11 ministructured catalyst beds,12 selective membranes,13 photonic band gap materials,13 and for organic synthesis14 has attracted considerable attention. Compared with “microreactors” fabricated f
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