Effects of polymer matrices to the formation of silicon carbide (SiC) nanoporous fibers and nanowires under carbothermal reduction

SiC fibers with varied nano-scale morphologies (i.e., nanowires, nanoparticles, etc) were successfully fabricated by the electrospinning of preceramic polyureasilazane (PUS) with either poly(methyl methacrylate) (PMMA) or polystyrene (PS) into composite fibers that were subsequently carbothermally reduced to ceramics via pyrolysis in argon at 1560 degrees C. While SiC fibers from either composite fibers contained polycrystalline cubic SiC (beta-SiC) structure, their fiber morphologies and atomic compositions differed due to the distinct thermal behaviors and decomposition pathways of PMMA and PS. Pyrolysis at 1000 degrees C produced fibrous mats of amorphous SiCO from PUS/PMMA with high O (32.5%) content or from PUS/PS with high C (74.7%) content. These differences led to distinct SiC fiber morphologies from further pyrolysis at 1560 degrees C, i.e., an interconnected fibrous mat of nanoparticle-filled porous core and wrinkled sheath fibers from PUS/PS and fragmented nanoparticle-filled porous fibers intermixed with abundant 100 nm diameter nanowires with straight, beaded and bamboo-like morphologies from PUS/PMMA.