Fast Sol–Gel Preparation of Silicon Carbide–Silicon Oxycarbide Nanocomposites


  • Based in part on the dissertation submitted by M. D. Clark for a Ph.D. in Chemical Engineering, at the University of Houston, Houston, Texas 77204-4004, USA.
  • M. D. Clark and R. Krishnamoorti were supported by the Air Force Office for Sponsored Research and the National Science Foundation under grant number FA9550-06-1-0422 and CMMI-0708096, respectively. This work is supported by a National Science Foundation Early Faculty Career Award under a Division of Materials Research Award Number 0954110 (LSW and ELC). M. D. Clark also partially supported by a GAANN fellowship from the U.S. Department of Education administered by the University of Houston.

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Silicon carbide nanofiber dispersion within a silicon oxycarbide glassy ceramic was achieved through a combination of a fast sol–gel procedure for in situ ceramic matrix synthesis and nanofiber conversion from sacrificial multiwalled carbon nanotube templates. Nanotubes were dispersed using both surfactant adsorption and a covalent sidewall modification scheme with gel-grafting capabilities. The combination of high temperature processing and silicon monoxide precursor concentrations allowed substantial carbothermal reduction of the nanotube templates, yielding silicon carbide nanofibers. The resulting nanocomposites were examined for density, Vickers microhardness, Young's modulus, and fracture toughness. The surfactant-assisted route inhibited ceramic densification, offering virtually no mechanical property enhancement. In contrast, the covalently functionalized nanotube templates at 0.8 wt% loading enhanced tensile modulus of 77% while simultaneously maintaining both Vickers microhardness and fracture toughness. These results indicate strong interfacial adhesion between the nanofiber surface and host matrix despite the abrupt chemical changes experienced during the high temperature processing.