Nano-Scale Composite Structure of Polymer-Route Si-C-M-O Fibers Characterized by Small-Angle X-Ray Scattering

摘要

The structural evolution during the organic-to-inorganic conversion by pyrolyzing polymetalocarbosilane fibers into Si-C-M(=Ti, Al)-O fibers was measured by small-angle X-ray scattering(SAXS) using a point-collimated CuKa X-ray beam and a two-dimensional imaging plate detector. The SAXS profile for the Si-C-M-O fibers comprises two spatially distinct components on a length scale of 1 to 100 nm; an anisotropic SAXS profile in a lower scattering vector Q<0.5 nm{sup}(-1) region and an isotropic one in a higher Q>1 nm{sup}(-1) region, where Q=4πsinθ/λ,. The anisotropic SAXS profiles suggest that a single Si-C-M-O fiber of a few μm in diameter is formed by bundling together thousands of fine filaments of about 10 nm in diameter along with the long axis of the fiber. However, the anisotropic structure of Si-C-Al-O fibers is totally modified into an isotropic one in Si-C-Al fibers prepared by heating the Si-C-Al-O fibers above 1900 K in an argon gas stream, because of the formation of an aluminum oxide-rich phase at the interface boundaries among β-SiC nanocrystalline grains. The isotropic SAXS profiles, which sensitively depend on the pyrolyzing temperature, are contributed from theβ-SiC nanoparticles embedded in an amorphous matrix of the fiber. The very high mechanical strength of the Si-C-M-O fibers originates from the formation of a carbon-rich shell-like interface boundary surrounding theβ-SiC nanoparticles which are sharply separated from the amorphous matrix.