Abstract
The pyrolysis of Si-C-O fiber (Nicalon) coated with an oxide film has been investigated. Nicalon fiber was heated in an O2 stream, and was subsequently heated in an Ar stream at temperatures from 1573 to 1773K. The mass change of the fiber was determined with a thermobalance. The reaction products were examined by X-ray diffraction, SEM and TEM observations. During formation of the oxide film, the amorphous fiber core grew to the microcrystalline β-SiC. The mass of Nicalon coated with the oxide film did not change, when heated in an Ar stream, indicating the suppression of the pyrolysis of the fiber core. Because of the suppression, the high temperature strength of the core was appreciably retained. The oxide film was smooth, and crystallized from amorphous silica to cristobalite only partially during the heat treatment in Ar. Hence, it is considered that the SiO2 layer retards the pyrolysis of the fiber core by restricting the outward transport of the gaseous products, SiO and CO.
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