Polyborosilazane-Derived Ceramic Fibres In The Si-B-C-N Quaternary System For High-Temperature Applications

Amorphous Si-B-C-N ceramic fibres prepared at 1000 deg C from a melt-processable boron-modified polysilazane were annealed in the temperature range 1000-1800 deg C in a nitrogen atmosphere to identify the changes in the thermal and structural stability as well as in the related fibre strength. Fibres were shown to be extremely stable up to 16000 deg C without decomposition and measurable changes in their amorphous structure. At higher temperatures, X-ray diffraction a and thermogravimetry analysis indicated that the structural and thermal properties of fibres were probably controlled by the carbothermal decomposition of a minor part of the silicon nitride phase providing Si3N4/SiC nanograins in the material at high temperature.