KINETICS OF PYROLYSIS OF SI-TI-C-O FIBER

To investigate the mechanism of the pyrolysis of Si-Ti-C-O fibre (Tyranno), the rate of pyrolysis has been measured with a thermobalance at temperatures from 1673 to 1973 K under an argon atmosphere. The pyrolysis product was examined by chemical analysis, X-ray diffraction and TEM observation. Results were compared with those of Ti free fibre (Nicalon). The amorphous Si-Ti-C-O fibre crystallized to beta-SiC and TiC, with evolution of SiO and CO. TEM observation showed the spherical growth of the crystallites of SiC. The pyrolytic rate of Si-Ti-C-O fibre was larger than that of Si-C-O fibre (Nicalon). While the crystallites of SiC in Nicalon grew markedly during holding at high temperatures after the completion of the pyrolysis, the coarsening of the crystallites in Tyranno was retard. The pyrolytic rate was analyzed by means of Avrami-Erofeev equation. The mean value of the exponent in the rate equation was m = 1.4. The activation energy was 368 kJ/mol. The pyrolysis of Si-Ti-C-O fibre was controlled by the nucleation and growth of SiC crystallites.