OXIDATION-KINETICS OF AMORPHOUS SI-TI-C-O FIBERS

The mechanism of oxidation of amorphous Si-Ti-C-O fibers has been investigated. Using two types of fibers with different content of oxygen, T-1 (18%O) and T-2(13%O), the rate of oxidation has been measured with thermo-balance in an oxygen atmosphere at temperatures from 873 to 1773 K. The mass of the fiber was increased by the oxidation. The amorphous fibers was unchanged even at higher temperatures. The amorphous silica was formed at lower temperatures, while the cristobalite was formed at higher temperatures. The kinetics of the oxidation followed the contracting-disc formula rate for diffusion control: (1 - X) ln (1 - X) + X = kt. The oxidation rate of T-1 was sharply reduced by densification of the porous oxide film at 1073-1173 K. The activation energies for the oxidation of T-1 were 23 kJ/mol at 873-1073 K, and 72 kJ/mol at 1173-1773 K, and for the oxidation of T-2 it was 70 kJ/mol at 873-1173 K. It is considered that the oxidation rate of Si-Ti-C-O fiber is controlled by the gaseous diffusion through the micro-pores in the oxide film.