Crystallization process of polymer-derived ceramic fibers with nano-structure

The crystallization processes of 2 kinds of Si-Ti-C-O fibers with different C/Si molar ratios of 0.99 and 1.65 were characterized. Both the as-received fibers have a microstructure where beta-SiC nanocrystals (3-5 nm) are dispersed over an amorphous matrix, but the fiber with C/Si = 1.65 additionally contains some carbon units (< 3 nm) around beta-SiC nanocrystals. For the fiber with C/Si = 0.99, the crystallization proceeded drastically with time, and was involved with a rapid gas evolution. On the other hand, for the fiber with C/Si = 1.65, the crystallization was controlled by the presence of free carbon, and it resulted in a slower gas evolution. However, the free carbon subsequently began to disappear with time: instead, a new carbon layer was formed at the fiber surface. The electrical resistivity reflected the above microstructural changes.