Polymer-Derived SiC/ B4 C/ C Nanocomposites: Structural Evolution and Crystallization Behavior.

Structural evolution and crystallization behavior between 600°C and 1450°C during the preparation of bulk SiC/ B4 C/ C nanocomposites by the pyrolysis of CB- PSA preceramic were investigated. The CB- PSA preceramic converts into carbon-rich Si- B- C ceramics up to 800°C. Structural evolution and crystallization of Si- B- C materials could be controlled by adjusting the pyrolytic temperature. The Si- B- C ceramics are amorphous between 800°C and 1000°C. Phase separation and crystallization begin at 1100°C. The crystallization of β- SiC takes place at 1100°C and B4 C nanocrystallites generate at 1300°C. The sizes of β- SiC and B4 C nanocrystals increase with the pyrolytic temperature rising. In addition, the boron-doping effect on structural evolution was studied by comparing the crystallization and graphitization behavior of Si- B- C ceramics and the corresponding Si- C materials. Boron is helpful for the growth of β- SiC nanocrystals and the graphitization, but harmful for the nucleation of β- SiC crystallites. [ABSTRACT FROM AUTHOR]