Polymer‐Derived SiC / B ₄ C / C Nanocomposites: Structural Evolution and Crystallization Behavior

Abstract

Structural evolution and crystallization behavior between 600°C and 1450°C during the preparation of bulk SiC / B 4 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 B 4 C nanocrystallites generate at 1300°C. The sizes of β‐ SiC and B 4 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.