Radiation-induced amorphization and swelling in ceramics

Irradiation-induced amorphization and swelling of ceramics including graphite have been studied through in-situ observation of electron microscopy, electron energy loss spectroscopy and convergent beam electron diffraction. Amorphization occurs below 500 K for highly-oriented pyrolytic graphite (HOPG) and below 300 K for SiC under electron irradiation. The amorphization fluences of HOPG and SiC required for full amorphization show no flux dependence. The displacement threshold energy is determined to be 12 eV for HOPG from the electron energy dependence of the amorphization fluence which is equivalent to 1 dpa. An atomistic model for describing the irradiation-induced amorphization and swelling of graphite is proposed. A high concentration of C2 molecules and their clusters between basal plans induce abrupt swelling along the c-axis within 4x10-3 dpa and fade the periodical structural image at 4x10-2 dpa. The concentration of vacancies increases gradually up to 1 dpa at which amorphization is completed. (orig.)