EFFECT OF NEUTRON-IRRADIATION ON PASSIVE OXIDATION OF SILICON-CARBIDE

Hot-pressed SiC and pressureless-sintered SiC polycrystalline specimen s were neutron-irradiated in the Japan Materials Testing Reactor up to 4.5 x 10(24) n/m(2) (E > 1.0 MeV). The bulk specimens were crushed in to powders to increase surface area. Weight change of the specimen and released CO2 gas content were measured after isothermal annealing bet ween 500 and 1300 degrees C in oxidizing atmosphere using an electric balance and a gas chromatograph, respectively. There was no significan t difference between irradiated and unirradiated specimens, for both h ot-pressed and pressureless-sintered specimens. All of the weight gain data and amount of evolved CO2 satisfied a parabolic rate law against oxidation time. Apparent activation energy of the reaction confirmed the diffusion of O-2 molecules through amorphous SiO2 layer. However, apparent activation energy decreased by the irradiation only in pressu reless-sintered SiC containing B, suggesting the effect of transmuted atoms, or Li.