Thermal properties of neutron-irradiated SiC; effects of boron doping

The temperature dependence (250C to 10000C) of thermal conductivity for siliconized (reaction bonded) SiC and alpha phase (sintered) SiC irradiated to neutron fluences of 4 to 8x1024n/m2 (E > 1 MeV) were studied utilizing the heat pulse technique. The fluences are equivalent to 0.8 and 1.6 dpa and the sample temperature during irradiation was approx. equal to 140 0C. Silicon carbide exhibits a significant decrease in thermal conductivity after irradiation, specifically a factor of approx. equal to 5 decrease is observed for siliconized SiC. Comparisons were made with SiC samples doped with 10B, 11B, and natural boron to investigate the effects of impurity doping. It was found that the presence of natural boron and 11B have no significant effect on the thermal conductivity of irradiated SiC, whereas SiC doped with 10B exhibits a slightly larger decrease in thermal conductivity due to the conductivity after irradiation can explain the decreased resistance against thermal shock of irradiated SiC. The decrease in thermal conductivity is due to enhanced phonon scattering by radiation-induced vacancies and dislocations. Results on annealing effects and comparison with mechanical properties are presented. (orig.)