Limits on irradiation-induced thermal conductivity and electrical resistivity in silicon carbide materials

Thermal conductivity and electrical resistivity of SiC materials is given for fast neutron fluences up to 7.7 × 1025 n/cm2 at irradiation temperatures of 300, 500 and 800 °C. In situ radiation-induced conductivity is also measured for ionizing dose rates up to ∼5 Gy/s (X-ray). Thermal conductivity degradation for CVD SiC is presented in detail exhibiting a substantial reduction from the non-irradiated value of ∼370 W/m K. Thermal conductivity of irradiated stoichiometric fiber, CVI SiC matrix composite is also given. A thermal defect resistance approach is used to analyze this data yielding optimum irradiated thermal conductivity for SiC. Neutron irradiation has a permanent, but small effect on electrical conductivity. In the absence of impurity doping effects the neutron damage tends to increase resistivity by less than an order of magnitude. Those SiC materials with electrical resistivities less than ∼0.1 S/m undergo little increase in conductivity due to ionizing irradiation, while more than a two order of magnitude increase in electrical conductivity is measured for the highest resistivity form of SiC studied.