Thermal conductivity evaluation of ion irradiated Si3N4 and ZrN ceramics using spatial domain thermoreflectance

Nitride ceramics have been investigated for different applications in the nuclear industry, such as space nuclear power, fusion reactor diagnostics and plasma heating, inert matrix fuels, and accident tolerant fuels. Although thermal conductivity remains one of the most important properties to track following irradiation, traditional techniques such as laser flash and xenon flash are limited to bulk sample characterization, which requires lengthy and cost-consuming neutron irradiation. This work used spatial domain thermoreflectance (SDTR) for the micrometer-scale measurement of thermal conductivity in 15 MeV Ni ion-irradiated silicon nitride and zirconium nitride from 1 to 50 dpa and 300 to 700 & DEG;C. The SDTR-measured unirradiated thermal conductivity was found to be consistent with the published data on bulk samples. Electrically conductive ZrN exhibits modest reduction after irradiation which is minimal at the highest irradiation temperatures. In electrically insulating Si3N4, the reduction is more significant and unlike ZrN, the reduction remains significant even at a higher irradiation temperature. The thermal resistance evolution following irradiation was compared with lattice swelling, which was determined using grazing incidence x-ray diffraction, and radiation-induced defects were observed using transmission electron microscopy. A saturation value was observed between 15 and 50 dpa for thermal conductivity degradation in both nitride ceramics and a direct correlation with high-temperature defect recombination was observed, as well as the potential presence of additional carrier scattering mechanisms. Published under an exclusive license by AIP Publishing.

Automated summary

Nitride ceramics have wide applications in the nuclear industry, and thermal conductivity is an important property. In this study, spatial domain thermoreflectance was used to measure the thermal conductivity of irradiated silicon nitride and zirconium nitride, and the effects of irradiation on thermal conductivity were investigated. The results showed that irradiation had minimal effect on the thermal conductivity of zirconium nitride, while it had a significant impact on the thermal conductivity of silicon nitride, and the impact became more significant at higher irradiation temperatures. Additionally, a saturation phenomenon in thermal conductivity degradation was observed, which was correlated with lattice swelling and defect recombination.