Neutron irradiation damage in aluminum oxide and nitride ceramics up to a fluence of 4.2×10

High-purity Al ₂O ₃ and AlN ceramics were concurrently irradiated in the JOYO experimental fast reactor up to 4.2×10 26 n/m 2 (E>0.1 MeV ) at 650–1008 K. Changes in macroscopic length and lattice parameter were measured. Macroscopic swelling of Al ₂O ₃ was observed to be 1.2–2.3% and was larger at higher irradiation temperature. The change in lattice parameter of Al ₂O ₃ was very little compared to the macroscopic length change. The a-axis remained at the unirradiated value, whereas the c -axis expanded slightly. Microstructural observations showed the formation of dense and tangled dislocations and a dense array of microvoids. Macroscopic swelling of AlN was observed to be 1.8–2.1%. The change in lattice parameter of AlN was also very little compared to the macroscopic length change. The a-axis expanded very slightly, whereas the c -axis contracted. The formation of a high density interstitial dislocation loop on the basal plane was observed. The thermal diffusivity reduced by 64–74% and 96–97% in alumina and in AlN, respectively.