Neutron irradiation damage in aluminum oxide and nitride ceramics up to a fluence of 4.2×1026 n/m2

High-purity Al2O3 and AlN ceramics were concurrently irradiated in the JOYO experimental fast reactor up to 4.2×1026 n/m2(E>0.1 MeV) at 650–1008 K. Changes in macroscopic length and lattice parameter were measured. Macroscopic swelling of Al2O3 was observed to be 1.2–2.3% and was larger at higher irradiation temperature. The change in lattice parameter of Al2O3 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.