Neutron irradiation damage in MgO, Al 2O 3 and MgAl 2O 4 ceramics

Abstract

The consequences of point defect aggregation in single-crystal and polycrystalline Al 2O 3 and MgAl 2O 4 and polycrystalline MgO, irradiated to fast-neutron (>0.1 MeV) doses ⩽2–3 × 10 26 n m −2, have now been investigated over a range of temperatures using macroscopic density measurements of swelling and transmission electron microscopy of defect aggregates. Al 2O 3 irradiated between 925 and 1100 K exhibits 2–4 vol% swelling, dense dislocation networks and aligned voids, while single-crystal MgAl 2O 4 spinel irradiated under similar conditions, does not swell and forms only isolated interstitial dislocation loops which do not unfault. Planar arrays of voids form either side of grain boundaries in polycrystalline MgAl 2O 4 spinel, however. MgO irradiated at 430 K swells 2.8% and contains a high density of small elongated loops and exhibits a tendency towards dislocation network formation despite the low irradiation temperature. Al 2O 3 and MgAl 2O 4 irradiated at 430 K exhibits dense arrays of small loops. The nature and origin of the observed aggregate defect structures are described and correlated with swelling behaviour and with previous studies which are reviewed.