SWELLING, THERMAL-DIFFUSIVITY AND MICROSTRUCTURAL INVESTIGATION OF NEUTRON-IRRADIATED SINGLE-CRYSTALS OF NONSTOICHIOMETRIC SPINEL

Single crystals of nonstoichiometric magnesium aluminate spinel (MgO.3Al2O3) were neutron-irradiated in the Japan Materials Testing Reactor (JMTR) to fluences (E > 1 MeV) from 8.3 x 10(22) n/m2 at 373 K to 5.2 x 10(24) n/m2 at 1058 K. Changes in macroscopic length, lattice parameter and thermal diffusivity for the specimen irradiated to a fluence of 8.3 x 10(22) n/m2 at 373 K were +0.065%, +0.076% and -27%, respectively. On the other hand, those for the specimen irradiated to a fluence of 2.4x10(24) n/m2 at 743 K were +0.008%, +0.021% and -1%, respectively. Microstructural examination by transmission electron microscopy revealed no evidence of any agglomerated damage for the specimen irradiated to a fluence of 8.3x10(22) n/m2 at 373 K, whereas a number of finer intersitial Frank loops (approximately 20 nm in diameter) having the Burgers vector of the [111] {111} type were observed in the specimen irradiated to a fluence of 2.4x10(24) n/m2 at 743 K. The specimen irradiated to a fluence of 5.2x10(24) n/m2 at 1058 K formed precipitates in the spinel phase, which was identified to be the type II intermediate phase of spinel.