Effect of Nonstoichiometry on Neutron-Irradiation-Behavior of Spinel

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In this study, the effects of nonstoichiometry on neutron-induced damages of spinel were investigated by measuring length change, lattice parameter change, change in thermal diffusivity, changes in mechanical properties after neutron irradiation of synthetic spinel with different stoichiometry. The recovery of these properties was also evaluated. Furthermore, neutron-induced damages of other ceramics were observed for comparison. The main results obtained were summarized as follows. (1) Macroscopic length change and lattice parameter changes of spinel irradiated at lower temperatures corresponded well each other and increased with increasing n. The change in Vickers hardness was the same tendency. After annealing, the macroscopic length and lattice parameter shrunk gradually from the irradiation temperature to 550℃, then made small peak at 650℃, finally it was not changed above 800℃. From this results, it is suggested that the recombination of Frenkel pairs up to 800℃ and rearrangement in cations at around 650℃ are happened. (2) Knoop microhardness anisotropy of n=3 spinel was measured before and after irradiation, and after post-irradiation annealing. It was changed by neutron irradiation, but recovered to that of before irradiation after annealing. The anisotropy profile of n=3 spinel was different from that of stoichiometric spinel, due to the different degree of cation distribution. Change in Vicker's hardness by neutron irradiation was proportional to the square of volume change. (3) Cation distribution of spinel in tetrahedral sites and octahedral sites could not be detected by X-ray microprobe analysis coupled with profile analysis and temperature calibration on a present EPMA apparatus. By use of ALCHEMI analysis, it could be detected, and it was found that cation distribution in spinel changed toward more random distribution by neutron irradiation. (4) Physical property change in Al_2O_3, AlN, SiC and Si_3N_4 after heavy neutron irradiation was evaluated.