Effect of Nonstoichiometry on Neutron-Irradiation-Behavior of Spinel

本研究通过测量不同化学计量比合成尖晶石在中子辐照后的长度变化、晶格参数变化、热扩散系数变化和力学性能变化，研究了非化学计量比对尖晶石中子损伤的影响。对这些性能的恢复也进行了评估。此外，还观察了其他陶瓷的中子损伤，以供比较。取得的主要结果概括如下。(1)低温辐照后尖晶石的宏观长度变化与晶格参数变化有很好的对应关系，且随n的增加而增大，维氏硬度的变化趋势相同。退火后，宏观长度和晶格参数从辐照温度到550℃逐渐缩小，然后在650℃处出现小的峰值，在800℃以上基本不变。结果表明，在800℃左右发生了Frenkel对的重组，在650℃左右发生了阳离子重排。(2)测量了n=3尖晶石辐照前后和辐照后退火后的Knoop显微硬度各向异性。经中子辐照后发生了变化，但经退火后又恢复到辐照前的水平。由于阳离子分布程度不同，n=3尖晶石的各向异性分布与化学计量比尖晶石的各向异性分布不同。中子辐照引起的维氏硬度变化与体积变化的平方成正比。(3)在现有的EPMA仪器上，X射线微探针分析结合剖面分析和温度校准无法检测尖晶石在四面体和八面体位置的阳离子分布。利用ALCHEMI分析可以检测到它，发现中子辐照使尖晶石中的阳离子分布向更随机的分布转变。(4)研究了Al_2O_3、AlN、SiC和Si_3N_4在重中子辐照后的物性变化。

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.