Analysis of recovery process of low-dose neutron irradiation-induced defects in silicon nitride-based ceramics by thermal annealing

• Published in: Journal of nuclear materials Vol. 455; no. 1-3; pp. 464 - 469
• Main Authors: Rueanngoen, Areerak, Kanazawa, Koumei, Imai, Masamitsu, Yoshida, Katsumi, Yano, Toyohiko
• Format: Journal Article
• Language: English
• Published: 01.12.2014
• Subjects: Annealing; Ceramics; Crystal defects; Crystal structure; Irradiation; Recovery; Sialons; Silicon nitride
• ISSN: 0022-3115
• DOI: 10.1016/j.jnucmat.2014.07.066

Two kinds of silicon nitride ceramics consisting of different polymorphs were neutron-irradiated up to 8.5 x 10 super(24) n/m super(2) (E > 0.1 MeV) at 563 K, and their annealing behaviors were compared to those of previously reported SiAlON polymorphs subjected to the same irradiation condition. The macroscopic length change of alpha -and beta -Si sub(3)N sub(4) and alpha - and beta -SiAlON were 0.11%, 0.06%, 0.12% and 0.14%, respectively. Based on swelling data and microstructural observations, the low dose neutron irradiation-induced defects in silicon nitride-based ceramics were considered to be primarily point defects. In order to investigate the kinetics of defect recovery, these irradiated specimens were isothermally and isochronally annealed continuously up to 1473 K. Macroscopic length change decreased gradually with increasing annealing temperature. Recovery curves of isochronal annealing of alpha -Si sub(3)N sub(4) and alpha -SiAlON were similar, and those of beta -Si sub(3)N sub(4) and beta -SiAlON were also similar. The recombination rate constant as a first-order reaction increased with the increasing of the isothermal annealing temperature. A two-stage recovery process was considered between the irradiation temperature and 1473 K. The activation energies at higher temperatures were almost double those at lower temperatures in both Si sub(3)N sub(4) and SiAlON. At lower temperatures range the recovery should occur by annihilation of close-spaced Frenkel pairs. On the other hand, at higher temperatures, the recovery process may be governed by the annihilation of separated Frenkel pairs. In addition, the activation energies for defect recovery in Si sub(3)N sub(4) were larger than defects in SiAlON. Recovery characteristics of alpha - and beta -phases were different in both crystals that are suggested to be due to differences in crystal structures.