Recovery behavior of neutron irradiated α- and β-SiAlON ceramics by thermal annealing up to 1473 K

Abstract

Hot-pressed α- and β-SiAlON ceramics were neutron-irradiated in the Japan Materials Testing Reactor up to a fluence of 8.5×1024n/m2 (E>0.1MeV) at 563K. Irradiated SiAlON ceramics were isothermally and isochronally annealed up to 1473K in a precision dilatometer, and macroscopic length change of α- and β-SiAlON ceramics were examined. During isochronal annealing, the recovery of both SiAlONs started at a temperature about 50–100K higher than the irradiation temperature. Although the macroscopic length change for isochronal annealing decreased gradually up to 1473K, the recovery was not completed. The macroscopic length change of β-SiAlON decreased more continuously than that of α-SiAlON. During isothermal annealing, the length gradually recovered as increasing annealing time at each annealing temperature. The activation energy of macroscopic volume recovery at lower temperature range was calculated as the first-order reaction. For α- and β-SiAlON from 723 to 1073K, the values were 0.09 and 0.06eV, respectively. On the other hand, for higher temperature range, the activation energy was calculated as the second-order reaction, and to be estimated as 0.49eV for α-SiAlON from 1273 to 1373K, and 0.33eV for β-SiAlON from 1123 to 1473K, respectively. These values suggested that the recovery process was governed by the recombination of different type of Frenkel pairs and depended on its polymorphs.