The effect of swift heavy ion irradiation on the microstructures of Si3N4 and AlN

Abstract

The development of novel materials with future nuclear applications is of ongoing concern. As part of this investigation we address two major issues concerning such applications. Firstly, improving the performance of structural materials in the reactor core for new and existing reactors and also the processing and storage of nuclear waste. The focus of this investigation is on Si3N4 and AlN which are under consideration as candidate materials for inert matrix fuel hosts. These materials will experience high levels of different types of radiation in the reactor core such as fission fragments and α-radiation. Due to the convenient similarities in mass and energy the effects of fission fragments are simulated by means of swift heavy ion implantation and α-radiation by He implantation. The combined effects of SHIs and He on these materials is also studied, since there is some indication from literature that SHI irradiation may significantly modulate the behaviour of gaseous species in some materials. To simulate the effects if SHIs; Si3N4 and AlN samples were irradiated with Xe and Bi ions, with energies ranging from 167 MeV to 2.6 GeV and temperatures ranging from LNT to 700 °C. The effects of α-particles were simulated with 20 keV He. The He irradiated samples were also subsequently annealed at 600 °C for 20 minutes to facilitate diffusion and agglomeration. The microstructure of the annealed samples was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) before and after SHI implantation. In general, the results showed that latent ion tracks are formed in Si3N4, but not in AlN