Lithia porcelains as promising breeder candidates — II. Structural changes induced by fast neutron irradiation

Abstract

The promise of lithia ceramics as candidate breeder materials necessitates investigations on radiation damage induced structural variations. Prepared porcelain systems consisting of β-eucryptite (Li 2O.Al 2O 3.2SiO 2), its solid-solution (Li 2O.Al 2O 3.3SiO 2) and β-spodumene (Li 2O.Al 2O 34SiO 2), previously characterized, were irradiated by fast neutrons at room temperature. A 252Cf source (2 MeV) was used to give fluences of 1 × 10 5, 1 × 10 8 or 1 × 10 10 n/cm 2. Samples of each group received fluences in a one-shot technique, i.e. new samples were used for each fluence before being subjected to structural testing. Damage was assessed by X-ray diffraction (XRD) and infrared (IR) spectral analyses. Relevance dilatation changes were followed through coefficient of change with temperature up to 1000 °C. Surface morphologies were examined using scanning electron microscopy (SEM) and selected area electron diffraction (SAED). XRD patterns revealed various degrees of imperfections that were reflected as shifts in lattice planes. The IR spectral bands suffered shift, especially in the fingerprint region, parallel with the fluence intensity. Coefficient of contraction and/ or expansion evidenced various degree of damage, which upon intense irradiation annealed to the original values. SEM micrographs revealed that large grains comprising either β-eucryptite or β-spodumene bodies are much more affected by fast neutrons compared to smaller grains detected in the body containing the solid-solution. Additional evidence was obtained by the SAED results, where the continuous polycrystalline rings of both β-eucryptite and β-spodumene turned upon irradiation to the amorphous metamict state simulating the initial solidsolution structure. The latter acquired higher crystalline order, as well as polycrystalline habit. The degrees of induced imperfections were found to be dependent on initial crystallinity. The higher sensitivity to fast neutrons of β-eucryptite was related to its higher lithia content rather than its hexagonal spiral structure compared to the tetragonal β-spodumene. Intense irradiation caused annealing of the produced damage observed by fragmentation of the grains and various degree of amorphism.