Thermal expansion-crystallite size-strain relations in fast neutron irradiated lithia porcelain

Abstract

Factors affecting radiation induced defects in lithia aluminosilicate porcelain were investigated. Porcelains with β-eucryptite (Li₂O · Al₂O₃ · 2SiO₂), its solid solution (SS) (Li₂O · Al₂O₃ · 3SiO₂) and β-spodumen (Li₂O · Al₂O₃ · 4SiO₂) were prepared and vitrified. Irradiation was performed at room temperature with three fluences from ²⁵²Cf. X-ray line profile analysis, thermal expansion and scanning electron microscopy were carried out pre- and post-irradiation.

Results showed that when large crystallites were present in strain free body such as β-spodumen (tetragonal) their sizes were greatly influenced. Both high strain and large crystallite size in hexagonal β-eucryptite were severely reduced. In the solid solution (SS) β-eucryptite having minimum crystallite size and strain free level, defects appeared as swelling of the crystallites. Accompanying morphological changes conformed with the above findings. The negativity of thermal expansion increased with low fluences rather than higher ones leading to recovery of induced defects. The optimum neutron fluence, inducing maximum change, proved to be composition dependent. A wave behaviour of the induced change was interpreted in terms of radiation damage followed by saturation and further annihilation.