A comprehensive study on the phase composition, mechanical properties and stability of Li4SiO4-Li2ZrO3 biphasic ceramics

Abstract

Lithium orthosilicate (Li₄SiO₄) is regarded as a candidate for tritium breeding in fusion reactors. In this study, the Li₄SiO₄-Li₂ZrO₃ biphasic was developed to improve the sinterability, density, and mechanical properties of Li₄SiO₄. The Li₄SiO₄-xLi₂ZrO₃ (x = 0.5, 1) composite powders were prepared using solid-state reaction via in-situ method. Li₆Zr₂O₇ existed in the ceramic powders at low calcination temperatures. When the calcination temperature was increased to 900 °C, Li₆Zr₂O₇ was transformed into Li₂ZrO₃ due to the decomposition of Li₆Zr₂O₇ at high temperatures. The TEM observation confirmed that the powders consisted of Li₄SiO₄ and Li₂ZrO₃. The Li₄SiO₄ and Li₄SiO₄-xLi₂ZrO₃ (x = 0.5, 1) pebbles were fabricated by the sol-gel method. The measurement results showed that the pebbles had a narrow size distribution and fine sphericity. The density of Li₄SiO₄-Li₂ZrO₃ pebbles reached 96.01% of the theoretical density when it was sintered at 1000 °C for 4 h. Compared with the Li₄SiO₄, the grain size of ceramic pebbles was significantly reduced. Owing to decreased grain size, 139.0 N crush load for the pebbles and 92.4 MPa bending strength for the sintered bodies were achieved. Besides, the ceramics with the Li₄SiO₄ to Li₂ZrO₃ ratio of 2: 1 exhibited preferable mechanical properties. Further, to investigate the chemical stability of biphasic ceramics, the structure and mechanical properties were examined under high temperatures and continuous inert gas purging, simulating the working condition of fusion reactors. It was shown that there was almost no change in phase composition and grain size after purging for 60 h at 650 °C. For the mechanical properties, the crush load was decreased initially due to the cracking in the surface region of the ceramic and then increased because the cracking was recovered.