Low-temperature synthesis of Li₄SiO₄ pebbles as tritium breeding material by SiO₂ coating approach

ABSTRACT

Li₄SiO₄ pebbles are widely selected as attractive ceramic tritium breeding materials for the test blanket modules (TBM) of international thermonuclear experimental reactor (ITER). In this work, SiO₂ coating approach was first employed to synthesize precursor powders for fabricating the Li₄SiO₄ pebbles. Lithium source and silicon source were mixed by hydrolyzing tetraethyl orthosilicate (TEOS) in the Li₂CO₃ solution. Compared with the traditional solid state method, the precursor powders synthesized by SiO₂ coating approach displayed distinct coating structure, which was able to effectively lower the phase formation temperature and the sintering temperature of Li₄SiO₄ pebbles, and then decrease the grain size of Li₄SiO₄ pebbles. Thermogravimetry and different scanning calorimetry (TG-DSC) and X-ray diffraction (XRD) analyses indicate that the phase formation temperature of Li₄SiO₄ synthesized by SiO₂ coating approach is far below that of the conventional solid state reaction. Then, wet method was employed to prepare green spheres with the as-prepared precursor powders. Finally, Li₄SiO₄ pebbles with small grain size (average value 1.12 µm), high phase purity, good sphericity, and uniform microstructure could be obtained by sintering the green spheres at a low temperature of 625°C, which are expected to show favorable tritium release behavior and be used as tritium breeding materials for blankets.

KEYWORDS:

• Characterization
• coating
• grain size
• Li₄SiO₄
• low temperature
• microstructure
• pebble
• tritium breeders