Synthesis and characterization of lithium silicate powders

Abstract

Lithium-based ceramics, such as Li 2O, LiAlO 2, Li 4SiO 4, Li 2SiO 3, Li 2TiO 3and Li 2ZrO 3, have long been recognized as promising tritium breeding-materials for D-T fusion reactor blankets. Among these candidate materials, lithium orthosilicate (Li 4SiO 4) and lithium metasilicate (Li 2SiO 3) are recommended by many ITER research teams as the first selection for the solid tritium breeder. Li 4SiO 4 has even been selected as the breeder material for the helium-cooled solid breeder test blanket module (HCSB TBM) in China and EU. In present study, the processes of solid-state reaction between amorphous silica and Li 2CO 3 powders was studied by thermogravimetry analysis–differential scanning calorimetry (TGA/DSC); the lithium silicate powders were synthesized at 700, 800 and 900 ° C with Li:Si molar ratios of 0.5, 1, 2 and 4, respectively, using solid-state reaction method. The as-prepared lithium silicates were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results show that the phase composition and morphology of the as-prepared samples change with the different synthesis conditions. At low temperature of 700 ° C, all samples contain the amorphous silica, and the major crystalline phase is Li 2SiO 3 with different microstructure for Li/Si ratio of 0.5, 1 and 2. As for Li / Si = 4 , 98% purity of Li 4SiO 4 can be obtained at 700 ° C. At high temperature of 900 ° C, the significant sinterization effect will occur in all samples and Li 4SiO 4 will even decompose. The results also show that pure Li 4SiO 4 can be synthesized by calcining at 800 ° C for 4 h, and its’ solid-state reaction synthesis may be divided into two steps: (1) 515–565 ° C: Li 2 CO 3 + SiO 2 → Li 2 SiO 3 + CO 2 ; (2) 565–754 ° C: Li 2 CO 3 + SiO 2 → Li 2 SiO 3 + CO 2 and then Li 2 SiO 3 + Li 2 CO 3 → Li 4 SiO 4 + CO 2 . While Li / Si = 2 , 99% purity of and pure Li 2SiO 3 can be obtained at 800 and 900 ° C, respectively.