Feasibility Study of a New Fabrication Method for the Li4SiO4 Pebbles

The production of reliable, stable, and durable breeder blanket material is one of the most important open challenge of fusion reactor technology. A new low temperature fabrication method for producing lithium orthosilicate (Li4SiO4) pebbles based on the drip casting was developed at DICI - University of Pisa. The pebbles were produced starting from a suspension of Li4SiO4 precursors prepared by sol-gel method, which was dripped through the experimental device and coagulated into solid spheres in a saline solution. Li4SiO4 pebbles were finally obtained after sintering at high temperature. The pebbles produced are stable and well-sized (about 1.5 mm diameter). Pebbles have been analyzed in order to determine their physical and mechanical characterization. To the aim, SEM and X-ray diffractometer analyses were performed as well as compression tests by Instron machine. The pebbles obtained from the drip casting have a mechanical strength (about 11 N) comparable with that of the others solid breeder in pebbles form. In addition, if compared to these latter they have same roundness and sphericity. Results confirmed the feasibility of drip casting forming technique, and provided further useful information for the optimization of the proposed new fabrication process.

A Comprehensive Study on Li4si1-xtixo4 Ceramics for Advanced Tritium Breeders

Hetero-elements doped lithium orthosilicate has been considered as advanced tritium breeders due to its superior performances. In this work, Li4Si1-xTixO4 ceramics were prepared by proprietary hydrothermal process and multistage sintering. The reaction mechanism of Li4Si1-xTixO4 was put forward. XRD and SEM analyses indicate that insertion of Ti leads to lattice expansion, enhances the sinterability and changes the fracture mode. The compressive tests show that the crush load increases almost four times by increasing x from 0 to 0.2. However, the thermal conductivity and ionic conductivity are the best when x=0.05 and x=0.1, respectively. Thermal cycling stability of Li4Si1-xTixO4 pebbles was further appraised through investigating the changes of microstructure and crush load. After undergoing thermal cycling, the Li4Si1-xTixO4 still show higher crush load compared with Li4SiO4, despite Ti segregation in some samples. The x=0.05 sample exhibits excellent thermal cycling stability. To be sure, Ti doping improves the overall performance of Li4SiO4.