Fabrication and Phase Evolution of Li₄SiO₄ Porous Ceramics by Cold Sintering Combined with Annealing-Induced Pore Formation

Lithium orthosilicate ceramics are key tritium breeder materials for the solid‐state tritium breeding blanket of magnetic confinement fusion reactors. The design of their porous microstructure is critically important for enhancing tritium release and extraction efficiency Traditional high-temperature sintering tends to cause grain coarsening, formation of secondary phases, and the closure of open pores, making it difficult to obtain the desired porous microstructure. This work proposes a novel fabrication strategy for porous Li₄SiO₄ ceramics based on a “cold sintering-induced hydrolysis — annealing-driven reactive pore formation” approach. It is found that applying a single condition (either 700 MPa pressure or 300 ℃ temperature alone) fails to fully decompose the precursors. However, the synergistic application of high pressure (700 MPa) and moderate temperature (200~300 ℃) drives the complete hydrolysis of Li₄SiO₄ into Li₂SiO₃ and Li₂CO₃, yielding highly dense green bodies with a relative density as high as 97%. Furthermore, the cold sintering pressure significantly influences the final relative density after annealing, and increasing the cold sintering temperature from 200 ℃ to 300 ℃ transforms the post‐annealing microstructure from macroscopic oriented cracks to uniformly distributed pores. After annealing at 800 ℃, Li₂SiO₃ and Li₂CO₃ in the compact react to re-form Li₄SiO₄, while the simultaneous release of CO₂ gas creates a well‐distributed porous structure within the ceramic matrix. The annealed ceramics exhibit an average grain size of 1.29μm and a relative density of 86%. This study provides a new technical route for the low-temperature fabrication and pore structure design of solid tritium breeder materials.