Preparation and characterization of lithium-titanate pebbles by solid-state reaction extrusion and spherodization techniques for fusion reactor

For the development of TBM for fusion reactors, lithium containing ceramics as against the metal are preferred as tritium breeding material. Lithium titanate (Li₂TiO₃) is one such chosen ceramic tritium breeder. Li₂TiO₃ pebbles are conventionally prepared by sol-gel process and wet process. Solid state reaction of lithium carbonate with titanium dioxide is preferred route for the bulk production of Li₂TiO_3. Thermo-gravimetric and differential thermal analysis (TG-DTA) techniques have been used in the present study to understand the solid state reaction of intimate mixture of lithium carbonate and titanium dioxide. It was found out that single phase lithium titanate (Li₂TiO₃) is produced at 750 °C and the reaction is completed in 6 h. Fine powders of lithium titanate obtained after milling and classification were mixed with aqueous solution of PVA to prepare green pebbles of desired size and shape. The pebbles were subsequently sintered at 900 °C and the effect of sintering time on the properties of sintered pebbles was studied. The reaction mechanisms and the product qualities obtained by the solid state reaction, extrusion and spherodization techniques are discussed in this paper.     

35T／H循环床锅炉埋管破裂分析

某３５Ｔ／Ｈ循环床锅炉埋管运行仅２个月，即发生管子破裂。采用光学显微镜、化学分析和力学性能测试方法对裂管进行了分析，结果表明，由于埋管局部区域超温，促使珠光体球化，最终导致力学性能下降而破裂。提出了预防措施。     

Synthesis & fabrication of lithium-titanate pebbles for ITER breeding blanket by solid state reaction & spherodization

⁶Li produces tritium by (n, α) nuclear reaction, ⁶Li + ¹n → ⁴He + ³H. Lithium titanate (Li₂TiO₃) enriched with ⁶Li, is the most promising candidate for solid test blanket module (TBM) material for fusion reactors. Various processes are reported in literature for the fabrication of Li₂TiO₃ pebbles for its use as TBM material. A process has been developed based on the solid state reaction of lithium-carbonate and titanium-dioxide for the synthesis of lithium titanate and pebble fabrication by extrusion, spherodization and sintering. This paper discusses the sequence of steps followed in this process and the properties obtained. Analytical grade titanium-dioxide and lithium-carbonate were taken in stoichiometric ratio and were milled to ensure thorough intimate mixing and obtain fine particles less than 45 μm before its calcination at 900 °C. Following calcination, the agglomerated product was again milled to fine particles of size less than 45 μm. Aqueous solution of ploy-vinyl-alcohol was added as binder prior to its feeding in the extruder. The extruded strips were spherodized and spherical pebbles were dried and sintered at 900 °C for different duration. Pebbles of desired density and porosity were obtained by suitable combination of sintering temperature and duration of sintering. Properties of the prepared pebbles were also characterized for sphericity, pore size distribution, grain size, crushing load strength, etc. The values were found to be conforming to the desired properties for use as solid breeder. The attractive feature of this process is almost no waste generation.