Research On The Fabrication Technology Of Lithium-based Ceramic Breeder Materials

Thermonuclear fusion requires deuterium (D) and tritium (T) fuel. It is necessary to produce tritium artificially because there is no naturally tritium source available. All fusion reactors are equipped with tritium breeding blankets in order to meet the tritium requirements. Lithium-based ceramic tritium breeder is considered as the key function of the tritium breeding blanket. Development of advanced fabrication technology of ceramic breeder materials is of great significance for the progress of nuclear fusion. In this paper, the synthesis process of ceramic powders and the fabrication technology of ceramic pebbles based on Li2TiO3and Li4Si04were researched systematically. And on this basis, two advanced tritium breeding materials, Li2Ti03core-shell pebbles with added lithium and Li2TiO3-Li4SiO4composite ceramic breeders, have been studied. The preparation technology and performance of these two materials were carried out.The main results were summarized as follows:(1) The performance of Li2TiO3and Li4SiO4powders obtained by solid-state reaction method was mainly influenced by calcinations temperature. The optimal calcinations temperatures for Li2TiO3and Li4SiO4were800℃and708℃, respectively. The performance of Li2TiO3and Li4SiO4powders prepared by combustion synthesis method was mainly influenced by the ratio of fuel to oxidizer. The optimized ratio for Li2TiO3was1.2. Corresponding, the as-prepared Li2TiO3powder had largest surface area (9.61m2/g) and a nano grain size (about50nm). Meanwhile, the optimized ratio for Li4SiO4was1.4. Corresponding, the as-prepared Li4Si04powder had largest surface area (5.27m2/g) and fine grain size (<0.5μm). The sintering activity of combustion synthesis powders was obviously higher than that of the solid-state reaction powders, and the best sintering temperature of combustion synthesis powders could reduce100-200℃.(2) Li2TiO3pebbles were fabricated by wet process based on gel-casting technology. When the dispersant dosage was0.6%and ball milled2h, Li2TiO3ceramic slurry had the best fluidity and stability. The curing time of slurry was mainly influenced by temperature and the dosage of initiator and catalyst. When the dosage of initiator and catalyst was0.3%and0.1%, respectively, the slurry solidified rapidly in the medium at high temperature and remained stable for a long time at room temperature. The best sintering temperature of Li2TiO3pebbles was different according to the performance of powder. The best sintering temperature for Li2TiO3pebbles prepared using solid-state reaction powder and combustion synthesis powder was1100℃and1050℃, respectively. The as-prepared Li2TiO3pebbles had good sphericity and uniform size distribution. The relative density of pebbles was higher than80%and the average crush load of pebbles was greater than30N.(3) A new kind of ceramic pebble fabrication process named as graphite bed method was developed. The solid content of slurry was the main influence factor on sphericity by graphite bed method. For Li2TiO3pebbles preparation, the best solid content was45wt%. Li2TiO3pebbles sintered at1100℃had the best performance. The relative density of pebbles was87%with grain size ranged from2to10μm, and the average crush load was50N. The performance of Li4SiO4pebbles was highly affected by raw materials. Li4Si04pebbles using Li2CO3and SiO2as raw materials had more uniform and dense structure than which using Li4SiO4as raw material. After sintered at950℃, the relative density of Li4SiO4pebbles using Li2CO3and SiO2as raw materials was87%with grain size ranged from2to9μm, and the average crush load was36N.(4) The reprocessing of Li2TiO3pebbles was investigated by graphite bed method for the purpose of reuse burned Li2TiO3pebbles. It’s demonstrated that Li2TiO3pebbles can be reprocessed by graphite bed method without performance degradation. Most properties of the reprocessed pebbles, such as density, crush load, grain size and porosity, was similar as that of the reference pebbles.(5) Li2TiO3core-shell pebbles with added lithium have been proposed and prepared. The shell thickness of Li2TiO3core-shell pebbles can be controlled precisely by manipulating washing time. When washing20seconds, the shell thickness was100μm. The fabricated pebbles exhibited heterogeneous structure with a Li2TiO3-Li4Ti04complex phase core and a pure Li2TiO3shell. The core-shell pebbles have the advantages of high lithium density and good physicochemical stability. The optimal sintering temperature was950℃from the consideration of microstructure and crush load. The structure and crush load of the pebbles was also influenced by Li/Ti ratio. When the Li/Ti ratio was lower than2.7, the pebbles had high crush load and fine microstructure.(6) Li2TiO3-Li4Si04composite ceramic breeders have been prepared. Li2TiO3-Li4Si04composites ceramics had good compatibility, and Li2TiO3did not react with Li4Si04. When lithium atoms losses occurred, lithium atoms would migrate from Li4SiO4to Li2TiO3. During the sintering process of Li2Ti03-Li4Si04composites ceramic pebbles, LiSiO4promoted its densification, while Li2TiO3refined grains and adjusted porosity. Composites ceramic pebbles had superior performance than single-phase ceramic pebbles. When the ratio of Li2TiO3and Li4SiO4was1:1, composites ceramic pebbles displayed high relative density (85%), good crush load (76N) and fine grain size (<5μm) after sintered at1050℃,...