| Fusion energy is an significant way to solve energy issue due to its merits of clean,safety and renewability,and it has been recognized as one of the leading forms of energy in the future.As the core functional materials to produce the tritium of the tritium breeding blanket in a fusion reactor,the selection of the breeding materials is very important.Lithium-based ceramics are considered as promising tritium breeding materials for their inherent thermal stability and chemical inertness.The functions of solid tritium breeders are tritium breeding and energy conversion in the fusion reactor,so they must meet the requirements of high lithium density,high thermal conductivity,high melting point,low tritium retention,high neutron irradiation,low activation and good material compatibility,and so on.However,all of the existing solid tritium breeders can not meet all requirements perfectly.Therefore,the studies on improving the characterization of the existing solid tritium breeders have aroused widely attention.A lot of modification studies have been carried out abroad,but there is still a lack of the related study in China.In view of this,the purpose of this study is to develop some new solid tritium breeders which possess better properties than the existing solid tritium breeder materials.Li4SiO4 has been selected as the first candidate in China's TBM.To improve its thermal conductivity and mechanical property,titanium element,which has the same charge and a longer atomic radius,was chosen to replace the silicon in Li4SiO4.The fabrication and characterization of Ti doped Li4SiO4(Li4Si1-xTiO4)were studied.LiOH·H2O,SiO2 and anatase(TiO2)were used as the raw materials to synthesize the powder of Li4Si1-xTixO4 by the solid state reaction method.And,the pebbles were fabricated using the melting spray and freeze drying method.Compared with the melting method,the freeze drying method was more convenient to control the diameter of the pebbles,and the size distribution of Li4Si1-xTixO4 pebbles prepared were narrower.Besides,inert gas He was necessary to maintain the phase purity of Li4Si1-xTixO4 pebbles during the sintering process.The morphology,structure,thermal conductivity and mechanical properties of Li4Si1-xTixO4 pebbles were characterized by the way of X-ray diffraction(XRD),SEM-EDS,Micro Flash Analyzer and the universal testing machine.The Li4Si1-xTixO4 pebbles prepared by freeze drying method had a diameter of 1.03 mm,good sphericity of 1.04,density of 84%T.D.and porous structure.Moreover,the thermal conductivity of Li4SiO4 with 20%and 30%Ti adopted were significantly improved,and the mechanical properties of Li4Si1-xTiO4 pebbles,which were sintered at 1000?,were obviously better than that of Li4SiO4.Additionally,Li2O has great potential to be a tritium breeding material fort its high lithium density,high thermal conductivity and melting point.This woks also explored the preparation process of Li2O pebbles by the freeze drying method.To improve its stability,a layer of SiO2 was coated on the surface of Li2O pebbles by Vacuum Magnetron Sputtering,Li2O pebbles were obtained by the thermal decomposition of Li2CO3 green spheres which were fabricated by freeze drying method.The calcination temperature for removing PVA in the gel-spheres was 650?.The Li2CO3 green spheres were heated in vacuum and then transformed to Li2O pebbles.The thermal decomposition temperature was decided at 720 ?.The sintering temperature of Li2O pebbles should not be higher than 900 ?.It is found that the water absorption rate of Li2O-TiO2 core-shell ceramic pebbles is slowed down,and its stability is obviously improved by the comparison test of water vapor adsorption. |
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