Synthesis Of ?-Li₂TiO₃ With Well-developed Supercell Structure Via Supercritical Hydrothermal Method

?-Li₂TiO₃ has become a spotlight in the research of solid tritium breeding materials due to many special performances,such as high density of lithium atom,higher chemical stability and higher thermal conductivity,lower temperature zone?200 400 °C?,lower activation characteristics and lower tritium solubility better compatibility with the structural materials,excellent tritium release characteristics at lower temperature.?-Li₂TiO₃ has supercell structure with an ordered rocksalt structure,and it occupied by Li layers and LiTi2 layers.The pure Li layers are considered as the channel for tritium release,corresponding to the?002?supercell lattice plane.Well developed supercell structure and reasonable sintering density of the pebbles are two important factors to increase the tritium breeding performance.Therefore,the smaller size,better distribution of mean particle size of ?-Li₂TiO₃ particles,and reasonable density of tritium breeder ?-Li₂TiO₃ pebbles are more appropriate for the international thermonuclear experimental reactor.The performance and application effect of tritium breeding is closely related to the preparation process.Its performance is affected by various processing conditions,which can be optimized by improving the various process parameters.Meanwhile,the practicability and economy of preparation plant should also be taken into account.The stability of ?-Li₂TiO₃ supercell structure can be obtained under reasonable synthesis conditions.In this thesis,the ?-Li₂TiO₃ particles were synthesized by supercritical hydrothermal method.The higher solvent diffusion coefficient,the greatly density and the stable structure of ?-Li₂TiO₃ were achieved by optimization of the supercritical hydrothermal synthesis parameters.The hydrothermal processing parameters of ?-Li₂TiO₃ matrix particles were optimized by the orthogonal experimental design.The ?-Li₂TiO₃ particles were synthesized via sub-and supercritical hydrothermal reaction.XRD,FE-SEM,TEM and Raman spectroscopy measurements were used to evaluate the properties of the particles.The effects of various related process factors on the upgrowth/growth of ?-Li₂TiO₃ cells were studied.The formation mechanism and kinetics of formation of ?-Li₂TiO₃ were also studied.The main conclusions are as follows:?1?The hydrothermal processing parameters of ?-Li₂TiO₃ matrix particles are optimized by the orthogonal experimental design.The significant order of the value of I?002?/I?133?and grain size on the properties of ?-Li₂TiO₃ particles is as: hydrothermal reaction time > hydrothermal temperature > Li+ concentration >packing ratio.?2?The influence of hydrothermal temperature and hydrothermal reaction time on the properties of ?-Li₂TiO₃ particles is significant.When the hydrothermal reaction time is 10 h,the ?-Li₂ Ti O₃ powder with good performance could be obtained.With the increase of hydrothermal temperature,the value of I?002?/I?133?of ?-Li₂ Ti O₃ powder and particle uniformity increased.However,the average grain size increased when the temperature is higher than 375 °C.The optimized parameters for both well-developed ?-Li₂TiO₃ supercell and smaller ?-Li₂TiO₃ grain size are determined as: the hydrothermal temperature of 375 °C;the hydrothermal reaction time for 10 h;the Li+ concentration of 0.2 mol/L;and the packing ratio of 50 %.?3?The pure Li layer of the ?-Li₂TiO₃ hydrothermal precursor was found to have Li vacancies and the substitution of Ti atoms to Li atoms.The Ti atoms in the pure Li layer of the ?-Li₂TiO₃ powder obtained from the heat after the ordinary hydrothermal conditions and in supercritical hydrothermal conditions leave the pure Li layer,and enter into the LiTi2 layer.And the crystal lattice structure is fully developed.?4?The influence of hydrothermal temperature,hydrothermal reaction time,Li+ concentration and the packing ratio on the vibration peak intensity of the ?-Li₂TiO₃ powder was determined by Raman spectroscopy.In the optimization of the packing ratio and Li+ concentration,using Origin to calculate the relative integral strength of the?002?crystal face diffraction peak with temperature and reaction time,we found when hydrothermal reaction time was 10 h at 375 °C,the growth of ?-Li₂TiO₃ powder was better than that of 400 °C.?5?The ?-Li₂ Ti O₃ pebbles with a better sphericity of 1.01,a mean diameter of 1.81 mm and I?002?/I?133?of 2.25 are fabricated by a indirect chemical method with ?-Li₂TiO₃ particles synthesized via supercritical hydrothermal method.And the fabricated pebbles can be used for solid tritium breeding materials.