Study On Synthesis Process And Mechanism Of Tritium Breeding Materials Li₂TiO₃ By Microwave-assisted Solution Combustion

Li2TiO3 is considered to be one of the most promising solid tritium breeding materials because of its high melting point, high thermal conductivity, excellently tritium release performance, low activation energy under irradiation environment, excellent chemical stability, high lithium atom density, and good compatibility with structural material. The synthesis of tritium breeding materials Li2TiO3 has extensively taken researchers' attention.Solution combustion synthesis, which has the advantages of simple operation, low reaction temperature, high purity of product, and good chemical uniformity, is seen as a highly efficient and rapid method to prepare nano-oxide. But some disadvantages exist, such as large particle size, uneven distribution of particle size, difficulty in synthesis of some complex oxides in one step.According to the problems above, we combine microwave heating technology with solution combustion technology to prepare Li2TiO3 ceramics powders. Temperature fields of the precursor solution were numerical simulated. Effect of key technological parameter on phase composition and morphology of as-prepared Li2TiO3 ceramics powders was systematically investigated, and mechanism of microwave promoting and inducing combustion synthesis was detailed analysed. And the formation process of Li2TiO3 was also discussed. The main results of this study are listed as following.(1) Finite difference time domain me thod was adopted to numerical simulated the temperature field of precursor solution by microwave heating. The results show that microwave was volumetric and internal heating. The temperature field distribution in precursor solution was ball- like, and the central area temperature is higher with small temperature gradient.(2) Effect of key technological parameter on phase composition and morphology of as-prepared Li2TiO3 ceramics powders was systematically investigated. When microwave power was 1200 w, fuel ratio 1.5, the as-prepared Li2TiO3 ceramics powders were pure monoclonal crystal, with an average particle size of 4.63?m, grain size of 40 nm, fringe spacing of 0.475 nm, and a cube- like shape. When power was low(600 W), a small amount of LiNO3 and TiO2 coexisted in the product. When power was high(1500 W), the crystallinity was improved, appearing sintering phenomenon. Metal cation also had great influence on phase composition. When metal cation was 0.15mol/L, the as-prepared powder was pure phase. With metal cation increasing, t TiO2 and LiNO3 appeared in the product.(3) From the point of thermodynamics and dynamics, the mechanism of microwave promoting and inducing combustion synthesis was respectively detailed analysed. The results show that compared with traditional heating, the reaction activation energy reduced(? E/R = 625 K), but the reaction rate increased(ln(A) = 5.1 m2/s) by microwave heating. And with power improving, the heating time and reaction time was significantly shortened. In addition, microwave heating can effectively avoid the decomposition of urea, ensuring the follow-up reaction.(4) By analyzing the phase composition of products in different stages, the formation process of Li2TiO3 was also discussed.