细晶结构TiO2/Li4Si1-xTixO4陶瓷氚增殖剂高温稳定机理及离子辐照行为研究

Lithium orthosilicate is recognized as a good candidate for the solid tritium breeding materials due to its high lithium content, favorable tritium release behavior and low neutron activation behavior. It has been reported that fine-grained lithium-based ceramics have unique advantages in improving the mechanical property, tritium release performance and radiation resistance, whereas the grains of fine-grained single phase Li4SiO4 ceramics are more likely to grow, and thus resulting in the degradation of the performance. Considering that solid solution structure and second phase doping can improve the stability of high temperature structure. In this work, the lithium-based ceramics with the microstructure, namely Li4Si1-xTixO4 acts as substrate and TiO2 particles are added as the second phase, will be fabricated by combing modified hydrothermal method and two-step sintering or microwave sintering process. The microstructure is expected to improve the physical and chemical properties as well as high temperature stability. The evolution of the microstructure during high temperature and thermal cycle tests, as well as the resulting performance changes will be systematically discussed. The ion irradiation damage behavior of the ceramics with different microstructure will also be studied. The micro-mechanism of solute element and TiO2 particles will be revealed. The results can provide the theoretical and experimental basis for the modification of the microstructure and properties of solid tritium breeding materials.

正硅酸锂陶瓷因具有锂密度高、释氚性能优异以及中子活化率低等优点，成为固态氚增殖剂的首选材料之一。研究表明细晶结构锂陶瓷在提高氚增殖材料力学性能、释氚性能及抗辐照性能方面具有独特的优势，但实际工况下细晶的单相正硅酸锂陶瓷晶粒易长大，从而导致材料性能退化。本项目基于固溶体结构与第二相掺杂可改善陶瓷高温结构稳定性的思想，拟采用改进的水热法结合两步烧结/微波烧结技术，设计和制备具有“以Li4Si1-xTixO4固溶体为基体，TiO2颗粒为第二相粒子”微观组织特征的锂陶瓷，以同步提高细晶结构正硅酸锂陶瓷氚增殖剂的高温稳定性及物化性能，进而系统研究高温、热循环下陶瓷微观组织结构变化对性能的影响规律，以及不同微观组织结构特征陶瓷的离子辐照损伤行为，揭示溶质Ti与TiO2颗粒单独和耦合作用的微观机制。研究结果可为锂陶瓷氚增殖剂的结构和性能优化提供理论基础和实验依据。

作为氚增殖材料，锂陶瓷具有化学稳定性好、可在更高的温度下使用等优点。研究表明细晶结构锂陶瓷具有良好的释氚性能和抗辐照性能，但如何改善细晶结构锂陶瓷的高温稳定性是使其应用研究取得突破性进展的主要瓶颈。本项目通过在正硅酸锂基体中引入异质元素或掺杂氧化物纳米颗粒，设计和制备细晶结构正硅酸锂固溶体与第二相掺杂正硅酸锂陶瓷（TiO2/Li4SiO4、Li4Si1-xTixO4、Li4+xSi1-xAlxO4、La2O3/Li4+xSi1-xAlxO4），阐明了Li4Si1-xTixO4、Li4+xSi1-xAlxO4合成过程，以及异质元素与第二相颗粒对抑制陶瓷晶粒长大的作用；研究了纳米氧化物颗粒/异质元素掺杂对正硅酸锂陶瓷微观组织及性能（压碎载荷、比热、热扩散系数、热导率、离子电导率）的影响规律，揭示了异质元素与第二相颗粒对改善陶瓷各项性能的作用机理，确定了陶瓷各项性能合理匹配的最佳微观组织结构参数；热循环试验结果证实通过引入异质元素调整晶体内部变形量或通过在陶瓷基体中弥散分布氧化物纳米颗粒钉扎晶界，能够有效抑制陶瓷在烧结过程中及其在高温工况环境中的晶粒长大，从而改善正硅酸锂陶瓷高温稳定性；离子辐照试验结果表明通过细化晶粒提高晶界密度或在陶瓷基体中弥散分布第二相颗粒可减少辐照缺陷的产生、抑制陶瓷由晶相向非晶相的转化。