高导热氮化硅陶瓷反应挥发液相烧结及晶内晶间纯化机制

Si3N4 ceramics are expected as the next-generation insulating substrate materials for high-power electronic devices due to the properties combining structure and thermal performance. It has become the hit research area in the world. However, it is still the question that the promotion of thermal conductivity of Si3N4 ceramics needs a long time sintering at high temperature in high pressure N2 atmosphere. In this project, we design the high temperature liquid phase with the properties of high oxygen affine, low viscosity, and reaction-volatilization via the addition of LiF and RE2O3 compound additives. The movement of impurity oxygen can be controlled from intar- to inter-granular, and finally, remove from sintering system by volatilization. For the reason above, the purification of intar- and inter-granular canbe promoted, and the high thermal conductivity can be reached via sintering at lower temperature with shorter time. In this project, the mechanical of reaction-volatilization in Li-F-Si-O-RE-N liquid phase，the choice of RE with high oxygen affinity, the purification of grains via reaction-volatilization solution-precipitation process and the volatilization of the intergranular phase will be researched. The key scientific problems of oxygen distribution in liquid/crystal phase via reaction-volatilization solution-precipitation process, and the role of volatilization liquid phase on intergranular structure evolution and intergranular phase remove will be solved. The aims of this project are to illuminate the mechanism of intra- and inter-granular purification in reaction-volatilization liquid phase sintering process, and to construct a new green efficient preparation technology for high thermal conductivity Si3N4 ceramics.

高导热Si3N4陶瓷作为热/力结构功能一体化材料有望成为新一代绝缘基板材料，近年来成为国内外研究热点，然而其高热导率仍然需要通过高温高氮压下长时间烧结才能获得。为此，本项目提出采用LiF和稀土氧化物复合助剂获得具有反应挥发特性的高亲氧低粘度液相，控制杂质氧从晶内移至晶间并通过反应挥发移出烧结系统，从而加速晶内和晶间纯化过程，达到高导热Si3N4陶瓷低温短时间制备的目的。本项目通过对含Li、F液相的反应挥发机制，高亲氧稀土离子的选择，反应挥发条件下的溶解-析出纯化过程和晶间相移除过程的研究，力图解决溶解-析出纯化过程中氧在液相/晶相中的分配，可挥发液相在晶间结构演化中的作用及去除等关键科学问题，阐明反应挥发液相烧结过程中晶内晶间纯化机制，建立绿色高效的高热导Si3N4陶瓷制备新工艺，从而获得综合性能优异的高导热Si3N4陶瓷。

高导热氮化硅陶瓷作为热/力结构功能一体化材料有望成为新一代绝缘基板材料，近年来成为国内外研究热点，但存在高导热氮化硅陶瓷制备烧结温度高、烧结时间长，不利于生产实际的主要问题。因此，研究高导热氮化硅陶瓷的低温短时间制备具有重要的应用意义和学术价值。本研究采用LiF-Y2O3、Li2O-Y2O3两种复合助剂，在空气环境下利用无压烧结在1650oC制备了高密度的氮化硅陶瓷，确定了空气条件下低温烧结氮化硅陶瓷的方法和最佳Li-Y比例。利用热压烧结技术制备了完全致密的氮化硅陶瓷，确定了挥发性液相烧结工艺，探明了LiF和Li2O在氮化硅烧结致密化过程，相变过程，微观结构演化和力/热性能演化中的作用。本项目所取得的成果，对于理解挥发性液相烧结过程，探索低温快速制备高导热氮化硅陶瓷具有重要的应用价值和科学意义。