仿植物细胞结构高取向石墨/AlN复合材料的界面约束及导热/热膨胀异向协同调控

Highly oriented graphite is one of the most promising thermal management materials at present. How to suppress the high thermal expansion perpendicular to layer direction while achieve the full potential of its ultrahigh thermal conductivity along layer direction is the challenging issue need to be clarified eagerly. In this project, inspired by the plant cell structure, we propose a novel idea for materials design by using the rigid ceramic skeleton cell wall to support the oriented flake-like graphite (GF) particles cytoplasm, which keeps the high thermal conductivity along layer direction of GF particles while using the effects of interfacial confinement of thermal expansion perpendicular to layer direction of GF particles by ceramic skeleton, to realize the coordinated adjustment of the thermal properties in different orientations. A new process of “surface coating-vacuum filtrating-hot pressing” has been developed for the preparation of oriented graphite/AlN composite (OGAC) with plant cell structure, which possesses many excellent properties, such as high thermal conductivity in the in-plane direction and low coefficient of thermal expansion (CTE) in the through-plane direction. In order to further reveal the natures of interfacial confinement and performance adjustment of OGAC, the relationship among fabrication process, microstructure and thermal conductivity/expansion properties will be systematically investigated. We focus on the influence of geometrical dimensions of AlN cell-wall, the microstructures and stresses of AlN/graphite interface on the thermal expansion property, and then the mechanism of interfacial confinement can be clarified. Moreover, the quantitative structure-activity relationship model of “microstructure-thermal properties” will be built, and the coordinated adjustment mechanism for the thermal conductivity and thermal expansion properties in different orientations will be disclosed. Finally, an optimization between the thermal conductivity and thermal expansion properties of the OGAC would be achieved. The project could provide a new approach to design and preparation of oriented ceramic composites with light weight and integrated structural/functional properties.

高取向石墨材料是最具前景的热管理材料之一，在发挥其片层方向超高导热的同时，如何抑制穿层方向高热膨胀是一挑战性难题。受植物细胞结构启发，本项目提出采用刚性陶瓷骨架（胞壁）约束支撑定向排列的片状石墨（胞质）的显微结构设计新思路，在保持石墨层向高导热的同时，借助胞壁的界面约束效应抑制石墨穿层方向热膨胀，以实现导热/热膨胀异向协同调控。通过表面包覆-真空抽滤-热压烧结新工艺制备层向高导热、穿层方向低膨胀的仿植物细胞结构高取向石墨/AlN复合材料。为了进一步揭示界面约束及性能调控的科学本质，项目拟在系统研究制备工艺-显微结构-热性能关联性基础上，重点考察AlN胞壁几何尺寸、AlN/石墨界面结构和应力状态对热膨胀的影响，揭示界面约束机理；着重构建材料“显微结构-热性能”构效关系，阐明热性能异向协同调控机制，最终实现性能跃升。项目成果可为新型轻质结构/功能一体化各向异性复合材料设计制备提供新思路和新方法。

高取向石墨材料是最具前景的热管理材料之一，在发挥其片层方向超高导热的同时，如何抑制穿层方向高热膨胀是一挑战性难题。受植物细胞结构的启发，本项目提出采用刚性陶瓷骨架（胞壁）约束支撑定向排列的片状石墨（胞质）的显微结构设计新思路，在保持石墨层向高导热的同时，借助胞壁的界面约束效应抑制石墨穿层方向热膨胀，以实现导热/热膨胀异向协同调控。为实现这一目标，本项目重点研究了仿植物细胞结构高取向石墨/AlN复合材料的制备工艺及显微结构调控机理、显微结构对热性能的影响规律及界面约束机理、以及“显微结构-热性能”构效关系的建立和导热/热膨胀的异向协同调控。首先，采用“球磨混合-真空抽滤-等离子活化烧结（PAS）”和“溶胶凝胶-碳热还原-PAS”的新工艺均成功出制备仿植物细胞结构高取向石墨/AlN复合材料，研究了AlN含量对复合材料力学和热物理性能的影响，阐明了三维连续AlN陶瓷骨架对石墨穿层方向的热膨胀约束机理。在此基础上，采用具有优异力学性能的碳纳米管（CNTs）作为增强相提高仿植物细胞结构高取向石墨/AlN复合材料的力学性能，研究了CNTs含量对复合材料力学和热物理性能的影响。此外，为提高陶瓷骨架增强相在石墨基体中的均匀性和连续性，也通过熔盐包覆工艺在片状石墨颗粒石墨表面分别包覆均匀的SiC、WC涂层，再结合PAS工艺成功制备出骨架均匀连续的SiC、WC增强高取向石墨复合材料。其中，所制备的仿植物细胞结构高取向石墨/AlN复合材料，其弯曲强度、层向热导率、穿层方向热膨胀系数分别为~80MPa、442 W∙m-1∙K-1和7×10-6 K-1左右，完全满足高功率器件用新型热管理材料的应用需求。本项目的研究结果也为新型轻质结构/功能一体化各向异性复合材料的设计制备提供了新思路和新方法。基于上述研究结果，已发表学术论文25篇，其中SCI论文23篇；申请国家发明专利7项，其中已授权4项；其它结果正在整理中。另外，本项目培养9名研究生，其中博士生3名，硕士生6名。