三维连通石墨烯/铝复合材料的界面调控及导热机制

High thermal conductivity materials are crucial to efficient heat dissipation of high power devices such as semiconductor laser, large-scale integrated circuit, and active phased array antenna. Since graphene has a super high thermal conductivity and aluminum is a widely used light metal, graphene/Al composite is expected to be an ideal candidate. However, the graphene/Al composite currently shows a very low thermal conductivity owing to the difficulty of dispersing graphene nanosheets to metal matrix and the large interfacial thermal resistance coming from a vast number of graphene/Al interfaces. In this proposal, Al matrix composite reinforced by a three-dimensional interconnecting graphene network is proposed to solve the above-mentioned problems. The graphene network provides a path for heat conduction, which is totally different from the traditional route of dispersing graphene nanosheets to metal matrix. The graphene/Al composites are produced by a gas pressure infiltration technique using graphene aerogels. The graphene/Al interface is modified by introducing a carbide layer that is derived from metal oxides loaded on graphene surfaces. The research is focused on three critical issues: (a) nucleation and growth mechanism of interfacial carbides at the nanoscale, (b) capillary phenomena between liquid aluminum and graphene voids, and (c) thermal conductive mechanism in Al matrix composite reinforced by a graphene network. The complement of the research will provide scientific basis for the thermal conductivity enhancement of the graphene/Al composites. The output of the research will not only open a new avenue for application of graphene to metal matrix composites, but also offer scientific guideline for investigations of graphene/polymer and graphene/ceramics composites.

高导热材料是解决半导体激光器、大规模集成电路、有源相控阵天线等高功率器件散热问题的关键，由于石墨烯具有超高热导率并且铝是广泛使用的轻质金属，石墨烯/铝复合材料是理想的导热材料。然而，由于石墨烯纳米片在金属基体中难以分散且石墨烯/铝界面过多而产生较大界面热阻，目前所报道石墨烯/铝复合材料热导率很低。有别于石墨烯纳米片在铝基体中均匀分散的传统方法，本项目利用石墨烯气凝胶通过气压浸渗制备三维连通石墨烯/铝复合材料，并在石墨烯表面负载金属氧化物引入碳化物界面层，利用石墨烯连通网络提供导热通道，有望大幅提高复合材料热导率。围绕纳米尺度下界面碳化物形核长大机制、铝液与石墨烯孔隙之间的毛细现象、三维连通石墨烯/铝复合材料导热机制等三个科学问题开展研究，为提高石墨烯/铝复合材料导热性能提供科学依据。本研究为石墨烯在金属基复合材料应用开辟新思路，并为石墨烯/聚合物、石墨烯/陶瓷复合材料提供理论参考。

随着功率密度急剧升高，散热问题成为制约电子器件性能发挥和服役寿命的重要因素，开发高导热电子封装材料是当前的研究热点。环氧树脂由于耐热温度高、黏合性能好、固化收缩小等诸多优点而在电子封装领域获得广泛应用，然而环氧树脂固有的低热导率已经难以应对电子器件的散热需求。具有优异导热性能的石墨烯作为导热填料有望提高环氧树脂的导热性能，然而由于石墨烯纳米片与环氧树脂基体界面过多、石墨烯构型非定向、石墨烯结构不完整等问题，石墨烯增强环氧树脂复合材料的导热性能与预期值存在很大差距，远未体现石墨烯的高导热特性。为了开发高导热石墨烯/环氧树脂复合材料，本项目将纳米尺度的石墨烯组装成宏观尺度的石墨烯气凝胶，经过高温退火处理恢复石墨烯的结构和导热特性，再将环氧树脂熔渗至石墨烯气凝胶，在环氧树脂基体中形成石墨烯三维导热通路，在较低石墨烯填充量下大幅提高石墨烯/环氧树脂复合材料的热导率。通过调控石墨烯气凝胶的还原程度、孔径分布、空间构型、体积分数等，减少石墨烯/环氧树脂界面数量，克服导热通路的形成障碍，恢复石墨烯的高导热特性，从而提高石墨烯/环氧树脂复合材料的导热性能。所获热导率67.81W/mK是目前所报道石墨烯/环氧树脂复合材料的最高值，为高功率电子器件散热提供了理想的封装材料。研究结果阐明了石墨烯气凝胶孔径结构的调控机制和石墨烯/环氧树脂复合材料导热性能的提高机理，研究思路为石墨烯与其他高分子材料复合制备提供了有益参考。项目还开展了石墨烯/石蜡复合材料和石墨烯/铝复合材料的研究工作。发表论文11篇，申请专利3项，培养研究生7名。

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