基于高O/C原子比碳源热解制备高强韧石墨烯/热解碳原位复合材料研究

To develop thin-walled carbon/carbon composites (C/C) with high strength and excellent toughness used in next-generation high-tech aerospace equipment, it is important and necessary to reinforce pyrocarbon matrix using nanomaterials. In earlier studies, nanofibers have been used to reinforce and toughen pyrocarbon. However, nanofiber reinforced pyrocarbon always shows a large performance scatter and a great degradation of mechanical properties after a high-temperature treatment. To address the problem, theoretical work predicts that graphene is more beneficial to be used as nano-reinforcement due to its ultrahigh specific surface area, large surface-to-volume ratio and excellent mechanical property. However, due to the obvious technical defects for the doping of graphene in pyrocarbon, graphene materials are always unevenly distributed, entangled and weakly-bonded with pyrocarbon, showing a poor reinforcing role. In this project, based on the previous findings, i.e. a fast, simple, and easy-to-control method for scalable graphene growth can be developed via the pyrolysis of CH3OH with a large O/C atomic ratio, we present a novel method to prepare graphene/pyrocarbon in-situ composites by co-pyrolyzing CH3OH and other hydrocarbon gases such as CH4 and C3H8. This method is easy to realize the uniform compositing between graphene and pyrocarbon on macro and micro scales, which contributed to the formation of strongly-bonded nano-interfaces with large area and wide distribution. The nucleation and growth mechanism of graphene, co-pyrolyzing process, and the influence factors on the microstructure, morphology and orientation of graphene doped in the in-situ composites will be investigated. The general law of action between co-pyrolyzing processes and mircostructures and mechanical properties of graphene/pyrocarbon in-situ composites will be explored. Based on this, the performance controlling methods will be established and graphene/pyrocarbon composites with high strength and excellent toughness will be prepared. The present work will provide a meaningful way for the development of high-performance graphene reinforced C/C.

对热解碳基体实施纳米强韧化是发展高强韧薄壁碳/碳复合材料的重要途径。针对一维纳米纤维强韧热解碳研究中的瓶颈问题（界面高温退化、强韧效果不足），用石墨烯替代纳米纤维，利用其比表面积高、表面-体积比大的特性，构筑纳米增强体与热解碳共价强界面结构是潜在的解决方法。然而，现有复合技术易导致石墨烯分布不均匀、团聚、与热解碳界面结合弱等不足，大大降低了石墨烯的强韧效果。本项目基于前期发现，即高O/C原子比碳源（CH3OH）热解生成石墨烯的本性，创新提出将CH3OH与CH4、C3H8混合热解，利用各自的热解属性，实现石墨烯与热解碳同步共沉积、实现二者在跨尺度空间中的“无死角”均匀复合，构筑“尺度小、面积大、分布广、强结合”界面的新思路。系统研究石墨烯的形核与生长机理、混合热解过程、石墨烯取向与形性调控方法，揭示石墨烯与热解碳的原位复合过程、产物性能调控机制，制备出高性能的石墨烯/热解碳复合材料。

纳米增强是制备高性能薄壁C/C复合材料的有效途径，对推动空天飞行器跨代发展具有重要意义。针对常规一维纳米增强存在的均匀性控制难、高温易退化等问题，项目提出原位掺杂二维石墨烯纳米增强体，通过构筑“尺度小、面积大、分布广、强结合”界面，实现C/C强韧化的新思路。系统开展了高O/C原子比碳源的热解工艺规律、石墨烯原位掺杂结构与取向调控方法、石墨烯/热解碳界面的精细结构、石墨烯/热解碳原位复合材料力学性能与强韧机制等方面研究。发展了甲醇热解自生石墨烯，甲醇+甲烷和甲醇+乙醇混合热解制备三维互锁高强韧碳基体和高定向高导热碳基体，细观层状高强韧碳基体等新方法，实现了对C/C复合材料界面、基体等组元的不同方式强韧化，使C/C强度和韧性得到同步提升。项目的最重要发现是，混合热解体系中含氧自由基对PAHs中间态基团结构与尺寸的裁剪作用是影响石墨烯形核与生长行为，石墨烯面内形貌和空间分布取向的关键因素。这种裁剪作用受到含氧自由基种类和数量的影响，可通过改变热解体系中甲醇含量与热解程度加以调控。石墨烯纳米片在三维空间内随机取向分布（形成纳米互锁结构）对提高C/C强韧性至关重要。石墨烯掺杂取向可通过改变PAHs尺寸间接控制，可实现石墨烯在热解碳内部的各向同性掺杂或高度定向掺杂。项目提出了周期压应力层状强韧基体结构，建立了微观纳米强韧结构与细观力学单元之间的直接关联，对发展共性的强韧化方法具有重要意义。本项目研究内容作为重要支撑获教育部自然科学一等奖1项，指导成功研制了高导热薄壁散热翅片等构件，在核能、航天等领域获得验证应用。