摘要: Three-dimensional (3D) graphene networks have aroused great interest because they effectively solve the agglomeration problem of graphene powder and improve its utilization efficiency. Such a material also has the advantages of a porous structure, lightweight, high thermal conductivity and superior electrical conductivity, and is widely used in thermal management and electromagnetic interference shielding. To fully understand 3D graphene networks, we summarize the different preparation strategies and properties of isotropic and anisotropic 3D graphene networks. The latest research progress of thermal interface materials, phase change materials, electromagnetic interference shielding materials and microwave absorbing materials is reviewed. Finally, the development and outlook for 3D graphene networks are proposed. This review provides new perspectives and research directions for the future development of 3D graphene networks in heat dissipation and electromagnetic interference shielding for 5G electronic devices.
摘要: The development of modern technology has posed greater and more urgent needs for thermal management materials. Aligned carbon nanotube arrays and carbon/carbon composites have aroused extensive interest as ideal lightweight and stable thermal management materials because of their low thermal expansion coefficient, excellent thermal conduction and high-temperature resistance. Here, we first review the thermal conducting mechanism of carbon materials. We then describe the general fabrication methods, the main factors affecting the thermal conductivity of aligned carbon nanotube arrays and carbon/carbon composites as well as their use in thermal management. The preparation-structure-performance relationships are outlined and the strategies for achieving high thermal conductivity are summarized. Finally, a critical consideration of the challenges and prospects in the thermal management applications of aligned carbon nanotubes and carbon/carbon composites is given.
摘要: Graphene, because of its outstanding thermal and electrical conductivity, has been regarded as one of the promising materials for heat dissipation and electromagnetic shielding, and has recently attracted widespread attention. We summarize the current research status of reduced graphene oxide films, graphene films and graphene-based composite films for thermal management, including their preparation and applications. The key factors that determine the thermal conductivity of graphene films are discussed to figure out the main challenges, especially in the scalable manufacture of graphene-based films in the near future.
摘要: As the power consumption and heat generation of electronic devices continue to increase, higher demands are being placed on thermal management materials for heat dissipation. Graphene has been widely used as a thermally conductive filler to improve the thermal conductivity of polymers. However, the poor dispersibility of graphene nanoplates in polymers dramatically limits their practical use in thermal management. A promising strategy to increase the thermal conductivity of polymer composites is to construct interconnected three-dimensional graphene networks. This review summarizes the recent advances in the construction and applications of three-dimensional graphene-based polymer composites and ways to improve their thermal conductivity. The current challenges and prospects for the preparation and applications of these materials are considered.
摘要: Accumulated heat is the primary problem that needs to be solved in current electronic products. There is an urgent need for designing innovative high-performance thermal interface materials (TIMs) with excellent heat dissipation performance. Based on the development status of TIMs, graphene paper-based TIMs that are ultrathin thickness and have high through-plane thermal conductivity show great potential. From this perspective, we introduce four types of graphene paper (including graphene/polymer composite papers, graphene/metal composite papers, graphene/ceramic composite paper, and graphene/carbon composite paper) and vertically aligned graphene paper as TIMs. Based on the applications of these TIMs, their advantages and limitations are discussed. Finally further research prospects are proposed to promote the practical applications of graphene paper-based TIMs.
摘要: Aromatic polyimide (PI)-based graphite nanofibers were obtained from the graphitization of graphene oxide (GO)-doped electrospun PI nanofibers. GO improves the PI molecular orientation, crystalline structure and thermal conductivity of the resulting nanofibers. The degree of PI molecular orientation in the nanofibers is increased by the GO during fiber preparation. This improvement in molecular orientation produces an increase in the thermal conductivity of the graphite nanofibers, and the addition of only 0.1% GO has a significant effect. The GO not only affects the thermal conductivity, but improves the PI molecular orientation and its role as nucleation centers during graphitization. This approach and the resulting high thermal conductivity materials show great potential for practical applications.
摘要: Thermal management has attracted much recent attention due to the rapid development of 5G communication and electronic devices. Reduced GO/polyimide carbon (rGO/PI-carbon) films were prepared by a one-pot“grafting-welding” strategy, where GO was first grafted with amino groups using 1,3-bis(4-aminophenoxy) benzene, then polymerized with polyamic acid (PAA) and pyromellitic dianhydride to connect the GO sheets, before carbonization and graphitization. The rGO/PI film with a mass ratio of GO to PAA of 7% exhibits an increase in in-plane thermal conductivity (1 102 W(m·K)−1) of 48.92% compared with the rGO film. It also has a superior bending performance and survives 2 000 bend cycles with a small radius test while suffering an electrical resistance increase of less than 10%. Grafting-welding of rGO with PI carbon produces effective paths for phonon transport between the graphene sheets, reducing phonon scattering, which makes it a candidate for thermal interface materials for heat dissipation.
摘要: Multi-wall carbon nanotubes (CNTs) were modified by nano-TiC using a pressureless spark plasma sintering technology. The TiC-modified CNTs (T-CNTs) were added to mesocarbon microbeads (MCMBs) to prepare high performance isostatically pressed graphite materials. The structures of the T-CNTs and the prepared isotropic graphite materials were characterized by XRD, SEM and TEM. The mechanical and thermal properties of isotropic graphite reinforced by T-CNTs were measured by a micro-controlled electronic universal testing machine, laser thermal conductivity meter and thermal expansion coefficient meter. Results showed that the nano-TiC was successfully grown on the surface of CNTs. Compared with the isotropic graphite prepared from MCMBs without T-CNTs, the isotropic graphite with T-CNTs has a significant improvement in physical properties (density, open porosity and volume shrinkage). Its flexural strength and degree of graphitization increased by 70% and 10%, respectively, and the thermal properties were also improved to some degree.
摘要: 将环氧树脂（EP）分别涂敷于聚酰亚胺石墨带（GPTs）和聚酰亚胺石墨膜（GPFs），通过真空热压成型与分别采用堆叠和叠层方法制备得到GPTs/EP复合材料和GPFs/EP复合材料。借助 XRD、SEM和PLM等手段对GPF及其环氧树脂基复合材料的晶体结构、形貌和光学织构进行表征，并研究GPF的体积分数和尺寸对其复合材料导热性能的影响。结果表明，相比于GPFs/EP复合材料，GPTs/EP复合材料的导热性能在不同方向显示出较大波动，其热导率和热扩散系数总体上随GPF体积分数的增加而增大，GPF体积分数为80%时热导率为453~615 W (m·K)−1。而对应的 80 % GPFs/EP复合材料热导率稳定可达894 W (m·K)−1，并具有高取向的“三明治”结构。但在平行于热压方向上两类复合材料热导率都很低，GPF体积分数为80%时，GPTs/EP复合材料和GPFs/EP复合材料的热导率分别为1.82 W (m·K)−1和1.15 W (m·K)−1。
摘要: The microstructural characteristics of high thermal conductivity mesophase pitch-based carbon fibers were investigated by XRD, Raman spectroscopy, SEM and TEM. The relationship between microstructural characteristics and thermal conductivity is discussed. Results show that the radial structure is always accompanied by a splitting stucture. La has more significant impact on the thermal conductivity than Lc. The Raman spectroscopy ID/IG value of the cross section was used as an essential index to evaluate the thermal conductivity of the carbon fibers. The microstructural characteristics including large graphite crystallite size, high preferred orientation along the fiber axis, and few defects contribute to the high thermal conductivity of the carbon fibers.
摘要: The matrix graphite (MG) of pebble fuel elements for a High Temperature Gas-cooled Reactor (HTGR), composed of 71wt% natural graphite, 18 wt% artificial graphite and 11 wt% phenolic resin-derived carbon, was purified by high temperature treatment (HTT), and its properties and microstructure were analyzed to investigate the effect of different HTT temperatures and optimize the purification temperature. Results showed that with increasing HTT temperature, its density and thermal conductivity gradually increased, but pore size and d002 gradually decreased. The rate of erosion caused by friction as the fuel pebbles move in the reactor also decreased. The ash content decreased significantly from to 18.2 to 12.3×10−6 after HTT at 1 600 ℃, but changed little when the HTT temperature was further increased to 1 900 ℃, especially for catalytic metals such as Fe, Ni and Ca that are related to its corrosion rate. The microstructure improvement and ash content reduction at high temperatures jointly contributed to the increase in the anti-corrosion performance of MG. Based on properties such as crushing strength, erosion resistance, and corrosion rate, a HTT of 1 600 ℃ is adequate although the MG gradually became more ordered with a further increase of HTT temperature from 1 600 to 1 900 ℃. This determination of an appropriate HTT temperature for the production of MG for the fuel elements of an HTGR should improve the production efficiency and reduce the mass production cost of this material for a commercial HTGR.