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Since 2014, the Key Laboratory of Carbon Materials of the Chinese Academy of Sciences has made important progress in the field of graphene flexible heat sinks. The 709 Group of the Shanxi Coal Chemistry Research Institute of the Chinese Academy of Sciences cooperated with the relevant team of Tsinghua University and the Institute of Metal Research of the Chinese Academy of Sciences, and successfully developed a high thermal conductivity graphene/carbon fiber flexible composite film based on the academic advantages of graphene and carbon fiber. Related results were announced on March 20th. It was published in "Advanced Functional Materials" (Adv. Func. Mater., 2014, 24: 4222-4228) and was selected as a magazine insert to focus on the report. At the same time, the 708 group of the Shanxi Coal Chemical Institute cooperated with the 709 group and systematically studied the evolution mechanism of the thermal conductivity of the graphene oxide film in the carbonization process, and obtained a high-performance thermal reduction graphene oxide film. Related results were published online on July 16th. "Journal of Materials Chemistry" (J. Mater. Chem. A, 2014, DOI: 10.1039/C4TA02693D).
Graphene is a single-layered carbon atom crystal with two-dimensional sp2 bonds and unlike three-dimensional materials, its low-dimensional structure can significantly reduce the boundary scattering of phonons at grain boundaries and give it a special phonon diffusion mode. Studies have shown that the thermal conductivity (K) of graphene at room temperature has exceeded the limit of bulk graphite (2000W/m•K), carbon nanotubes (3000~3500W/m•K), and diamond isotope isomorphs, reaching 5300W /m•K, far more than silver (429W/m•K) and copper (401W/m•K) and other metal materials. Excellent thermal and mechanical properties make graphene have great potential for thermal management, but these properties are based on the microscopic nanoscale and are difficult to use directly. Therefore, macroscopic assembly of nano-graphene to form a thin film material while maintaining its nano-effect is an important approach for the large-scale application of graphene.
In general, graphene oxide films increase in thermal conductivity after annealing but also become brittle and brittle. However, if one-dimensional carbon fiber is used as a structural reinforcement and two-dimensional graphene is used as a heat-conducting functional unit, a structure/function integrated carbon/carbon composite film can be constructed through self-assembly technology. This all-carbon film has a multi-stage structure similar to that of reinforced concrete, and its thickness is controllable between 10 and 200 μm. The thermal conductivity at room temperature is up to 977 W/m•K and the tensile strength exceeds 15 MPa. This study has solved the practical problem of the heat conduction of graphene and is a breakthrough in the field of graphene in Shanxi Coalification.
The thin film material is easily obtained with graphene oxide as a precursor, but this material needs heat treatment to recover its thermal/electrical conductivity. The results show that 1000oC is the key point of the film's performance torsion. The performance of the film is qualitatively changed at this point. The thermal conductivity of the film transitions quickly from 6.1W/m•K to 862.5W/m•K, and it is raised to 1043.5W at 1200oC. /m•K. This discovery not only solved the basic scientific problem of thermochemical conversion of graphene, but also provided the basis for the large-scale preparation of graphene thermal conductive film.
The graphene-based film can be used as a flexible heat-dissipating material to meet the heat dissipation requirements of high-power, high-integration systems such as LED lighting, computers, satellite circuits, laser weapons, and handheld terminal devices. These research results provide a new perspective for the design of structural/functional integrated carbon/carbon composites.
The research work was funded by the National Natural Science Youth Fund, the Knowledge Innovation Project Prospective Project of the Chinese Academy of Sciences, the Natural Science Foundation of Shanxi Province, and the first-class independent innovation base project of the Taiyuan Science and Technology Bureau.
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