Preparation And Characterization Of Carbon Nanocoils/Graphite Composite With High Thermal Conductivity

With the rapid development of science and technology, the developed ofmaterials with high thermal conductivity and heat dissipation has become animportant materials basis in the thermal management system. Carbon materials withhigh thermal conductivity as thermal management materials have been widely used inelectronics and aerospace fields.In this work, we introduced carbon nanocoils (CNCs) between the layers ofexpanded graphite (EG) by chemical vapor deposition (CVD), and then a series ofCNC-GT blocks with high thermal conductivity and resilience were made by ahot-pressing equipment at high temperature and pressure environment. We studied theeffects of catalyst loading, growth time and growth conditions on morphology ofCNCs on or between EG layers, meanwhile, we also studied the effects of themorphology of CNCs, pressing time and pressing pressure on the thermalconductivity in the in-plane direction (λ∥) and in the cross-plane direction (λ⊥) ofCNC-GT block and the resilience of CNC-GT block.The results showed that the iron and nickel catalysts could be loaded between thelayers of EG effectively by vacuum impregnation process, and when the growthtemperature was800℃and mixed gas atmosphere was C2H2=65sccm, H2=200sccm,Ar=75sccm, the vertical CNCs could be obtained between EG layers. The resultsshowed that when the growth time was120minutes, the CNCs could evenlydistributed between the EG layers and the orientation perpendicular to the graphitesurface is clear. Meanwhile, the density of CNCs growing on EG was increased whenthe growth time was prolonged, and with the increase of hot-pressing pressure, thedensity of CNC-GT block was increased and the porosity of CNC-GT block wasdecreased. The results showed that the λ⊥of CNC-GT block was increased with theincrease of growth time and hot-pressing pressure, and the λ⊥of CNC-GT block wasmuch higher than GT block without CNCs, meanwhile, the λ∥was slightly decreased.The λ⊥of CNC-GT block could reach up to23.6W/(m·K) which was5times higherthan that of GT block when the growth time was120minutes, the pressure was40MPa and the temperature was1600℃, while the λ∥of the CNC-GT block could bestill maintained a high value of284.1W/(m·K). Results also showed that theresilience ratio of CNC-GT block was increased with the increasing growth time, themaximum value could up to84.1%which was10.2%higher than GT block, and the compressibility of CNC-GT block was decreased with the increasing growth time, theminimum value could up to17%which was3.1%lower than GT block. Thus theCNC-GT block with high thermal conduction and high resilience could be applied inelectronic devices as flexible shim.