ALD-assisted Synthesis Of Nano-carbon Matrix Composites And Their Microwave Absorbtion Properties

In order to accelerate the modernization of stealth technology,and solve the increasingly electromagnetic pollution,the design and development of highly efficient absorbing materials has become a hot issue in current research.Nano-carbon materials possess good conductivity,strong dielectric loss,low density,and excellent mechanical properties.Among many absorbing materials,they are the most promising functional material that can meet the strict requirements of"thin,light,wide,and strong"for absorbing materials.However,because of the too strong electrical conductivity,the incident electromagnetic waves are easily reflected on its surface,and cannot be attenuated.Adjusting the impedance matching of nano-carbon materials is still a challenge.In this paper,nano-carbon materials?carbon nanofiber and graphene?were modified based on the characteristics of three-dimensional conformality and controllability of ALD technology.Due to the optimized impedance matching and introduced multiple loss mechanisms,the microwave absorption performance of nano-carbon based absorbers was improved obviously.The main contents include:?1?In this work,we improved the microwave absorbtion performance of carbon fiber-based material by regulating their component.Based on ALD method,the CNF was pretreated by ozone to inprove the hydrophilicity.Then,the Mn O₂ nanoflakes was introduced on the surface of CNF through a hydrothermal process.Microwave absorbing test show that the dielectric constant of CNF was reduced effectively by the introduction of low-conductivity manganese oxide.In addition,the voids formed by manganese oxide nanosheets might benifical for improving the impedance matching of CNF@Mn O_x.Due to the best impedance matching,the CM2 sample obtained the best microwave absorption performance with the minimum RL value of-47.2 d B at a frequency of 9.4 GHz,and the maximum EAB of 5.0 GHz.?2?In this work,we improved the microwave absorbtion performance of graphene-based material by regulating the micro-structure.Three-dimensional structure of Ni@CNO/G and Ni@CNT/G were successfully synthesized by using ALD and CVD techniques.The particle size of Ni nanoparticles is a key factor in regulating the three-dimensional structure.Microwave absorbing test show that this two special structure both express outstanding microwave absorption property.Due to the excellent intrinsic loss capability,Ni@CNO/G obtained the best microwave absorption performance in the C-band,with a minimum RL value of-45.5 d B at 6.2GHz.For Ni@CNT/G 200,its EAB can cover approximately 75%of the test frequency in the coating thickness range of 1-5 mm.It can be ascribed to the good impedance matching.?3?In this work,we design and prepared a novel microwae absorbtion materials for application in the ocean.Ni Al-LDH ultra-thin nanosheets were grown in situ on the surface of graphene by using ALD technology and hydrothermal synthesis method.By controlling the number of Al₂O₃ deposition cycles to precisely control the content of Ni Al-LDH nanosheets,good impedance matching can be achieved.100 Ni Al-LDH/G exhibits excellent microwave absorption performance with the filler content of only 7 wt%.The minimum RL value is–41.5d B?obtained at 17.8 GHz?and the maximum EAB is 4.4 GHz.In addition,the electrochemical measurements show that the 7wt%Ni Al-LDH/G coating can provide long-term corrosion protection for carbon steel.Therefore,Ni Al-LDH/graphene composites can be used as effective anticorrosive wave absorbing materials.