Preparation And Microwave Absorption Properties Of Imidazole Organic Skeleton And Its Composites

At present,absorbing materials are widely used in civil and military fields.On the one hand,electromagnetic radiation has caused great troubles for people's production and life,not only endangering their health,but also causing serious damage to large-scale instruments and equipment;On the other hand,some military equipment also put forward more requirements for stealth.However,the current absorbing materials can't meet more and more requirements,so it is necessary to develop a microwave absorbing material that can satisfy the"thin,light,wide and strong".In this thesis,zinc-based zeolite imidazolide framework material?ZIF-8?was successfully prepared at room temperature.A core-shell iron/carbon?Fe/C?composite was prepared by carbonizing ZIF-8 and coating Fe₃O₄.The degree of carbonization of Fe/C can be controlled by different temperatures.Research shows that the Fe/C obtained after the introduction of Fe₃O₄ greatly improves the impedance matching characteristics of the composite of Fe₃O₄ particles and ZIF-8?Fe₃O₄@ZIF-8?.The obtained Fe/C-700 has a maximum reflection loss?RL?of-40 dB and an effective absorption bandwidth?RL<-10 dB?of 6.0 GHz?11.2 to 17.2 GHz?when the thickness is 1.5 mm.Then,the cubic structure of magnetic Fe₃O₄ nanoparticle carbon coating?Fe/NPC?was obtained by in-situ growth method by controlling the reaction conditions.The material not only maintains the advantages of low density of sample iron oxide nanoparticles and ZIF-8?IONP@ZIF-8?,but also maintains the defect of impedance mismatch of IONP@ZIF-8.Among them,when the matching thickness of sample Fe/NPC-800 is 1.8 mm,RL can reach 5.6 GHz?12.4-18 GHz?.Finally,in order to further explore the influence of the microstructure of the microwave absorbing material on the absorbing effect,we designed a composite structure of ZIF-8 coated hydroxy iron fiber.By in situ growth,carbonization is controlled to obtain iron fiber@ZIF-8,and then different temperatures are calcined under suitable conditions to obtain iron fiber and carbon composite.Studies have shown that the iron fiber and carbon composite material under the condition of 800degree calcination greatly improved the characteristics of the iron fiber@ZIF-8impedance matching.At a thickness of 2.0 mm,the effective absorption bandwidth is6.0 GHz?12.0-18.0 GHz?.The strongest absorption at a frequency of 7.9 GHz is-40dB at a thickness of 3 mm.In this thesis,light microwave absorbing materials are prepared based on metal-organic framework?MOFs?,which improves the defect of poor impedance matching characteristics of raw material ZIF-8 and improves the microwave absorbing characteristics of composite materials.It provides an effective reference value for further research on using metal-organic framework materials as microwave absorbing materials.