Preparation And Properties Of Fe-based Electromagnetic Absorbing Composites With Thermal Conductivity

With the development of the military in the 40s,the military stealth concept developed,with the expansion of stealth concept,absorbing stealth has become one of the important indicators of weapons and equipment.At the same time,with the rapid development of modern science and technology,all kinds of electrical,communication and electronic equipment application of electromagnetic radiation pollution has become a new pollution source,inhibit and eliminate electromagnetic hazards become one of the current research hotspot.As a kind of functional material that can inhibit and eliminate electromagnetic wave energy,wave absorbing material not only shines brilliantly in military electromagnetic stealth,but also develops rapidly in the fields of civil electromagnetic compatibility.With the rapid development of science and technology and nano engineering,the performance of electromagnetic absorbing materials put forward a more comprehensive and higher quality requirements.Absorbing materials is no longer satisfied with the characteristics of"thin,light,wide,strong",but the different requirements for complex application scenarios,such as complex weather resistance,corrosion resistance,high thermal conductivity,high temperature environment.Absorption materials more and more requirements compatible with various properties,its application field will be in the direction of"compatibility,compound".In recent years,the integration and power of precision electronic equipment are increasing,and the density in the system is more and more,and many waste heat will be formed in the operation of the equipment.Because of the poor air circulation and narrow space in the electronic device,not only the electromagnetic wave environment is complex,but also the waste heat is difficult to radiate/transmit to the external environment in time,which will cause the temperature of the device to rise,and the equipment performance is reduced more seriously and may be damaged.Therefore,it is one of the hot research directions of wave absorbing materials to meet the thermal conductivity.When there are many influencing factors for the absorption and thermal conductivity of composite materials and different factors,this study comprehensively analyzes the influence of various factors on the performance of composite materials by studying the structural parameters of thermal conductivity,components and forming process of fmaterials.Based on the principle of thermal conductivity and dielectric regulation,this study carried out the preparation of thermal absorption composites and dielectric regulation mechanism of thermal conductivity,carried out research on Fe-based thermal absorption composites,and obtained the regulation methods and mechanisms of thermal conductivity and wave absorption with practical guiding significance.In terms of thermal conductivity,the influence of thermal packing modification on the absorption and thermal conductivity of the dielectric regulation,the self-composite treatment process is adopted to improve the dielectric matching of the absorption material and improve the absorption performance.The specific work is as follows:（1）Through vibrating small ball mill,using mechanical alloying method,melt Al N on the surface of Si C particles to enhance the binding of particles in the double ceramic powder,and then the prepared double ceramic components Al N-Si C doped with CIP to obtain Al N-Si C/CIP conductive thermal absorption composite material.When the material thickness is 1.5mm,the CIP+15 wt%has the best Al N-Si C composite,with a band width of 4.2GHz beyond-5 d B,and the extreme reflection loss obtained at 3.9GHz of-9.4d B.Compared with the pure CIP of the undoped thermal conductivity filler,the absorption performance loss is very small,but the thermal conductivity is greatly improved.At this time,the thermal conductivity of the thermal absorption composite is 3.405W/（m·K）,which is 37.3%higher than that of pure CIP.（2）Treat the boron nitride（BN）and silicon carbide whiskers（Si Cw）with KH560 and KH550,respectively,to obtain NH₂-Si Cw and Epoxy-BN.The two were combined to form a new dual-ceramic Si Cw-BN thermal filler,and then the prepared two-ceramic component Si Cw-BN was doped with CIP by ultrasound to obtain Si Cw-BN/CIP thermal absorption composites.When the material thickness is 1.5mm,the CIP+5 wt%Si Cw-BN composite has the best absorption performance.The extreme value of reflection loss obtained at 2.8GHz is-10.3d B,and the absorption bandwidth over-5 d B is 3.8GHz.Compared with the pure CIP of the undoped thermal conductivity filler,the absorption performance loss is very small,but the thermal conductivity is greatly improved.At this time,the thermal conductivity of the thermal absorption composite material is 3.042W/（m·K）,which is 22.7%higher than that of the pure CIP.（3）The nano-nitride（n BN）and Al N were modified by dopamine hydrochloride and KH560 to obtain the nano-nitride-coated thermal ceramic filler,and then the double ceramic component n BN-Al N was doped with CIP to obtain n BN-Al N/CIP conductive thermal absorption composite material.At a material thickness of 1.5mm,the CIP+5 wt%n BN-Al N composite shows the best absorption characteristics,the extreme value of reflection loss at 2.6GHz is-10.1d B,and the absorption bandwidth over-5 d B is 3.4GHz.Compared with the pure CIP of the undoped thermal conductivity filler,the absorption performance loss is very small,but the thermal conductivity is greatly improved.At this time,the thermal conductivity of the thermal absorption composite material is 2.838W/（m·K）,which is 14.4%higher than that of pure CIP.（4）A dielectric low frequency absorption material is designed,and a new idea of self-composite——spherical and sheet iron composite is proposed.The XRD spectra revealed that only theα-Fe phase was observed in all of the samples.Through the electromagnetic characteristics,the impedance matching characteristics of self-composite absorbing material is significantly improved.The results show that mixing with raw spherical CIP effectively reduces the dielectric parameters of the ball-milling FCI powder.With the increase of the spherical CIP of the raw material,the RL peak moves towards the high frequency direction,and the effective absorption bandwidth（Reflection loss<-10d B）is significantly increased to 3.56GHz（1.5 mm thickness）.This indicates that self-composite processing can significantly improve the reflection loss and effective absorbing bandwidth of CIP.