Study On The Click Preparation And Microwave Properties Of Silicon Nitride Based Nano-hybrid Materials

The rapid development of 5G communication technology has promoted the rapid progress of electronic equipment,and the increasingly fierce international military competition has accelerated the rapid development of various high-tech military weapons and equipment,especially unmanned aerial vehicle（UAV）.Therefore,high-performance microwave absorbing materials have aroused great interest of scientific experts and technicians.Problems such as poor impedance matching and narrow absorption band will occur when a single material is used.In this paper,the dielectric loss type material silicon nitride,conductivity loss type material and magnetic loss type material are connected together through covalent bonds through the click chemistry method.Through the synergistic effect of different loss mechanisms,the rich heterogeneous interface of the composite material and the integrated effect of each component connected together through covalent bonds,the formation of conductive channels inside the molecule,thus improving the attenuation of electromagnetic wave.This paper focuses on the relationship between the structure,morphology and microwave absorption properties of composites with different feeding ratios.XRD,FTIR,XPS and SEM,TEM were used to characterize and study the crystal structure,element type and microstructure of the obtained products,and the electromagnetic parameters of the samples were detected by vector network analyzer（VNA）.The main contents are as follows:（1）Carbon nanotubes and silicon nitride were used as raw materials,MWCNTs-ALK was obtained by introducing end-alkyne on the surface modification of MWCNTs,and Si₃N₄-N₃ was obtained by introducing azide group after the surface modification of Si₃N₄.The two components were covalent bonded by clicking reaction.The two components were characterized by XRD,FTIR,XPS and SEM.The results showed that MWCNTs/Si₃N₄ nano-hybrid materials were successfully prepared by click reaction.The microwave absorption performance of nano-hybrid materials was tested when the feeding ratio of MWCNTs and Si₃N₄was 1:2,the sample absorption layer thickness is 3.0 mm,the minimum reflection loss(RL_min)was-30.7 d B,and the maximum effective absorption bandwidth(EAB_max)was 4.14 GHz（d=1.5 mm）.Compared with the product after physical blending,the absorption bandwidth and minimum reflection loss are significantly improved.This is mainly attributed to the covalent bond between MWCNTs and Si₃N₄ in the nano-hybrid materials,and the formation of more conductive channels inside the molecules,more electrons participate in the polarization process,thus increasing the ability to dissipate electromagnetic waves.（2）Based on the optimal ratio of impedance matching（MWCNTs:Si₃N₄=2:1）in MWCNTs/Si₃N₄ binary nanohybrid materials,the conducting polymer polyaniline（PANI）was introduced and the nano-hybrid materials（MWCNTs/Si₃N₄/PANI）were prepared by in-situ polymerization.The nano-hybrid MWCNTs/Si₃N₄/PANI coated with different amounts of polyaniline were characterized by XRD,FTIR,XPS,SEM and TEM.The results showed that PANI was successfully synthesized,fibrous and massive silicon nitride and MWCNTs were coated with polymer.To characterize microwave absorbing properties of the composite material,found that,with the increasing of the amount of polyaniline composite materials|RL_min|increasesd firstly,then decreased.When the feeding ratio of MWCNTs:Si₃N₄:aniline was 2:1:3,the RL_minof MWCNTs/Si₃N₄ before coating was-17.86 d B,the thickness of the absorption layer was 3.0 mm,and the EAB_maxwas 2.88 GHz when the thickness of the absorption layer was 1.5 mm.The RL_min and EAB_max of the coated MWCNTs/Si₃N₄/PANI composite at1.5mm thickness of the absorption layer was-28.32 d B and 4.0 GHz.After polyaniline coating of ternary composites under a thinner absorbed layer absorption,EAB_max and|RL_min|were further improved.By adjusting the amount of PANI coating used on MWCNTs/Si₃N₄,the synergistic effects of impedance matching,interfacial polarization and dipole polarization can be achieved,and high performance absorbing materials can be prepared.（3）In order to compare the absorption properties of binary nano hybrid materials coated with different conductive polymers,the introduction of conductive polymer polypyrrole（PPy）,using in situ polymerization method to prepare MWCNTs/Si₃N₄/PPy nano hybrid materials,the properties of nano-hybrid MWCNTs/Si₃N₄/PPy coated with different amounts of PPy were characterized by XRD,FTIR,XPS,SEM and TEM.The results showed that PPy,fibrous and massive silicon nitride and MWCNTs were successfully synthesized.The microwave absorbing properties of nano hybrid material test,found that with the increasing of the amount of PPy,nano hybrid material|RL_min|increased firstly,then decreased.When the feeding ratio of MWCNTs:Si₃N₄:Py was2:1:4,nano hybrid material wave absorption performance is best.The RL_min and EAB_max of MWCNTs/Si₃N₄/PPy composites were-40.14 d B and 6.88 GHz（d=2.0mm）when the thickness of the absorption layer was 2.5 mm.The results showed that compared with the binary composite material,the EAB_max and|RL_min|of ternary composites coated with PPy increased significantly;in addition,compared with the composite material after PANI coated,the composite coated with PPy exhibited higher EAB_max and|RL_min|but the absorption layer thickness also increased slightly.（4）MWCNTs/Fe₃O₄/Si₃N₄ nano-hybrid materials were prepared successfully by adding nano-ferric oxide as magnetic loss mechanism and clicking reaction according to different feeding ratios.The results showed that Fe₃O₄ was successfully synthesized by solvothermal method,and Fe₃O₄ was successfully modified by carboxylation and terminal alkynylation.In XPS analysis,the presence of triazole ring peaks indicated that the three monomers successfully performed the click reaction.When the feeding ratio MWCNTs:Fe₃O₄:Si₃N₄=1:1:2,the RL_minand EAB_max of the sample were-24.95 d B and 2.88 GHz（d=2.0 mm）when the thickness of the absorption layer was4.0 mm.After the introduction of spherical Fe₃O₄ particles into MWCNTs/Si₃N₄composites,MWCNTs,Si₃N₄ and Fe₃O₄ interweave together to form a conductive network,which effectively promotes the transmission of electrons and thus generates induced current,and promotes the dissipation of electromagnetic waves.At the same time,the irregular massive silicon nitride,carbon nanotubes and Fe₃O₄ interweave together to form a large number of heterogeneous interfaces.The appearance of a large number of heterogeneous interfaces promotes the interface polarization and improves the electromagnetic wave dissipation of the composite.Figures[54]Tables[8]References[136]...