Preparation And Electromagnetic Wave Absorption Property Modulation Of SiCN Based Composite Ceramics

With the development of advanced electronic equipment and telecommunications applications,microwave technology has penetrated many aspects of our lives,such as wireless communications,radar,meteorological and astronomical observations.It makes people’s lives comfortable and convenient,but brings the problem of electromagnetic pollution problems.Therefore,it is necessary to explore high performance electromagnetic wave(EMW)absorbing materials with strong absorption strength,wide frequency band,thin thickness and light weight.Polymer-derived SiCN ceramics have many advantages,including light weight,high thermal stability,good corrosion and oxidation resistance.Additionally,it has unique microstructure and certain dielectric properties,which can be used in the field of EMW absorption.However,pure SiCN ceramics have the problems of single loss mechanism,poor impedance matching,and limited EMW absorption performance.Therefore,in this paper,SiCN composite ceramics with excellent EMW absorption performance(NixSiy/graphene/SiCN ceramics,Ni2Si/SiCN ceramics and Co2Si(Co)/SiCN ceramics)were successfully prepared by constructing various loss mechanisms and optimizing the impedance matching performance.Zeolite imidazolium ester skeletons(ZIFs)are a highly potential EMW absorbing material,so ZIF-67/SiCN were prepared in this paper.Additionally,ZIF-67 was further treated to successfully synthesized high-performance CoFe/C@NCNTs absorbers.The main contents are described as follows:The NixSiy/graphene/SiCN composite ceramics were prepared by introducing Ni and graphene into polysilazane(PSZ)using the polymer-derived ceramics(PDCs)route.The phase composition,chemical composition,morphology and EMW absorption properties of NixSiy/graphene/SiCN composite ceramics were investigated.The results suggests that the introduction of Ni not only facilitates the formation of various phases,including Si3N4,Ni2Si,Ni31Si12,graphite carbon and Si2N2O,but also catalyzes the in-situ generation of onedimensional carbon nanotubes(1D CNTs).When the addition content of Ni was 6 wt%and the addition content of graphene was 2 wt%,the NixSiy/Graphene/SiCN composite ceramics exhibited the optimal EMW absorption performance.The minimum reflection Loss(RLmin)of NixSiy/Graphene/SiCN composite ceramics reached-52.13 dB at 7.6 GHz with the thickness of 2.7 mm,and widest effective absorption bandwidth(EAB)reached 3.56 GHz(14.44-18 GHz)at 1.26 mm.The dielectric loss was enhanced by carbon materials(turbostratic carbon,1D CNTs and 2D graphene)and various phases,while the magnetic loss was improved by NixSiy(Ni,Ni2Si,Ni31Si12).The synergism of multiple loss mechanisms and good impedance matching lead to good EMW absorption properties of NixSiy/Graphene/SiCN ceramics.The Ni2Si/SiCN ceramics were prepared by introducing nickel tetrahydrate(Ni(Ac)2·4H2O)into PSZ.The effects of Ni(Ac)2·4H2O addition on the phase composition,morphology and EMW absorption properties of the Ni2Si/SiCN composite ceramics were investigated.The results showed that a large number of multi-walled carbon nanotubes(MWCNTs)were in-situ formed in Ni2Si/SiCN ceramics after introducing Ni(Ac)2·4H2O.Besides,some crystalline phases,such as Si3N4,β-SiC,Ni2Si,Si2N2O and turbostratic carbon,were observed.The morphology and electromagnetic parameters ofNi2Si/SiCN ceramics could be effectively regulated by changing the addition content of Ni(Ac)2·4H2O.The Ni2Si/SiCN ceramics with the Ni(Ac)2·4H2O addition content of 15 wt%presented the best EMW absorption property.Its RLmin reached-60.71 dB at 9.44 GHz with the thickness of 2.20 mm and EAB broadened to 4.36 GHz(13.64-18 GHz)at 1.38 mm.The excellent properties should be mainly attributed to the synergistic effects of good impendence matching,conduction loss and polarization relaxation loss.Co2Si(Co)/SiCN composite ceramics were prepared by introducing cobalt acetate tetrahydrate(Co(Ac)2·4H2O)into PSZ.The phase composition,morphology and EMW absorption properties of Co2Si(Co)/SiCN composite ceramics at different pyrolysis temperatures(1000-1400℃)were studied.When pyrolysis temperature was 1300℃,carbon nanowires(CNWs),Co2Si,Si2N2O,SiC and Si3N4 were in-situ generated and the best EMW absorption performance was obtained.The RLmin reached-50.04 dB at 4.81 mm and the EAB broadened to 3.48 GHz(14.52-18 GHz)at 1.31 mm.The excellent EMW absorption performance mainly comes from the coexistence of multiple loss mechanisms,including the magnetic loss of Co2Si,the conduction loss of CNWs,and the heterogeneous interfaces polarization between varieties of nanocrystals and amorphous ceramic matrix.ZIF-67 was successfully synthesized and introduced into the PSZ to prepare ZIF-67/SiCN ceramics.The results showed that the ZIF-67/SiCN ceramics achieved RLmin of-23.76 dB at 2.41 mm and an EAB of 3.68 GHz(14.32-18 GHz)at 1.37 mm.Furthermore,in this paper,ZIF-67 was further processed and CoFe/C@NCNTs were successfully prepared.The morphology and electromagnetic parameters of CoFe/C@NCNTs were analyzed.It was found that the nitrogen-doped carbon nanotubes(NCNTs)were in-situ generated in the CoFe/C@NCNTs material.Compared with that of Co/C material,the EMW absorption performance of CoFe/C@NCNTs material was significantly enhanced.When the mass ratio of Fe@ZIF-67 to melamine was 1:1,the obtained CoFe/C@NCNTs samples had the best EMW absorption performance.Its RLmin reached-60.10 dB at 14.32 GHz with the thickness of 2.13 mm and EAB broadened to 5.92 GHz(12.08-18 GHz)at 2.03 mm.Therefore,CoFe/C@NCNTs-1 is expected to be used as a high-performance absorbent in the field of EMW absorption.In summary,the SiCN composite ceramics prepared in this paper have excellent EMW absorption properties and are expected to be EMW absorbing material for high temperature applications.And the MOFs-derived CoFe/C@NCNTs composites have strong absorption strength and wide EAB,which are very promising high-performance absorbers.