Electromagnetic Wave Absorbing Properties And Mechanism Of Polymer-derived SiCN(O)-based Ceramics

At present,because of its advantages including low-temperature ceramiczation and superior high-temperature dielectctric properties,the development of polymer derived ceramics(PDCs)in the field of electromagnetic wave absorption has attracted more and more attentions.It is considered to be highly great candidate of new functional and structural wave absorption materials at high temperature.However,the chanllenges,like poor matching between absorbents and impedances,harsh conditions for doping modification,etc.,has limited the application of PDCs as wave absorption materials.Therefore,to fabricate PDCs-based EMW absorption material with high and tunable performances,namely to realize the integration of material structure and function,will be the focus of the future development of(EMW)absorbing materials.In view of the current problems of PDCs absorbing material in preparation,performance and designed application,etc,polysiloxane(PSO)and polysilazane(PSZ)are used as polymer precursor to fabricate SiCN,C/SiCN and Fe/C/SiCN by doping modification with introducing nano-Fe.The absorbing performance and mechanism are investigated.Furthermore,new SiCN and Fe/C/SiCN ceramic fibers are prepared with assistance of electrostatic spinning technology.Digital Light Processing(DLP)is used to print the DLP-SiOC ceramics and DLP-SiCN(Fe)ceramics and EMW aborsorbing performance and mechanisim of PDCs with s different structures are studied.The main research conclusions are as follows:(1)The PSZ polymer precursor in 800℃ has completed the transformation from the polymer to the basic of the ceramic,showing good thermal stability.SiCN ceramic abtained from 1100℃ sobviously improves the dielectric performance,in section frequencies of 15.5～16.2 GHz,the material reflection loss is less than-10 dB,the RLmin is-19 dB,suggesting its development potential in the field of absorbing materials.SiCN ceramic with carbon materials have obviously improved the dielectric properties,increased dielectric loss,enhanced the electromagnetic wave absorbing properties.The imaginary part of the dielectric constant of SiCN-MLG at 11.2 GHz is 3.4,and the loss tangent is about 0.67.The imaginary part and the loss tangent of SiCN-CNT at 10.6 GHz are 3.1 and 0.57,respectively.The RLmin of SiCN-MLG and SiCN-CNT in thickness of 3 mm minimum are-48 dB and-54 dB respectively,and the effective electromagnetic wave absorption bandwidth are about 1.5 GHz and 0.8 GHz.Ceramics with proper amount of nano Fe powders can improve impedance matching of Fe/C/SiCN ceramics,play the role of electromagnetic loss together,improve the performance of electromagnetic wave absorption significantly,reduce the loss of the electromagnetic wave reflection,and broaden the effective absorption band.Especially for adding nano Fe powder mass fraction 9 wt%Fe/C/SiCN-9 samples,the carbon nanotubes generates under the catalysis of the amount of Fe particles,at the same time it can improve the dielectric and magnetic properties of the sample,adjust the impedance matching of the materials effectively,enhance the wave absorption performance.The effective wave absorption spectrum the EAB and minimum reflection loss RLmin are 3.03 GHz and-31.06 dB,respectively(2)Combined PDCs with electrostatic spinning process,SiCN fibers are prepared with Si-C-N network based amorphous structure.With the increase of sintering temperature,nanometer phase carbon,SiCxNy,the amorphous SiC and Si3N4 gradually generate,promoting the material interface polarization and dipole polarization greatly.Conductive nano phase is good to form the carrier conductive channel,increasing conductance loss.Especially for the SiCN fiber prepared at 1100℃,it has excellent dielectric properties of electromagnetic attenuation coefficient and impedance matching performance,and its electromagnetic loss mainly consists of dipole loss and interface loss.When the thickness is only 1.08 mm,its effective absorption band is 3.17 GHz(11.95～15.12 GHz),and the Rlmin can reach-13.43 dB.Modifing SiCN fibers with different contents of acetylacetone iron magnetic precursor as functionalization are prepared.SiCN(Fe)composite fibre shows excellent one-dimensional fiber structure,the CNTs generating by in-situ Fe3Si effectively improve the dielectric and magnetic properties and impedance matching properties of SiCN(Fe)fibers.The electromagnetic wave absorption performance is mainly composed of dipole polarization loss,interfacial polarization loss and eddy current loss caused by the SiCN(Fe).The composite fiber shows excellent electromagnetic absorption performance.When the thickness is only 1.38 mm,the RLmin value of SiCN-1 fiber can reach-47.64 dB.For SiCN-1.5 fibers,the effective absorption band is up to 4.28 GHz(13.72～18 GHz),and the thickness is only 1.35 mm.(3)We printed two typical porous structure bracket structure and gyroid structure.The DLP-SiOC ceramics as a kind of new absorbing materials with special structure design ability,shows good dielectric properties based on the manufacturing technology.We print the DLP-SiOC ceramics with the adjusted shape and complex structure,which has realized the integration of structure and function.The turbine carbon shows in the ceramic after pyrolysis with t he existence of graphite and SiC clusters,increasing the internal interface polarization relaxation and dipole polarization,and improving the DLP-SiOC electromagnetic wave absorption properties of the ceramic significantly.For 1200℃ samples,its EAB and minimum reflection loss RLmin are 4.9 GHz at thickness of 1.58 mm and-23.5 dB.For 1300℃ samples,the EAB and the RLmin are 2.1 GHz mm and-52 dB at thickness 1.08.(4)Based on material manufacturing technology,we successfully print the complex porous structure of diamond DLP-SiCN(Fe)ceramic materials,integrates the organization function of new absorbing materials.By introducing modification ferrocene on precursor polymer and the catalytic reaction occurs in the pyrolysis process.The turbine carbon,graphite and SiC generates to increase the dipole and interface polarization of materials,improves the dielectric properties of materials.Preparation of SCN-0 have good performance of electromagnetic wave absorption,the samples at thickness of 1.51 mm shows effective absorbing band of 4.82 GHz(13.18～18 GHz),and at the thickness of 4.67 mm,RLmin is-13.43 dB.With the addition of ferrocene,the wave absorption performance of ceramics improves significantly,for SCN-1,when the thickness is only 2.34 mm,its RLmin value can reach-61.34 dB,effective absorbing band can reach 4.28 GHz(1.23 mm,13.72～18 GHz).