Research On The Preparation And Electromagnetic Wave Absorption Properties Of (Si_0.2Ti_0.2Nb_0.2Ta_0.2V_0.2)C High Entropy Carbide And Its Composites

With the innovation of information technology and the rapid development of anti-stealth technology,wave-absorbing materials are receiving more and more attention in both civil and military applications.Among them,as modern military stealth equipment,wave-absorbing materials also need to meet the requirements of multiple functions such as environmental adaptation,high temperature resistance,and impact resistance.High-entropy carbide ceramics have excellent mechanical properties,oxidation resistance,high-temperature mechanical properties and low thermal conductivity,and also have certain electromagnetic wave absorption properties,which is a promising high-temperature wave-absorbing material,but the poor wave absorption properties limit the wide application of high-entropy carbide in the field of high-temperature wave absorption.In this paper,(Si_0.2Ti_0.2Nb_0.2Ta_0.2V_0.2)C High Entropy Carbide（hereinafter referred to as（Si-Ti-Nb-Ta-V）C）powder was prepared by molten salt method and its microscopic morphology and wave absorption properties were investigated.composite material.PPy _NWs/Fe₃O₄/（Si-Ti-Nb-Ta-V）C composites were prepared by compounding Fe₃O₄/（Si-Ti-Nb-Ta-V）C composites with conductive polypyrrole nanowires(PPy _NWs)using mechanical mixing method.The microstructures of（Si-Ti-Nb-Ta-V）C powder,Fe₃O₄/（Si-Ti-Nb-Ta-V）C composites and PPy _NWs/Fe₃O₄/（Si-Ti-Nb-Ta-V）C composites were analyzed by means of XRD,SEM and TEM;the electromagnetic wave absorption properties of the materials were tested by vector network analyzer,and the electromagnetic wave absorption mechanism of（Si-Ti-Nb-Ta-V）C,Fe₃O₄/（Si-Ti-Nb-Ta-V）C and PPy _NWs/Fe₃O₄/（Si-Ti-Nb-Ta-V）C composites were analyzed,and the main contents and results of the study are as follows:The effects of the preparation process on the microstructure and electromagnetic wave absorption properties of（Si-Ti-Nb-Ta-V）C powders were investigated.With the increase of heat treatment temperature,the diffraction peaks of the high-entropy carbide powder sharpened and narrowed,and there were no spurious peaks at 1500℃,and it had a single rock salt phase,face-centered cubic spinel structure,forming a high-entropy single-phase solid solution;with the increase of carbon doping in the raw material,the product grain refinement and lattice constant decreased;extending the holding time,the crystal particles had gradually developed and grown,and the crystallinity slightly increased,but there was no significant change.At the heat treatment temperature of 1500℃,the amorphous carbon doping（C:Si,Ti,Nb,Ta,V）1:1 in the raw material,and the holding time of 60 min,the lowest reflection loss（RL）of the（Si-Ti-Nb-Ta-V）C powder prepared under the filling amount of 70 wt%in the paraffin matrix gradually shifted to the lower frequency with the increase of the thickness,and when the coating thickness was The lowest RL value reaches-34.7 dB at 3.72 GHz when the coating thickness is 4.2 mm,and the effective absorption bandwidth（EAB）is 2.2 GHz when the coating thickness is 1.3 mm.The electromagnetic wave loss capability of（Si-Ti-Nb-Ta-V）C samples mainly comes from the dipole polarization due to the local strain caused by lattice disorder.relaxation loss and the interfacial polarization relaxation loss due to the large number of interfaces introduced by the high entropy carbide particles of（Si-Ti-Nb-Ta-V）C.The Fe₃O₄/（Si-Ti-Nb-Ta-V）C composites were prepared by mechanical mixing method and their wave absorption properties were investigated.The minimum RL and effective absorption bandwidth of the samples increased and then decreased with increasing Fe₃O₄ doping,and the optimum sample was obtained at a Fe₃O₄/（Si-Ti-Nb-Ta-V）C mass ratio of 1.5:1,with the best RL value of-25.8 dB at a filling of 70 wt%,a thickness of 2.2 mm and a frequency of 9.3 GHz;at a thickness of 2.6 mm,the EAB of11.45-8.05 GHz.The effective absorption bandwidth increases from 2.2 GHz to 3.4GHz compared to the（Si-Ti-Nb-Ta-V）C sample with the same filling.the increased electromagnetic wave loss capability of the Fe₃O₄/（Si-Ti-Nb-Ta-V）C sample is mainly attributed to the increased conduction loss and magnetic loss of the magnetic absorbing material Fe₃O₄.PPy _NWs/Fe₃O₄/（Si-Ti-Nb-Ta-V）C composites were synthesized by the template method and prepared by the mechanical mixing method,and their wave absorption properties were investigated.The wave absorption properties of Fe₃O₄/（Si-Ti-Nb-Ta-V）C were further improved by introducing PPy _NWs to build a conductive network.When the PPy _NWs doping is 10 wt%and the filling is 50 wt%,the PPy NWs/Fe3O4/（Si-Ti-Nb-Ta-V）C composite obtains the lowest RL value of-17.6 dB at a thickness of 1.4mm and a frequency of 17 GHz,and the maximum EAB of 4.18 GHz（11.03-15.2 GHz）is obtained at a thickness of 1.8 mm,and its EAB covers C（4-8 GHz）,X（8-12 GHz）and Ku（12-18 GHz）bands,and the EAB of the high-entropy composite is increased from 3.40 GHz to 4.18 GHz compared to Fe₃O₄/（Si-Ti-Nb-Ta-V）C,while the filling level decreases from 70 wt%to 50 wt%,with a wider effective absorption band and ultrathin coating thickness.With the increase of PPy _NWsdoping,the main loss mechanism of the composite changed from dielectric loss to conductive loss.The electromagnetic wave loss capability of the PPy _NWs/Fe₃O₄/（Si-Ti-Nb-Ta-V）C samples originated from the 3D conductive network formed by the intertwined PPy _NWs with large aspect ratio and the synergistic effect of（Si-Ti-Nb-Ta-V）C and Fe₃O₄ particles extended the transmission path of electromagnetic waves within the matrix,causing a huge conductive loss,the interfacial loss of PPy _NWs/Fe₃O₄/（Si-Ti-Nb-Ta-V）C materials and the dipole polarization relaxation loss from the（Si-Ti-Nb-Ta-V）C high-entropy carbide ceramics.The electromagnetic wave absorption capacity of PPy _NWs/Fe₃O₄/（Si-Ti-Nb-Ta-V）C is greatly improved,and the density of the system is reduced to achieve the purpose of increasing the effective absorption bandwidth,which has important applications in the field of electromagnetic wave absorption in C,X and Ku bands.