Enhanced electromagnetic wave absorption performance of SiCN(Fe) fibers by in-situ generated Fe3Si and CNTs

The SiCN(Fe) fibers with excellent one-dimensional microstructure and electromagnetic wave (EMW) absorption performance were synthesized by combining polymer-derived ceramics (PDCs) method and electrospinning. The in-situ generation of Fe₃Si and CNTs by adding ferric acetylacetonate (FA) into the raw materials effectively improved the dielectric properties, magnetic properties and the impedance matching performance of the SiCN(Fe) fibers. The EMW absorption performance of SiCN(Fe) fibers were mainly based on dipole polarization loss, interface polarization loss and eddy current loss. The RL_min value of SiCN(Fe) fibers reached ?47.64 dB at 1.38 mm and the effective absorption band (EAB, RL ≤ ?10 dB) reached 4.28 GHz (13.72–18 GHz, 1.35 mm).     

Enhanced EMW absorption properties of SiCN/Fe/Ni ceramics modified with Fe/Ni bimetal

The SiCN/Fe/Ni ceramics codoped with iron acetylacetonate (FA) and nickle acetylacetonate (NA) was synthesized by polymer-derived ceramics (PDCs) method in this study. The microstructure, phase composition and electromagnetic wave (EMW) absorption properties of the samples were analyzed. The polarization loss and conduction loss of materials were analyzed by the direct current (DC) multimeter and the contribution rate of polarization loss was more than 94% in the whole frequency band. The results showed that C, SiC, Fe₂Si, Ni₃Si, γ- (Fe, Ni) and CNTs were formed after pyrolysis which provided lots of heterogeneous interface and enhanced the interfacial polarization. Meanwhile, Ni could enter the lattice of Fe and formed a unique electronic configuration, which reinforced the conductivity and stability of Fe. In addition, the in-situ generated Fe₂Si and Ni₃Si provided magnetic loss and conduction loss. The RL_min value of SiCN/Fe/Ni-3 ceramic was ?52.06 dB at 1.54 mm and the effective absorption band (EAB, RL ≤ ?10 dB) reached 4.21 GHz (13.79–18 GHz, 1.43 mm).     

Enhanced electromagnetic microwave absorption properties of SiCN(Fe) ceramics produced by additive manufacturing via in-situ reaction of ferrocene

SiCN(Fe) ceramics with excellent electromagnetic wave (EMW) absorption performance were successfully prepared from a preceramic polymer doped with ferrocene. Additive manufacturing (Digital Light Processing), providing enhanced structural design ability, was employed to fabricate samples with complex architectures. During pyrolysis, ferrocene catalyzed the in-situ formation of a large amount of turbostratic carbon, graphite and SiC nanosized phases, which formed carrier channels in the electromagnetic field and increased the conductivity loss. Meanwhile, it also increased the dipole polarization, interface polarization and the dielectric properties of the material, which finally enhanced the EMW absorption capacity of SiCN(Fe) ceramics. When containing 0.5 wt% ferrocene, the material showed good performance with EAB 4.57 GHz at 1.30 mm, and RL_min −61.34 dB at 2.22 mm. The RL_min of 3D-SiCN-0.5 ceramics was −6 dB, and the RL of the X-band was lower than −4 dB at 2 mm.     

Polymer-derived Co2Si(Co)/SiCN composite ceramics with tunable microwave absorption properties

In this paper, Co₂Si(Co)/SiCN composite ceramics were synthesized by simple precursor-derived ceramics method. The phase composition, morphology, and microwave absorption properties of Co₂Si(Co)/SiCN composite ceramics at different pyrolysis temperatures (1000–1400°C) were studied. When pyrolysis temperature was 1300°C, carbon nanowires (CNWs), Co₂Si, Si₂N₂O, SiC and Si₃N₄ were in situ generated and the best electromagnetic wave (EMW) absorption performance was obtained. The minimum reflection loss reached−50.04 dB at 4.81 mm, and the effective absorption bandwidth 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. By adjusting the sample thickness from 1 to 5 mm, the effective absorption of S1300 can cover the entire X and Ku bands, from 3.36 to 18 GHz. This study provides a simple way to synthesize high performance ceramic-based microwave absorbing materials.     

Microstructure and EMW absorption properties of CVI Si3N4–SiCN ceramics with BN interface annealed in N2 atmosphere

A kind of chemical vapor infiltration (CVI) Si₃N₄–BN–SiCN composite ceramic with excellent electromagnetic wave (EMW) absorbing properties is obtained by CVI BN interface and SiCN matrix on porous Si₃N₄ ceramics, and then annealed at high temperatures (1200°C‐1500°C) in N₂ atmosphere. The crystallization behavior, EMW absorbing mechanism and mechanical properties of the composite ceramics have been investigated. Results showed CVI SiCN ceramics with BN interface were crystallized in the form of nanograins, and the crystallization temperature was lower. Moreover, both EMW absorbing properties and mechanical properties of CVI Si₃N₄–BN–SiCN composite ceramics firstly increased and then decreased with the increase in annealing temperature due to the influence of BN interface on the microstructure and phase composition of the composite ceramics. The minimum reflection coefficient (RC) and maximum effective absorption bandwidth (EAB) of the composite ceramics annealed at 1300°C were ?47.05 dB at the thickness of 4.05 mm and 3.70 GHz at the thickness of 3.65 mm, respectively. The flexural strength and fracture toughness of the composite ceramics annealed at 1300°C were 94 MPa and 1.78 MPa/m^1/2, respectively.     

Si3N4-BN-SiCN ceramics with unique hetero-interfaces for enhancing microwave absorption properties

SiCN-based ceramics with broadband and strong microwave absorption properties are desired for the structural and functional integration of ceramic matrix composites. The elemental composition and thermal expansion coefficients of the ceramics matrix crucially affect its microstructure and electromagnetic wave (EMW) absorption properties. BN layer with lower electrical conductivity and higher specific area, exhibits both the impedance matching characteristic and EMW attenuation in the process of multiple reflections, electrical conductivity loss, dipole polarization and interfacial polarization. Therefore, Si₃N₄-BN-SiCN ceramics, which were synthesized using chemical vapor infiltration (CVI) method, construct unique hetero-interface of Si₃N₄-BN, Si₃N₄–SiCN and BN-SiCN. Therefore, the Si₃N₄-BN-SiCN ceramics have outstanding EMW absorption performance and realize an effective absorption bandwidth (EAB) that covers the whole X band and the minimum reflection coefficient (RC) reaches -18.43 dB at a thickness of 3.37 mm.     

Electromagnetic wave absorption properties of polymer-derived magnetic carbon-rich SiCN-based composite ceramics

In this paper, the mixture of Fe and Ni nanoparticles (abbreviated as FeNi) was added to liquid polysilazane (PSZ) as a magnetic source, to prepare a series of magnetic carbon-rich SiCN-based composite ceramics by adjusting the mass ratio of FeNi through the polymer derivation method. The phase composition, microstructure, conductivity, electromagnetic wave (EMW) absorption performance and mechanism of composite ceramics prepared were discussed. The analysis shows that the introduction of magnetism has adjusted the impedance matching and improved the magnetic loss performance of composite ceramics on the whole, and the dielectric loss ability of composite ceramics has been strengthened benefiting from the formation of conductive path of CNTs precipitated by FeNi catalysis in the matrix. Therefore, the addition of magnetic particles improves the EMW absorption peak intensity and effective absorption bandwidth (EAB) of composite ceramics. When the addition amount of FeNi was 5 wt%, the sample 5# exhibited the best comprehensive EMW absorption performance: Its minimum reflection loss (RL_min) was ?18 dB and the EAB was 2.5 GHz when the thickness was 1 mm, the EAB covering the C, X and Ku bands can be obtained by adjusting the thickness from 1.0 mm to 4.0 mm. Through calculation, the EAB (EAB_tf) of 5# with a thickness of 1 mm and a filling rate of 1 wt% can reach 50, which is significantly higher than that of a series of SiCN-based composite ceramics previously reported. In addition, the density of 5# was 2.3 g/cm³, and its compressive strength (CS) can reach 337 MPa. The data shows that the composite ceramic 5# prepared in this experiment has the merits of light weight, excellent comprehensive EMW absorption performance and good compression resistance, and is expected to be one of the promising materials in the field of new-generation EMW absorbers.     

The heterointerface of graphene in-situ growth for enhanced microwave attenuation properties in La-doped SiBCN ceramics

The electromagnetic wave (EMW) absorbing materials are widely applied to attenuate the useless and harmful EMW generated from wireless communication and 5G networks, which could protect the human health and electronic device safety. In this study, La-doped SiBCN ceramics with broadband EMW absorption capability were prepared via generating abundance of heterointerfaces, as graphene were in-situ grown by La₂O₃ catalyzing. The graphene in-situ formed in the ceramics can be attributed to the La atom decreasing the potential energy of the free carbon ring nucleation from −760.9 Ha to −8984.3 Ha. Consequently, the electrical conductivity of the SiBCN ceramics improved from 12.360 S/m to 18.025 S/m, the minimum reflection loss (RL_min) obtained was −26.48 dB at 7.2 GHz and the effective absorption bandwidth (EAB) was 6.32 GHz (11.68–18.00 GHz) at a thickness of 1.7 mm. At 700 °C, the RL_min and EAB values reached −43.18 dB and 4.2 GHz, respectively. The enhanced EMW absorbing capability can be attributed to the rationally tailor the heterointerfaces to improve the polarization loss and conduction loss of the SiBCN ceramics. The interfaces between graphene and amorphous phases generate built-in electric fields and space chare regions to strengthen the interface polarization, while the electrons migrating rapidly in the graphene and other crystals improved the electrical conductivity. The positive effect of heterointerfaces regulation of graphene in-situ growth improved the dielectric loss capacity of the SiBCN ceramics; therefore, this study provides a feasible method to enhance the EMW absorption capability of polymer-derived ceramics.     

Effect of BN content on the structural,mechanical, and dielectric properties of PDCs-SiCN(BN) composite ceramics

Hexagonal boron nitride (h-BN) with low dielectric loss and high temperature resistance opens up new opportunities for the preparation of polymer-derived SiCN ceramics (PDCs-SiCN ceramics) with excellent mechanical and dielectric properties. BN-containing polymer-derived SiCN composite ceramics (PDCs-SiCN(BN) composite ceramics) with different BN content were prepared via a pyrolysis process of ball-milling-blended Polyvinylsilazane/boron nitride (PVSZ/BN) precursors. BN is stably embedded in the SiCN tissue and tightly bound with it. The appropriate content of BN greatly improves the mechanical properties of PDCs-SiCN ceramics, as BN reduces the number of pores and prevents crack expansion. Additionally, BN is also beneficial in lowering the dielectric loss of PDCs-SiCN ceramics because of the weakened polarization relaxation behavior. PDCs-SiCN (BN) composite ceramics have optimal mechanical and dielectric properties when the BN content is 1 wt%. The flexural strength, flexural modulus and compression strength of PDCs-SiCN(BN) composite ceramics with 1 wt% BN doping content were 189.37 MPa, 46.38 GPa, and 399.02 MPa, respectively. Its average dielectric loss (tanδ_ε) at 12.4-18 GHz is 0.0049.     

Enhanced electromagnetic wave absorption of Fe-doped silicon oxycarbide nanocomposites

Polymer-derived ceramics (PDCs), such as SiOC, SiCN, SiBCN, and SiC are considered the best candidates for designing high-performance microwave absorber due to their controllable structure, homogeneous element composition at atom level, tunable electromagnetic and electrochemical properties. Herein, Fe ions doped silicon oxycarbide (Fe ions-SiOC) ceramics have been successfully fabricated via solvothermal method. The electromagnetic absorption performances of the nanocomposites prove to be controllable via tailoring Fe ion contents. The Fe ions effectively enhance both the interfacial polarization of amorphous SiOC, and the dielectric properties of the nanocomposites but barely effect magnetic properties of the nanocomposite. As for 0.16 mol/L-SiOC ceramics annealed at 1450°C, the effective absorption bandwidth as high as 2.00 GHz and reflection loss of −59.60 dB at 5.40 GHz with the thickness of 4.55 mm are obtained. Such work opens up a novel and simple route to scale up the PDC-based materials with broadband and excellent microwave absorbing performances.     

Microstructure and electromagnetic wave absorption property of reduced graphene oxide-SiCnw/SiBCN composite ceramics

In this account, RGO-SiC_nw/SiBCN composite ceramics were fabricated using polymer derived ceramic (PDC) combined with chemical vapor infiltration (CVI) technology. Dielectric property of as-obtained RGO-SiC_nw/SiBCN composite ceramics was significantly enhanced thanks to established conductive pathway through overlapped nanoscale SiC_nw and micro-sized RGO. The minimum RC of composite ceramics with 0.5 wt% GO and 2.29 wt% SiC_nw at thickness of 3.6 mm reached -42.02 dB with corresponding effective absorption bandwidth (EAB) of 4.2 GHz. As temperature rose from 25 to 400 °C, permittivity increased with enhanced charge carrier density and then it decreased due to oxidation process of RGO from 400 to 600 °C. The minimum reflection coefficient (RC) was recorded as -39.13 dB and EAB covered the entire X-band at 600 °C. EMW absorption ability was evaluated after high-temperature oxidation experiment under protective effect of wave-transparent Si₃N₄ coating. RGO-SiC_nw/SiBCN composite ceramics maintained outstanding EMW absorption ability with minimum RC of -10.41 dB after oxidation at 900 °C, indicating RGO-SiC_nw/SiBCN composite ceramics with excellent EMW absorption characteristic even at high temperatures and harsh environments.     

Theoretical prediction and experimental verification on EMI shielding effectiveness of dielectric composites using complex permittivity

The evaluation and optimization of EMW absorbing properties have been widely studied, but little research focused on EMI shielding properties predicted by complex permittivity. Based on the transmission-line theory, shielding effectiveness (SE) of a dielectric composite was evaluated by the reflection coefficient (Г) and transmission coefficient (T) which were calculated by the complex permittivity. SiC_f/SiCN composites containing different content of CVI SiCN matrix are attractive for their tunable dielectric properties, which may vary from EMW absorption to EMI shielding. Therefore, SiC_f/SiCN composites are typical dielectric composites used for experimental verification, and the results indicate that the dielectric composites without CVI SiCN phase have good EMW absorbing properties, while they exhibit good EMI shielding effectiveness with CVI SiCN phase. This work builds a relationship between the EMI shielding effectiveness and the complex permittivity, and obtains the optimized complex permittivity for excellent EMI shielding effectiveness.     

Enhanced electromagnetic wave absorbing properties of Si-O-C ceramics with in-situ formed 1D nanostructures

The Si-O-C ceramics were prepared by polymer-derived ceramic method using polysiloxane/FeCl₃ as precursor with the FeCl₃ content of 1.0 wt%. The microstructure, dielectric properties, and electromagnetic wave (EMW) absorbing properties in X band of the Si-O-C ceramic were investigated. It was found that the pyrolysis temperature has a great influence on the amount of in-situ formed CNTs and the transformation from CNTs to 1D SiC nanostructures. With the temperature rising from 1000 to 1500°C, the SiC formed with various morphologies including SiC microspheres, needle-like SiC, and SiC nanowires which were transformed from CNTs. The EMW absorbing properties were dramatically improved when the pyrolysis temperature raised to 1500°C; the minimum reflection loss (RL) was −58.37 dB of sample with a thickness of 2.95 mm at 10.11 GHz, and the absorbing band (RL ≤−20 dB) of sample at a thickness of 3.0 mm covers 3.8 GHz (8.2-12.0 GHz), which means more than 99% of the EMW were absorbed. The enhancement of EMW absorbing properties of bulk Si-O-C ceramics was attributed to the interfacial polarization induced by in-situ heterogeneous nanostructures with complex interfaces.     

Effect of boron content on the microstructure and electromagnetic properties of SiBCN ceramics

Electromagnetic wave (EMW) absorbing materials have excellent potential for various applications in civil engineering and the military. In this study, siliconboron carbonitride (SiBCN) ceramics with excellent EMW absorption capability and oxidation resistance were obtained by adjusting the boron content. The results revealed that the graphite crystallite size in the SiBCN ceramics increased from 3.42 to 3.78 nm, whereas the thickness of the oxide layer decreased from 16.6 to 8.2 μm. The highest electrical conductivity and permittivity for the SiBCN ceramics were obtained when the boron content was 5%. The minimum reflection loss was ?35.25 dB at 10.57 GHz and a ceramic thickness of 2.0 mm. At a temperature of 600 °C, the SiBCN ceramic exhibited excellent EMW attenuation ability; particularly, the minimum reflection loss reached ?29.18 dB at 9.65 GHz and a ceramic thickness of 2.5 mm. The superior EMW absorption properties of the SiBCN ceramics at high temperatures can be ascribed to the synergistic effect of relaxation and conductivity. The results suggest that boron could enhance the transformation of amorphous carbon into crystalline graphite and increase the number of heterointerfaces and conductive paths. This work provides a method for obtaining SiBCN ceramics with excellent EMW absorption properties.     

SiCN ceramics with controllable carbon nanomaterials for electromagnetic absorption performance

Different kinds of carbon nanomaterials, free carbon (C_free), graphene, and N-containing graphene (NG), in single-source-precursors-derived SiCN ceramics, were in situ generated by modifying polysilazane with divinylbenzene, dopamine hydrochloride and melamine, respectively. Adjusting the carbon source brings phase structure and electromagnetic wave absorption (EMA) properties differences of SiCN/C ceramics. In situ C_free enhances the EMA capacity of SiCN ceramics by improving their electrical conductivity of 9.2 × 10⁻⁴ S/cm. The electrical conductivity of SiCN ceramics with 2D graphene sheets balloons to 2.5 × 10⁻³ S/cm, causing poor impedance match thus leading to a worse EMA performance. In situ NG in SiCN ceramics has a low electrical conductivity of 5.6 × 10⁻⁸ S/cm, making for excellent impedance match. The corrugated NG boosts dielectric loss, interfacial, and dipole polarization. NG-SiCN nanocomposites possess an outstanding EMA performance with RL_min of −61.08 dB and effective absorption bandwidth of 4.05 GHz, which are ∼2.4 times lower and ∼4 times higher than those of SiCN, respectively.     

Preparation of SiCf/Si–O–C composites by impregnation pyrolysis of polysiloxane and its electromagnetic wave absorption properties

High-temperature structural electromagnetic wave (EMW) absorption materials are increasing in demand because they can simultaneously possess the functions of mechanical load-bearing, heatproof, and EMW absorption. Herein, SiC_f/Si–O–C composites were prepared by precursor impregnation pyrolysis using continuous SiC fibers needled felt as reinforcement and polysiloxane as a precursor, respectively. The phase composition, microstructure, complex permittivity, and EMW absorption properties of SiC_f/Si–O–C composites after annealing at various temperatures were investigated. The annealing at 1400–1500°C affects positively the EMW absorption performance of the composites, because the β-SiC microcrystals and SiC nanowires were generated by the activation of carbothermal reduction reaction in the composites, and the aspect ratio of SiC nanowires increased with the rise of temperature. The composites exhibit optimal EMW absorption performance, with the effective absorption bandwidth covering the entire X-band and the minimum reflection loss (RL_min) of −32.8 dB at 4.0 mm when the annealing temperature is raised to 1500°C. This is because that the impedance matching is improved as the rising of ε′ and decreasing of ε″ due to the conversion of free carbon in the composite into SiC nanowires.     

Construction of core-shell ZnO@ZnO/FeNi microrods with improved impedance matching and electromagnetic wave absorption performance

Functional core-shell heterostructure, which can integrate the characteristics of multiple components to achieve synergistic effects, have been widely explored in electromagnetic wave (EMW) absorption materials. In this work, core-shell ZnO@ZnO/FeNi microrods (MRs) derived from ZnO@ZnFeNi hydroxide (ZnFeNi OH) are prepared by a simple hydrothermal reaction and subsequent pyrolysis process. The introduction of FeNi alloy helps to optimize the impedance matching of ZnO, thus improving the EMW absorption performance. The different impedance matching properties of core-shell ZnO@ZnO/FeNi MRs are realized by adjusting the ZnO/FeNi shell thickness by changing the hydrothermal reaction time. When the hydrothermal time is 10 h, the core-shell ZnO@ZnO/FeNi MRs supplies the optimal EMW absorption performance with the minimum reflection loss of −53.7 dB and the widest absorption bandwidth of 5.3 GHz at a filler content of 33%. The synergistic effect of ZnO–FeNi interfacial polarization and the strong dielectric-magnetic loss are responsible for its superior EMW absorption performance. This work provides a valuable strategy for constructing core-shell dielectric@ magnetic composites to obtained high efficiency absorber.     

Dielectric properties of Si3N4–SiCN composite ceramics in X-band

Si₃N₄–SiCN composite ceramics were successfully fabricated through precursor infiltration pyrolysis (PIP) method using polysilazane as precursor and porous Si₃N₄ as preform. After annealed at temperatures varying from 900 °C to 1400 °C, the phase composition of SiCN ceramics, electrical conductivity and dielectric properties of Si₃N₄–SiCN composite ceramics over the frequency range of 8.2–12.4 GHz (X-band) were investigated. With the increase of annealing temperature, the content of amorphous SiCN decreases and that of N-doped SiC nano-crystals increases, which leads to the increase of electrical conductivity. After annealed at 1400 °C, the average real and imaginary permittivities of Si₃N₄–SiCN composite ceramics are increased from 3.7 and 4.68 × 10^?3 to 8.9 and 1.8, respectively. The permittivities of Si₃N₄–SiCN composite ceramics show a typical ternary polarization relaxation, which are ascribed to the electric dipole and grain boundary relaxation of N-doped SiC nano-crystals, and dielectric polarization relaxation of the in situ formed graphite. The Si₃N₄–SiCN composite ceramics exhibit a promising prospect as microwave absorbing materials.     

Fabrication of Ni/ZnO/C hollow microspheres decorated graphene composites towards high-efficiency electromagnetic wave absorption in the Ku-band

Developing light-weight, thin thickness and high-efficiency electromagnetic wave (EMW) absorbers is an effective strategy for dealing with the increasingly serious problem of electromagnetic radiation pollution. Herein, nickel/zinc oxide/carbon (Ni/ZnO/C) hollow microspheres decorated graphene composites were facilely prepared through the high-temperature pyrolysis of bimetallic NiZn metal-organic frameworks (MOFs) precursors. Morphological characterization results manifested that the Ni/ZnO/C microspheres with unique hollow structure were almost evenly anchored on the wrinkled surfaces of flake-like graphene. Moreover, the influences of additive amounts of graphene oxide (GO) in the MOFs precursors on the crystal structure, graphitization degree, micromorphology, magnetic properties, electromagnetic parameters and EMW absorption performance were investigated in detail. It was found that the superior EMW absorption performance could be achieved through facilely adjusting the additive amounts of GO in the precursors. As the additive amount of GO was equal to 60 mg, the obtained composite showed the comprehensive excellent EMW absorption performance. Notably, the optimal minimum reflection loss reached ?57.5 dB at 16.5 GHz in the Ku-band under an ultrathin matching thickness of merely 1.34 mm, and the broadest effective absorption bandwidth achieved 5.6 GHz (from 12.4 to 18 GHz) when the thickness was 1.5 mm. Furthermore, the underlying EMW absorption mechanisms of as-prepared composites were revealed. It was believed that our results could be valuable for the structural design and EMW absorption performance modulation for MOFs derived magnetic carbon composites.     

Design and fabrication of Al2O3f/SiCN composite with excellent microwave absorbing and mechanical properties

A new kind of structural and functional integration ceramic matrix composite material was prepared from high-performance alumina (Al₂O₃) fibers and absorbing silicon carbonitride (SiCN) ceramics via a combination of polymer infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI) methods. The Al₂O₃ fiber annealed at its cracked temperature had enhanced permittivity, because the sizing agent on the Al₂O₃ fiber surface was cracked into pyrolysis carbon. For PIP + CVI Al₂O_3f/SiCN composites, PIP SiCN matrix with low conductivity was used as the matching phase, while CVI SiCN matrix with medium permittivity and dielectric loss was regarded as the reinforcing phase distributed in porous PIP SiCN matrix and inter-bundles of Al₂O₃ fiber to improve their mechanical and microwave absorption properties. The fracture toughness and flexural strength of Al₂O_3f/SiCN composite were determined to be 9.4 ± 0.5 MPa m^1/2 and 279 ± 28 MPa, respectively. Based on the design principles for impedance matching, the Al₂O_3f/SiCN composites before and after oxidation were used as loss and impedance layers, respectively. It was found that the optimized composite had the lowest reflection coefficient (RC) of −70 dB and the effective absorption bandwidth covering the whole X-band. In conclusion, Al₂O_3f/SiCN composite can serve as a high-temperature structural material with excellent microwave absorption properties for aerospace applications.