High-temperature Microwave Absorption Research Articles

Cost-Effective Preparation and High Performance of High-Temperature Electromagnetic Wave Absorbing Materials Based on Graphene Nanosheets

High cost and resistance to harsh working conditions are challenges faced by most microwave absorbers for wide applications. Here, a low-cost graphene-based high-temperature microwave absorbing material is prepared. When the ratio is adjusted appropriately, excellent absorbing performance can be achieved at room temperature: C-2 is the most efficient material with respect to microwave absorption: it has an effective absorption bandwidth as wide as 4.6 GHz, and the minimum reflection is -39.2 dB with a thickness of 1.5 mm. Using the permittivity and TG data of the composites at 800 °C attained, it is demonstrated that the decomposition temperature of composites can be increased from 450° to 820°. When the mass ratio of graphene nanosheets and water glass is 1:2, the composites have the best high-temperature microwave absorption performance: C-2 exhibited the microwave absorption ability with a minimum reflection loss value of approximately −29.6 dB at 16.4 GHz, a thickness of 1.5 mm even at 800 °C.

Outstanding high-temperature microwave absorption properties of La0.9Sr0.1MnO3/Ba3.75La9.5Ti18O54 composite ceramics

High-temperature microwave-absorbing materials are crucial for achieving radar stealth in high-speed equipment. In response to this necessity, we investigated xLa0.9Sr0.1MnO3/(1-x)Ba3.75La9.5Ti18O54 composite ceramics under variable temperatures, where x ranges from 20 to 50 wt%. X-ray diffraction analysis indicates the coexistence of La0.9Sr0.1MnO3 and Ba3.75La9.5Ti18O54 when x ranges from 20 to 30 wt%, transforming into a perovskite-structured solid solution with a higher proportion of La0.9Sr0.1MnO3. Variable-temperature direct current conductivity reveals a controllable transition from dielectric behavior to semiconductor behavior, resulting in the dielectric properties of composite ceramics shifting from low-loss to high-loss characteristics. For x values ranging from 20 wt% to 40 wt%, there consistently exists a corresponding temperature and frequency range ensuring specific absorption performance. Notably, the composite ceramic with x=30 wt% and a thickness of 1.1 mm demonstrates an effective absorption bandwidth (RL<-10 dB) of 1.75 GHz within the temperature range of 400–600℃. These findings suggest that composite ceramics comprising La0.9Sr0.1MnO3 and Ba3.75La9.5Ti18O54 hold promise as high-temperature microwave-absorbing materials.

Carbon vacancies regulation strategy for boosting the high-temperature microwave absorption performance of (Co0.2Mo0.2V0.2Nb0.2Ta0.2)Cx high-entropy carbides

High-entropy carbides with controlled carbon content have the advantages of high thermal stability and good oxidation resistance, which make them potential for the application of high-temperature microwave absorbing materials. In...

Facile synthesis of hollow SiC/C nanospheres for high-performance electromagnetic wave absorption

Hollow silicon carbide/carbon (SiC/C) nanospheres have found wide applications owing to their excellent dielectric properties, high surface area, thermal insulation, and low effective density at high temperatures. However, their hollow structure is typically obtained by removing the templates using strong acids, which can lead to massive waste and severe pollution. Herein, a three-layer nanospheres containing resorcinol-formaldehyde (RF) and SiO2 (RF@SiO2@RF) were first prepared by a simple one-step method and used as precursors. Subsequently, monodispersed hollow SiC/C nanospheres (90 ± 5 nm in diameter) prepared in-situ through carbon thermal reduction. The hollow structure was formed by pyrolysis, eliminating the extra procedure to remove templates. The structure, size, and composition of the nanospheres were precisely controlled via synthesis temperatures (1400, 1450, 1500 °C) and using different raw material ratios. The obtained hollow SiC/C nanospheres demonstrated remarkable resistance to high temperature resistance. The specific surface area of the optimised hollow SiC/C nanospheres reached 301.9 m2 g−1. Their reflection loss (RL) value achieved −41.34 dB at 14.58 GHz, and the effective absorption bandwidth(EAB)was 4.0 GHz (12.77–16.78 GHz) with a thickness of 1.70 mm. The results of this study confirm that the proposed method allows for an in-situ synthesis of hollow SiC/C nanospheres for high temperature microwave absorption with low matching thickness.

Temperature-dependent dielectric properties and high-temperature microwave absorption performance of Ti3SiC2/Al2O3-13%TiO2 coatings

Ti3SiC2 exhibits considerable potential for high-temperature microwave absorption due to its relatively high melting point and conductivity. In this study, we successfully prepared Ti3SiC2/Al2O3-13%TiO2 heterogeneous coatings through granulation and plasma spraying techniques. This investigation covered composition, microstructure, oxidation resistance, and a focused analysis of the temperature-dependent permittivity of the coatings. The augmentation in Ti3SiC2 content leads to an escalation in the polarized component, consequently elevating susceptibility to dielectric dispersion. With rising temperature, polarization within the coatings gradually establishes, prompting a transition from polarization relaxation loss to conduction loss as the dominant dielectric loss mechanism. At 5 wt% Ti3SiC2 content, the coating achieves an effective bandwidth of 2.2 GHz at 873 K, with a mere 1.4 mm thickness. Moreover, the coating maintains exceptional oxidation resistance below 700 °C. Ti3SiC2/Al2O3-13%TiO2 coatings manifest as strong contenders for high-temperature microwave absorption applications, and plasma spraying emerges as a promising technique for fabricating high-performance microwave absorption coatings.

Temperature-dependent dielectric and wide-temperature-range microwave absorption properties of La0.8Sr0.2MnO3/Al2O3–13%TiO2 coatings

The advancement of absorption materials and coating preparation technology is crucial to address the challenges posed by electromagnetic interference and pollution in high-temperature extreme environments. Here, by using a granulation and plasma spraying strategy, we successfully fabricated a series of La0.8Sr0.2MnO3/Al2O3–13%TiO2 (LSMO/AT13) high-temperature microwave absorption coatings that have excellent dielectric properties and extremely thermal stability. The results showed that the LSMO/AT13 coatings exhibited remarkable oxidation resistance, withstanding high-temperature aerobic environments of up to 1000 °C. Based on the temperature-dependent permittivity of the coatings, the establishment process of polarization and the transformation of loss mechanism were observed and explained. With the increase of temperature, the main dielectric loss mechanism of the coatings transitions from polarization loss to conductive loss. Thanks to the coordinated effects of impedance and loss, the coatings are capable of effectively absorbing microwave over a wide temperature range. When the LSMO content was 30 wt% and the thickness was 1.9 mm, the effective bandwidth ranged from 1.7 GHz to 2.4 GHz at temperatures below 773 K. This study demonstrates the promising application of LSMO/AT13 microwave absorption coatings for ultra-high temperature environment, and provides a reference for the design and optimization of high-temperature microwave absorption coatings.

Fabrication of thin and lightweight cobalt-coated quartz fiber/aluminosilicate composites for high-temperature microwave absorption

Fabrication of thin and lightweight cobalt-coated quartz fiber/aluminosilicate composites for high-temperature microwave absorption

High-temperature multispectral stealth metastructure from the microwave-infrared compatible design

Microwave and infrared stealth technology plays an important role in the development of military equipment and national defense. However, with the development of high Mach number weapons, it is urgent to develop the new materials with high temperature multispectral compatible stealth. In this paper, a new multispectral stealth metastructure is proposed, which can achieve high temperature microwave absorption and infrared stealth simultaneously. The metastructure is optimized based on Large-Mutation Genetic Algorithm (LMGA), and the high temperature resistant patterned resistive film (PRF) is reasonably distributed to dissipate the incident microwave energy. The high temperature infrared stealth is realized by the dual regulation of high-strength thermal insulation skeleton and low emissivity infrared metasurface to reduce target infrared radiation. Effective bandwidth (≤−10 dB) at 1000 °C is 2–3.5 GHz and 5.4–18 GHz. Low thermal insulation (∼0.104 W/(m·k)) and low infrared emissivity (∼0.39 at 800 °C) can reduce the target infrared radiation energy by 91.7%. This research provides an effective way to design microwave infrared compatible stealthy materials with huge multifunction.

High-temperature stability core-shell engineered Ti3AlC2@C@SiO2 for excellent microwave absorbing properties

Layered structure Ti3AlC2 (TAC) has good thermal stability and excellent electrical conductivity, which is expected to be a great high-temperature electromagnetic microwave absorber. Herein, we derive TAC@C@SiO2 composites by catalytic chemical vapor deposition (CCVD) technology and Stöber process. Core-shell engineering can accomplish a mass loss of just 0.20% at 500°C for 1 h. An outstanding microwave absorption performance can be achieved with a minimum reflection loss of −31.63 dB and the maximum absorption bandwidth of 2.08 GHz at the matching thickness of 2.0 mm with the synergistic effect of abundant polarization mechanism and multiple scattering. Additionally, this research can serve as a guide for the utilization of TAC in the field of high-temperature microwave absorption materials, and can also provide suggestions for the design of environment-adaptable core-shell absorbers.

Excellent electromagnetic wave absorption properties of SiCN ceramic aerogels via a controlled hydrosilylation reaction

AbstractPolymer‐derived ceramic materials exhibit adjustable composition, microstructure, and dielectric properties and are widely used as high temperature microwave absorption materials in the aerospace field. In this study, polymer‐derived SiCN ceramic aerogels with excellent electromagnetic wave absorption (EMA) properties were successfully fabricated through a combination of the sol‐gel, freeze‐ drying, and polymer precursor conversion methods. The hydrosilylation reaction between the Si‐H bond in polysilazane (a polymer ceramic precursor) and the C = C bond in divinylbenzene (a cross‐linking agent) occurs to form a wet gel. The effects of the molar ratios of the two bonds (C = C/Si‐H) on the microstructure and EMA properties of the SiCN ceramic aerogels were systematically studied. At a C = C/Si–H molar ratio of 1.25:1, the minimum reflection loss of the SiCN ceramic aerogels is −37.57 dB at 10.88 GHz. Moreover, the corresponding effective absorption bandwidth covers almost the entire X‐band, showing excellent EMA properties.

Polymer-derived SiOC reinforced with core–shell nanophase structure of ZrB2/ZrO2 for excellent and stable high-temperature microwave absorption (up to 900 °C)

Microwave absorbing materials for high-temperature harsh environments are highly desirable for aerodynamically heated parts and engine combustion induced hot spots of aircrafts. This study reports ceramic composites with excellent and stable high-temperature microwave absorption in air, which are made of polymer-derived SiOC reinforced with core–shell nanophase structure of ZrB2/ZrO2. The fabricated ceramic composites have a crystallized t-ZrO2 interface between ZrB2 and SiOC domains. The ceramic composites exhibit stable dielectric properties, which are relatively insensitive to temperature change from room temperature to 900 °C. The return loss exceeds − 10 dB, especially between 28 and 40 GHz, at the elevated temperatures. The stable high-temperature electromagnetic (EM) absorption properties are attributed to the stable dielectric and electrical properties induced by the core–shell nanophase structure of ZrB2/ZrO2. Crystallized t-ZrO2 serve as nanoscale dielectric interfaces between ZrB2 and SiOC, which are favorable for EM wave introduction for enhancing polarization loss and absorption. Existence of t-ZrO2 interface also changes the temperature-dependent DC conductivity of ZrB2/SiOC ceramic composites when compared to that of ZrB2 and SiOC alone. Experimental results from thermomechanical, jet flow, thermal shock, and water vapor tests demonstrate that the developed ceramic composites have high stability in harsh environments, and can be used as high-temperature wide-band microwave absorbing structural materials.

Stereolithographically 3D Printed SiC Metastructure for Ultrabroadband and High Temperature Microwave Absorption

AbstractBroadband microwave absorption is essential on the realms of electromagnetic compatibility and protection in civil application scenarios. However, coordination of material and structure is difficult without proper iterative design between material and structure resulting in insurmountable drawbacks of traditional microwave absorption medium operating under high temperature erosion. Herein, SiC metastructure is manufactured in bulk by stereolithographic 3D printing. The dielectric loss tangent of SiC sintered body is over 0.5 and up to 1.5 at most showing good electromagnetic energy dissipation properties. The optimized SiC metastructure with complicated suspended features achieves −10 dB broadband microwave absorption from 6.96 to 40 GHz at room temperature (RT) across total frequency range of 33.04 GHz. The proposed SiC metastructure is able to endure in situ 1000 °C and ex situ 1600 °C erosion in air atmosphere maintaining −10 dB effective bandwidth in 4.54–40 and 10.89–39.67 GHz, respectively. Broadband microwave absorption under oblique incidence from 0° to 60° is also achieved in a wide temperature range from RT to 1600 °C. The densification of SiC results in a high mechanical strength of 217.36 MPa for structural load bearing applications. The intrinsic electromagnetic variation of SiC under different temperature is relaxed and adapted to the metastructure design. The functions of broadband microwave absorption and high temperature protection are integrated into one metastructure.

Evaluation of Microwave Absorption Performance of Annealed Cr2AlC at Different Temperatures

Cr2AlC (CAC) has attracted increasing attention due to high conductivity and excellent oxidation resistance, which is useful for high-temperature microwave absorption. However, systematic research on microwave absorption performance of CAC at high temperatures is still lacking. In this work, CAC was synthesized by salt bath method followed by annealing at 500 °C–950 °C. Effects of various annealing temperatures on compositions and electromagnetic properties were studied. Results revealed slight oxidation of CAC at annealing temperature of 500 °C, with formation of small amounts of Al2O3 and Cr2O3 on the surface. Increase in annealing temperature to 950 °C generated Al2O3 and Cr2O3 components in CAC. CAC annealed at 500 °C showed better microwave absorption properties than annealed at 950 °C and pure CAC. Effective absorption bandwidth (Reflection loss, RL < −10 dB) of CAC annealed at 500 °C was estimated to 2.3 GHz (9.7–12.0 GHz), and RLmin was −28.1 dB with thickness of 2.0 mm. The reason for this had to do with appropriate micro-oxidation, which could increase the permittivity of CAC and enhance dielectric loss capability for electromagnetic waves. In sum, these findings look promising to have referential significance for the application and promotion of CAC in the field of high temperature microwave absorption.

TiN/Fe2Ni2N/SiO2 composites for magnetic-dielectric balance to facilitate temperature-stable broadband microwave absorption

Dielectric ceramics composites are potential high-temperature microwave absorption materials (MAMs), and the critical challenge is to achieve high-efficiency and temperature insensitive absorption characteristics suitable for wide temperature and frequency range. Herein, the electromagnetic attenuation properties of TiN/Fe 2 Ni 2 N/SiO 2 composites are studied in detail. The magnetic ceramic composites proposed exhibited stable attenuation behaviors at a wide temperature range (293–873 K). Notably, the optimal reflection loss (RL) value had reached −32.4 dB with a thickness of 2.8 mm at 373 K, and the effective absorption bandwidth (EAB) covered 3.89 GHz at 873 K. The excellent high-temperature attenuation capacity is attributed to the balancing strategy of dielectric and magnetic losses, as well as multiple polarization loss behaviors. The results showed that introducing magnetic components to form magnetic ceramic composites might shed light on the development of the TiN ceramic family for promising MAMs at a wide temperature range. • Magnetic TiN/Fe 2 Ni 2 N nanocomposites were fabricated via an in-situ ammonia calcination process. • The introduction of Fe 2 Ni 2 N can compensate for the issue of impedance mismatch at elevated temperatures. • The magnetic-dielectric balance strategy achieves stable and efficient high-temperature microwave attenuation behavior.

Sandwich structure SiCf/Si3N4–SiOC–Si3N4 composites for high-temperature oxidation resistance and microwave absorption

SiC fiber reinforced ceramic matrix composites (SiCf-CMCs) have been widely used as structural-functional materials at high temperatures. However, their mechanical and electromagnetic wave (EMW) absorbing properties will deteriorate due to high-temperature oxidation. Therefore, unique sandwich structure, consisting of inner Si3N4 impedance layer, middle porous SiOC loss layer and dense oxidation-resistant Si3N4 layer, was proposed to enhance multiple material properties in oxidation environment. Herein, SiCf/Si3N4–SiOC–Si3N4 composites was fabricated by alternating chemical vapor infiltration (CVI) and polymer infiltration pyrolysis (PIP) methods. For these composites, SiC fiber is used as both reinforcing phase and electromagnetic (EM) absorber. CVI Si3N4 matrix was distributed in inner and outer layer of the SiCf/Si3N4–SiOC–Si3N4 composites. While inner Si3N4 layer between BN interphase and SiOC matrix forms nano-heterogeneous interphase to consume EM energy and enhance mechanical properties of composites, outer dense and oxidation-resistant CVI Si3N4 coating serves to maintain properties. PIP SiOC matrix exhibits porous structure that can effectively deflect cracks and achieve multiple scattering of EMW. SiCf/Si3N4–SiOC–Si3N4 composites with sandwich structure demonstrated excellent EMW absorbing properties and mechanical performance in high-temperature oxidation environments.

Entropy-driven phase regulation of high-entropy transition metal oxide and its enhanced high-temperature microwave absorption by in-situ dual phases

High-temperature microwave absorbers are significant for military equipment which experiences severe aerodynamic heat. In this work, high-entropy oxide (HEO) (FexCoNiCrMn)mOn with excellent high-temperature microwave absorption is studied. Driven by the effect of entropy, the composition of the oxide can be transformed from spinel-type phase (FexCoNiCrMn)3O4 to corundum-type phase (FexCoNiCrMn)2O3 with the increasing content of iron. Only spinel-type or corundum-type structure composes the oxide when x ≤ 3 or x ≥ 5. But in-situ dual phases can coexist when x equals 4 during phase transition. Interestingly, obliged to abundant heterogeneous interfaces and crystal defects in the dual-phase HEO, magnetic property, dielectric polarization, and microwave loss ability are all well enhanced. The Smith chart analysis demonstrates the impedance matching condition is well improved due to the enhanced loss ability. These findings pave a new way for the adjustment of electromagnetic properties of HEO by entropy-driven phase regulation. Meanwhile, the dual-phase absorber can achieve better than 90% absorption in 9.6–12.4 GHz at 800 °C with a thickness of 2.6 mm, a low thermal diffusivity of 0.0038 cm2/s at 900 °C, and excellent high-temperature stability, which indicates it's promising as a high-temperature microwave absorber.

Effect of SiC interphase on the mechanical, high-temperature dielectric and high-temperature microwave absorption properties of the SiCf/SiC/Mu composites

In this study, SiC interphase was prepared via a precursor infiltration-pyrolysis process, and effects of dipping concentrations on the mechanical, high-temperature dielectric and microwave absorption properties of the SiCf/SiC/Mu composites had been investigated. Results indicated that different dipping concentrations influenced ultimate interfacial morphology. The SiC interphase prepared with 5 wt% PCS/xylene solution was smooth and homogeneous, and no bridging between the fiber monofilament could be observed. At the same time, SiC interphase prepared with 5 wt% PCS/xylene solution had significantly improved mechanical properties of the composite. In particular, the flexural strength of the composite prepared with 5 wt% PCS/xylene solution reached 281 MPa. Both ε′ and ε′′ of the SiCf/SiC/Mu composites were enhanced after preparing SiC interphase at room temperature. The SiCf/SiC/Mu composite prepared with 5 wt% PCS/xylene solution showed the maximum dielectric loss value of 0.38 at 10 GHz. Under the dual action of polarization mechanism and conductance loss, both ε′ and ε′′ of the SiCf/SiC/Mu composites enhanced as the temperature increased. At 700 °C, the corresponding bandwidth (RL ≤ −5 dB) of SiCf/SiC/Mu composites prepared with 5 wt% PCS/xylene solution can reach 3.3 GHz at 2.6 mm. The SiCf/SiC/Mu composite with SiC interphase prepared with 5 wt% PCS/xylene solution is expected to be an excellent structural-functional material.

Temperature-insensitive and enhanced microwave absorption of TiB2/Al2O3/MgAl2O4 composites: Design, fabrication, and characterization

Developing high-temperature microwave absorption (MA) materials remains a challenge in the field of radar stealth. Here, we propose a design concept of meta-structure for temperature-insensitive and broadband MA. The three-phase TiB2/Al2O3/MgAl2O4 composites are prepared to realize the temperature-insensitive MA properties, which is ascribed to the interaction of different components in terms of the electrical conductivity, dipolar polarization and interfacial polarization as temperature increases. On this basis, we design and fabricate a three-layer meta-structure composed of the SiO2 ceramics as environmental adaptation layer, the patch-type and flat composites as MA layers. Compared with flat composites, the meta-structure can optimize its effective permittivity, thereby realizing enhanced MA properties at elevated temperatures. This meta-structure can realize a reflection loss (RL) less than −5 dB at 8.2–18.0 GHz in the temperature range of 25 °C to 1100 °C. The experiment matches well with the simulation. The temperature-insensitive and enhanced MA properties are attributed to the consequence of the combination of traditional absorbing materials and metamaterial structures.

High-Temperature Dielectric and Microwave Absorption Property of Atmospheric Plasma Sprayed Al2O3-MoSi2-Cu Composite Coating

Al2O3-MoSi2 coating has excellent high-temperature stability. On this basis, Al2O3-MoSi2-Cu composite high-temperature absorbing coating was prepared by atmospheric plasma spraying method. The phase transition characteristics of Al2O3-MoSi2-Cu spraying feedstock under high temperatures were analyzed by thermogravimetric test, the phase analysis of coating was performed by an in situ XRD test at different temperatures, and the microstructure of the coating was characterized by SEM. The test results of high-temperature microwave absorption performance show that, in high-temperature air atmosphere, the Cu in the coating is gradually transformed into Cu2O by oxygen atom diffusion, and the microwave absorption performance of the coating gradually increases with the increase in temperature. The 1.7 mm-thick coating at 500 °C has the best absorbing performance with a reflection loss (RL) value of −17.96 dB and an effective absorbing bandwidth (RL &lt; −10 dB) in X-band of 2.42 GHz. The prepared Al2O3-MoSi2-Cu composite high-temperature absorbing coating takes into account the dual advantages of high-temperature stability and high-temperature absorbing properties.

High-temperature dielectric and microwave absorption performances of TiB2/Al2O3 ceramics prepared by spark plasma sintering

High-temperature dielectric and microwave absorption performances of TiB2/Al2O3 ceramics prepared by spark plasma sintering