Electromagnetic absorption (EMA) materials with light weight and harsh environmental robustness are highly desired and crucially important in the stealth of high-speed vehicles. However, meeting these two requirements is always a great challenge, which excluded the most attractive lightweight candidates, such as carbon-based materials. In this study, SiCnw-reinforced SiCNO (SiCnw/SiCNO) composite aerogels were fabricated through the in-situ growth of SiCnw in polymer-derived SiCNO ceramic aerogels by using catalyst-assisted microwave heating at ultra-low temperature and in short time. The phase composition, microstructure, and EMA property of the SiCnw/SiCNO composite aerogels were systematically investigated. The results indicated that the morphology and phase composition of SiCnw/SiCNO composite aerogels can be regulated easily by varying the microwave treatment temperature. The composite aerogels show excellent EMA property with minimum reflection loss of −23.9 dB@13.8 GHz, −26.5 dB@10.9 GHz, and −20.4 dB@14.5 GHz and the corresponding effective bandwidth of 5.2 GHz, 3.2 GHz, and 4.8 GHz at 2.0 mm thickness for microwave treatment at 600 °C, 800 °C, and 1000 °C, respectively, which is much better than that of SiCN ceramic aerogels. The superior EMA performance is mainly attributed to the improved impedance matching, multi-reflection, multi-interfacial polarization, and micro current caused by migration of hopping electrons.

/pdf/microwave-induced-in-situ-formation-of-sic-nanowires-on-4xjypeeau5.pdf

Microwave induced in-situ formation of SiC nanowires on SiCNO ceramic aerogels with excellent electromagnetic wave absorption performance

Silicon carbide (SiC) is considered to be one of the promising EM absorbing materials due to its good oxidation resistance, low density and chemical inertness, and can be used in high-temperature and harsh environments. In this paper, C-SiC wires with different stacking faults densities were prepared by microwave heating following with post heat-treatment under different conditions. Dielectric measurements indicate that their permittivities increase with the increase in stacking faults density in 2-18 GHz. TEM observation suggests that the stacking faults were formed by embedding 2H-SiC segments in 3CSiC matrix, which resulting in the type-II 2H/3C-SiC heterostructures. Since both the VBM and CBM of 3C-SiC are lower than those of 2H-SiC, respectively, a large conduction-band offset would occur. This may cause plenty of interface dipoles and following with large dipole polarization loss, which might be the origin of high dielectric permittivity of SiC wires.

/pdf/stacking-faults-induced-high-dielectric-permittivity-of-sic-avmx3tld7m.pdf

Stacking Faults Induced High Dielectric Permittivity of SiC Wires: Preparation, Mechanism and Properties

Electrospinning synthesis of SiC/Carbon hybrid nanofibers with satisfactory electromagnetic wave absorption performance

Three-dimensional carbon foam reinforced by the chemical vapour deposition (CVD) SiC coating possessed an enhanced microwave absorbing performance. The effect of the CVD SiC on the properties of the carbon foam was researched. As a result, the microwave absorbing performance improved with the thicker SiC coating as the minimum reflection loss value decreased from −20.67 to −33.65 dB while the bandwidth frequency increased from 5.04 to 5.94 GHz, which was ascribed to the stronger basis dielectric response networks and interface polarization. In addition, the internal relation between the impedance matching value and attenuation coefficient was illustrated to further dig the absorbing mechanism, followed by a simple schematic diagram. Given the excellent performance of the basic material and exceptional structure characteristics, it has the prospect of becoming a superior functional composite in absorbing applications.

Reticulated SiC coating reinforced carbon foam with tunable electromagnetic microwave absorption performance

A new stacking bed method to prepare high-quality silicon carbide whiskers (SiCws) with high yield has been proposed. To provide a steady and high concentration SiO atmosphere during the carbotherm...

High Yield Silicon Carbide Whiskers from Rice Husk Ash and Graphene: Growth Method and Thermodynamics

Seeds-induced synthesis of SiC by microwave heating

Silicon carbide (SiC) whiskers with different morphologies are fabricated by microwave heating of SiO2-coated coal mineral particles at different temperatures and different holding times in an oxygen-containing environment The atomic diffusion processes and growth mechanism of the SiC whiskers are simulated It is found that a closed capsule of SiO2 appears during microwave heating, within which the SiC whiskers are formed SiC crystals can be prepared at 1100 °C for 10 min The optimized synthesis condition is approximately 1100 °C for 20 min Higher temperatures or/and holding times lead to the re-oxidation of the SiC crystals A layer of amorphous SiO2 wraps around the SiC whisker surface and generates coated composites at all temperatures Crystallite knots are observed embedding on the SiC whiskers at 1300 °C due to the surface cleaning and activating effects of microwave plasma The knots are smoothed at 1500 °C due to local atomic diffusion and grain growth motivated by the microwave coupling effect The variations in the microwave plasma and the coupling effect at different heating stages also give rise to unique growth phenomena For the sample synthesized at 1100 °C for 20 min, the high permittivity values present in the SiC whiskers lead to the excellent EM absorption properties at high frequency

Investigation on the growth mechanism of SiC whiskers during microwave synthesis

Influences of pre-forming on preparation of SiC by microwave heating

β-SiC powders were synthesized by microwave sintering at 1400-1850°C for 60 minutes with coal minerals. Raw materials were prepared with a sol-gel method by coating SiO2 on coal mineral particles, and microwave sintering was conducted in a microwave chamber with TE666 resonant mode. Heating rates were controlled by input microwave power and heating behavior during the microwave sintering was also investigated. XRD, SEM, Raman, TEM techniques were carried out to characterize samples. It was found that different particle size of coal mineral particles gave rise to different heating effect, leading to different growth mechanisms of SiC crystals. This might be the unique features for microwave sintering. Particular SiC crystals dominated for small coal mineral particles, which attributed to microwave plasma effect. While SiC whiskers or fibers dominated for large coal mineral particles, which corresponded to microwave coupling effect. Microwave coupling effect prevailed for low heating rate which was apt to form particular SiC crystals. Whereas, higher heating rate enhanced microwave plasma and primarily resulted in SiC whiskers or fibers.

Investigation on heating behavior during the preparation of SiC crystals by microwave sintering

The invention discloses a preparation method of SiC crystal whiskers. The preparation method includes following steps: (1) preparing a precursor from a carbon source and a silicon source; and (2) pressing the precursor into chips, embedding the chips in quartz sand and performing a sintering synthetic reaction with microwave to obtain the SiC crystal whisker. In the preparation method, quick synthesis of the SiC crystal whisker is achieved in a manner of direct synthesis through the microwave by means of an excellent wave-absorption performance of carbon to obtain the SiC crystal whisker in which crystallization is excellent. In a microwave sintering method, a material is sintered on the basis of dielectric loss of the material itself. Compared with an industrially conventional heating method, the microwave sintering method can achieve volume heating, is less in pollution, is short in sintering period and is low in energy consumption. The SiC crystal whisker is uniform in size, is high in length-diameter ratio, is good in crystallization degree, is less in defect and is high in yield. The method is simple in technology, is convenient to operate, is short in production period, is low in sintering temperature and energy consumption, is less in pollution, is suitable for large-scale industrialized production and has a wide application prospect.

Song Bozhen

Papers

Seeds-induced synthesis of SiC by microwave heating

Investigation on the growth mechanism of SiC whiskers during microwave synthesis

Influences of pre-forming on preparation of SiC by microwave heating

Investigation on heating behavior during the preparation of SiC crystals by microwave sintering

Preparation method of SiC crystal whisker