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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 Fe 3 Si 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). [ABSTRACT FROM AUTHOR]

The SiCN precursor was prepared by cross-linking process using polysilazane (PSZ) as raw materials. The cross-linking behavior and dielectric properties of SiCN precursor were analyzed. The results indicated that the main reactions during cross-linking process were double bond addition reaction, hydrosilylation reaction, dehydrogenation coupling reaction and transamination reaction. The SiCN precursor was made up of Si-C-N network structure and the main chemical bonds were Si-C, Si-N and C-C. The appropriate cross-linking temperature of SiCN precursor was 600 °C. Furthermore, the increasing content and crystallization degree of free carbon could improve the dielectric properties of SiCN precursor. [ABSTRACT FROM AUTHOR]

Porous BN p /Si 3 N 4 ceramics were prepared by gas pressure sintering method as a candidate wave-transparent material. The effects of BN particle additions ranging from 0 wt% to 15 wt% on the phase compositions, microstructures, mechanical performance and dielectric properties were investigated. With the increase of BN content, the apparent porosity of the BN/Si 3 N 4 ceramics increased greatly from 2.3% to 21.2%. Although the mechanical properties were partially weaken, the dielectric performance of the porous BN/Si 3 N 4 was largely enhanced at the same time. For the 10% BN/Si 3 N 4 porous composite ceramics, the permittivity and dielectric loss was 33.5% and 62.2% lower than that of the porous Si 3 N 4 without BN content, respectively. Specifically, when 10% BN particles were added, the porous BN p /Si 3 N 4 has a porosity of 20.5% and the permittivity and dielectric loss were 5.14 and 0.0085 respectively with bending strength of 190.1 MPa and fracture toughness of 4.16 MPa m 1/2 , which can meet the required value of wave transparent materials. [ABSTRACT FROM AUTHOR]

The SiBCN composite fibers with strong electromagnetic wave (EMW) absorption performance were successfully prepared via polymer-derived ceramics (PDCs) and electrospinning methods at relatively lower preparation temperature. The results showed that the in-situ generated free carbon which existed in the matrix in the form of simple substance and was characterized by low crystallinity. The graphite carbon improved the dielectric loss and properties of SiBCN composite fibers. In particular for the SiBCN composite fibers pyrolyzed at 1300 °C, the in-situ generated nano β-SiC crystallization increased the EMW absorption performance significantly. The minimum reflection loss (RL min) of the SiBCN-3 reached − 54.91 dB at 2.35 mm and the effective absorption band (EAB, RL ≤ −10 dB) reached 4.72 GHz (13.28–18 GHz, 1.75 mm). Hence, the SiBCN fibers prepared at relatively lower temperature give good absorption performance and predict a broader application prospect in the field of EMW absorption materials. • SiBCN fibers with excellent EMW absorption performance were successfully prepared. • The in-situ generated free carbon improved the dielectric loss and properties of SiBCN fibers. • The minimum reflection loss (RL min) of SiBCN-3 reached − 54.91 dB at 2.35 mm. • The effective absorption band (EAB, RL ≤ −10 dB) of SiBCN-3 reached 4.72 GHz (13.28–18 GHz) at 1.75 mm. [ABSTRACT FROM AUTHOR]

The SiC nanotubes were synthesized on porous Si 3 N 4 matrix by polysilazane immersion-pyrolysis. The β-SiC and free C contents increased with the increasing dipping times, which cause some clear vibration and loss peaks of the dielectric constant patterns emerged at around 12.9 GHz and 14.7 GHz in the samples of 20 wt% and 30 wt% benzoic acid, respectively. The reflectivity of the obtained ceramics were −7dB ∼ −10dB from the frequency of 8 GHz–18 GHz, which means that the amount of 80%–90% electromagnetic wave could be attenuated. The ceramics containing 40 wt% benzoic acid showed the high loss, low reflectivity and a wide absorbing band, indicating the high absorbing efficiency and good dielectric properties. Image 1 • The SiC NTs were synthesized. • 80%-90% EMI was attenuated for 10GHz. • The low R values means good absorbing ability. [ABSTRACT FROM AUTHOR]