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

Abstract

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/m1/2, respectively.

Electromagnetic wave absorbing properties of glucose‐derived carbon‐rich SiOC ceramics annealed at different temperatures

“…1,2,[7][8][9] Of all the critical electromagnetic wave absorption materials, polymer-derived ceramics (PDC), including SiOC, SiBCN, SiCN, and Si 3 N 4 , have captured growing attention due to their controllable microstructure, lightweight, excellent thermomechanical properties, and a wide absorption frequency. 10,12,15 Xue et al 16 developed a Si 3 N 4 -BN-SiCN nanocomposite that manifested excellent absorption properties with the minimum reflection loss of −47.05 dB at the thickness of 4.05 mm. Duan et al reported a series of SiOC ceramic-based nanocomposites modified by nano-SiC, SiC nanowires, or hyperbranched ferrocene, which possessed strong absorption capability and wide absorption bandwidth.…”

“…Duan et al reported a series of SiOC ceramic-based nanocomposites modified by nano-SiC, SiC nanowires, or hyperbranched ferrocene, which possessed strong absorption capability and wide absorption bandwidth. 10,12,15 Xue et al 16 developed a Si 3 N 4 -BN-SiCN nanocomposite that manifested excellent absorption properties with the minimum reflection loss of −47.05 dB at the thickness of 4.05 mm. Li et al 17 also fabricated a porous SiCN ceramic by pyrolysis of a kind of polysilazane.…”

Formation of nanocrystalline graphite in polymer-derived SiCN by polymer infiltration and pyrolysis at a low temperature

“…By heat-treatment with or without Fe catalyst [19,20], they have successfully enhanced the dielectric properties of SiCN and Si 3 N 4w reinforced SiCN (Si 3 N 4w /SiCN). Liu et al [21] and Xue et al [22][23][24] also demonstrated the improvement of dielectric properties of Si 3 N 4w /SiCN by the adjustment of carbon content and heat-treatment of the chemical vapor deposited SiCNs. From these studies we can see that SiCNs pyrolyzed at low temperatures (< 1500 ℃) generally possess dielectric properties comparable to those of an insulator due to low conductivity of amorphous carbon and Si-C-N network.…”

Enhanced electromagnetic wave absorption of Fe‐doped silicon oxycarbide nanocomposites

“…For the magnetic materials, the conclusion is totally reversed . Therefore, amounts of absorbing materials have a poor impedance and relatively narrow absorbing frequency range …”