Crystallization Mechanism of CVD Si3N4-SiCN Composite Ceramics Annealed in N2 Atmosphere and Their Excellent EMW Absorption Properties

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• 作者：Jimei Xue ; Xiaowei Yin ; Hongxing Pan ; Xiaofei Liu ; Litong Zhang and Laifei Cheng
• 刊名：Journal of the American Ceramic Society
• 出版年：2016
• 出版时间：August 2016
• 年：2016
• 卷：99
• 期：8
• 页码：2672-2679
• 全文大小：1958K
• ISSN：1551-2916

文摘

To tailor a new electromagnetic wave (EMW) absorbing material with lower reflection coefficient (RC) and larger operating frequency band, the CVD Si₃N₄–SiCN composite ceramics were prepared from SiCl₄–NH₃–C₃H₆–H₂–Ar system and then annealed at the temperatures of 1400–1700°C in N₂ atmosphere. Effect of the annealing temperatures on the microstructure, phase composition, permittivity, and microwave-absorbing properties of the ceramic were investigated. Results showed that the CVD Si₃N₄–SiCN ceramics gradually crystallized into nanosized SiC grains, Si₃N₄ grains and graphite (T ≤ 1600°C), and then the grains grew up at T = 1700°C. The permittivity, dielectric loss, and electrical conductivity of as-annealed CVD Si₃N₄–SiCN ceramics (T ≤ 1600°C) increased firstly due to the formation of conductivity and polarity network and the increase in nanograin boundary, and then decreased at 1700°C because of the growth of nanograins and the disappearance of nanograin boundary. The minimal RC and effective absorption bandwidth of the as-annealed CVD Si₃N₄–SiCN ceramic at 1600°C was −41.67 dB at the thickness of 2.55 mm and 3.95 GHz at the thickness of 3.05 mm, respectively, demonstrating that the totally crystallized CVD Si₃N₄–SiCN ceramic (T = 1600°C) had the superior microwave-absorbing ability.