Mechanism of Microwave Dielectric Response in Laminated Cf-Si3N4 Composites

doi:10.15541/jim20160172

Abstract

Abstract:

Laminated C_f-Si₃N₄ composites were prepared by gelcasting followed by pressureless sintering at 1600℃ in N₂ atmosphere, using short carbon fiber, α-Si₃N₄ powder as starting materials. Microwave dielectric properties of C_f-Si₃N₄ composites were investigated in X-band using a network analyzer. Moreover, theoretical model regarding microwave dielectric responses was established by modification of Debye model, and the corresponding mechanism was discussed intensively. Results show that there exists percolation phenomenon in permittivity of laminated C_f-Si₃N₄ composites with surface density of short carbon fibers increasing due to formation of connected carbon fiber network. Additionally, the relaxation time of C_f-Si₃N₄ composites converges to multiple values immediately after carbon fibers network being formed, which results from inhomogeneity of microstructure, conductivity and coatings of short carbon fibers. And this dispersity can then weaken as surface density of short carbon fibers increasing. Consequently, the characteristic function of tangent loss evolves from multi-relaxation time model to uni-relaxation time model based on numerical analysis.

Key words: laminated Cf -Si3N4 composites, dielectric response, relaxation time

CLC Number:

TQ174

ZHOU Wei, XIAO Peng, LUO Heng. Mechanism of Microwave Dielectric Response in Laminated C_f-Si₃N₄ Composites[J]. Journal of Inorganic Materials, 2017, 32(1): 86-90.

Figures/Tables 6

Table1 Surface density of short carbon fibers inside Cf -Si3N4 composites

Samples	1#	2#	3#	4#	5#	6#
Surface density /(mg^.cm^-2)	0.3067	0.6134	0.7667	0.9201	1.2268	2.4530

Fig. 1 Macro and micro morphology of Cf-Si3N4 composites(a) Macro morphology of Cf-Si3N4 composites, (b) Macro morphology of carbon fibers, and (c) Micro morphology of Cf-Si3N4 composites

Fig. 2 (a)Permittivity and (b)dielectric loss tangent diagram of Cf -Si3N4 composites with different surface density chopped carbon fibers

Fig. 3 Cole-Cole diagram of sandwich-structure Cf -Si3N4 composites

Fig. 4 Experimental and theoretical curves of dielectric loss tangent vs frequency

Fig. 5 Piecewise fitted curves of dielectric loss tangent of Cf -Si3N4 4#

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Mechanism of Microwave Dielectric Response in Laminated C_f-Si₃N₄ Composites

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