Effect of Composition and Structure on the Specific Resistivity of Continuous Silicon Carbide Fibers

doi:10.3724/SP.J.1077.2012.00162

Abstract

Abstract:

Three kinds of continuous SiC fibers with different specific resistivity were prepared by the pyrolysis of cured polycarbosilane fiber, and the structure and composition of the three fibers were characterized. Results show that SiC fibers with different specific resistivity can be obtained by changing the curing and pyrolysis conditions. And the total free carbon content and the ability to crystallize will no longer affect the specific resistivity notably when the fiber is covered with an excess carbon layer, as a result the fiber will have a low electrical resistivity. The excess carbon layer in the circular outer part is originated form the re-pyrolysis and deposition of hydrocarbon volatiles. Removal of the carbon by oxidative treatment may affect the surface property and also promote the magnitude of specific resistivity. The influence of the surface property on the specific resistivity is considerable which should not be neglected.

Key words: polycarbosilane, silicon carbide fiber, excess carbon, specific resistivity

CLC Number:

TQ343

WANG De-Yin, SONG Yong-Cai, JIAN Ke. Effect of Composition and Structure on the Specific Resistivity of Continuous Silicon Carbide Fibers[J]. Journal of Inorganic Materials, 2012, 27(2): 162-168.

Figures/Tables 9

Table 1 Chemical composition of three continuous SiC fibers

Fiber type	Composition/ wt%			n(C)/n(Si)	Specific resistance/(Ω·cm)
Fiber type	Si	C	O	n(C)/n(Si)	Specific resistance/(Ω·cm)
SiC-1	51.9	27.4	18.1	1.23	(3.6±0.4)×10^-1
SiC-2	50.5	28.3	13.9	1.31	(4.0±1.7)×10³
SiC-3	52.5	32.6	9.4	1.45	(2.2±1.6)×10²

Fig. 1 29Si MAS NMR spectra of the three continuous SiC fiber

Table 2 29Si MAS NMR data of the three continuous SiC fibers

δ	-15	-30	-72	-107	SiC_xO_y / at%	SiO₄ / at%
Assignment	SiC₄	SiC₂O₂	SiCO₃	SiO₄
Peak area	SiC-1	1	0.39	0.33	0.20	37.5	10.5
	SiC-2	1	0.22	0.21	0.12	27.7	7.7
	SiC-3	1	0.18	0.14	0.10	22.5	7.0

Table 3 Free carbon content data of the three continuous SiC fibers

Fiber	Formula ^a	Formula ^b	ΔC_f	Free carbon content /at%
SiC-1	SiC_1.23O_0.61	SiC_0.67O_0.67	0.56	19.7
SiC-2	SiC_1.31O_0.48	SiC_0.75O_0.50	0.56	20.1
SiC-3	SiC_1.45O_0.31	SiC_0.79O_0.41	0.66	23.9

Fig. 2 XRD patterns (a) and HRTEM images of the three continuous SiC fibers (b) SiC-1; (c) SiC-2; (d) SiC-3

Fig. 3 AES depth profiles and survey scans of three kinds of SiC fibers

Fig. 4 Model of the SiC-1 fiber with an excess carbon layer in the circular outer part

Fig. 5 AES depth profile and survey scan of the SiC-1 fiber after thermal exposure at 600℃ in air

Fig. 6 Gas evolution during heat treatment of the cured polycarbosilane fiber

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