组成和结构对连续SiC纤维电阻率的影响

doi:10.3724/SP.J.1077.2012.00162

摘要/Abstract

摘要：

通过烧成制备了电阻率量级大小不同的三种连续SiC纤维, 对纤维的元素组成、结晶性能和表面结构进行了分析. 结果表明: 通过调整不熔化及烧成工艺参数可以获得电阻率量级不同的连续SiC纤维. 当纤维表层具有一定厚度的高富碳层结构时, 纤维的电阻率受整体自由碳含量与结晶性能的影响不再显著, 此时, 纤维将具有较低的电阻率. 富碳层的产生与不熔化纤维烧成时分解产生的烃类小分子的重新裂解沉积有关. 通过低温氧化除去纤维表面的富碳层可以使纤维电阻率增大. 表面结构对连续SiC纤维的电阻率大小有重要影响.

关键词: 聚碳硅烷, SiC纤维, 富碳, 电阻率

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

中图分类号:

TQ343

王得印, 宋永才, 简科. 组成和结构对连续SiC纤维电阻率的影响[J]. 无机材料学报, 2012, 27(2): 162-168.

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.

图/表 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

图1 三种连续SiC纤维的固态Si MAS NMR图谱表2 三种纤维的29Si MAS NMR数据

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

图2 三种连续SiC纤维的XRD图谱(a) HRTEM照片(b, c, d )

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

图3 三种纤维的表面AES图谱及全扫描图谱

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

图4 具有富碳表层的SiC-1纤维的模型

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

图5 600℃空气热处理后连续SiC-1纤维表面AES图谱及全扫面图谱

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

图6 烧成过程中PCS不熔化纤维释放出的气体量随烧成温度的变化情况

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

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