Boron-carbon doped Silicon Carbide Fibers: Preparation and Property

doi:10.15541/jim20180218

Abstract

Abstract:

The B-C doped SiC precursor was obtained by blending of polycarbosilane, polyborosilicate and xylene soluble pitch at low temperature. The resulted precursor was melt-spun into precursor fibers. The B-C doped silicon carbide fibers were finally obtained by pre-oxidation and high temperature heat-treatment of the precursor fibers successively. The composition and microstructure of B-C doped SiC precursor and its fibers were characterized by IR, XRD and SEM. Effect of the heat-treatment temperature on the composition, structure, mechanic property and oxidation resistance was studied. The results show that the introduction of boron in SiC fibers restrains the growth of SiC grains at high temperature treatment effectively, and simaltaneously improves the thermal stability of the C-doped SiC fibers. B-C doped silicon carbide fibers obtained by heating the pre-oxidized fibers at 1600 ℃ were mainly composed of β-SiC and a small amount of O, B and N. B-C doped SiC fibers ownse better oxidation resistance than the C-doped SiC fibers, which can be attributed to the formation of borosilicate film during the high-temperature oxidation of the B-C doped SiC fibers. This film plays a role effectively in preventing the pith carbon in the doped fibers from oxidation.

Key words: polycarbosilance, polyborosilazane, doping, SiC fiber, anti-oxidation

CLC Number:

TQ343

Han-Qing YU, Zhi-Jun DONG, Guan-Ming YUAN, Ye CONG, Xuan-Ke LI, Yong-Ming LUO. Boron-carbon doped Silicon Carbide Fibers: Preparation and Property[J]. Journal of Inorganic Materials, 2019, 34(5): 493-501.

Figures/Tables 11

Fig. 1 FT-IR spectra of raw materials and B-C-doped SiC precursor (a) and 11B NMR spectra of B-C-doped SiC precursor (b)

Fig. 2 XRD patterns of C doped SiC fibers (a) and B-C doped SiC fibers (b), dependence of grain size on the heat-treatment temperature for the doped SiC fibers (c)

Fig. 3 SEM images and EDS patterns of C doped SiC fibers after heat treatment at (a, b) 1300,(c) 1400, (d) 1500, and (e) 1600 ℃

Fig. 4 SEM image s(a, c-f), EDS patterns (b) and EDS mapping (g~k) of B-C doped SiC fibers after heat-treatment at different temperatures

Fig. 5 Dependence of tensile strength on the heat-treatment temperature for C doped and B-C doped SiC fibers

Table 1 Chemical composition of C doped SiC fibers after heat-treatment at different temperatures

Composition/wt%	900 ℃	1300 ℃	1400 ℃	1500 ℃
Si	42.68	51.82	54.98	64.54
C	36.46	31.76	30.87	25.75
O	20.68	16.42	14.15	9.71

Table 2 Chemical composition of B-C doped SiC fibers after heat-treatment at different temperatures

Composition/wt%	900 ℃	1300 ℃	1400 ℃	1500 ℃
Si	47.94	58.73	61.90	71.43
C	34.75	30.32	28.36	23.48
O	16.95	12.58	9.34	4.80
B	0.21	0.22	0.22	0.23
N	0.15	0.15	0.16	0.16

Fig. 6 XRD patterns of C doped (a) and B-C doped (b) SiC fibers after isothermal oxidation at 1000, 1200 and 1400 ℃ in air for 1 h

Fig. 7 SEM images, EDS patterns of C doped SiC fibers after isothermal oxidation at 1000 ℃ (a), 1200 ℃ (b), and 1400 ℃ (c) in air for 1 h

Fig. 8 SEM images of B-C doped SiC fibers after isothermal oxidation at 1000 (a), 1200 (b), 1400 ℃ (c, d) in air for 1 h

Fig. 9 XPS wide scan spectra (a) and high resolution XPS spectra for B1s (b) and Si2p (c) region of the B-C doped SiC fibers after oxidation at 1200 ℃ for 1 h

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