Effects of Al and O Content on Transformation from SiAlCO to Si(Al)C Fibers after High Temperature Treatment

doi:10.15541/jim20150402

Abstract

Abstract:

Continuous SiAlCO fibers were prepared by polymer-derived method using polyaluminocarbosilane (PACS) with various Al contents as precursor. The O content of the fibers was controlled by different curing methods. The effects of the Al and O content on SiC_xO_y decomposition, β-SiC grain growth, and fiber morphological evolution in the heat-treatment process were investigated. The results reveal that SiC_xO_y decompostion initiates at 1300℃ and completes at 1700℃ for all kinds of fibers, which is irrelevant to Al and O contents. Al in the fibers is beneficial to reduction of both coarse SiC crystallites and interconnected pores on the surface, and increases suppressing effects on the growth of β-SiC under the tempertature above 1700℃, resulting in densification. Excessive carbon is eliminated as CO and CO₂ by oxygen from SiAlCO fibers during annealing process. However, excessive oxygen creates big pores in fibers, harmful to densification. A densified Si(Al)C fiber with a decently large crystallite size of β-SiC can be achieved with an optimal Al and O content of 0.6wt% and 9wt%, respectively.

Key words: SiAlCO fibers, SiCxOy decomposition, β-SiC, densification, Si(Al)C fibers

CLC Number:

TQ174

YUAN Qin, SONG Yong-Cai. Effects of Al and O Content on Transformation from SiAlCO to Si(Al)C Fibers after High Temperature Treatment[J]. Journal of Inorganic Materials, 2016, 31(4): 393-400.

Figures/Tables 11

Table1 Chemical compositions of SiAlCO fibers

Sample	Oxidation temperature before EB/℃	Si/wt%	C/wt%	Al/wt%	O/wt%	C/Si
SiAlCO2-6	-	57.27	36.71	0.24	5.78	1.496
SiAlCO2-9	160	55.88	35.08	0.20	8.84	1.465
SiAlCO2-13	190	54.16	32.21	0.22	13.41	1.388
SiAlCO3-6	-	55.20	36.93	0.33	7.54	1.561
SiAlCO3-9	160	54.77	35.42	0.33	9.48	1.509
SiAlCO3-13	190	53.63	33.02	0.36	12.94	1.437
SiAlCO6-6	-	55.77	36.27	0.62	7.36	1.517
SiAlCO6-9	160	54.69	35.03	0.57	9.71	1.495
SiAlCO6-13	190	54.10	32.69	0.53	12.68	1.410

Fig. 1 Surface (a) and cross section (b) SEM images of SiAlCO2-9

Fig. 2 29Si-NMR spectra of SiAlCO fibers

Fig. 3 Oxygen content of SiAlCO fibers with different Al contents vs heat-treatment temperature

Table2 Chemical compositions of SiAlCO fibers after heat-treatment at 1700℃

Sample	Si/wt%	C/wt%	O/wt%	Al/wt%	C/Si
SiAlCO2-6	62.53	37.27	0.06	0.39	1.396
SiAlCO2-9	65.72	33.80	0.04	0.44	1.200
SiAlCO2-13	68.73	31.07	0.02	0.48	1.060
SiAlCO3-6	62.31	37.36	0.15	0.47	1.406
SiAlCO3-9	63.33	36.34	0.04	0.57	1.345
SiAlCO3-13	66.97	32.70	0.03	0.64	1.145
SiAlCO6-6	62.03	37.11	0.11	0.75	1.396
SiAlCO6-9	63.02	36.06	0.08	0.84	1.335
SiAlCO6-13	65.55	33.50	0.04	0.91	1.222
Tyranno SA(edge)^[12]	68.00	31.30	-	0.50	1.080
Tyranno SA(core)^[12]	62.90	36.10	0.40	0.60	1.340

Fig. 4 XRD patterns of the SiAlCO6-9 fiber after heat- treatment at different temperatures

Fig. 5 β-SiC crystallite size of SiAlCO fibers with different Al content vs heat-treatment temperature

Fig. 6 β-SiC crystallite size varied with Al content for the SiAlCO fibers after heat-treatment at different temperatures

Fig. 7 Surface morphologies of SiAlCO fibers after heat-treatment at 1700℃ (a)-(c) SiAlCO2-6~SiAlCO2-13, (d)-(f) SiAlCO3-6~SiAlCO3-13, (g)-(i) SiAlCO6-6~SiAlCO6-13

Fig. 8 Surface morphologies of SiAlCO3-13 fiber after sinterment at 1900℃

Fig. 9 Surface morphologies of SiAlCO fibers after heat-treatment at 1900℃ (a) SiAlCO6-6, (b) SiAlCO6-9, (b) SiAlCO6-13

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