Preparation of Alumina Ceramic Continuous Fibers with Inorganic Acidic Aluminum Sol as Precursor

doi:10.15541/jim20230153

Abstract

Abstract:

As a high-temperature-resistant structural reinforcement material with excellent performance, alumina continuous fiber has been widely used in various fields. However, its large-scale preparation is still a great challenge due to the technical difficulty. Herein, the alumina continuous fibers were prepared using self-made aluminum sol and commercially available silica sol as precursors, in which the microstructure and composition of aluminum sol were studied to reveal their excellent spinnability. Preparation of alumina-based gel continuous fibers with length longer than 1500 m was realized by Sol-Gel combined dry spinning technology. After calcination at 1100 ℃ for 30 min, the continuous ceramic fiber composed of γ-Al₂O₃ and amorphous SiO₂ with the diameter and mean tensile strength of 10 μm and 2.0 GPa was successfully obtained. Microstructure analyses revealed high relative density of the ceramic fibers, in which the γ-Al₂O₃ nanocrystals with size of 10-20 nm uniformly distributed in amorphous SiO₂, resulting in excellent mechanical properties. This preparation process is environment-friendly, simple and controllable, showing great potential in practical application. The test for high temperature resistance revealed that the alumina continuous fiber can work for a long time at 1000 ℃ while it can endure as high as 1300 ℃ for a short-time service.

Key words: alumina continuous ceramic fibers, Sol-Gel technology, aluminum sol, dry spinning

CLC Number:

TB321

JIA Yuna, CAO Xu, JIAO Xiuling, CHEN Dairong. Preparation of Alumina Ceramic Continuous Fibers with Inorganic Acidic Aluminum Sol as Precursor[J]. Journal of Inorganic Materials, 2023, 38(11): 1257-1264.

Figures/Tables 11

Fig. 1 (a) 27Al NMR spectra of aluminum sol prepared with different n(Al(OH)3)∶n(AlCl3) and (b) particle size distributions of hybrid sol with n(Al(OH)3)∶n(AlCl3) at 1:0.35

Fig. 2 Rheological curves of sol (a) Apparent viscosities of the sol with different solid contents as a function of shear rate, and (b) relationship between apparent viscosity of spinnable sol and temperature

Fig. 3 SEM images of the gel fibers (a) Overview; (b) Fiber’s surface

Fig. 4 FT-IR spectra (a), TG-DSC curves (b) of the gel fibers, and (c) XRD patterns of the fibers calcined at different temperatures

Fig. 5 SEM images of surfaces and cross sections of the fibers calcined at different temperatures

Table 1 Densities and strengths of fibers calcined at different temperatures

Calcination conditions	Tensile strength/GPa	Cv of tensile strength/%	Density/(g·cm^-3)	Crystalline size/nm	Phase composition
900 ℃/30 min	1.5	12.33	2.86	9.80	γ-Al₂O₃ + amorphous
1000 ℃/30 min	1.6	11.26	2.91	10.36	γ-Al₂O₃ + amorphous
1100 ℃/30 min	2.0	12.68	2.95	10.77	γ-Al₂O₃ + amorphous
1200 ℃/30 min	1.4	12.17	2.85	11.63	γ-Al₂O₃ + amorphous

Fig. 6 TEM (a) and high resolution TEM (b) images of alumina ceramic continuous fiber with insets in (a) showing low magnification image and SAED pattern of the fiber

Fig. 7 XRD patterns of alumina continuous fibers after heat-treatment under different conditions

Table 2 Mechanical properties of alumina continuous fibers after heat treatment under different conditions

Calcination conditions	Shrinkage ratio of diameter/%	Tensile strength/GPa	Cv of tensile strength/%	Retention rate/%	Phase composition
Original fiber	—	2.035	13.70	—	γ-Al₂O₃ + amorphous
1000 ℃/1 h	0	2.002	12.89	98.38	γ-Al₂O₃ + amorphous
1100 ℃/1 h	0	1.933	13.01	94.99	γ-Al₂O₃ + amorphous
1200 ℃/1 h	0.82	1.842	14.02	90.52	γ-Al₂O₃ + amorphous
1300 ℃/0.5 h	1.95	1.579	14.57	77.59	Mullite +γ-Al₂O₃ + amorphous
1400 ℃/0.5 h	2.36	0.419	15.03	20.59	Mullite
1000 ℃/20 h	0.28	1.926	13.24	94.64	γ-Al₂O₃ + amorphous
1000 ℃/40 h	1.66	1.857	13.95	91.25	γ-Al₂O₃ + amorphous

Fig. S1 SEM images of alumina ceramic continuous fiber after heat-treatment at different temperatures (overview (a1-e1), surface (a2-e2), cross section (a3-e3)) (a) 1000 ℃/1 h; (b) 1100 ℃/1 h; (c) 1200 ℃/1 h; (d) 1300 ℃/0.5 h; (e) 1400 ℃/0.5 h

Fig. S2 SEM images of alumina ceramic continuous fiber at 1000 ℃ with different holding time (overview (a1-b1), surface (a2-b2), cross section (a3-b3)) (a) 1000 ℃/20 h; (b) 1000 ℃/40 h

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