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The swung gel fibers were heated to 400 ℃ at 0.5, 1, 1.5, 2, 2.5, 3 and 4 ℃·min-1 of heating rate, respectively, and soaked for 1 h; then heated to 600 ℃ at 3 ℃·min-1 of heating rate and soaked for 1 h; at last calcined at 1 000, 1 100, 1 200, 1 300, and 1 400 ℃ for 1 h, respectively. The average single fiber tensile strengths of fibers after calcining at 600 ℃ or higher temperatures were determined and their surface morphology was observed. The results show that: (1) when the heating rate below 400 ℃ is 0.5-1 ℃·min-1, the average single fiber tensile strengths of 95 polycrystalline alumina fibers after calcining at 600 ℃ and 1 000-1 100 ℃ exceed 1 000 and 800 MPa, respectively, surface of the fibers after calcining at 1 000-1 100 ℃ is smooth, α-Al2O3 appears at 1 200 ℃, and a large amount of α-Al2O3 forms above 1 300 ℃; (2) when the heating rate exceeds 3 ℃·min-1, the fibers pulverize obviously.
The swung gel fibers were heated to 400 ° C at 0.5, 1, 1.5, 2, 2.5, 3 and 4 ° C · min -1 of the heating rate, respectively, and soaked for 1 h; then heated to 600 ° C at 3 ° C · min -1 of the heating rate and soaked for 1 h; at last calcined at 1 000, 1 100, 1 200, 1 300, and 1 400 ° C for 1 h, respectively. The average single fiber tensile strengths of fibers after calcining at 600 ° C or higher temperatures were determined and their surface morphology was observed. The results show that: (1) when the heating rate below 400 ° C is 0.5-1 ° C.min-1, the average single fiber tensile strengths of 95 polycrystalline alumina fibers after calcining at 600 ° C and 1 000-1 100 ° C exceed 1 000 and 800 MPa, respectively, the surface of the fibers after calcining at 1000-1 100 ° C is smooth, α-Al2O3 appears at 1 200 ° C and a large amount of α -Al2O3 forms above 1 300 ℃; (2) when the heating rate exceeds 3 ℃ · min-1, the fibers pulverize obviously.