M. Takeda et al./ Composites Science and Technology 59(1999)813-819 10 um x2,k81 20 um Fig. 7. SEM photographs of(a) Hi-Nicalon M and(b) Nicalon M after the exposure for 10 h in argon at 2273K but also by N2 elimination, which is known in silicon nitride ceramics Si3N4→3Si+2N2 1673 K 10 hours These fibers evolved CO, Sio, and N2 gas at high tem perature because of their decomposition, resulting in weight loss. Oxygen and nitrogen in silicon non-oxide 台A别 ceramics are unstable at elevated temperature in an inert 1573 K 10 hours atmosphere. Hi-Nicalon'm exhibited outstanding ther- mal stability as compared to the other polymer-derived As Recelved ceramic fibers The changes in physical and chemical properties after thermal exposure were examined. Fig. 8 shows XRD 405060708090 patterns for NicalonM and Hi-Nicalon TM fibers before nd after thermal exposure. Obvious B-Sic crystal growth and a disordered stacking structure [19are Fig 9. X-ray difiraction patterns of HPZ fiber before and after ther. observed in both fibers after exposure at 1873 K for 10 h mal exposure tests. in argon. The B-Sic crystallite size of Hi-NicalonTM after the treatment is smaller than that of Nicalon TM.In the case of Hi-Nicalon TM. excess carbon in the fiber 30L△ Tyranno Lox M 口HPz Hi-Nicalon c 20 As15001600170018001900 3040506070 Temperature(K) Fig. 8. X-ray diffraction patterns of Hi-NicalonM and Nicalon Fig. 10. B-SiC crystalline size of ceramic fibers after the exposure for before and after thermal exposure test. 10 h in argon.but also by N2 elimination, which is known in silicon nitride ceramics. Si3N4 ! 3Si ‡ 2N2 These ®bers evolved CO, SiO, and N2 gas at high tem￾perature because of their decomposition, resulting in weight loss. Oxygen and nitrogen in silicon non-oxide ceramics are unstable at elevated temperature in an inert atmosphere. Hi-NicalonTM exhibited outstanding ther￾mal stability as compared to the other polymer-derived ceramic ®bers. The changes in physical and chemical properties after thermal exposure were examined. Fig. 8 shows XRD patterns for NicalonTM and Hi-NicalonTM ®bers before and after thermal exposure. Obvious -SiC crystal growth and a disordered stacking structure [19] are observed in both ®bers after exposure at 1873 K for 10 h in argon. The -SiC crystallite size of Hi-NicalonTM after the treatment is smaller than that of NicalonTM. In the case of Hi-NicalonTM, excess carbon in the ®ber Fig. 8. X-ray di€raction patterns of Hi-NicalonTM and NicalonTM before and after thermal exposure test. Fig. 9. X-ray di€raction patterns of HPZ ®ber before and after ther￾mal exposure tests. Fig. 7. SEM photographs of (a) Hi-NicalonTM and (b) NicalonTM after the exposure for 10 h in argon at 2273 K. Fig. 10. -SiC crystalline size of ceramic ®bers after the exposure for 10 h in argon. M. Takeda et al. / Composites Science and Technology 59 (1999) 813±819 817