COMBINED EFFECTS OF EXPOSURE TO SALT (NACL) WATER AND OXIDATION ON THE STRENGTH OF UNCOATED AND BN-COATED NICALON(TM) FIBERS

The environmental stability of uncoated and boron nitride-coated (BN-c oated) Nicalon(TM) fiber has been investigated by studying the effect of annealing in air at 1000 degrees C (2 h) on the strength of the fib ers. The results imply that uncoated and BN-coated fibers both degrade in strength, with the BN-coated fiber suffering a higher strength los s, The degradation is significantly enhanced if the fibers are exposed to salt (NaCl) water prior to the air anneal, if the concentration of salt is >0.5 wt%, The BN-coated Nicalon(TM) fibers also have been stu died at 800 degrees and 900 degrees C; the degradation in strength due to salt water exposure is greater at 800 degrees C than that at 900 d egrees or 1000 degrees C.