MICROSTRUCTURAL STABILITY OF NICALON AT 1000-DEGREES-C IN AIR AFTER EXPOSURE TO SALT (NACL) WATER

When either uncoated or BN-coated Nicalon fibers are exposed to water saturated with NaCl before being annealed in air at 1000 degrees C, ac celerated degradation of the structure of the fiber occurs. The fiber surface oxidizes to tridymite instead of vitreous silica, and the crys tallites of SIC in Nicalon begin to grow. These findings suggest that prior exposure to salt water may cause appreciable debit in the mechan ical strength of Nicalon fibers with time at 1000 degrees C in air.