The pyrolysis temperature dependence of tensile strength has been studied for silicon nitride fibers produced by pyrolysis of perhydropolysilazane fibers in N2. The tensile strength of silicon nitride fibers increased up to 4300MPa with increasing pyrolysis temperature. Catastrophic drops in tensile strength took place following crystallization of Si3N4. Crystalline Si precipitated at 1100°C and crystallization of α-Si3N4 took place at 1200°C in silicon nitride fibers (B) derived from perhydropolysilazane fibers in which the Si/N atomic ratio deviated from 3/4 in the presence of excess Si. Crystallization of α-Si3N4 took place at 1400°C in silicon nitride fibers (A) produced from perhydropolysilazane fibers with the near stoichiometric composition. Silicon nitride fibers (A) retained high tensile strength even after exposing above 1300°C.
