HIGH TEMPERATURE RESISTANCE SiC ( Al) FIBERS

The precursor, Polyalumicarbosilane (PACS) of super-high temperature resistance SiC ( Al) fibers was synthesized by the reaction of polysilocarbosilane, or PSCS, with Al ( AcAc)₃. The process to prepare SiC ( Al) fibers by PACS is in four steps: (1)Melt-spinning of PACS into "green fibers", (2) Curing the fibers to make fibers infusible, (3) Pyrolysis of the cured fibers at 1300℃ in inert atmosphere, (4) Sintering of the pyrolyzed fibers. The composition of SiC ( Al) fibers is described in the formula Si₁C_1.15O_0.026Al_0.013, in which there are mainly β-SiC grains in size of 95nm, 0.87wt% aluminum, small amount of α -SiC, SiC_xO_y phase and free carbon. The content of SiC_xO_y phase and free carbon is much lower than that of Nicalon fibers. The content of oxygen and silicon on the surface of the fibers is some higher than inside; while Si, C, O and Al are uniformly distributed inside the fibers. The average tensile strength of SiC ( Al) fibers is 2.3 GPa, with the average diameter 13 μm. The initial tensile strength of the fibers remains 95% after the treatment at 1400℃ for 1h in argon. After sintering at 1800℃ for 1h in argon, SiC ( Al) fibers remain the initial tensile strength by 71%. The high temperature stability of the fibers is better than that of Nicalon, but inferior to that of Tyranno SA.