Evolution of crystallization and its effects on properties during pyrolysis of Si–Al–C–(O) precursor fibers

The high-temperature resistant Si–Al–C–(O) fibers were prepared through polymer-derived method using continuous polyaluminocarbosilane (PACS) fibers. Evolutions of the crystallization during the pyrolysis of the Si–Al– C–(O) precursor fibers were investigated by a series analysis. The structure of the fibers transforms from organic state to inorganic state and the crystalline phases appear during the pyrolysis. The b-SiC crystallite size increases when the temperature is higher than 1,300 C. At the same time, the a-SiC appears. At 1,600 and 1,800 C, the grain size of b-SiC of the fibers is 15.4 and 22.1 nm, respectively. The growth of b-SiC and the appearing of a-SiC have a great influence on the properties of the fibers. The change of the tensile strength of the pyrolysis products is divided into three stages with the growth of the crystal. The tensile strength of the Si-Al-C fibers is higher than 1.9 GPa.