Composition and Structure of Polymer-derived Aluminium-containing SiC Fibers

A ceramic fiber with the SiC(OAl) composition, named KD-A, was prepared by the melt-spinning of precursor polyaluminocarbosilane, air-curing, and pyrolizing at 1300 ℃. The KD-A fiber was converted into SiC(Al) fiber, named KD-SA, by sintering at 1800 ℃. The composition and structure of the two kinds of fibers were characterized by chemical element analysis, AES, SEM, XRD, RMS, and 29Si, 13C, 27A1 MAS NMR. The compositions of KD-A and KD-SA fibers are in the formula SiC1.31O0.25Al0.018 and SiC1.03O0.013Al0.024, respectively. The compositions of KD-A and KD-SA fibers on the surface are different from that of inside of the fibers. The surfaces of KD-A and KD-SA fibers are smooth and even, and there are no hole, crack and groove. KD-A fiber contains free carbon, small amount of β-SiC micro-crystal and aluminium embedded in an intergranular phase SiCxOy, which is ascribed to a non-crystalline SiC fiber. KD-SA fiber contains a large number of β-SiC, a small amount of α-SiC and Al2O3, which is ascribed to a crystalline SiC fiber with a nearly stoichiometric composition.