Evolution of the Ceramic Structure during Thermal Degradation of a Si-Al-C-O Precursor

Solid-state magic angle spinning nuclear magnetic resonance (MAS NMR), X-ray diffraction (XRD), and scanning electron and transmission electron microscopy (SEM and TEM) are used to study thermal degradation of a Si-Al-C-O ceramic precursor in nitrogen. A polysilane (PS) and aluminum acetylacetonate (AlAce) in the weight ratio AlAce\PS = 2 were reacted to synthesize the precursor. Solid state 29Si and 27Al MAS NMR spectra of the precursor confirm the occurrence of chemical reactions between PS and AlAce during synthesis. A complete three-dimensional Si-O-Al network forms at 900 C. Crystalline phases appear at 1300 C, and the pyrolyzed product at 1700 C is a solid solution of 2H-SiC and AlN. Solid state 29Si and 27Al MAS NMR and XRD provide detailed information about the phase formation and transformation. The morphological development and microstructure evolution are further characterized by SEM and TEM.