Pyrolytic conversion studies of blended polycarbosilane and polyaluminasilazane

Multinuclear solid-state NMR spectroscopy, FTIR and Raman experiments are employed to investigate the pyrolytic conversion of blended polycarbosilane and polyaluminasilazane (denoted CA) up to 800 °C, with the aim of studying structural evolutions and interactions between polycarbosilane and polyaluminasilazane during the pyrolysis process. Vinyl and SiCH3 units can react with Si–H, SiCH3 and Si–CH2–Si groups below 400 °C. These crosslinking reactions can increase the ceramic yield of the blended precursors. At 500 °C aromatic carbon is formed, and N–H and Si–H groups vanish at 600 °C and 700 °C, respectively. At 600 °C, SiCH3 and Si–H units can further react with SiCN3, SiC2N2, N–H and C–H units. An amount of amorphous carbon and CSi4 and CSi3H groups are detectable at 800 °C. Even at this temperature there are still many aromatic protons. In addition, there are also SiC4, SiC3N, SiCN3 and SiN4 units. Silicon forms SiN4 more readily than SiC4. Many AlN5 groups transform into AlN6 groups. The D and G bands of graphite are observed in CA pyrolyzed at 1400 °C. According to the XRD patterns, the reflection of crystalline β-Si3N4 vanishes at 1700 °C, and the residue pyrolyzed at 1800 °C mainly contains a large number of 2H-SiC/AlN solid solution crystals and a few β-SiC crystals.