Carbon-rich SiCN ceramics derived from phenyl-containing poly(silylcarbodiimides)

Novel phenyl-containing polysilylcarbodiimides were synthesized and their thermolysis and crystallization behavior up to 2000 °C was investigated. The Si/C ratio of the preceramic polymer was varied in a defined way by starting from dichlorosilanes with different organic substituents, namely R and R′ with R = phenyl and R′ = H, phenyl, methyl or vinyl. Several techniques were employed to study the structural features of the polymers and their thermolysis products. The temperature of crystallization depends on the carbon content of the precursors. Thus, in the sample with the highest carbon content the separation of β-SiC from the amorphous SiCN matrix is observed at T > 1500 °C, resulting in the highest temperature of thermal stability against crystallization ever reported for a SiCN ceramic derived from polysilylcarbodiimides. Moreover, no crystallization of β-Si3N4 was observed.