Si-B-C-N ceramic precursors derived from dichlorodivinylsilane and chlorotrivinylsilane.: 2.: Ceramization of polymers and high-temperature behavior of ceramic materials

Starting from five different Si-B-C-N polymeric precursors with B/N atomic ratios ranging from 1:3 to 1:0.5, ceramic materials were synthesized by thermolysis at 1400 T in about 70-75% yield. During this transformation, the Si/B/N ratio remained roughly constant, whereas H and C contents were reduced. The crystallization behavior of as-obtained ceramics was studied by X-ray diffraction. SiC was detected as the first crystalline phase forming during thermolysis or subsequent annealing. Further phase evolution can be predicted following thermodynamic calculations depending on the composition which is, for the different as-obtained materials, located in or close to the phase fields BN + Si3N4 + C, BN + Si3N4 + SiC + C, BN + SiC + C, or BN + B4+deltaC + SiC + C. The SiC-poor (Si3N4-rich) material was not high-temperature stable and decomposed releasing nitrogen, whereas SiC-rich (Si3N4-poor) materials were mass stable up to 2000 degreesC.