Pyrolysis of polyborosilazane and its conversion into SiBN ceramic

The polyborosilazane was prepared by coammonolysis of boron trichloride and methyldichlorosilane with hexamethyldisilazane. The decarburisation process of the polyborosilazane under ammonia was studied. The results suggested carbon was effectively removed under ammonia and the removal of carbon mainly occurred during the temperature range of 400-600 degrees C. After pyrolysed at 900 degrees C under ammonia, the carbon content was only 0.29 wt-%. Further heat treatment at 1500 degrees C under argon yielded SiBN ceramic. The structure and morphological properties of SiBN ceramic were studied by solid Si-29 nuclear magnetic resonance, X-ray diffraction and scanning electron microscopy. The results showed that the SiBN ceramic was amorphous and possessed a smooth surface. The contents of boron, silicon and nitrogen in the SiBN ceramic are 10.9, 42.6 and 38.48 wt-% respectively.