Characterization of a boro-silicon oxynitride prepared by thermal nitridation of a polyborosiloxane

Fine physicochemical characterization has allowed proposing of a mechanism for the nitridation pathway of a polyborosiloxane polymer into a new ceramic material in the SiBON system. A polyborosiloxane, a polymer consisting of SiOB linkages, was synthesized by the condensation reaction between tetrachlorosilane SiCl4 and boric acid B(OH)3. The polymer was then thermally nitridated under flowing ammonia into an oxynitride of boron and silicon. This conversion was observed using various structural techniques: chemical analysis, X-ray diffraction, infrared spectroscopy and X-ray photoelectron spectroscopy. The nitridation process can be divided in two main stages: (i) between 400 and 800°C, BN bonds are formed by BO bond cleavage; (ii) above 1000°C, SiN bonds are formed by SiO bond cleavage. The oxynitride remains amorphous even at 1300°C. Pyrolysis up to 1700°C led to a partial crystallization of hexagonal boron nitride.