CHARACTERIZATION OF A BORO-SILICON OXYNITRIDE PREPARED BY THERMAL NITRIDATION OF A POLYBOROSILOXANE

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