Boron nitride matrices and coatings from boryl borazine molecular precursors

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Abstract
Thermal treatment of 2,4,6-[(NHPr i ) 2 B(NPr i )] 3 B 3 N 3 H 3 in vacuo led to a polyborazine in which the borazine rings are mainly linked by –N–B–N– bridges. Pyrolysis of up to 1400 °C resulted in the formation of high crystallinity hexagonal boron nitride which has been characterised by ESCA, powder X-ray diffraction and FTIR spectroscopy. Precursor has been used to prepare carbon fibres/BN microcomposites by dipping bundles of fibres into a solution of followed by pyrolysis up to 1200 °C. Optical micrographs and SEM analysis have shown that the BN matrices were compact and displayed good adherence properties onto graphite substrates. By contrast, BN coatings obtained from a polymer derived from B(NHPr i ) 3 displayed poor adherence properties. These results are related to the hydrocarbon chain ratio of each preceramic polymer. The effectiveness of the BN protective coatings in preventing oxidation has been measured by isothermal gravimetry in air. As expected, by considering the quality of the coatings, those obtained from showed the most interesting properties.

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