Texture, structure and chemistry of a boron nitride fibre studied by high resolution and analytical TEM

The present work is devoted to a TEM (transmission electron microscopy) study of the texture, structure and chemistry of a boron nitride (BN) fibre. The general structure of the fibre consists of two concentric parts; the near surface region is finely nano-crystallised, while the bulk of the fibre exhibits larger crystallites, although still of nanometric sizes. All grains appear to be randomly oriented with respect to the fibre axis, which makes the mechanical properties of this material remain modest. From a crystallographic point of view, both hexagonal and rhombohedral BN forms have clearly been identified by high resolution TEM (HRTEM). From a chemical point of view, EELS (electron energy loss spectroscopy) analysis shows that the N/B atomic ratio remains close to one, although it tends to decrease slightly from the outer surface to the ‘core’. No significant amount of impurities (e.g. carbon and oxygen) has been detected. The study of the B–K and N–K edges reveals a great similarity between the hexagonal and the rhombohedral forms.