Carbon–boron–nitrogen alloys from borazarene-derived mesophase pitches Original Research Article

Synthetic routes to new C–B–N-containing mesophase materials from borazarene-type precursors have been explored. Such mesophases have the potential for forming C/BN alloys which could be processed in analogous ways to carbonaceous mesophases, e.g. into cokes, fibres and composites. Carbon–boron–nitrogen-based mesophase pitches have been generated at ambient pressure by pyrolysis of borazarenes in the presence of AlCl3. The AlCl3 is essential for mesophase formation in these systems. Pyrolyses of 10-chloro-9-aza-10-boraphenanthrene and 2,2′-bis(dichloroborylamino)biphenyl have both yielded black, optically anisotropic pitches. These precursors form C/BN ceramic alloys which are turbostratic following heat treatment to 1000 °C. The alloys show a clear advantage in terms of their oxidation resistance, compared with that of carbon derived from naphthalene mesophase pitch, despite contamination with AlCl3, which probably catalyses their oxidation.