Carbon-rich boron carbide in the eutectic product synthesized by resistance heating of B2CN in graphite

Rhombohedral boron carbide has been synthesized by resistance heating of B2CN in graphite. The boron carbide and graphite form a clad morphology in a eutectic product containing ∼39 wt.% of carbon. Graphite with different interlayer spacing has been observed. A wide range of carbon-rich concentration for the boron carbide indicating strong carbon segregation has been detected. Precise measurements of lattice parameters and composition analysis for the boron carbides suggest that more than 20 at.% of carbon may have dissolved into some sections of the rhombohedral boron carbide crystals. Positions of the extra carbon atoms in the rhombohedral structure are discussed.