Synthesis of low density and high hardness carbon spheres containing nitrogen and oxygen

The synthesis of new carbon compounds is of considerable interest in modern materials science. The recent report by Niu et al. of the experimental realization of the β-C₃N₄ covalent solid predicted theoretically by Liu and Cohenhas opened up the possibility of producing a new family of materials with a hardness close to that of a diamond. In the present work we report the growth for the first time of a new all covalent material with contains C, N and O. The material was produced by thermal decomposition of an hydrocarbon at high temperatures. Most of the solid has the chemical composition; C_xN_yO_z with x {reversed tilde equals} 4, y {reversed tilde equals} 1 and z {reversed tilde equals} 0.025 and is made of filaments forming a web. The material has a density of 1.59 g cm^-3 which corresponds to that of the low density graphites and hardness of 1929 kg mm^-2 (Vickers). This last value is larger than that corresponding to the hardest known steels. High resolution electron microscopy, electron diffraction and X-ray diffraction indicate that the crystalline nature of the C₄NO_0.025 corresponds with a cubic lattice with a = 7.38 Å. The results of this work show the possibility of producing light materials with a very large hardness which might yield useful applications.