Simple and rapid conversion of silicon carbide to nanodiamonds at ambient pressure

Nanodiamonds (NDs) were prepared under ambient pressure by sublimation decomposition of silicon carbide in an intermediate frequency furnace for only 8 min. The synthesis proceeded in the temperature range of 2600-2800 °C without any catalyst or highly active gas components (such as H2, alkane, and halogen). The conversion began at 2600 °C and produced NDs with particle sizes in the range of 1-5 nm with a uniform particle shape and excellent dispersion. The linear reaction kinetics allowed for rapid transformation to any depth with reasonable control of the temperature. The linear rate constant (Kl) for the reaction at 2800 °C was 37.5 mm/h, which is 31.2 times that of the reaction at 2600 °C. The SiC sublimation decomposition produced carbon atoms that filled the SiC lattice vacancies or were combined with the suspended carbon chain bonds to form sp3 carbon, while the diffusion of amorphous carbon atoms promoted nucleation and growth of diamond. High-resolution transmission electron microscopy analysis indicated that the NDs were separated from the SiC matrix by break-off due to propagation of the reaction front. This SiC sublimation decomposition method is considered simple, fast, environmentally friendly and promising for industrial-scale production.