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℃ without any catalyst or highly active gas components(such as H2,alkane,and halogen).The conversion began at 2600℃ 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(K_(l))for the reaction at 2800℃ was 37.5 mm/h,which is 31.2 times that of the reaction at 2600℃.The Si C sublimation decomposition produced carbon atoms that filled the Si C 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 Si C matrix by break-off due to propagation of the reaction front.This Si C sublimation decomposition method is considered simple,fast,environmentally friendly and promising for industrial-scale production.