Formation of diamond powders from melamine under high pressure and high temperature

High pressure pyrolysis of melamine has been attracting great interest recently, due to it being considered as a suitable precursor to realize the g-C₃N₄ and even superhard C₃N₄. In this work, we studied the detailed pyrolysis behavior of melamine at 22 GPa. Melamine was stable at 800 ℃, and decomposed to diamond in the form of powder at 1500-2000 ℃ under this pressure condition. At 2000 ℃, the pure cubic diamond powders with 0.1-0.5 μm grain size were obtained. The diamond particles exhibited euhedral forms and dispersed to each other, we proposed that these novel features were caused by the presence of liquid N₂ and NH₃ during diamond formation. The high pressure pyrolysis of melamine may provide a new means of producing micrometer-sized diamond powders.