Effects of NaN₃ Added in Fe-C System on Inclusion and Impurity of Diamond Synthesized at High Pressure and High Temperature

Effects of NaN₃ added in Fe-C system to synthesize nitric diamond at high pressure and high temperature are investigated. Diamond crystals with high nitrogen concentration are synthesized by the system of Fe-C and NaN₃ additive at pressure 5.8GPa and at temperatures 1750-1780K for 15min. The synthetic diamond crystals have a cubo-octahedral or octahedral shape with yellowish green or green colour. Some disfigurements are observed on the surfaces of most diamond crystals. The composition and content of inclusions formed by iron in diamond are changed and iron nitride is detected in diamond crystals synthesized with Fe-C-NaN₃ additive. As the amount of NaN₃ additive increases, Fe₃C decreases and iron nitride increases with α-Fe being nearly constant. Moreover, the nitrogen concentrations in diamond crystals synthesized with 1.5wt% NaN₃ additive is up to 2250ppm in substitutional form.