Effects of the additive NaN3 added in powder catalysts on the morphology and inclusions of diamonds synthesized under HPHT

In this paper, the effects of the additive NaN3-added in powder catalysts to synthesize nitric diamond were studied in a cubic anvil high-pressure and high-temperature apparatus (SPD-6 × 1200). Diamond crystals with perfect shape were successfully synthesized using NaN3-added Fe90Ni10 catalyst under pressure 5.4 GPa and temperature 1600 K for 15 min. The temperature and pressure of crystals growth were increased with an increase of the content of NaN3. The V-shape section for the diamond's growth, which is the region between the solvent/carbon eutectic melting line and diamond/graphite equilibrium line under pressure and temperature, was moved upwards. The synthetic diamonds exhibited perfect cubo-octahedral shape or octahedral shape with green or densely green in color. However, some orderly accidented lines were observed on the surfaces of most of the diamond crystals synthesized with NaN3-added in Fe90Ni10. These lines might be formed during the procedure of crystal growth according to the results of the scanning electron microscope images. Moreover, the Mössbauer spectrometry for these diamonds indicated that the concentrations of inclusions formed by iron in diamonds were changed and iron nitride was detected.