Effect of micro-crystal graphite on the growth rate of type-IIa large diamonds

Type-Ⅱa large diamonds have been Synthesized under high pressure and high temperature(HPHT) which the nitrogen getter Ti(Cu) was added to FeNiCo catalyst.The black powder was precipitated around the diamonds which grow along {111} at about 5.4GPa and 1600K.The black powder,which was precipitated on the growth of type-Ⅱa large diamonds,was characterized as micro-crystal graphite by the testing of X-ray diffraction(XRD) and scan electron microscope(SEM).With the growth-time prolonged the large diamonds were covered with the cap which was shaped by the black powder.It can be shown from the experiments that the average growth rate of type-Ⅱa large diamond was reduced from 1.15mg/h(40h) to 0.75mg/h(50h) by micro-crystal graphite.The measures were adopted to reduce the quantity of micro-crystal graphite and avoid it to affect the growth rate of large diamonds.