Property of the HPHT diamonds using stack cell and Zn coating with pressure

Fine diamond powders are synthesized with a 420 f cubic press and stack-cell composed of Kovar (Fe54Ni29Co17) (or Kovar+7 μmthick Zn electroplated) alloy and graphite disks. The high pressure high temperature (HPHT) process condition was executed at 1500 °C for 280 seconds by varying the nominal pressure of 5.7̃10.6 GPa. The density of formation, size, shape, and phase of diamonds are determined by optical microscopy, field emission scanning electron microscopy, thermal gravimetric analysis-differential thermal ammnlysis (TGA-DTA), X-ray diffraction (XRD), and micro-Raman spectroscopy. Through the microscopy analyses, we found that 1.5 μm super-fine tetrahedral diamonds were synthesized for Zn coated Kovar cell with whole range of pressure while ̃3 μm superfine diamond for conventional Kovar cell with < 10.6 GPa. Based on 750 o C exothermic reaction of diamonds in TGA-DTA, and characteristic peaks of the diamonds in XRD and micro-Raman analysis, we could confirm that the diamonds were successfully formed with the whole pressure range in this research. Finally, we propose a new process for super-fine diamonds by lowering the pressure condition and employing Zn electroplated Kovar disks.