微晶石墨对Ⅱa型宝石级金刚石单晶生长的影响

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

将除氮剂Ti(Cu)添加到FeNiCo合金触媒中在高温高压下合成出优质Ⅱa型宝石级金刚石单晶。在压力5.4GPa、温度1600K的条件下沿{111}面合成Ⅱa型宝石级金刚石过程中伴随有黑色粉末析出。采用X射线衍射(XRD)和扫描电子显微镜(SEM)对该黑色石墨粉末的测试表明其为微晶石墨。随着生长时间的延长,这种微晶石墨粉末形成小帽覆盖在金刚石上使金刚石的平均生长速度从30h的1.15mg/h降为50h的0.75mg/h。采取一定工艺措施大大降低了微晶石墨的析出,避免了其对金刚石生长速度的影响。

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-Ⅱ a 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.