直接转化法合成大尺寸纯相多晶金刚石

在不同热力学条件下，以不同碳源为初始材料，采用直接转化法合成不同晶粒尺寸、不同颜色的纯相多晶金刚石块体（φ6 mm×6 mm），并用X射线衍射、Raman光谱及扫描电镜等方法检测验证。采用维氏压痕法测得纳米结构的黄色透明样品硬度为130~270 GPa（加载3 N）。对黄色透明样品进行砂轮对磨实验，其磨耗比达1.658×106，约为现在市场上主流钴基石油用金刚石复合片的25倍。差热分析表明:黄色透明样品的热稳定性与克拉级单晶金刚石基本持平；以纳米结构多晶金刚石与金刚石大单晶对磨，测定其磨耗比为2.5，表现出比金刚石大单晶更优越的耐磨性。 

Synthesizing bulk polycrystalline diamond by method of direct phase transition

Pure-phase bulk polycrystalline diamonds are prepared through direct phase transition at ultrahigh pressure and high temperature. The phase composition and microstructure of the pure-phase bulk polycrystalline diamonds are studied by SEM, XRD and Raman spectrum. It is found that with different raw materials and different conditions, diamond samples have different colors and different grain sizes but they are all pure-phase polycrystalline diamonds.The average grain sizes for yellow-transparent and green samples are about 25 nm and 35 μm, respectively. The size of synthesized diamond blocks is φ6 mm×6 mm. The Vicker's hardness of yellow-transparent polycrystalline diamond, HV, is 130-270 GPa at the load of 3 N. According to China National Quality Supervision & Inspection Center for Abrasives, the abrasion ratio of yellow-transparent sample is 1.658×106, which is 25 times higher than that of commercial Co-based PCD used on oil bits. TG/DSC shows that the thermal stability of the yellow-transparent sample is almost the same as that of carat-level single-crystal diamond.Contrast grinding test, using NPD to grind against carat-level single-crystal diamond, shows that the abrasion ratio for the nano-structured polycrystalline diamond is 2.5, which demonstrates that the abrasion performance of NPD is much better than that of carat-level single-crystal diamond.