合成腔体尺寸对Ib型六面体金刚石单晶生长的影响

Effects of cavity size on the growth of hexahedral type-Ib gem-diamond single crystals

利用液压缸直径为550 mm的大缸径六面顶压机,在5.6 GPa,1200—1400?C的高压高温条件下,分别采用单晶种法和多晶种法,开展了Ib型六面体宝石级金刚石单晶的生长研究,系统考察了合成腔体尺寸对Ib型六面体金刚石大单晶生长的影响.首先,阐述了合成腔体尺寸对合成设备油压传递效率的影响,研究得到了设备油压与腔体内实际压力的关系曲线;其次,选择尺寸为Φ14 mm的合成腔体,分别采用单晶种法和多晶种法(5颗晶种),进行Ib型六面体金刚石大单晶的生长实验,研究阐述了Φ14 mm合成腔体的晶体生长实验规律;再次,为了解决液压缸直径与合成腔体尺寸不匹配的问题,将合成腔体尺寸扩大到26 mm,并开展了多晶种法六面体金刚石大单晶的生长研究,最多单次生长出14颗优质3 mm级Ib型六面体金刚石单晶,研究得到了Φ26 mm合成腔体生长3 mm级Ib型六面体金刚石单晶的实验规律,并就两种腔体合成金刚石单晶的总体生长速度与生长时间的关系进行了讨论;最后,借助于拉曼光谱,将合成的优质六面体金刚石单晶与天然金刚石单晶进行对比测试,对所合成晶体的结构及品质进行了表征.

In the paper, using the one-seed method and multiseed method separately, the hexahedral type-Ib diamonds are synthesized in a cubic anvil under high pressure and high temperature. This cubic anvil is of Φ550 mm hydraulic cylinder with the sample chambers of 14 mm or 26 mm in diameter under 5.6 GPa and 1200–1400？C. The Fe Ni Mn Co alloy is chosen as catalyst. The high-quality abrasive diamonds each with a diameter of 0.9 mm are used as seed crystals.High purity-graphite powder（99.99%, purity） is selected as the carbon source. The effects of cavity size on the growth of hexahedral type-Ib Gem-diamond single crystal are studied carefully. The Relationship between oil pressure and synthesis pressure is obtained in our studies. When the pressure is transmitted the same distance, in the catalyst melt,the pressure loss is less than in the pressure transmitting medium. By expanding synthesis cavity size, the pressure transmission efficiency of the oil pressure increases significantly, which can be attributed to the transmission distance shortening in the pressure transmitting medium and transmission distance lengthening in the catalyst melt. Using theΦ14 mm synthesis cavity, by the one-seed method, the 5 mm grade diamond single crystals of cubo-octahedral shape are synthesized, but the 5 mm grade diamond single crystals of perfectly hexahedral shape could not be synthesized.Choosing the Φ14 mm synthesis cavity, by the five-seed method, the 3 mm grade diamond single crystals in the center each present a perfectly hexahedral shape, but each outside of the crystals exhibits a cubo-octahedral shape. According to the application requirement for the type-Ib hexahedral diamond single crystal with a size of 3.0–3.5 mm on an industrial diamond single crystal tool, the diamond single crystals of perfect hexahedral shape are synthesized by the multiseed method. Using the Φ26 mm synthesis cavity, many 3 mm grade diamond single crystals of perfectly hexahedral shape are synthesized in one synthesis cavity. In our studies, up to 14 diamond single crystals of perfect hexahedral shape are synthesized in one synthesis cavity by the multiseed method. We find that the uniformity of temperature field of the Φ26mm synthesis cavity is better than that of the Φ14 mm synthesis cavity, so the Φ26 mm synthesis cavity is suitable for growing 3 mm grade diamond single crystals of perfect hexahedral shape by the multiseed method. In 35 h growth time,the overall growth rate of the Φ26 mm synthesis cavity（25.2 mg/h） synthesizing 14 diamonds in one time（9.4 mg/h） is2.68 times that of the Φ14 mm synthesis cavity by five-seed method. Moreover, the Raman spectra of the synthesized high-quality hexahedral type-Ib diamond single crystals and natural diamond single crystal indicate that the structure and quality of the synthesized high-quality diamond single crystal is better than that of a natural diamond.