以磷化铁为添加剂沿(111)面生长磷掺杂金刚石大单晶

掺杂是调控金刚石性能的一种重要手段。本文采用温度梯度法,在5.6 GPa、1 312 ℃的条件下,选用Fe₃P作为磷源进行磷掺杂金刚石大单晶的合成。金刚石样品的显微光学照片表明,随着Fe₃P添加比例的增加,金刚石晶体的颜色逐渐变深,包裹体数量逐渐增加,晶形由板状转变为塔状直至骸晶。金刚石晶形的变化表明Fe₃P的添加使生长金刚石的V形区向右偏移,这是Fe₃P改变触媒特性的缘故。红外光谱分析表明,Fe₃P的添加使金刚石晶体中氮含量上升,这说明磷的进入诱使氮原子更容易进入金刚石晶格中。激光拉曼光谱测试表明,随着Fe₃P添加比例的增加,所合成的掺磷金刚石的拉曼峰位变化不大,其半峰全宽(FWHM)值变大,这说明磷的进入使得金刚石晶格畸变增加。XPS测试结果显示,随着Fe₃P添加比例的增加,金刚石晶体中磷相对碳的原子百分含量也会增加,这意味着添加Fe₃P所合成的金刚石晶体中有磷存在。     

Growth of gem-grade nitrogen-doped diamond crystals heavily doped with the addition of Ba（N3）2

Additive Ba(N 3) 2 as a source of nitrogen is heavily doped into the graphite-Fe-based alloy system to grow nitrogendoped diamond crystals under a relatively high pressure (about 6.0 GPa) by employing the temperature gradient method.Gem-grade diamond crystal with a size of around 5 mm and a nitrogen concentration of about 1173 ppm is successfully synthesised for the first time under high pressure and high temperature in a China-type cubic anvil highpressure apparatus.The growth habit of diamond crystal under the environment with high degree of nitrogen doping is investigated.It is found that the morphologies of heavily nitrogen-doped diamond crystals are all of octahedral shape dominated by {111} facets.The effects of temperature and duration on nitrogen concentration and form are explored by infrared absorption spectra.The results indicate that nitrogen impurity is present in diamond predominantly in the dispersed form accompanied by aggregated form,and the aggregated nitrogen concentration in diamond increases with temperature and duration.In addition,it is indicated that nitrogen donors are more easily incorporated into growing crystals at higher temperature.Strains in nitrogen-doped diamond crystal are characterized by micro-Raman spectroscopy.Measurement results demonstrate that the undoped diamond crystals exhibit the compressive stress,whereas diamond crystals heavily doped with the addition of Ba(N 3) 2 display the tensile stress.     

基于有限元法分析宝石级金刚石的合成腔体温度场

以有限元法为理论分析手段模拟分析了温度梯度法合成宝石级金刚石大单晶的腔体温度场,实现了对宝石级金刚石的合成腔体内各位置温度同时测量.模拟结果表明:在宝石级金刚石合成过程中,其温度分布呈不均匀分布.腔体内高温区分布在样品(碳源+触媒)边缘,低温区分布在籽晶附近.样品腔内热量的传递方式和样品腔内的碳源输运方式相同,均由碳源的两侧向籽晶附近传输.籽晶附近轴向温度梯度大于径向温度梯度,导致单位时间内其轴向生长尺寸大于径向生长尺寸.宝石级金刚石腔体温度场分析的理论模型的成功构建,为新型宝石级金刚石腔体的研制提供了良好的设计基础,对促进优质宝石级金刚石的生长技术具有指导意义.     

基于有限元法确立碳化钨顶锤的破裂判据

以有限元法为理论基础,通过运行大型有限元软件,成功构建了铰链式六面顶压机配套顶锤的有限元理论模型,并确立了碳化钨顶锤的破裂判据。模拟结果表明:以小斜边末尾处为应力参考点,依据第四强度理论,能够对碳化钨顶锤的性能进行更加合理的数值分析。依据此判据可知:在顶锤锤面及小斜边附近,裂纹高发区分布在小斜边附近;在顶锤轴向上,裂纹高发区分布在距离顶锤锤面30 mm处。铰链式六面顶压机配套碳化钨顶锤的有限元模型以及碳化钨顶锤破裂判据的成功构建,为实现新型碳化钨顶锤的设计与研究奠定了基础,对促进实现铰链式六面顶压机腔体大型化具有现实意义。     

碳酸钙掺杂对Ⅰb型金刚石沿不同晶面生长行为的影响

作为天然金刚石生长环境的碳酸盐,研究其掺杂对人造金刚石晶体生长行为的影响具有重要的学术价值。本文运用高温高压下的温度梯度法,将碳酸钙(CaCO₃)按照不同比例掺杂到金刚石合成腔体内的碳源中,用以研究其掺杂对金刚石分别沿(100)或(111)晶面生长行为的影响。利用光学显微成像对掺杂合成金刚石晶体形貌的表征表明:随着碳酸钙掺量的增加,沿(100)面生长的金刚石晶形由塔状变为板状且出现了裂晶、连晶现象,晶体颜色先变浅再变黑,内部出现了包裹体;同样,沿(111)面生长的金刚石晶形由板状逐渐变为塔状且出现了裂晶、孪晶现象,晶体颜色逐渐变黑,内部包裹体增多。用激光拉曼光谱对掺杂金刚石晶体质量的表征表明:随着碳酸钙掺量的增加,沿(100)或(111)面生长的掺杂金刚石的拉曼峰位偏移量均增大,半峰全宽均变大。这说明碳酸钙掺杂使得金刚石晶格畸变增加、内应力变大。本文对碳酸钙掺杂影响沿两不同面生长金刚石的晶形、颜色、内部质量等行为的成因进行了分析,为本课题后续研究奠定了基础。     

基于三维有限元法模拟分析六面顶顶锤的热应力

以有限元法为理论分析手段模拟分析了国产六面顶压机配套顶锤内部的温度场和热应力分布.探寻出了XKY-6×2000 MN型六面顶压机顶锤内部的温度场分布以及热应力取值.模拟结果表明加热顶锤内部温度分布不均匀,不均匀的温度分布产生了热剪切应力,热剪切应力峰值达到0.62 GPa,分布在41.5°小斜面上.加热顶锤内部的剪切应力值较非加热锤内部的剪切应力值高出18.0％.模拟分析结果与金刚石的高压合成实验事实相符,在理论上解释了加热顶锤使用寿命较非加热顶锤使用寿命短的原因,此项工作对于提高大顶锤使用寿命,降低生产 关键词： 热应力 顶锤 有限元法 工业金刚石     

高压下国产六面顶压机铰链梁和工作缸的应力分析

运用有限元理论,基于ANSYS对国产六面顶压机的铰链梁、工作缸和销轴进行了接触分析。模型中首次引入销轴,约束销轴的运动,使凸耳处的载荷情况更接近实际工况,避免了对铰链梁和工作缸单独分析所进行的大量近似和简化。模拟结果表明:铰链梁上的vonMises应力峰值主要分布在凸耳内通孔处,最大应力值为348.32 MPa;工作缸上的von Mises应力峰值主要分布在工作缸底部圆弧处,最大应力值为242.87 MPa;应力峰值均低于许用应力(486.67 MPa)。模拟结果得到了大量高压实验的验证。     

Evolution of nitrogen structure in N-doped diamond crystal after high pressure and high temperature annealing treatment

In this paper, we have reported an investigation on the evolution of nitrogen structures in diamond crystals which contain nitrogen donor atoms in the range of 1500 ppm-1600 ppm following an annealing treatment at a high pressure of about 6.5 GPa and high temperatures of 1920 K-2120 K. The annealing treatment was found to completely transform nitrogen atoms originally arranged in a single substitutional form （C-center）, into a pair form （A-center）, indicated from infrared （IR） spectra. The photoluminescence （PL） spectra revealed that a small fraction of nitrogen atoms remained in C-center form, while some nitrogen atoms in A-center form were further transformed into N3 and H3 center structures. In addition, PL spectra have revealed the existence of two newly observed nitrogen-related structures with zero phonon lines at 611 nm and 711 nm. All these findings above are very helpful in understanding the formation mechanism of natural diamond stones of the Ia-type, which contains nitrogen atoms in an aggregated form.     

Effects of Mg on diamond growth and properties in Fe–C system under high pressure and high temperature condition

Diamond crystal crystallized in Fe–Mg–C system with Archimedes buoyancy as a driving force is established under high pressure and high temperature conditions. The experimental results indicate that the addition of the Mg element results in the nitrogen concentration increasing from 87 ppm to 271 ppm in the diamond structure. The occurrence of the {100}plane reveals that the surface character is remarkably changed due to the addition of Mg. Micro-Raman spectra indicate that the half width of full maximum is in a range of 3.01 cm~(-1)–3.26 cm~(-1), implying an extremely good quality of diamond specimens in crystallization.     

FEM simulations and experimental studies of the temperature field in a large diamond crystal growth cell

We investigate the temperature field variation in the growth region of a diamond crystal in a sealed cell during the whole process of crystal growth by using the temperature gradient method (TGM) at high pressure and high temperature (HPHT). We employ both the finite element method (FEM) and in situ experiments. Simulation results show that the temperature in the center area of the growth cell continues to decrease during the process of large diamond crystal growth. These results are in good agreement with our experimental data, which demonstrates that the finite element model can successfully predict the temperature field variations in the growth cell. The FEM simulation will be useful to grow larger high-quality diamond crystal by using the TGM. Furthermore, this method will be helpful in designing better cells and improving the growth process of gem-quality diamond crystal.