Effect of Carbon Source with Different Graphitization Degrees on the Synthesis of Diamond

Using three kinds of graphites with different graphitization degrees as carbon source and Fe-Ni alloy powder as catalyst, the synthesis of diamond crystals is performed in a cubic anvil high-pressure and high-temperature apparatus （SPD-6 × 1200）. Diamond crystals with perfect hexoctahedron shape are successfully synthesized at pressure from 5.0 to 5.5GPa and at temperature from 1570 to 1770K. The synthetic conditions, nucleation, morphology, inclusion and granularity of diamond crystals are studied. The temperature and pressure increase with the increase of the graphitization degree of graphite. The quantity of nucleation and granularity ofdiamonds decreases with the increase of graphitization degree of graphite under the same synthesis conditions. Moreover, according to the results of the M6ssbauer spectrum, the composition of inclusions is mainly Fe3 C and Fe-Ni alloy phases in diamond crystals synthesized with three kinds of graphites.     

Dependence of Limited Growth Rate of High-Quality Gem Diamond on Growth Conditions

The growth rate of diamond has been investigated for a long time and researchers have been attempting to enhance the growth rate of high-quality gem diamond infinitely. However, it has been found according to previous research results that the quality of diamond is debased with the increase of growth rate. Thus, under specific conditions, the growth rate of high-quality diamond cannot exceed a limited value that is called the limited growth rate of diamond. We synthesize a series of type Ib gem diamonds by temperature gradient method under high pressure and high temperature （HPHT） using the as-grown {100} face. The dependence of limited growth rate on growth conditions is studied. The results show that the limited growth rate increases when synthetic temperature decreases, also when growth time is prolonged.     

添加剂Si对NiMnCo触媒合成金刚石的影响

本文研究了添加剂Si对NiMnCo粉末触媒合成金刚石生长特性的影响.实验中将不同比例的无定形Si粉直接添加到Ni-Mn-Co-C体系中并均匀混合,在国产六面顶压机上进行了金刚石单晶的合成实验.结果表明,由于掺Si量的不同,合成金刚石的最低生长压力有所不同,"V"形区发生了移动;通过考察Ni-Mn-Co-C和Ni-Mn-Co-Si-C两种体系中合成金刚石的情况并借助于光学显微镜,发现两种体系所合成的晶体颜色变化并不大,但随着Si含量的增加,晶体的完整性变差,包裹体增多;通过XPS检测发现,在Ni-Mn-Co-Si-C体系所合成的金刚石当中存在SiC.     

优质立方六面体金刚石大单晶的生长研究

高温高压静压触媒法合成的金刚石单晶,往往呈现六八面体形貌,因为立方六面体单晶{100}面的生长区间相对较小.本研究利用高温高压温度梯度法,自制Fe-Ni合金触媒,通过对合成组装和工艺进行合理调整后,控制晶体在相对低温适合{100}面生长区域内生长,得到的晶体均呈现完整立方六面体形貌;同时为抑制包裹体和其他杂质的进入,人为的提高晶体的径向平铺生长速度,抑制其轴向生长速度.以在33 h内合成的优质立方六面体晶体为例,晶体最大方向尺寸达到7.3 mm,重1.2克拉,其径向生长速度达到0.22 mm/h,轴向生长速度仅为0.08 mm/h,增重速度为7.3 mg/h.     

天然和培育金刚石品质表征与呈色分析

金刚石是集最高硬度、超宽禁带、最高热导率等优异性能于一体的典型超硬多功能材料,天然金刚石储量低且价格昂贵,其中彩色天然金刚石在自然界中产储量极其稀少且致色机制较为复杂。高温高压法是制备金刚石的有效手段,然而调控金刚石颜色获得可控的彩色金刚石,仍面临极大挑战。本文通过对粉色、绿色天然和高温高压温度梯度法制备的金刚石进行一系列拉曼、荧光、红外和可见光吸收测试,详细地研究其品质、缺陷随温度变化及致色原因,发现彩色金刚石致色与电中性的N₂V缺陷(H₃)、剪切应力、塑性形变和NV⁰/NV^-色心等因素相关。通过各种手段获得不同颜色的金刚石不仅是为了其欣赏及收藏价值,其颜色的调控也有助于人们对金刚石形成机制的进一步了解,为培育彩色金刚石提供新的参考。     

Properties of B_4C-TiB_2 ceramics prepared by spark plasma sintering

By doping titanium hydride(TiH2) into boron carbide(B4C), a series of B4C + x wt% TiH2(x = 0, 5, 10, 15, and 20)composite ceramics were obtained through spark plasma sintering(SPS). The effects of the sintering temperature and the amount of TiH2 additive on the microstructure, mechanical and electrical properties of the sintered B4C-TiB2 composite ceramics were investigated. Powder mixtures of B4C with 0–20 wt% TiH2 were heated from 1400℃ to 1800℃ for 20 min under 50 MPa. The results indicated that higher sintering temperatures contributed to greater ceramic density. With increasing TiH2 content, titanium diboride(TiB2) formed between the TiH2 and B4C matrix. This effectively improved Young’s modulus and fracture toughness of the composite ceramics, significantly improving their electrical properties: the electrical conductivity reached 114.9 S·cm-1 at 1800℃ when x = 20. Optimum mechanical properties were obtained for the B4C ceramics sintered with 20 wt% TiH2, which had a relative density of 99.9±0.1%, Vickers hardness of 31.8 GPa,and fracture toughness of 8.5 MPa·m1/2. The results indicated that the doping of fine Ti particles into the B4C matrix increased the conductivity and the fracture toughness of B4C.     

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。     

Effect of the codoping of N—H—O on the growth characteristics and defects of diamonds under high temperature and high pressure

Diamond crystals were synthesized with different doping proportions of N—H—O at 5.5 GPa—7.1 GPa and 1370 °C—1450 °C. With the increase in the N—H—O doping ratio, the crystal growth rate decreased, the temperature and pressure conditions required for diamond nucleation became increasingly stringent, and the diamond crystallization process was affected. [111] became the dominant plane of diamonds; surface morphology became block-like; and growth texture, stacking faults, and etch pits increased. The diamond crystals had a two-dimensional growth habit. Increasing the doping concentration also increased the amount of N that entered the diamond crystals as confirmed via Fourier transform infrared spectroscopy. However, crystal quality gradually deteriorated as verified by the red-shifting of Raman peak positions and the widening of the Raman full width at half maximum. With the increase in the doping ratio, the photoluminescence property of the diamond crystals also drastically changed. The intensity of the N vacancy center of the diamond crystals changed, and several Ni-related defect centers, such as the NE1 and NE3 centers, appeared. Diamond synthesis in N—H—O-bearing fluid provides important information for deepening our understanding of the growth characteristics of diamonds in complex systems and the formation mechanism of natural diamonds, which are almost always N-rich and full of various defect centers. Meanwhile, this study proved that the type of defect centers in diamond crystals could be regulated by controlling the N—H—O impurity contents of the synthesis system.     

优质立方六面体金刚石大单晶的表征研究

利用高温高压温度梯度法制备的优质六面体金刚石大单晶样品进行了颜色均一性、拉曼光谱和红外光谱表征,并与国外著名金刚石公司元素六和日本住友电气公司的优质六面体金刚石单晶样品性能进行了比较。就颜色均一性而言,跟国外样品相比,我们的金刚石样品颜色黄色相对更加均匀,而元素六样品中存在明显的浅色{110}生长区域;样品的1332 cm-1金刚石拉曼峰半宽要小于元素六样品,但大于日本住友金刚石样品;显微红外对金刚石样品中氮含量测试结果发现,金刚石样品氮含量在240 ppm左右,远远高于日本住友公司和元素六公司,这可能与金刚石单晶的生长速度最快有直接关系。     

高压下尼龙1010-单壁碳纳米管复合材料的结晶行为

 采用XKY-6×1200MN型六面顶压机,在不同温度、压力条件下处理30 min后制备了尼龙1010(PA1010)-单壁碳纳米管（SWCNT）复合材料的高压结晶样品,通过X射线衍射（XRD）、差热分析仪（DSC）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）,研究了高压处理样品的结晶行为、结构变化及形貌特征。结果表明：在1.0~2.5 GPa压力下,属于高压熔体结晶;在3.0和4.5 GPa压力下属于高压退火处理;高压结晶或高压退火均有助于聚合物片层晶体的增厚,并且高压熔体结晶的增厚效果优于高压退火处理。XRD结果表明,PA1010的三斜晶型在高压处理后保持不变,高压熔体结晶或高压退火都可以使(100)晶面和(010)晶面间距减小,即高压处理致使聚合物分子链紧密堆积。DSC结果表明：在高压熔体结晶过程中,升高压力和温度可以得到片层厚度较大的PA1010晶体;在2.0 GPa、350 ℃下获得的高压结晶样品的熔点和结晶度最高,分别达到208.5 ℃和64.6%。SEM和TEM结果表明：与常压结晶样品相比,高压结晶样品内部出现c轴厚度超过150 μm的大尺寸晶体;SWCNT与PA1010基体之间形成相互穿插的网络结构,刚性的SWCNT作为高压成核剂促进PA1010晶体生长和增厚。