高温高压下金刚石单晶生长过程的声发射动态特征

采用声发射技术对高温高压下人造金刚石单晶的生长过程进行了动态检测。结合合成压块的断口形貌,对金刚石单晶生长过程对应的主要声发射参数进行了分析。结果表明,声发射信号的能量计数、振铃计数、幅度和上升时间等特征参数能客观反映金刚石单晶在高温高压下的动态生长规律,为研究金刚石单晶的生长机制提供了重要的实验依据。     

Ib型金刚石大单晶的限形生长

金刚石的限形生长有利于其后续加工.对于磨料级金刚石限形生长的研究已经比较透彻,但金刚石大单晶的限形生长尚缺乏全面系统的研究.本文以Fe Ni(64wt%:36wt%)合金为触媒,利用高温高压下的温度梯度法在5.6 GPa时对不同温度下分别沿(100)面和(111)面生长的Ib型金刚石大单晶的晶形进行了研究.研究表明:随着温度的升高,沿(100)晶面生长的金刚石大单晶的晶形分别为板状、塔状直至尖塔状,而沿(111)面生长的金刚石大单晶的晶形则分别为塔状和板状;分析了不同温度下分别沿(100)面和(111)面生长金刚石大单晶不同晶形高径比的变化情况.利用不同压力和温度下的金刚石大单晶合成实验绘制了沿(100)和(111)面生长金刚石大单晶的晶形在V形生长区域内的分布示意图,表明沿(111)面生长的金刚石大单晶V形区温度下限明显比以(100)面生长的高,而沿这两面生长金刚石大单晶的V形区温度上限差别并不明显.对不同生长面V形区温度上下限的差别进行了解释,据此实现了Ib型金刚石大单晶的限形生长.     

高温高压金刚石单晶生长界面的研究

 利用扫描电镜及Auger电子谱技术研究了高温高压下金刚石单晶生长界面的特性，观察到了金刚石单晶表面及金属膜表面的沟槽结构及金刚石-金属、金属-石墨两个主界面间的过渡层结构及界面间C原子电子组态的变化。     

国产六面顶压机多晶种法合成宝石级金刚石单晶

对国产六面顶压机平台下使用多晶种法合成宝石级金刚石单晶进行了系统的研究. 通过合理调整温度梯度法的合成腔体组装, 采用多晶种法, 探索多晶种法金刚石合成的压力和温度区间, 在单个合成腔体内放置3–5颗金刚石晶种, 成功合成出多颗(3–5)优质Ib型宝石级金刚石单晶. 多颗晶种的引入, 单次实验合成的多个金刚石晶体晶形及品质一致; 同时, 晶体的整体生长速度也有明显的增大. 多晶种法金刚石单晶合成的研究, 可以有效地利用腔体空间、提高单次金刚石单晶合成的效率, 解决压机大型化下高温高压资源利用率低的问题; 同时, 为宝石级金刚石单晶商业化生产提供重要的依据. 关键词： 金刚石 国产六面顶 多晶种 温度梯度法     

类天然金刚石的高温高压合成研究

本文利用高温高压(HPHT)法分别合成出普通Ib型、高氮型和高氮含氢型金刚石单晶，然后对金刚石单晶进行高温高压退火处理成功制备出IaA型，IaAB型类天然金刚石大单晶. 详细研究了氮在不同退火温度下的聚集行为，及氢存在情况下C心氮的转化情况. 研究发现高氮型金刚石中氮的聚集行为直接受退火温度的影响，随着退火温度的上升，氮的聚集态转化率升高. 1850 ℃时氮的聚集态转化率达到100%，晶体颜色几乎为无色，红外吸收谱与天然IaA型钻石基本无差别. 氢的存在有利于氮原子从C心聚集到A心和B心. 退火高氮含氢晶体得到可与天然金刚石相媲美的IaAB型类天然金刚石. 此外，我们在较低压力2.5 GPa下对Ib型金刚石退火成功制备出IaA型金刚石.     

FeMn粉末触媒对合成金刚石的影响

 利用FeMn粉末触媒在国产六面顶压机上进行了合成金刚石单晶的实验,研究了高温高压条件下（5.7 GPa、1 550 ℃）,石墨-FeMn粉末触媒体系中金刚石单晶的生长特性。通过光学成像显微镜观测表明：合成出的金刚石单晶呈浅黄色,晶形完整,且都是八面体,晶体里含有白色物质,粒度集中在0.3~0.5 mm;通过扫描电镜观测了晶体的表面形貌,表面有熔坑;通过穆斯堡尔谱,发现粉末触媒里主要是FeMn合金和独立状态的Fe,金刚石内部主要是Fe和Fe₃C;利用X射线荧光光谱,检测出样品里有Fe和Mn元素。     

温度对Ib型和IIa型金刚石大单晶(100)表面特征的影响

本文在5.6 GPa, 1250–1340 ℃的条件下, 利用温度梯度法, 以FeNiMnCo 合金为触媒, 沿籽晶的(100)晶面成功合成了不同晶形的优质Ib型和IIa型金刚石大单晶. 利用激光拉曼附件显微镜, 分别对上述不同温度下合成的两类金刚石样品上表面(100)面的中心区域及棱角区域进行观察分析. 研究发现, Ib型和IIa型金刚石大单晶(100)晶面上从中心到棱角处黑色纹路的分布逐渐变黑变密集; 另外, 随着金刚石合成温度的升高, Ib型金刚石大单晶(100)面上黑色纹路由稀疏逐渐变稠密, 而IIa型金刚石大单晶的黑色纹路较为稀疏; Ib型金刚石大单晶的形貌特征表现为从低温晶体的不规则分布过渡到中温、高温晶体的典型树枝状分布. IIa型金刚石大单晶(100)面特征随温度变化规律与Ib型的类似. 这两类金刚石大单晶表面特征的差异可能是由于IIa 型金刚石具有比Ib型更小的生长速度和更少的氮含量. 最后, 对两类塔状金刚石大单晶进行拉曼光谱测试分析, 结果表明IIa型金刚石大单晶的品质较Ib型金刚石大单晶好.     

合成腔体尺寸对Ib型六面体金刚石单晶生长的影响

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 ℃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Φ 14 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Φ 14 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Φ 26 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.     

高温高压法人造金刚石合成中工艺曲线的确定

以SPD6×2000型六面顶压机为合成设备,在高温高压条件下确定了合成金刚石的最低成核压力.采用合理的二次升压工艺方法,在暂停油压86MPa,生长油压94MPa,合成功率3500W的条件下成功地减少了劣晶的生成,合成出了晶型完整、表面平整的优质金刚石单晶.结果表明在最低成核压力点下对石墨进行再结晶的处理对合成高品级金刚石是完全必要的.     

高温高压条件下石墨的再结晶与金刚石单晶的生长

 用电子显微镜观察到了在高温高压条件下再结晶石墨的形状随温度变化而改变的规律。实验表明：从石墨向金刚石的转变，与石墨在催化剂——溶剂合金中的再结晶状态有关，类球形再结晶石墨是转变成金刚石小单元的基础。金刚石晶体的不同形态及其多样化的表面结构表明金刚石单晶的生长具有比较复杂的过程。研究了具有一定规则形状由类球形再结晶石墨晶粒组成的聚合体，这种聚合体将在适当温度压力下转变成金刚石颗粒。本研究给出了生长粗颗粒、晶形完整的金刚石单晶的原则办法。     

A relation between a metallic film covering on diamond formed during growth and nanosized inclusions in HPHT as-grown diamond single crystals

One of the most important characteristics and basic phenomena during diamond growth from liquid metal catalyst solutions saturated with carbon at high temperature–high pressure (HPHT) is that there exists a thin metallic film covering on the growing diamond, through which carbon-atom clusters are delivered to the surface of the growing diamond by diffusion. A study of microstructures of such a metallic film and a relation between the thin metallic film and the inclusions trapped in HPHT as-grown diamond single crystals may be helpful to obtain high-purity diamond single crystals. It was found that both the metallic film and the HPHT as-grown diamond single crystals contain some nanostructured regions. Examination by transmission electron microscopy suggests that the microstructure of the thin metallic film is in accordance with nanosized particles contained in HPHT as-grown diamond single crystals. The nanosized particles with several to several tens of nanometers in dimension distribute homogeneously in the metallic film and in the diamond matrix. Generally, the size of the particles in the thin metallic film is relatively larger than that within the diamond matrix. Selected area electron diffraction patterns suggest that the nanosized particles in the metallic film and nanometer inclusions within the diamond are mainly composed of f.c.c. (FeNi)₂₃C₆, hexagonal graphite and cubic γ-(FeNi). The formation of the nanosized inclusions within the diamond single crystals is thought not only to relate to the growth process and rapid quenching from high temperature after diamond synthesis, but also to be associated with large amounts of defects in the diamond, because the free energy in these defect areas is very high. The critical size of carbide, γ-(FeNi)and graphite particles within the diamond matrix should decrease and not increase according to thermodynamic theory during quenching from HPHT to room temperature and ambient pressure. Received: 13 September 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-0531/295-5081; E-mail: yinlw@sdu.edu.cn     

Microstructure of high-pressure-synthesized diamonds under rapid quenching and electron irradiation

A type of synthetic diamond single crystal about 0.4–0.5 mm in dimension prepared under high pressure–high temperature (HPHT) in the presence of a FeNi molten catalyst was quenched from HPHT and irradiated with 300 keV electrons at room temperature. Transmission electron microscopy was employed to examine the microstructure of the diamond single crystal before and after electron irradiation. It was found that there exists a large amount of cellular interfaces in the quenched diamond sample, which indicates the growth condition of the diamond under HPHT. Hexagonal dislocation loops about several tens of nanometers in dimension were observed in the high-pressure-synthesized diamond single crystal before electron irradiation, which strongly suggests that a number of vacancies were quenched-in due to rapid quenching from high temperature at the end of diamond synthesis, and were aggregated in the synthetic diamond to form vacancy disks on the (111) plane, the collapse of such vacancy disks forming vacancy-type dislocation loops. After electron irradiation, it was found that defect clusters present as interstitial-character dislocation loops were formed in the electron-irradiated region of the diamond. The interstitial dislocation loops grow with increase of the irradiation time. The present study, in comparison to previous work on ion implantation on diamond, indicates that electron irradiation does not induce a phase transformation but produces interstitial dislocation loops due to the migration of interstitial atoms and vacancies. The result of the study directly indicates that interstitials and vacancies in diamond are mobile at room temperature under electron irradiation. Nitrogen, as the most important kind of impurity contained in the HPHT as-grown diamond, probably acts as nucleation of the interstitial loops. Received: 16 November 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. E-mail: yinlw@sdu.edu.cn     

HPHT Synthesis of Different Shape Coarse-Grain Diamond Single Crystals

Synthesis of coarse-grain diamond crystals is studied in a China-type SPD6× 1670T cubic high-pressure apparatus with high exact control system. To synthesize high quality coarse-grain diamond crystals, advanced indirect heat assembly, powder catalyst technology and optimized synthesis craft are used. At last, three kinds of coarse- grain diamond （about 0.85 mm） single crystals with hexahedron, hex-octahedron and octahedron are synthesized successfully under HPHT （about 5.4 GPa, 1300-1450℃）. The growth characters of different shape crystals are discussed. The results and techniques might be useful for the production of coarse-grain diamonds.     

山东产大颗粒高温高压合成钻石的多种谱学方法研究

山东济南中乌新材料有限公司利用六面顶油压机生产出大颗粒钻石,为了掌握这些合成钻石的品质及与天然钻石的区分方法,采用宽频诱导发光光谱仪（GV5000）、红外光谱仪、钻石特征光谱检测仪（PL5000）、激光诱导击穿光谱仪和X射线能谱仪,对该公司生产的225粒无色、蓝色和黄色高温高压（HPHT）合成钻石进行检测,并与天然钻石对比。HPHT合成钻石样品的晶形以（111）晶面和（100）晶面共存的聚形为主导。原石切磨成圆钻形成品的出成率在20%~67%之间,净度级别为VVS-P,颜色级别为D-H。通过GV5000分析,三种颜色样品均可观察到立方八面体生长结构发光图案,无色HPHT合成钻石为强蓝色荧光和磷光,发光峰位于495 nm,与晶格中的顺磁氮有关;蓝色HPHT合成钻石为蓝-绿蓝色荧光和蓝色磷光,发光峰位于501 nm,与晶格中的顺磁氮、硼有关;黄色HPHT合成钻石为弱绿色荧光和磷光,显示556和883 nm Ni+相关发光峰,这些特征可与天然钻石相区分。红外光谱分析表明,无色HPHT合成钻石在1 332~1 100 cm-1无明显氮相关吸收,在2 802 cm-1有B0相关吸收,为含有少量硼的Ⅱa型;蓝色HPHT合成钻石位于1 294 cm-1有与B-相关的强吸收,归属为Ⅱb型;黄色HPHT合成钻石位于1 130和1 344 cm-1有与孤氮相关的明显吸收,归属为Ⅰb型。PL5000光致发光光谱显示,三种颜色HPHT合成钻石可检测到659,694,707,714和883 nm等镍相关缺陷发光峰。相比之下,无色和黄色天然钻石通常为Ⅰa型,具有1 282和1 175 cm-1等聚合氮的红外光谱吸收,光致发光光谱通常可检测到415 nm（N₃）零声子线,由孤氮、硼和镍等缺陷导致的光谱特征极为罕见。因此,红外光谱和光致发光光谱特征可作为重要的鉴别依据。激光诱导击穿光谱仪检测到无色HPHT合成钻石的出露包裹体主要成分为Fe。X射线能谱分析显示,对于含包裹体较多的样品,无色和蓝色HPHT合成钻石可检测到Fe,黄色HPHT合成钻石可检测到Fe和Ni,为其中包裹体的成分,这可作为HPHT合成钻石鉴定性特征。综上所述,通过GV5000超短波紫外荧光和磷光测试,配合红外光谱和光致发光光谱特征,结合包裹体成分特征,可以有效区分该研究的合成钻石和天然钻石。     

Effects of additive NaN_3 on the HPHT synthesis of large single crystal diamond grown by TGM

In this paper,large single crystal diamond with perfect shape and high nitrogen concentration approximately 1671-1742 ppm was successfully synthesized by temperature gradient method (TGM) under high pressure and high temperature (HPHT).The HPHT synthesis conditions were about 5.5 GPa and 1500-1550 K.Sodium azide (NaN3) with different amount was added as the source of nitrogen into the synthesis system of high pure graphite and kovar alloy.The effects of additive NaN3 on crystal growth habit were investigated in detail.The crystal morphology,nitrogen concentration and existing form in synthetic diamond were characterized by means of scanning electron microscope (SEM) and infrared (IR) absorption spectra,respectively.The results show that with an increase of the content of NaN3 added in the synthesis system,the region of synthesis temperature for high-quality diamond becomes narrow,and crystal growth rate is restricted,whereas the nitrogen concentration in synthetic diamond increases.Nitrogen exists in diamond mainly in dispersed form (C-centers) and partially aggregated form (A-centers).The defects occur more frequently on crystal surface when excessive NaN3 is added in the synthesis system.     

单颗金刚石切削无氧铜的声发射关联维特征*

声发射技术可以实现无氧铜切削加工特征的监测与评价。采用声发射技术监测单颗金刚石磨粒旋转切削无氧铜，利用G-P算法重构出声发射时域信号相空间，采用自相关函数法计算出相空间时间延迟参数，通过相空间双对数曲线的计算，得到不同切削工况下的关联维数。研究结果表明，进给速度和切削速度对声发射信号影响较不显著，切深与声发射信号振幅呈正效应关系；声发射信号双对数曲线呈现阶段性增加趋势，并逐渐收敛于饱和状态，关联维数随着嵌入维数的增加先快速下降后趋于平稳；金刚石切削无氧铜的声发射信号具有混沌运动变化特性，在较小嵌入维数时，关联维数与切深和切削速度呈现线性负效应关系，与进给速度呈现线性正效应关系。该研究为无氧铜的切削加工提供理论参考。     

Analysis of acoustic emission signals originating from bainite and martensite formation

In this paper the characteristics of acoustic signals generated during bainite and martensite formation are studied. The results are discussed in a semi-quantitative manner, since a thorough quantitative analysis of the signals is not feasible because of the limited frequency bandwidth of the system and the effect of internal sample reflections on the signal. The frequency spectra of acoustic emission signals are interpreted using a dislocation source model adopted from acoustic emission studies of plastic deformation. It is assumed that the predominant source of acoustic emission (AE) during displacive transformations is the movement of dislocations, i.e. the slip taking place during growth in order to relieve internal stresses. The results show that the mean frequency of AE signals generated during bainite formation is significantly larger than that of martensitic AE signals. This difference in the spectral density of the AE signals can be attributed to the difference in interface motion of the two transformations, and the consequent different behaviour of the dislocations involved.     

Industrial diamonds grown in Ni70Mn25Co5--graphite--sulfur system under HPHT

This paper reports that diamond single crystals were synthesized from sulfur-added Ni70Mn25Co5+C system under high pressure and high temperature(HPHT).It was found that additive sulfur had inhibited the nucleation and growth of diamond to some extent.X-ray diffraction of the collected sample indicated that under the synthesis conditions,a new compound MnS had been formed through the reaction of additive sulfur with manganese in the catalyst.The MnS has a fcc structure,and its average crystal size was about 30 nm.By scanning electron microscope,the {111} surface of diamond was found to be flat,while there was usually a large depression on the central region of {100}.Further observation showed that there were many small upside-down pyramidal pits in the expression.The results of x-ray photoelectron spectroscopy shows that MnS can only be detected in the depression in the range of detection precision.It was inferred that MnS had been dissolved in the melted alloy during the growth experiment,and precipitated in the sequent quenching process.     

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.