"柱状"金刚石晶体的高温高压合成

利用普通触媒和自行研制的新型触媒A,在国产六面顶压机上分别进行了合成金刚石单晶的实验.研究表明,普通粉末触媒合成出的金刚石单晶呈黄色,晶形完整,晶形是六-八面体,晶体透明度较好,并且合成出晶体的粒度比较集中,大约为0.3 mm.用新型触媒A合成的金刚石单晶呈绿色,并且晶形以长条晶体出现,长度集中在(0.5～0.7)mm.用SEM电镜观察到,前一种晶体晶形完整,表面光滑,后一种晶体表面也比较平整,存在"V"形缺陷.含氮量分析结果表明,用普通粉末触媒合成的金刚石的含氮量较低.     

优质毫米级粗颗粒金刚石单晶的高温高压合成

粗颗粒工业金刚石的合成与普通工业金刚石相比,需要较长的生长时间,而且其合成条件相对于普通工业金刚石单晶更为苛刻.文章总结了在具有高精密化控制系统的国产SPD 6×1670T型六面顶压机上进行的优质粗颗粒金刚石单晶的合成研究.在粉末触媒合成金刚石工艺的基础上,提高了压力和温度控制系统的精密化程度,引入了旁热式组装,改良了合成工艺,通过精密地控制金刚石的成核量与生长速度,以及采用最佳粒度的触媒,在高温高压条件下(～5.4GPa,～1360℃)成功合成出尺寸达到1.0mm的(18目)粗颗粒金刚石单晶,并分析了晶体的形貌和表面特征.     

(FeMn)xAl(1-x)-C体系金刚石的高温高压合成

利用FeMn-C体系以及添加剂Al,在国产六面顶压机上分别进行了合成金刚石单晶的实验,研究了在高温高压条件下(5.6～5.8 GPa ,1400℃～1600℃)(FeMn)xAl(1-x) - C (0≤x≤1)体系金刚石生长特性.通过光学成像显微镜、扫描电镜(SEM)和显微红外光谱、穆斯堡尔谱等分别对合成后的金刚石晶体的颜色与形貌,含氮量以及内部杂质进行了测试分析.研究结果表明,(FeMn)xAl(1-x)-C体系可合成晶面完整的八面体金刚石晶体;无Al(x=1) 添加时,合成晶体的生长速度较快,添加Al(x≠1)后,晶体生长速度明显变慢;无Al添加时,体系合成晶体的含氮量较高,而添加Al后,含氮量明显降低;无Al添加时,合成晶体内部的包裹体主要成分是Fe3C和Fe,添加Al以后,合成晶体内包裹体主要成分是FeAl合金.     

优质细颗粒金刚石单晶的高温高压合成与表征

文章利用国产六面顶高温高压设备,根据对金刚石合成不同区域的生长特点,通过对合成工艺的调整,实现了对体系中金刚石成核率与生长速率的控制,并成功合成出了具有完整晶形,尺寸大约在2~10μm的优质细颗粒金刚石单晶。通过热重-差热分析以及Raman光谱测试发现,合成具备完整晶面的细粒度金刚石单晶抗氧化强度大于表面粗糙的同粒度的金刚石微粉破碎料,且合成的晶体内部存在较小的残余应力。     

Ⅱa型工业金刚石的高温高压合成

对Ⅱa型工业金刚石的高温高压合成进行了研究,成功地合成出了优质Ⅱ a型工业金刚石.通过考察有除氮剂、无除氮剂两种体系中合成金刚石的情况,结果发现,合成金刚石的最低压力点及温度并没有发生太大的变化;借助于光学显微镜发现,有除氮剂体系合成出的晶体颜色比原触媒体系合成的晶体要浅,且多为六-八面体;通过IR检测后发现,有除氮剂体系合成金刚石的含氮量明显低于原触媒体系合成金刚石的含氮量;借助扫描电子显微镜(SEM),对两种体系所合成金刚石表面的形貌进行了观察.     

优质金刚石合成的一般规律及分析

从晶体生长的一般规律出发,论述了碳原子的活化速度、堆积速度、熔蚀速度以及晶体生长速度与优质金刚石生长的关系,阐述了优质金刚石的合成方法,并提出了具体操作建议.     

优质Ⅱb型宝石级金刚石大单晶的高温高压合成

实验在国产六面顶压机上利用温度梯度法合成优质Ⅱb型宝石级金刚石.研究发现在约5.5GPa和约1300℃的条件下,添加剂硼的加入使合成Ⅱb型金刚石的形貌较Ⅱa型宝石级金刚石有较大不同,文章分析了产生该现象的原因;实验还发现随着硼添加量的增加,所合成Ⅱb型宝石级金刚石的颜色由浅变深.结果实验获得了尺寸达4mm的优质Ⅱb型宝石级金刚石大单晶.     

间接加热合成工业金刚石工艺的研究

在工业金刚石的合成过程中,合成工艺对其有着重要的影响。文章在国产六面顶高压设备上,利用膜生长法,在F e-N i-C体系中对影响金刚石合成的工艺参数进行了考察,通过对合成工艺的调整,成功实现了对生长速度的有效控制,并成功合成出平均粒度为0.6mm的优质金刚石单晶。     

用掺杂N、H化合物的粉末触媒合成金刚石的研究

氮和氢元素是天然及人工合成金刚石中重要的杂质元素，对金刚石的性能有着十分重要的影响。本工作中，先利用有机氮氢化合物三聚氰胺的分解提供氮与氢源，研究了大量的氮和氢在粉末触媒合成金刚石中对金刚石生长的影响。结果表明：大量的氮和氢的存在，将严重抑制金刚石的成核。然而，用含少量的添加剂氮化物MxN的粉末触媒在国产六面顶压机上却能合成出优质金刚石单晶。利用光学显微镜观察，发现所合成的金刚石多为六八面体，晶形完整；在大多数用含添加剂氮化物的触媒合成的金刚石的晶面上有凹线出现。用扫描电镜对凹线的形貌进行了细致的观察。随着铁基粉末触媒中添加剂氮化物含量的增加，合成金刚石的压力和温度条件逐渐增高，金刚石生长的“V形区”上移。     

Change of luminescence character of Ib diamonds with HPHT treatment

Type Ib high pressure synthetic diamonds have been examined using photo- and cathodo-luminescence topography and spectroscopy before and after heat treatment. The type Ib crystals were grown from Fe instead of Ni and Co in order to avoid influence of Ni and Co luminescence centers. The crystal exhibited the 389-nm band and a broad band with a maximum around 550 nm as well as additional weak peaks at 485 and 535 nm. With annealing at 1800°C and 6 GPa, the peaks were annealed out and the N3, H3 and 575-nm bands appeared instead. The H3 and 575-nm bands were stronger in {113} sectors than in {111}, whereas the N3 band was weaker in the {113} sectors.     

HPHT treatment of CO2 containing and CO2-related brown diamonds

Ten type I diamonds containing CO₂ and three diamonds related to these (referred to as “Pseudo CO₂” diamonds) were treated by the HPHT process to observe changes in colour, colour distribution, inclusions, luminescence and spectral features in the visible to the mid-infrared regions. All samples were of predominantly brown colour before the treatment and had rather inhomogeneous colour distribution not related to strain like in classic type Ia brown diamonds. Upon HPHT treatment most of them changed to a more yellow hue, with a greenish modifying colour, but the dominant colour was still brown. The modification of colour was found to be much more discreet than it is the case for deformation-related type Ia brown diamond and the colour was not at all related to known centers such as H3. The colour modifications were caused by the destruction of broad absorption bands in the Vis–NIR spectrum by the HPHT process and generally increased transmission from 400 to 700 nm, likely related to a slight increase in single nitrogen, but no typical HPHT annealing related colour centers such as H3 and H2 were produced in the spectra of the samples. This could be confirmed by the luminescence when excited by shortwave and longwave UV light, under which all samples showed a yellow emission that was practically not modified by the treatment.The infrared spectra of the 10 CO₂ diamonds, defined by the presence of at least the CO₂ stretching (ν₃) and bending (ν₂) absorptions, were unusually modified by the HPHT treatment: the treatment caused the CO₂ bands to increase in intensity in diamonds with low to medium CO₂ content, and the apparently diminished the intensity of the nitrogen-related one phonon absorptions (when present). In the spectra of the three “Pseudo CO₂” samples, which lack by definition the CO₂ peaks, the CO₂ peaks were created and the one phonon absorption reduced by the treatment. The photoluminescence spectra exhibiting several unpublished emission peaks remained practically unchanged by HPHT processing: none of the emissions were annealed out and no new centers created.The data obtained by HPHT treatment leads us to propose, that the theory of solid CO₂ inclusions being responsible for the CO₂ absorptions in diamond may be erroneous, and that the CO₂ may be present structurally. Thus it is proposed that structurally bonded oxygen may play an important role in such diamonds.The present study indicates that treated CO₂ and “Pseudo CO₂” diamonds can in most cases not be identified by the methods available in well-equipped gemmological laboratories, since no detectable defect centers appear to be induced by the treatment.     

The effect of HPHT treatment on the spectroscopic features of type IIb synthetic diamonds

The effect of high pressure high temperature treatment on the spectroscopic features of boron-doped type IIb synthetic diamonds has been studied. Synthetic HPHT diamond crystals with different concentrations of boron acceptors were annealed at temperatures in the range 1800–2650 °C under a stabilizing pressure of 7–7.5 GPa. Fourier-transform infra-red absorption spectroscopy and cathodoluminescence were applied to study the effect of the annealing. We found that for annealing temperatures up to 2650 °C, the IR absorption features related to neutral boron acceptors did not change in intensity, demonstrating that single substitutional boron was not affected by the treatment. This finding is in good agreement with the recent first-principle calculations of Goss and Briddon (Phys. Rev. B 73 (2006) 085207) predicting very high activation energies for migration of substitutional boron in the diamond lattice. For diamonds with boron concentration of about 1 ppm, it was found that annealing at 2650 °C for 1 h produced an intense CL emission band peaking at 2.85 eV, which is known to be related to dislocations. It was suggested that dislocations in the studied boron-doped diamonds were formed due to plastic deformation occurred during anneals.     

高氮含量金刚石的高温高压合成与表征

利用自制的高氮含量合金触媒,在国产六面顶压机上合成出了深绿色磨料级工业金刚石.对所合成的晶体做了光学显微(OM)观察和红外光谱(FTIR)测试.结果表明,所合成的晶体中除常见的六-八面体外,还出现了较多的长条晶体,且长条晶体多是由六-八面体的(100)或(111)面不均匀生长而成的;晶体的含氮量随合金体系中氮含量的增加而提高,最高含氮值达24×10-3.     

高压高温下纤锌矿型氮化硼(wBN)的合成及其结构的转变

wBN通常是在动态超高压高温条件下由六方氮化硼(hBN)直接转变而成的.文章就静态高压高温条件下wBN的合成问题、高压下wBN转变为类石墨型氮化硼的规律性及其机制、高压高温下对wBN向cBN的转变以及Si3N4在该转变过程中对cBN颗粒生长的影响等进行叙述.     

细颗粒cBN的高温高压合成研究

在高温高压条件下(压力为4.5~5.0GPa,温度为1300℃~1500℃)采用锂基多元触媒合成出了粒度较为均一、晶形完整的细颗粒cBN。实验发现,在触媒体系确定的条件下,合成细颗粒cBN的关键在于温度压力区间以及合成时间的控制,高压低温及较短的合成时间有利于细颗粒cBN的合成。     

A new approach to investigation of nickel defect transformation in the HPHT synthetic diamonds using local optical spectroscopy

The analysis of spatial photoluminescence distribution along a plate from synthetic diamond as grown at 1500 °C allowed us to study a sequence of formation of nitrogen–nickel optically active centers and to build maps in some cases. Several groups of vibronic systems with specific spatial distribution along the sample were separated: nitrogen-vacancy pairs in the thin near- surface layer, low-temperature centers with blue emission, nickel–nitrogen complexes with a single nickel ion and those with several nickel ions.