片、粉状触媒合成腔体内压力、温度的变化分析

对比分析了片状触媒合成体系和粉状触媒合成体系,在金刚石合成过程中,合成腔体内压力、温度的变化情况,并结合金刚石合成特征区分布图,分析辽些压力、温度变化对合成金刚石品质的影响,由此,指出粉状触媒是合成金刚石用触媒材料的较佳形态。     

片状和粉状触媒合成金刚石的试验研究

通过对片状触媒和粉状触媒合成金刚石的实验，比较了两种触媒合成金刚石的优缺点，分析了粉末触媒合成金刚石优于片状触媒的原因，对金刚石合成有一定的实际意义。     

触媒合金对合成金刚石的影响

静压法合成金刚石,石墨向金刚石转变是借助触媒金属或合金的作用来实现的.实验表明,在金刚石的合成中,不同的合金不仅所需要的压力和温度不同,而且合成的效果也有明显的差异.因此,研究合金的性能对金刚石合成的影响及如     

高强度粗颗粒金刚石的合成技术研究

在高温高压下,六方晶格的石墨转变为立方晶格的金刚石。选用灰分含量少、气孔分布均匀的T621A石墨为碳源,选择化学成分范围偏值小、杂质含量少的镍锰钴合金为触媒以及优质粉压叶腊石为传压介质,在高温、适压、长时间及其它条件下,合成高强度粗颗粒的优质金刚石取得了良好的效果。     

触媒合金合成金刚石的效果

在合成金刚石时，使用不同成份和类型的触媒合金或金属，不但合成工艺条件不同，而且，合成金刚石的产量、质量、颗粒大小、晶体颜色和机械性质等亦有差异。为了探讨触媒合金性能与金刚石晶体生长的关系，我们对不同成份和类型的触媒材料的性能进行了分析和合成效果实验，从中发现成份和冶炼轧制工艺不同的触媒合金，其晶体结构、晶粒大小、杂质含量和表面结构等都是有差异的。这是影响合成效果的重要原因。因此，研究合成金刚石用的触媒材料是具有理论和实际意义的。     

合成粗颗粒金刚石的技术研究

为合成粗颗粒(24～46目)、高强度(22～24kg/cm~2)单晶人造金刚石,介绍了所用的石墨原料、触媒种类、装料方式以及合成参数,并讨论了合成机理。     

合成金刚石的趋势

高压合成金刚石尽管合成金刚石不断生产，但天然金刚石因其硬度和光学性能同珍贵的宝石一样，占有独特的地位。在高温和很高压力时，金刚石稳定的碳形态，材料科学家需要采取对策。高压物理学和技术的先驱—P·W·布瑞奇曼，据说每当他想从其早期的装置有可能获得较高的压力时，他总想把石墨转化为金刚石作为他的第一个实验。     

碳的相图和金刚石的合成

根据合成金刚石的实验数据以及对石墨和金刚石熔化温度的测定，目前已作出了碳的完整相图如下：     

人造金刚石触媒合金简介

触媒合金是我国目前人造金刚石行业普遍采用的重要原材料之一。从理论上讲,在高温高压条件下石墨可以直接转变为金刚石,但需要特高的压力和温度,最低压力为12万大气压,最低温度为2800℃。采用静压法合成金刚石,在目前的技术条件下,要制造这样的高     

人造金刚石合成过程中触媒金相组织的变化及合成过程研究

研究了金刚石合成过程中不同时期触媒金属全相组织的变化，讨论了人造金刚石的合成过程，给人造金刚石合成机理的研究提供了一些客观依据。最后作者阐述了自己对转化机理的见解。     

A carbon-rich multiphase inclusion in a Chinese diamond and its geochemical implications

A multiphase inclusion in a diamond from Liaoning province, China consists of an olivine covered with large plates of graphite. Both phases are enclosed in a thin layer of glass that separates the multiphase inclusion from the host diamond. Microcrystallites of diamond and graphite are embedded in the olivine and graphite plates. The characterization and distribution of all phases has been determined using micro-Raman, infrared and Auger spectroscopy, and electron microprobe analysis. The structural form and morphology of the microcrystallites of diamond and graphite in the olivine suggests they formed contemporaneously with the olivine and the host diamond. An alternative suggestion is that they formed from carbon previously dissolved in the olivine at high pressure and temperature. The genesis of the large graphite plates on the surface of the olivine and beneath the glass film is less easily understood, especially as the composition of the glass is not fully documented. The occurrence of glass associated with other inclusions in diamond has been recognized previously by others although the compositions are varied. This is the first record of diamond and graphite occurring within a silicate inclusion in diamond.     

Formation of metastable graphite inclusions during diamond crystallization in model systems

Metastable graphite inclusions have been studied in diamond, forsterite, and orthopyroxene synthesized in silicate-carbonate-fluid and aqueous chloride systems at 6.3–7.5 GPa and 1400–1600°C. The graphite inclusions were studied using optic microscopy and Raman spectroscopy. It has been established that graphite in diamond and liquidus silicate minerals is represented by a highly ordered variety. Depending on parameters of runs, the graphite inclusions are hexagonal, irregular polygonal, or rounded in shape. The morphology of graphite inclusions involving metastable graphite in run products is compared with previously established crystallization sequence of carbon phases. It has been revealed that the protogenetic graphite inclusions in diamond are rounded, and this shape was caused by dissolution of the newly formed graphite. Polygonal graphite inclusions are syngenetic and represented by metastable graphite that crystallized contemporaneously with diamond.     

The first finding of graphite inclusion in diamond from mantle rocks: The result of the study of eclogite xenolith from Udachnaya pipe (Siberian craton)

A xenolith of eclogite from the kimberlite pipe Udachnaya–East, Yakutia Grt+Cpx+Ky + S + Coe/Qtz + Dia + Gr has been studied. Graphite inclusions in diamond have been studied in detail by Confocal Raman (CR) mapping. The graphite inclusion in diamond has a highly ordered structure and is characterized by a substantial shift in the band (about 1580 cm^–1) by 7 cm^–1, indicating a significant residual strain in the inclusion. According to the results of FTIR spectroscopic studies of diamond crystals, a high degree of nitrogen aggregation has been detected: it is present mainly in form A, which means an “ancient” age of the diamonds. In the xenolith studied, the diamond formation occurred about 1 Byr, long before their transport by the kimberlite melt, and the conditions of the final equilibrium were temperatures of 1020 ± 40°C at 4.7 GPa. Thus, these graphite inclusions found in a diamond are the first evidence of crystallization of metastable graphite in a diamond stability field. They were formed in rocks of the upper mantle significantly below (≥20 km) the graphite-diamond equilibrium line.     

In situ X-ray observations of the decomposition of brucite and the graphite–diamond conversion in aqueous fluid at high pressure and temperature

 An experimental technique to make real-time observations at high pressure and temperature of the diamond-forming process in candidate material of mantle fluids as a catalyst has been established for the first time. In situ X-ray diffraction experiments using synchrotron radiation have been performed upon a mixture of brucite [Mg(OH)₂] and graphite as starting material. Brucite decomposes into periclase (MgO) and H₂O at 3.6 GPa and 1050 °C while no periclase is formed after the decomposition of brucite at 6.2 GPa and 1150 °C, indicating that the solubility of the MgO component in H₂O greatly increases with increasing pressure. The conversion of graphite to diamond in aqueous fluid has been observed at 7.7 GPa and 1835 °C. Time-dependent X-ray diffraction profiles for this transformation have been successfully obtained. Received: 17 July 2001 / Accepted: 18 February 2002     

Structures, origin and evolution of various carbon phases in the ureilite Northwest Africa 4742 compared with laboratory-shocked graphite

Mineralogical structures of carbon phases within the ureilite North West Africa 4742, a recent find, are investigated at various scales by high-resolution transmission electron microscopy (HRTEM), Raman microspectrometry and X-ray diffraction. Ureilites are the most carbon-rich of all meteorites, containing up to 6 wt.% carbon. Diamond, graphite and so-called “amorphous carbon” are typically described, but their crystallographic relationships and respective thermal histories remain poorly constrained. We especially focus on the origin of “amorphous carbon” and graphite, as well as their relationship with diamond.Two aliquots of carbon-bearing material were extracted: the insoluble organic matter (IOM) and the diamond fraction. We also compare the observed structures with those of laboratory-shocked graphite.Polycrystalline diamond aggregates with mean coherent domains of about 40 nm are reported for the first time in a ureilite and TEM demonstrates that all carbon phases are crystallographically related at the nanometre scale.Shock features show that diamond is produced from graphite through a martensitic transition. This observation demonstrates that graphite was present when the shock occurred and is consequently a precursor of diamond. The structure of what is commonly described as the “amorphous carbon” has been identified. It is not completely amorphous but only disordered and consists of nanometre-sized polyaromatic units surrounding the diamond. Comparison with laboratory-shocked graphite, partially transformed into diamond, indicates that the disordered carbon could be the product of diamond post-shock annealing.As diamond is the carrier of noble gases, whereas graphite is noble gas free, graphite cannot be the sole diamond precursor. This implies a multiple-stage history. A first generation of diamond could have been synthesized from a noble gas rich precursor or environment by either a shock or a condensation process. Thermally-induced graphitization of chondritic-like organic matter could have produced the graphite, which was then transformed by shock processes into polycrystalline nanodiamond aggregates. The formation of the disordered carbon occurred by diamond post-shock back-transformation during post-shock heating. The noble gases in the first generation diamond could then be incorporated directly into the disordered carbon during the transformation.     

Formation of epigenetic graphite inclusions in diamond crystals: experimental data

To elucidate the conditions of formation of epigenetic graphite inclusions in natural diamond, we carried out experiments on high-temperature treatment of natural and synthetic diamond crystals containing microinclusions. The crystal annealing was performed in the CO–CO₂ atmosphere at 700–1100 °C and ambient pressure for 15 min to 4 h. The starting and annealed diamond crystals were examined by optical microscopy and Raman spectroscopy. It has been established that the microinclusions begin to change at 900 °C. A temperature increase to 1000 °C induces microcracks around the microinclusions and strong stress in the diamond matrix. The microinclusions turn black and opaque as a result of the formation of amorphous carbon at the diamond–inclusion interface. At 1100 °C, ordered graphite in the form of hexagonal and rounded plates is produced in the microcracks. A hypothesis is put forward that graphitization in natural diamond proceeds by the catalytic mechanism, whereas in synthetic diamond it is the result of pyrolysis of microinclusion hydrocarbons. The obtained data on the genesis of graphite microinclusions in diamond are used to evaluate the temperature of kimberlitic melt at the final stage of formation of diamond deposits.     

New Data on Diamond–Graphite Relationships in the Gneisses of the Kokchetav Massif (Northern Kazakhstan)

The results of studying an aggregate of graphite-and-diamond crystal in tourmaline 5 μm of the Kokchetav massif by the method of transmission electron microscopy are presented. The detail studies of the interface between the crystals of graphite and diamond have revealed the absence of disordered graphite that is detail partially graphitized diamond. Intense deformation changes in the graphite crystal occurred after it was captured by tourmaline at the regression stage, which led to considerable kinking of the graphite crystal along the a-axis. Thus, the coexistence of graphite and diamond crystals cannot be unambiguously interpreted as a product of partial diamond graphitization. Graphite could have crystallized syngenetic with a diamond crystal or at the retrograde stage in the graphite stability field.

     

The characterisation and origin of graphite in cratonic lithospheric mantle: a petrological carbon isotope and Raman spectroscopic study

Graphite-bearing peridotites, pyroxenites and eclogite xenoliths from the Kaapvaal craton of southern Africa and the Siberian craton, Russia, have been studied with the aim of: 1) better characterising the abundance and distribution of elemental carbon in the shallow continental lithospheric mantle; (2) determining the isotopic composition of the graphite; (3) testing for significant metastability of graphite in mantle rocks using mineral thermobarometry. Graphite crystals in peridotie, pyroxenite and eclogite xenoliths have X-ray diffraction patterns and Raman spectra characteristic of highly crystalline graphite of high-temperature origin and are interpreted to have crystallised within the mantle. Thermobarometry on the graphite-peridotite assemblages using a variety of element partitions and formulations yield estimated equilibration conditions that plot at lower temperatures and pressures than diamondiferous assemblages. Moreover, estimated pressures and temperatures for the graphite-peridotites fall almost exclusively within the experimentally determined graphite stability field and thus we find no evidence for substantial graphite metastability. The carbon isotopic composition of graphite in peridotites from this and other studies varies from δ¹³ C_PDB = ? 12.3 to ? ?3.8%o with a mean of-6.7‰, σ=2.1 (n=22) and a mode between-7 and-6‰. This mean is within one standard deviation of the-4‰ mean displayed by diamonds from peridotite xenoliths, and is identical to that of diamonds containing peridotite-suite inclusions. The carbon isotope range of graphite and diamonds in peridotites is more restricted than that observed for either phase in eclogites or pyroxenites. The isotopic range displayed by peridotite-suite graphite and diamond encompasses the carbon isotope range observed in mid-ocean-ridge-basalt (MORB) glasses and ocean-island basalts (OIB). Similarity between the isotopic compositions of carbon associated with cratonic peridotites and the carbon (as CO₂) in oceanic magmas (MORB/OIB) indicates that the source of the fluids that deposited carbon, as graphite or diamond, in catonic peridotites lies within the convecting mantle, below the lithosphere. Textural observations provide evidence that some of graphite in cratonic peridotites is of sub-solidus metasomatic origin, probably deposited from a cooling C-H-O fluid phase permeating the lithosphere along fractures. Macrocrystalline graphite of primary appearance has not been found in mantle xenoliths from kimberlitic or basaltic rocks erupted away from cratonic areas. Hence, graphite in mantle-derived xenoliths appears to be restricted to Archaean cratons and occurs exclusively in low-temperature, coarse peridotites thought to be characteristic of the lithospheric mantle. The tectonic association of graphite within the mantle is very similar to that of diamond. It is unlikely that this restricted occurrence is due solely to unique conditions of oxygen fugacity in the cratonic lithospheric mantle because some peridotite xenoliths from off-craton localities are as reduced as those from within cratons. Radiogenic isotope systematics of peridotite-suite diamond inclusions suggest that diamond crystallisation was not directly related to the melting events that formed lithospheric peridotites. However, some diamond (and graphite?) crystallisation in southern Africa occurred within the time span associated with the stabilisation of the lithospheric mantle (Pearson et al. 1993). The nature of the process causing localisation of carbon in cratonic mantle roots is not yet clearly understood.