超细石墨粉体高温高压合成金刚石研究

为研究超细石墨粉体合成金刚石的可能性,以5000目的超细石墨粉和Fe70Ni30触媒为原料,用静态高压技术合成出金刚石.研究结果表明:以超 细石墨粉为碳源材料合成金刚石是完全可行的,但在合成晶体里发现有大量缺陷存在;合成金刚石单产接近120ct,明显要高于相同合成腔体和工艺条件下合成普通金刚石的单产;晶体粒度平均为270 μm左右,小于相同条件下以200目人造石墨粉为原料合成晶体的粒度.以超细石墨粉体为碳源材料合成金刚石的生产工艺等各方面影响因素有待深入研究.     

Testing diamond strength at high pressure

We present two designs to measure the strength of diamond, natural or synthetic, above 30 Mbar. Both designs are based on the Rayleigh-Taylor instability carried out on a laser system providing a truncated ignition pulse. The first is an indentation technique which can be challenging to diagnose because of the low-Z value of carbon. The second is similar to that used in DAC (diamond anvil cell) experiments with a flat diamond squeezing a highly perturbed gold foil and provides the required high-Z diagnostics. Based on two-dimensional hydrocode simulations we conclude that the second technique is superior because of its sensitivity to diamond strength coupled with the benefit of diagnostics at these extremely high pressures.     

Conversion of polycyclic aromatic hydrocarbons to graphite and diamond at high pressures

The polycyclic aromatic hydrocarbons (PAH): naphthalene, anthracene, pentacene, perylene, and coronene were submitted to temperatures up to 1500 °C at 8 GPa. To avoid catalytic action of metals on thermal conversion, graphite was used as container material. Moreover, graphite is very permeable to the gaseous products of thermal decomposition of PAH. The resulting thermal transformations and their evolution were studied by X-ray diffraction, Raman spectroscopy and scanning electron microscopy as a function of temperature for 60-s treatments. The nature of the initial compounds clearly affects the products of the different stages of carbonization and the first steps of graphitization. This becomes hardly discernible in the final stages of graphitization above 1000 °C. Above 1200 °C, graphite with high crystallinity forms in all cases. The temperature of the beginning of diamond formation does not seem to be influenced by the nature of the initial PAH and is equal to ∼1280 °C for all investigated compounds. Diamonds formed from the PAH are high-quality 5-40 μm single crystals. The p,T values of diamond formation here obtained are significantly lower than those previously known for direct graphite-diamond transformation.     

Effect of hydrogen implantation on the graphite used in high pressure diamond synthesis

The objective of the present work is to investigate the effect of hydrogen implantation on graphite in the high pressure diamond synthesis. A comparison of the graphite/diamond conversion for different fluences of hydrogen implantation revealed that the diamond nucleation and the total mass yield are always higher (up to 46%) than in experiments without implantation. The maximum nucleation for the studied cases occurred at a fluence of 1×10¹⁷ hydrogen ions/cm². This behavior is not observed when other ions, such as krypton and argon, are implanted on the graphite, or when hydrogen is present in the reaction cell but not implanted on the graphite. The results were interpreted as a consequence of the creation of additional tetrahedral sp³ bonded carbon atoms when the graphite is hydrogen implanted, which would act as effective diamond nucleation sites in the high pressure synthesis.     

Energetics of stress relaxation of glassy polymers at high pressure

Kinetic changes of relaxation of the shift stress of glassy poly(methyl methacrylate) were studied when temperatures and pressures were changed in isobaric, isothermal, and isochoric conditions. In isochoric conditions the relaxation rate depends slightly on temperature. The volume of the polymer is the main parameter for the rate of stress relaxation. Isobaric and isochoric activation energies and activation vohime of stress relaxation were determined. The results are shown to satisfy the thermodynamic relation of the activation parameters of the relaxation process. The dimensions of elementary kinetic unit of the stress relaxation process were estimated.     

Epitaxial growth on nickel-plated diamond seeds at high pressure and high temperature

Epitaxial growth on nickel-plated diamond seeds at high pressure and high temperature (HPHT) was observed with graphite as carbon source. The thickness of the electroplating nickel film which acts as a catalyst/solvent ranges from 54.6 μm to 255.6 μm. The relationship between the Ni film thickness and diamond growth rate is investigated. When the nickel film thickness is from 90 μm to 129 μm, diamond crystals can nearly grow up to three times as large as the original seeds at ∼ 5.8 GPa and ∼ 1460 °C within 14 min. The mechanism of the crystal growth with nickel-plated diamond seeds under HPHT is discussed. The results and techniques might be useful for high quality saw-grade diamonds production and large diamond single crystal growth.     

Formation of highly oriented layers of graphite in glass-like carbon heat-treated under pressure

A glass-like carbon of homogeneous structure cured up to 1000°C (GC-10) was heat-treated under pressure of 5 kbar. The heat treatment was performed in two different cell arrangements; in one arrangement quasi-hydrostatic pressure was dominant and in the other there were many contact points between the carbon investigated and small angular grains of glass-like carbon heat-treated to 2000°C. In the first arrangement, the glass-like carbon did not graphitize even at 1900°C. In the second, graphitization was observed above 1750°C. Below 1700°C, optically anisotropic areas were initiated at contact points with the angular grains where the stress concentrations occur. These areas show turbostratic structure. At a little higher temperature, they transform to graphite. The graphitized parts in cross section look like bamboo leaves and grow into the bulk of the carbon at the expense of nongraphitized parts. The graphite layers were found to align perpendicularly to the compressive stress, contrary to our previous report. The previously observed orientation was probably due to oriented regions originally present in the starting material. The mechanism of the spreading of the graphitization from the stress concentration points at the surface is discussed.     

Ion bombardment induced cone formation on glassy carbon and graphite surfaces

Surfaces of various types of carbon were bombarded with 750 eV argon ions at low pressures to a total ion dosage of about 10²⁰ ions/cm². This dosage was sufficient to produce distinctive conical protrusions at the surfaces of all samples. The study shows that sputtering is an effective way to roughen carbon surfaces.     

氢预处理与高压影响下石墨的Raman光谱研究及在金刚石高温高压合成中的意义

氢预处理及高压作用后石墨的Raman光谱的研究表明：酸浸泡及氢等离子体预处理均可以在石墨中造就有利于金刚石成核的-CH3：C—H类金刚石碳区，并使石墨的有序度显著降低；5．4GPa高压作用后，氢预处理石墨的有序度会有所提高．但不会超过常压下未经氢预处理石墨的有序度；高压下石墨向金刚石转变，石墨片层确实有褶曲，但在此之前可能存在一个石墨与氢等造就类金刚石碳区有关的必然环节。     

Fabrication of graphitic layers in diamond using FIB implantation and high pressure high temperature annealing

We have used high pressure high temperature annealing (HPHT) for graphitisation of implanted layers in diamond created by 30 keV Ga⁺ focused ion beam. Electron microscopy has been used to investigate the implanted layers. It has been revealed that, unlike annealing at vacuum pressure, the graphitization during HPHT annealing occurred through epitaxial growth of graphite (002) planes parallel to (111) diamond planes. High quality of graphite was confirmed by high resolution electron microscopy and electron energy loss spectroscopy.     

Synergistic effect of nitrogen and hydrogen on diamond crystal growth at high pressure and high temperature

Diamond crystals co-doped with nitrogen and hydrogen atoms are successfully synthesized in the metal–carbon system with melamine (C₃N₆H₆) additive in a series of experiments at temperatures of 1200–1740 °C and pressures of 5.0–6.0 GPa. Experimental results show that the crystallization of our obtained diamonds changes significantly, which is attributed to the simultaneous incorporation of nitrogen and hydrogen into the diamond crystal structure. IR measurement shows that the intervention of hydrogen effectively changes the nitrogen concentration and substitutional form, accompanied by a non-uniform distribution of nitrogen and hydrogen in the synthesized diamond. Raman measurement indicates that such non-uniform distribution of nitrogen and hydrogen in the synthesized diamond leads to the change of internal structure of diamond crystals. For the crystals co-doped with hydrogen and nitrogen, a special feature of photoluminescence spectroscopy is typically observed at 536 nm. Base on our results, a possible incorporated route is introduced for the crystallization diamond with simultaneous incorporation of nitrogen and hydrogen.     

纳米聚晶金刚石的高压高温合成

利用自行研制的二级大腔体静高压装置,通过高温超高压下石墨向金刚石的直接转变,合成出了纳米聚晶金刚石块体材料.合成压力约为17GPa,温度约为2300℃.微区X射线衍射分析表明,石墨转变成了立方相的金刚石,扫描电子显微镜及X射线全谱拟合分析显示,合成出来的金刚石晶粒尺寸约16nm.压痕法测得的样品维氏硬度为100GPa以上.     

Comparison of glassy carbon and boron doped diamond electrodes: Resistance to biofouling

Carbon based electrodes are widely used for in vivo and in vitro electrochemical studies. In particular, monoamine neurochemistry has been investigated using carbon microfibre electrodes. Similarly, glassy carbon (GC) is the preferred material for many biochemical applications, such as electrochemical detection in chromatography. More recently, boron doped diamond (BDD) has been utilized for biosensing, as its carbon sp³ structure is expected to provide better resistance to analyte fouling. However, the main factor limiting the use of electrochemical sensors for biological studies is the effect of the biological matrix. Indeed, in vivo or in situ measurements expose the sensor to a complex matrix of proteins, which adsorb on the sensing surface and interfere with the electrochemical measurements.Here, we compare the performance of three carbon based electrodes: GC, GC with low surface oxides and BDD. The redox species ruthenium(III) hexaammine (outer-sphere), ferrocyanide (surface sensitive) and the biologically significant dopamine have been investigated in protein and blood-mimicking matrices. Cyclic voltammetry and electrochemical impedance spectroscopy have been used to examine the effect of spectator molecules and reaction products on electrode mechanisms.Our results show that BDD generally exhibits the best performance for most conditions and reactions and should therefore be preferred for measurements in biologically fouling environments. Furthermore, surface oxides seem also to improve resistance of the GC electrode to biofouling.     

Simultaneous growth of well-aligned diamond and graphitic carbon nanostructures through graphite etching

A hot filament chemical vapor deposition process based on hydrogen etching of graphite has been developed to synthesize diamond and graphitic carbon nanostructures. Well-aligned diamond and graphitic carbon nanostructured thin films have been synthesized simultaneously on differently pretreated silicon substrates in a pure hydrogen plasma. Graphitic nanocones, diamond nanocones and carbon nanotubes were selectively grown on uncoated, diamond and nickel pre-coated silicon substrates, respectively, in a single deposition process. The nanocones are solid cones with submicron scale roots and nanometer-size sharp tips. The nanotubes are hollow tubes with outer diameter of approximately 50 nm. The orientation of the well-aligned carbon nanostructures depends on the direction of the electric field at the samples surface. Nucleation and growth of diamond on the nanocones were further investigated under similar conditions without plasma. Diamond nanocomposite films have been obtained by depositing a nanocrystalline diamond film on the layer of diamond nanocones.     

Anodic behavior of sertindole and its voltammetric determination in pharmaceuticals and human serum using glassy carbon and boron-doped diamond electrodes

The electrochemical oxidation of sertindole was investigated using cyclic, linear sweep voltammetry at a glassy carbon and boron-doped diamond electrodes. The aim of this study was to determine sertindole levels in serum and pharmaceutical formulations, by means of electrochemical methods. In cyclic voltammetry, depending on pH values, sertindole showed one or two irreversible oxidation responses. These two responses were found related to the different electroactive part of the molecule. Using second and sharp oxidation peak, two voltammetric methods were described for the determination of sertindole by differential pulse and square wave voltammetry at the glassy carbon and boron-doped diamond electrodes. Under optimized conditions, the current showed a linear dependence with concentration in the range between 1 × 10⁻⁶ and 1 × 10⁻⁴ M in acetate buffer at pH 3.5 and between 4 × 10⁻⁶ and 1 × 10⁻⁴ M in spiked human serum samples for both methods. The repeatability, reproducibility, selectivity, precision and accuracy of all the methods in all media were investigated and calculated. These methods were successfully applied for the analysis of sertindole pharmaceutical dosage forms and human serum samples. No electroactive interferences from the tablet excipients and endogenous substances from biological material were found.