Study on growth of coarse grains of diamond with high quality under HPHT

The growth of coarse grains of diamond was observed with graphite as carbon source and Fe₈₀Ni₂₀ alloy powder as catalyst at HPHT in a China-type SPD 6×1670T cubic high-pressure apparatus with highly exact control system. To synthesize coarse grains of diamond crystal with high quality, advanced indirect heat assembly, powder catalyst technology and catalyst with optimal granularity were used. Especially the nucleation of diamond and the growth rate were strictly controlled by the optimized synthesis craft. At last, diamond crystals (about 0.85 mm) in the perfect hex-octahedron shape were successfully synthesized at ~5.4 GPa and ~1360℃ in 60 min. The characteristic of crystal growth with powder catalyst technology under HPHT was discussed. The results and techniques might be useful for production of coarse grains of diamond.     

Analysis of the carbon source for diamond crystal growth

The lattice constants of diamond and graphite at high pressure and high temperature （HPHT） were calculated on the basis of linear expansion coefficient and elastic constant. According to the empirical electron theory of solids and molecules （EET）, the valence electron structures （VESs） of diamond, graphite crystal and their common planes were calculated. The relationship between diamond and graphite structure was analyzed based on the boundary condition of the improved Thomas-Fermi-Dirac theory by Cheng （TFDC）. It was found that the electron densities of common planes in graphite were not continuous with those of planes in diamond at the first order of approximation. The results show that during the course of diamond single crystal growth at HPHT with metal catalyst, the carbon sources forming diamond structure do not come from the graphite structure directly. The diamond growth mechanism was discussed from the viewpoint of valence electron structure.     

Growth and characterization of large, high quality cubic diamond crystals

High quality cubic diamond crystals were grown using the temperature gradient method at high pressure and high temperature(HPHT),in a new FeNi alloy as solvent.The crystals were grown at relatively low temperatures suitable for the growth of {100} faces.An increase in the radial growth rate,and inhibition of the axial growth caused the growth of large,high quality cubic diamond single crystals at high growth rates.For example,over 33 h,the radial growth rate was 0.22 mm/h,while the axial growth rate was only 0.08 mm/h;the growth rate by weight was also increased to 7.3 mg/h.The yellow color of our crystal samples was more uniform than samples from Sumitomo Corporation of Japan and Element Six Corp.The Raman FWHW of the 1332 cm 1 peak in our diamond sample was smaller than the Element Six Corp.sample,but larger than that of the Sumitomo Corp.sample.The nitrogen content of our diamond samples was 240 ppm,which was much higher than the Sumitomo and Element Six samples because of the higher growth rate of our diamond samples.     

活性碳,碳黑,石墨与金刚石晶种的生长

介绍了活性碳、碳黑与石墨在过剩压驱动下金刚石晶种的生长．对两种无定形碳以及石墨在触媒中的分散溶解输运与再结晶进行了观察，对活性碳、碳黑在金刚石晶种生长中的机理作了探索性的讨论．三种碳片上的晶种均有明显长大，无定形碳作晶种生长的碳源是可行的     

Effect of additive boron on type-Ib gem diamond single crystals synthesized under HPHT

The boron-doped type-Ib gem diamond crystals were synthesized successfully by adding amorphous boron into a system of graphite and Kovar catalyst under high pressure and high temperature (HPHT).The effect of additive boron on type-Ib gem diamond was extensively studied including the growth characteristic,morphology and nitrogen concentration.The synthesized boron-doped type-Ib gem diamond crystals were characterized by optical microscope (OM),scanning electron microscope (SEM) and infrared spectrometer (IR)...     

Low temperature thermodynamic study of the stable and metastable phases of vanadium

The low temperature thermodynamics of the stable phase of vanadium has been assessed by the polynomial and Debye models from the experimental data available in literature. By means of the con-strained nonlinear least squares curve fitting arithmetic,two sets of parameter values have been de-termined. Expressions of the thermodynamic functions Cp(T) and G(T)-H(298.15 K) at 0―298.15 K are presented. The low temperature thermodynamics of the metastable phase of vanadium can only be extrapolated by the Debye model. The expression of the thermodynamic function Cp(T) at 0―298.15 K is presented.     

Compression behavior and equation of state of Ni77P23 amorphous alloy

The compression behavior of Ni77P23 amorphous alloy is investigated at room temperature in a diamond-anvil cell instrument using insitu high pressure energy dispersive X-ray diffraction with a syn- chrotron radiation source. The equation of state is determined by fitting the experimental data accord- ing to Birch-Murnaghan equation: -ΔV/V0=0.08606P-3.2×10-4P2 5.7×10-6P3. It is found that the structure of Ni77P23 amorphous alloy is stable under pressures up to 30.5 GPa.     

Structural and electrical properties of ZnO films on freestanding thick diamond films

In this paper, ZnO films are deposited on freestanding thick diamond films （FTDF） by plasma-assisted metal organic chemical vapour deposition （MOCVD）. Diethyl zinc （DEZn）, O2 and N2O are applied as precursors and different substrate temperatures are used to achieve high quality ZnO films. The influence of substrate temperature on the properties of ZnO films is systematically investigated by X-ray diffraction （XRD）, Hall measurements and electron probe microanalysis （EPMA）. Experimental results demonstrate that ZnO films deposited at 600℃ and 73 Pa display a fine electrical quality and Zn/O atomic ratio plays an important role in the electrical property of ZnO films.     

Estimate of carbonate production by scleractinian corals at Luhuitou fringing reef, Sanya, China

Carbonate production by scleractinian corals not only maintains coral reef growth, but also represents an important source of atmospheric carbon dioxide. In this paper the carbonate production by scler-actinian corals at Luhuitou fringing reef, Sanya, Hainan Island, China, is investigated with an ecological census-based method. Averaged carbonate production is 1.16 ± 0.55 kg·m-2·a-1 and 3.52 ± 1.32 kg·m-2·a-1 on the reef flat and reef slope, respectively, depending on the composition and distribution of cor...     

Fabrication of metal nanoclusters on graphene grown on Ru（0001 ）

Monolayer graphene was epitaxially grown on Ru（0001） through exposure of the Ru（0001） to ethylene at room temperature followed by annealing in ultrahigh vacuum at elevated temperatures. The resulting graphene structures were studied by scanning tunneling microscopy （STM）, X-ray photoelectron spectroscopy （XPS）, and ultraviolet photoelectron spectroscopy （UPS）. The graphene/Ru（0001） surface was used as a periodic template for growth of metal nanoclusters. Highly dispersed Pt clusters with well controlled size and spatial distribution were fabricated on the surface.     

Petrographic and geochemical characterization of seep carbonate from Alaminos Canyon,Gulf of Mexico

Seep carbonates were collected from the Alaminos Canyon lease area, Gulf of Mexico. The carbonates are present as slabs and blocks. Bivalve shell and foraminifer are the dominant bioclasts in carbonate. Pores are common and usually filled with acicular aragonite crystals. XRD investigation shows that aragonite is the dominate mineral （98%）. Peloids, clotted microfabirc and botryoidal aragonite are developed in carbonate and suggest a genesis linked with bacterial degradation of the hydrocarbons. The δ^13C value of bioclasts in carbonate is from -4.9‰ to -0.6‰, indicating that the carbon source is mainly from sea water as well as the small portion incorporation of the seep hydrocarbon. The microcrystalline and sparite aragonite shows the δ^13C value from -31.3‰ to -23.4‰, suggesting that their carbon is derived mainly from microbial degradation of crude oil. ^14C analyses give the radiocarbon age of about 10 ka. Rare earth elements （REE） analyses of the 5% HNO3-treated solution of the carbonates show that the total REE content of the carbonates is low, that is from 0.752 to 12.725 μg·g^-1. The shale-normalized REE patterns show significantly negative Ce anomalies. This suggests that cold seep carbonate is most likely formed in a relatively aerobic environment.     

Preparation and magnetic properties of CoFe2O4/TiO2 composite films

Using （Ti（OC4H9）4） and metal chlorates as starting materials, CoFe2O4/TiO2 composite films were prepared by sol-gel method. The effects of heat treatment temperature and pH of the precursor on microstructure and magnetic properties were studied. The phase structure of the samples was examined by X-ray diffraction. The microstructure was examined by scanning electron microscope, atomic force microscope and polarized microscope. The magnetic property was measured by vibrating sample magnetometer. The results show that the crystals of different phases grow up independently. CoFe2O4 is uniformly embedded into the TiO2 matrix in the prepared composite films, and the growth of composite films is dependent on the heat treatment temperatures and PH of the precursor. The average size of CoFe2O4 crystal is 19 nm in Nanocomposite film prepared when the heat treatment temperature is 800℃ and the pH of the precursor is between 2 and 3. The magnetism of the composite films is enhanced as the heat treatment temperature increases.     

人工合成金刚石的体扩散机制

本文研究了在合金触媒参与下石墨转变为金刚石的机理。认为在超高压高温条件下,石墨以碳原子集团的形式扩散到溶剂合金中,形成似胶体溶液的扩散区。在合金触媒的催化作用下,正离子化的碳原子集团相变成金刚石结晶基元。结晶基元达到过饱和时,经体扩散在合金与石墨的界面上形核生长,沿金刚石[111]和[100]方向长大,长成立方-八面体。     

Spread of double-walled carbon nanotube membrane

A single-layer double-walled carbon nanotube (DWNT) membrane, with 100 cm2 in area, 50 nm in thickness, was spread by adding a few drops of ethanol (or acetone) on the purified DWNTs. Compared with acetone, ethanol is more efficient in spreading DWNT films. The spreading rate of DWNT mem-brane increases with the ethanol concentration, and it also first increases with temperature (below 60℃), then decreases as the temperature rises to above 60℃.     

Effects of carbon diffusing field in alloy solvent on the growth of tower-shape diamond single crystal

High-quality type-Ib tower-shape diamond single crystals were synthesized in cubic anvil high pressure apparatus (SPD-6×1200) at 5.4 GPa and 1250-1450°C. The (100) face of seed crystal was used as the growth face, and FeNiMnCo alloy was used as the solvent/catalyst. Two kinds of carbon diffusing fields (type-B and type-G) were simulated by finite element method (FEM). Using the two kinds of carbon diffusing fields, many diamond single crystals were synthesized. The effects of carbon diffusing fields on the ...     

Diamond synthesis from a system of chromium-carbide and Ni70Mn25Co5 alloy

In order to ascertain the mechanism of interaction between carbide and metallic catalyst and formation of diamond under high pressure and high temperature, and find a new method to synthesize diamond with special properties, it is necessary to investigate the reaction behavior of different carbides and metallic solvent_catalysts under high pressure and high temperature. A system of Cr-3C-2 powder and Ni 70Mn 25Co 5 alloy in weight ratio of 1∶6 was treated under 6 0 GPa and 1 500℃ for 20, 30 or 60 min respectively. X_ray diffraction of the samples indicated the Cr 3C 2 decomposed partially after high pressure and temperature treatment, and Cr 7C 3, Cr and diamond formed respectively. There was not any trace of graphite in the samples. The result suggested that the separated carbon atoms could form diamond directly without conversion process of graphite into diamond. The observation of SEI, WDX and EDX also showed that diamond crystals were synthesized in the system, which have perfect surfaces and shapes, with the average grain size of about 40 μm. The properties of the crystals are being investigated.     

Recent accumulation rate at Dome A, Antarctica

Based on the horizon of β activity and the density profiles, recent accumulation rate at Dome A, Ant-arctica is calculated to be 0.023 m water equivalent per year. This value is comparative to the accumu-lation rates deduced from the other inland sites of Antarctica. Clear-sky precipitation (or diamond dust) dominates the total precipitation at Dome A region. We speculate Dome A as a potential site to discover the oldest ice in Antarctica due to its tremendous ice thickness (>3000 m), extremely low accumulation rate, and low ice velocity.     

电镀晶种法合成金刚石单晶实验研究

目的寻求一种合成金刚石大单晶的有效方法。方法采用在金刚石单晶上面电镀一层金属镍膜作为触媒,镀有镍膜的金刚石晶种被规则地放在石墨片上预先刻好的洞中,每两个洞之间保持相等的间距,然后与其他石墨片交替组装在高温高压下进行实验合成。结果实验结果表明,在合成压力、温度和时间分别~5.8 GPa、~1 460℃和14 min的条件下,合成后的单晶尺寸约是原晶种的3倍。与传统的合成工艺相比较,合成后的金刚石单晶具有较好的形貌与质量。结论采用电镀晶种法合成对高品级金刚石大单晶的合成具有一定参考意义。     

A study on the double melting behavior of poly（trimethylene terephthalate）

Double melting behavior of poly（trimethylene terephthalate） （PTT） was studied in detail by means of differential scanning calorimetry （DSC） and optical microscopy. The results indicate that the low-temperature melting peak of PTT at ca. 218℃ for the samples crystallized isothermally at 203℃ is associated with the melting of crystals produced by secondary crystallization, while the high-temperature melting peak of it at about 227℃ is related to the melting of the crystals produced by primary crystallization. The results further demonstrate that the PTT crystals growing non-isothermally during cooling process are thermodynamically unstable and can undergo structure reorganization during the DSC heating scan. The reorganized crystals melt at temperature higher than the crystals produced by secondary crystallization at 203℃. Consequently, for the non-fully crystallized samples, the crystals grown during cooling also exhibit contribution to the high-temperature melting peak.     

Preparing amphiphilic acidic zeolite via chemically coating alkylamine

Amphiphilic ODA/HY and ODA/ Hβ zeolites have been prepared via chemically coating octadecylamine (ODA) with alcohol as solvent. IR and titrimetric results indicate that ODA molecules are chemisorbed on the acidic sites in zeolite, showing the higher thermostability and alcohol-resistance. These am- phiphilic zeolites contain both the hydrophobic and hydrophilic groups, orient at the liquid-liquid phase-boundary in both cyclohexane/water and water/carbon tetrachloride systems, and exhibit the potential to be used in the phase-boundary catalysis and adsorption. No by-products with strong acid- ity are formed in this approach, therefore, it can be used to prepare amphiphilic acidic zeolites with low Si/Al ratio.