Synthesis of boron-doped diamond with laser heated diamond anvil cell

Boron-doped diamond has been synthesized from graphite mixed with different ratio of B₄C at high pressure high temperature (HPHT) using laser heated diamond anvil cell. The starting composition was transformed to diamond compound at pressure ∼9 GPa, 2300–2400 K as indicated by the in-situ X-ray diffraction pattern with synchrotron radiation source. Raman spectrum of the recovered specimen from HPHT state confirmed that boron has been doped into diamond lattice.     

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.     

Microstructures of metallic film and diamond growth from Fe-Ni-C system

The microstructures of metallic film surrounding diamond have been systemically studied using the transmission electron microscopy (TEM) and the atom force microscopy (AFM). The film can be divided into three layers (inner layer near diamond, external layer near graphite and middle layer). The graphite cannot be directly transformed into diamond in the film at HTHP; there exists a parallel relationship between (−111) of γ-(Fe,Ni) and (110) of Fe₃C in the inner layer; the sawtooth-like step morphology found by AFM on the film is similar to that of corresponding diamond surface. A new model for diamond growth at HPHT is proposed from the parallel relationship and sawtooth-like step morphology. It is believed that Fe₃C may be a transitional phase in the course of diamond growth, γ-(Fe,Ni) in the inner layer can absorb carbon atom groups with lamella structure from Fe₃C, and then the carbon groups stack on growing diamond.     

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。     

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.     

Study on the HPHT synthetic diamond crystal from Fe-C（H） system and its significance

Investigations of crystal habit, micro-topographic imaging, micro-composition and micro-structural analysis of HPHT synthetic diamonds from the Fe-C（H） system indicate that most of them have an octahedral habit. The crystals grow mainly layer-to-layer from center to periphery. HPHT synthetic diamond is smaller in size than natural diamond because it only goes through nucleation and growth in the early stage. In the middle and late stages, due to the coalescence of diamond grains related to differences of surface energy, the growth of HPHT synthetic diamond is limited. The active energy （E） of transforming single nitrogen into a nitrogen-pair is lowered and the time of transforming single nitrogen into a nitrOgen-pair is shortened because of the existence of hydrogen. Therefore, aggregate nitrogen （A-centers） may exist in synthetic diamond from HPHT and explosive detonation processes. It needs further discussion on a worldwide view that the time of natural diamond formation extracted from nitrogen aggregation is some hundred million years. Consideration of the way in which surface energy influences the growth of diamond can help to understand some of the remaining issues （e.g. growth mechanism, etc.） in the HPHT synthetic process and effectively explain the formation of natural diamond in terms of HPHT thermodynamic theory. Especially, it is important to pay more attention to the influence of hydrogen on surface energy in that hydrogen may be a ＂bridge＂ for explaining the formation of HPHT synthetic and natural diamond.     

Mechanism of diamond-to-graphite transformation at diamond-stable conditions

The diamond-to-graphite transformation at diamond-stable conditions is studied by temperature gradient method （TGM） under high pressure and high temperature （HPHT）, although it is unreasonable from the view of thermodynamic considerations. It is found that, at diamond-stable conditions, for example, at 5.5 GPa and 1550 K, with fine diamond grits as carbon source and NiMnCo alloy as metal solvent assisted, not only large diamond crystals, but metastable regrown graphite crystals would be grown by layer growth mechanism, and the abundance of carbon source in the higher temperature region is indispensable for the presence of metastable regrown graphite crystals. From this transformation, it is concluded that, with metal solvent assisted, although the mechanism of crystal growth could be understood by the macro-mechanism of solubility difference between diamond and graphite in metal solvents, from the point of micro-mechanism, the minimum growth units for diamond or graphite crystals should be at atomic level and unrelated to the kinds of carbon source （diamond or graphite）, which could be accumulated free-selectively on the graphite with Sp2Tr or diamond crystals with sp3 bond structure.     

Selective interfacial bonding and thermal conductivity of diamond/Cu-alloy composites prepared by HPHT technique

Cu-based and Cu-alloy-based diamond composites were made by high-pressure-high-temperature (HPHT) sintering with the aim of maximizing the thermal conductivity of the composites. Improvements in interfacial bonding strength and thermo-physical properties of the composites were achieved using an atomized copper alloy with minor additions of Co, Cr, B, and Ti. The thermal conductivity (TC) obtained exhibited as high as 688 W·m-1·K-1, but also as low as 325 W·m-1·K-1. A large variation in TC can be rationalized by the discrepancy of diamond-matrix interfacial bonding. It was found from fractography that preferential bonding between diamond and the Cu-alloy matrix occurred only on the diamond {100} faces. EDS analysis and Raman spectra suggested that selective interfacial bonding may be attributed to amorphous carbon increasing the wettability between diamond and the Cu-alloy matrix. Amorphous carbon was found to significantly affect the TC of the composite by interface modification.     

触媒对人造金刚石组织及性能的影响

本文研究了触媒对合成金刚石的组织及性能的影响。结果表明:触媒晶粒细小均匀,夹杂物较多时,有利于金刚石的形核,获得的细小金刚石较多,单次产量较高,但完整晶形所占比例较少,单颗粒抗压强度较低。而当触媒晶粒较粗大,为变形晶粒,夹杂物数量较少时,则得到与上述相反的结果。     

Crystallization dynamics of supersaturated NaClO4 aerosols studied by high-speed photography

Single supersaturated NaClO4 aerosol droplets on a quartz substrate were observed by a high-speed video camera for their morphologic changes with decreasing relative humidity （RH）. The supersaturated droplets were found to form anhydrous NaClO4 at -10% RH. Three stages were roughly observed in this process, i.e., the main stem appearance, primary and secondary branches growth, and the deep dehydration. The main stem grew steadily and finished in 120 ms. Affected by both crystal precipitation and water evaporation, primary branches grew for 1200 ms, accompanied by a slower growth of secondary branches. The deep dehydration was more complicated, and lasted for a longer time.     

Synthesis and antimutagenic effects of selena-morpholine hydrate

The synthesis of selenamorpholine hydrate was described and its antimutagenic effects were investigated by the Ames tests. The results indicated that the mutation induced by the indirect mutagen 2-AF was inhibited obviously by selenamorpholine hydrate at the dosage of Se 0. 16～100 μg /dish for 35.8%～53.7%(TA97) and the mutation induced by direct mutagen Dexon was inhibited for 6.2%～30.0%(TA97) and 2.3%～34.1%(TA100). The mutagenesis of the indirect mutagen cyclophosphamide was suppressed for 5.4%～16.1% by selenamorpholine hydrate at the dosage of Se 0. 16～100 μg /dish.     

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)...     

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 ...     

Catalyst enhanced chemical vapor deposition of nano-particle nickel films on teflon surface

Films formed with nanosized nickel particles on teflon surface were prepared by means of catalyst enhanced chemical vapor deposition (CECVD) with Ni(dmg)₂, Ni(acac)₂, Ni(hfac)₂, Ni(TMHD)₂, and Ni(cp)₂ as precursors, and complexes Pd(hfac)₂, PdCl₂ and Pd(η ³-2-methylallyl)acac as catalyst under carrier gas (H₂). The film growth rate depends on the precursors and substrate temperature. The chemical value, purity and surface morphology of the Ni particle films were characterized by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The films obtained were shiny with silvery color, and consisted of grains with a particle size of 50–140 nm. The Ni was metallic of which the purity was about 90%–95% from XPS analysis. SEM micrograph showed that the film had good morphology.      

Growth of the Huoersuosi anticline （north Tianshan Mountains） by limb rotation since the late Miocene

The Huoerguosi anticline, located in the north Tianshan Mountains piedmont fold-and-thrust belt, is a trending east-west fault-related fold. In the cross section along the Jingou River, its south limb is composed of the pre-growth strata of the Anjihaihe （E2.3a）, the Shawan （（E3-N1）s）, the Taxihe （N1t） and the lower part of the Dushanzi （N2d） Formations, trending east-west and dipping to south 55°, and the growth strata of the upper part of the Dushanzi （N2d） and Xiyu （（N2-Q1）x） Formations, dips of which decrease from 55° at the base of the growth strata to 47° at the bottom of the Xiyu （（N2-Q1）x） Formation to -0° at the top of the Xiyu （（N2-Q1）x） Formation. The strata at the north limb of the anticline are vertical or over-turned, and are cut by the breakthrough thrusts to result in the drag fold. In the depth, the anticline is symmetric, and its core comprises the Cretaceous and the Jurassic coal-bearing beds. In the seismic profile, the seismic reflectors of pre-growth strata at the south limb of the anticline dip to south constantly, and ones of the growth strata fan southward, whose dips decrease upward. The geometry of the south limb growth strata outcropped along the Jingou River valley and the deep structure of the anticline shown in the seismic profile indicate that the Huoerguosi anticline is a detachment fold anticline growing by limb rotation. Based on the growth model and magnetostratigraphic age, during the growing process of the Huoerguosi anticline, the average shortening rate absorbed by the south limb is -0.46 mm/a, and the average uplifting rate of the anticline is -0.86 mm/a which exceeds the average deposition rate, which is in accordance with the fact that the top of the anticline is intensely eroded. Considering symmetric geometry of the Huoerguosi anticline and ignoring the breakthrough thrusts, the shortening of the whole anticline should be more than -0.92 mm/a, doubling the shortening rate determined from the growth at the south limb.     

Crystallization kinetics of sea-salt aerosols studied by high-speed photography

Morphological changes with decreasing relative humidity(RH) of supersaturated sea-salt aerosol droplets on a quartz substrate were observed using a high-speed video-camera.Stable gypsum(CaSO4·2H2O) or the metastable hemihydrate(CaSO4·0.5H2O) were precipitated as the RH decreased.The dynamic process of crystal growth under steady-state humidity was studied by controlling the RH;the metastable hemihydrate was precipitated at 70.5%-77.1% RH,and the apparent crystal growth rate was between 1.42 and 2.33 μm3/s.Stable gypsum was formed at 80.7%-82.2% RH,and the apparent crystal growth rate was between 0.70 and 0.81 μm3/s.     

Holocene climatic and environmental changes recorded in Baahar Nuur Lake core in the Ordos Plateau, Inner Mongolia of China

A 5.3 m lake core was drilled in Baahar Nuur Lake in the Ordos Plateau, and measurements of meangrain size, organic δ 13C (δ 13Corg), organic carbon content (TOC), C/N, carbonate content, carbonate δ 13C(δ 13Ccar) and δ 18O (δ 18Ocar) were conducted for retrieving the Holocene chronosequence of climaticchanges based on 15 AMS 14C dates. The record documented four major stages of climate change inthe Ordos Plateau: (IV) a cold and dry condition before ～7.65 14C ka BP; (III) a warm and humid stagebetween ～7.65 and ～5.40 ka BP; (II) a generally drier and cooler climate since ～5.40 ka BP with twohumid events occurring from ～4.70 to ～4.60 ka BP and from ～4.20 to ～3.70 ka BP, and (I) a dry climatecharacterized by complete desiccation of the lake after 3.70 ka BP. Stage III can be further divided intothree sub-stages: (IIIa) a warm and humid episode from ～7.65 to ～6.70 ka BP, (IIIb) a warm and relativelydry episode from ～6.70 to ～6.20 ka BP, and (IIIc) the magthermal and maghumid episode of the Holo-cene from ～6.20 to ～5.40 ka BP.     

Microstructural evolution of titanium matrix composite coatings reinforced by <Emphasis Type="Italic">in situ</Emphasis> synthesized TiB and TiC by laser cladding

Titanium-based composite coatings reinforced by in situ synthesized TiB and TiC particles were successfully fabricated on Ti6Al4V by laser cladding using Ti-B₄C-Al or Ti-B₄C-C-Al powders as the precursor materials. The microstructural and metallographic analyses were made by X-ray diffraction (XRD), optical microscope (OM), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). The results show that the coatings are mainly composed of α-Ti cellular dendrites and a eutectic transformation product in which a large number of coarse and fine needle-shaped TiB and a few equiaxial TiC particles are homogeneously embedded. A thin dilution zone with a thickness of about 100 μm is present at the interface, and it consists of a few TiB and TiC reinforcements and a large number of lamella grains growing parallel to the heat flux direction in which a thin needle-shaped microstructure exists due to the martensitic transformation. The microstructural evolution can be divided into four stages: precipitation and growth of primary β-Ti phase, formation of the binary eutecticum β-Ti+TiB, formation of the ternary eutecticum β-Ti+TiB+TiC, and solid transformation from β-Ti to α-Ti.     

Fe-Ni-C粉末触媒体系金刚石的合成与表征

利用FeNi粉末触媒在六面顶压机上进行工业金刚石单晶的合成与表征. 结果表明: 在Fe-Ni-C体系合成了优质的六面体、 六-八面体及八面体金刚石单晶; 金刚石{111}晶面的生长属于二维层状生长机制; 金刚石中的包裹体主要由FeNi合金组成.     

Seasonal variations and environmental controls on stalagmite calcite crystal growth in Heshang Cave,central China

Stalagmite growth rates are usually considered to reflect changes in paleoclimate and paleoenvironment. However, how exactly growth rates are affected by climate and environment is still unclear. We launched a monitoring and modeling program that lasted approximately 4 years on two active drip sites in Heshang Cave, central China. We collected comprehensive quantitative data on growth rates, cave temperature, CO₂ concentration, drip rate and drip-water chemistry to better understand the relationship between stalagmite growth and cave environment. By laying out glass substrates, we successfully grew stalagmite calcite crystals with rhombic characteristics, and quantified growth rates by measuring the long and short axes of calcite crystals under a microscope. Combined with coeval environmental data, we explicitly examined the roles of cave temperature, drip rate and drip-water chemistry in controlling the micro-scale growth of stalagmite calcite. Results show that growth of stalagmite calcite crystals at two drip sites exhibited similar seasonal variations − generally faster in the summer months, at ∼3 μm d⁻¹, and slower during the late winter to early spring, at ∼1.5 μm d⁻¹. Variations in calcite growth rates were mainly determined by changes in cave temperature, with the growth rate increasing by 8.1%/°C and 6.6%/°C at the two locations. This indicates the potential use of stalagmite growth rates as a seasonal-resolution paleo-temperature proxy in some ventilated caves. On the other hand, the effect of drip rate and drip-water Ca²⁺ and SIC values on growth rates were not significant.