含化学热沉的气膜冷却流动与换热研究

为了进一步提高涡轮入口温度,提出一种新型气膜冷却方法~含化学热沉的气膜冷却方法。对于新方法来讲,化学热沉的存在会影响气膜孔下游的流场,从而影响主流与固体壁面的换热。建立简化理想化学热沉模型,采用标准k-ε湍流模型对该方法进行数值模拟,结果表明,化学热沉的存在降低了气膜孔出口下游不远处壁面附近的温度,同时增大了壁面处混合气膜与壁面之间的对流换热系数.

碳氢燃料热裂解机理及化学动力学模拟

发动机设计中,燃烧室的热管理问题日益突出.其根源必然涉及到碳氢燃料的化学机理模型.讨论了大分子烃类燃料热裂解反应的反应类型,分析了各反应类型的详细动力学以及对热裂解反应的灵敏度、重要性.根据热裂解反应类型有限和基于物质的一维表示,开发了大分子烃类反应机理的自动生成程序ReaxGen.建立了相应的热、动力学数据库,探讨了如何建立碳氢燃料的详细热裂解化学动力学模型.最后我们建立了正庚烷热裂解反应的详细机理,并用该机理模型模拟预测了产物分布和转化率,理论上计算了热沉值.所得结果与文献结果进行对比讨论.

超临界碳氢燃料蒸汽重整一维模型研究

为了获得关键参数对超临界碳氢燃料蒸汽重整化学热沉分布特性的影响,建立了超临界碳氢燃料蒸汽重整非稳态一维计算模型,通过与实验数据的对比验证了模型的准确性,并基于该模型采用RP-3的四组分替代模型对RP-3蒸汽重整过程中入口流速、压力和含水量等关键参数对热沉沿流向分布特性的影响进行了研究。结果表明:随着入口流速的增加,蒸汽重整反应化学热沉的峰值减小,且出现峰值的位置逐渐向出口移动。随着压力的升高,相同位置处的化学热沉都减少,但是出现峰值的位置不变。在入口含水量由5%增大到12%的过程中,微通道同一位置处的化学热沉增大,且化学热沉的最大值也是增大的,峰值出现的位置向微通道出口移动。

Effect of deposition parameters on micro-and nano-crystalline diamond films growth on WC-Co substrates by HFCVD

The characteristics of hot filament chemical vapor deposition（HFCVD） diamond films are significantly influenced by the deposition parameters, such as the substrate temperature, total pressure and carbon concentration. Orthogonal experiments were introduced to study the comprehensive effects of such three parameters on diamond films deposited on WC-Co substrates. Field emission scanning electron microscopy, atomic force microscopy and Raman spectrum were employed to analyze the morphology, growth rate and composition of as-deposited diamond films. The morphology varies from pyramidal to cluster features with temperature decreasing. It is found that the low total pressure is suitable for nano-crystalline diamond films growth. Moreover, the substrate temperature and total pressure have combined influence on the growth rate of the diamond films.

Microstructures and formation mechanism of headstand pyrocarbon cones developed by electromagnetic-field-assisted CVD

Novel headstand pyrocarbon cones （HPCs） with hollow structure were developed on the surfaces of pyrocarbon layers of the carbon/carbon （C/C） composites at 650-750 °C by the electromagnetic-field-assisted chemical vapor deposition in the absence of catalysts. The fine microstructures of the HPCs were characterized by high-resolution transmission electron microscopy. The results show that the textural features of the HPCs directly transfer from turbostratic structure in roots to a well-ordered high texture in stems. And the degree of high texture ordering decreases gradually from the stem to the tail of the HPCs. The formation mechanism of the HPCs was inferred as the comprehensive effect of polarization induction on electromagnetic fields and particle-filler property under disruptive discharge.

Preparation, characterization and electrochemical properties of boron-doped diamond films on Nb substrates

A series of boron-doped polycrystalline diamond films were prepared by hot filament （HF） chemical vapor deposition on Nb substrates. The effects of B/C ratio of reaction gas on film morphology, growth rate, chemical bonding states, phase composition and electrochemical properties of each deposited sample were studied by scanning electron microscopy, Raman spectra, X-ray diffraction, microhardness indentation, and electrochemical analysis. Results show that the average grain size of diamond and the growth rate decrease with increasing the B/C ratio. The diamond films exhibit excellent adhesion under Vickers microhardness testing （9.8 N load）. The sample with 2% B/C ratio has a wider potential window and a lower background current as well as a faster redox reaction rate in H2SO4 solution and KFe（CN）6 redox system compared with other doping level electrodes.

EFFECT OF GRID BIAS ON DEPOSITION OF NANOCRYSTALLINE DIAMOND FILMS

A positive grid bias and a negative substrate bias voltages are applied to the self-made hot filament chemical vapor deposited （HFCVD） system. The high quality nanocrystalline diamond （NCD） film is successfully deposited by double bias voltage nucleation and grid bias voltage growth. The Micro-Raman XRD SEM and AFM are used to investigate the diamond grain size, microstructure, surface morphology, and nucleation density. Results show that the obtained NCD has grain size of about 20 nm. The effect of grid bias voltage on the nucleation and the diamond growth is studied. Experimental results and theoretical analysis show that the positive grid bias increases the plasma density near the hot filaments, enhances the diamond nucleation, keeps the nanometer size of the diamond grains, and improves the quality of diamond film.

GENETIC OPTIMIZATION OF HOT FILAMENT PARAMETERS IN HFCVD SYSTEM

In HFCVD system the substrate temperature is a key factor which deeply affects the quality of diamond films. Th e magnitude and the variation of the substrate temperature must be limited in a suitable range to deposit diamond films of uniform thickness over large areas. In this paper, the hot filament parameters are investigated on the basi s of GAs to realize a good substrate temperature profile. Computer simulations d emonstrate that on parameters optimized by GAs a uniform substrate temperatur e field can be formed over a relatively large circle area with R s=10 cm.

Si-doped diamond films prepared by chemical vapour deposition

The effects of Si doping on morphology, components and structure characteristics of CVD diamond films were studied. Si-doped CVD diamond films were deposited on Si substrate by adding tetraethoxysilane （TEOS） into acetone as source of reactant gas. The morphology and microstructure of diamond films were characterized by scanning electron microcopy （SEM）. The crystalline quality of diamond films was studied by Raman spectroscopy and X-ray diffractometry （XRD）. The surface roughness of the films was evaluated with surface profilometer. The results suggest that Si doping tends to reduce the crystallite size, enhance grain refinement and inhibit the appearance of （11 I） facets. Raman spectra indicate that Si doping can enhance the formation of sp2 phase in diamond films. Moreover, Raman signal of SiC was detected, which suggests the existence of Si in the diamond films. Smooth fine-grained diamond （SFGD） film was synthesized at Si to C ratio of 1%.

Amorphous SiO_2 interlayers for deposition of adherent diamond films onto WC-Co inserts

Amorphous Si O2（a-Si O2） films were synthesized on WC-Co substrates with H2 and tetraethoxysilane（TEOS） via pyrolysis of molecular precursor.X-ray diffraction（XRD） pattern shows that silicon-cobalt compounds form at the interface between a-Si O2 films and WC-Co substrates.Moreover,it is observed by transmission electron microscope（TEM） that the a-Si O2 films are composed of hollow mirco-spheroid a-Si O2 particles.Subsequently,the a-Si O2 films are used as intermediate films and chemical vapor deposition（CVD） diamond films are deposited on them.Indentation tests were performed to evaluate the adhesion of bi-layer（a-Si O2 ＋ diamond） films on cemented carbide substrates.And the cutting performance of bi-layer（a-Si O2 ＋ diamond） coated inserts was evaluated by machining the glass fiber reinforced plastic（GFRP）.The results show that a-Si O2 interlayers can greatly improve the adhesive strength of diamond films on cemented carbide inserts;furthermore,thickness of the a-Si O2 interlayers plays a significant role in their effectiveness on adhesion enhancement of diamond films.

Effect of deposition temperature on properties of boron-doped diamond films on tungsten carbide substrate

Boron-doped diamond(BDD)films were deposited on the tungsten carbide substrates at different substrate temperatures ranging from 450 to 850°C by hot filament chemical vapor deposition(HFCVD)method.The effect of deposition temperature on the properties of the boron-doped diamond films on tungsten carbide substrate was investigated.It is found that boron doping obviously enhances the growth rate of diamond films.A relatively high growth rate of 544 nm/h was obtained for the BDD film deposited on the tungsten carbide at 650°C.The added boron-containing precursor gas apparently reduced activation energy of film growth to be 53.1 kJ/mol,thus accelerated the rate of deposition chemical reaction.Moreover,Raman and XRD analysis showed that heavy boron doping(750 and 850°C)deteriorated the diamond crystallinity and produced a high defect density in the BDD films.Overall,600-700°C is found to be an optimum substrate temperature range for depositing BDD films on tungsten carbide substrate.

Influence of methane on hot filament CVD diamond films deposited on high-speed steel substrates with WC-Co interlayer

Diamond films were deposited on high-speed steel substrates by hot filament chemical vapor deposition （HFCVD） method. To minimize the early formation of graphite and to enhance the diamond film adhesion, a WC-Co coating was used as an interlayer on the steel substrates by high velocity oxy-fuel spraying. The effects of methane content on nucleation, quality, residual stress and adhesion of diamond films were investigated. The results indicate that the increasing methane content leads to the increase in nucleation density, residual stress, the degradation of quality and adhesion of diamond films. Diamond films deposited on high-speed steel （HSS） substrate with a WC-Co interlayer exhibit high nucleation density and good adhesion under the condition of the methane content initially set to be a higher value （4%, volume fraction） for 30 min, and then reduced to 2% for subsequent growth at pressure of 3 kPa and substrate temperature of 800 ℃.

Preparation of diamond/Cu microchannel heat sink by chemical vapor deposition

A Ti interlayer with thickness about 300 nm was sputtered on Cu microchannels, followed by an ultrasonic seeding with nanodiamond powders. Adherent diamond film with crystalline grains close to thermal equilibrium shape was tightly deposited by hot-filament chemical vapor deposition(HF-CVD). The nucleation and growth of diamond were investigated with micro-Raman spectroscope and field emission scanning electron microscope(FE-SEM) with energy dispersive X-ray detector(EDX). Results show that the nucleation density is found to be up to 1010 cm-2. The enhancement of the nucleation kinetics can be attributed to the nanometer rough Ti interlayer surface. An improved absorption of nanodiamond particles is found, which act as starting points for the diamond nucleation during HF-CVD process. Furthermore, finite element simulation was conducted to understand the thermal management properties of prepared diamond/Cu microchannel heat sink.

Growth of Nano Crystalline Diamond on Silicon Substrate Using Different Etching Gases by HFCVD

We investigate the effects of etching gases on the synthesis of nano crystalline diamonds grown on silicon substrate at the substrate temperature of 550℃ and the reaction pressure of 4 kPa by hot filament chemical vapor deposition method, in which CH4 and H2 act as a source and diluting gases, respectively. N2, H2, and NH3 were used as the etching gases, respectively. Results show that the optimum conditions can be obtained only for the case of H2 gas. The crystal morphology and crystallinity of the samples have been examined by scanning electron microscopy and X-ray diffraction, respectively.

Low Temperature Plasma CVD Grown Graphene by Microwave Surface-Wave Plasma CVD Using Camphor Precursor

Hydrocarbon precursor such as methane has been widely used to grow graphene films and the methods of growing quality graphene films are dominated by thermal CVD （chemical vapor deposition） system. Graphene films grown by plasma process are generally highly defective which in turns degrade the quality of the films. Here, using a green precursor, camphor we demonstrate a simple and economical method to get high-quality graphene film on copper substrate by micro wave surface-wave plasma CVD at relatively low temperature 550℃. Graphene film grown using camphor shows superior quality than that of the film grown using methane. Results revealed that camphor precursor is a good alternative to hydrocarbon precursors for graphene research.

Tetraalkylammonium Fluorosilicates as Precursors for Electrochemical Deposition of Silicon Coatings. Synthesis and Thermal Stability

Several TAAFS （tetraalkylammonium hexafluorosilicates） with different cations were synthesized. Their thermal properties were studied showing that obtained complexes are stable enough to be suitable for electrochemical deposition of silicon coatings under temperatures at least up to 200 ℃.

Enhanced Property of Thin Cuprous Oxide Film Prepared through Green Synthetic Route

Thin cuprous oxide films have been prepared by chemical vapor deposition(pulsed spray evaporation-chemical vapor deposition)method without post-treatment.The synthesis of cuprous oxide was produced by applying a water strategy effect.Then,the effect of water on the morphology,topology,structure,optical properties and surface composition of the obtained films has been comprehensively investigated.The results reveal that a pure phase of Cu2O was obtained.The introduction of a small quantity of water in the liquid feedstock lowers the band gap energy from 2.16 eV to 2.04 eV.This finding was mainly related to the decrease of crystallite size due to the effect of water.The topology analyses,by using atomic force microscope,also revealed that surface roughness decreases with water addition,namely more uniform covered surface.Moreover,theoretical calculations based on density functional theory method were performed to understand the adsorption and reaction behaviors of water and ethanol on the Cu2O thin film surface.Formation mechanism of the Cu2O thin film was also suggested and discussed.

Geochemical characteristics of hydrothermal sediments from Iheya North Knoll in the Okinawa Trough

Thirty sediment subsamples were recovered from the Iheya North hydrothermal field （with an average of 38 m away from the hydrothermal vent） in the middle Okinawa Trough. Samples were obtained by the ROV （Remote Operated Vehicle） Faxian during the virgin cruise of the R/V Kexue in 2014 with the application of push cores. The chemical compositions of the sediments show that the hydrothermal sediments near the hydrothermal vent are mainly composed of SO3, ZnO and Fe203. Moreover, the hydrothermal sediments are also highly enriched in Pb, As, Sb, Hg, Se, Ag, Ba, Mo and Cd comparing with previous analysis results. On the other hand, the concentrations of St, Hg andAg in studied sediments are strongly and positively correlated, these elements can be used as an hydrothermal indicator. In addition, a factor analysis of the sediments suggested that the sediments were mainly influenced by hydrothermal origin, and terrestrial and biogenic input are limited in studied area. It is also suggested that different stages of crystallization were involved in the formation of hydrothermal chimney from factor analysis.

Thermodynamic analysis of manufacturing polysilicon from Si HCl_3,Si Cl_4 and H_2

Production of polysilicon by chemical vapor deposition of SiHCI3 with a fluidized bed reactor is a competitive technology. As equilibrium conversion can be approached in a fluidized bed reactor, a reliable thermodynamic analysis is very important. However, inconsistent thermodynamic analysis results have been reported in the lit- erature. The present work studied the effects of thermodynamic data and species selection, and recommended that JANAF was the best Cp data source and the minimum set of species included the following eight species： H2, HCI, SiC[4, SiCl2, SiHCI3, SiH2CI2, SiH3C] and Si. Then, the influence of operating conditions on the equilibrium was studied. For the SiHC｜3-H2 system, both the yield of silicon and selectivity to silicon reached their maximum at （up to 1100 ℃）, and low pressure and high H2 feed ratio were of benefit for silicon production. For the SiHCI3- SiCI4-H2 system, silicon could be produced only at 900-1400 ℃, and reducing pressure and increasing H2 feed ratio enhanced the yield of silicon. Meanwhile, the operation map for zero net by-production of SiCI4 by directly recycling the produced SiCl4 was determined.

Thermal conductivity determination of suspended mono- and bilayer WS2 by Raman spectroscopy

We report the thermal conductivities of monolayer （1L） and bilayer （2L） WS2 grown by chemical vapor deposition （CVD）, which are determined by use of temperature and excitation dependences of E2g^1 and A1g Raman modes. The first-order temperature coefficients of E2g^1 and Alg modes in both supported and suspended WS2 layers were extracted. The frequency shift of the A3g mode with temperature is larger than that of the E1 mode for 1L-WS2, which is 2g attributed to stronger electron-phonon coupling for the A1g mode than that for the E12g mode. Moreover, by use of the shift of the phonon mode induced by laser heating, the thermal conductivities at room temperature were estimated to be 32 and 53 W/（m.K） for 1L- and 2L-WS2, respectively. Our results provide fundamental information about the thermal properties of WS2 layers, which is crucial for developing applications of atomically-thin WS2 devices.