常压下用金属有机化学气相沉积法在HP40钢表面制备纳米氧化铝薄膜及表征

常压下用金属有机化学气相沉积法(MOCVD),以仲丁醇铝(ATSB)为前驱体、氮气为载气在HP40钢表面制备了纳米氧化铝薄膜;用光学显微镜、扫描电子显微镜及能谱仪、X射线衍射仪、原子力显微镜等研究了沉积温度等参数对氧化铝薄膜沉积速率的影响,并对其形貌进行了观察。结果表明:随着沉积温度从503K升高到713K,薄膜沉积速率从0.1mg·cm~(-2)·h~(-1)增加到0.82mg·cm~(-2)·h~(-1);当沉积温度在593～653K范围内,可获得晶粒尺寸为10～15nm的纳米氧化铝薄膜;反应的表观活化能随氮气与ATSB蒸气混合气流速增加而降低,不同的混合气流速有不同的反应级数,ATSB的反应级为0.7±0.02。     

An experimental study on laminar CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript> premixed flames under an electric field

This work investigates the electric field effect on gas temperature, radiative heat flux and flame speed of premixed CH₄/O₂/N₂ flames in order to gain a better insight into the mechanism of controlling the combustion process by electrophysical means. Experiments were performed on laminar Bunsen flames (Re<2200) of lean to rich mixture composition (φ =0.8–1.2) with slight oxygen enrichment (Ω=0.21-0.30). The Schlieren flame angle technique was used to determine the flame speed, and thermocouple measurements at the post flame gas were conducted. The radiative heat flux was measured by using a heat flux meter. At high field strengths, coincident with the appearance and enhancement of flame surface curvatures, an apparent change in flame speed and gas temperature was observed. However, the application of an electric field had no significant effect on flame speed and temperature when the flame geometry was unaltered. This was supported by radiative heat flux showing negligible electric field effects. The modification in flame temperature and flame speed under electric field was attributed to the field-induced flame stretch due to the body forces produced by the ionic winds. This additional flame stretch, coupled with the influence of non-unity Lewis number, accounts for such changes. This reinforces the idea that the action of an electric field on flames with a geometry that remains practically undeformed produces very minimal effect on flame speed, temperature and radiative heat flux. A possible mechanism of combustion control by the application of flame stretch using electric field was introduced.     

CVD金刚石涂层拉丝模的研制与应用

:以市售大孔径 (>2mm)硬质合金拉丝模为衬底 ,经酸腐蚀去钴、研磨和还原处理后 ,以氢气和丙酮为原料 ,用穿孔直拉热丝CVD法制备了金刚石涂层。利用扫描电镜和喇曼谱图对涂层均匀性进行了评估。初步应用试验表明 ,金刚石涂层的附着力能满足实际拉伸要求 ,涂层拉丝模的工作寿命可提高 3～ 5倍。     

Comparative characterization of chemical vapor deposition diamond films by scanning cathodoluminescence microscopy

Thin diamond films grown by chemical vapor deposition (CVD) process on Si substrates under similar deposition conditions in the microwave-excited (MW) and direct current (DC) plasma discharges were taken for comparative examination. Raman spectra, photoluminescence (PL) spectroscopy, and color cathodoluminescence scanning electron microscopy (CCL-SEM) have been used for characterization of the structure and composition features of poly-crystalline diamond films. No essential difference in Raman spectra for the CVD diamond films was detected. A significant difference was revealed in the PL spectra and in CCL-SEM images.     

高性能CVD金刚石薄膜涂层刀具的制备和试验研究

采用电子增强热丝EACVD法,以WC-Co硬质合金刀具为衬底制备金刚石涂层刀具,研究了提高涂层附着力的衬底预处理新方法,探讨了抑制Co催石墨化作用的有效措施,提出了改善金刚石薄膜表面粗糙度CVD后处理新工艺。研究结果表明,采用了Ar-H2微波等离子体刻蚀脱碳预处理方法对于提高金刚石薄膜涂层的附着力有明显效果,添加适量粘结促进剂,可有效地抑制CVD沉积过程中钴向表层扩散引起的催石墨化作用。采用分步沉积新工艺是减小金刚石薄膜表面粗糙度的有效方法。所制备的高附着力和低粗糙度的金刚石薄膜涂层刀具切削性能明显改善,对实现高效高精度切削加工具有十分重要的意义。     

CVD金刚石厚膜焊接刀具的试验研究

提出一种制作CVD金刚石厚膜焊接刀具的新工艺。采用电子辅助化学气相沉积法 (EACVD)制备直径10 0mm、厚度 0 8～ 1mm的金刚石厚膜 ;通过对金刚石刀头表面进行金属化处理 (化学气相沉积W膜 ) ,改善了金刚石的耐高温性及与低熔点合金焊料的浸润性 ,可在大气环境下实现金刚石刀头与刀架的焊接。车削试验结果表明 :用新工艺制作的金刚石刀具适用于精密加工     

Effects of additive and preheat on the partially premixed CH4-air counter flow flames considering non-gray gas radiation

Detailed structures of the counterflow flames formed for different inlet fluid temperatures and different amount of additives are studied numerically. The detailed chemical reactions are modeled by using the CHEMKIN-II code. The discrete ordinates method and the narrow band based WSGGM with a gray gas regrouping technique (WSGGM-RG) are applied for modeling the radiative transfer through non-homogeneous and non-isothermal combustion gas mixtures generated by the counterflow flames. The results compared with those obtained by using the SNB model show that the WSGGM-RG is very successful in modeling the counterflow flames with non-gray gas mixture. The numerical results also show that the addition of CO₂ or H₂O to the oxidant lowers the peak temperature and the NO concentration in flame. But preheat of fuel or oxidant raises the flame temperature and the NO production rates. O₂ enrichment also causes to raise the temperature distribution and the NO production in flame. And it is found that the O₂ enrichment and the fuel preheat were the major parameters in affecting the flame width.     

Numerical modeling for the H2/CO bluff-body stabilized flames

This study investigates the nonpreximed H₂/CO-air turbulent flames numerically. The turbulent combustion process is represented by a reaction progress variables model coupled with the presumed joint probability function. In the present study, the turbulent combustion model is applied to analyze the nonadiabatic flames by introducing additional variable in the transport equation of enthalpy and the radiative heat loss is calculated using a local, geometry independent model. Calculation are compared with experimental data in terms of temperature, and mass fraction of major species, radical, and NO. Numerical results indicate that the lower and higher fuel-jet velocity flames have the distinctly different flame structures and NO formation characteristics in the proximity of the outer core vortex zone. The present model correctly predicts the essential features of flame structure and the characteristics of NO formation in the bluff-body stabilized flames. The effects of nonequilibrium chemistry and radiative heat loss on the thermal NO formation are discussed in detail.     

Growth and properties analysis of metal-organic chemical vapor deposited MgZnO films on -AlO substrates

Mg_xZn_1-xO (0 < x ? 0.12) thin films with the wurtzite structure have been successfully grown on c-Al₂O₃ substrates by metal-organic chemical vapor deposition (MOCVD). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), photoluminescence (PL) spectrometry, and transmission measurements are performed to study the characteristics of Mg_xZn_1-xO thin films. Results show that with increasing Mg content, the diffraction peak of Mg_xZn_1-xO thin films shifts towards a higher diffraction angle (the biggest shift is 0.22°), and the full width at half maximum (FWHM) of the diffraction peak is broadened. Meanwhile, a blue-shift occurs at the near-band-edge (NBE) emission peak and the largest blue-shift of the band gap of the Mg_xZn_1-xO films is 113 meV with Mg content x = 0.12. Therefore, the energy band gap of the Mg_xZn_1-xO films is determined by Mg content in the thin films and the energy band gap increases with an increase of Mg content.     

Chemical vapor synthesis of nanocrystalline perovskites using laser flash evaporation of low volatility solid precursors

One key requirement for the production of multinary oxide films by chemical vapor deposition (CVD) or nanocrystalline multinary oxides particles by chemical vapor synthesis (CVS) is the availability of precursors with high vapor pressure. This is especially the case for CVS where much higher production rates are required compared to thin films prepared by CVD. However, elements, which form low valent cations such as alkaline earth metals, are typically only available as solid precursors of low volatility, e.g., in form of beta-diketonates. This study describes laser flash evaporation as precursor delivery method for CVS of nanocrystalline perovskites. Laser flash evaporation exploits the nonequilibrium evaporation of solid metal organic precursors of low vapor pressure by absorption of the infrared radiation of a CO(2) laser. It is shown that stoichiometric, nanocrystalline particles consisting of SrZrO(3) and SrTiO(3) can be formed from corresponding mixtures of beta-diketonates which are evaporated nonselectively and with high rates by laser flash evaporation.     

Design of "model-friendly" turbulent non-premixed jet burners for C2+ hydrocarbon fuels

Experimental measurements in laboratory-scale turbulent burners with well-controlled boundary and flow configurations can provide valuable data for validating models of turbulence-chemistry interactions applicable to the design and analysis of practical combustors. This paper reports on the design of two canonical nonpremixed turbulent jet burners for use with undiluted gaseous and liquid hydrocarbon fuels, respectively. Previous burners of this type have only been developed for fuels composed of H(2), CO, and/or methane, often with substantial dilution. While both new burners are composed of concentric tubes with annular pilot flames, the liquid-fuel burner has an additional fuel vaporization step and an electrically heated fuel vapor delivery system. The performance of these burners is demonstrated by interrogating four ethylene flames and one flame fueled by a simple JP-8 surrogate. Through visual observation, it is found that the visible flame lengths show good agreement with standard empirical correlations. Rayleigh line imaging demonstrates that the pilot flame provides a spatially homogeneous flow of hot products along the edge of the fuel jet. Planar imaging of OH laser-induced fluorescence reveals a lack of local flame extinction in the high-strain near-burner region for fuel jet Reynolds numbers (Re) less than 20,000, and increasingly common extinction events for higher jet velocities. Planar imaging of soot laser-induced incandescence shows that the soot layers in these flames are relatively thin and are entrained into vortical flow structures in fuel-rich regions inside of the flame sheet.     

计算机自动控制的热壁低压MOCVD系统的建立及其应用

本文根据金属有机物化学气相沉积系统的原理和特点,建立了计算机自动控制的热壁低压ＭＯＣＶＤ系统。     

Morphologic and cathodoluminescence studies of diamond films by scanning electron microscopy

Using recent papers on scanning electron microscopy (SEM) of chemical vapor deposition (CVD) diamond films, two analytical applications of the SEM are discussed: the morphologic investigations (secondary electron emission mode) and the recognition of impurities and defects [cathodoluminescence (CL) mode]. Studies of CVD diamond films by SEM demonstrate that the morphologies of these films are affected by synthesis conditions, especially by substrate temperature, methane concentration, and total pressure in the reactor. CL spectra and images are useful tools for clarifying the relationship between emission centers and different types of defects generated during the process of diamond crystal growth. The paper shows that the investigations of the morphology, crystallinity, local CL emission, as well as the surface distribution of CL spectra on CVD diamond films by SEM led to the correlative information for quality estimation of films in comparison with natural diamond.     

ZnO薄膜非线性光学特性的实验研究

利用金属有机化学气相沉积(MOCVD)技术在蓝宝石衬底上生长一层高质量的ZnO薄膜。为了考察沉积温度对样品的非线性特性的影响,在200~500 ℃生长了一系列ZnO薄膜。用X射线衍射谱(XRD)及扫描电镜(SEM)对样品结构进行了评价。以Nd:YAG激光器输出的1.06 μm的激光为基频光,对ZnO薄膜样品的二阶及三阶非线性光学特性进行了实验研究。实验发现,对于250 ℃沉积温度的样品有较强的非线性效应,实验测得的二阶非线性极化张量 χ ⁽²⁾_ZZZ=9.2 pm/V, 三阶有效非线性系数χ⁽³⁾=5.28×10^－20 m²/V²。     

改善CVD金刚石薄膜涂层刀具性能的工艺研究

用热丝CVD法,以丙酮和氢气为碳源,在WC-Co硬质合金衬底上沉积金刚石薄膜,在分析了工艺条件(衬底温度、碳源浓度、反应压力)对金刚石薄膜性能的影响的基础上,提出了分步沉积法改善金刚石薄膜涂层刀具性能的新工艺.结果表明,合理控制工艺条件的新工艺对涂层薄膜质量、形貌和粗糙度、薄膜与衬底间的附着力、刀具的耐用度及切削性能有显著影响,对获取实用化的在硬质合金刀具基体上沉积高附着强度、低粗糙度金刚石薄膜的新技术具有重要的意义.     

硬质合金刀具基体沉积低表面粗糙度金刚石薄膜的工艺研究

CVD金刚石薄膜刀具的表面粗糙度是影响刀具切削性能的重要参数。为通过改进CVD沉积工艺减小金刚石薄膜表面粗糙度 ,提出了适当提高碳源浓度和合理控制沉积气压两项新的工艺方法 ,并通过切削试验研究了其对金刚石薄膜刀具耐用度及切削性能的影响     

利用平面激光诱导荧光技术及CH滤镜测量微喷管射流火焰OH及CH基元

微射流火焰形貌观测及火焰中重要基元的准确测量,对利用微尺度火焰燃烧特性研制开发微型燃烧动力系统具有重要意义。本文建立了微喷管射流火焰实验及光学测量系统,对H_2和CH_4微射流火焰进行了实验研究,测量了两种重要基元(CH,OH)的空间分布。首先,探索了相机曝光时间对H_2微射流火焰成像的影响,得到了不同流速下H_2微射流火焰形貌的变化规律。其次,采用平面激光诱导荧光测量技术得到了不同燃料流速下H_2及CH_4微射流火焰中OH基元分布,同时还利用单反相机加CH滤镜通过长时间曝光(30s)的方法获得了CH_4微射流火焰中CH基元的分布。结果表明,火焰图像清晰度随曝光时间增加提高,曝光时间30s时可获得H_2微射流火焰的清晰照片;采用分辨率2 048×2 048的ICCD相机可获得微尺度火焰OH基元分布的清晰图像。微射流火焰形貌及重要基元的实验结果表明相关数值计算方法准确可靠。     

CVD金刚石厚膜焊接刀具的制造及切削性能

用于制造金属切削刀具的金刚石主要有四种类型：（1）天然单晶金刚石；（2）人工合成单晶金刚石；（3）聚晶金刚石复合片（PCD）；（4）化学气相沉积（CVD）金刚石膜。近年来，随着CVD金刚石工艺的发展，CVD金刚石对具的应用越来越广泛。CVD金刚石对具有两类：CVD金刚石薄膜涂层刀具和CVD金刚石厚膜焊接刀具。由于金刚石厚膜焊接刀具兼有单晶金刚石和金刚石薄膜涂层刀具的优点，从而具有广阔的应用前景。本文主要介绍金刚石厚膜的制备、厚膜刀具的制造及厚膜刀具的切削性能。     

Friction and wear of diamondlike carbon on fine-graindiamond

Friction and wear behavior of ion-beam-deposited diamondlikecarbon (DLC) films coated on chemical-vapor-deposited (CVD),fine-grain diamond coatings were examined in ultrahigh vacuum,dry nitrogen, and humid air environments. The DLC films wereproduced by the direct impact of an ion beam (composed of a 3 :17 mixture of Ar and CH₄) at ion energies of 1500 and700 eV. Sliding friction experiments were conducted withhemispherical CVD diamond pins sliding on four differentcarbon-base coating systems: DLC films on CVD diamond; DLC filmson silicon; as-deposited, fine-grain CVD diamond; andcarbon-ion-implanted, fine-grain CVD diamond on silicon. Resultsindicate that in ultrahigh vacuum theion-beam-deposited DLC films on fine-grain CVD diamond (similarto the ion-implanted CVD diamond) greatly decrease both thefriction and wear of fine-grain CVD diamond films and providesolid lubrication. In dry nitrogen and in humid air,ion-beam-deposited DLC films on fine-grain CVD diamond films alsohad a lowsteady-state coefficient of friction and a low wear rate. Thesetribological performance benefits, coupled with a wider range ofcoating thicknesses, led to longer endurance life and improvedwear resistance for the DLC deposited on fine-grain CVD diamondin comparison to the ion-implanted diamond films. Thus, DLCdeposited on fine-grain CVD diamond films can be an effectivewear-resistant, lubricating coating regardless of environment.     

Calculation of concentration depth profiles in electron probe microanalysis

Based on a multiple reflection model, the concentration depth profiles of gold diffused into a silver substrate are determined. To conclude the structure of the sample from the measured intensity of radiation, an accurate correction procedure is necessary. A new model was developed for this purpose. Since the new electron probe microanalysis (EPMA) correction procedure is also valid for tilted samples, measurements with different geometries could be performed. The different angles of incidence and take-off angles allow for a better comparison of theory with experiment. One advantage of the applied multiple reflection model is that it can be extended comparatively easily with the analysis of layered specimens. Measurements of some specimens with one layer on a substrate are reported. The mean deviation of calculated thicknesses is about 10%. To calculate depth profiles, gold was evaporated with physical vapor deposition on silver foils. The thicknesses of evaporated gold films were 50 and 100 nm. Then the specimens were annealed at a temperature of approximately 400°C. Finally, the concentration depth profiles were quantified with EPMA. The shape of the profiles was derived from a simple diffusion model valid for the samples under consideration. To check the shape of the functions obtained, a comparison with measurements by secondary ion mass spectrometry was performed.