电弧增材成形中熔积层表面形貌对电弧形态影响的仿真

电弧增材成形常采用单道多层或多道搭接的熔积方式,不同的熔积方式下对应的熔积层表面形貌不同,从而影响电弧的形态及其传热传质过程.本文建立了纯氩保护电弧增材成形的电弧磁流体动力学三维数值模型,以及不同表面形貌的熔积层模型,并在保持阳极与阴极之间距离和熔积电流不变的条件下,通过模拟计算获得增材成形特有的单道和多道搭接熔积条件下的不同表面形貌对应的电弧形态以及相应的温度场、流场、电流密度、电磁力、电弧压力分布.数值模拟结果表明:平面基板上起弧情况下电弧中心具有较高的温度、速度、电流密度以及压强;单道多层熔积情况下熔积层数对电弧的各个参量影响较小;多道搭接熔积情况下电弧呈非对称分布,电弧中心温度较前两者低,电流密度、电磁力和电弧压强的分布偏向熔积层一侧.     

Film deposition by laser-induced vacuum arc evaporation

Recent results of a study of the deposition process and the technological development of laser-arc are presented. Studies of the influence of arc current on film deposition were carried out for Ti, TiC, and C. On the basis of these results, specific multilayered structures have been prepared. As an example, a Ti/TiC multilayer system with 25-nm single layers is described. Results of structural and chemical analysis by means of Auger electron spectroscopy (AES) are presented. They show that diamond-like carbon film with a refractive index in the range of between 2.05 and 2.5 can be deposited effectively     

我国等离子体工艺研究进展

扼要综述了我国等离子体材料工艺研究的新近进展。内容包括：热等离子体源,等离子冶金、化工,超细粉合成,喷涂;低气压非平衡等离子体源,镀膜,表面改性,等离子浸没离子注入,电晕放电,介质阻挡放电,滑动弧等及其应用,当前,各类薄膜制备和表面改性的研究工作更为活跃。     

EELS plasmon studies of silver/carbon core/shell nanocables prepared by simple arc discharge

A method for the fabrication of large quantities of high quality silver nanocables encapsulated in carbon nanotubes (Ag@C) using a hydrogen arc is presented. A growth mechanism based on the generation of poly-aromatic hydrocarbons by the hydrogen arc is proposed. The size-dependent electronic structures of the resultant materials are investigated using electron energy loss spectroscopy (EELS). The surface plasmon and bulk-excitation character observed by EELS are discussed. As the diameter of Ag@C nanocable decreases, the surface and bulk plasmons of the silver core shift to lower energy and the peaks broaden. Measurements of electrical conductivity exhibits a liner current–voltage character with a conductivity of 0.5×10⁴ S/cm for the nanocable structure. PACS 81.05.Tp; 81.07.-b     

On the determination of energy fluxes at plasma–surface processes

A summary is given of different methods for the determination of the energy influx and its influence on the thermal balance and energetic conditions of substrate surfaces during plasma processing. The discussed mechanisms include heat radiation and kinetic and potential energy of charged particles and sputtered neutrals. For a few examples such as magnetron sputtering of a-C:H films, sputter deposition of aluminum on microparticles, and titanium deposition in a hollow-cathode arc evaporation device the energetic balance of substrates during plasma processing is presented. Received: 6 July 2000 / Accepted: 12 December 2000 / Published online: 3 April 2001     

Ion beam formation of the catalytically active surface of titanium electrodes

Ion beam assisted deposition (IBAD) of platinum with a rare earth metal on titanium substrates is carried out from a neutral fraction of vapor and ionized plasma of a pulsed electric arc. Ions of the metal being deposited serve as assisting ions in the process. The deposited coatings are analyzed by RBS, SEM, and EMA methods. The electrocatalytic activity of titanium electrodes with the coatings is studied in the electrochemical reactions of hydrogen and oxygen evolution, as well as methanol and ethanol oxidation. Electrodes with coatings containing platinum are found to exhibit a high level of electrocatalytic activity in all test reactions.     

Prediction of gas tungsten arc welding properties in mixtures ofargon and hydrogen

A theory of gas tungsten arc welding (GTAW) arcs that treats the tungsten electrode, the arc, and the workpiece as a unified system has been applied to make predictions in two dimensions of the temperature distributions in the arc, the tungsten cathode, and the workpiece, for any given arc current and gas mixture. Predictions of arc temperatures, radii, and voltages are compared for argon and mixtures of argon and hydrogen. It is found that arcs in gas mixtures containing hydrogen are more constricted and have a higher maximum temperature and arc voltage than arcs in pure argon. The addition of hydrogen also significantly increases the volume of molten material in the weld pool due to the higher thermal conductivity of argon-hydrogen mixtures at temperatures at which molecules of hydrogen dissociate. Predictions are also compared for workpieces of steel and aluminum. The volume of molten material is very much less for aluminum, despite its lower melting point, because of the higher thermal conductivity of aluminum. Predicted arc voltages as a function of current for a mixture of 10% hydrogen in argon are in good agreement with experimental results     

Penning型负氢离子源诊断

为了给小型医用回旋加速器提供负氢离子,研制了一台Penning型负氢离子源。采用发射光谱法对该负氢离子源进行了诊断,同时结合离子源功率变化对离子源工作状态进行了分析。实验测量了不同氢气流量、离子源弧流及磁场条件下,该离子源等离子体氢原子巴尔末系中前三条谱线的相对光强和离子源功率变化,分析了不同工作条件对离子源工作状态的影响。结果表明：在可调节范围内,该离子源的工作状态主要受氢气流量的影响,对离子源弧流及磁场的变化不敏感。     

Plasma scattering experiments with a periodic Nd:YAG laser at 1.06μm and A Si-avalanche detector

First spectra obtained by scattering from a hydrogen arc plasma using a periodically pulsed cw-pumped Nd:YAG laser are presented. Because of its high quantum efficiency at 1.06 μm a large-area Si-avalanche diode followed by a capacitance-compensating amplifier is used as detector.     

MHD plasma physics in rail accelerators for hydrogen-pelletinjection in fusion reactors

The behavior of the electromagnetic and thermal quantities in a plasma arc placed between two conducting rails is analyzed. The plasma hydrogen drives the hydrogen pellets for the refueling of magnetic fusion reactors. Considering the general equations of electromagnetism and of plasma fluid dynamics and assuming steady-state conditions in a frame which is moving at the same rate as the plasma arc armature, a one-dimensional model is deduced. The effects of an applied magnetic field on the behavior of all flow variables are investigated. Results indicate that the adverse effects of plasma arc heating can be reduced by the application of a magnetic-induction field normal to the current path in the armature. At the maximum acceleration pressure (30 bar) applicable to the hydrogen pellet in the proposed one-dimensional model, the arc temperature at the pellet backend falls from 20000 to 14000 K when a magnetic induction of about 5 T is applied     

含氢电极真空弧放电等离子体时空分布特性研究

真空弧离子源在真空镀膜、材料表面改性、真空大电流开关、加速器离子注入等领域有广泛应用,目前国内外对真空弧放电等离子体的研究主要针对纯金属或合金电极,对含氢电极的研究和公开报道较少.本文利用高时空分辨的四分幅图像诊断系统,结合氢和钛原子特征线单色器件,研究了含氢钛电极的真空弧微秒级脉冲放电等离子体的轴向和径向时空分布特性.研究表明:在真空击穿阶段,阳极区域发光更为明显,阳极电极解吸附释放的氢原子是引发击穿的主要放电介质;在真空弧阶段,阴极-绝缘-真空三结合点处产生圆锥状阴极斑,喷射出大量的等离子体以维持弧放电,同时电极内壁非阴极斑区域也有少量等离子体产生,等离子体中H原子的轴向和径向空间分布均比Ti原子均匀.     

脉冲磁过滤阴极弧沉积中基片台悬浮电位研究

通过测量脉冲磁过滤阴极弧等离子体沉积系统中的基片台悬浮电位，发现了弧源接地方式对基片台悬浮电位与等离子体电位影响很大。当阳极接地时基片台悬浮电位可达－60V，而弧源悬浮时却只有－5V。因此，要获得相似沉积条件的沉积薄膜，弧源接地方式不同，给基片施加偏压也应有所不同。     

The behavior of vacuum arc discharges on hydrogen impregnatedelectrodes

This paper reports on experimental studies of the behavior of vacuum arcs at hydrogen impregnated electrodes. The arc discharges were analyzed by high speed photography, open shutter photography, measurement of arc voltage and current, and measurements of the erosion in dependence on the level of impregnation for a wide range of arc currents. The results show that impregnation of electrodes with hydrogen reduces the erosion rate, causes smaller crater dimensions, changes the macroparticle size, and decreases the current per spot. For a given current the arc voltage depends on the degree of impregnation. At low current it decreases with increasing impregnation. Furthermore, the arc discharge burns more stable on impregnated electrodes. The total erosion rate decreases significantly due to the reduction of the droplet fraction. The spot movement is faster than on nonimpregnated electrodes     

Penning型负氢离子源诊断

 为了给小型医用回旋加速器提供负氢离子,研制了一台Penning型负氢离子源。采用发射光谱法对该负氢离子源进行了诊断,同时结合离子源功率变化对离子源工作状态进行了分析。实验测量了不同氢气流量、离子源弧流及磁场条件下,该离子源等离子体氢原子巴尔末系中前三条谱线的相对光强和离子源功率变化,分析了不同工作条件对离子源工作状态的影响。结果表明：在可调节范围内,该离子源的工作状态主要受氢气流量的影响,对离子源弧流及磁场的变化不敏感。     

Microstructure, magnetic and transport properties of magnetoresistive Cu80Fe x Ni20?x (x?=?5, 10 and 15 at.%) ribbons

The generation of copper nanoparticles in an arc furnace by the evaporation/condensation method is systematically investigated. The evaporation/condensation process is advantageous because it allows direct synthesis using pure metals as starting materials avoiding reactions of expensive and potentially poisonous precursors. In the presented system, a transferred direct current arc provides the energy for evaporation of the metal target. In order to prevent an oxidation of the particles in the process, the synthesis is conducted in an atmosphere of inert gases (purity grade 5.0). The arc stability and its effect on particle synthesis are investigated. The experiments reveal excellent long-term arc stability for at least 8?h continuous operation delivering aerosols with high reproducibility (±10?% of average particle size). The influences of the arc current and length, the flow rates of the applied gases and the injection of hydrogen in the plasma zone on the particle size distributions and the agglomerate structure are studied. The produced copper nanoparticles are characterized by scanning mobility particle sizing and scanning electron microscopy. The average particle size could be well controlled in a size range 4?C50?nm by selecting appropriate operating parameters.     

Measurement of hydrogen transport functions by means of precision arc experiments

Motivated by discrepancies of measured and calculated hydrogen transport coefficients, pure hydrogen arc plasmas have been investigated again in the wide temperature range from 5000 to 27,000 K. The plasmas are generated in cascaded arc chambers with 2, 3, and 5 mm channel diam. Temperature diagnostics are performed by side-on spectroscopy in the Balmer region, using an automatic data acquisition system and computer processing. The immediate results are in excellent agreement with precision measurements by other authors. The electricalE—I characteristics are recorded using cascade plates as probes. These characteristics and the temperature measurements together yield the transport coefficients as a function ofT. The present results for the electrical conductivity are in very good agreement with theory. As for the heat conductivity, some improvements could be achieved in the relative dependence, but the experimental values are still above the theoretical ones. In the region of low ionization this discrepancy is explained by deviations from LTE in the arc plasma. Here, a rigid PLTE analysis is presented.     

On the Production of Methane by Electrical Arcs in Ultra High Vacuum

By mass spectrometry of residual gas in UHV-arc-chambers a cycle of production of methane has been found for clean electrodes, consisting in release of hydrogen during the arc, its re-adsorption on freshly formed metal surfaces, followed by surface reactions of hydrogen with carbon impurities, and finally desorption of the resulting methane at room temperature after the arc. Existing methane is decomposed in part during an arc. In the pressure region ≦ 10^?4 Pa most of the residual gas is transformed to CH₄ if the electrodes contain metals with high gettering activity.     

Current-voltage characteristics of a reflex discharge with a hollow cathode and self-heating electrode

Results are presented from experimental studies of the current-voltage characteristics of a reflex discharge with a self-heating electrode used in a source of atomic hydrogen. The processes occurring in a discharge cell and governing the main features of the characteristics obtained are investigated theoretically. An explanation of the general features of the discharge is proposed. It is shown that an abrupt decrease in the discharge voltage with increasing hydrogen flow rate is associated with penetration of the plasma into the hollow cathode and the ignition of a hollow cathode discharge. It is demonstrated that, as the discharge current increases, the glow discharge gradually transforms into an arc discharge with a heated cathode.     

Electrochemical insertion into and the detection of hydrogen in amorphous silicon solid electrolytes

The specific features of amorphous silicon are mainly contributed by the incorporation of hydrogen into the silicon during the vapour deposition process but, in spite of the considerable progress in the development of amorphous silicon cells, two major problems exist - light induced degradation and hydrogen evolution. As a result, there is a need to be able to measure and adjust the hydrogen content of the amorphous silicon. It is shown that this can be achieved using a potentiometric sensor, based on a proton conductor, and electrochemical tritation. Experiments show that it is possible to detect changes in hydrogen at all temperatures, using solid electrolytes, but that it is only possible to titrate hydrogen into the amorphous silicon at elevated temperatures. Paper presented at the 1st Euroconference on Solid State Ionics in Zakynthos, Greece, 11–18 Sept. 1994     

带状真空电弧磁过滤器等离子体分布特性及制备类金刚石膜研究

采用大尺寸矩形石墨靶作为真空阴极电弧源, 研制了带状真空电弧磁过滤器. 使用法拉第杯和朗缪尔探针对90 ℃弯曲磁过滤器中的带状等离子体出口所在平面的15个区域的离子能量和密度进行了测试; 用该带状真空电弧磁过滤器制备了类金刚石膜(diamond-like carbon, DLC); 对相应位置上的类金刚石膜进行了Raman分析和膜厚测量. 结果表明: 磁过滤器出口所在平面的15个划分区域中离子能量分布接近麦克斯韦分布, 离子能量分布与类金刚石膜的结构具有明显的对应特征, 离子密度分布与DLC膜膜厚分布相互之间具有相关性.