Laser-Monitor-Assisted Investigation of the Regions of Closure of Current on the Electrodes of an Atmospheric-Pressure Low-Current Carbon Arc

The results are given of observations of regions of closure of current on the electrodes of an atmospheric-pressure low-current carbon arc, performed using a laser monitor immediately during the time of burning of the arc. It is found that the time of existence of a cathode crater on a graphite cathode is 0.2–0.3 s. An analysis of images of the region of closure of current on a pyrographite cathode reveals evidence of melting of pyrographite. A comparison of images of the region of closure of current on the electrodes of a carbon arc with the available literature data on the conditions of closure of current on the anode and cathode enables one to establish the origins of the various details of images of the region of closure of current on the cathode and anode of a low-current carbon arc. The results of this comparison further lead one to conclude that a low-current electric arc is an arc with liquid cathode and anode spots, and that the melting process is a stabilizing factor as regards the current density in those spots.     

The volt-ampere characteristics of a DC arc plasmatron with a distributed anode spot

A new DC plasmatron with a hot rod cathode and cold nozzle anode was proposed and tested at atmospheric pressure, generating nearly spectrally clean plasmas of air, air/diesel fuel mixture, oxygen, and CF₄. The arc Volt-Ampere characteristic (VAC) is an integral indicator reflecting the general behavior of all the arc parts, among which the most important are the by-electrode layers and positive column. The sensitivity of the VAC to the gas flow velocity in the technologic channel confirmed the external vortex nature of the anode arc spot, which does not hide inside the anode orifice, but exits it and interacts with the gas flow.     

Visualization of the process of metal heating and melting in the anode zone in an arc discharge with a tungsten electrode

Pictures of an electric arc burning in argon, obtained by means of a digital camera, within the different domains of wavelengths of the visible spectrum are presented. Maps of the thermal fields of the heating spot are plotted, and the plasma temperature in the anode arc zone is calculated. The application potential of the digital image technology in the visible wavelength domain for analysis of the processes directly in the anode arc zone and for estimation of the arc column parameters is shown.     

Anode Mode of Vacuum Arc in a Multirod Electrode System

The effect of the plasma of a high-current vacuum arc on the anode rods in a rod electrode system, which leads to the melting of the surface of copper anode rods and to the formation of droplets of the electrode material, is investigated. High-speed photography is used to register the formation of anode spots, and the sizes of the spots are determined at discharge currents from 30 to 100 kA. A one-dimensional nonstationary model of the melting of the anode and of the formation of droplets in the anode spot of a vacuum arc is proposed. The model is in satisfactory agreement with the results of observation of traces of melting on the anodes of used dischargers in a rod electrode system and with high-speed photographs of glow of the discharge plasma and spots on electrodes in a model of the rod electrode system.     

Anode mode in cathodic arc deposition apparatus with various cathodes and ambient gases

The anode mode of a vacuum arc in a cathodic arc deposition apparatus was observed as a function of ambient gas pressure ranging from 0.01 to 300 Pa. The chamber (400 mm in diameter and 600 mm in length) made of stainless steel (SUS304) acted as the anode. The arc was operated at a relatively low constant current of 50 A. The cathode materials used were Al, Ti, Fe, Ni, and Cu, and ambient gases were He, Ne, Ar, H₂, N₂, O₂, and CH₄. The principal results are as follows. (1) As the pressure was increased, the anode mode changed from diffuse-arc to footpoint to plane luminous to anode-spot mode. (2) The anode mode and resultant arc voltage increase were strongly dependent on gas species, and weakly on the cathode material. (3) Comparing diatomic and polyatomic (H₂, N₂, O₂, and CH₄) with mono-atomic molecule gases (He, Ne, and Ar), the onset pressure of the anode mode transition in the former was lower, the arc voltage higher, and the footpoints more numerous, smaller, and clearer. Both the dependence of the ambient pressure and the influence of the cathode materials and gas species on the anode mode changes were explained by the ion deficiency theory.     

活性剂增加不锈钢A-TIG焊熔深机理研究

目的研究涂敷活性剂条件下1Cr18Ni9Ti奥氏体不锈钢的熔深增加机理。方法采用B1活性剂,涂敷在1Cr18Ni9Ti奥氏体不锈钢表面,进行A-TIG焊试验,分析活性剂对电弧形貌、阳极斑点、电弧电压和焊缝熔深的影响情况。结果涂敷活性剂后,电弧和阳极斑点都发生了收缩,电弧宽度由4.97 mm变为4.12mm,减小了17.1%,阳极斑点长轴长度由9.92 mm变为8.22 mm,短轴长度由4.75 mm变为4.35 mm,电弧电压提高了2.7 V,阳极区和弧柱区收缩,提高了弧柱电场强度;相同参数下,涂敷活性剂后熔宽缩小0.62mm,熔深增加了3.01 mm,显著增加熔深。结论阳极斑点收缩和电弧收缩是活性剂增加不锈钢A-TIG焊熔深的主要原因。     

Numerical analysis and experiments on transferred plasma torches for finding appropriate operating conditions and electrode configuration for a waste melting process

Thermal plasma characteristics of transferred plasma torches are numerically and experimentally investigated under atmospheric conditions to find the effects of operating variables and electrode arrangements on them. A control volume method and a modified SIMPLER algorithm are used for numerical analysis, and the temperature distributions of argon plasma are calculated in different torch operating conditions of a typical transferred arc torch. Transferred plasma torches are designed and fabricated, which have six different electrode arrangements, respectively, consisting of a conical rod cathode and a nozzle in the torch, and a distant anode material. The dynamic behaviors of arc voltage are measured to obtain stable arc conditions, and a similarity criterion is determined to analyze static behaviors of arc voltage. For predicting the heat transfer rate to melted material from arc column, measurements are made for the heat loss at the anode material and fractions of input power transferred to the anode. Furthermore, thermal plasma temperatures are measured by the optical emission spectroscopy of an Ar I line. As a result of the present work, an appropriate electrode configuration and operating conditions for waste melting process are presented for the optimization of transferred plasma torches.     

Singularities of interaction between a cathode stream and anode vapors in a vacuum arc: Numerical simulation results

Numerical simulation is performed of the process of interaction of cathode and anode ions in a highcurrent vacuum arc with evaporating anode. The presence of the friction force between ion flows, as well as of the friction work, leads to heating and acceleration of slow anode ions and deceleration of fast cathode ions. The boundaries of stable passage of current are determined, associated with the presence of the limiting value of density of anode vapors     

Products on electrodes in an argon-methane magnetically rotating arc at atmospheric pressure

The arc discharge method in a hydrocarbon atmosphere has a promising application in the nanocarbon synthesis field due to its high yield. In this paper, products on electrodes in an argon-methane magnetically rotating arc at atmospheric pressure are investigated. Different nanocarbons are obtained on the cathode and anode surfaces, respectively. Material analysis indicates that the products on the cathode are mainly carbon tubes. Some carbon tubes are well-aligned in one direction, and the others have a coil-like structure. The products on the anode are a mixture of graphene nano-flakes and aggregate hollow carbon particles. The hollow carbon particles exhibit a chain-like structure with internal space to be connected. To the authors’ knowledge, this is possibly the first time that aggregate hollow carbon particles with a chain-like structure have been observed in the absence of any catalyst. Based on the configuration of arc plasma, the formation mechanism of electrode products is briefly proposed.     

基于MHD的小间隙真空电弧仿真研究

真空开关电弧电流过零前的电弧等离子体状态对真空开关能否顺利开断具有十分重要的影响。本文在建立小间隙真空电弧磁流体动力学(MHD)模型的基础上,采用通用计算流体力学仿真软件对电弧电流过零前0.5 ms时的电弧等离子体的特性进行数值仿真研究。计算得到了真空电弧等离子体压力、等离子体密度、离子纵向速度、阳极表面纵向电流密度和电弧电压等的空间分布。仿真结果表明:从阴极到阳极,真空电弧等离子体压力和密度逐渐增大,而等离子体速度逐渐减小;阳极表面电流密度存在较大径向梯度,最大值低于形成阳极斑点的极限收缩电流,阳极仍不活跃。仿真得到的等离子体密度分布与高速摄像机拍摄得到的CMOS图像光强基本吻合,计算得到的电弧电压与测得的电弧电压是一致的,从而验证了本模型的可行性。     

Thin film deposition using a plasma source with a hot refractory anode vacuum arc

Vacuum arc generated plasma was used to deposit metallic Al, Zn, and Sn coatings on glass substrates. An arc mode with a refractory anode and an expendable cathode (the “hot refractory anode vacuum arc”), overcomes macroparticle (MP) contamination experienced in other arc modes. I = 100–225 A arcs were sustained between a water-cooled coating source cathode and an anode, which was heated by the arc, separated from each other by a 10-mm gap, for times up to 150 s. The distance from the arc axis to the substrate (L) was 80–165 mm. Film thickness was measured with a profilometer. It was found that the deposition rate increased with time to a peak, and then decreased to a steady-state value. The peak occurred earlier when using short anode (9 mm long), e.g., with the Al cathode, L = 110 mm, and I = 200 A, the peak was at t _p = 15 s after arc ignition while with the long anode t _p = 45 s. t _p decreased with I, from 45 s with I = 100 A, to 10 s with I = 225 A with the short anode. The peak is believed to appear due to initial condensation of cathode material (including MPs) on the cold anode, and its subsequent evaporation as the anode heated. In the later HRAVA steady state, a balance between condensation and evaporation on the anode is established. The deposition rate peak was significant with low melting temperature Al and Zn cathodes, which produce many MPs, and negligible with Cu and Ti cathodes.     

Protecting the anode foil of a high-current electron accelerator against arc-discharge damage

The mechanism of anode foil damage during the extraction of a high-power pulsed electron beam from a high-current diode has been experimentally studied on a TEU-500 electron accelerator [1]. It is established that the breakage of the anode foil is caused by the appearance of cathode spots on its surface, the intense electron emission from these spots during positive voltage pulses (postpulses following the main negative pulse of accelerating voltage), and the formation of arc discharge in the interelectrode gap. The improvement of diode matching to the pulse-forming line of the accelerator and the use of an auxiliary electrode (anode) forming additional vacuum discharge gap (crowbar) with the cathode practically excludes the anode foil breakage by arc discharge and significantly increases the working life of the foil (up to ∼10⁵ electron beam pulses).     

Anode jet generation conditions affected by the radial current density distribution for maintaining current continuity

To perform high-quality welding, the heat input from the arc to the base metal is controlled. However, an anode jet sometimes occurs. In such cases, control is difficult and weld defects occur. This study elucidates how anode jet generation is affected by the radial current density distribution for maintaining the current continuity. The anode jet starts to occur at 15–20 mm of interelectrode distance. The arc temperature decreases because the arc radius increases. Then electrical conductivity decreases sharply depending on the temperature. If electrical conductivity decreases, then the current density decreases, and the arc cannot maintain the current continuity. When the mean current density is 8.7 × 10⁵ A/m², the flow velocity is zero at 15 mm. Therefore, this minimum value of the mean current density is the anode jet generation condition.     

A spectroscopic detecting system for measuring the temperaturedistribution of silver breaking arc using a CCD color camera

This paper describes a spectroscopic detecting system that utilizes a CCD color camera to observe the distributions of two spectral intensities along the axis of an arc column. Following this, the distributions of Ag I 421 nm and Ag I 547 mm spectra observed along the axis of an arc column and the arc temperature calculated from the two spectra when silver contacts interrupt a circuit of dc 50 V and 3.3 A are presented. The spectral intensities of excited silver atoms are strongest near the cathode and become weaker with distance from the cathode contact. The temperature in the cross section of an arc column is highest in the axis of the arc column. The temperature along the axis of arc column is highest near the cathode and becomes weaker with distance from the cathode. Furthermore, in this study it is clarified that CN band spectra exist near the anode contact     

阴极真空弧沉积中靶室第二阳极作用对系统性能的影响

介绍了阴极真空弧沉积中 ,弧源在阴极接地和阳极接地两种不同工作状态下的工作特性。发现阳极接地时 ,因沉积靶室入口法兰的第二阳极作用 ,聚焦磁场对弧源放电稳定性的影响不如阴极接地时明显。因此可以加较高的聚焦磁场 ,从而获得流强较高和较稳定的沉积等离子体束     

The Shunting of Current and the Resultant Variation of Voltage in Channels of Plasmatrons with Self-Adjusting Length of Electric Arc

The characteristics of pulsation processes in dc plasmatrons with the cathode located in the channel center and the anode in the form of a cylindrical or a conical channel wall are investigated in plasmas of argon and nitrogen at atmospheric pressure. The fast Fourier transform of signals and their subsequent computer processing are used to obtain the dependences of the frequency of fluctuations of the arcing voltage on the working parameters of the plasmatron, namely, the electric arc current, the flow rate of plasma-forming gas, and the channel diameter. For plasmatrons with the self-adjusting length of the electric arc, analysis is performed of the mechanism of reclosing of the anode region of the arc, i.e., of the electric arc shunting associated with the stretching of the current filament by a flow of gas and with the electrodynamic interaction of different filament regions. A formula is derived which defines the dependence of the characteristic frequency of fluctuations of the arcing voltage on the external parameters of the problem, namely, the arc current, the flow rate of the working gas, and the characteristic channel diameter. It is demonstrated that the pattern of the dependence of the frequency of voltage fluctuations on the gas flow rate may vary with the values of the parameter of magnetohydrodynamic interaction. The formula generalizes the experimental results of numerous researchers obtained in a wide range of variation of the external parameters.     

The preparation of carbon-coated iron nanocrystals produced from Fe2O3-containmg composite anode in arc discharge

Using an Fe₂O₃-containing composite anode instead of an Fe-containing composite anode in the Kratschmer-Huffman carbon arc method, carbon-coated Fe (not Fe₂O₃) nanocrystals are produced both in the soot on the reactor walls and in the cathode deposits. The encapsulates also contain a little iron carbide, but do not contain iron oxides, as identified by transmission electron microscopy ( TEM ) and X-ray diffraction (XRD). As compared with Ni₂O₃- and Co₂O₃-containing composite anodes, the action of the Fe₂O₃-containing composite anode is unique. When the Fe₂O₃ contents in the composite graphite rod for the carbon arc nanocrystal production are increased in the range 5-33 wt.%, the effect on the structure and diameter distribution of the iron nanocrystals is investigated. The diameter distribution of iron nanocrystals is about 1–30 nm. The effect of helium pressure in the range 80–680 torr on the yield of C_60/70 in carbon soot produced from the composite graphite rod has also been examined. We present a novel result about the relationship of C_60/70 yields and helium gas pressure using a composite anode differing remarkably from the result using a homogeneous graphite anode in arc discharge.     

TiB2/Cu复合材料的电弧侵蚀行为

采用放电等离子烧结法（SPS）制备TiB₂质量分数为1wt%~5wt%的TiB₂/Cu复合材料,测试其导电率和硬度。当TiB₂质量分数由0增至5wt%时,复合材料的导电率由96.9%（International Annealed Copper Standard,IACS）降至65.1%（IACS）,布氏硬度由42.8增至65.2。对所制备的不同TiB₂质量分数的TiB₂/Cu复合材料在直流24 V、不同电流条件下进行电接触实验,探究TiB₂添加量和电流对TiB₂/Cu复合材料耐电弧侵蚀性能的影响。结果表明,TiB₂/Cu复合材料的平均燃弧时间、平均燃弧能量和材料损耗量随着电流的增加而增加,TiB₂/Cu复合材料的阴极损耗量高于阳极,整体上TiB₂/Cu复合材料由阴极向阳极转移。在24 V和25 A条件下,不同TiB₂质量分数的TiB₂/Cu复合材料的燃弧时间和燃弧能量随操作次数增加不断波动,整体上呈逐渐增加的趋势,3wt% TiB₂/Cu复合材料的稳定性最高,平均燃弧时间和燃弧能量最低。随着TiB₂质量分数的增加,TiB₂/Cu复合材料损耗量降低,表面蚀坑变浅。     

Anodic current density of an electric arc with carbon electrodes

We present the results obtained in measuring the current density of anode spots in a carbon arc in air and we show its relationship to the magnitude of the arc current, analogous to the cathode spot.     

The Effect of External Magnetic Field on a Vacuum Arc

The effect of an external longitudinal magnetic field on the time required for anode spot formation in a high-current (5 to 12 kA) vacuum arc is experimentally studied, and the minimal value of a magnetic field inhibiting the anode spot formation is determined. The experimental results are compared with theory. The phenomenon of break of current in a low-current (100 to 300 A) vacuum discharge upon superposition of a magnetic field with transverse component on the discharge is investigated. The probability of break of current increases with the magnetic field. The possible mechanism of break of current is discussed.