Numerical Study of a Free-Burning Argon Arc with Anode Melting

Numerical modeling of free burning arcs and their electrodes is useful for clarifying the heat transfer phenomena in the welding process and to elucidate those effects which determine the weld penetration. This paper presents predictions for a stationary welding process by the free-burning argon arc. The whole region of the welding process, namely, tungsten cathode, arc plasma and stainless steel anode is treated in a unified numerical model to take into account the close interaction between the arc plasma and the molten anode. The time dependent development of two-dimensional distributions of temperature and velocity, in the whole region of the welding process, are predicted at a current of 150 A. The weld penetration geometry as a function of time is thus predicted. It is shown also that different surface tension properties can change the direction of re-circulatory flow in the molten anode and dramatically vary the weld penetration geometry.     

Numerical Prediction of the Noise Emission from a Turbulent Argon Thermal-Plasma Jet Issuing into Ambient Air

This paper attempts to predict the noise emission characteristics of a turbulent argon thermal-plasma jet issuing into ambient air. The flow, temperature and concentration fields and turbulence characteristics of the turbulent plasma jet are computed at first, and then the noise emission from the plasma jet to a sideline far-field observer is calculated using the approach proposed by Fortuné and Gervais (AIAA J. 37(1999)1055) for predicting the noise emission from a turbulent, hot but non-ionized, air jet after some modification. The diffusion of ambient air into the turbulent argon plasma jet is handled using the turbulence-enhanced combined–diffusion-coefficient method. Velocity fluctuation correlations (aerodynamic noise source) in the plasma jet are calculated still using the K-ɛ two-equation turbulence model, but the temperature-velocity fluctuation correlations (entropic noise source) within the jet are calculated by solving a second-order turbulent Reynolds heat-flux transport equation in order to better deal with the contribution of temperature fluctuation to the noise emission. It is shown that among the contributions of aerodynamic noise source, entropic noise source and their mixed effect, the entropic noise source (i.e. the temperature-velocity fluctuation correlations) is dominant for the noise emission from the turbulent plasma jet to the sideline observer. The noise intensity increases with increasing plasma jet temperature or velocity. The predicted noise frequency spectrum characteristics and noise intensity levels are shown to be reasonably consistent with available experimental data.     

Effects of Copper Vapor on Heat Transfer from Atmospheric Nitrogen Plasma to a Molten Metal Anode

As an object of nitrogen plasma operated with an arc current to 200 A, an arc length about 35 mm, we evaluated heating efficiency from arc plasma to the molten copper anode and the water-cooled solid copper anode. The heating efficiency to the molten anode is smaller than that to the solid anode by about 20%. We focused on copper vapor concentration in plasma as a possible cause for a decrease in heating efficiency, and estimated it by means of the Cu and the N spectral line measurement. Simple numerical analysis, taking into consideration measured copper vapor concentration, suggested that an increase in electrical conductivity due to copper vapor, made the plasma temperature change and consequently caused a decrease in thermal conductivity. We concluded that one of the reasons for a decrease in heating efficiency would be caused by copper vapor contamination.     

Effect of Anode Arc Root Position on the Behavior of the DC Non-transferred Plasma Jet at Field Free Region

A special bi-anode plasma torch that can change the anode arc root position without changing working gas flow rate has been developed to investigate the effect of anode arc root position on the behavior of the plasma jet. It has two nozzle-shaped anodes at different axial distances from the cathode tip. The arc root can be formed at anodes either close to the cathode tip (anode I) or far away from it (anode II) to obtain different attachment positions and arc voltages. The characteristics of pure argon plasma jets operated in different anode modes were measured in the field free region by using an emalpy probe, and the thermal efficiency of the torch was determined by measuring the temperature differences between cooling water flowing in and out of the torch. The results show that compared with the normal arc operated in anode I mode, the elongated arc operated in anode II mode significantly reduced the plasma energy loss inside the torch, resulting in a higher temperature and a higher velocity of the plasma jet in the field free region.     

覆盖的氩原子簇过热的分子动力学模拟(英)

通过分子动力学模拟研究了覆盖较高熔点的原子的氩原子簇．原子族由177个氩原子和72个覆盖原子组成．覆盖原子的势能参数ε比氩原子大50％，该原子簇比纯氩原子簇熔点过热2K．模拟结果表明，覆盖的原子簇过热的原因是：在达到熔点之前，体系缺少氩原子构成的自由表面，仍然是覆盖原子的有序表面．     

Effect of Cathode Nozzle Geometry and Process Parameters on the Energy Distribution for an Argon Transferred Arc

The influence of two nozzle geometries and three process parameters (arc current, arc length and plasma sheath gas flow rate) on the energy distribution for an argon transferred arc is investigated. Measurements are reported for a straight bore cylindrical and for a convergent nozzle, with arc currents of 100 A and 200 A and electrode gaps of 10 mm and 20 mm. These correspond to typical operating parameters generally used in plasma transferred arc cutting and welding operations. The experimental set up consisted of three principal components: the cathode-torch assembly, the external, water-cooled anode, and the reactor chamber. For each set of measurements the power delivered to each system component was measured through calorimetric means, as function of the arc’s operating conditions. The results obtained from this study show that the shape of the cathode torch nozzle has an important influence on arc behaviour and on the energy distribution between the different system components. A convergent nozzle results in higher arc voltages, and consequently, in higher powers being generated in the discharge for the same applied arc current, when compared to the case of a straight bore nozzle. This effect is attributed to the fluidynamic constriction of the arc root attachment, and the consequential increase in the arc voltage and thus, in the Joule heating. The experimental data so obtained is compared with the predictions of a numerical model for the electric arc, based on the solution of the Navier–Stokes and Maxwell equations, using the commercial code FLUENT©. The original code was enhanced with dedicated subroutines to account for the strong temperature dependence of the thermodynamic and transport properties under plasma conditions. The computational domain includes the heat conduction within the solid electrodes and the arc-electrode interactions, in order to be able to calculate the heat distribution in the overall system. The level of agreement achieved between the experimental data and the model predictions confirms the suitability of the proposed, “relatively simple” model as a tool to use for the design and optimization of transferred arc processes and related devices. This conclusion was further supported by spectroscopic measurements of the temperature profiles present in the arc column and image analysis of the intensity distribution within the arc, under the same operating conditions.     

火花源直读光谱仪测定阳极铜中19种杂质元素

利用火花源直读光谱对阳极铜进行直接快速分析,通过改进原分析程序,增加了氧元素分析通道。可快速准确测定阳极铜中19种杂质元素,并计算出主铜含量,RSD为0.01%～4.00%,满足了生产控制要求,已应用于阳极铜的日常检测工作中。     

Separation of Gold from Sulfide Using a Plasma Arc Fuming Process

Transferred-arc plasma treatment of iron sulfides containing gold is examined from both thermodynamic and experimental points of view. Three cases are analyzed: argon plasma with sulfide, argon plasma with a carbon–sulfide mixture, and argon–methane plasma with sulfide. The carboreduction of the materials appears to be well adapted for gold separation by fuming, but experimentally the process is limited by the poor mixing of graphite with molten material. The reduction with a CH₄ (10%) plasma is a proved alternative to the aforementioned process. A gold extraction efficiency of 90% is achieved for batch smelting operations.     

数值模拟在应用电化学课程教学中的应用

针对应用电化学课程理论性强、应用性广的特点,以电镀铜章节的教学为例,讨论了数值模拟方法在应用电化学课程教学中的应用。该方法能够将电化学工程中常用的重力场、流场等与电化学过程相耦合,以有限元方法得到域的解,从而将抽象的方程式直观地用图像、动画等多媒体形式呈现出来,使课堂教学变得生动形象,有利于提高课堂教学效率,激发学生的学习兴趣,培养学生的创新精神和实践能力。     

Comparative Study of Flow Characteristics Inside Plasma Torch with Different Nozzle Configurations

A numerical analysis of the influence of different nozzle configurations on the plasma flow characteristics inside D.C plasma torches is presented to provide an advanced nozzle design basis for plasma spraying torches. The assumption of steady-state, axis-symmetric, local thermodynamic equilibrium, and optically thin plasma is adopted in a two-dimensional modeling of plasma flow inside the plasma torch. The PHOENICS software is used for solving the governing equations, i.e. the conservation equations of mass, momentum, and energy along with the equations describing the K-epsilon model of turbulence. The calculated arc voltages are consistent with the experimental results when arc current, gas inflow rate, and working gas are the same as the experimental parameters. Temperature, axial velocity contours inside plasma torches, profiles along the torch axis and profiles at the outlet section are presented to show the plasma flow characteristics. Comparisons are made among those torches. The results show that torches with different anode nozzle configurations produce different characteristics of plasma flows, which suggest some important ideas for the advanced nozzle design for plasma spraying. In order to validate the model and to show its level of predictivity, a comparison of the model with experimental results encountered in the literature is presented in the last part.     

An Ab Initio Study of the Complexes Formed by the Positive Acetylene Ion with the Hydrogen and Nitrogen Molecules and the Argon Atom

The complexes formed by the positive acetylene ion with the hydrogen molecule, the nitrogen molecule, and the argon atom are investigated with ab initio calculations using the 6-311G** and the 6-31+G(2df,2pd) basis sets. MP2/6-311G** energies and optimum geometries are obtained, as well as single-point MP3, MP4, and QCISD(T) energies with the MP2/6-311G** optimized geometries. Single-point calculations are performed with the 6-31+G(2df,2pd) basis set at MP2/6-311G** optimized geometries.     

铜在鱼体中的积累规律研究

采用实验室模拟对鱼所生存的人工水环境中投Cu的方式,通过鱼对Cu的吸收富集研究了鱼体中Cu的积累规律及其Cu对部分鱼内脏的毒性影响。揭示不同质量浓度下,单一重金属离子在鲫鱼体内积累的动态变化规律以及铜对鲫鱼属于剧毒重金属。结果表明,在较低的质量浓度下Cu在鲫鱼各组织器官中的积累量随质量浓度的增加而增加、随时间的延长而增加,达到一定时间后积累趋于平衡;在高质量浓度环境下Cu在鲫鱼各组织器官中的积累量有时随时间的延长反而有所下降,但针对不同组织来说其积累能力由大到小顺序一般为:内脏,鱼鳃,肌肉。采用主要的分析方法是微波溶样消解法和火焰原子吸收分光光度法。     

Study of a transferred-arc plasma reactor with a converging wall and flow through a hollow cathode

In this paper the behavior of an arc in a transferred-arc plasma reactor with a converging wall geornetrr and flow through a hollow cathode is investigated numerically with emphasis on the fluid dynamics. The general conservation equations and auxiliary relations for the calculation domain are established based on reasonable assumptions Then, the coupled nonlinear differential equations are solved with suitable boundary conditions and temperature-dependent argon plasma properties at atmospheric pressure, by employing an efficient finite-difference method. The results, for a hollow cathode geornetrr with low injection flow rates, clear/y demonstrate the existence of the Maecker elect which is responsible Joy the formation of two recirculation zones. As the plasma gas flow rate is increased, the downstream recirculation zoner is swept away leaving only an upstream recirculation zone.     

Influence of Plasma Treatment on the Electroless Deposition of Copper on Carbon Fibers

Air and nitrogen glow discharge were used to replace chromic acid pretreatment to deposit copper film on carbon fiber surfaces from an CuSO₄‐HCHO electroless system. A greater copper uptake and a more uniformly coated copper film were obtained for plasma‐treated carbon fibers. The adhesion between the copper film and the carbon fibers was also improved. An orthogonal table L₉(3⁴) was used to study the effects of discharge pressure, discharge power, time and gas type on the copper uptake. Scanning electron microscopy (SEM), reflection absorption infrared spectroscopy (RAIR) and X‐ray photoelectron spectroscopy (XPS) at different depths were applied to characterize the physical and chemical changes of the surface of the carbon fibers. The results showed that after plasma treatment, the carbon fiber surface became rough and several types of polar oxygen groups, such as carboxylic acid COOH, esters COOC, quinones Ph?O, etc., were introduced into the carbon fiber surface. A mechanism of plasma treatment effects on copper electroless deposition on the carbon fiber surface is also suggested.     

铅试金富集条件对KSCN滴定铜阳极泥中银的影响

针对铅试金重量法测定铜阳极泥中银时存在 Pb、Bi、Pd、Cu、Te 等元素干扰的问题,建立了铅试金捕集贵金属—硫氰酸钾滴定测定铜阳极泥中银。选取代表性、银品位较高的铜阳极泥为样品,在熔渣硅酸度 K=1.5,温度由 900℃升至 1100℃用时 40min 条件下熔炼 30min,在 920℃以 1.0g/min 金属铅的速度进行灰吹,灰吹结束后立即关闭电源,降温取出灰皿,合粒硝酸溶解后采 用 KSCN 直接滴定银,优化条件下银品位测定平均值为 86.31 kg/t（n=4）、RSD=0.42%,加标回收率在 98.85%~99.52%、RSD=0.28%。该法可有效消除 Pb、Bi、Pd、Cu、Te 等元素对银测定的影响,提高检测铜阳极泥中银品位的精确度。     

A Spectrophotometric Study of the Determination of Copper with Dithiooxamide in Acidic Media

Abstract

A spectrophotometric method for the determination of copper has been developed based on the development of a red color in acidic solution using dithiooxamide as the chromogenic agent. The molar absorptivity is 7.04 × 10³ 1. mol^?1 cm^?1 at 525 nm. Relatively few ions interfere.     

双层铜金属薄膜纳米压痕机械性能的分子动力学模拟

多层金属薄膜的机械性质在纳米组件的设计上是非常重要的.目前,纳米尺度材料的机械性质测量的最主要方法为纳米压痕检测技术.本文应用分子动力学理论对双层铜金属薄膜界面的结构形态与特性进行分析探讨.选用FCC结构单晶铜的(100)面,(110)面和双层铜金属薄膜作为探讨界面性质的材料,进而探讨了单晶铜及双层铜金属薄膜的纳米压痕变形性质.     

An overall mechanism for the deposition of plasma polymers from methane in a low-pressure argon plasma jet

An overall mechanism for plasma polymer deposition from a methane-seeded argon plasma jet was established from experimental measurements and a simplified model of reaction kinetics within the plasma jet. Total mass deposition rates were obtained at various substrate positions and methane flow rates. Methane consumption was estimated from residual gas analysis. The influence of substrate coolant temperature on deposition rate was evaluated. The model was based on particle densities, jet temperature, and jet velocity data published previously, and reaction rate constants from the literature were used. No adjustable parameters were employed in this model. Experimental results for total deposition rate and methane consumption were in good agreement with model predictions. The overall deposition mechanism consists of three steps: Penning ionization of methane by excited argon neutrals, followed by dissociative recombination of CN _x ⁺ to yield CH, followed by incorporation of CH into the growing film upon impact. Contributions of species other than CH to the total deposition rate are minor, and adsorption is not a prerequisite for incorporation into the growing film.     

Hydrogen/argon plasma jet with methane addition

Spatial distributions of plasma parameters are presented for a H₂/Ar plasma jet with addition of methane. The plasma has been generated at atmospheric pressure by a 200 A (20 kW) nontransferred do arc. Optical emission spectroscopy has been used for the measurements assuming the plasma jet to be optically thin and to have an axial symmetry. Local spectral ernissivity values have been evaluated using a routine Abel inversion procedure. Half- width and emissivity of H spectral line have been measured to determine the electron density and temperature of the plasma. The densities of excited C, CH radicals have been evaluated from the absolute emissivities of relevant molecular emission bands measured in limited spectral intervals in the visible spectrum. The emissivity ratios have been used to fund rotational and vibrational temperatures. The results supply information on methane decomposition and the behavior of molecular radicals in close-to-thermal plasma jets.     

A Histidine Residue and a Tetranuclear Cuprous-thiolate Cluster Dominate the Copper Loading Landscape of a Copper Storage Protein from Streptomyces lividans

The chemical basis for protecting organisms against the toxic effect imposed by excess cuprous ions is to constrain this through high-affinity binding sites that use cuprous-thiolate coordination chemistry. In bacteria, a family of cysteine rich four-helix bundle proteins utilise thiolate chemistry to bind up to 80 cuprous ions. These proteins have been termed copper storage proteins (Csp). The present study investigates cuprous ion loading to the Csp from Streptomyces lividans (SlCsp) using a combination of X-ray crystallography, site-directed mutagenesis and stopped-flow reaction kinetics with either aquatic cuprous ions or a chelating donor. We illustrate that at low cuprous ion concentrations, copper is loaded exclusively into an outer core region of SlCsp via one end of the four-helix bundle, facilitated by a set of three histidine residues. X-ray crystallography reveals the existence of polynuclear cuprous-thiolate clusters culminating in the assembly of a tetranuclear [Cu₄(μ₂-S-Cys)₄(Ν^δ1-His)] cluster in the outer core. As more cuprous ions are loaded, the cysteine lined inner core of SlCsp fills with cuprous ions but in a fluxional and dynamic manner with no evidence for the assembly of further intermediate polynuclear cuprous-thiolate clusters as observed in the outer core. Using site-directed mutagenesis a key role for His107 in the efficient loading of cuprous ions from a donor is established. A model of copper loading to SlCsp is proposed and discussed.