The behavior of titanium,stainless steel,and copper-nickel alloys as plasma torch cathodes

Cathode erosion continues to be a problem hindering the widespread application of plasma technology. In this work, cathode erosion was studied on titanium, stainless steel 314, copper-nickel 10% and 30%, and copper 122 for magnetically rotated arcs operating in argon, nitrogen, and argon/hydrogen mixtures at a constant magnetic flux density of 0.1 T Titanium and stainless steel gave very low erosion rates in argon (0.2 and 0.3, g/C respectively). Cupronickels were shown to be suitable for nitrogen and hydrogen plasmas. The slope of hydrogen solubility versus temperature in the cathode material was found to be important in determining hydrogen plasma erosion characteristics. When the plasma gas has a high solubility in the cathode material, or can react with the cathode, a negative erosion rate may result. When gas solubility in the cathode is low, oxide stability and mode of electron emission may govern the erosion rate. A high gas solubility in the cathode material, as with hydrogen, can result in mechanical erosion due to micro-explosions near the cathode surface.     

A Sheath Collision Model with Thermionic Electron Emission and the Schottky Correction Factor for Work Function of Wall Material

This paper is a further development of the collisional sheath model at the thermionic cathode for two temperature modeling of thermal arcs that was recently suggested by Pekker and Hussary. In the present work, the Schottky correction factor to the work function of the electrode material is calculated taking into account the friction of ions in the sheath, while in the model of Pekker and Hussary it was calculated neglecting this friction. The model is applied to the cathode spot at the tungsten cathode in argon. It is demonstrated that a virtual cathode can be formed in the atmospheric pressure argon plasma at the cathode surface if the cathode current density is sufficiently small. The heat flux to the thermionic cathode due to charged particles and the heat flux to the plasma due to thermionic electrons are calculated. The obtained results are compared with the model of Pekker and Hussary. The sheath potential drop and the heat fluxes calculated by this model can be used as boundary conditions at the wall for the electric potential and for the energy equations for the electrons and heavy particles (ions and neutrals) in two temperature modeling of thermal plasma.     

Cathode erosion phenomena in a transferred-arc plasma reactor

Phenomena occurring on file surface of a thoriated tungsten cathode operating in a transferred-arc reactor were investigated. The effects of cathode geometry (pointed-tip vs. flat-tip) and plasma gas composition (argon vs. helium) on the rate and mechanisms of cathode erosion were studied experimentally by examining the morphology of the surface before and after runs of prespecified duration, up to one hour in length. For flat-tip cathodes in argon, the major characteristic was the migration of thoria and its concentration at segregated sites. Both geometries in helium operated at much higher temperatures, around the boiling point of tungsten, giving rise to extensive vaporization of cathode material, followed by apparent redeposition of the ionized species carried by file ionic current, in characteristic ringlike sites on the surface. Erosion rates were low and similar in magnitude, except for pointed-tip cathodes operated in argon, where the formation of a large molten sphere of tungsten and its subsequent release gave rise to a higher rate of erosion.     

Relating Spectroscopic Measurements in a Plasma Cutting Torch to Cutting Performance

The relationship between plasma properties and cutting performance for a plasma arc cutting system was investigated. Plasma properties such as temperature and composition were measured using spectroscopic techniques in a 200 amp oxygen plasma cutting system. In addition to the plasma properties, the symmetry of the cylindrical cutting arc was also quantified. Cutting performance was measured by analyzing the edge quality of sample cuts. The most important measure of edge quality for this study was the angle of the cut edge. Operating parameters investigated included the effect of shield gas flow and geometry changes caused by cathode erosion. The measured plasma properties are used to account for the observed increase in recommended cutting speed for different consumable designs which operated at the same current level. A strong correlation was also shown between the measured arc symmetry and the cutting performance.     

Axial mass transport and distribution of particles in D.C. arc plasma

A model is proposed to establish the axial distribution of added substances in an arc plasma. Particles with a higher ionization degree in the plasma are retained by the cathode. This causes a decrease in the axial transport velocity of particles newly arriving in the vicinity of the cathode. Consequently, this decrease of transport velocity causes an increase in the density of particles and their radiation density. Such an assumption is confirmed by measurement of the axial transport velocities. The theoretical consideration here is based on the works of Boumans and Krinberg and Smirnova, and takes into account the stated phenomena of decrease of axial transport velocities near the cathode. Using the results of the experimentally determined axial radiation density distribution, the axial distribution of particle transport velocities was calculated. The proposed model to establish the axial distribution of added substances contributes to the explanation of cathode layer enrichment of radiation density.     

Spectroscopic study of a magnetically rotating arc between opper electrodes in contaminated argon

The effects of N₂ and CO contaminants in atmospheric-pressure argon on an arc rotating between two concentric copper electrodes has been studied using optical spectroscopy of copper lines. The axial temperature of the magnetically driven arc in Ar + %N₂ was determined to be around 10,000 K for arc currents of SO to 200 A. The diffusion process of the copper vapor from the cathode was also studied. A copper density maximum 1 mm from the cathode along the arc column was found in Ar + %N₂. Removal of the contaminated cathode surface layers by the arc when contaminant injection in the plasma gas was stopped was found to be a slow process with a time scale depending on the type of the gas contaminant. The presence of gas contaminant in the electrode material controls the cathode erosion mechanism and the overall arc behavior in the transition between a contaminated to a pure argon arc.     

Study on Arc Movement in Hollow Electrode Plasma Generators with Impressed Double Magnetic Fields

In order to prolong cathode lifetime of hollow electrode plasma generators, a method of impressed double magnetic fields with an alternating frequency is presented in this paper. The alternating frequency of the double magnetic fields is an important factor that influences the erosion rate on the area between the two coils' central planes. By analyzing the arc movement in the hollow cathode with a simplified theoretical model, the spiral curve shape of the radial arc and the relationship between the optimal alternating frequency and the intensity of magnetic fields are obtained. A photoelectric method is employed to measure the arc root rotation speed in the hollow cathode, and then the optimal alternating frequency is calculated as 319 Hz for the experimental conditions. The life testing with this alternating frequency showed that the cathode lifetime could be prolonged significantly.     

Characterization of the arc cathode attachment by emission spectroscopy and comparison to theoretical predictions

Emission spectroscopic diagnostics of electron temperature distribution and electron number density distribution in the cathode region have been carried out employing an OMA/spectrometer system. Single color and two color pyrometry of cathode temperature distributions have also been performed. The experimental results are compared with results of a theoretical model formulated previously to study the arc cathode interaction.The results show that the plasma in the cathode region strongly deviates from LTE. Thermionic cooling is the major cooling mechanism of cathodes at high arc currents. The work function of 2% thoriated tungsten cathodes increases during arcing due to fast evaporation of thorium from 2% thoriated tungsten cathodes.     

Modeling and Spectroscopic Investigations on the Evaporation of Zirconia in a Thermal rf Plasma

The evaporation process of zirconia powders injected in a thermal rf plasma is investigated. Both model calculations and optical emission spectroscopy are used to study the evaporation behavior. Gas temperatures and velocity distributions are determined numerically from conservation laws and Maxwell equations. The influence of plasma and particle parameters on the thermal history of entrained particles is discussed. Asymmetric Abel inversion is applied to detect asymmetric emission profiles in the plasma source. Spectroscopic measurements reveal that evaporated zirconium is concentrated near the axis of the plasma. Numerical calculations show that line-integrated emission profiles can be used to distinguish the cases of complete and incomplete evaporation. Axial emission profiles confirm that the evaporation zone is shifted upstream of the plasma when smaller precursor particles are used.     

Development of a laser ablation-hollow cathode glow discharge emission source and the application to the analysis of steel samples.

A novel atomic emission spectrometry comprising laser ablation as a sampling source and hollow cathode plasma for the excitation of ablated sample atoms is proposed. In this arrangement, a conventional Grimm-type discharge lamp is employed, but the polarity of the power supply is reversed so that the cylindrical hollow tube acts as a cathode and the glow discharge plasma is produced within this tube. A laser is irradiated to introduce sample atoms into the discharge plasma. Ablated atoms are excited by collisions with electrons and gas species, and emit characteristic radiation upon de-excitation. The experiments were conducted only in an atmosphere of helium gas so as to avoid a rapid erosion of the cathode hollow tube. Phase-sensitive detection with a lock-in amplifier was utilized to reject the continuous background emission of the plasma gas and emissions of sputtered atoms from the tube material. The unique feature of this technique is that the sampling and excitation processes can be controlled independently. The proposed technique was employed for the determination of Cr, Mn, and Ni in low-alloyed steel samples. The obtained concentrations are in good agreement with the reported values. The relative standard deviation (RSD), a measure of the analytical precision, was estimated to be 2-9% for Cr, 3-4% for Mn, and 4-11% for Ni determination.     

Study of the dynamic and static behavior of de vortex plasma torches: Part II: Well-tye cathode

This work was devoted to the study of the dynamic and static behavior of de vortex plasma torch with a well-type cathode (power level below 100 kW). The dynamic behavior of the torch was characterized by the fulctuations of arc voltage and current, plasma jet radiation, and acoustic pressure. Characteristic frequencies of the arc root movement inside the torch were observed. By numerical simulation (with the numerical codeMelodie, it was shown that the position of the erosion diameter) of the axial velocity along the cathode channel near the wall. The static behavior of the torch was inverstigated for different cathode designs. The variations of voltage U with arc current I, gas flow rate G nature of the gas and cathode design were represented by semiempirical relationships established between dimensionless numbers. By dimensional analysis, the behavior of this torch was compared with that of two powerful torches: the Aerospatiale and the Plasma Energy Corporation torches.     

Synthesis of aluminum nitride in transferred arc plasma furnaces

Ultrafine particles of aluminum tnitride (AIN) arc produced by a transferred an plasma. Two devices are used: a transferred arc plasma on aluminum natal in nitrogen or nitrogenlammonia atmospheres, and a item concept of transferred arc plasma when, DC anode and cathode ares are coupled together above an alumintun melt. Equilibrium chemical compositions mere calculated. The temperature distributions in the plasma are measured hr emission spectroscopy Flit, powder, made from 99.8%, aluminum ingot, it as analyzed and confirmed to be 99.3%, of hexagonal phase aluminum nitride. In othertests, from 99.99% aluminum ingot, a translucent AIN vinter was obtained. The densification behavior was assessed by hot pressing and by pressureless sintering, with and without additives. The thermal conductivities are given.     

The axial density distribution of radiation emitted by traces in the plasma of a D.C.ARC

Summary The axial radiation density distribution was determined for elements of different ionization potentials present in traces in the arc plasma. The sample was evaporated from the lower electrode (anode), while the diameter and shape of the upper electrode (cathode) were varied. The cathode layer enrichment was found to be affected by the cathode shape.

---

Axiale Verteilung der Strahlungsdichten der Spurenelemente im Bogenplasma

Zusammenfassung Die axiale Verteilung der Strahlungsdichten der Spurenelemente wurde mit verschiedenen Ionisierungspotentialen im Bogenplasma bestimmt. Die Probe wurde aus der unteren Elektrode (Anode) verdampft, wobei der Durchmesser und die Form der oberen Elektrode (Kathode) variiert wurden. Dabei wurde gezeigt, daß die Verteilung der Strahlungsdichten von der Form der Kathode abhängt.

     

The effect of multi-component aerosol particles on quantitative laser-induced breakdown spectroscopy: Consideration of localized matrix effects

Spectral measurements were performed in a laser-induced plasma to assess the changes in sodium or magnesium analyte emission response from particle-derived sources with the addition of concomitant mass to the aerosol particles. Temporally resolved measurements revealed up to a 50% enhancement in analyte emission with the addition of the elements copper, zinc or tungsten at mass ratios from 1:9 to 1:19, although the enhancement generally diminished by delay times of 60 μs. Additional measurements in magnesium–cadmium aerosol particles were performed to assess the temporal profile of plasma temperature in the spatial vicinity of the aerosol particles using the ion-to-neutral emission ratios. These measurements revealed a general increase in localized plasma temperature with increasing delay time, which is attributed with an initial suppression of plasma temperature about the aerosol particles as plasma energy is required to vaporize and ionize the aerosol particle mass. These measurements provide direct evidence of a matrix effect for aerosol particles, which is attributed primarily to perturbations in the localized plasma properties. These perturbations are minimized at longer plasma delay times; hence quantitative LIBS analysis of aerosol particles should be performed with careful attention given to the temporal plasma evolution. The data further elucidate the complex interactions between the plasma gas and the aerosol particles, during which the finite time-scales of particle dissociation, and heat and mass transfer are equally important.     

锂离子电池纳米结构正极材料LiV3O8的制备及性能

采用水热合成方法,在不同水热合成温度下制备了具有纳米结构的锂离子电池正极材料LiV3O8。并利用X射线衍射、透射电镜、恒流充放电、循环伏安以及电化学交流阻抗等测试手段对其结构、形貌和性能做了研究。结果表明,不同的水热合成温度影响到产物的结构、形貌和性能。随着水热温度的升高,粒子的直径随之增大,而形貌和尺寸的均一性则有所降低。电化学测试结果表明水热180℃得到产物的比容量较高,具有良好的电化学可逆性,而且随着水热温度的升高,材料的电荷转移电阻依次减小,有利于锂离子的嵌入与脱出,比容量也随之增加。可见材料的结构中存在一定的非晶缺陷,以及粒子具有一定范围内的尺寸分布,对材料的电化学性能有改善作用。     

Analytical Potentials and Features of Atomic Emission Analysis Using Electron-Impact Excitation of Atoms in Helium under Atmospheric Pressure

A device is described for the atomic emission analysis of vaporous samples using electron-impact excitation in helium under atmospheric pressure. The device consists of a cathode atomizer with a test sample applied onto it and the anode located at 1–3 mm from the cathode. The electrons emitted by the cathode upon heating are accelerated by applying a constant voltage to the electrodes. The mechanism for the formation of a non-self-sustained gas discharge between the cathode and anode is considered and the properties of the discharge are compared to those of the known discharges used in atomic emission spectrometry. The influence of atomization temperature and helium pressure on the analytical and background signals was studied. It is shown that, under certain conditions, the analytical signal increases with helium pressure. The relative detection limits attained for a number of elements are from tenths to dozens of nanogram per liter; this is two or three orders of magnitude lower than those in inductively coupled plasma atomic emission spectrometry and of the same order of magnitude as detection limits in inductively coupled plasma mass spectrometry.     

Numerical simulation of a free-burning argon arc with copper evaporation from the anode

A free-burning, high-intensity argon arc at atmospheric pressure was modeled during the evaporation of copper vapor from the anode to study the impact of the vapor to the entire plasma region. A uniform and a Gaussian radial velocity distribution are adopted for the copper vapor at the anode boundary with a net mass flow rate known from the experiment. The effect of both velocity distributions on the temperature, mass flow, current flow, and Cu concentration was studied for the entire plasma region. The cathode region is not affected by the evaporated copper, and the Cu vapor concentration in the arc core is negligible.     

Determination of plasma homovanillic acid by liquid chromatography with electrochemical detection.

We describe a simple method for extracting homovanillic acid (HVA) from plasma. An aliquot of 0.5 ml of the internal standard solution (3-hydroxy-4-methoxycinnamic acid in 0.2 mol/l phosphoric acid) and 0.5 ml of the sample are applied to a 1-ml Bond Elut C18 column prewashed with methanol and 0.2 mol/l phosphoric acid. The sample is drawn through the column at low speed. The column is washed with water and eluted with dichloromethane. The eluate is evaporated under vacuum at ambient temperature and the residue reconstituted with 250 microliters of the mobile phase. A 10-microliters aliquot of the resulting solution is injected onto a 150 mm x 4.6 mm I.D. column packed with 5-microns octadecylsilyl silica particles (Beckman). Peaks are detected coulometrically in the screening-oxidation mode with E1 = +0.25 V and E2 = +0.38 V. In the resulting chromatogram, HVA and the internal standard give sharp peaks and are well separated from solvent and other endogenous electroactive acids. The extraction recovery is 90-95% which allows the determination of 0.5 microgram/l analyte.     

Modeling the effect of the cathode geometry in a DC glow discharge ion source for mass spectrometry

A self-consistent, two-dimensional hybrid fluid-particle model is used to study the effect of cathode geometry on the plasma produced in an argon glow discharge for conditions typically of the commercially available glow discharge mass spectrometer system (VG9000 spectrometer and Megacell source). For a given power supply voltage and gas pressure, we show that the spatial distribution of the plasma in the discharge volume is strongly dependent on the cathode geometry. The plasma created in a discharge with a pin cathode tends to form a ring around the cathode, while the plasma in a discharge with a larger diameter, disk cathode is centered on-axis between the cathode face and the anode. The ion current arriving at the entry plane of the mass spectrometer thus depends strongly on the cathode geometry. This suggests that analytical performance can be enhanced by optimization of the cathode (sample) geometry.     

Catalyst-free fabrication of graphene nanosheets without substrates using multiwalled carbon nanotubes and a spark plasma sintering process

Catalyst-free graphene nanosheets without substrates were synthesized using pure solid carbon sources of multiwalled carbon nanotubes (MWCNTs) and a spark plasma sintering (SPS) process. Single and few-hundred-nanometer graphene nanosheets were formed from gas-phase carbon atoms which were directly evaporated from MWCNTs at a local high temperature.