Electrode Erosion Rate Research Articles

Investigations on enhanced plasma expansion in pseudospark discharge assisted by a magnetic switch

Electrode erosion caused by dense plasma in constrictive discharge channel is one of the fundamentally detrimental effects existing in pulsed discharge switches. An enhanced plasma expansion in pseudospark discharge assisted by a magnetic switch (MS) is observed from ICCD images in this paper, accompanied by reduced commutation loss, and the mechanisms are revealed by experiments and simulations. The characteristics of the discharge waveforms and channel images of the pseudospark discharge with and without a series-connected MS are compared, and the influence of the number of magnetic cores is studied. As the loop current increases, the discharge channel expands radically and reaches the maximum as the current rising rate reaches the maximum. As the number of magnetic cores increases from 0 to 8, the maximum diameter of the discharge channel increases from 16 mm to about 38 mm, and the commutation loss is reduced from 30 mJ to 11 mJ. The electrode erosion rate of the case with a MS is lower than that without a MS. A particle in cell/Monte Carlo collision model coupling to nonlinear external circuit elements is established. The simulation results fit well with the experiment phenomena, including the discharge waveforms and the profiles of the discharge channel. The distribution of ions shows more diffused features than that of electrons, while the distribution of electrons is more similar to the discharge channel observed in experiments. The enhanced plasma expansion is mainly caused by the higher radial acceleration component of the charged particles during the magnetically delayed time.

Stabilization Methods in the Submerged Arc Discharge Synthesis of Carbon Nanostructures

Many papers, in which the submerged arc discharge (SAD) method in nanoparticle synthesis was used, reported similar operating parameters, but different electrode erosion rate values, different yields and purities of the obtained nanostructures, and a different sort of contaminants present in the synthesis. Analyzing these articles, we found insufficient attention to ensure the arc power stability, which is a key factor guaranteeing the product homogeneity and quality. This paper presents an analysis of different control strategies, remarks their advantages and drawbacks, and proposes the most appropriate technique to be used in SAD. The most appropriate technique is proposed from the SAD stabilization method analysis.

Simplified Spark Pulser for Nanoparticles Generation

This article studies the possibility to design high-voltage pulser to sustain spark discharges in dielectric liquid using cheap and simple design. A spark pulser based on a zero-voltage switch oscillating circuit is used to power a high-voltage transformer. Sparks are ignited between copper electrodes in deionized water. The influence of input voltage and electrode gap on voltage and delay before breakdown, deposited charge, and energy is discussed. The effect of a spark gap device is also studied. Parameters of electric discharge are used to determine the capacitance and inductance of generator, through modeling of the equivalent electrical circuit. The utilization of the pulser in nanoparticles synthesis is evaluated by estimating the electrode erosion rate. In addition, the cavitation bubble generated by the spark is used to determine the pressure of the medium in which the spark and nanoparticles formation occur. Results show that the operation is similar to other setups.

Influence of CuCr electrode composition on 2D electron and metal vapor density distribution over vacuum arc

ShackHartmann-type laser wavefront sensors were utilized for the systematic investigation on Cr content dependence of 2D electron and metal vapor density distributions over vacuum arcs generated between CuCr electrodes, whose Cr content were 0 wt.%, 25 wt.%, 35 wt.%, 50 wt.% and 75 wt.%. The electron density was highest for the Cr25wt.% and Cr35wt.%, while the metal vapor density was lowest for the same CuCr electrode compositions. These experimental results demonstrated high consistency with previously reported CuCr composition dependence of electrode erosion rates, duration time of anode melting and residual charge after current zero. Furthermore, based on the present density data and previously proposed dielectric recovery processes, it was suggested that Cr25wt.% and Cr35wt.% are suitable for the interruption of intense-mode vacuum arcs; instead, Cr50wt.% and Cr75wt.% are useful for diffused arc interruption. The validity of this suggestion was supported by previous experimental studies reporting Cr content dependence of arc current interruption capacities and dielectric recovery speeds.

Effect of manufacturing method of Cu-Al electrode on performance during electric discharge machining of siliconised silicon carbide (SiSiC)

One of the most commonly employed non-traditional technique to machine very hard metals with complicated profiles is electrical discharge machining (EDM), wherein the material is removed by striking an electric spark between electrically conducting workpiece and tool electrode. This work is focused with an objective to analyze the effect of process parameters on work piece erosion rate (WER) keeping in view of productivity. The siliconised silicon carbide (SiSiC) is selected as work piece material with a consideration of variety of applications in different fields like: elements subjected to high-temperature environment such as gas turbines, bearings, manufacturing of molds, aerospace and lining of industrial furnaces. Efficient performance of the EDM process is obtained by the cathodic electrode and the anodic work piece. Response surface methodology (RSM) is applied in this study for analyzing the work piece erosion rate (WER) and electrode erosion rate (EER) along with the other influencing parameters like intensity of electric current, spark on-time and spark off-time, keeping flushing pressure constant at all the levels of the experimentation. Modeling of work piece erosion rate and electrode erosion rate is done using response surface methodology with the matrix obtained through Box Behnken Design (BBD). It is observed that there is increase in WER by 40% when Cu-Al (Stir Casting) tool electrode is used instead of Cu-Al (Powder Metallurgy) tool electrode for recommended settings. Hence it is concluded that for machining of SiSiC work material tool electrode manufactured by stir casting method is preferred over tool electrodes manufactured by powder metallurgy technique to increase the productivity.

The effect of circuit resistance on the particle output of a spark discharge nanoparticle generator

The present study investigates how systematic variation of the resistance of the discharge loop influences the nanoparticle output and the electrode erosion of spark discharge generators (SDGs). The size distribution of the nanoparticles, as well as the mass loss of gold electrodes was recorded while varying the total resistance of the discharge loop. It was demonstrated that the characteristics of the aerosol nanoparticles produced by SDGs as well as the erosion rate of electrodes strongly depend on the total resistance even at small values. It was found that by increasing Rtotal from 0.7 Ω to 6 Ω, the modal diameter of the gold particles decreased from 39 nm to 16.5 nm with the concomitant decrease of the erosion rate. Our data allowed concluding that a fair part of the few ohms of total resistance typical to SDGs can easily originate from the electric circuit which affects the particle output. This also means that in addition to the usual control parameters, the total resistance should also be monitored in an SDG, conveniently via monitoring the current, for the purpose of maintaining stable and reproducible NP production. Moreover, circuit resistance can even be considered to be a practical control parameter, if certain size particles are to be produced by an SDG.

Diode-rectified multiphase AC arc for the improvement of electrode erosion characteristics

An innovative multiphase AC arc (MPA) system was developed on the basis of a diode-rectification technique to improve electrode erosion characteristics. Conventionally, electrode erosion in AC arc is severer than that in DC arc. This originated from the fact that the required properties for the cathode and anode are different, although an AC electrode works as the cathode and the anode periodically. To solve this problem, a separation of AC electrodes into pairs of thoriated tungsten cathode and copper anode by diode-rectification was attempted. A diode-rectified multiphase AC arc (DRMPA) system was then successfully established, resulting in a drastic improvement of the erosion characteristics. The electrode erosion rate in the DRMPA was less than one-third of that in the conventional MPA without the diode rectification. In order to clarify its erosion mechanism, electrode phenomena during discharge were visualized by a high-speed camera system with appropriate band-pass filters. Fluctuation characteristics of the electrode temperature in the DRMPA were revealed.

Testing Results of Plasma Spraying Ceramics Coatings by Pulse Plasma Modulation Technology

The work below was done mainly in the USSR (Tajikistan) and partly continued in Israel. This technology provides substantially better coating performance compared with the respective individual processes (plasma, Cold Spraying, arc or oxy-fuel, etc.). The coatings of large areas can be accomplished at much higher quality and deposition rates than conventional plasma, arc or flame spray techniques and at a far lower cost. These benefits have been accomplished through a specially designed torch head and power supply modulation unit. The system does not require expensive argon-helium based plasma of hydrogen, nitrogen or helium mixtures but rather uses air plasma alone or in combination with hydrocarbon fuel. The plasma chemical technology overcomes a previously fundamental limitation of air plasma systems - oxidation of the coating. In addition, the proprietary design of the torch head and supply modulation unit produces both superior coating and substantially reduces the erosion rate of expensive torch electrodes thereby significantly increasing the resource of operating time of a plasma generator. Detailed design specifications and process validation experiments have been of successfully completed, and the design, technology and market of a pre-production prototype has passed through an evaluation by potential strategic partners with the impressive estimation.

Experimental study of electrode erosion and aging process of a specially designed gas switch under repetitive arc discharge

In this paper, a study concerning self-breakdown voltage characteristics, electrode erosion, and degradation of the insulator, of a two-electrode spark-gap switch has been presented based on experiments. A 6 μF pulse capacitor and a DC high voltage source (set at −40 kV) were utilized to achieve ∼0.1 pulses per second repetitive arc discharge between two fixed Cu-W (Cu30/W70) alloy electrodes in the 1.2 L airtight chamber of the switch. With average transfer charge of 2.2 C per shot, this switch was tested for 5800 shots altogether. The results demonstrated the electrode erosion rate of the cathode was 6.3434×10−6 cm3/C whereas that of anode was 5.4691×10−6 cm3/C. Besides, by analyzing electrode surfaces' morphology and PTFE insulator surfaces' compositions after 5800 shots with the help of a scanning electron microscope, a dynamic 3D aspheric metrology instrument, an X-ray photoelectron spectrometer, a metallographic microscope, and a Mettler-Toledo analytical balance, some evidence of physical processes and chemical reactions between plasma channel, electrode materials, and insulation materials could be observed. Moreover, the chamber was opened and inspected for 10 times during the whole procedure, thus providing an overall description of the variation of the switch. It should also be pointed out that owing to complex mechanisms during the aging process, the self-breakdown voltage followed a mixed Normal distribution other than any other simple distributions.

Comparison and Evaluation of Electrode Erosion Under High-Pulsed Current Discharges in Air and Water Mediums

In order to analyze the electrode erosion rate and erosion mechanism under high-pulsed current discharge in water and air, the erosion characteristics of the tungsten–copper (W–Cu) electrode under high-pulsed current were comparatively studied in the experiments. Based on the weight loss measurement, the cathode erosion rate, the anode erosion rate, and the total erosion rate of the electrodes discharged in water and air are obtained. Then the eroded surfaces after 100 shots are analyzed by electron transfer dissociation and energy dispersive X-ray spectroscopy, and concentrations of the metal ions after discharge in the water are measured and analyzed. Results show that the erosion of W–Cu electrode in water is more serious than that in air. Macromorphology of the eroded electrodes in water indicates that there are obvious arc spots caused by more focused arc and higher current density, leading to more serious erosion. Micromorphology shows that the electrode erosion in water is mainly caused by the evaporation of the metal, while the jet of the molten metal in air is the major erosion form. Apart from physical erosion caused by metal ablation and evaporation, the complex electrochemistry reaction, which is induced by the high-temperature arc in water, is one of the significant causes resulting in more serious erosion in water.

ダイオード整流を用いた多相交流アークの放電特性

The purpose of this study is to establish a multiphase AC arc (MPA) system for nanomaterial fabrication without electrode erosion issues. An innovative method to generate MPA with diode rectification was proposed to solve electrode erosion. Multi-diodes were placed between the electrodes and the transformer. Then, the electrodes were divided into pairs of W cathode and Cu anode. The electrode erosion rate in diode-rectified MPA was less than one-third of that in conventional MPA. The high-speed imaging of the electrode region revealed that the electrode temperature was successfully decreased in diode-rectified MPA due to its polarity characteristics. Moreover, the high-speed imaging of arc phenomena suggested that the stable arc discharge was successfully generated in diode-rectified MPA. Obtained results indicated that the diode-rectified MPA enabled us to establish nanomaterial fabrication process at high-productivity.

Design and Characteristics of a High Current Two-Electrode Graphite Gas Switch for the ICF Power System

In this paper, a two-electrode graphite gas switch was developed as the main discharge switch for the high-power laser system. A compact Marx generator designed to generate a 20 ns rise-time and −80 kV peak voltage to trigger the main discharge switch. A magnetic switch was designed to block the triggering pulse from the flashlamp load and permit the main discharge current to flow from the capacitor bank to the flashlamp load. The characteristics of the gas switch were measured under a 1.0-MJ capacitive pulsed power module for over 3300 discharge experiments with a total charge transfer 230 kC. The self-breakdown voltage and the surface characteristics of the electrodes indicated that the erosion of the gas switch was uniform. The lifetime was directly dependent on the electrode erosion rate. The gas switch can go on acting at a full current after the graphite electrodes were replaced.

Electrode erosion during submerged arc treatment of methylene blue water solution

Low voltage, low energy submerged pulsed arcs with a pulse repetition rate of 100 Hz, energy of 48 mJ and duration of 20 μs were used to determine the electrode erosion rate during treatment of 10 mg l−1 methylene blue (MB) dissolved in 40 ml of deionized water, with and without the addition of 0.5% H2O2. Anode/cathode pairs of Fe/Fe, Ti/Ti, Cu/Cu, Cu/Fe, Fe/Cu, Ti/Fe, Fe/Ti, Cu/Ti and Ti/Cu were used. Smaller cathode erosion was measured, in the solutions without H2O2, with copper cathodes than with other cathodes. Smaller anode erosion in the same conditions was demonstrated by using pairs with a Ti anode than with other anodes and larger erosion was found for Cu anodes. By adding H2O2 to the treated solution, smaller cathode erosion was measured by using pairs with a Ti cathode than with other cathodes and larger rates were measured for Fe cathodes. The largest anode erosion was observed for a Cu anode. The erosion of the anode and cathode depends on material combination of the electrode pairs, i.e. on the thermo physical properties of the electrode materials. The correlations of anode/cathode erosion ratio (Ga/Gc) with ratio (qam/qcm) for various electrode materials were found, where qam and qcm are heat fluxes in the body of the anode and cathode, respectively. The experimental data were fitted by curves described with equation Ga/Gc =A(qa/qc)−b where A and b are experimental constants.

Low jitter, high voltage, repetitive laser triggered gas switches

The Electra pulsed power system at the Naval Research Laboratory is capable of supplying 16 kJ to a low impedance load within 140 ns, and it allows continuous operation of up to 5 pulses per second for several hours. Four laser triggered SF6 gas switches transfer the stored pulse forming line energy to the load. Each switch has a hold-off voltage of more than 1 MV and transfers a charge of 10 mC per shot. This paper describes the redesign of the gas switch with hemispherical electrodes to a flat electrode configuration, which led to an improvement in switch reliability. A one sigma switch jitter of ±1.2 ns has been achieved for tens of thousands of continuous shots, with an electrode erosion rate as low as 1 mg/C. Detailed statistical analyses are provided when the switches are operated at a SF6 pressure of 0.36 - 0.69 MPa, with a laser trigger energy of 1 - 18 mJ at 266 nm, and a switch hold-off voltage ranging from 0.7 - 1.2 MV.

Analysis on Useful Lifetime of High-Power Closing Switch With Graphite Electrodes

High-power closing switches with graphite electrodes have been used in power-supply system for a large laser pump. The useful lifetime of this kind of switch is an interesting and important issue. Previous researchers have observed that the graphite erosion loss is proportional to the amount of transfer charge in a high-power pulsed discharge. Therefore, the erosion rate of graphite may be used for predicting and estimating the electrodes' useful lifetime. According to the mathematical model proposed in this paper, the lifetime of a closing switch with graphite electrodes is dependent upon several key parameters, including the dimensions of electrode, density, the erosion rate of graphite electrodes, undervoltage ratio, working temperature, and the amount of energy transfer. A mathematical formula describing the relationship between lifetime and those parameters has been deduced. Based on a newly developed spark-gap switch which can support over 100-C single transfer charge, this proposed lifetime model has been verified. This paper may quantitatively perform the function of guidance in engineering applications of graphite electrode switches in large pulsed-power facilities.

Modeling of a Microscale Short Vacuum Arc for a Space Propulsion Thruster

A model of generation of the plasma supported by the operation of a microscale vacuum arc was developed, considering the phenomena in the cathode and anode spots. The nonequilibrium layers produced by cathode and anode evaporation were studied, and the electrode erosion rates as well as the plasma parameters were calculated. The calculation for 50 A showed that the plasma is dense, with a degree of ionization of about 0.1, and consists of singly charged ions. The anode temperature and erosion rate exceed these parameters for the cathode. It was demonstrated that the relatively large anode erosion rate can cause the larger force in the short vacuum arc compared to the force generated in the long-gap arcs, and this effect should be taken into account when designing a microscale thruster.

Microplasma generation in a microscale short vacuum arc

A mechanism of plasma plume generation and plasma jet formation in a microscale vacuum arc (MVA) was proposed. The uniqueness of the subject is the force generated by a common plasma plume extracted from cathode and anode spots in a MVA. A calculating model for microplasma origin was developed taking into account the atom ionization and the phenomena in the nonequilibrium layers near evaporated surface in the cathode and anode regions. The plasma parameters as well as the electrode erosion rate were studied. It was found relatively large anode erosion rate and force at the anode surface in MVA in comparison to the force that usually occurs at the cathode in arcs with large gap. This important result of MVA was proposed to use in an exceptional microthruster concept for spacecraft propulsion and for anode microplasma source.

Influence of High Voltage Needle Electrode Material on Hydrogen Peroxide Formation and Electrode Erosion in a Hybrid Gas–Liquid Series Electrical Discharge Reactor

Formation rates of hydrogen peroxide and electrode erosion rates for a range of different electrode materials were determined in a gas–liquid pulsed electrical discharge reactor with a high voltage electrode needle in the liquid and a ground electrode suspended in the gas over the liquid. It was found that the H2O2 formation rates and efficiencies did not depend on the electrode material. Electrode erosion from lowest to highest followed the series: nickel chromium, thoriated tungsten, diamond-coated tungsten, stainless steel, tungsten carbide and tungsten copper alloy. Smooth crater-like morphology was found for nickel chromium, titanium and tungsten carbide and a much finer surface structure with small protrusions for the tungsten, tungsten copper and the copper. Doubling the electrode diameter lead to an increase in the H2O2 formation per eroded length by a factor of three but it also decreased the energy efficiency yield of H2O2 by more than 20%.

Ni–C powder synthesis by a submerged pulsed arc in breakdown mode

Abstract Powders of Ni–C nanoparticles were synthesized using a pulsed arc between Ni electrodes submerged in pure ethanol. The arc was ignited by inter-electrode breakdown. The ethanol was arc treated for 5 min with 1 μs duration pulses, at a repetition rate of ∼1 kHz. The pulse energy was in a range of 0.01–0.05 J. Powder samples were obtained by extracting liquid from the treatment vessel after a pre-determined sedimentation time, or by allowing the liquid to evaporate from the vessel, and collecting the residue. The samples were examined by HRSEM, EDX and XRD. It was found that a powder of Ni–C nanoparticles was produced. The powder consisted of carbon particles and nickel–carbon alloy particles. The latter were also coated by carbon. The carbon concentration in the Ni alloy was approximately triple of the maximum equilibrium solid solubility of carbon in nickel. The production rate of carbon was greater than the erosion rate of the Ni electrodes by factors of 2–6. The ratio of carbon production rate to electrode erosion rate decreased with the discharge energy. The size distribution of the produced particles was narrow. No particles with diameter more than 0.7 μm were observed.

W–C Electrode Erosion in a Pulsed Arc Submerged in Liquid

Electrode erosion was studied in pulsed arcs ignited between two electrodes comprised of 99.99% C (graphite) and 99.5% W submerged in deionized water or analytical (99.8%) ethanol. In the both cases the erosion rate increased proportionally to the pulse energy, and the total electrode erosion per unit energy was inversely proportional to the discharge pulse duration. Fifteen and sixty-μF discharge capacitors were used for formation of the pulses in water. It was obtained that, respectively (a) erosion of the tungsten anode (Wa) was by factors of 5–6 and ∼10 greater than that of the carbon (Cc) cathode; (b) erosion of the carbon anode (Ca) was by a factor of 1.34 greater and by a factor of 2.65 less than that of the tungsten cathode (Wc); (c) the total erosion rate of both electrodes (anode and cathode) per unit pulse energy for the Wa–Cc pair was greater by factors of 11 and 12.5 than that for the Wc–Ca pair.