Anode Voltage Drop Research Articles

Reversal of the electric field and the anode fall in DC arcs in air during contact opening

A unified one-dimensional model of an arc plasma in air, between copper electrodes, that includes the change of the gap distance is presented. The occurrence of multiple reversals of the electric field and the anode voltage drop is observed. The evolution of the spatial distribution of the electron and heavy particle temperatures with the gap distance and the opening speed is also studied. The model quantitatively predicts a number of plasma properties under conditions that are relevant to the contact separation in low-voltage switching devices.

Anode power deposition in applied field magnetoplasmadynamic thruster

Applied field magnetoplasmadynamic thrusters (AF-MPDTs) are one of the potential thrusters for high power space propulsion. However, the high anode power deposition limits the improvement in the thruster’s efficiency. According to previous research studies, the anode voltage drop is supposed to be the main factor of the anode power deposition in AF-MPDTs without considering the effect of the centrifugal force. Actually, the centrifugal force cannot be neglected when the magnetic field is high, where the anode voltage drop is not the only dominant factor of the anode power deposition. Due to the significant centrifugal force, there might be no obvious shortage of charge carriers near the anode surface in AF-MPDTs with propellant injection between the cathode and anode. The electrons will be compressed to the anode surface instead of the cathode. In order to investigate the reason for the anode power deposition in AF-MPDTs, a model considering the effect of the centrifugal force is established. The calculated anode power deposition shows good agreement with the corresponding experimental data. In addition, when the magnetic field is high, the viscous heating cannot be neglected, which is as significant as the anode sheath heating and Joule heating. Finally, in order to reduce the anode power deposition, a magnetic field distribution with a high value near the cathode and a low value near the anode is proposed. According to the evaluation by the model, the anode power deposition can be reduced by 30% via the new magnetic field when the magnetic field exceeds 0.1 T.

Carbon arc for nanoparticle production: Ablation rate calculation. Comparison to experiments

A graphite anode ablates in an arc system producing nanoparticles. Experiments show that the ablation rate increases sharply when the current density at the anode exceeds some critical value, which separates the low ablation and high ablation modes. According to the existing hypotheses, the high ablation mode takes place when the anode voltage drop, which is negative in the low ablation mode, turns positive. Based on the work of Nemchinsky [J. Appl. Phys. 130, 103304 (2021)], where the anode voltage drop was evaluated, in this paper, the thermal regime of the anode is considered. It is shown that the main heating mechanism is electron condensation on the anode. The main cooling mechanism is radiation in the low ablation mode and cooling by sublimation in the high ablation mode. In the last case, the energy necessary to compensate for the strong cooling effect of sublimation is delivered by electrons accelerated at the positive anode drop inside the anode sheath. The proposed model allows one to find the ablation rate for a wide range of arc currents and anode diameters. Comparison to the available experimental data shows reasonable agreement. Based on analysis of the experiments and calculations, it was hypothesized that the ablation rate is not sensitive to the presence of a catalyst.

Carbon arc for nanoparticles production: Anode ablation rate and the value of the anode voltage drop

Ablation of a graphite anode by an arc is used to produce nanoparticles. The flow of the ablated carbon particles hampers access of plasma ions to the anode sheath. While the ablation rate is low, ions are still capable of reaching the sheath, where they counter the electric charge of electrons, anode voltage drop is negative. At ablation rates higher than some critical value, the flow of the ablating particles sweeps the plasma ions from the anode proximity; electron electric charge dominates in the sheath and the anode voltage drop turns positive. In these regimes, ions in the plasma move away from the anode and, therefore, they should be generated inside the sheath. The processes in the plasma in the case of positive anode voltage drop together with the process of ion generation inside the sheath are considered. The dependence of the anode voltage drop on the ablation rate is calculated and compared with available experimental data. A good correspondence is found.

Positive anode sheath with ionization in an arc discharge

When the plasma is unable to provide the positive anode sheath with ions (small anode, low anode plasma conductivity, ablating anode), the ions must be generated inside the sheath itself. The Poisson equation for the sheath with ion generation is solved. The ion flux from the sheath to the neutral plasma is obtained as a function of the anode voltage drop. It is shown that in the case of highly intensive ion generation, the mode with monotonous potential ceases to exist. It is hypothesized that a double layer is formed. It is suggested that the analysis could be applicable to the anode layer of a glow discharge.

On the Modified Design of Anode Assembly in Hall-Héroult Cell Using Finite Element Method

The Hall-Heroult process is the most commonly used process for aluminum production by aluminum through an electrolytic reduction of alumina dissolved in an electrolytic bath at 960 C. The voltage drop for the anode group represents about 8% of the total cell voltage. The resistance between the connections that link the different parts of the anode assembly causes the increase the anode voltage during the electrolysis process. The factors affecting the anodic voltage drop, temperature and stresses distribution were investigated using the finite element method. These factors included the stub diameter, thimble flutes number and steel stub number. Thermal and electrical measurements were carried out on ten prebaked anodes cells to verify and validate the modelled result. In this paper, study the electro thermal model under the influence of mechanical loading of the anode assembly confirmed that the design of the steel stubs (in terms of diameter and number) are the main factors that greatly influence the reduction of the anodic voltage, while the thimble flutes number might have a little effect on the anodic voltage drop.

Effects of Stub Hole Button on Anode of Aluminum Reduction Cell

In China, a special anode design with a button in each stub hole is adopted by many smelters. To investigate the effects of the stub hole button on the anode, numerical simulations of the anode rodding process and the running process of the conventional anode without a stub hole button (design A) and the special design (design B) were conducted. In anode rodding, design B shows worse cooling capacity than design A, while the air gap of design B (0.39 mm to 0.94 mm) is larger than that of design A (0.3 mm to 0.45 mm). During the anode running process, the stub hole button could contact neither the cast iron nor the stub, and the anode voltage drop of design B is 26 mV larger than that of design A because the larger air gap deteriorates the cast iron–carbon contact. In conclusion, the stub hole button should be removed.

To the Question of Evaluation of the Anode Voltage Drop

The paper presents the results of the evaluation of the drop of anode voltage while the open burning arc between the steel plate (cathode) and the wire electrode CuSi3Mn1. Experiments were performed to determine the temperature of metal of electrode droplets at manual and mechanized deposit welding. The results of experimental determination of heat contents and temperature of metal of electrode droplets are represented on the chart.

Probe the micro arc softening phenomenon with pulse transient analysis in plasma electrolytic oxidation

Soft sparking can be utilized to dismiss the intrinsic porosity problem of plasma electrolytic oxidation (PEO) coatings on aluminum alloy, since this type of surface treatment generates a dense inner layer. Researchers usually recognize soft sparking through the anodic voltage drop, along with the decline in light and acoustic emissions. Analysis of V-I transients in the anodic pulse of bipolar DC current reveals the decline in RC time constant is a forerunner, which reflects the transition in micro arc state prior to the conventional definition. In studying the negative current dependence and the current frequency dependence of soft sparking, the results suggest the time constant may serve as an auxiliary indicator, monitoring growth activity variations and further assuring the dense inner layer. The role of time constant is exemplified in the soft sparking experiments at 500 Hz and duty 40%. Microstructure analysis reveals three relatively dense stacks separated by two layers of pores and loose grains. The porous layer is attributed to the micro arc state of less intense microdischarges, marked as a substantial drop in the R2C2 value. Matching between stratified layers and R2C2 rises-and-falls is verified in two electrolytic solutions with and without chromia inclusions. Thus, we suggest time constant as a probing tool of microdischarges softening to help analyze the events prior to voltage drop.

Formation of a Thin Luminescent Layer in LiF Crystals under Glow Discharge Radiation

The formation of thin layers of luminescent defects on the faces of planar lithium fluoride crystals located in the positive column and Faraday dark space of a glow gas discharge was studied by time-resolved confocal scanning luminescent microscopy and time-correlated single photon counting. The formation of aggregated color centers in the surface layers of crystals was established using the spectral and kinetic characteristics of luminescence appearing after irradiation. The role of gas discharge electrons, ions, and photons in the defect formation mechanism was considered. The defects were shown to be formed under the influence of vacuum ultraviolet (VUV) photons. The VUV radiation intensity distribution in the discharge gap was measured by the method of thermostimulated luminescence. The main source of this radiation was the anodic and cathodic voltage drop regions in a glow discharge.

Experimental Study of Heating of a Liquid Cathode and Transfer of Its Components into the Gas Phase under the Action of a DC Discharge

An atmospheric-pressure dc discharge in air (i = 10–50 mA) with metal and liquid electrolyte electrodes was studied experimentally. An aqueous solution of sodium chloride (0.5 mol/L) was used as the cathode or anode. The electric field strength in the plasma and the cathode (anode) voltage drops were obtained from the measured dependences of the discharge voltage on the electrode gap length. The gas temperature was deduced from the spectral distribution of nitrogen emission in the band N2(C3Π u → B3Π g , 0–2). The time dependences of the temperatures of the liquid electrolyte electrodes during the discharge and in its afterglow, as well as the evaporation rate of the solution, were determined experimentally. The contributions of ion bombardment and heat flux from the plasma to the heating of the liquid electrode and transfer of solvent (water) into the gas phase are discussed using the experimental data obtained.

Формирование тонкого люминесцирующего слоя в кристаллах LiF под действием излучения тлеющего разряда

AbstractThe formation of thin layers of luminescent defects on the faces of planar lithium fluoride crystals located in the positive column and Faraday dark space of a glow gas discharge was studied by time-resolved confocal scanning luminescent microscopy and time-correlated single photon counting. The formation of aggregated color centers in the surface layers of crystals was established using the spectral and kinetic characteristics of luminescence appearing after irradiation. The role of gas discharge electrons, ions, and photons in the defect formation mechanism was considered. The defects were shown to be formed under the influence of vacuum ultraviolet (VUV) photons. The VUV radiation intensity distribution in the discharge gap was measured by the method of thermostimulated luminescence. The main source of this radiation was the anodic and cathodic voltage drop regions in a glow discharge.

Instability phenomenon of high-frequency vacuum arc discharge associated with anode activity

Instability phenomena of high-frequency vacuum arcs with an ∼100-kHz current waveform and active anodes were observed by using high-speed photography and optical emission spectroscopy and analyzed with a conventional theoretical model. Our experimental and theoretical studies demonstrated that the instability mechanism for the transient vacuum arcs was completely different from that for the well-known quasi-stationary diffused arcs, where a cathode process predominantly contributes to the instability phenomena. In the case of the high-frequency vacuum arcs, the instability phenomena were mainly induced by a collaborative anode process operated by anode evaporation and anode voltage drop.

Thick oxide coatings formed by spark anodizing of Mg-Al alloy in alkaline phosphate-silicate electrolytes

Abstract Anodic coatings formed by spark anodizing (SA) with different electrolyte recipes often have distinct composition and properties. In this paper we report on the study of correlations between electrolytes and the coating properties of a thick SA layer (190 μm) formed on an AZ91D magnesium alloy. The voltage transient during this SA process in phosphate-silicate electrolyte solution is characterized by an abrupt anodic voltage drop after initial voltage increase, followed by a stabilized voltage plateau during which the microdischarge noise is completely suppressed. Microstructure investigations show that the cross-section of such SA thick coating contains three distinctive regions. In terms of composition, the outer layer contains uniform distribution of P and Si, and the middle and inner layers are dominated by Mg and O. Correspondingly, microstructures of these regions are also different, the inner layer with a cellular band and barrier structure is much more compact comparing to the middle layer. The individual thickness ranges for the cellular band and barrier regions are 500nm-2μm and 100–600 nm and their individual micro-hardness reaches about 3 GPa and 8 GPa respectively.

Anodic Bubble Behavior and Voltage Drop in a Laboratory Transparent Aluminum Electrolytic Cell

The anodic bubbles generated in aluminum electrolytic cells play a complex role to bath flow, alumina mixing, cell voltage, heat transfer, etc., and eventually affect cell performance. In this paper, the bubble dynamics beneath the anode were observed for the first time from bottom view directly in a similar industrial electrolytic environment, using a laboratory-scale transparent aluminum electrolytic cell. The corresponding cell voltage was measured simultaneously for quantitatively investigating its relevance to bubble dynamics. It was found that the bubbles generated in many spots that increased in number with the increase of current density; the bubbles grew through gas diffusion and various types of coalescences; when bubbles grew to a certain size with their surface reaching to the anode edge, they escaped from the anode bottom suddenly; with the increase of current density, the release frequency increases, and the size of these bubbles decreases. The cell voltage was very consistent with bubble coverage, with a high bubble coverage corresponding to a higher cell voltage. At low current density, the curves of voltage and coverage fluctuated in a regularly periodical pattern, while the curves became more irregular at high current density. The magnitude of voltage fluctuation increased with current density first and reached a maximum value at current density of 0.9 A/cm2, and decreased when the current density was further increased. The extra resistance induced by bubbles was found to increase with the bubble coverage, showing a similar trend with published equations.

Numerical study of the anode boundary layer in atmospheric pressure arc discharges

The anode boundary layer in atmospheric pressure arc discharges is studied numerically on the basis of the hydrodynamic (diffusion) equations for plasma components. The governing equations are formulated in a unified manner without the assumptions of thermal equilibrium, ionization equilibrium or quasi-neutrality. For comparison, a quasi-neutral model of the anode layer is also considered. The numerical computations are performed for an argon arc at typical values of the current density in anode layers (500–2000 A cm−2). The results of numerical modelling show that the common collisionless model of the sheath fails to describe the sheath region for the problem under consideration. For this reason, a detailed analysis of the anode sheath is performed using the results of unified modelling. In addition, the distributions of plasma parameters in the anode layer are analysed and the basic characteristics of the layer (anode voltage drop, sheath voltage drop, anode layer thickness, sheath thickness, heat flux to the anode) are calculated. Our results are found to be in good agreement with the existing theoretical predictions and experimental data. The dependence of the anode layer characteristics on the current density is also discussed.

Parametric study of electric arcs in aeronautical condition of pressure

This work deals with the characterization of DC electric arcs in aeronautical conditions of pressure (10 4 Pa–10 5 Pa). Characteristics of electric arcs such as the mean electric field in the arc column, the anode and cathode voltage drops, the length for which the arc extinguishes naturally and the mean energy dissipated per arc have been measured for three current values: 7, 70 and 300 A. The decrease of pressure leads to an increase in the arc length which can be two times longer in pressure conditions reached during a flight than in atmospheric pressure conditions. This is correlated with the variation of the mean electric field with pressure. Consequently, the energy dissipated per arc is also amplified.

Plasmatron for simulation of re-entry conditions in a planetary atmosphere

The characteristics of segmented plasmatron are presented. The arc is sustained in argon plasma and in plasma stream, argon, nitrogen and carbon-dioxide are introduced. The numerical simulation of argon electric arc and plasma stream is carried out and the temperatures and densities of electron and heavy particles are presented. Experimental and theoretical investigations determine and explain the influence of natural gas and flow rate injected into plasma stream on working plasmatron conditions. The anode voltage drop analysis shows that in plasmatron working at a current between 40 and 340 A, gas flow rate between 0.4 and 2 g/s and pressure from 5 to 100 kPa, this drop changes from negative to positive, influencing arc voltage value. The gas injection into plasma stream results in anode spot dynamic. Electric breakdowns accompanied by high voltage fluctuations are observed when argon or nitrogen is introduced while carbon dioxide eliminates this type of breakdown reducing the voltage fluctuations and ablation of electrodes.

USING OF HIGH PHOSPHORUS GRAY IRON FOR THE STUB- ANODE CONNECTION IN THE ALUMINIUM REDUCTION CELLS

High phosphorus gray iron (HPGI) is used to secure the steel stub of an anode rod to a prebaked anode carbon block in the aluminium reduction cells. During this work, a detailed characterization for HPGI was done. The variation in the chemical composition of the HPGI collar, anodic voltage drop, and collar temperature over the 30 days anode life cycle were studied and compared with HPGI microstructure at different stages of the experiment. The carbon content in HPGI during anode life cycle was reduced from 3.73 to 3.38%. Significant changes in the HPGI microstructure were observed after 3 and 30 days from the anode changing. The collar temperature increases over the anode life cycle and reaches to 850°C in four weeks after anode changing. Different changes in the anodic voltage drop values at the stub- collar-anode connection during anode life cycle were recorded. Two bench- scale experimental set-ups were designed and implemented to simulate the operating conditions in the steel stub/ HPGI collar/ anode block connection and used to measure the electrical resistance and resistivity respectively. Comparison with steel electrical resistivity showed the greatest importance to modify the current HPGI or producing new alloys with excellent electrical and mechanical properties. The steel stub and HPGI thermal expansion were measured and studied. Considerable permanent expansion was observed for the HPGI collar after the completion of the heating-cooling cycle.

The current-voltage characteristic of a hot-cathode electric arc at low pressures

It has been shown that in a hot-cathode electric arc operating at low pressures of the working gas, a positive anode voltage drop arises that results in an increase in discharge voltage with current even before the transition of the discharge into a constrained arc.