Anodic Arc Research Articles

Al2O3 thin films deposition by reactive evaporation of Al in anodic arc with high levels of metal ionization

The results of studying the parameters of the plasma generated in an arc with a self-heating hollow cathode and a vaporizable anode placed in a magnetic field of two oppositely connected solenoids are presented. Compression of the discharge column in an inhomogeneous magnetic field provides an increase in power density on the surface of the crucible anode to ~1 kW/cm2 and an increase in the degree of ionization of the metal vapor to 50–80%. Using the method of reactive evaporation of aluminum in the Ar/О2 gas mixture we obtained Al2O3 coatings at the rate of 4–8 μm/h under an ion current density of 6–11 mA/cm2, a bias voltage of 50–200 V, and a temperature of 620 °С. It is shown that, with an increase in the ion current density and ion energy, the fraction of the α-phase in the Al2O3 coating increases to 100%. The single-phase α-Al2O3 coatings are characterized by the predominant orientation of crystallites (300).

Al doped ZnO thin film deposition by thermionic vacuum arc

ZnO thin films are widely used in many application areas due to its various properties. The properties of the ZnO thin film strongly depend on the manufacturing method, doping elements and ratio and substrate material. In this paper, ZnO material was doped by Al element. Thermionic vacuum arc is a fast deposition technology for Al doped ZnO thin film manufacturing. TVA is physical vapor deposition technology, using anodic vacuum arc. It works under the high vacuum condition. The thin films were deposited onto amorphous glass, semi-crystal PET and single crystal Si substrate. Structural, morphological and optical properties of the Al doped ZnO thin films are presented. Thin films are in polycrystalline form and have high crystalline quality. According to the XRD analysis, metal oxide phases (ZnO and Al2O3) and bi-metal oxide (ZnAl2O4) phases were detected. It was found that crystallite sizes strongly depend on the substrate. The crystallite size of the thin film deposited on the Si substrate is approximately 100 nm. For the other sample, the value is very small; it is just about 20 nm. Considering the optical results of the samples, all films are transparent in visible region. Band gap and electronic structures of the Al doped ZnO thin films were investigated by optical method, photoluminescence and Raman spectra. The band gaps of the thin films were shifted towards to the high-energy region. Any impurity in deposited thin films cannot detect by the analyses devices.

Simulation Analysis of Arc Evolution Process in Multiple Parallel Contact Systems

Air circuit breaker (ACB) is widely used in power distribution system. The movable contact of ACB consists of multiple parallel contacts and the arc will be ignited between arcing contact and static contact when the short-circuit current appears. This paper focuses on the arc evolution process at various currents in multiple parallel contact systems. A 3-D magnetohydrodynamic model of a multiple parallel contact structures is developed. In this model, the anode consists to five parallel contacts, and they are separated by insulation material. The near-electrode layer with a nonlinear voltage-current density characteristic is modeled to describe the near-electrode voltage drop, and the difference between near-anode and near-cathode layers is considered. The magnetic vector potential approach is adopted to calculate the time-varying electromagnetic field produced by the current loop. The arc evolution processes at various currents are analyzed by current density and arc voltage. It is noted that the anode arc root appears on multiple contacts with the increase of current. The arc evolution process mainly depends on the arc resistance characteristic.

Time-Resolved Emission Spectroscopy Measurements during the Restrike Period in Arc Plasma Torch

Simultaneous optical, spectroscopic, and electrical measurements in the region of the arc anode attachment of the water-argon plasma torch are presented. A movement of the arc attachment along the anode surface together with its restrike mode is monitored. Temporal evolution of temperature during one cycle of the restrike mode is obtained in three different axial positions in the plasma column. Resulting temperature profiles show how the position of the arc attachment influences the plasma properties.

Role of return currents in the dynamics of a magnetically rastered plasma torch

The role of return currents in the plasma dynamics of a dc non-transferred arc plasma torch has been investigated. The anode arc root connects the main plasma column and return current in the anode and its motion governs the return current formation in the anode. Thus by investigating the return currents, we can explore complex spatio-temporal evolution of the plasma in detail. In this work, we have used electrical and magnetic diagnostics. The electrical diagnostic comprises of a high voltage probe, and the magnetic diagnostic consists of a garland of several B-dot probes incorporated inside the anode water cooling channels. The magnetic (B-dot) probes are designed to pick up the dominant component of the time-varying magnetic fields. Results show that, beyond a threshold, volume return currents transform to constricted line currents in the anode return path. This is attributed to eddy currents arising due to space varying rather than time varying return current components in the anode. The probes capture fast rotation of the arc root that is not captured by fast imaging. Also, arc root shunting (restriking) phenomena and its location on the anode periphery are clearly captured by the garland of magnetic probes. A physical model explaining the processes is also presented.

A Comparative Study of MO Films Deposited on AISI 310 and Alumina Surface Using Anodic Vacuum Arc

The Surface of Alumina and Stainless Steel was considered for thin film deposition of molybdenum by using Anodic Vacuum Arc. The evaporation was carried out at 0.07 mbar pressure and at a welding current of 60 Amperes where the temperature reached beyond 2500˚C and a thin layer of molybdenum was coated on the substrates. The corrosion rate, surface morphology, crystallite size and lattice strain were calculated by using Electrochemical Analyzer, Scanning Electron Microscope and X-Ray Diffraction respectively.

Investigation on the Geometrical Characteristics of Secondary Arc by Image Edge Detection

The image of secondary arc, which is a common phenomenon in ultrahigh voltage power system, contains a wealthy of information. To determine its geometrical characteristics, the secondary arc image is systematically processed involving gray scale, noise filtering, and image segmentation. To overcome the discontinuous and false edge caused by conventional operators, an improved algorithm is employed; the unrelated edges are fully removed, and the interrupted endpoints are dilated. Based on the results, the component and evolution of secondary arc are discussed; the correlation of the arc luminance and arc current is revealed. Occasionally, the arc roots and arc column have irregular motion behavior. Using the edge-detection technique, the detailed jumping location and velocity of anode arc root are tracked; the life expectancy and stability of coexistence of multicathode arc roots are determined; the morphology of short circuit of arc column is ascertained. Furthermore, the secondary arc dimension is estimated in this paper, including the arc radius and arc length. A number of formulas have been presented to predict the dimension. The obtained results are more accuracy than previous works.

The influence of TIG-Arc physical characteristics on the penetration and weld width under different Ar and He supply conditions

Abstract In the paper, the 5A03 aluminium alloy was employed to study the influence of TIG arc on the penetration and the weld width. And the split anode method with water-cooled copper plate was used to measure and record the distribution of arc current, under different flow ratio of argon and helium conditions. And a gas supply device controlled by a solenoid valve was employed to obtain the stable TIG welding arc of gas supply alternately at the frequency of 1 Hz and 4 Hz, and then collected the phenomenon of arc alternate by the high-speed camera. The experimental results indicated that the current density at the arc anode center of argon and helium supply alternately with different mixing ratio is lower than that of the pure argon-arc center. Nonetheless, the former is more uniform in current density within 2 mm from the arc center. Furthermore, it presented as a component arc of argon-arc and helium-arc switched, with the condition of argon and helium supply alternately at a frequency of 1 Hz and the arc power density is greater and concentrated, leading to the wider and deeper weld.

Regularities of self-organization of technological conditions during plasma-arc synthesis of carbon nanotubes

The emerging concept of self-organization under conditions of plasma-surface interaction is reflected in the present analytical study of the processes and causes of carbon nanotube formation in anodic arc discharge. Based on the energy balance and the interelectrode mass transfer, we created a mathematical model of self-organization of technological conditions required for carbon nanotube synthesis. The self-organization regularities of such parameters as carbon concentration, relative supersaturation above the growth surface and the surface temperatures of both electrodes have been determined by the phase portrait method. Unique possibilities of self-organized processes have revealed the ways of maintaining required synthesis stationarity. It has been shown that extremely low supersaturation of deposited vapors, substance accumulation above the growth surface and exposure to plasma are important factors for carbon nanotube formation. The structure formation mechanism under conditions of self-organized low supersaturation has been discussed. The stated self-organization regularities are also expected to take place in other fields of plasma nanoscience.

Measurement of Anode Arc Attachment Movement in DC Arc Plasma Torch at Atmospheric Pressure

Direct current (DC) arc plasma torches are widely used in various industrial applications. Studying processes in their anode area helps to extend their lifetime, and stabilize the plasma flow for plasma applications. This paper reports detailed observations of the fast movement (above 100 m/s) of the anode arc attachment in a hybrid water-argon DC arc plasma torch with an external anode. We measured a mean electrical conductivity of a plasma volume above the anode and found a relation between the attachment movement and the anode erosion. Further, we measured average attachment speed, the average period of the restrike process and the average distances travelled by the attachment under different experimental conditions such as different values of the arc electric current, argon flow rate and different anode configurations. For our measurements, we used a high-speed camera and a high-voltage probe. Our results are in agreement with a model of plasma generated by a hybrid plasma torch and with spectroscopy measurements. The results describe the movement of the anode arc attachment in detail and provide experimental data on average plasma electrical conductivity in hot anode areas. Both the measurements of the mean electrical conductivity and the procedure for quantitative comparisons of anode erosion can be used also in water plasma torches and theoretically also in gas plasma torches.

The Properties of Binary and Ternary Ti Based Coatings Produced by Thermionic Vacuum Arc (TVA) Technology

A series of the multicomponent thin films (binary: Ti-C; Ti-Ag and ternary: Ti-C-Ag; Ti-C-Al) were fabricated by Thermionic Vacuum Arc (TVA) technology in order to study the wear resistance and the anticorrosion properties. The effects of Ti amount on the microstructure, tribological and morphological properties were subsequently investigated. TVA is an original deposition method using a combination of anodic arc and electron gun systems for the growth of films. The samples were characterized using scanning electron microscope (SEM) and a transmission electron microscope (TEM) accompanied by selected area electron diffraction (SAED). Tribological properties were studied by a ball-on-disc tribometer in the dry regime and the wettability was assessed by measuring the contact angle with the See System apparatus. Wear Rate results indicate an improved sliding wear behavior for Ti-C-Ag: 1.31 × 10−7 mm3/N m (F = 2 N) compared to Ti-C-Al coating wear rate: 4.24 × 10−7 mm3/N m. On the other hand, by increasing the normal load to 3 N an increase to the wear rate was observed for Ti-C-Ag: 2.58 × 10−5 mm3 compared to 2.33 × 10−6 mm3 for Ti-C-Al coating.

Experimental study on ignition characteristics of kerosene–air mixtures in V-shaped burner with DC plasma jet igniter

In this paper, we investigate the effects of DC plasma jet igniter on ignition characteristics of the kerosene–air mixtures in V-shaped burner. The primary principles of DC plasma igniter design have been put forward to prolong the igniter life and improve ignition performance. The main characteristic of plasma igniter is that the anode arc root is fixed at anode nozzle outside surface other than the anode inner surface in conventional design. The electric characteristics of the plasma jet igniter including voltage–current characteristics, the arc column propagation, emission spectrum and anode arc root movement in a quiescent environment are investigated with high speed CCD together with a recording of the voltage and current. The entire ignition process of the plasma jet igniter is recorded by high speed CCD and the ignition delay times of the kerosene–air mixtures defined by the interval between the onset of the plasma igniter and the establishment of a stable flame are measured with two photomultipliers with one of 10 mm band pass filter centered at 780 mm (the plasma igniter emission spectrum of OI) and the other of 10 mm band pass filter centered at 430 mm (direct flame emission of CH(A2Δ→X2Π)). Results show that the plasma igniter works in a restrike mode and the anode spot movement is irregular. The plasma igniter jet contains abundance active particles inferred from the emission spectrum. The ignition delay times increase at first and then decrease with the increase of excess air coefficient ranging from 0.91 to 6.38. The delay times increase quickly when the mixtures are extremely lean or rich.

Microstructure and optical properties of ZnO nanorods prepared by anodic arc plasma method.

A one-dimensional ZnO nanostructure is a versatile and multifunctional n-type semiconductor. In this paper, ZnO nanorods were successfully prepared by the anodic arc plasma method in an oxidizing atmosphere. The composition, morphology, crystal microstructure, and optical properties of ZnO nanorods were characterized by using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and the corresponding selected-area electron diffraction (SAED), X-ray energy dispersive spectrometry (XEDS), ultraviolet-visible (UV-VIS) spectroscopy, Raman scattering spectrum (Raman), and photoluminescence spectrum (PL). The experiment results show that ZnO nanorods synthesized by this method possess hexagonal wurtzite crystal structure with good crystallization, no other impurity phases are observed, the crystalline size is about 18 nm, and the lattice constant distortion occurs compared to that of bulk ZnO. The morphology of the sample is a rod-like shape, the length ranges from 100 nm to 300 nm, the average diameter is approximately 20 nm, and the aspect ratio is relatively high. The UV-VIS absorption spectrum occurs red shift, The Raman spectrum further demonstrates that the major peaks are assigned to ZnO optical vibrational modes, and the PL spectrum exhibits coexistence properties of ultraviolet (UV) and green emission. The results prove that ZnO nanorods with hexagonal wurtzite crystal structure were successfully prepared by the anodic arc plasma method in an oxidizing atmosphere.

Modeling and numerical simulation of anode activity and arc motion in a transverse magnetic field

Vacuum interrupters based on transverse magnetic field contacts now are widely used in medium voltage circuit breakers. The arc motion under the transverse magnetic field (TMF) plays a decisive role in the interruption. In this paper, we focus on the movement of vacuum arc driven by TMF and anode thermal process during the arcing. Then, based on the principle of conservation, a transient two-dimensional anode activity model (subjected to TMF constricted arc) is established. The state change of material, evaporation from contacts and motion of molten pool are also considered in our model. By considering the arc motion in the anode activity model, the transient anode thermal process and the movement of constrict arc under TMF are studied, respectively. The simulation predicted that average speed of arc is not higher than 200m/s. In the simulation, the anode surface is completely melted near the current peak with 200 μm molten layer. In addition, the influence of movement of molten pool on the arc speed is analyzed, finding that the movement of the bath accelerates arc speed, but weakens the surface melting at the same time.

Anode Temperature Evolution in a Vacuum Arc With a Blackbody Electrode Configuration

The anode in a vacuum arc with a blackbody assembly was measured as a function of time. A 30-mm-diameter Cu cathode and a hollow Ta anode, 50 mm in diameter, were used for a plasma cavity. Cu plasma was ejected through an array of 250 holes of 0.6 mm diameter in the anode. The arc currents were $I = 175$ , 200, and 225 A and the arc duration was 160 s. The anode temperature was measured using high-temperature thermocouples in the top and side of the anode. The anode temperature increased sharply during a transient time of ~70–90 s and then, it slightly increased with time up to 160 s reaching at 1650 K ( $I = 175$ A) and 1850 K ( $I = 225$ A) at the top, and 150–200 K less in the side.

Stable synthesis of few-layered boron nitride nanotubes by anodic arc discharge

Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. To sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of ~100 A/cm2, is above the boron melting point (2350 K). With both electrodes made from the same boron-rich alloy, we found that the arc operation unstable due to frequent sticking between two molten electrodes and formation of molten droplets. Stable and reliable arc operation and arc synthesis were achieved with the boron-rich anode and the cathode made from a refractory metal which has a melting temperature above the melting point of boron. Ex-situ characterization of synthesized BNNTs with electron microscopy and Raman spectroscopy revealed that independent of the cathode material, the tubes are primarily single and double walled. The results also show evidence of root-growth of BNNTs produced in the arc discharge.

Plasma jet characteristics in vacuum arc with diffused cathode spot

Diffused vacuum arc, which is characterized by the absence of microparticles in cathode erosion products and by the irregular voltage oscillations, is considered to be a perspective plasma source for plasma reprocessing technology of spent nuclear fuel (SNF). The development of this technology requires data on ions energy in plasma jet. In this work parameters of plasma jet in diffused vacuum arc with a gadolinium cathode were studied by a retarding field analyzer, Langmuir and condensation probes. Gadolinium is regarded as a substance simulating SNF plasma. Ion energy spectrum was studied at arc currents of 30-75 A and voltages of 4-15 V at the distance of 20 cm above the arc anode. Dependencies of spectrum widths and most possible ion energies on arc voltages were obtained. The measured electron temperature was 2 eV, the maximum ion energy reached 70 eV. Experimental data were used to calculate adiabatic plasma expansion through the anode outlet.

Production of long, laminar plasma jets at atmospheric pressure with multiple cathodes

Plasma jets from conventional non‐transferred arc plasma devices are usually operated in turbulent flows at atmospheric pressure. In this paper, a novel non‐transferred arc plasma device with multiple cathodes is introduced to produce long, laminar plasma jets at atmospheric pressure. A pure helium atmosphere is used to produce a laminar plasma jet with a maximum length of >60 cm. The influence of gas components, arc currents, anode nozzle diameter, and gas flow rate on the jet characteristics is experimentally studied. The results reveal that the length of the plasma jet increases with increasing helium content and arc current but decreases with increasing nozzle diameter. As the gas flow rate increases, the length of the plasma jet initially increases and then decreases. Accordingly, the plasma jet is transformed from a laminar state to a transitional state and finally to a turbulent state. Furthermore, the anode arc root behaviours corresponding to different plasma jet flows are studied. In conclusion, the multiple stationary arc roots that exist on the anode just inside the nozzle entrance are favourable for the generation of a laminar plasma jet in this device.

Direct Observation of Anode Arc Root Behaviors in a Non-transferred Arc Plasma Device with Multiple Cathodes

To investigate the anode arc root behaviors, a non-transferred arc plasma devices with multiple cathodes is designed in this paper. A novel setup to investigate the dynamics of arc root is developed. Based on high speed photography and voltage waveform analysis, anode arc root behaviors are captured for the steady, takeover and restrike arc modes. The transition of a single arc root, the coexistence of multiple arc roots and the evolution of multiple arc roots are herein investigated. Results show that anode arc root behaviors for these three arc modes are quite different. The restrike, takeover and steady modes correspond differently to the longitudinal motion of single root, circumferential motion of a single root and stationary multiple arc roots, respectively. Moreover, contrary to past experimental results, the stationary multiple arc roots which exist on the anode just within the nozzle entrance and the process by which they form, are demonstrated for the first time.

Analysis of plasma characteristics and conductive mechanism of laser assisted pulsed arc welding

This study aims to investigate the arc plasma shape and the spectral characteristics during the laser assisted pulsed arc welding process. The arc plasma shape was synchronously observed using a high speed camera, and the emission spectrum of plasma was obtained by spectrometer. The well-known Boltzmann plot method and Stark broadening were used to calculate the electron temperature and density respectively. The conductive mechanism of arc ignition in laser assisted arc hybrid welding was investigated, and it was found that the plasma current moved to the arc anode under the action of electric field. Thus, a significant parabolic channel was formed between the keyhole and the wire tip. This channel became the main method of energy transformation between the arc and the molten pool. The calculation results of plasma resistivity show that the laser plasma has low resistivity as the starting point of conductive channel formation. When the laser pulse duration increases, the intensity of the plasma radiation spectrum and the plasma electron density will increase, and the electron temperature will decrease.