Increasing Discharge Voltage Research Articles

Influence of processing parameters on the characteristics of surface layers of low temperature plasma nitrocarburized AISI 630 martensitic stainless steel

Plasma nitrocarburizing was performed on solution-treated AISI 630 martensitic precipitation hardening stainless steel samples with a gas mixture of H2, N2, and CH4 with changing temperature, discharge voltage and amount of CH4. When nitrocarburized with increasing temperature from 380 °C to 430 °C at fixed 25% N2 and 6% CH4, the thickness of expanded martensite (α'N) layer and surface hardness increased up to 10 μm and 1323 HV0.05, respectively but the corrosion resistance decreased. Though the increase of discharge voltage from 400 V to 600 V increased α'N layer thickness and surface hardness (up to 13 μm and 1491 HV0.05, respectively), the treated samples still showed very poor corrosion behavior. Thus, to further improve the corrosion resistance, the influence of variation of the amount of CH4 in the nitrocarburizing process was investigated. Increasing the CH4 percentage aided higher corrosion resistance, although it decreased the α'N layer thickness. The most appropriate conditions for moderate α'N layer thickness, high surface hardness and better corrosion resistance than the solution-treated bare sample were established, which is plasma nitrocarburizing at 400 °C with 400 V discharge voltage and containing 25% N2 and 4% CH4.

Discharge voltage behavior of electric double-layer capacitors during high-g impact and their application to autonomously sensing high-g accelerometers

In this study, the discharge voltage behavior of electric double-layer capacitors (EDLCs) during high-g impact is studied both theoretically and experimentally. A micro-scale dynamic mechanism is proposed to describe the physical basis of the increase in the discharge voltage during a high-g impact. Based on this dynamic mechanism, a multi-field model is established, and the simulation and experimental studies of the discharge voltage increase phenomenon are conducted. From the simulation and experimental data, the relationship between the increased voltage and the high-g acceleration is revealed. An acceleration detection range of up to 10,000g is verified. The design of the device is optimized by studying the influences of the parameters, such as the electrode thickness and discharge current, on the outputs. This work opens up new avenues for the development of autonomous sensor systems based on energy storage devices and is significant for many practical applications such as in collision testing and automobile safety.

Discharge reliability in ablative pulsed plasma thrusters

Discharge reliability is typically neglected in low-ignition-cycle ablative pulsed plasma thrusters (APPTs). In this study, the discharge reliability of an APPT is assessed analytically and experimentally. The goals of this study are to better understand the ignition characteristics and to assess the accuracy of the analytical method. For each of six sets of operating conditions, 500 tests of a parallel-plate APPT with a coaxial semiconductor spark plug are conducted. The discharge voltage and current are measured with a high-voltage probe and a Rogowski coil, respectively, to determine whether the discharge is successful. Generally, the discharge success rate increases as the discharge voltage increases, and it decreases as the electrode gap and the number of ignitions increases. The theoretical analysis and the experimental results are reasonably consistent. This approach provides a reference for designing APPTs and improving their stability.

Preparation of silver-based solder foils by low-voltage magnetic pulsed compaction

Cadmium-free silver-based solder foils were fabricated using mechanically alloyed powders containing 56% silver–22% copper–17% zinc–5% tin by low-voltage magnetic pulsed compaction (LV-MPC) followed by liquid-phase sintering. The effects of processing parameters, such as discharge voltage, capacitance, coil turns, diameter–height ratio and compacting times, of LV-MPC on both the green density and the sintered density of compacts were analysed. The results showed that the green density increased with increasing discharge voltage, capacitance and coil turns. The green density also increased with increasing compacting times and diameter–height ratio, but the effect was relatively small because of the small filling height of the powder. The minimum thickness of solder foils fabricated by LV-MPC was approximately 0·2 mm. After sintering for 0·5 h at 480°C, the changing tendency of sintered density with different processing parameters was similar to that of green density with the same processing parameters. However, antidensification occurred and the sintered density declined slightly. The maximum relative densities of the samples after LV-MPC and liquid sintering were approximately 89 and 87% respectively.

Behavior of the S-phase of plasma nitrocarburized 316L austenitic stainless steel on changing pulse frequency and discharge voltage at fixed pulse-off time

Abstract A plasma nitrocarburizing process was carried out in a high pulse frequency regime, like 25 kHz and higher on AISI 316L austenitic stainless steel at different conditions, to observe the effect on S-phase layer formation with changing pulse frequency and duty factor. The S-phase layer thickness and hardness increase slightly with increasing the pulse frequency. And they also change slightly with increasing the duty factor up to 80%, but beyond 80%, their values remains almost the same. Considering the results of these experiments, further investigation was done with fixing the pulse-off time in order to explore the behavior of the nitrogen- and carbon-enriched layer formation. So, by fixing pulse-off time, different experiments were conducted with changing the pulse frequency in the high-frequency region and discharge voltage to analyze the behavior of the nitrogen- and carbon-enriched layers of plasma nitrocarburized 316L austenitic stainless steel. After treatment, the behavior of the nitrogen- and carbon-enriched layers were investigated by optical microscopy, micro-Vickers hardness testing, roughness testing, X-ray diffraction and potentiodynamic polarization testing. At a fixed pulse-off time, there is a slight increase in surface hardness along with carbon-enriched layer thickness and nitrogen-enriched layer thickness with increasing pulse frequency. However, the surface roughness does not increase very much with increasing the pulse frequency. The hardness difference and layer thickness difference between high and low pulse frequency, decreases with increasing the pulse-off time because of the minimizing effect of the duty factor. On the other hand, at a fixed pulse-off time, the thickness of the carbon-enriched layer increases sharply with increasing discharge voltage, though the nitrogen-enriched layer thickness does not change much. Hardness also increases sharply with increasing discharge voltage. Moreover, corrosion resistance decreases with increasing discharge voltage due to chromium-nitride formation.

Effect of high-energy electro-pulses on the compression deformation behavior of Ti-6Al-4V alloy

Compression tests of Ti–6Al–4V alloy were conducted using an electron universal testing machine with discharge voltages that range from 50 V to 70 V and strain rate of 0.01 s−1. Isothermal compression at equivalent temperatures was also performed on a universal testing machine with furnace, with the same strain rate. Results show that the deformability of Ti–6Al–4V alloy can be significantly improved by high-energy electro-pulses, and the deformation resistance and yield stress were also decreased. Moreover, the effect of high-energy electropulses on compression mechanical properties of Ti–6Al–4V alloy increased with increasing discharge voltage. However, elongation and deformation resistance of compressions with high-energy electro-pulses were higher than isothermal compressions at equivalent temperatures. This result proved that the deformability improvement of Ti–6Al–4V alloy by high-energy electro-pulses results from the joint effects of temperature and electro-plasticity. Fracture modes in different experimental conditions were analyzed by observing the fracture morphologies of specimens by using a scanning electron microscope. Under high-energy electro-pulses, the micro morphology of compression fracture changes from elongated oval to equiaxed dimples, and the fracture modes transfer from intergranular to transgranular fracture.

Influence of the electrode gap separation on the pseudospark-sourced electron beam generation

Pseudospark-sourced electron beam is a self-focused intense electron beam which can propagate without any external focusing magnetic field. This electron beam can drive a beam-wave interaction directly or after being post-accelerated. It is especially suitable for terahertz radiation generation due to the ability of a pseudospark discharge to produce small size in the micron range and very high current density and bright electron beams. In this paper, a single-gap pseudospark discharge chamber has been built and tested with several electrode gap separations to explore the dependence of the pseudospark-sourced electron beam current on the discharge voltage and the electrode gap separation. Experimental results show that the beam pulses have similar pulse width and delay time from the distinct drop of the applied voltage for smaller electrode gap separations but longer delay time for the largest gap separation used in the experiment. It has been found that the electron beam only starts to occur when the charging voltage is above a certain value, which is defined as the starting voltage of the electron beam. The starting voltage is different for different electrode gap separations and decreases with increasing electrode gap separation in our pseudospark discharge configuration. The electron beam current increases with the increasing discharge voltage following two tendencies. Under the same discharge voltage, the configuration with the larger electrode gap separation will generate higher electron beam current. When the discharge voltage is higher than 10 kV, the beam current generated at the electrode gap separation of 17.0 mm, is much higher than that generated at smaller gap separations. The ionization of the neutral gas in the main gap is inferred to contribute more to the current increase with increasing electrode gap separation.

Numerical and experimental investigation of inward tube electromagnetic forming

In this work, experimental and numerical simulation of high-speed inward forming of tubes on a die in electromagnetic forming (EMF) system using a compression coil is presented. A 2D axi-symmetric electromagnetic model is used to calculate magnetic field and magnetic forces. Modified loose-coupled simulations of electromagnetic and structural aspects of EMF process are reported and emphasized in this paper. During the simulation, in each time step, the transient magnetic forces are obtained from the electromagnetic model and used as input load to the mechanical model. Based on the calculated deformation, in each step, the tube geometry in the electromagnetic model is updated to calculate the electromagnetic forces in proceeding step. Tube material, AA 6061-T6, is assumed to obey the Johnson-Cook (J-C) rate-dependent model. Displacement and thickness variations of workpieces along the tube length are presented and discussed experimentally and numerically. The results demonstrate that various workpiece zones could be thickened or thinned based on various process parameters. In addition, it is seen that the increase of discharge voltage decreases the thickness at die radius and reverses the thickening trend at tip of the bead.

Effect of the Discharge Voltage on the Performance of the Hall Thruster**supported by National Natural Science Foundation of China (Nos. 11375039 and 11275034) and the Fundamental Research Funds for the Central Universities, China (Nos. 3132014328 and 3132015142)

In this paper, a two-dimensional physical model is established according to the discharging process in the Hall thruster discharge channel using the particle-in-cell method. The influences of discharge voltage on the distributions of potential, ion radial flow, and discharge current are investigated in a fixed magnetic field configuration. It is found that, with the increase of discharge voltage, especially during 250-650 V, the ion radial flow and the collision frequency between ions and the wall are decreased, but the discharge current is increased. The electron temperature saturation is observed between 400-450 V and the maximal value decreases during this region. When the discharge voltage reaches 700 V, the potential distribution in the axis direction expands to the anode significantly, the ionization region becomes close to the anode, and the acceleration region grows longer. Besides, ion radial flow and the collision frequency between ions and the wall are also increased when the discharge voltage exceeds 650 V.

Study of the Electrical Characteristics, Shock-Wave Pressure Characteristics, and Attenuation Law Based on Pulse Discharge in Water

Strong shock waves can be generated by pulse discharge in water. Study of the pressure characteristics and attenuation law of these waves is highly significant to industrial production and national defense construction. In this research, the shock-wave pressures at several sites were measured by experiment under different conditions of hydrostatic pressure, discharge energy, and propagation distance. Moreover, the shock-wave pressure characteristics were analyzed by combining them with the discharge characteristics in water. An attenuation equation for a shock wave as a function of discharge energy, hydrostatic pressure, and propagation distance was fitted. The experimental results indicated that (1) an increase in hydrostatic pressure had an inhibiting effect on discharge breakdown; (2) the shock-wave peak pressure increased with increasing discharge voltage at 0.5 m from the electrode; it increased rapidly at first and then decreased slowly with increasing hydrostatic pressure; and (3) shock-wave attenuation slowed down with increasing breakdown energy and hydrostatic pressure during shock-wave transfer. These experimental results were discussed based on the mechanism described.

Multi-scale dynamics in externally excited glow discharge plasma

Time series analysis of fluctuations excited due to external perturbation in a dc glow discharge plasma system is presented. Analysis shows that the observed data is non-Gaussian in nature and has purely deterministic behavior. The oscillations are bi-periodic in nature without any occurrence of chaos with increasing discharge voltage. Two dominant frequencies 100 KHz and 200 KHz with background noise are observed. The Hurst coefficient is also evaluated for the data sets and is seen to be greater than 0.5 for all the cases. The observed bi-periodic oscillations have their origin due to some nonlinearities in the system. The observed frequencies are found to be due to ionization instability and ion acoustic instability.

Regeneration of Acid Orange 7 Exhausted Granular Activated Carbon Using Pulsed Discharge Plasmas**supported by National Natural Science Foundation of China (No. 21207052), China Postdoctoral Science Foundation (No. 20110491353) and Jiangsu Planned Projects for Postdoctoral Research Funds, China (No. 1102116C)

In this paper, a pulsed discharge plasma (PDP) system with a multi-needle-to-plate electrodes geometry was set up to investigate the regeneration of acid orange 7 (AO7) exhausted granular activated carbon (GAC). Regeneration of GAC was studied under different conditions of peak pulse discharge voltage and water pH, as well as the modification effect of GAC by the pulse discharge process, to figure out the regeneration efficiency and the change of the GAC structure by the PDP treatment. The obtained results showed that there was an appropriate peak pulse voltage and an optimal initial pH value of the solution for GAC regeneration. Analyses of scanning electron microscope (SEM), Boehm titration, Brunauer-Emmett-Teller (BET), Horvath-Kawazoe (HK), and X-ray Diffraction (XRD) showed that there were more mesopore and macropore in the regenerated GAC and the structure turned smoother with the increase of discharge voltage; the amount of acidic functional groups on the GAC surface increased while the amount of basic functional groups decreased after the regeneration process. From the result of the XRD analysis, there were no new substances produced on the GAC after PDP treatment.

Experimental and numerical research on process formability in magnetic pulse forming of AZ31 magnesium alloy sheets

The plain strain of AZ31 magnesium alloy sheet in magnetic pulse forming was investigated by numerical simulation and experimental method. Combination of uniform pressure coil and Holmberg’s specimen was employed to evaluate the plain strain of AZ31 sheet. The numerical simulation for magnetic pulse plain strain of AZ31 sheet is performed by means of ANSYS FEA software. The magnetic flux density of uniform pressure coil was distributed uniformly, especially at the center of gauged area of AZ31 sheet directly in relation to the deformation behavior of AZ31 sheet. The velocity of typical point increases as increasing energy, and the more position closes to the center of sheet the higher velocity achieves. The forming height is increased with increasing discharge voltage. Compared with C=768 µF and C=1536 µF, the capacitance of 1152 µF is more effective for forming, which is confirmed by experiments. The peak velocity at the center of sheet is about 105 m/s. The major strains of magnetic pulse plane strain lie approximately in the strain ranges of 5.83-6.45%. However, the 3.22-3.82% (major strain) are the limit strains in quasi-static condition. The experimental results indicate that the major strain of AZ31 sheet improves about 75% compared with the quasi-static case.

Experimental investigation on plasma-assisted combustion characteristics of premixed propane/air mixture

A detailed study on the plasma-assisted combustion (PAC) characteristics of premixed propane/air mixture is presented. The PAC is measured electrically, as well as optically with a multichannel spectrometer. The characteristics are demonstrated by stable combustion temperature and combustion stability limits, and the results are compared with conventional combustion (CC). Stable combustion temperature measurements show that the introduction of PAC into combustion system can increase the stable combustion temperature, and the increment is more notable with an increase of discharge voltage. Besides, the rich and weak limits of combustion stability are both enlarged when plasma is applied into the combustion process and the increase of discharge voltage results in the expansion of combustion stability limits as well. The measurements of temperature head and emission spectrum illustrate that the kinetic enhancement caused by reactive species in plasma is the main enhancement pathway for current combustion system.

Microstructure evolution during magnetic pulse welding of dissimilar aluminium and magnesium alloys

Microstructure evolution has been investigated for magnetic pulse welding of dissimilar aluminium and magnesium alloys using optical microscopy, laser confocal microscopy and electron backscatter diffraction. The welded joints were made with discharge voltages of 4kV, 4.5kV and 5kV and they are characterised by the aluminium region, the weld interface and the magnesium region. The interfacial waves become more regular and much smoother with increasing discharge voltage from 4kV to 5kV. The grains were extremely refined and the grain size became larger with increasing distance to the weld interface at a discharge voltage of 5kV. The gradual grain refinement closer to the weld interface can be attributed to dynamic recrystallization. Different recrystallization behaviour was observed for the aluminium region and the magnesium region near the weld interface. The occurrence of the extension twinning {1 0 1¯ 2} in the dynamic recrystallized grains indicating twin related dynamic recrystallization behaviour in the magnesium region near the weld interface.

Investigation and quantification of nonlinearity using surrogate data in a glow discharge plasma

Detection of nonlinearity has been carried out in periodic and aperiodic floating potential fluctuations of DC glow discharge plasma by generating surrogate data using iterative amplitude adjusted Fourier transform method. We introduce “delay vector variance” analysis (DVV) for the first time, which allows reliable detection of nonlinearity and provides some easy to interpret diagram conveying information about the nature of the experimental floating potential fluctuations (FPF). The method of false nearest neighbourhood is deployed on the FPF's to find a good embedding so as to be acquainted with the precise knowledge of m, which is desirable for carrying out DVV analysis. The emergence of nonlinearity with increase in discharge voltage has been ensured by taking into consideration the total energy present in different band of frequencies excited due to nonlinear processes. Rejection of null hypothesis has been verified by performing the rank test method that confirms the presence of nonlinearity quantitatively.

Gap current voltage characteristics of energy-saving pulse power generator for wire EDM

The characteristics of the gap current voltage are directly used to estimate the gap status and are helpful in understanding the gap discharge mechanism and in adjusting the process parameters in wire electrical discharge machining (WEDM). Current and voltage waveforms were studied to analyze the gap current voltage characteristics of an energy-saving pulse power generator during a discharge pulse period. The discharge voltage was increasing with discharge time, and the gap current waveform was triangular other than the traditional rectangular waveform. A gap detection model of the energy-saving pulse power generator was established to analyze further the gap current voltage characteristics theoretically. Experiment analysis of different workpiece materials and current peak values showed that the gap discharge voltage and short circuit voltage continuously increase. The triangular waveform and increasing discharge voltage were caused by the increasing gap current in the process because the sustaining voltage was absent in the discharge status. And the gap current voltage characteristics were nonlinear.

Enhanced charge efficiency and reduced energy use in capacitive deionization by increasing the discharge voltage

Capacitive deionization (CDI) is an electrochemical method for water desalination using porous carbon electrodes. A key parameter in CDI is the charge efficiency, Λ, which is the ratio of salt adsorption over charge in a CDI-cycle. Values for Λ in CDI are typically around 0.5–0.8, significantly less than the theoretical maximum of unity, due to the fact that not only counterions are adsorbed into the pores of the carbon electrodes, but at the same time coions are released. To enhance Λ, ion-exchange membranes (IEMs) can be implemented. With membranes, Λ can be close to unity because the membranes only allow passage for the counterions. Enhancing the value of Λ is advantageous as this implies a lower electrical current and (at a fixed charging voltage) a reduced energy use. We demonstrate how, without the need to include IEMs, the charge efficiency can be increased to values close to the theoretical maximum of unity, by increasing the cell voltage during discharge, with only a small loss of salt adsorption capacity per cycle. In separate constant-current CDI experiments, where after some time the effluent salt concentration reaches a stable value, this value is reached earlier with increased discharge voltage. We compare the experimental results with predictions of porous electrode theory which includes an equilibrium Donnan electrical double layer model for salt adsorption in carbon micropores. Our results highlight the potential of modified operational schemes in CDI to increase charge efficiency and reduce energy use of water desalination.

고효율 백색 발광다이오드 구현을 위한 고점도 형광체 정량 토출 공정 연구

Currently various studies are underway for dispensing high-viscosity phosphor. These studies have reported limita- tions and challenges in the dispensing process. The discharged amount of phosphor was approximately the same each time which is important for the implementation of high-efficiency white LED technology. This paper present high-viscosity phosphor dis- pensing process for white LED implementation by using electrostatic printing technology. The voltage controlled DOD (Drop- On-Demand) discharge experiment was studied to determine angle of drop meniscus at nozzle and dot diameter. With increase in Discharge voltage, the discharge angle of meniscus increased while dot diameter decreased. Therefore it can be concluded that we can control the discharge rate by controling the discharge angle of meniscus.

Enhanced capacity for lithium–air batteries using LaFe0.5Mn0.5O3–CeO2 composite catalyst

LaFe0.5Mn0.5O3 and Ce-incorporated LaFe0.5Mn0.5O3 catalysts for Li–air batteries were synthesized by co-precipitation (CP) and micro-emulsion methods with the increasing Ce/(La+Ce) ratios from 0 to 0.5. Ce has a low solubility in LaFe0.5Mn0.5O3 perovskite lattices. Instead of forming single-phase La1−x Ce x Fe0.5Mn0.5O3 perovskite, a multi-phase LaFe0.5Mn0.5O3–CeO2 composite was obtained even for Ce/(La+Ce) = 0.05. Such catalysts were used in the cathode of Li–air batteries and the discharge test showed that LaFe0.5Mn0.5O3–CeO2 composite catalyst can effectively improve the specific capacity with the highest capacity of ~4700 mAh/g for Ce/(La+Ce) = 0.05 (by CP). There is also a 0.05 V increase in discharge voltage compared with the reference cell without catalyst, with the discharge voltage plateau at ~2.75 V. The overall ranking in terms of capacity was Ce/(La+Ce) = 0.05 > Ce/(La+Ce) = 0.1 > Ce/(La+Ce) = 0.5 > Ce/(La+Ce) = 0. The capacity increase for Ce/(La+Ce) = 0.05 and 0.1 samples is attributed to the enhanced oxygen storage/release capability and the increased conductivity with the incorporation of CeO2.