Disk Cathode Research Articles

Optical Emission Spectroscopy of Cadmium Dominated Discharges Applied for Assessment of Explosion Protection

An assessment for the safe use of electrical equipment in explosive atmospheres can be performed with the aid of a spark test apparatus. Therefore, an anodic tungsten wire with 200 µm diameter is moved along the surface of a rotating cadmium disc (cathode). The explosion chamber enclosing the electrodes is filled with a highly explosive mixture of hydrogen and air. Depending on surface topology and relative movement of the contact pair, discharges occur randomly. A model contact device is used to investigate the plasma properties and the discharge characteristics near the thermo-chemical ignition threshold of the explosive atmosphere that typically occur at voltages around 30V and currents around 30mA.Spectroscopic investigations reveal that the emission of the discharges is dominated by atomic lines of cadmium, which allow the determination of distribution temperatures.

High-rate performance of binder-free LiFePO4 cathode prepared by using various types of conductive carbons

• A binder-free disc prepared by pressing the mixture of LiFePO 4 and holey graphene. • The binder-free disc has excellent electrical contact and flexibility. • The initial capacity of binder-free LiFePO 4 disc is 111.7 mAh cm -3 at the 1 C rate. • The binder-free LiFePO 4 disc exhibits excellent cycling stability in 150 cycles. A series of binder-free LiFePO 4 cathode discs prepared by dry-pressing the mixture of LiFePO 4 and various conductive carbon. Among those cathode discs, the cathode disc with thickness of 70 μm, prepared at the pressure of 334 MPa and composed of LiFePO 4 and layered holey graphene (CDLL-70 disc) exhibits the best electrochemical performance in the electrolyte of 1.0 mol L -1 lithium bis(trifluoromethanesulphonyl)imide and 0.1 mol L -1 LiNO 3 in ethylene glycol dimethyl ether: dioxolane in 1: 1 weight %. LiFePO 4 in the CDLL-70 disc exhibits the stable olivine structure (Space group: Pmnb, JCPDS 40-1499) after charge-discharged for 100 cycles. The CDLL-70 disc exhibits excellent electrical contact between LHG matrix and LiFePO 4 particles for homogeneous structure. The CDLL-70 disc exhibits the discharge capacity of 111.7 mAh cm -3 (138.2 mAh g -1 ) (1 st cycle) and 111.2 mAh cm -3 (137.5 mAh g -1 ) (150 th cycle), respectively. The capacity retention rate of the CDLL-70 disc in 150 cycles is 99.5%. Therefore, the CDLL-70 disc exhibits the excellent rate performance and cycle stability for its excellent flexibility.

Assessing the influence of calcium on X65 carbon steel pitting using an artificial pit

AbstractCorrosion products that form on carbon steel in sweet (CO2) environments can protect the steel by retarding interactions between the substrate steel and a corrosive electrolyte. Such protective films could become damaged at local sites leading to potential differences and the emergence of galvanic currents with the consequence of pitting in certain envfironments. The large protected surface (with a higher positive potential) becomes a cathode while the tiny exposed surface (with a lower positive potential) becomes the anode. Films formed in a Ca2+‐rich environment often comprise mixed calcium and iron carbonates in the form, CaxFe(1−x)CO3. This work utilized an artificial pit to investigate pitting under CaxFe(1−x)CO3 film conditions. Mixed carbonate films were grown on cathode discs (25‐mm diameter) for 96 h at pH 7.5, 50°C. Freshly polished anode pins were screwed onto the cathode disc and the galvanic currents were measured for 24 h. The anode/cathode area ratios were varied by using pins of 1, 2, and 3 mm diameter. Scanning electron microscope, X‐ray powder diffraction, and energy‐dispersive X‐ray were employed to examine the electrode surfaces after the test while surface profilometry was conducted to obtain pit profiles on the anode pins. Galvanic current increased with the addition of 682 ppm Ca2+ to the solution while pseudopassivation occurred under mixed calcium–iron carbonate films. The galvanic current was observed to drop as corrosion products formed on the anode electrode. Profilometry revealed the emergence of pits on the anode electrode. The pitting threshold was commensurate with the magnitude of the galvanic current density recorded.

A two-stage μCAT-MPD thruster: toward millinewton thrust

We discuss our efforts aimed at simultaneous improvement of the levels of thrust, thrust-to-power ratio (TPR) and efficiency of the two-stage micro-cathode arc thruster with magneto-plasma-dynamical second stage (μCAT-MPD). Such efforts include planar construction of the first stage (μCAT) with tightly-pressed ring anode and central disc cathode, enhanced hardness and durability of the inter-electrode dielectric gap provided by deposited boron-copper thin film, refractory (Mo) second-stage electrode, higher and stabilized second-stage voltage, and improved thermal isolation of the permanent magnet from the discharge area. Aforementioned features allowed achieve the average thrust of milli-newton range – up to 1.7 ± 0.3 mN, together with high TPR of 37 μN/W and efficiency of 50%, remaining low mass (~ 100 g) and low consuming power (~ 50 W) of the thruster.

Production of Iron Alloy by Direct Electrolytic Reduction Using Suspension Electrolysis in an Alkaline Electrolyte

Iron alloys were produced by suspension electrolysis in a 50 wt% NaOH–H2O electrolyte at 383 K, and Fe–Cr and Fe–Ni alloys were obtained using a suspension of Fe2O3+Cr2O3 and Fe2O3+Ni(OH)2 particles, respectively. Highly ordered columnar deposits comprising cubic Fe–Cr particles with approximately 5-micrometer-long sides were obtained on a disk cathode with a current efficiency higher than 90% at 100–300 mA･cm−2. In contrast, disordered columnar deposits of Fe–Ni particles with diameters of approximately 1.0 μm were obtained on a disk cathode with a current efficiency of approximately 50% at 200 mA･cm−2. The proposed method affords iron alloys with compositions in the stainless-steel region that depend on the electrolysis conditions, namely, the current density and Fe2O3/Cr2O3 or Fe2O3/Ni(OH)2 content ratio.

Magnetohydrodynamic modeling and simulation of a vacuum arc plasma jet with a ring anode under different external magnetic fields

Supersonic plasma has been widely used. A vacuum arc ion source provides one possible method for generating supersonic plasma. An external magnetic field can effectively avoid the wall loss of the plasma in the ion source and improve the ion yield. In this work, a two-dimensional magnetohydrodynamic model is established, considering different components including ions and electrons. With the help of simulation, we explore the physical characteristics of the supersonic vacuum arc plasma formed from a copper disk cathode. The characteristics that we focus on include plasma composition, current density distribution, plasma velocity, and plasma temperature. These characteristics as well as the ion yield are compared when different magnetic fields generated by solenoids near the cathode are applied, as well as when the arc current is different. The results show that, in the absence of an external magnetic field, ions expand freely with the approximate axial velocity and average ion charge state. With the increase of external magnetic flux density, the wall loss of the plasma will decrease, and the axial velocity and average ion charge state will increase, but the magnetic saturation phenomenon exists. The simulation results are consistent with the experimental results.

Investigating the interactions of hydrogen and nitrogen with the tantalum cathode of a novel ionization vacuum gauge with a straight path of electrons

The outgassing characteristics of a tantalum disk cathode mounted inside a novel ionization gauge were investigated in comparison to an yttrium-coated iridium-filament cathode mounted inside an extractor gauge. Both gauges were exposed to nitrogen or hydrogen at a pressure of 2.4 × 10−5 mbar, and the outgassing rates were measured periodically during subsequent pumping. For the novel ionization gauge, two contributions to the outgassing, i.e., the thermal outgassing from the cathode and the electron-stimulated desorption from the Faraday cup, were studied separately. The tantalum cathode showed rapid outgassing of nitrogen after exposure, while the outgassing after exposure to hydrogen was much lower. Hydrogen is mainly released from the Faraday cup when electrons collide with it. The extractor gauge showed a more-than-3-times higher outgassing rate after hydrogen exposure than after nitrogen exposure. The tantalum cathode and the Faraday cup in the novel ionization gauge showed absorption equilibrium after just 30 min.

Effect of Annealing and Ion Beam Irradiation on AC Electrical Properties for Gold Sputtered PM-355

Deposition of different gold thickness on PM-355 cleaned by ethanol forming thin films using magnetron sputtering. Gold layer with thickness 300, 400, 500, 700, 1000, 1300, and 1500 nm were deposited to prepare Au / PM-355 thin films. Then, ac electrical properties response of thin films for a wide frequency range 20Hz - 5MHz were measured at roomtemperature. Meanwhile, the measurements of ac conductivity, dielectric constant, and dielectric loss factor were plotted at different frequencies to determine the optimum thickness. Hence, the comparison was done between optimum Au thickness thin films cleaned by two organic solvents and ethanol before annealing at different frequencies. Also, study the effect of annealing and ion beam that extracted radially from conical anode and disc cathode ion source on optimum Au thickness thin film electrical properties. It is found that the annealing increases both dielectric constant, dielectric loss, and ac conductivity of optimum Au thin film at different frequencies. Despite, the nitrogen ion beam effected on these thin films by decreasing the dielectric constant and ac conductivity for all thin films except the chloroform one. Finally, study the comparison between the annealing and followed by ion irradiation thin films. It is noticed the decrease in ac electrical conductivity and dielectric constant at different frequencies.

Production of low-energy, high-current electron beams in a gun with a controlled explosive emission cathode

The operating characteristics of an electron gun with a controlled explosive emission cathode have been investigated. The multichannel initiation of explosive electron emission from the (copper disk) cathode occurs due to the use of simultaneously operating resistively uncoupled arc plasma sources built in the cathode. Three gun operation options were tested, namely with a vacuum, a gas-filled, and a plasma-filled diode. In the last case, a plasma anode was formed using a high-current reflective (Penning) discharge or a hybrid discharge combining a Penning discharge with vacuum arcs. The cathode unit has shown a high emissive power (a factor of 1.5–2 higher than that of a conventional gun with a plasma anode and a multiwire copper explosive emission cathode). Stable operation of the gun was observed at an accelerating voltage of amplitude 5–30 kV, in contrast to at least 17–20 kV required for stable operation of the conventional gun. The gun operation with a vacuum and a gas-filled diode provided a considerably more efficient energy transfer from the power supply to the electron beam.

Particle-in-Cell Simulation Studies of Electron and Ion Dynamics in Positive Polarity Rod-Pinch Diode

Flash X-ray (FXR) sources for dynamic radiography operate in different electron beam diode geometries depending on the applied voltage and impedance of the pulse power systems driving them. Rod-pinch (RP) diode is a suitable candidate for accelerating voltages up to few MeVs. It is desirable to have a small source size (0.5–3 mm) with a higher X-ray dose for a better figure of merit (FoM) “for short pulse” radiographic sources. A 3-D particle-in-cell (PIC) simulation study to optimize the RP source geometry for voltages in the range 0.8–3 MeV is presented here. Single disk and double disk cathodes were studied for the cathode to anode radius ratio of 10 and having a 1 mm anode radius. Comparison has been made with space charge–limited (SCL) model for cylindrical diode and critical current model for both single species electron only, as well as with both electron and ion PIC simulation. The electron current collected at the anode tip for single disk cathode and double disk cathodes has been compared for various accelerating voltages. Double-disk cathode with a 3 mm separation between the disks would provide better FoM as an X-ray source for operating voltages in the range 0.8–3 MV.

Metal-free nitrogen-doped graphenic materials as cathode catalysts for the oxygen reduction reaction in polymer electrolyte membrane fuel cells

Exhibiting a very high surface area, a good electrical conductivity and a high density of active sites, nitrogen-doped graphenic materials are considered as promising catalysts for the oxygen reduction reaction (ORR). Seldom studied in acidic media, N-doped graphenic foams were tested here as the cathode catalysts of a polymer electrolyte membrane fuel cell (PEMFC). The materials were prepared via a solvothermal-based process, by reacting either cyclohexanol and ethanolamine or 1-(2-hydroxyethylethyl) piperidine with metallic sodium, under high pressure and temperature. Membrane electrode assemblies were prepared with a Pt/C anode, 212 Nafion membrane, and an 8 mm disk cathode based on the graphenic materials. The performance exhibited by the PEMFC was evaluated using chronopotentiometry and impedance spectroscopy, depending on the synthesis conditions. The kinetic parameters of the ORR were estimated by interpretation of the experimental data: the high Tafel slope found might express the partial control of oxygen diffusion through the graphenic microporous structure. Relationships between the electrochemical behavior of the materials and their structural properties are discussed. Moderately crystallized materials with a low oxygen content showed the highest catalytic properties, with a current density larger than 30 mA cm−2 and a maximum power density at 2.3 mW cm−2.

Preliminary experimental research of a Ka-band radial transit time oscillator.

Radial transit time oscillator (RTTO) can be relied on to generate effective coherent electromagnetic radiation in the millimeter wave domain. In this paper, the preliminary experimental research on a Ka-band RTTO is reported for the first time. In experiments, the radial electron beam emitted from the knife edge of the disk cathode is guided by the radial magnetic field. The bombardment trace on the nylon target verifies the emission and transportation uniformity of the radial e-beam. When the diode voltage is 410 kV, the beam current is 7.8 kA, and the magnetic field is 0.6 T, the RTTO can output microwaves with the power of 320 MW and the frequency of 31.35 GHz. As the diode voltage increases from 350 kV to 430 kV, the output microwave power will grow accordingly. Taking the ohmic loss into consideration, the experimental results are in agreement with the simulation ones.

Operational characteristics of disc and spherical cathode electrodes in dc plasma discharge

In this work, the effective of shapes for disc and spherical cathode electrodes on the operational conditions of dc discharge has been studied. Paschen curve was studied of the two cathode shapes electrodes at the discharge voltage (0- 450 V) at 38 mm distance between the electrodes. Theoretically, the distributions of equipotential line and electric field before the minimum discharge voltage between the electrodes were estimated by using SIMION software. The study showed the effect of the geometry of the cathode electrode on the operational conditions where the discharge voltages require for the spherical shape was greater than the disc at minimum values in Paschen curve. The results showed a diagnostics of plasma using a single Langmuir probe that electron temperature and ion density for spherical cathode shape was higher than the disc by, 20% and 17.9% respectively.

Simulator of Planar Electrodes Plasma Characteristics using Different Gases

Simulator Plasma Source for Planar Electrodes, SPSPE, is designed to verify the experimental results of planar anode and cathode which are obtained previously using nitrogen gas. Experimentally, the glow discharge is carried out at operating pressure values in the range of 0.1- 0.6 Torr and the disc anode - disc cathode distance equal to 10 cm using nitrogen gas. The comparison between SPSPE and the experimental values at different product of pressure and distance values for breakdown voltage, discharge current and the second Townsend coefficient using nitrogen gas is made. It is found a good match between SPSPE and the experimental values. Also, the first Townsend coefficient is calculated by SPSPE at different product of pressure and distance values using nitrogen gas, while breakdown voltage and discharge current are calculated by SPSPE at different product of pressure and distance values using nitrogen, argon and carbon dioxide gases. It is found that the minimum breakdown voltage values are equal to 472.77, 232.26 and 349.27 volts at minimum product of pressure and distance values equal to 1.5, 1 and 0.75 Torr.cm using nitrogen, argon and carbon dioxide gases, respectively. Also, it is found that the minimum discharge current values are equal to 0.5228 mA and 3.65 mA at minimum product of pressure and distance value equal to 1 Torr.cm using nitrogen and argon gases, respectively. While minimum discharge current value equal to 7.8 mA is obtained at minimum product of pressure and distance value equal to 0.75 Torr.cm using carbon dioxide gas.

A study of zirconium plasma flow generated by a vacuum arc evaporator

In the industry of hard coatings, the vacuum arc evaporator is one of the commonly used devices due to its high productivity, reliability and ability to operate in a non-gaseous medium. Apart from this, the imposition of an external magnetic field allows to control the localization of the arc spots both on the simple and sectioned (i.e. made from different materials) cathode surfaces. Another important feature of the vacuum arc evaporators is their capability to generate multi-charged ions. Applying a high voltage negative bias to the substrate, there can be formed the coatings with high adhesion due to the implantation effect. This paper presents some results of the study of the plasma flows generated by an industrial vacuum arc evaporator with a sectioned disk cathode composed of a zirconium in its central part with a titanium ring surrounding it. The mode of evaporator functioning is such that the arc spot motion gets limited by the zirconium disk, which results in producing the zirconium plasma flow. The quantitative characteristics and the energy distribution function of ions have been measured by a multigrid probe with a retarding potential. It has been proved that the multiply charged ions make up a significant part of the flow. The relations between the detected ion components are found as 87.4% Zr+, 10.6% Zr2+, 1.5% Zr3+ and 0.3% Zr4+. The presence of multi-charged ions is also confirmed by optical spectrometry measurements.

Characterization and optimization of low-energy broad-beam ion source

In this work, a cold-cathode ion source was modified to produce a broad beam that could be successfully used in a variety of applications. The ion source features gave reliable, long-term, maintenance-free operation. The ion source was surrounded by a magnetic field to produce uniform plasma in limited volume at low gas pressures (10−3 torr). The output ion beam current was up to 700 μA, and the diameter of the cold cathode was broad (∼25 mm). The stainless steel cathode disk and the cylindrical anode were separated by a Teflon flange. The fabrication of the source was simple, and a stable discharge medium was obtained by adjusting the operating conditions, such as discharge voltage, magnetic field intensity and argon (Ar) gas pressure. Also, the output ion beam was measured at different acceleration voltages. Moreover, the ion beam profile is characterized at different magnetic field intensities.

Accurate controlled deposition of silver nanoparticles on porous silicon by drifted ions in electrolytic solution

In this study, a low-cost, simple, single-step low-voltage operation and a well-controlled method for deposition of uniformed and unique size distributions of silver nanoparticles (AgNPs) on the porous silicon (PS) layer were achieved via controlling the drift velocity of electrons in an aqueous solution of AgNO3. The laser diode of 530 nm and 60 mW/cm2 laser wavelength and illumination power density was employed to prepare PS layer by a laser-assisted etching process. The PS layer was incorporated on the platinum disk cathode electrode, and a stainless steel plate as an anode was employed. Low applied operating voltage of about 3V DC at different drift currents of 10, 20, 30 and 40 mA for 2 min was applied to sustain the drift motion of Ag2+. Structural properties of AgNPs layer were examined via the field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) pattern. These measurements exposed that AgNPs were adjusted by controlling the drift current, and a uniform AgNPs with specific unique sizes were obtained. Grain size, specific surface area and nucleation sites of metallic AgNPs were intensely influenced by the drift current.

Control the deposition uniformity using ring cathode by DC discharge technique

Simulation of direct current (DC) discharge plasma usingCOMSOL Multiphysics software were used to study the uniformityof deposition on anode from DC discharge sputtering using ring anddisc cathodes, then applied it experimentally to make comparisonbetween film thickness distribution with simulation results. Bothsimulation and experimental results shows that the deposition usingcopper ring cathode is more uniformity than disc cathode

Optimizing the Position of a Rotating Substrate during Magnetron Deposition of Thickness-Uniform Coatings

An analytical model of the sputter deposition on an inclined flat rotating substrate, which is shifted relative to the magnetron, is developed for a magnetron with a disk cathode. The angular distribution of sputtered atoms, the profile of the cathode erosion zone, and the energy efficiency of sputtering that were measured directly on the magnetron, were used as the initial data. The magnetron was used to verify the results of calculations. This made it possible to indirectly take such effects as scattering and diffusion of the sputtered material during its transport to the substrate into account, as well as the design features of the magnetron. The calculation and experimental verification of its accuracy were carried out for Cu. The results of the numerical analysis of the presence of such a substrate position, which is optimal according to the criterion of the maximum sputtered-material transfer to the substrate, are presented. It was shown that there is only one set of optimal positioning parameters that meet this requirement. A comparative analysis of the efficiency of material transfer with and without a substrate tilt was performed. It was shown that a tilt provides a significant (more than 60% for the magnetron used) increase in the material transfer. These results can be used to optimize the sputter deposition process with increased requirements for the thickness uniformity of a coating and for the complex development of the deposition equipment.

Synthesize of Silver Nanoparticles by Arc Discharge Method Using Two Different Rotational Electrode Shapes

Arc discharge technique was modified by using non-traditional rotational electrode and AC applied voltage. Two different systems were designed and locally fabricated to improve the properties of prepared yields. The rotational speed of the target, shape of the electrode and type of dielectric medium have a great effect on the yield, shape, size, stability and mass production. Ethanol as a dielectric medium was used in this study and compared with published works. The yields were characterized by Particle Size Analyzer, high-resolution electron microscope (HRTEM), inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), the ultraviolet–visible spectrophotometer (UV–Vis) and Zeta potential. All characterizations show that spherical silver nanoparticles are successfully produced for both systems. The results showed that the size of the nanoparticles prepared by cylindrical rotating electrode system is (23.45 ± 0.16) compared with those produced by disk rotating electrode system with size (26.83 ± 0.44). According to the obtained data the shape of the used cathodes was greatly affected the mass production rate of the nanoparticles, it was found that the rate in case of the cylindrical cathode was (46 ± 0.6 mg/min) compared with those prepared in case of disk cathode (34 ± 0.9 mg/min) and both rotational electrodes yielded more than simple arc discharge (23 ± 0.8 mg/min).