Current Density Measurements Research Articles

Characteristics of ECM polishing influenced by workpiece corner feature and electrolyte flow

When polishing workpiece with inner corner feature using electrochemical machining (ECM) process, the surface quality at corner area is much poorer than that at other areas, and the surfaces of upstream area and of downstream area are much different. In this paper, the characteristics of this corner area phenomenon was investigated. Since the current density has a great influence on the surface roughness in ECM process, understanding the current density distribution on workpiece surface helps to analyze the corner area phenomenon and clarify process characteristics. Current density distribution considering the influences of several factors such as corner shape and inter electrodes gap (IEG), bubbles and electrolyte flow, were obtained with simulation and verified by experiments. ECM polishing with different fillet radius of the corner under different current densities were carried out. The observation experiments of machining by-products flowing with electrolyte flushing between machining gap, as well as the measurement of current densities at different areas, were conducted. The experimental results showed accordance with the simulation results. It was found the corner shape greatly influence the current density thus the surface roughness at the corner area, while the transport and accumulation of gas bubbles with electrolyte flow is one of the main reasons for the difference of surface roughness between the upstream area and the downstream area.

Electrical, Structural, and Thermal Properties of Ferrite/Superconductor (Ni0.5Zn0.5Fe2O4)x/YBa2Cu3O7-δ) Nanocomposite Materials

The superconductor YBa2Cu3O7-δ (Y123) is prepared by the solid-state route, while the nanosized Ni0.5Zn0.5Fe2O4 (Ni-Zn ferrite) is synthesized via citric acid sol-gel technique. The composite material of the type (Ni0.5Zn0.5Fe2O4)x/YBa2Cu3O7-δ, where x = 0.00, 0.03, 0.10, and 0.50 wt%, is prepared by a modified solid-state method to study the effect of doping Ni-Zn nanosized ferrite on the superconducting, structure, and thermal properties of Y123. The prepared samples show Meissner effect which confirmed the presence of superconducting phase at liquid nitrogen temperature (77 K). The prepared samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersion of X-ray (EDX), infra-red (IR) spectroscopy, thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), DC resistance by four-probe, and critical current density measurements. It was found that by increasing Ni0.5Zn0.5Fe2O4 nanoparticles in the Y123 compound, the unit cell volume of the orthorhombic phase decreases, but the transition temperature Tc and critical current density Jc decrease for low doping (x = 0.03 wt%) then increase (x = 0.10 and 0.50 wt%) for Ni0.5Zn0.5Fe2O4 doped in Y123. The transport properties of the (Ni0.5Zn0.5Fe2O4)x/YBa2Cu3O7-δ composite as electrical resistance R, Tc, and Jc are interpreted according to Bean’s critical state model and charge-vortex interaction combined with vortex pinning in Y123 high-Tc mixed-state type-II superconductor. The critical current density Jc decreased for low doping of nanosized Ni-Zn ferrite into Y123 with ratio of 0.03 wt% and increased by increasing doping ratio to 0.50 wt%. The physical properties are improved by the coexistence of the superconductor Y123 and nanosized Ni-Zn ferrites in nanocomposite material.

Non-invasive time-resolved measurements of anomalous collision frequency in a Hall thruster

The time-resolved cross-field electron anomalous collision frequency in a Hall thruster is inferred from minimally invasive laser-based measurements. This diagnostic is employed to characterize the relationship between the dominant low-frequency “breathing” oscillations and anomalous electron transport mechanisms. The ion Boltzmann equation combined with a generalized Ohm's law is used to infer key quantities including the ionization rate and axial electric field strength which are necessary in computing the total electron cross-field collision frequency. This is accomplished by numerically integrating functions of velocity moments of the ion velocity distribution function measured with laser-induced fluorescence, in conjunction with current density measurements at a spatial boundary. Estimates of neutral density are used to compute the classical collision frequency profile and the difference in the total collision frequency, and this quantity describes the anomalous collision frequency. This technique reveals the anticipated trends in electron transport: few collisions in the acceleration region but a collision frequency approaching the cyclotron frequency farther downstream. The time-resolved transport profiles indicate that the anomalous collision frequency fluctuates by several orders of magnitude during a breathing cycle. At troughs in the discharge current, classical collisions may dominate; at peaks in the discharge current, anomalous collisions dominate. These results show that the breathing mode and electron transport are directly correlated. This finding is discussed with regard to existing numerical models for the breathing mode and interpretations of anomalous electron transport.

Design of the Synthetic Aperture Microwave Imager Upgrade for measurement of the edge current density on MAST-U

The Synthetic Aperture Microwave Imager (SAMI) has demonstrated the feasibility of 2D Doppler backscattering for measurement of the edge magnetic pitch angle on MAST and NSTX-U. The aim of SAMI-Upgrade (SAMI-U) is to build on this methodology to produce higher quality pitch angle data simultaneously in multiple spatial locations, enabling calculation of the edge current density. This movement from proof of principle to production quality necessitates several alterations to the design. There will be a fourfold increase in the number of antennas, as minimising the sidelobe level is key to ensuring maximum resolution in the reconstructed Doppler backscattered power map. SAMI-U will actively probe the plasma with two frequencies at the same time. These correspond to two different backscattering locations in the edge plasma which allows the edge current density to be calculated from the measured magnetic field vector. Dual-polarised sinuous antennas will be used in the array as they are planar and broadband. Polarisation separation is necessary for differentiation between the O-and X-mode cut off surfaces, as their locations can be separated by up to a few centimetres. Due to spatial constraints many of the components will be placed on a PCB behind each antenna. FPGAs will be used to stream the high data throughput, over 16 GB s−1, into PC memory.

Magnetic Levitation Control Based on Flux Density and Current Measurement

This paper presents an active magnetic levitation application that exploits the measurement of coil current and flux density to determine the displacement of the mover. To this end, the nonlinear behavior of the plant and the physical sensing principle are modeled with a finite element approach at different air gap lengths and coil currents. A linear dynamic model is then obtained at the operating point as well as a linear relation for the displacement estimates. The effectiveness of the modeling approach and the performance of the sensing and control techniques are validated experimentally on an active magnetic levitation system. The results demonstrate that the solution is able to estimate the displacement of the mover with a relative error below 3% with respect to the nominal air gap. Additionally, this approach can be exploited for academic purposes and may serve as a reference to implement simple but accurate active magnetic levitation control using low-cost, off-the-shelf sensors.

Investigation of the structural, magnetic and electrical properties of the Au doped YBCO superconductors

In this study, a systematic investigation of Au-added YBa2Cu3O7−x (YBCO) samples has been undertaken mainly to understand their structural, magnetic as well as electrical behavior. In order to get high quality of superconducting bulk samples, optimum preparation conditions have been provided. The bulk samples were produced by conventional solid state reaction method at 930 °C under the low oxygen atmosphere. The bulk samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive X-ray, dc electrical resistivity (ρ-T), critical current density and ac magnetic susceptibility measurements. The samples were carried out by means of powder X-ray diffraction for phase analyses, and lattice parameters, SEM for microstructure examinations. From XRD and SEM results, an increase in the intensity of main peaks and average grain size but a increase in the lattice parameter c with addition of Au in comparison with the unadded sample. In addition to this, onset-offset critical transition temperature ( $${T}_{c}^{on}, {T}_{c}^{off}$$ ) was determined from dc electrical resistivity ( $$\rho -T$$ ) as a function of temperature measurements. Moreover, the transition temperature (Tc) and the critical current density (Jc) are enhanced upon Au addition when compared with unadded YBCO superconductor sample. The increment of Au content decreased the transition temperature and the critical current density values. From the AC susceptibility measurements, inter-grain, intra-grain peak temperature and superconducting transition temperature were determined. The possible reasons for the observed improvements in structural, magnetic and electrical properties due to the Au addition in the YBCO samples were discussed by comparison with other studies about addition of transition metals in high temperature superconductors.

Anchored Cu2O nanoparticles on graphene sheets as an inorganic hole transport layer for improvement in solar cell performance

We study the effect of dependent Cu2O nanoparticles (NPs) to the graphene oxide sheets (DCG), on the performance of dye-sensitized solar cells and the electron lifetime. Aqueous Cu2O nanoparticles were prepared and anchored on the graphene sheets by arc discharge method and then used as a coating layer to increase the electron lifetime in photoanode. Results show that open-circuit voltage of the cell increases up to 0.7V by use of DCG/TiO2 as a photoanode. In addition, performance characterization of the prepared cells by current density versus voltage (J–V) measurements show that the fill factor (FF) and power conversion efficiency (η) increase from η = 1.5% and FF = 52% for TiO2 photoanode (as a reference) to η = 3.48% and FF = 65% for DCG/TiO2 photoanode. The electron lifetime of the prepared samples was measured by open-circuit voltage-decay measurement (OCVD). Results show that the open circuit voltage and the electron–hole lifetime increase as well for TiO2 /DCG photoanode. To explore the effect of electron–hole concentration on the cell performance, we perturbed the electron–hole generation rate by three different illuminations and then measured the OCVD. Results show that the timescale of power decay for TiO2/DCG photoanode in high illumination is about 150 s.

Synthesis of novel tetra (4-tritylphenoxy) substituted metallophthalocyanines and investigation of their aggregation, photovoltaic, solar cell properties

4-(4-tritylphenoxy) phthalonitrile was synthesized and characterized. Copper, zinc and cobalt phthalocyanines were obtained by reaction of 4-(4-tritylphenoxy)phthalonitrile with CuCl2, ZnCl2, CoCl2 metal salts. New compounds were characterized by using electronic absorption, nuclear magnetic resonance spectroscopy, infrared. The aggregation investigation for phthalocyanine complexes carried out in different concentrations tetrahydrofuran. Copper, cobalt and zinc phthalocyanines were used as sensitizers in dye-sensitized solar cell structures (DSSC) by growing on TiO2 coated on FTO (Fluorine doped Tin Oxide) conductive glass substrates. Current density (J) versus voltage (V) measurements were applied to investigate the photovoltaic properties of the synthesized complexes. The calculated power conversion efficiencies (η%) of the complexes using the obtained current density (J) versus voltage (V) curves show that these devices can be used as promising sensitizers in solar cell applications.

Estimating the performance of lithium beam measurements of current density and electron density in an H-mode pedestal.

The lithium beam is an effective diagnostic tool for investigation of stability and particle transport in the pedestal. It was used successfully to measure edge current density on DIII-D, achieving qualitative agreement with neoclassical models. Electron density profiles were also measured. Proposed upgrades will continue these measurements with higher reliability as well as explore edge current measurements using spectroscopy. The optics will be redesigned to optimize throughput and aperture broadening and to replace the photomultiplier tubes with avalanche photodiodes. The new system will yield detailed measurements of the pedestal, complementing existing diagnostics for investigating pedestal stability, edge localized mode cycle, and particle transport through the pedestal.

Light-driven water oxidation using hybrid photosensitizer-decorated Co3O4 nanoparticles

Cobalt nanoparticles (NPs) have been prepared by hydrogenation of the organometallic complex [Co(η3-C8H13)(η4-C8H12)] in 1-heptanol in the absence of any other stabilizer and then transformed into Co3O4 NPs using mild oxidative reaction conditions. After deposition onto glassy carbon rotating disk electrodes, the electrocatalytic performance of the Co3O4 NPs in water oxidation has been tested in 1M NaOH. The activity has been benchmarked with that of state-of-the-art Co3O4 NPs through electrochemically-active surface area (ECSA) and specific current density measurements. Furthermore, the covalent grafting of photosensitive polypyridyl-based RuII complexes onto the surface of Co3O4 NPs afforded hybrid nanostructured materials able to photo-oxidize water into O2, while steady-state and time-resolved spectroscopic measurements gave some further insight into kinetics and pertinent reaction steps following excitation. These first-row transition metal oxide hybrid nanocatalysts display better catalytic performance than simple mixtures of non-grafted photosensitizers and Co3O4 NPs, thus evidencing the advantage of the direct coupling between the two entities for the photo-induced water oxidation reaction.

Particle and heat flux diagnostics on the C-2W divertor electrodes.

A suite of diagnostics was developed to measure particle and heat fluxes arriving at the divertor electrodes of the C-2W experiment at TAE Technologies. The divertor electrodes consist of 4 concentric rings, each equipped with a bolometer, electrostatic energy analyzer, and thermocouple mounted at two opposing azimuthal locations. These probes provide measurements of the power flux to the divertor electrodes as well as measurements of the ion current density, ion energy distribution, and total energy deposition. The thermocouples also provide calibration points for inferring the heat deposition profile via thermographic imaging of the electrodes with a fast infrared camera. The combined measurements enable the calculation of the energy lost per escaping electron/ion pair, which is an important metric for understanding electron heat transport in the open field lines that surround the field-reversed configuration plasma in C-2W.

The influence of phosphoric acid migration on the performance of high temperature polymer electrolyte fuel cells

In high temperature polymer electrolyte fuel cells, phosphoric acid migration induces flooding of the anode gas diffusion layer at high current densities. The present study focuses on determining the influence of phosphoric acid flooding of the anode GDL on hydrogen mass transport limitations. Two methods for quantifying the performance losses at high current densities, related to acid migration, are discussed: anodic limiting current density measurements and electrochemical impedance spectroscopy. It is demonstrated that the limiting current measurements, the common method for determining transport resistances, is unable to detect the changes induced by acid migration, due to the transient time required when switching to the required low hydrogen concentrations, while EIS is able to capture the changes induced by acid migration because it is faster and less invasive. For diluted hydrogen, an increase of the transport resistance is measured, however the effect on the cell performance is negligible. The time constants for anode GDL flooding and de-flooding are determined based on the EIS data and found to be 8.1 ± 0.1 min for flooding and about 5.8 ± 0.9 min for de-flooding under the applied conditions.

Study of microstructure and magneto-transport properties in Bi1.6Pb0.4Sr2Ca3GdxCu4Oδ superconducting systems

The role of Gd addition in the Bi1.6Pb0.4Sr2Ca3GdxCu4Oy (x = 0.0, 0.1, 0.2, 0.3 and 0.4) system was examined by X-ray powder diffraction, scanning electron microscopy, critical current density (Jc) and magneto-transport measurements. The samples were fabricated by the conventional solid state reaction method. The analysis showed that the critical temperature (Tc) and hole number (p) of the materials decreased while the room temperature resistances increased with the addition of Gd. The resistance–temperature dependence for the low-resistance regions of the transition can be determined by the thermally activated flux flow model. The upper critical field [Hc2(T)] values calculated by using this model decreased with the addition of Gd. Furthermore, it was observed that the activation energy (U0) decreased both with the increase in the amount of Gd and applied magnetic field. The degradation of the superconducting properties of the samples may be related to the alteration of the structural, electronic and magnetic properties of the materials depending on the presence of the Gd ions. As a result, the decrease in the number of holes and the magnetic properties of Gd ions are thought to be the fundamental reasons for the deterioration of the superconducting properties of the materials. It has been observed that Gd additions from the microstructure studies of the materials affected the surface morphology negatively.

The electrical, magnetic and 57Fe Mössbauer studies of Al doped PrFeO3 polycrystalline materials

The structural, electrical, magnetic and 57Fe Mössbauer studies of sol-gel synthesized polycrystalline Pr1-xAlxFeO3 (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) samples are reported in this paper and the phase purity of the materials was confirmed from Rietveld refinement of XRD pattern. From the magnetization studies it is observed that the Al doping at Pr site changed the magnetic ordering of the system at both room and low temperatures. The observed isomer-shift values from room temperature Mössbauer spectroscopy confirmed the charge state of the Fe ions and magnetic ordering in the compounds. Leakage current is observed to decrease with Al doping in the present work. From the leakage current density (J-E) measurements, it is observed that the space charge limited conduction (SCLC) dominates the conduction in lower and higher field regions for all the samples.

Effect of Osmotic Pressure by Salt Concentration on Corrosion Resistance of Anti-Corrosive Paint

Recently, many types of constructional steels have been often exposed to severely corrosive environments due to acid rain with increasing environmental contamination. To control corrosion problems, a painting protection method has been widely applied to numerous constructional steels on land as well as offshore. Therefore, development of anti-corrosive paint with good quality of corrosion resistance is very important from an economical perspective. In this study, four types of anti-corrosive paint were coated to test specimens, and then, were immersed in various salt solutions (0.1, 3 and 9% NaCl solution) for 11 days. Corrosion resistance of these samples by effect of osmotic pressure with various salt concentration was investigated with electrochemical methods such as measurement of corrosion potential, impedance and corrosion current density. Corrosion current density of these samples submerged in 0.1% NaCl solution exhibited highest value than those immersed in 3% and 9% NaCl solutions because water, dissolved oxygen and chloride ion etc. is easily to invade towards inner side of coating film due to increasing osmotic pressure compared to 3% and 9% NaCl solutions. However, corrosion current densities of all samples in the case of submerged in 9% NaCl solution exhibited higher values compared to 3% NaCl solution.Thus, a large amount of chloride ion dissolved in 9% NaCl solution plays a more critical role in corrosion behavior of coated steel rather than osmotic pressure. Consequently, the corrosion mechanism between coated steel and bare steel plates is different from each other because of presence of osmotic pressure between salt solution and coating film of coated steel plate. As a result, corrosion resistance of tcoated steel plate may be depend on the osmotic pressure as well as salt concentration

Effective charge collection area during conductive and photoconductive atomic force microscopy

Conductive atomic force microscopy (C-AFM) has been widely used to map the nanoscale electrical properties of conducting polymers, nanomaterials, and organic electronic devices. While these measurements provide valuable insight into the spatial dependence of electrical performance, reported current densities and electrical conductivities measured by C-AFM are consistently much higher than those measured at the macroscopic scale. Here, we demonstrate that these anomalously high current densities and conductivities arise from ignoring current spreading and hence underestimating the current-carrying area. We present a simple experimental means of estimating the effective charge collection area during C-AFM measurements. Using semiconducting polymer poly(3-hexylthiophene) films as a test case, we find that the effective charge collection area can be as much as three orders of magnitude larger than the mechanical contact area between the probe and the film. Calibrated conductivity maps are obtained, with a quantitative correspondence with accepted values, and C-AFM photocurrent measurements of a nanostructured hybrid organic-inorganic solar cell active layer yield short-circuit current densities that match those reported for macroscopic devices. Finally, we address the observation that current spreading increases the effective charge collection area beyond the size of the probe-sample contact but does not preclude an imaging resolution below 10 nm.

Characterization of Atomic Layer Deposited Cobalt Oxide

The electrical, optical, and structural properties of cobalt oxide films deposited via atomic layer deposition using Co(Cp)2 and O3 are investigated. At 250 °C, growth is 0.50 Å per cycle and smooth uniform films are deposited across a 5" wafer with atomic force microscopy showing a root mean square roughness of 0.4 nm. Spectroscopic ellipsometry indicates a refractive index of approximately 2.8 at 632.8 nm while grazing incidence X-ray diffraction of as-deposited films shows cubic Co3O4, a p-type semiconducting phase. Semiconducting behavior is supported by current density versus electric field measurements.

Microstructural influence on ferroelectric domain pattern and piezoelectric properties of Na0.5Bi0.5TiO3 thin films

Sodium bismuth titanate (Na0.5Bi0.5TiO3: NBT) thin films were fabricated under various growth conditions (substrate temperature from 400 °C to 650 °C and oxygen pressures from 50 to 200 mTorr) by using pulsed laser deposition technique. The films grown at low partial pressures (< 100 mTorr) exhibited a preferred orientation along the <220> direction and at higher partial pressures (> 100 mTorr) exhibited polycrystalline nature. The microstructures were tuned from coarse faceted grains to fine spherical grains by varying the ambient pressures and the growth temperatures. The ferroelectric domain studies reveal that in case of fine spherical grains, the domain pattern was dominated by the surface morphological features and in the case of coarse faceted grain structure, domain features were independent of its morphology. Fast Fourier Transform (FFT) spectrum analysis of the domain patterns confirmed that only highly oriented films possessed periodic domain pattern and the periodicity is in the range of 140–240 nm. Further, the estimated piezocoefficient value (d33) increased from 16 to 31 pm/V with increasing the oxygen partial pressures (50–200 mTorr) and substrate temperatures (400–650 °C). The leakage current density measurements confirm that films grown at low partial pressures possess relatively larger leakage current density at room temperature.

Photoionization microscopy: Hydrogenic theory in semiparabolic coordinates and comparison with experimental results

Photoionization microscopy (PM) is an experimental method allowing for high-resolution measurements of the electron current probability density in the case of photoionization of an atom in an external uniform static electric field. PM is based on high-resolution velocity-map imaging and offers the unique opportunity to observe the quantum oscillatory spatial structure of the outgoing electron flux. We present the basic elements of the quantum-mechanical theoretical framework of PM for hydrogenic systems near threshold. Our development is based on the computationally more convenient semiparabolic coordinate system. Theoretical results are first subjected to a quantitative comparison with hydrogenic images corresponding to quasibound states and a qualitative comparison with nonresonant images of multielectron atoms. Subsequently, particular attention is paid on the structure of the electron's momentum distribution transversely to the static field (i.e., of the angularly integrated differential cross-section as a function of electron energy and radius of impact on the detector). Such 2D maps provide at a glance a complete picture of the peculiarities of the differential cross-section over the entire near-threshold energy range. Hydrogenic transverse momentum distributions are computed for the cases of the ground and excited initial states and single- and two-photon ionization schemes. Their characteristics of general nature are identified by comparing the hydrogenic distributions among themselves, as well as with a presently recorded experimental distribution concerning the magnesium atom. Finally, specificities attributed to different target atoms, initial states, and excitation scenarios are also discussed, along with directions of further work.

Self-validating electrochemical methodology for quantifying ionic currents through pipeline coatings

An enhanced electrochemical method for accurately measuring cathodic protection (CP) currents through protective coatings has been developed as a means of quantifying the permeability and ‘cathodic shielding’ characteristics of nominally intact coating films. This method takes advantage of the fact that cathodic currents could significantly affect the alkalinity of areas under disbonded coatings to self-validate the correctness of current density measurements. In addition, the method provides a high level of accuracy and control over the environment. The method was evaluated using a series of ideally CP-shielding and non-CP-shielding materials, as well as, commercial pipeline coatings. A robust correlation of the measured current with generation of hydroxyl ions and the local alkalinity was established in all cases. For some commercial field joint epoxy pipeline coatings, results suggest that low CP levels could allow sufficient ionic current through a coating to promote a high-alkalinity local environment. However, this may not be the case for fusion-bonded epoxy coatings, which shielded CP and maintained a near-neutral pH under the coating.