Current Density Measurements Research Articles

Characterization of a Multicusp Ion Source With Two-Grid Extraction System for Studying Extraction and Transport of Ion Beam

A low-energy multipole line cusp ion source with two-grid extraction system has been developed and characterized for studying the role of the charge exchange processes on ion beam extraction, transport, and neutralization. The ion source is operated for extraction of Ar <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ion beam of current 50–240 mA at energies 850–1650 eV. The characterization of the ion beam is carried out at various axial positions along a 200–815-mm beam path with a background pressure of 4– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−5</sup> Torr. An 11-channel Faraday cup array is used to measure the radial profiles of ion current density and angular beam divergence at these positions. The beam divergences are found to be in the range of 6°–15° for beam perveance of 0.50– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.75\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−9</sup> AV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3/2</sup> . The attenuation of ion beam current along the beam path is observed due to the charge exchange neutralization of the energetic ions in the presence of high background pressure. Since ion current density along the beam path can be reduced by both the charge exchange processes and beam divergence, the accounting of beam particles, i.e., energetic ions and neutrals, at larger distances is difficult by the measurements of ion current density using the Faraday cup alone. The flux of energetic particles (energetic ions and fast neutrals) is therefore obtained by a thrust measurements on a beam target fixed at a distance of 800 mm from the ion source. The neutralization of the ion beam obtained by the emission of electrons from a hot filament neutralizer is also investigated in the presence of the charge exchange processes. Space-charge neutralization is provided initially by the secondary electrons emitted from the vessel walls or by the charge exchange processes even without the neutralizer operating at the desired temperature. However, the current neutralization is achieved only by the electrons emitted from the hot filament neutralizer operating in a space-charge-limited mode.

Distribution of ion pairs into a bilayer lipid membrane and its effect on the ionic permeability.

This work reports the distribution constant of a target ion and a counter-ion between an aqueous phase and an artificial bilayer lipid membrane (BLM) and its influence to the ionic permeability through a BLM. A theoretical formula for ionic permeability through a BLM based on the distribution of the target ion and the counter-ion is also proposed and validated by analyzing the flux of a fluorescent cation [rhodamine 6G (R6G+)] through the BLM in the presence of counter-ions (X- =Br-, BF4-, and ClO4-). The transmembrane flux was evaluated by simultaneous measurement of the transmembrane current density and the transmembrane fluorescence intensity as a function of the membrane potential. The distribution constant of R6G+ and X- between the aqueous and BLM phases was determined by a liposome-extraction method. The measured ionic permeability exhibited non-linear dependent on the aqueous concentration of R6G+ or X-, but proportional to the concentration of R6G+ and X- inside the BLM evaluated from the distribution constant of R6G+ and X-. The proportionality demonstrates that the distribution of cations and anions between the aqueous and BLM phases dominates the flux of ion transport through the BLM. The proposed formula can express the dependence of the transmembrane current on the membrane potential and the concentrations of R6G+ and X- in the aqueous phase.

Effect of Temperature and Cl- Concentration on the Catalytic Activity of a Stainless-Steel Oxide

Galvanic couples between high-strength, noble metal fasteners, such as those made out of titanium or stainless-steel, can cause extensive damage in aluminum alloy airframes. These galvanic couples can drive higher rates of oxidation than would be expected for general corrosion and the corrosion damage can become a stress concentration point for the nucleation of cracks. Understanding the factors that govern the catalytic activity for the oxygen reduction reaction on stainless-steel oxides is important for enabling predictions of the amount of corrosion that can occur for a given set of environmental conditions. We have focused on measurements of the diffusion limited current density for oxygen reduction on UNS S13800 stainless-steel in solutions of varying NaCl concentrations from 0.1 M to 4.6 M and air temperatures ranging from 10oC to 40oC. Estimates of the oxygen diffusion limited current were obtained from potentiodynamic polarization measurements under the various electrolyte concentrations and environmental conditions. The experimental data was then compared with calculated ilim values for the same conditions and assuming a constant diffusion layer thickness. Regression and physics-based models for the effect of environmental conditions on the experimental data have been developed and are used to estimate the effect of the electrolyte on the stainless-steel oxide.The U.S. Naval Research Laboratory sponsored this work under work unit 1L66. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Office of Naval Research, the U.S. Navy, or the U.S. government.

Enhancement of inverted organic solar cell parameters by post-production annealing process

The post-production thermal annealing process of the polymer photoactive layer of organic solar cells at ideal temperatures is one of the crucial factors for solar cell performance since the photovoltaic performance of polymer-based organic solar cells is strongly affected by thermal annealing of the photoactive layer. In this study, inverted organic solar cells with enhanced efficiency using a blended poly (3-hexyl-thiophene) (P3HT) and phenyl C61butyric acid methyl (PCBM) subjected to post-production thermal annealing have been reported. The confocal Raman and atomic force microscopy measurements were performed to obtain the information about the material properties and surface morphology of electron selective layer of ZnO and polymer photoactive layer of P3HT:PCBM. To find out the ideal temperature for annealing, the post-production heat treatment procedure was applied to the polymer photoactive layer in between 90 °C and 210 °C by 20 °C steps. The current density versus voltage (J-V) measurements of Glass/ITO/ZnO/Polymer/MoO3/Ag devices showed that the application of post-production heat treatment to the polymer photoactive layer with a temperature of around 150 °C significantly enhanced the solar cell parameters of devices. The power conversion efficiency (PCE) values were calculated as 1.90% and 3.91% for the reference device without annealing and the annealed device at 150 °C, respectively. Additionally, it was observed that the performance of the solar cell increased due to the decrease in R S value and the increase in the roughness of the polymer surface with annealing process.

Semianalytical modeling of the mass transfer in microfluidic electrochemical chips.

This paper reports a mass transfer model of a reactant flowing in a large aspect ratio microfluidic chip made of a channel with electrodes on the side walls. A semianalytical solution to the two-dimensional Fickian diffusion of a reactant in a microchannel, including the electrochemical reaction at the electrode interface and the velocity profile obtained from the Navier-Stokes equations in a fully developed laminar regime, is found. The solution is written in the Laplace domain in terms of transfer functions. The proposed solution is an extension of the Lévêque approximation describing the reactant diffusion from the electrode to the middle of the microfluidic channel. The main applications of this work are the use of the obtained transfer functions for the measurement of the Faradic current density or the chemical concentration at the electrode interface. The study can also be extended to the heat transfer in microfluidic electrochemical chips (temperature or heat flux measurements at the electrode interface).

Mass flux and current density distributions of electrospray plumes

Performance and lifetime analysis of electrospray thrusters requires accurate knowledge of the mass and charge distributions of the plume. Mass flux and current density distributions were measured for a single capillary electrospray emitter using EMI-Im and found to be substantially different across a wide range of flow rates and emission voltages. Mass flux measurements yield an n∼3 super-Gaussian profile across all flow rates and voltages, while current density measurements change shape from n∼1.5–2.5 super-Gaussian profiles monotonically with decreasing flow rate, where n=1 is Gaussian and higher n values correspond to increasingly more flat-top “super-Gaussian” profiles with steeper drop-off toward higher angles. For increasing flow rate, the mass flux profile grows while maintaining its shape, whereas the current density profile exhibits higher kurtosis, i.e., plumes that distribute proportionately more charge to higher angles. Additionally, higher extraction voltages exhibited tilted emission that led to highly off-axis plumes, ∼10°, for both mass flux and current density. Lifetime and performance assessments of electrospray thrusters must consider that mass flux and current density in the plume display different distribution shapes and trends in shape across changes in extraction voltage and flow rate.

Current density and temperature distribution measurement and homogeneity analysis for a large-area proton exchange membrane fuel cell

Homogeneous distribution of electro-chemical reaction rates among the activation surface is critical for improving the performance and durability of automotive proton exchange membrane fuel cells (PEMFCs). Segmented measurement technology is commonly used to characterize the local physical-parameter distribution in the PEMFC. In this study, the local current density (LCD) and temperature distributions of a PEMFC with the activation area of 108 cm2 and various cathode flow fields are experimentally investigated. A homogeneity parameter is introduced to evaluate the homogeneity of LCD distribution. The results show that the performance and LCD distribution uniformity of the cell with dot-parallel flow field are much better than that with parallel and parallel-serpentine flow fields. The temperature distribution is generally positively correlated with LCD distribution. For the LCD distribution, the high LCD region firstly appears in the cathode downstream region, and gradually transfers upstream with increasing the current load. With the increase of inlet humidity, the LCD near the cathode inlet is improved due to the improvement of membrane hydration. Increasing the cathode stoichiometry can effectively improve the uniformity of LCD distribution, and mitigate the local oxygen starvation, especially at high loads.

Application of Bayesian optimization for high-performance TiO /SiO /c-Si passivating contact

We report on the application of Bayesian optimization (BO), which could accelerate the time-intensive process optimization of many parameters, to fabrication of the high-performance titanium oxide/silicon oxide/crystalline silicon passivating contact. The process contains pre-deposition treatment to form SiOy interlayer, atomic layer deposition (ALD) of TiOx, and hydrogen plasma treatment (HPT) as post-process. We attempted to optimize seven parameters for ALD and HPT by dealing with samples treated by three kinds of chemical solutions in the same batch. This permits to perform BO for each structure at the same time and determine the superior pre-deposition treatment. Consequently, carrier selectivity S10 estimated by independent measurements of the saturation current density and contact resistance was significantly improved by BO of only 12 cycles and 10 initial random experiments. These results certify that BO could efficiently provide experimental conditions in multidimensional parameter space although we need to consider the impact of the metallization process on the passivation performance.

Nonlinear Magnetic Gradients and Complete Magnetic Geometry From Multispacecraft Measurements

AbstractTopological configurations of the magnetic field play key roles in the dynamics of space plasmas. This study presents a novel algorithm that can estimate the quadratic magnetic gradient as well as the complete geometrical features of magnetic field lines, based on magnetic field and current density measurements by a multiple spacecraft constellation at four or more points. The explicit estimators for the linear and quadratic gradients, the apparent velocity of the magnetic structure and the curvature and torsion of the magnetic field lines can be obtained with well‐predicted accuracies. The feasibility and accuracy of the method have been verified with two demonstrations. The algorithm has been successfully applied to exhibit the geometrical structure of a flux rope. This algorithm has wide applications for studying a variety of magnetic configurations in space plasmas.

Dose measurement in the TEM and STEM

Practical aspects of dosimetry are considered, including the measurement of electron-beam current and current density. Complications that arise in the case of a focused probe or a STEM image are discussed and solutions proposed. Advantages of expressing the radiation dose in Grays are listed and a simple formula given for converting electron fluence to Gray units, based on a near constancy of the stopping power per atomic electron. Comparisons with stopping-power calculations and EELS measurements suggest that this formula is accurate to within 5%. Based on the stopping power formula, a new way of measuring the local mass-thickness of light-element specimens is proposed. The average energy loss per inelastic collision is shown to be higher than previous expectations.

A Dynamic Multi-Scale Model for Solid Oxide Cells Validated on Local Current Measurements: Impact of Global Cell Operation on the Electrodes Reaction Mechanisms

A dynamic physically based model has been developed to unravel the complex relationships between the overall Solid Oxide Cells (SOCs) response and the reaction mechanisms taking place in the electrodes. This numerical tool combines modules for different length-scales from the electrode microstructure up to the single repeat unit. First, models have been developed to emulate digital twins of electrode microstructures made of the classical SOCs materials [1]. The microstructural properties of the active layers and the current collectors are then computed on the synthetic volumes and used as inputs in the electrochemical models. The microscale models for the active layers take into account the mass and the charge transport phenomena for the solid and gas phases. For each electrode, the proposed reaction mechanism is split in a sequence of elementary steps with different pathways that can be activated depending on the polarization [2, 3]. The electrode models are finally coupled with a macroscopic description including the cell geometry and the design of the gas channels [4]. This model allows computing the cell polarization curves, the overpotentials and the EIS together with the distribution of the local current density and gas composition in the single repeat unit. This multiscale model has been used to study a typical cell made of the classical SOCs materials: the electrolyte was in Yttria Stabilized Zirconia (YSZ) whereas the hydrogen and oxygen electrodes were respectively composed by a cermet of Nickel and YSZ (Ni-YSZ) and a composite of Lanthanum doped Strontium Cobaltite Ferrite and Ceria doped Gadolinium Oxide (LSCF-CGO). For this cell, the representativeness of the electrodes synthetic microstructures have been checked on reconstructions obtained by tomographic techniques. It has been shown that the synthetic electrodes reproduce accurately the real microstructures. Moreover, the models at the electrode level have been carefully validated on polarizations curves and Electrochemical Impedance Spectra (EIS) measured on symmetrical cells using a three-electrode setup. It is worth noting that the electrodes of the tested symmetrical cells were manufactured using the same materials and composition than the complete cell. Finally, a specific attention has been paid in this work to validate the approach with an original experimental setup allowing the measurement of the local current densities on the full cell without electrode segmentation. This setup is composed of nine symmetrical-spaced pins that perform the measurement of local polarization curves from the inlet to the cell outlet. A campaign of tests has been carried out in fuel cell and electrolysis mode with different temperatures and flow rates. A good agreement has been found between the experimental and simulated data. It has been shown that the model is able to reproduce the evolution of the local polarization curves with a higher current density at the cell inlet. Furthermore, the simulated EIS for the cell have been found to be consistent with the experimental ones. The fully validated model has been used to analyze the cell operation in electrolysis and fuel cell mode. The reaction pathways associated to the elementary steps in the active layers have been discussed depending on the position within the electrodes and the polarizations. This model will then be used to implement the degradation laws such as the Ni agglomeration and compute the loss of cell performances and the remaining useful lifetime [5]. Moreover, the model could be applied to interpret the evolution of the EIS upon operation.[1] H. Moussaoui, J. Laurencin, Y. Gavet, G. Delette, M. Hubert, P. Cloetens, T. Le Bihan, J. Debayle, Stochastic geometrical modeling of solid oxide cells electrodes validated on 3D reconstructions, Computational Materials Science. 143 (2018) 262-276.[2] F. Monaco, E. Effori, M. Hubert, E. Siebert, G. Geneste, B. Morel, E. Djurado, D. Montinaro, J. Laurencin, Electrode Kinetics of Porous Ni-3YSZ Cermet Operated in Fuel Cell and Electrolysis Modes for Solid Oxide Cell Application. Under review. [3] E. Effori, J. Laurencin, E. Da Rosa Silva, M. Hubert, T. David, M. Petitjean, L. Dessemond, E. Siebert, An elementary kinetic model for the LSCF and LSCF-CGO electrodes for solid oxide cells: impact of oxygen partial pressure and degradation on the electrode response. Under review. [4] J. Laurencin, D. Kane, G. Delette, J. Deseure, F. Lefebvre-Joud, Modelling of solid oxide steam electrolyser: Impact of the operating conditions on hydrogen production. Journal of Power Sources. 196 (2011) 2080-2093.[5] M. Hubert, J. Laurencin, P. Cloetens, B. Morel, D. Montinaro, F. Lefebvre-Joud, Impact of Nickel agglomeration on Solid Oxide Cell operated in fuel cell and electrolysis modes. Journal of Power Sources. 397 (2018) 240-251. Figure 1

Investigation of physical and structural properties of cs doped y1ba2cu3o7 superconductors

In this work, YBa2‑xCsxCu3O7‑δ (x= 0.05, 0.1, 0.2 and 0.3 wt. %) samples were prepared by using solid state reaction method. Some electrical, physical and structural properties of these compounds were examined by using SEM (scanning electron microscopy), XRD (X-ray diffraction), electrical resistivity, critical current density and AC susceptibility measurements, respectively. On the basis of the SEM measurements, it would seem that increasing the amount of Cs doping, the porous structures decrease and the grain size increases up to approximately 50 μm. Unit cell parameters were calculated by employing XRD measurements. On the basis of the data obtained from X-ray diffraction, Cs atoms displaced Ba atoms in the crystal structure. From the measurements of electrical resistivity at 80 K-120 K temperature, it was determined that the highest transition temperature was 91.5 K after addition of 0.05 wt. % Cs. The critical transition temperature was decreased by increasing the amount of Cs doping. Critical current density measurements on the same samples showed that as the amount of Cs doping increases, the values of Jc decrease. AC magnetic susceptibility measurements showed a sharper transition to the superconducting state in YBa2‑xCsxCu3O7‑δ (x= 0.05, 0.1, 0.2 and 0.3 wt.%) samples with the increase in the additive amount.

In situ detection of electrochemical reaction by weak measurement.

In the field of electrochemical energy storage systems, the use of in situ detection technology helps to study the mechanism of electrochemical reaction. Our group has previously in situ detected the electrochemical reaction in vanadium flow batteries by total internal reflection (TIR) imaging. In order to further improve the detection resolution, in this study, the weak measurement (WM) method was introduced to in situ detect the electrochemical reaction during the linear sweep voltammetry or the cyclic voltammetry tests with quantitative measurement of the absolute current density, which lays a foundation for replacing the TIR for two-dimensional imaging of electrochemical reactions in vanadium flow batteries, oxygen/hydrogen evolution reaction, surface treatments, electrochemical corrosion and so on.

A pluggable current collector for in-operando current measurements in all-vanadium redox flow batteries with flow field

Understanding current distribution in operating Vanadium redox flow batteries (VRFBs) is vital for improving battery design and performance as the non-uniform current density distribution is known as a major cause of the corrosion and side reactions in VRFBs. However, the existing method for current density measurement in the VRFB with flow field is complex and the rib conductive structure of graphite plate is changed which reduces the measurement accuracy and reliability. In this study, we propose a novel pluggable current collector for in-operando current distribution measurements which greatly simplifies the current density distribution measurement process in VRFBs with flow field. The new method relies on eight pluggable graphite units in a flow plate frame to replicate the actual serpentine flow field structure, thereby providing higher measurement reliability compared to the existing methods which are mostly invasive. Using the new method, current density distributions at different electrode compression ratios (CR) and inflow electrolyte rates are investigated. It is found that insufficient supplemental reactant in electrode border region is the main reason for the uneven current density distribution and the current density non-uniformity is intensified in the initial and final stages of cycling process. Increasing CR can improve the current density in the electrode core region. The overall current density uniformity in a VRFB with serpentine flow field can be enhanced by increasing the inflow electrolyte rate. The developed method is believed to facilitate the understanding of the coupled local reactions and transport processes and guide on the future design of VRFBs.

Local Two-Phase Flow and Performance in Polymer Electrolyte Water Electrolysis Cells

Over the past decade, investigations[1-3] have been carried out to better understand the two-phase flow characteristics within a polymer electrolyte water electrolyzer (PEWE) and optimize the porous transport layer (PTL) morphology to improve the system performance and efficiency. Zhang, et al.[3] used a high-speed camera and transparent cell to study the strong influence of temperature and current density on bubble growth rate. Ito, et al. [4] showed that PTL porosity has a minor effect on cell performance while pore diameter greatly influences performance. They categorized the type of two-phase flow experienced by an electrolyzer by using liquid/gas superficial velocity plots. Furthermore, they showed that bubble detachment diameter strongly influenced the two-phase flow regime at any operating point. In a similar direction, Majasan, et al.[5] showed that longer flow path length promotes gas accumulation and results in annular flow at high current density, negatively impacting cell performance. Immerz et al.[6] also suggested that increased local ionic resistance down-the-channel may be attributed to large bubble accumulation. Therefore, the impacts of two-phase flow characteristics on mass transport as well as ohmic losses need to be better understood.Although the serpentine flow-field is very useful to study transport phenomena within a PEWE, it is rarely used as in commercial and large-scale PEWE system; the parallel channel-land configuration is a more conventional flow-field architecture. Through this work we hope to understand how architectural features in the flow field impact local performance to inform next-generation design. Furthermore, this work focuses on characterizing the two-phase flow and bubble accumulation occurring within the PEWE and understanding its relationship with performance. Initial experimental results revealed that the parallel flow-field outperforms the triple serpentine flow-field at high (50 ml/min) flowrates as seen in Figure 1a. This may be caused by the shorter channel lengths that do not exacerbate bubble accumulation near the outlet. Preliminary calculations of the superficial gas/liquid velocities have supported this conclusion (Figure 1c). However, at lower flowrates the parallel flow-field was observed to underperform and exhibit severe mass transport limitations. We believe that the fluid velocity in the channels at these low flowrates (6 ml/min) was insufficient to facilitate proper bubble detachment at the channel/PTL interface. This led to the formation of a large and spread out region of mass transport limited current density as seen in figure 1b. In conclusion, insights into local two-phase flow characteristics and their impact on performance in a PEWE cell will be described in this presentation[1] Lopata, J., et al., Effects of the Transport/Catalyst Layer Interface and Catalyst Loading on Mass and Charge Transport Phenomena in Polymer Electrolyte Membrane Water Electrolysis Devices. Journal of The Electrochemical Society, 2020. 167(6): p. 064507 DOI: 10.1149/1945-7111/ab7f87.[2] Lopata, J.S., et al., Considering Two-Phase Flow in Three-Dimensional Computational Fluid Dynamics Simulations of Proton Exchange Membrane Water Electrolysis Devices. ECS Transactions, 2020. 98(9): p. 653-662 DOI: 10.1149/09809.0653ecst.[3] Li, Y., et al., In-situ investigation of bubble dynamics and two-phase flow in proton exchange membrane electrolyzer cells. International Journal of Hydrogen Energy, 2018. 43(24): p. 11223-11233 DOI: https://doi.org/10.1016/j.ijhydene.2018.05.006.[4] Ito, H., et al., Experimental study on porous current collectors of PEM electrolyzers. International Journal of Hydrogen Energy, 2012. 37(9): p. 7418-7428 DOI: https://doi.org/10.1016/j.ijhydene.2012.01.095.[5] Majasan, J.O., et al., Two-phase flow behaviour and performance of polymer electrolyte membrane electrolysers: Electrochemical and optical characterisation. International Journal of Hydrogen Energy, 2018. 43(33): p. 15659-15672 DOI: https://doi.org/10.1016/j.ijhydene.2018.07.003.[6] Immerz, C., et al., Local Current Density and Electrochemical Impedance Measurements within 50 cm Single-Channel PEM Electrolysis Cell. Journal of The Electrochemical Society, 2018. 165(16): p. F1292-F1299 DOI: 10.1149/2.0411816jes. Figure 1

Measurement and assessment of corona current density for HVDC bundle conductors by FDM integrated with full multigrid technique

This paper presents an intensive measurement and analysis of monopolar ionized fields in bundled high voltage direct current (HVDC) conductors using the finite difference method based on the full multigrid technique. The positive feature of this study is that it considers the comprehensive representation of the bundle conductor, unlike the existing studies that approximate the bundle conductor with an equivalent conductor radius. Firstly, the proposed method is compared with previous experimental results. Secondly, a flexible laboratory model for the bundled HVDC conductors is constructed. Thirdly, the laboratory model is exploited to validate the numerically computed current density distribution on the ground plane and corona current for different bundles’ numbers and different distances between bundles. Bundles of one, two, and four conductors are adopted in the experimental setup. For the same applied voltage, the results verified that the corona current decreases by increasing the bundles’ number and/or minimizing the spacing between bundles. Consequently, the obtained results confirmed that corona power losses can be minimized, without needing the traditional procedures that involve increasing either the conductor radius or its height above the ground. The results of the proposed numerical approach concurred well with the present and past laboratory results.

Modelling picosecond and nanosecond laser ablation for prediction of induced damage on textured SiNx/Si surfaces of Si solar cells

AbstractThis study investigated the laser‐induced damage arising from 266 and 532 nm laser ablation of SiNx films on alkaline textured Si surfaces with nanosecond and picosecond pulse durations using a combination of optical‐thermal simulations and measurements of carrier recombination current density. Simulations predict that the melting depth is limited to within 150 nm of the SiNx/Si surface after 266 nm ps laser irradiation due to the greater absorption in both the SiNx and Si resulting in more direct ablation, while temperatures exceeding the melting temperature of Si are predicted to extend up to 1000 nm into the Si substrate with 532 nm ps pulses leading primarily to spallation. Ablation of the SiNx by 266 nm ps irradiation is predicted to be more homogeneous on smaller sized pyramids due to the increased absorption of double‐bounce reflected light on the pyramid faces. This finding has implications for applications requiring uniform ablation of dielectrics on textured Si surfaces. Ablation of SiNx by the longer wavelength 532 nm ps pulses also increases carrier recombination compared to that incurred with 266 nm ps pulses due to the increased melting depth. Longer ns pulses result in less steep temperature gradients and, for 266 nm pulses, an increased melting depth compared to ps pulses. Consequently, shorter ps UV pulses are preferred for SiNx ablation on Si surfaces due to their reduced laser damage penetration, whereas the less steep temperature gradients resulting from ns 532 nm pulses are beneficial for laser doping to form selective emitters.

Enhanced Transport Critical Current Density of Tl-1212 Bulk Superconductor Added with Nickel-Zinc Ferrite Nanoparticles

High temperature superconductor Tl-1212 with nominal starting composition (Tl0.85Cr0.15)Sr2CaCu2O7-δ was prepared with high purity oxide powders using a solid state reaction method. Small amounts of nickel-zinc ferrite nanoparticles (Ni0.5Zn0.5Fe2O4) at compositions 0.01, 0.02, 0.05 and 0.10 wt. % were added into Tl-1212 superconductors. The effect of Ni0.5Zn0.5Fe2O4 nanoparticles’ addition on the critical temperature (Tc), transport critical current density (Jc), phase formation, and morphology was studied. The samples were characterized using electrical resistance measurement, transport critical current density measurement, powder X-ray diffraction method (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Zero-resistance critical temperature (Tc-zero) was found to rise from 97 K to 99 K with increasing Ni0.5Zn0.5Fe2O4 nanoparticles concentration. The highest value recorded for transport critical current density (Jc) was 3,120 mA/cm2 at 77 K, which exhibited by sample with 0.02 wt. % of Ni0.5Zn0.5Fe2O4 nanoparticles. All samples showed a dominant Tl-1212 phase and exhibited tetragonal lattice structure in the P4/mmm space group. SEM micrographs showed close-packed microstructure with low porosity. EDX mapping showed that Ni0.5Zn0.5Fe2O4 nanoparticles were well distributed in the Tl-1212 samples. This study demonstrated that Ni0.5Zn0.5Fe2O4 nanoparticles have functioned as effective flux pinning centers to Tl-1212 superconductors and thus significantly enhanced its Jc.

Internal cathodic protection to study the erosion‐corrosion of AISI 1018 carbon steel

AbstractSteel elbows used in pipelines carrying potash slurry may undergo material loss due to mechanical erosion and/or electrochemical corrosion. Cathodic protection was used to study the effects of flow velocity and slurry concentration on the protection current density required to maintain AISI 1018 carbon steel elbows at a set electric potential. A flow loop with a peristaltic pump was used to pump a slurry consisting of silica sand in a saturated potash brine through the steel elbows. The protection current density measurements were performed under varying slurry flow velocities of 2.5, 3.0, 3.5, and 4.0 m/s and varying slurry concentrations ranging from 0‐35 wt%. The results show maximum values of protection current density were required for mid‐range slurry concentrations. It is concluded that, within the parameters of study, high flow velocities require higher protection current density than low flow velocities. Furthermore, high flow velocities result in a local maximum protection current density being reached at lower slurry concentrations; conversely, a local maximum protection current density is reached at higher slurry concentrations in lower flow velocities. The contrast in local maximum protection current densities likely occurs due to additional particle‐particle collisions at higher velocities causing the maximum mass transfer rate of oxygen to be reached at lower slurry concentrations. SEM micrographs show that wear becomes more evenly distributed with increasing flow velocity due to the homogeneous distribution of particles in the flowing medium.

Effect of flue gas desulfurization gypsum addition on critical chloride content for rebar corrosion in fly ash concrete

The effect of flue gas desulfurization (FGD) gypsum addition on the critical chloride content (Ccrit) for rebar depassivation in fly ash concrete was studied. Open circuit potential and electrochemical impedance spectroscopy were employed for measurements of corrosion potential and corrosion current density, respectively. The results demonstrate that adding FGD gypsum decreases the Ccrit. Evolutions of corrosion potential and corrosion current density are found to obey a 3-parameter Weibull distribution. XRD analyses indicate that adding FGD gypsum facilitates the formation of ettringite phase, which increases the solid volume of hydrates. MIP results demonstrate that adding FGD gypsum decreases the critical pore diameter, which restrains the chloride transport. The improved chloride resistance can counterbalance the negative effect induced by the lower Ccrit, consequently postponing the corrosion initiation.