Parallel-plate Electrode System Research Articles

Electrochemical Redox Conversion of Formate to CO via Coupling Fe-Co Layered Double Hydroxides and Au Catalysts.

Formate has been considered an inactive molecule and thus cannot be further reduced under CO2 reduction conditions, which limits its widespread application as feedstock. Here we present an electrochemical redox conversion of formate to CO through the potential-dependent generation of carbon dioxide radical anions (CO2 ⋅- ) on Fe-Co layered double hydroxides (Fe-Co LDHs) and the subsequent reduction of CO2 ⋅- to CO on Au catalysts. We present an electrodeposition protocol for the synthesis of Fe-Co LDHs with precise composition control and find that Fe1 Co4 exhibits a promising potential window for CO2 ⋅- formation between 1.14 and 1.4 V and an optimized potential at 1.24 V at a neutral pH condition. We further determined the formation of CO2 ⋅- at 1.24 V via electron paramagnetic resonance and CO2 at >1.4 V through differential electrochemical mass spectrometry. This work provides a redox chemistry route for converting formate into CO through a coupled slit parallel-plate electrode system.

In situ resistivity measurement of metal surfaces to track down dislocations caused by high field conditioning

AbstractConditioning of a metal surface in a high-voltage system is the progressive development of resistance to vacuum arcing over the operational life of the system. This is relevant for accelerator cavities, where high level of performance is only achievable after a long conditioning period. Beyond the accelerator research field, this is an important topic for any technology where breakdowns can cause device failure, either by directly disrupting device operation or by causing cumulative hardware damage.We are developing a direct method to measure the surface resistivity of a metal surface that is being conditioned with a HV DC system by inducing a high frequency (GHz) radio-frequency current in the parallel-plate electrode system. If the system can function as a resonant cavity, the surface resistivity data would be encoded in its quality factor (Q-factor). The changes in the resistivity measured in cryogenic conditions would indicate a formation of dislocations under the surface, something that has been speculated as an important process behind the conditioning.In this paper, we present two modified designs of the electrode system, which will act as a resonant cavity, the results of 3D EM simulations and experimental results regarding the characterization of this resonant system.

Compact Flow-Through Electrochemical Cell - A Novel Perspective in Industrial Manufacture of Perchlorates

Background: Sodium Perchlorate is one of the major starting intermediate product for the manufacture of various Perchlorates viz, Ammonium perchlorate as solid oxidizer and Strontium Perchlorate as Secondary Injection Thrust Vector Control (SITVC) in launch vehicles. This critical product is manufactured industrially by electrochemical oxidation of Sodium Chlorate solution at the anodic surface. Lead dioxide is preferred in various perchlorate cells because of its low cost. Infrequent detachment of Lead dioxide deposits from the substrate during electrolysis is a grave issue confronted by associated electrochemists in bulk manufacture of chemicals. Moreover, a cheaper alternative for continuous manufacture of Sodium Perchlorate using Lead dioxide electrodes has been an onus among various industrial electrochemists. Objective/ Benefits: Development of a suitable compact flow through electrochemical cell using superfluous or detached Lead dioxide crystals as ‘particle’ electrodes is the major objective of this paper. This compact bed electrochemical cell, is extraordinarily helpful when confronting with lesser reactant concentration or time consuming reactions. Besides, this proposal adds on flexibility in trimming the size of cells when compared with bulky design of conventional cells. Another objective was to demonstrate continuous electrosynthesis of Sodium perchlorate using Lead dioxide without resorting to expensive Platinum. Method: A suitable single bed and a dual bed compact electrochemical cell was made using HDPE body, perforated Poly Propylene distributor, detached Lead dioxide particles, nylon mesh, etc. Four such dual bed cells were made for final demonstration for continuous electro synthesis application. Results: From various experimental trials, an optimum values for temperature, flow rate and current load were determined as 600°C, 800 mL/min and 80 A respectively, in single bed system. Inorder to avoid current penetration issue, dual bed cells were employed. Subsequently, critical operational strategy and systematic configuration for arrangement of dual bed cells were made for demonstrating continuous bed electrochemical cells. Conclusion An average current efficiency of about 78.5% could be achieved which is 20-25 % higher than conventional parallel plate electrode system.

Statistics of vacuum breakdown in the high-gradient and low-rate regime

In an increasing number of high-gradient linear accelerator applications, accelerating structures must operate with both high surface electric fields and low breakdown rates. Understanding the statistical properties of breakdown occurrence in such a regime is of practical importance for optimizing accelerator conditioning and operation algorithms, as well as of interest for efforts to understand the physical processes which underlie the breakdown phenomenon. Experimental data of breakdown has been collected in two distinct high-gradient experimental set-ups: A prototype linear accelerating structure operated in the Compact Linear Collider Xbox 12 GHz test stands, and a parallel plate electrode system operated with pulsed DC in the kV range. Collected data is presented, analyzed and compared. The two systems show similar, distinctive, two-part distributions of number of pulses between breakdowns, with each part corresponding to a specific, constant event rate. The correlation between distance and number of pulses between breakdown indicates that the two parts of the distribution, and their corresponding event rates, represent independent primary and induced follow-up breakdowns. The similarity of results from pulsed DC to 12 GHz rf indicates a similar vacuum arc triggering mechanism over the range of conditions covered by the experiments.

A Novel Method for Monitoring Hydration Process of Cement Paste Material

A new measurement system is developed to monitor the early hydration of cementitious materials based on measured dielectric properties of the material in low electromagnetic frequency range. The objectives of this paper were to evaluate the changes in the electromagnetic properties for samples with different fly ash content and to establish the reliability of the measurement technique by comparing with results obtained by traditional method such as thermal method that is either time consuming or impractical. The method adopted in the present experimental work is a parallel plate electrode system (PPES). The suggested monitoring device for concrete hydration and strength development is based on the relationship between the electromagnetic properties such as dielectric constant, loss factor and the strength development during hydration process and curing time. In this research the electromagnetic properties of concrete is found to be dependent on the hydration and strength of concrete. Therefore the development of microstructure and concrete compressive strength can be determined by monitoring its electromagnetic properties in the frequency range of 1 to 100 kHz.

Microbial inactivation utilizing impulse waveform

Inactivation of Escherichia coli has been successfully performed by the utilization of impulse voltage waveform. The process involves in microbial inactivation is pulsed electric field (PEF) treatment. PEF utilizes short-duration high-voltage pulses for microbial inactivation by the process of electroporation. Inactivation rate was measured against peak electric field, number of applied pulses, and energy input to unit volume of liquid. Two different electrode configuration spherical–spherical and parallel-plate electrode systems were used. The results indicate that parallel-plate electrode system results in better inactivation rate than spherical electrode system. With applied electric field of 24 kV/cm and 20 pulses, six log reductions were achieved in parallel-plate electrode system indicating that inactivation rate is strongly dependent on electrode configuration, peak electric field, and applied pulses.

Electrokinetic concentration and patterning of colloids with a scanning laser

Optically-based lab-on-a-chip systems have the distinct advantage of being dynamically controlled in real time, providing reconfigurable operations that can be tuned to perform a variety of tasks. This manuscript demonstrates the concentration of liquid-suspended microparticles using a focused near-infrared laser (980 nm) and a parallel-plate electrode system. The parallel-plate electrodes consisted of an indium tin oxide-coated coverslip and a gold-coated glass substrate. When the laser was applied at 36 mW, the indium tin oxide surface is locally heated creating sharp temperature gradients on the order of 0.07(o) C/μm. When an AC field was applied, electrothermal hydrodynamic forces generated microfluidic vortices. At an AC frequency of 40 kHz, the optically controlled electro-hydrodynamics aggregated colloids at the center of fluid motion on the surface of the indium tin oxide coverslip. The nature of colloid aggregation, translation, and patterning was explored when the translational velocity of the laser spot was varied. This manuscript describes the design of the laser scanning system using commercially available components and the fabrication of the parallel-plate chip. The effect that the laser scanning rate has on the heat transfer, fluid velocity, and colloid aggregation is discussed.

Improving cranberry shelf-life using high voltage electric field treatment

Cranberries ( Vaccinium macrocarpon Aiton) were treated with high voltage electric fields (HVEF) of 2, 5 or 8 kV cm −1 in strength for 30, 60 or 120 min in a parallel plate electrode system. The treated berries were stored at ambient conditions (23 °C and 65% RH) for three weeks to study the effect of treatments on their respiration rate, physiological loss of mass (PLM), colour, total soluble solids (TSS) and skin puncture strength. Resulting respiration rates were in the range of 11.69–14.56 mL CO 2 kg −1 h −1 after the first week of storage, and increased to 13.95 and 21.33 mL CO 2 kg −1 h −1 by the end of third week. For both two and three weeks of storage, HVEF-treated cranberries showed significantly lower respiration rates than the control. This particular attribute indicates the potential of HVEF for improving shelf-life. The PLM of HVEF-treated cranberries were in the range of 23.2–30.4% after three weeks of storage. There was no significant difference between treated and untreated berries in terms of absolute L ∗, a ∗ and b ∗ colour values; however, the colour difference value Δ E ∗ab of treated berries was somewhat greater. The TSS content of various HVEF-treated cranberries was in the range of 7.27–7.69 °B, similar to the TSS content of untreated berries (7.4 °B) before storage. The skin puncture strength of different HVEF-treated cranberries was in the range of 11.7–14.3 N; while the untreated berries (11.2 N) showed lower values prior to storage.

Determination of moisture content of in-shell peanuts by parallel-plate impedance measurements in cylindrical sample holder

This paper describes a method to determine the moisture content of in-shell peanuts with a parallel-plate electrode system fitted inside a cylinder by using impedance measurements made on the system. Two parallel-plate electrodes were mounted inside a cylinder, made of acrylic material, and the space between the plates was filled with in-shell peanuts (80–100 g). The impedance measurements were made on the parallel-plate system at 1 and 9 MHz, and the average moisture content (MC) of the peanut pods (in-shell peanuts) was determined from a semi-empirical equation. The calculated MC values were compared with standard oven-determined values and were within 1% of the standard oven values for 90% of the samples tested in the moisture range between 6% and 19%. Two parallel-plate sensors with different plate separations and peanuts from the 2004 and 2005 harvests, were used in these measurements. The method, being rapid and nondestructive, is suitable for the development of a practical instrument for measurement of moisture content in in-shell peanuts.

A numerical modelling of microdischarge threshold in uniform electric fields

This paper deals with the novel idea of controlling the electric stress in a hybrid air–solid dielectric insulation. In a parallel-plate electrode system, the electric stress can be reduced if the electrodes are covered with thick non-conducting dielectric coatings. Free charges are generated by microdischarges developing between the electrodes and are deposited at the dielectric surfaces. As a consequence, a counteracting electric field component results, which causes a reduction of the electric field in the air gap and an enhancement of the field in the dielectric coatings; i.e. the electric stress is forced into the dielectric coatings by the charges. A computation of the threshold voltage of the microdischarges is presented. The charge simulation technique is used for field calculation, irrespective of the thickness of the dielectric layer and the values of the charges deposited on the dielectric surfaces. The calculated threshold voltages are compared with those estimated before analytically and those measured for different gap lengths.

Electric field and dielectrophoretic force on a dielectric particle chain in a parallel-plate electrode system

This paper presents results of calculations of the electric field and dielectrophoretic force on a dielectric particle chain suspended in a host liquid lying between parallel-plate electrodes. The method of calculation is based on the method of multipole images using the multipole re-expansion technique. We have investigated the effect of the particle permittivity, the tilt angle (between the chain and the applied field) and the chain arrangement on the electric field and force. The results show that the electric field intensification rises in accordance with the increase in the ratio of the particle-to-liquid permittivity, Γε. The electric field at the contact point between the particles decreases with increasing tilt angle, while the maximal field at the contact point between the particles and the plate electrodes is almost unchanged. The maximal field can be approximated by a simple formula, which is a quadratic function of Γε. The dielectrophoretic force depends significantly on the distance from other particles or an electrode. However, for the tilt angles in this paper, the horizontal force on the upper particle of the chain always has the direction opposite to the shear direction. The maximal horizontal force of a chain varies proportional to (Γε − 1)1.7 if the particles in the chain are still in contact with each other. The approximated force, based on the force on an isolated chain, has been compared with our calculation results. The comparison shows that no approximation model agrees well with our results throughout the range of permittivity ratios.

Photoinduced electro-motive-force of sulfur doped plasma CVD methane film

Plasma chemical vapor depositions using methane gas mixed with argon or hydrogen were carried out in a reaction chamber with a parallel plate electrode system at a discharge frequency of 13.56 MHz. A photocell of a transparent conductor-insulator-metal sandwich was fabricated. Photoinduced electro-motive-force was detected for the film when SF 6 gas was added in the mixture gas. The origin of electro-motive- force was supposed to be caused on the activated charge density gradient. The activation energy was about 3 eV, where doped sulfur induced acceptor in the film.

Charging of Glass Substrate by Plasma Exposure

It is probable that charge-up of a glass substrate during plasma processing such as ashing and/or etching deteriorates the production yield of thin-film transistor-liquid-crystal-display (TFT-LCD) devices. In order to keep the production yield at a high level, it is necessary to understand the charging mechanism of glass surface in plasma and then offer countermeasures for the process. We measured the surface potential of the glass substrate during plasma processing. We exposed the glass substrate to plasma in a parallel-plate electrode system by introducing Ar, O2 or SF6 gas into the plasma reactor and exciting with 13.56 MHz RF or DC power supply. As a result, we found that the charging of the glass substrate in plasma depended considerably on the power source and the gas species. We discussed the phenomenon in terms of the behavior of molecular ions in plasma.

Plasma Grafit Polymerized Styrene as an Electron-beam Resist

AbstractPlasma graft polymerized styrene was formed by a reactor with a parallel plate electrode system on a pulsed plasma polymerized styrene film in a monomer vapor, where the pulsed plasma polymerization was performed by a low frequency 100%pulse modulation of 13.56 MHz power source in styrene vapor. The pulse duration was varied in the range of 0.01∼1 sec and ON time/duty cycle ratio was 1/10 and 1/20. The processes were monitored by a quartz crystal microbalance. The initial stage of plasma polymerization and grafting are discussed in this paper. Also sub 100 nm lines and spaces pattern on the resist delineated by an electron-beam pattering machine was developed by hexane.

Effects of O2 and SF6 on CH4 Plasma CVD Film.

CH4 plasma CVD films were formed by a reactor with a parallel plate electrode system at a discharge frequency of 13.56MHz with using a mixture gas of CH4/H2 and H4/Ar. The deposition rates were measured as a parameter of gas pressure, and discharge power in order to discuss deposition mechanisms. The effects of O2 and SF6 addition in the mixture gases were also examined. Addition of oxygen gas in the mixture gas of CH4/H2 enhanced the growth rates, which were proportional to the radiation intensity ratio CH/Hα in the plasma. On the other hand, the addition of oxygen gas in the mixture gas of CH4/Ar decreased the growth rate. It was observed that oxygen atoms were extracted from the film during the process, however sulfur atoms were doped into the film. These experiments suggested the possibility of film property control.

Electrification of glass substrate surface by plasmas

It is probable that charge-up of a glass substrate during plasma processing, such as ashing and/or etching, deteriorates the production yield of TFT-LCD devices. In order to control the production yield, it is necessary to understand the electrification mechanism of glass surface in plasma and then offer countermeasure to the process. We measured the surface potential of the glass substrate during discharge. We exposed the glass substrate to plasma in a parallel-plate electrode system by introducing Ar, O 2 or SF6 gas into the plasma reactor and exciting with 13.56MHz RF or DC power supply. As a result, we found that the charging of the glass substrate in plasma was considerably affected by gas species and power sources. We discussed the phenomenon from a viewpoint of the ionizatiation and the movement of molecular ions in plasma.

Study of the behavior of a bubble attached to a wall in a uniform electric field

In order to investigate the effects of a uniform electric field on a bubble attached to a wall, numerical analyses and experiments have been carried out. The orthogonal curvilinear coordinate system generated numerically has been employed for the numerical studies based on a finite-difference solution of the governing equations. The steady bubble shape is obtained under the fixed contact radius condition as part of the solution of the free boundary problem. Along with the shape determination, the Laplace equation for electric potential is solved simultaneously. In experimental studies, an air bubble attached to one plate of a parallel-plate electrode system has been visualized under an applied electric field. The numerical and experimental results show generally good agreements. An air bubble on the lower electrode is found to be extended in the direction parallel to the applied electric field. The elongation increases with an increase of the electric field strength. Consequently, the contact angle also increases with an increase of the electric field strength if the contact radius is fixed. On the other hand, if the contact angle is fixed, the contact radius decreases as the electric field strength increases. It has been observed experimentally that the bubble departure volume remains nearly constant under the uniform electric field. This fact suggests that the downward electric force exerted on the bubble surface is nearly the same as the decrease in the surface tension force due to contact radius decrease under the uniform electric field.

Deposition mechanisms of a-SiGe:H films in pulse-discharge CVD

Pulse-discharge (PD) CVD techniques were applied to deposition of hydrogenated amorphous silicon germanium (a-SiGe:H) films. In the PD-CVD, high-voltage rectangular pulses with a small duty cycle were applied periodically to a parallel plate electrode system, and SiH4-GeH4 gas mixtures were decomposed in the pulse discharge. The film quality improved remarkably with decreasing electrode gap. To understand this, experimental and theoretical analyses were carried out. The primary radicals generated by electron impact dissociation of source molecules are the key for improving the quality of the film: when the primary radical is the dominant precursor for film deposition, the film quality improves.

Estimation of the electron-collision initiation rate constant for the plasma polymerization and deposition of ethane using a transport-based model

The plasma polymerization and deposition of ethane in a parallel-plate electrode system was predicted using gas-phase transport equations and published gas-phase kinetic rate constants, with the assumption that the deposition rate was limited by the production of monomer free radicals and their diffusion to the deposition surface. The kinetic rate constant for radical initiation by electron collision with ethane was adjusted to bring the modelpredictionsfor mass deposition into line with experimental measurements reported in the literature for 12 combinations of power, gas fowrate, and pressure. Furthermore, the shapes of the predicted deposition profiles were made to closely match the experimental profiles by introducing an adjustable parameter to account for plasma boundary effects and two coefficients to account for nonradical polymerization (constant for all conditions). The best-fit electron-collision initiation constant was compared with theoretical predictions for oxygen and hydrogen in a manner explainable by bond strengths and vibrational degrees of freedom.

Diurnal patterns in brain biogenic amines of rats exposed to 60-Hz electric fields.

Levels of brain neurotransmitters and their metabolites, as well as concentrations of enzymes associated with their synthesis and metabolism, fluctuate during the day in patterns defined as circadian. The present study examined these rhythms in albino rats exposed to 60-Hz electric fields. Thirty-six animals were exposed to a 39 kV/m field for 4 weeks, 20 h/day, in a parallel-plate electrode system. A group of 36 sham animals was similarly handled and housed in a nonenergized exposure system. On the sampling day, animals were sacrificed at 4-h intervals throughout the 24-h day. Brains were removed, dissected, and kept frozen until chemically analyzed. The levels of biogenic amines and their acidic metabolites in the striatum, hypothalamus, and hippocampus were determined by high-performance liquid chromatography with electrochemical detection (HPLC-ECD) methods. Repeated exposure to 60-Hz electric fields produced significant alterations in the diurnal rhythms of several biogenic amines: dihydroxyphenylacetic acid (DOPAC, the primary metabolite of dopamine in the rat) in the striatum, and norepinephrine, dopamine, and 5-hydroxyindoleacetic acid (5-HIAA; serotonin metabolite) in the hypothalamus. Levels of serotonin in the striatum and hypothalamus showed clear circadian patterns that was not affected by the field. No diurnal or field-related changes were observed in the hippocampal amines.