Point Electrode Research Articles

Morphological Changes at the Interface of the Nickel‐Yttria Stabilized Zirconia Point Electrode

The , Ni/YSZ point electrode has been investigated using long‐term potential step measurements and impedance spectroscopy at 1273 K. Morphological and structural changes at the electrode interface were evaluated by electron microscopy, energy dispersive X‐ray analysis, and Raman spectroscopy ex situ. The anodic current was found to induce a self‐catalytic effect on the electrode, and the anodic “steady state” current increased to more than twice the initial value with a time constant of about 40 h. In contrast, cathodic polarization reduced the performance of the electrode, and the cathodic current decreased significantly with a time constant of about 20 h. Redistribution of material in the reaction zone is suggested to control most of the changes in electrode activity. At anodic overpotentials it was observed that Ni was transported to the electrolyte surface, forming a “necklace” of Ni particles around the electrode/electrolyte contact. This is believed to increase the three‐phase boundary (TPB) length and account for the higher activity of the electrode. At cathodic overpotentials the transfer of Ni to the YSZ was found to be restricted, and it is proposed that agglomeration of dispersed metal particles reduced the TPB length, and accordingly the cathodic current. In addition to the morphological modifications, the catalytic properties of the surfaces were significantly altered as the electrode was polarized. Transformation from cubic to tetragonal YSZ, due to segregation of the material, was observed on the surface of the electrolyte when the sample was kept at working conditions for long periods of time (135 days). The passage of current was not found to generate any permanent phase transformation in the YSZ.

Precise and fast calculation of the motor unit potentials detected by a point and rectangular plate electrode

To reduce the time of computation of a motor unit potential (MUP), the shape of intracellular action potential (IAP) and (or) MU anatomy are generally simplified. A method of MUP presentation is suggested. It provides accuracy of the MUPs calculated for any distance and size of rectangular electrodes together with considerably reduced computational load and time. No simplification of the IAP shape or location of muscle fibres of different diameters and lengths is required. The MUP generated by N temporally and spatially dispersed single fibre action potentials is considered to be the output signal of a linear timeshift invariant system for potential generation. The input signal is the first temporal derivative of the IAP. The common impulse response (CIR) is the sum of potentials produced at the electrode by N pairs of dipoles propagating from the motor end-plates to the ends of the corresponding fibres. The potentials of each dipole at the rectangular plate electrode are determined analytically. Thus, the MUP is calculated as a single convolution between the input signal and CIR for a rectangular electrode of any size.

Precise and fast calculation of the motor unit potentials detected by a point and rectangular plate electrode.

To reduce the time of computation of a motor unit potential (MUP), the shape of intracellular action potential (IAP) and (or) MU anatomy are generally simplified. A method of MUP presentation is suggested. It provides accuracy of the MUPs calculated for any distance and size of rectangular electrodes together with considerably reduced computational load and time. No simplification of the IAP shape or location of muscle fibres of different diameters and lengths is required. The MUP generated by N temporally and spatially dispersed single fibre action potentials is considered to be the output signal of a linear time-shift invariant system for potential generation. The input signal is the first temporal derivative of the IAP. The common impulse response (CIR) is the sum of potentials produced at the electrode by N pairs of dipoles propagating from the motor end-plates to the ends of the corresponding fibres. The potentials of each dipole at the rectangular plate electrode are determined analytically. Thus, the MUP is calculated as a single convolution between the input signal and CIR for a rectangular electrode of any size.

An integral equations solution of the forward D.C. geoelectric problem for a 3-D body of inhomogeneous conductivity buried in a halfspace

This paper presents an integral solution of the forward D.C. geoelectric problem for a 3-dimensional (3-D) target body of non-uniform conductivity σ T( x, y, z) buried in the halfspace z≥0. The derived formulae constitute a combination of boundary and volume integrals. Numerical calculations are performed for the case of a 3-D rectangular prism embedded in the halfspace, while the exciting potential is due to a single point electrode on the surface of the earth. Isoline and profile curves are presented for the anomalous potential (due to the prism), for the total potential, as well as profile curves for the apparent resistivity ρ a/ ρ 1 (using 3-electrode Schlumberger array). It is shown that the presence of the 3-D prism is most pronounced in profile curves of anomalous potential and apparent resistivity.

Transcutaneous electrical nerve stimulation is superior to opioid for microlaryngeal endoscopic surgery

S238 INTRODUCTION: Transcutaneous electrical nerve stimulation (TENS) is commonly used for stimulation therapy of pain. The aim of this study was to evaluate the effect of TENS for microlaryngeal endoscopic surgery. METHODS: After obtaining approval from the Protection of Human Subjects Committee of Jikei University Hospital and informed consent from each patient, 33 adult patients (ASA physical status I or II), undergoing microlaryngeal endoscopic surgery were studied. Each patient was randomly assigned to one of three groups (general anesthesia [G] [n=11], general anesthesia with opioid [O] [n=11], and general anesthesia with TENS [T] [n=11]). G consisted of simple anesthesia with isoflurene (1-1.5%), nitrous oxide (67%) and oxygen (33%). O was the same as G but with butorphanol (0.04 mg/kg) given intravenously. T was the same as G but with TENS employing Silver Spike Point (SSP) electrodes (Nihon Medix, Japan) for continuous stimulation (5 Hz) with Trimix 1 (Nihon Medix, Japan) during anesthesia. Pore sites were bilateral Gokoku (LI4) and Ashisanri (S36). The voltage level was that immediately before each patient felt subjective pain before the induction of anesthesia. We measured blood pressure (BP) and heart rate (HR) before [baseline] and after insertion of the laryngeal scope, and the time to extubation of the trachea (ET), and we counted the number of cases in whom systolic BP increased to more than 180 mmHg. Results were analyzed using ANOVA followed by a Bonferroni T-test and chi-square test. P<0.05 was considered to be significant. RESULTS: There were no significant differences among the groups in age, height, body weight and anesthetic time. T showed a significantly decreased HR compared with G and O. O showed a significantly increased ET compared with G and T. BP did not change significantly in each group, but T showed a significant decrease of high BP(>or=to180 mmHg) compared with G and O (Table 1).Table 1DISCUSSION: TENS was superior to butorphanol in decreasing HR and BP in microlaryngeal endoscopic surgery.

Effect of Transcutaneous Acupuncture-point Electrical Stimulation (TAES) on Post-tonsillectomy Pain in Children

S333 Although TAES has some analgesic effects on various types of pain [1], there have been few reports on magement for post-operative pain [2]. In this study we examined the effects of TAES on post-tonsillectomy pain in children. METHODS: With institutional approval and each parent's informed consent, 30 pediatric patients (4-9 years old) undergoing tonsillectomy under general anesthesia were divided randomly into TAES group (n=14) and control group (n=16). Patients were not premedicated, and induction was completed with nitrous oxide, sevoflurane (2.0-3.0 %) and oxygen. After premedication with atropine (0.01 mg/kg), tracheal intubation was facilitated with vecuronium (0.1 mg/kg). Anesthesia was maintained with sevoflurane, 1.5-2.5%, nitrous oxide, 50%, and oxygen. After anesthetic induction in TAES group, bilateral Hoku and Neikuan points of upper extremities were located with acupoint detector (Kimura Medical Co., Japan). Silver spike point electrodes were placed at 4 acupuncture sites. These electrodes were alternately stimulated by 2 Hz of bidirectional exponential waveform for 2 seconds and 20Hz of that for 2 seconds during the surgery, using TAES apparatus (ANESTY-10, Nihon Medix Co. Japan). Peak output of inpulses was 100 V. There were no other differences between groups. Any narcotics were given intraoperatively. All patients had 10 mg/kg of acetaminophen suppository given at the end of surgery for postoperative pain management. The postoperative state was assessed by the patient's parent at 30, 60 and 120 minutes after the end of surgery, using the visual facial scale (VFS) which contained 20 drawings of a single face from best mood (1 point) to worst mood (20 points). Parents were not informed of the randomization result, but were fully informed how to assess the VFS. Chi-square test, Fisher's exact probability test. Mann-Whitney test, and Wilcoxon signed rank test were used for statistical analysis and P<0.05 was considered to be significant. Data were expressed as mean +/- SE. RESULTS: There were no significant differences between 2 groups in sex, age, height, body weight, and operation time. Mean TAES time was 60 +/- 5 min. Table 1 shows the changes in VFS (Best mood; 1, Worst mood; 20).Table 1In 120 min after OP, patients with VFS scors <10 were more frequent in TAES group (8/14) than in control group (1/16). There were no complications related to TAES. CONCLUSIONS: This study indicates that TAES during general anesthesia is effective for post-tonsillectomy pain management in pediatiric patients. TAES is an useful noninvasive method. More effective stimulation methods or other stimulating points should be investigated.

Current density distribution measurement of negative point-to-plane corona discharge

The current density distribution on the plate electrode of a point-to-plane corona discharge is measured with a computer-controlled measuring system. The measurements are taken by rotating the plate which consist of built-in arrays of orthogonal probes. The current-density distribution can be measured for different separation distances between the point electrode and the plane electrode while the applied high voltage can be varied from the voltage required for the onset of corona discharge to 30 kV. The current-density distribution of a single needle is symmetric around its center point within the accuracy of the measurement system. However, the current-density distribution is radially nonuniform. The computer-controlled measuring system is capable of measuring the current distribution of single point and multipoint electrodes.

Influence of Tank Bottom Shear Stress on Complete Fluidization of Spherical Solid Particles in a Square Surface Agitation Tank.

The influence of tank bottom shear stress on complete fluidization of spherical solid particles in a square surface agitation tank is investigated. The shear stress on the tank bottom is measured by the electrochemical method, which utilizes the reduction of dissolved oxygen on point electrodes embedded in the tank bottom.The shear stress has a different value for each point electrode. It is found that complete fluidization of particles is attained when the shear stress all over the tank bottom exceeds the minimum shear stress required for the fluidization of particles, which is dependent on the properties of the particle and surrounding liquid in the tank. The empirical equation, which shows the relationship between the minimum shear stress required for the fluidization of particle and the properties of particle and liquid in the tank, is obtained. By use of this equation, the relationship between the minimum impeller speed required for complete fluidization and experimental conditions is further discussed.

Voltammetric studies of electrochemical processes at the interface Pt/BICUVOX.10 between 300 and 600 °C

Electrochemical processes occurring at the interface Pt/BICUVOX.10 were investigated by cyclic voltammetry and potentiostatic current-potential curves, taken under steady-state conditions, in different mixtures of nitrogen and oxygen at temperatures between 300 and 600 °C. Similar experiments were carried out for comparison at the Pt/YSZ interface. Point or paste electrodes were used. The equilibrium of the oxygen electrode is not established below 500 °C at both interfaces any more. Reasons for this behavior are presented. It is concluded on the basis of a comparison of the shape of voltammograms at different interfaces that BICUVOX.10 is reduced and oxidised electrochemically. Simultaneously a reoxidation of the solid elctrolyte by O 2 from the gas phase occurs. At temperatures below 500 °C the reoxidation is not fast enough to avoid a hysteresis at cathodic currents of the voltammograms. At higher temperatures and larger partial pressures of O 2 the hysteresis disappears.

Neutron Emission from Palladium Point Electrode in Pressurized Deuterium Gas under DC Voltage Application

The nuclear reaction in palladium electrode under highly non-uniform electricfield has been studied using a neutron counting system. Excess neutroncounts were observed with deuterium loaded palladium point electrodes indeuterium gas atmosphere in 9 out of 24 runs after activation by flashoverbetween electrodes during DC high voltage application. Similar neutron bursttook place without the activation under a DC glow discharge condition in 2runs out of 37 runs. The tip surface of these two electrodes after the burstwas observed to be covered by a large amount of carbon using X-ray photoelectron spectroscopy. Several craters of about 10μm in diameter wereformed on the tip surface of one of the two electrodes.

Electrophysicochemical characteristics of a waterpen point corona discharge

Some interesting electrophysicochemical characteristics of waterpen point-to-plate discharges with DC and AC power have been investigated in a room atmosphere. The metal point electrode of a conventional point-to-plate air gap is severely bombarded by energetic ions from the discharge region near the point. Concurrently, the temperature of the point is greatly increased. There are different characteristics for the waterpen point discharge, because the surface temperature of the waterpen point stays low due to the evaporation of the moisture from the waterpen point. In this paper, the discharges and electrophysicochemical characteristics of a waterpen point and a Pt metal point have been studied to evaluate the differences. It was found that mists and sprays are dispersed from the waterpen point due to the bombardment of ions. Also, a positive corona is effective for mist dispersion, a negative corona disperses sprays, and AC corona disperses both mists and sprays. The AC discharge of the waterpen point generated more ozone of 56 ppm, while it was the negative DC discharge of the Pt point that produced more ozone of 30 ppm. The AC discharge of the waterpen point produced 0.11 ppm at 10 kV, and the Pt point produced 0.10 ppm at 15 kV. The DC discharge of the both points showed no NO formation.

Electric field and space charge of spherical electrode at high voltage concentric with a grounded conductive sphere

The solution of the space-charge Poisson's equation is presented for a spherical electrode at high voltage concentric with a grounded conductive sphere. The obtained electric field is given in terms of the ion current emitted by the electrode and an integration constant. Both parameters are functions of boundary conditions. Using measured values of the ion current for a range of boundary conditions and applying these boundary conditions to determine the integration constant suggest a minimum value for the ion mobility of 1.9/spl times/10/sup -4/ m/sup 2//V.s. Approximate formulas for the ion current and the electric field in terms of the independent parameters were also developed. Also, it was shown that this spherical system with its solution can be used to make accurate evaluation of the ion mobility. The obtained solutions can be applied with good approximation to many practical electrostatic systems involving point electrode at high voltage generating ions. Although the subject matter is very general and could have a fundamental research aspect, in this paper, it is meant to be applied to the area of electrostatic powder paint coating. Therefore, all the examples of boundary conditions and illustrations are typical of the electrostatic powder paint coating.

Voltammetric studies of the Au|YSZ interface at temperatures between 300 and 600°C

Abstract Electrochemical processes occurring at the gold|yttria stabilised zirconia interface were studied by cyclic voltammetry and steady-state current potential curves in different mixtures of oxygen and nitrogen at temperatures between 300 and 600°C. Point and paste electrodes were employed. The equilibrium of the oxygen electrode is not established at temperatures below 450°C any more. Contrary to Pt electrodes, the electrochemical formation and reduction of an oxide are reflected by the shape of cyclic voltammograms. However, gold oxide is not formed from O 2 in the gas phase.

Triggering of Negative Corona

The parameters of both low-current and high-current modes of DC negative corona discharge are described. The experiments were carried out in point-plane gaps in stagnant media of pure nitrogen, nitrogen, ambient air and in a dust-free air flow. A number of different types of point electrodes were used, including points covered by layers of TiO 2 and HfO 2 of controlled thickness. An overview of different methods of the triggering of the high-current mode is given. Discharges were initiated using x-ray radiation, laser radiation, UV radiation from different sources, and flux of positive ions. The correspondence of the model of dielectric switching mechanism as the triggering mechanism of high-current mode to the experimental results is discussed. Besides, the possible mechanisms limiting the repetition rate of Trichel pulses at its lower values (< 10 4 s -1 ) are analysed.

Voltammetric studies of electrochemical processes at the interface Pt|YSZ between 300 and 600°C

Abstract Electrochemical processes occurring at the interface platinum|yttria-stabilized zirconia were investigated by cyclic voltammetry and potentiostatic current-potential curves, taken under steady-state conditions, in different mixtures of oxygen and nitrogen at temperatures between 300 and 600°C. Point or paste electrodes were used. The exchange current of the rate-determining step of the oxygen reduction becomes very small below 500°C. Therefore, the equilibrium of the oxygen electrode is no longer established. A layer of chemisorbed oxygen atoms is formed anodically on the contact surface of the point electrode, not by the dissociation of O 2 at the three-phase boundary. The shape of the cyclic voltammograms is discussed.

Anomalous stochastic behavior of partial discharge on aluminum oxide surfaces

The stochastic properties of pulsating partial discharge (PD) generated by applying a low-frequency sinusoidal alternating voltage to a point electrode touching an aluminum oxide (Al2O3) surface in air have been investigated. The time dependence of such statistical characteristics as mean numbers of positive and negative PD pulses per half cycle and the amplitude and phase distributions of individual positive and negative PD pulses selected according to their order of occurrence in a cycle were extracted from records of the amplitudes and phases of all PD events that occurred while the voltage was applied for times up to 40 min. The discharge characteristics exhibit a dramatic sensitivity to the impurity content of Al2O3. In the case of high-purity (99.9%) Al2O3, the positive-PD pulses cease within 30 s after application of the voltage from which time the negative-PD pulses persist indefinitely in a relatively stationary pattern. The cessation of positive PD was not observed for Al2O3 samples of lower purity (96% or lower). A modified version of a previously developed Monte Carlo simulator of ac-generated PD that includes effects of transport and decay of surface charge between PD events was used to gain insight into the conditions that could give rise to the observed long-term behavior of PD for high purity Al2O3.

Dynamics of the YSZ-Pt interface

Yttria stabilized zirconia (YSZ)-Pt point electrodes were examined by linear potential sweep, potential step and impedance measurements at 1000 °C in air. Inductive loops and hysteresis phenomena with long relaxation times were found. Atomic force microscopy showed changes of the interface between Pt and YSZ induced by the current passage. These changes involve transport of solid and are slow enough to explain the large time constants. The low frequency capacitance and inductive loop forming an entire circle indicate the presence of gas reservoirs at the YSZ-Pt interface.

Electrode reaction at platinum / ceria surface modified YSZ interface

The electrode reaction was examined on ceria coated YSZ by a platinum point electrode in H2-H2O atmosphere at 973 K- 1173 K. The thickness of the ceria coating layer was altered from 0 to 2.5 µm, fabricated by a laser ablation and by a vacuum vapor deposition method on YSZ single crystals. The electrode / electrolyte interface conductivity increased with 1/4 powers ofp(H2) andp(H2O) on both ceria coated and non-coated YSZ. The interface conductivity was significantly improved on a thicker ceria coating surface than 1 µm. The effective electrode reaction radius also increased in a thick ceria coating. The18O/16O exchange experiment at low oxygen partial pressure revealed that the oxygen surface exchange rate of ceria is not high compared with that of YSZ. It can be concluded that the bulk ionic conduction of ceria makes a more effective contribution to the electrode reaction than the surface catalytic activity in H2-H2O atmosphere.

A Possible Reaction Mechanism for the Oxidation of H2 on Ni/YSZ Cermet Electrodes

Polarisation curves and ac-impedance spectra have been recorded for Ni/YSZ cermet electrodes and for Ni point electrodes on an YSZ electrolyte at 1000°C. Kinetic data fit the rate equations derived for a reaction scheme where the electrochemical step is near equilibrium and a subsequent chemical reaction is rate determining, assumed to be the reaction between protons and oxide ions on the electrolyte surface. The very high capacitance observed for the cermet electrodes is briefly discussed.

A novel preparation of gold films by electrodeposition at the interface between a Na(AuCl4)-CuSO4 aqueous phase and an immiscible hexyl acetate organic phase

Electrolysis at the interface between a Na(AuCl4)–CuSO4 aqueous phase and an immiscible hexyl acetate phase resulted in continuous growth of gold films along the interface. To maintain filmy growth of gold, it was effective to stimulate displacement of predeposited copper with gold by applying a rectangular or triangular potential in a given range. Two types of electrodes were applied: from a point electrode the film grew concentrically like a blooming flower, and from a line electrode the film grew unidirectionally toward the counter electrode as a spreading wave. A long time electrolysis could be performed by circulating and filtering the aqueous solution. The film contained no trace of copper and was very thin (<1μm).