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In this article, the dissipation of predeposited surface charges on the SiC/epoxy coated insulator is investigated. Similar to Part I of this study, the analysis is carried out for the system of a pair of finger-shaped metallic electrodes placed on flat material samples and different types of material precharging are considered. Specifically, two cases based on different types of electrode–sample contacts (Cases 1 and 2, similar to Part I) are examined as well as surface charging by external corona (Case 3). It is shown that surface charge dissipation in Cases 1 and 2 takes place in two stages, whereas three stages in the charge decay process are identified in Case 3. It is shown that the rate of charge dissipation is strongly affected by the increase of the content of SiC filler in the coating material. The experimental results obtained for different cases are compared and discussed by employing results of the calculations of the electric field in the experimental setups and surface conductivities and surface trap characteristics obtained in Part I. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on silicon carbide (SiC)/epoxy coatings with different contents of SiC filler, 3, 5, 7, and 10 wt%, is investigated using flat samples of epoxy substrate. In the experiments, a pair of finger-shaped electrodes was attached to the sample’s surface using direct pressing and conductive adhesive providing two different types of contacts and, respectively, surface charging methods. The electrodes were energized by applying dc voltage for various time intervals and resulted surface charge distributions between the electrodes were measured. It was found that depending on the contact type, charging duration, and filler content, different patterns of homocharge or heterocharge appeared on the material surface. Physical reasons for the observed effects are analyzed based on the calculated electric field distributions in the experimental setup, results of the auxiliary tests on material charging in a limited air volume, and surface trap energy distributions measured by utilizing the isothermal surface potential decay (ISPD) method. Application of SiC/epoxy coating for controlling surface charge accumulation is discussed. [ABSTRACT FROM AUTHOR]

The introduction of solid dielectrics to electrode surfaces will change the motion behaviours of free metallic particles and in turn affect partial discharge (PD) characteristics in transformer oil. To estimate the influence, the metallic particles movement in flowing oil was compared between different cases with and without insulating paper covering electrodes here. When the electrodes were bare, particles executed up‐down movements repeatedly in the vertical direction. As the electrodes were paper‐covered, the particles would settle on the paper surface for a period of time. Simultaneously, the PD characteristics caused by metallic particles were measured. When the electrodes were bare, the discharges concentrated in 0–90° and 300–360° and the PD magnitude reached 390 pC. When the double electrodes were paper‐covered, the PD magnitude decreased by 67% and the concentration phases of PDs would migrate to 45° and 160°. In order to analyse the experimental results, a simulation model with a paper‐covered boundary was constructed. Simulated trajectories of particles were in accord with the experiment results. Base on the model, the particle motion characteristics were obtained and the electric field distribution between the particle and electrode was calculated. Finally, the influence of paper‐covering on PD characteristics was discussed. [ABSTRACT FROM AUTHOR]

A wire beam electrode (WBE) method for investigating the crevice corrosion has been demonstrated by mapping non-uniform corrosion processes occurring on copper and copper alloys including the pure copper UNS No. C11000 (Cu), brass UNS No. C28000 (Cu–Zn alloy) and tin bronze UNS No. C51900 (Cu–Sn alloy) in mass 0.6% NaCl solution with the crevice spacings of d=103 μm and 206 μm. It was found that the sequence of three copper alloys in susceptibility for the crevice corrosion was that Cu–Zn alloy > Cu–Sn alloy > pure Cu. The average galvanic current of the Cu–Sn alloy in the covered region was changed from cathode to anode when the crevice spacing was increased to 206 μm. To sum up, it is feasible to study the behaviours of crevice corrosion within the different crevice spacings with the WBE method. [ABSTRACT FROM AUTHOR]

This work aims to study the variation mechanism of corrosion-resistance performance of the oxidization film spontaneously generated on Ti-6Al-4V (TC4) titanium alloy surface by using the open circuit potential (OCP), Alternating Current (AC) impedance, and polarization curve. Combined with the method of wire beam electrode, the corrosion behaviors of the microregion of TC4 titanium alloy immersed in 3.5% NaCl solution during the formation of film were investigated. Results show that the corrosion-resistance performance of TC4 titanium alloy increased with the formation of oxidization film, with the electrochemical testing results showing that the OCP and AC impedance values were increased, while the corrosion current density reduced. When the time of film formed on the surface of the alloy was 24 h, the impedance value of the TC4 alloy was an order of magnitude greater than that before oxidation, then the impedance value was no longer increased and the corrosion-resistance performance was best. The anode current and localized corrosion characteristics of the TC4 titanium alloy submerged in 3.5% NaCl solution during the earlier formation stage of film were great. With the formation of oxidized film, the peak value of anode current and its region gradually reduced, and both standard deviations of the circuit potential and circuit were narrowed, as well as the reduction in the difference of localized corrosion. [ABSTRACT FROM AUTHOR]

Surface charges generated by previous discharges at the solid-gas interface in a void can affect the characteristics of subsequent ones. In this paper, the effect of discharge area variation on the stochastic characters of partial discharge (PD) magnitude was investigated by changing the void size. It is found that the uniformity of PD magnitude increased when void diameter was reduced. In order to clarify this, the corresponding discharge area variation was obtained by Pockels effect of Bismuth Silicon Oxide (BSO) crystal. As void diameter became smaller, due to the limitation of cavity walls, the fluctuation of discharge area became weaker, and hence the uniformity of PD magnitude increased. Besides, the result that the fluctuation of PD magnitude decreased when PD void height became larger was obtained. Considering the safety of BSO crystal, surface charge distribution was not measured by experiment for this case. Instead, a simulation model was constructed to obtain it. As a result, discharge area became larger when void height increased. According to this, it is inferred that the expanding of discharge area may be affected by cavity walls in the experiment. Therefore, the changing tendency of the uniformity of PD magnitude with the void height can be explained when the void area remained unchanged. These results suggest that the variation of discharge area can affect the stochastic character of PD magnitude and further investigation is needed to clarify the PD mechanism. [ABSTRACT FROM AUTHOR]

An approach of combining simple precipitation method and thermal annealing was developed to synthesize Co chromite spinel nanoparticles that could be applied as the cathode material for supercapacitors. The nanoparticle modified electrode displayed a high specific capacitance of 418 F/g at the scan rate of 5 mv/s in a three-electrode system. [ABSTRACT FROM PUBLISHER]

Sato's equation has been employed to calculate the pulse current caused by dielectric barrier discharge (DBD). However, it was derived from the gas discharge in a gap between both metallic electrodes. Hence, due to the existence of surface charges, the applicability of Sato's equation to DBD needs to be clarified. In this paper, the models about gas discharge in a gap between electrodes, one electrode and one layer of barrier dielectric, and between two layers of barrier dielectric are established. And the discharge current for each circumstance is obtained by Sato's equation and by Pedersen's theory simultaneously. The latter was used to explain the mechanism of pulse current method which considers the effect of surface charges. It's found that Sato's current in the gap between both electrodes is consistent with that obtained by Pedersen's theory, which results from the equivalence of the two methods where charge diffusion is neglected. Besides, in the gap between one electrode and one layer of barrier dielectric, the current obtained by the two methods is consistent under positive polarity of applied voltage, while it's inconsistent under the negative one. Moreover, the inconsistency in the gap between two layers of barrier dielectric appears under both polarities of applied voltage. These simulation results show that using Sato's equation to calculate pulse current may be not suitable for DBD or PD, which ignores the accumulation of surface charge. [ABSTRACT FROM PUBLISHER]

Piezoceramic disks with spiral interdigitated electrodes (SIDEs) on their surfaces are proposed to produce in-plane torsion. With constant electrode spiral angle (Type I) and constant pitch between adjacent electrodes (Type II), two typical types of the SIDEs are developed and studied. Working principles of the discal piezoelectric actuators are explained and their static in-plane torsional deformations are formulated. Finite element simulations are used to investigate the static and dynamic properties of the actuators. Non-ideal distributions of electric fields appear serious suppressions on the actuating abilities, even worse for Type I actuator. Due to unsymmetric piezoelectric strains in the thickness direction, bending deformations of the disks are inevitable. Prototype actuators with fixed boundary at the radius of 12 mm are fabricated and tested. With a driving voltage of 400 V p-p at 1 Hz, the maximum quasi-static in-plane torsional angles are 0.00458° for Type I actuator and 0.00605° for Type II actuator at the radius of 6 mm. With a driving voltage of 10 V p-p , the vibration amplitudes at the radius of 6 mm are 0.00105° at 86.0 kHz for Type I actuator and 0.00149° at 84.4 kHz for Type II actuator at the first in-plane torsional vibration modes. [ABSTRACT FROM AUTHOR]

Simultaneous discharge, characterized by single current pulse corresponding with more than one discharge spot in one PD (partial discharge), was often observed in the partial discharge sequences, especially for the first discharge after voltage application. As it tends to be of larger magnitude than other PDs, to clarify its mechanism is important for understanding PD. In this paper, a combination measurement system of surface charge distribution and PD current was developed to identify simultaneous discharge in the samples with double-spheres plate electrode. Besides, a single square voltage pulse was applied so that only one discharge took place at a sphere electrode and the effect of residual charges can be excluded. Based on these, we investigated the effects of photoionization and overvoltage on the probability of simultaneous discharges. Photoionization effect was considered by adjusting the distance and adding a barrier between two sphere electrodes. When two spheres were separated by a glass slide, the simultaneous discharge probability was smaller than that without one. Besides, as the gap distance between two spheres increased, the simultaneous discharge probability diminished. These indicated that photoionization contributed to simultaneous discharges. Furthermore, simultaneous discharge probability became higher as the overvoltage increased, in both cases with and without glass slide. [ABSTRACT FROM AUTHOR]

This article presents a finite element analysis of a polarized piezoelectric tube driven by helical electrodes. It is thanks to a helical coordinate meshing and local coordinate system association with each element that the problem of piezoelectric coupling has been studied. The numerical results agree well with the experimental data without the need of compensation factors as in previous works. The developed model was used to determine the electromechanical coupling coefficients of the tubes in axial and torsional modes. The electromechanical coupling coefficient depends on the helical angle of the electrode. In the axial mode, electromechanical coupling coefficient goes through a maximum value of 25% when the helical angle of the electrode is close to 30°, while in the torsional mode, the maximum value of electromechanical coupling coefficient was reached at a helical angle near 60°. The analysis investigates the tube size effects and shows the potential uses of piezoelectric tubes as an actuator or energy harvesting device. The presented model could be used to analyze the electric fields in the tube during the polarization process or to analyze the mechanical stress (without any limitation due to Saint-Venant’s principle) imposed by the simplified analytical approaches available in the literature. The developed approach can also be used for theoretical analysis of the helical/spiral piezoelectric element. [ABSTRACT FROM PUBLISHER]

An impact rotary motor based on a bulk piezoelectric torsional actuator with grooved helical electrodes is proposed. The prototype actuator, with dimensions of Φ 8 mm × 10 mm, produces a maximum torsional angle of 0.035° with a driving voltage of 2200 Vp-p. Its first torsional resonant frequency is 32 kHz with the fixed-free boundary condition. The rotational speed of the developed motor is proportional to both the amplitude and the frequency of the driving voltage in low frequency range. With a saw-shaped driving voltage of 1400 Vp-p at 8 kHz, the motor can rotate at a speed of 22.5 r/min with a braking torque of 0.1 mN·m, and the stall torque can reach up to 1.6 mN·m. Although its maximum efficiency is less than 0.1%, the motor produces a rather small step angle with a large driving torque. It is suitable for ultrahigh precision positioning. [ABSTRACT FROM PUBLISHER]

The vibration characteristics of a piezoelectric fiber actuator with helical electrodes are studied theoretically and experimentally. Its working principle indicates that the torsional, longitudinal, and tangential deformations of the fiber are coupled. A simplified dynamic model is deduced to investigate the properties of the coupled vibrations and their corresponding equivalent circuits are also provided. Resonant frequencies and mechanical coupling coefficients in free-free boundary condition are calculated. The trends of resonant frequencies as functions of the electrode helical angle and fiber length are discussed and validated in experiments. [ABSTRACT FROM PUBLISHER]