Brush and propagating brush discharges on insulating sheets in contact with a grounded conductor

This is a report of an experimental investigation of the brush and propagating brush discharges on charged insulating surfaces in contact with a grounded backing plate to gain a guide for the risk assessment of ignition by the discharges on insulating coats and liners often used in chemical processes. Based on the result, we provide unified expressions of the charge transferred by brush discharge and of a criterion for the onset of propagating brush discharge with the estimation of their discharge energies for the quantitative analysis of ignition hazards associated with the coats and liners.     

MIE experiments and simultaneous measurement of the transferred charge – A verification of the ignition threshold limits

Using the apparatus for the determination of the MIE a wide series of experiments have been carried out in hydrogen/air, ethene/air, propane/air and acetone/air mixtures. The transferred charge as a criterion to judge the ignition potential is determined to verify the thresholds of transferred charge given in the standards. The stored charge in the capacitance before the discharge is compared to the transferred charge in the spark. The correlation of ignition energy and transferred charge is examined and the thresholds of the transferred charge are discussed. The MIE of the above-mentioned mixtures are reviewed taking into account the measurement uncertainty.     

On value of transferred charge in silent discharge under atmospheric pressure

The dependence of the ratio of a charge transferred inside a discharge gap and a charge transferred in an outer circuit on the width of the discharge gap was measured in a silent discharge in oxygen, air and argon under atmospheric pressure. These dependences lie below theoretical curves derived from a one-dimensional model.     

Low-frequency dielectric-barrier discharge in the Townsend mode

An analytic model is proposed of a dielectric-barrier discharge in the Townsend mode, in which the space charge is small compared to the charge accumulated on the dielectric surface. The discharge mode depends substantially on the ratio between the frequency of the external voltage and the ion drift time through the gap. A low-frequency case is investigated, in which the space charge can be ignored. The analytic expressions obtained agree well with experiments and numerical simulations. The physical mechanism for the onset of relaxation oscillations in the Townsend mode is revealed. The time behavior of a dielectric-barrier discharge is qualitatively described, and its basic scaling parameters are determined.     

The dependence of ozone generation efficiency in silent discharge on a width of a discharge gap

The generation of ozone was studied experimentally in silent discharge on oxygen and air under the atmospheric pressure. The concentration of ozone was detected by means of UV absorption. It is shown that we must recount the charge (Q _T) transferred in outer circuit to the charge (Q _s) transferred in the discharge gap to establish the energetic load of ozone generation w[gO₃/Wh]. The width 0.8–1.1 mm of discharge gap was determined as optimal for ozone generation.     

Contact charging between surfaces of identical insulating materials in asymmetric geometries

The charging that occurs when a pair of insulating surfaces of identical chemical composition are rubbed (i.e. triboelectric charging) remains poorly understood. It is believed that asymmetry in contact plays an important role in this charging. To study this phenomenon, we have developed an experimental methodology that asymmetrically rubs two surfaces by contacting a rotating cylinder with a stationary cylinder – the rubbing is asymmetric in that the contacting area is much greater on the rotating cylinder than on the stationary cylinder. We find that the charge transfer occurs with a spatial distribution of charge, in terms of magnitude and polarity, on the contacted area. The direction of the average charge transfer is material dependent: for Teflon–Teflon contact, the surface with the larger contacting area charges positively, but for Nylon–Nylon contact the surface with the larger contacting area charges negatively. This difference is interpreted as being due to a negatively-charged species transferred in the case of Teflon (electrons or negative ions), but a positively-charged species transferred in the case of Nylon (positive ions).     

Numerical simulation of particle size effects on contact electrification in granular systems

Based on the contact charge transfer model between two particles due to a single collision proposed by Apodaca, the contact charges carried on a particle is derived due to multiple collisions, including the repeat collisions between two particles and the collisions with different particles, in mixed-size granular system of identical material. The effect of the particle size on the charges carried on the particle is simulated. The results indicate that for a mixed-size granular system, due to multiple collisions among particles, there exists a threshold particle radius, the particles with radius higher than which and the particles with radius lower than which carry opposite charges. The threshold particle radius is equal to mean value of particle size in the mixed-size granular system. Basically, the polarity of the charges carried on the largest particle is same as the polarity of the transfer charge carrier, and in case of the positive charge transferred, the largest particle will be positively charged and the smallest particle will be negatively charged, and vice versa. In the same size region, the more dispersive the particle size is, the more the net charges can be produced. In normal-distributed granular system, the magnitude of contact charge is determined mainly by the particle size distribution, size region, total particle number and the relative impact velocity.     

Barrier Discharge The Transferred Charge and Ozone Synthesis

We have undertaken an experimental investigation of the influence of the conditions of barrier discharge implementation such as: the discharge gap value, the type of gas, and the polarity and dielectric permittivity of the dielectric electrode on the value of charge transferred in a micro-discharge. It is shown that the increase in the specific capacitance of the electrodes leads to proportional increase in the transferred charge value, reaching 100–200 nC in a discharge gap 1 mm, in air. In this case the amplitude and duration of a current pulse in the microdischarge reach, respectively, 10 to 15 A and 40 ns. It is also demonstrated that in air with increase in the discharge gap value one can observe a decrease in the efficiency of the ozone synthesis whereas in oxygen there exists a more complicated dependence: the maximum of efficiency is observed at a discharge gap value of 0.7 to 1.0 mm.     

Elastic anomalies in superlattices: An explanation

An explanation for the elastic anomalies that have been previously reported in metallic superlattices is presented. The explanation, valid for superlattices with sharp interfaces, makes use of the charge transfer which occurs when two metals with different work functions are in contact. However, contrary to the case of bulk materials where the transferred charge remains localized at the surface, in thin layers the transferred charge is distributed throughout the layer. This change in charge distribution explains the observed anomalies in the lattice constants and in the elastic properties.     

用PET薄膜覆盖金属丝网电极实现大气压空气中均匀放电

将325^#不锈钢丝网电极和0.1 mm厚的PET薄膜紧贴在一起,平整地固定在Rogowski电极基座上,用50 Hz工频电压源及并联稳压电容,在大气压下2 mm空气间隙中实现了均匀放电.实验表明：将放电电流和电荷量波形作为判断放电均匀性的依据并不是完全可靠的,它只能判断放电在时间上的一致性,而不足以判断放电在空间上的均匀性.只有拍摄曝光时间不大于100ns的放电图像,才能可靠地判断放电的均匀性.在金属丝网电极覆盖PET薄膜的大气压气体放电实验中,这种放电图像被拍摄到,并说明大气压空气中的均匀放电只是汤森放电,而非辉光放电. 关键词： 大气压辉光放电 金属丝网电极 驻极体 高速摄影     

A noncontact method to study the charge state of the semiconductor-insulator interface

We present a method for investigating the charge state of the semiconductor-insulator interface using the measurements of the contact potential difference between the surface of the insulator film and a vibrating probe. In this method, the surface electrostatic potential is changed through charge variation at the outer surface of the insulator. The charge value is determined by the time of the structure exposure to a corona discharge. The method is applied for investigating the effect of exposure of a silicon-silicon dioxide system to radiation and pulse magnetic fields.     

Simulation of the discharge process in a barrier discharge cell based on a three-parameter model

Electric parameters of a barrier discharge cell with flat tips are studied experimentally and numerically for Xe/NF₃ (50 : 1) and Xe/SF₆ (50 : 1) gas mixtures. The discharge process is simulated using a three-parameter model. The dependences of the computational model parameters on the pressure of the Xe/SF₆ (50 : 1) gas mixture and on the electrode spacing are presented. Comparison of experimental and theoretical results shows that the error of simulation of the main discharge parameters (current, voltage drop, and transferred charge) does not exceed 10%.     

Contact electrification between polymers and steel

Electrification occurs when metals are put into contact with polymers, and the mechanism is still not fully understood. In this paper, experimental study of contact electrification between a metal and polymers was conducted. Effects of contact cycle, load, and nominal area on electrification were investigated. Results showed that electrification charge increased with real contact area. However, experimental results showed that charge density increased with nominal area and decreased with load. The key factor that determined the charge density was contact stress. Charge density decreased with contact stress linearly. A quantitative relationship between charge density and contact stress was proposed.     

Investigation of a single dielectric barrier discharge in submillimeter air gaps: Uniform field

The characteristics of a single discharge in 0.01–0.2-cm air gaps are investigated under atmospheric pressure between the metal electrodes and in the presence of a polymer barrier on one of the electrodes. The experimentally determined surface charge density distributions are satisfactorily described by a 2D Gaussian function with the proposed parameters. In the uniform field, the breakdown voltage weakly depends on the presence of a dielectric barrier. At the same time, the change from the positive to negative polarity of the metal electrode leads to a manifold increase in the discharge current and in the surface charge. The breakdown occurs under considerable overvoltage; the estimates indicate the streamer mechanism of the breakdown.     

Experimental investigation on the measurement deviations in recording brush discharges from insulating surfaces by Coulombmeters

The total charge on a charged sheet before and after a provoked brush discharge, their difference “C”, the induced charge “A” on different probes immediately before the discharge and their transferred charge “B” measured by commercially available Coulombmeters have been measured for probes from 2 mm to 25 mm in diameter including human thumb and shielded probe. The brush discharges were provoked on PTFE discs 10 cm–20 cm. The results obtained can be used for correct estimation of the incendivity of brush discharges between 10 nC and 90 nC.     

Effect of the third component on charge transfer character in ternary organic solar cells with a cascade-type electronic structure

By incorporating a third component into the host donor/acceptor organic components, we theoretically investigate the effects of its electronic structure and spatial location on charge transfer character. It is found that both of the two factors can modulate the distribution of transferred charges, and thus change the role of the third component in charge transfer (i.e., electron donor or acceptor). The binding energy of the formed charge transfer (CT) state is also determined by the two factors. Especially, we find an optimized spatial location of the third component, at which the binding energy of the formed CT state has a minimum value. It suggests that charge separation can be promoted. These findings will provide us a clear direction on how to optimize the electronic structure and spatial location of the third component to further improve the charge transfer and separation in ternary organic solar cells.     

Analysis of charge injection processes including ESD in MEMS

The effect of charge injection due to human body model (HBM) electrostatic discharge (ESD), charged device model (CDM) ESD and triboelectrification in capacitive microelectromechanical systems' (MEMS) structures is analyzed. The results show that as feature size is reduced, the effect remains constant for charging by triboelectrification. However, HBM ESD injected charge produces a change which is inversely proportional to the square of the gap separation and CDM ESD injected charge produces a change which is inversely proportional to the square of the plate area.     

Detection of current-induced spins by ferromagnetic contacts

Detection of current-induced spin accumulation via ferromagnetic contacts is discussed. Onsager's relations forbid that in a two-probe configuration, spins excited by currents in time-reversal symmetric systems can be detected by switching the magnetization of a ferromangetic detector contact. Nevertheless, current-induced spins can be transferred as a torque to a contact magnetization and can affect the charge currents in many-terminal configurations. We demonstrate the general concepts by solving the microscopic transport equations for the diffuse Rashba system with magnetic contacts.     

Surface-charge-governed ion transport in nanofluidic channels

A study of ion transport in aqueous-filled silica channels as thin as 70 nm reveals a remarkable degree of conduction at low salt concentrations that departs strongly from bulk behavior: In the dilute limit, the electrical conductances of channels saturate at a value that is independent of both the salt concentration and the channel height. Our data are well described by an electrokinetic model parametrized only by the surface-charge density. Using chemical surface modifications, we further demonstrate that at low salt concentrations, ion transport in nanochannels is governed by the surface charge.     

Full counting statistics of multiple Andreev reflections

We derive the full distribution of transmitted particles through a superconducting point contact of arbitrary transparency under voltage bias. The charge transport is dominated by multiple Andreev reflections. The counting statistics is a multinomial distribution of processes, in which multiple charges ne (n=1,2,3, ...) are transferred through the contact. For zero temperature we obtain analytical expressions for the probabilities of the multiple Andreev reflections. The current, shot noise, and high current cumulants in a variety of situations can be obtained from our result.