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.     

Contact electrification phenomena on phosphor particle surfaces

Contact electrification phenomena are reviewed to understand phosphor powder behavior. The origin of contact electrification is described in terms of the acid–base concept for solid surfaces. Electric charges produced by contact electrification affect phosphor properties. Various examples related to contact electrification are shown: particle surface modification, dispersion in liquids, adhesion strength to a substrate, electrostatic coating, interaction between a phosphor and mercury in a fluorescent lamp, and electron emission ability in a fluorescent lamp.     

Contact electrification of polymers due to electron transfer among mechano anions,mechano cations and mechano radicals

Many studies have been reported for contact electrification based on the electron transfer from donors to acceptors. However, the chemical structures of donors and acceptors have not been identified. Here we calculated the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of model structures of mechano anions, mechano cations and mechano radicals which were produced by the heterogeneous and homogeneous scissions of covalent bonds comprising polymer main chain in vacuum at 77 K. We identified the donors are mechano anions(HOMO) and mechano radicals(HOMO), and the acceptors are mechano cations(LUMO) and mechano radicals(LUMO). The contact electrification is due to the electron transfer from the donors to the acceptors during contacting on the friction surface, and produces mosaic nano-scopic domains with opposite sign. The sign of the net charge of polymer was deduced from the number of paths of electron acceptance reaction. The relative sign of charge and position on the triboelectric series were deduced from their chemical structure.     

Gasoline electrification: moisture and temperature influence

In the last decades, car manufacturers have introduced plastic materials into the vehicle fuel circuit. Do these modifications have an influence on electrostatic hazards? Several accidents were listed in Japan and the United States while filling the tank. Flow electrification was suspected to be responsible for some of these accidents. In this context, our laboratory studies flow electrification of fuels on the surface of dielectric and conducting materials on different conditions (fuels, moisture, temperature, Reynolds number, etc.).This paper is interested in flow electrification variation depending on atmospheric conditions (moisture and temperature) and on Reynolds number. We propose to evaluate the electrostatic hazards according to these parameters for a commercial gasoline/stainless steel interface.An experimental setup was developed in our laboratory. It consists of a loop representing fuel flowing through a pipe under a specific gas environment (controlled air moisture and gasoline temperature). The current generated by fuel flow is measured. This study allows to determine the main experimental parameters that modify flow electrification phenomenon in fuel.     

A method of charge measurement for contact electrification

A method for studying contact electrification charge between different materials was developed. Physical models for the contact electrification measurement system of metal/metal, metal/insulator and insulator/insulator were proposed, where the relationships between charge and measuring potential were developed. According to the models, an electrification charge measurement system was built. As an example of using the method, contact electrification experiment between polytetrafluoroethylene (PTFE) and carbon steel plates was conducted. Comparison of the charge results by this method and Faraday cup method was made, which suggested that the current method reduced the error resulted from the charge dissipation.     

Modelling of electrification in steady state and transient regimes

A microscopic model of electrification phenomena in steady state and transient regimes has been developed. The model has been applied for analysis of experimental data failing to be explained in the frame of classical macroscopic approach. Various boundary conditions have been studied regarding the possibility of experiential data fitting. The hybrid boundary condition has been suggested for explaining steady state and transient experiments. The proposed boundary condition can be related to the coexistence of two reactions on the active surface. The first reaction runs under the diffusion control (fast reaction) and the second one is limited by the kinetics (slow reaction).     

An investigation on the static electrification of dimethyl ether

Static electrification characteristics of dimethyl ether (DME) were studied considering accidents during unloading (discharging) operations. Producing mist flow, static electrification by the mist was studied as a first step. Influences of flow velocity on the charge generation, produced potential, charge generation ratio, electrostatic energy, etc. were investigated experimentally. Although the produced charge is not too big, it will be requested to pay full attention during the handling process, considering the igniting characteristics of DME.     

风沙运动的电场-流场耦合模型及气固两相流数值模拟

沙尘暴和尘卷风等风沙运动的静电场是空气流场中沙粒间的碰撞摩擦带电及沙粒粒径的分层效应引起的, 本文耦合沙粒摩擦荷电模型和风沙运动气固两相流模型, 提出了离散单元法与计算流体动力学结合的数值方法. 数值模拟计算表明电荷呈中性的沙粒临界直径为300 μm; 在充分发展的水平风沙流中, 细小的沙粒带负电, 较大直径的沙粒带正电, 所模拟的沙粒带电的荷质比及水平风洞试验段的电场强度与实验测量值一致, 验证了风沙运动的电场-流场耦合模型及数值计算方法的合理性. 本文基于沙粒摩擦荷电机理的风沙运动气固两相流模型提供了理解风沙运动静电场产生的一种物理机理.     

First-principles calculation of contact electrification and validation by experiment

Contact electrification is one of the most well-known phenomena in physics and examples arise in almost every industry. However, a scientific basis for contact charging remains unknown. Here, we present a theoretical study of contact electrification, supported by experiments, to calculate for the first time charge transfer between material surfaces from first principles physics. Electronic structure calculations and experiments are performed on single-crystal alumina (sapphire) and silicon oxide (quartz) surfaces, which have well-ordered structures that enable rigorous modeling. Both experiments and calculations show that sapphire charges positively and quartz charges negatively. The calculations cannot determine the magnitude of charge densities remaining on separated surfaces from first principles, as these are non-equilibrium effects, but our analysis is consistent with experimentally obtained charge densities of 10 μC/m². These results indicate the possibility of quantitatively predicting and explaining contact electrification from only the molecular structure of material surfaces.     

Theory of local electrification of cavitation bubbles: new approaches

The theory of local electrification of cavitation bubbles has been generalised. The major cases for a local electrification of bubbles in a cavitation field were considered; i.e., fragmentation and deformation of cavitation bubbles. The splitting of cavitation bubbles was considered taking into account surface tension, bubble perturbation, Stokes force and electrostatic forces between like charges on the wall of the collapsing neck of the fragment bubble. The problem of the uncompensated charge on the surface of the deformed cavitation bubble is solved. For this purpose radial deformations are considered in terms of the paraboloid of rotation and axial deformation approximated by one cavity hyperboloid of rotation. The maximum electric strength is accounted for. An explanation for some physical and physico-chemical effects in cavitation fields is proposed in terms of the electrical theory of the local electrification of cavitation bubbles.     

C60 as flow electrification inhibitor in mineral insulating oil

The paper presents the concept of using C₆₀ fullerenes as streaming electrification process inhibitor in mineral insulating oil. For the research, 20 samples of oil were prepared; one pure and 19 containing from 1 mg/l to 512 mg/l of C₆₀.The electrification current was measured using a wireless electrometer spinning disk system for rotational speeds from 0 rpm to 400 rpm. The research revealed the C₆₀ ability to significantly reduce the constant component of streaming electrification current in mineral transformer oil. The C₆₀ additive causes also the significant change in flow electrification mechanism as indicated by current versus flow velocity relations.     

Contribution to static electrification of mineral oils and natural esters

A failure of an insulation system of a power transformer can result into an interruption of a power supply and subsequently to a large economic damage. In some cases, the malfunction is so serious that a transformer may explode and catch fire resulting in a direct threat to the life of the device operator. These devices rely on a combined insulation system oil-paper. The oil in a transformer not only impregnates the pressboard paper insulation, hence increases its electric breakdown strength, but also acts as a coolant of active parts of the device. During the cooling, the oil flows in the transformer tank around the core, windings and isolation barriers from hardened paper. At the interface of two dielectrics, the oil and the cellulose in the transformer, electrostatic charges appear. The charges of one polarity are carried in the oil, and the charges of the opposite polarity remain captured in the barrier that is formed by the internal structure of the transformer. The accruing of a certain amount of charge leads to discharges along the surface of the solid insulation and therefore to its partial damage. Ultimately, this can lead to the damage of the whole insulation system of the transformer by its breakdown. At present, the mineral oils are used as the main liquid insulating medium because of their good electrical insulating and cooling properties. On the other side, there is a high environmental burden for their operation and maintenance as well as the subsequent disposal of the discarded oil. The natural esters may be used as a replacement for the mineral oil. They go well with the environment, they are biodegradable and in case of the transformer malfunction, its disposal costs less money.This paper presents the results of the experiments of electrostatic charging of the mineral oils and natural esters and their comparison. The charging process in the transformer is modelled using a metal cylindrical container with a forced flow of oil using a controlled rotating circular disc from a hardened paper. The results indicate that increasing intensity of friction, increases the electrical charge, which is generated at the interface of the solid phase and the liquid. In these experiments two types of mineral oils were studied. For comparison, two types of natural esters (sunflower and colza oils) were selected and used in the same experiments. The charging of the oils was examined at various temperatures ranging from 25 °C up to 70 °C.     

The role of fluid turbulence on contact electrification of suspended particles

A probabilistic version of a well-known phenomenological model for contact electrification is used to examine the effect of fluid turbulence on charge development for suspended particles as a function of the particle Stokes number. The distribution of particle collisions and particle charge appear to approach asymptotic states for high values of the Kolmogorov-scale Stokes numbers, exhibiting approximately normal distributions. The influence on particle contact electrification of differences in initial charge carrier density and in particle size are examined.     

A lightning initiation mechanism: application to a thunderstorm electrification model

The use of numerical models has greatly increased our understanding of the electrical and microphysical process within electrified clouds. We use the University of Washington, 1.5-dimensional thunderstorm model to examine the effects of including a runaway electron based lightning initiation mechanism. We find that this mechanism can significantly alter the electrification history of modeled storms and produce vertical electric field profiles that are very similar to those of observed storms. To cite this article: R. Solomon et al., C. R. Physique 3 (2002) 1325–1333.     

Impact of various stresses on the streaming electrification of transformer oil

In this contribution the influence of various stresses and their combined impact on the electrostatic charging tendency of oil is studied. Various physicochemical properties were measured according to ASTM Standards to detect changes in oil quality. A free radical reagent, 2.2 diphenyl-1-picrylhydrazyl (DPPH), was added to oil before and after the application of stresses to determine free radical concentration. The results obtained show that the application of stresses contributes to an increase in the electrification current. These results also demonstrate that electrification current is affected by the quantity of the free radicals.     

航空发动机喷流起电机理建模与试验研究

以研究航空发动机喷流起电的机理以及喷流起电对飞行器整体带电特性的影响为目的, 对起电机理进行了建模和实验验证. 首先以流体运动方程为基础, 建立了航空发动机带电粒子浓度的动态仿真模型, 仿真得到发动机燃烧过程中的各类粒子浓度变化情况. 其次, 设计了用于发动机喷流起电探测的静电感应传感器, 对装配涡扇发动机的某型飞行器进行了地面试验测试, 得到了发动机启动、稳定运行、加速、减速、停止等状态的动态电位. 仿真及实验结果详细地描述了发动机喷流起电的机理, 以及喷流起电会使飞行器带负电的结论, 为进一步分析飞行器飞行过程中整体带电特性提供了指导. 关键词： 航空发动机 喷流起电 传感器     

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.