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Surface potential decay (SPD) of a corona charged polymeric material is a powerful tool to characterise electrical properties such as charge transport, trapping/detrapping and recombination. Over the years, various predictive simulation techniques have been proposed to describe charge transport within the material. Despite recent progress, it appears that there have been a few attempts to theoretically interpret the nature of the charge migration on the insulation surface. The aim of the present paper is to introduce a new technique with differential evolution algorithm (DEA) to reveal the steady state surface potential decay experimental results. Experimental measurement was carried on a thin film of polyethylene terephthalate (thickness: 0.5 mm; surface: 50 mm × 50 mm). The domains of variation of the factors used were respectively: 1000 V to 1800 V; 25 to 55 °C; 50 % to 80 %. The simulation results show that computational modelling and optimization approaches may improve the effectiveness to characterise electrical properties of polymers. More importantly, these studies demonstrate that DEA is effective and performs better than the experimental design method. [ABSTRACT FROM AUTHOR]

Understanding and modelling the static charge decay on an insulating material surface have been the topic of numerous research works since the nineteenth century. After an introduction on this historical context, a selection is presented here covering the various phenomena that may be held responsible for the decay: ion deposit from the surrounding atmosphere, charge injection and transport through the conduction and trapping levels of the solid, internal polarization by free carrier motion or dipole polarization, as well as surface conduction and migration of the deposited charge along the surface. Surface potential measurements are a convenient technique to study these various types of charge motion but the underlying complexity concerning their interpretation is often neglected. Depending on the context, the law of electrostatics may produce a hyperbolic as well as an exponential decay. On an insulating polymer, or any other disordered insulator, charge transport is dispersive, and conduction as well as dipolar polarization responses are described by time power laws. The knowledge of this time response is not sufficient to build a convincing physical model, because of the universality of this response, which leaves many degrees of freedom to interpret the data. Knowledge of the possible elementary processes and their signatures in the observables is therefore requested before the implementation of curve-fitting procedures. • Main processes responsible for charge decay on insulators are reviewed. • Potential decay follows usually time power laws. • Environment may influence decay process by neutralization by atmospheric ions. • Charge may drift by hopping between traps, or be screened by volume polarization. • Surface conductivity influence on potential decay in various contexts is analyzed. [ABSTRACT FROM AUTHOR]

This paper presents the surface modification and charge transportation mechanism of thin polyimide films. Here, we demonstrate that the surface modification of these films, by using the fluorine gas-phase, improves the charges mitigation and, thereafter, suppress the space charges. The experimental results indicate that the thermal step current for fluorine coated films reduce significantly in comparison to pure polyimide films. The thin layer of fluorine coating helps to release the surface charge, reduce the charge injection from the electrode, provide hindrance for charges to penetrate into the bulk of the films and the higher degree of charge disappearing helps to reduce the space charge growth. [ABSTRACT FROM AUTHOR]

With the aim of exploring an alternative method of nano-doping in cellulose paper and improving flashover strength of oil-impregnated paper, radio frequency (RF) magnetron sputtering method is introduced into the structural modification of insulating paper for converter transformers. In this experiment, insulating paper was treated with ZnO sputtering for 0, 7.5, 15 and 30 min, respectively. The surface morphology of dry paper was observed with a scanning electron microscope. The bonding mode of sputtered ZnO particles with cellulose matrix was investigated via attenuated total reflection infrared (ATR-IR) spectroscopy and mechanical property of the sputtered samples were studied. Surface and volume conductivities of the oil-impregnated sputtered paper were measured. Moreover, the charge dissipation characteristics of sputtered insulating paper was investigated by means of surface potential decay. In addition, trap distribution and carrier mobility of specimen were further obtained. Finally, the DC flashover strength were tested. The results showed that ZnO magnetron sputtering had a distinct influence on the structure of the insulating paper, resulting in the formation of hydrogen bond and chemical bond and an increase of the surface and volume conductivities. ZnO sputtering was found to decrease the initial potential and accelerate charge decay. Moreover, appropriate sputtering enhanced the surface flashover strength.

To investigate the effect of fluorination on surface electrical performance of ethylene propylene rubber (EPR), four pieces of EPR specimens are prepared and fluorinated for different duration ranging from 120 min to 480 min. The surface morphology and element compositions of experimental specimens are tested. The surface potential decay and complex permittivity are measured. The tracking discharge property and the erosion properties after tracking test are investigated. The surface charge transport and electrical property tailoring mechanism are discussed. The results show that when the fluorination duration is from 120 min to 360 min, the surface morphology gradually becomes flat and compact with time, and the surface resistance to electrical tracking is improved. While an excessive fluorination with the duration of 480 min leads to a significant increase in surface conductivity and a weakening in the resistance to electrical tracking, which is mainly due to a change in surface morphology. The recommended fluorination duration for an optimised surface property is between 240 and 360 min for EPR specimen.

Surface potential decay (SPD) measurements have been considered as the most appropriate technique to investigate the electrical properties of insulating materials. Its main interest is to avoid any contact with the surface; providing that charge is deposited by means of a DC corona discharge. Besides, the interpretation of the surface potential evolution remains a major problem. For this reason, this study aims at considering surface potential measurements and the mechanisms of the potential decay and transport processes that might be involved in the decay. To reach a conclusion, samples that were used took the form of polyethylene terephthalate films (thickness: 0.5 mm; surface: 50 mm x50 mm). A negative corona discharge produced in a needle-grid-plate electrode system was employed to charge the surface of the film samples. All surface potential decay measurements were carried out in a commercial climatic chamber, where relative humidity RH and temperature T were rigorously controlled. Initially, we have shown an injection process of the charge deposited on the surface of the material. The investigation on the kinetics of charge carriers (charge carrier mobility), allowed us to determine the mobility of the charge derived in the material. We noted a strong dependence of the charge density put on the evolution of SPD. [ABSTRACT FROM AUTHOR]

Measurements of DC electric conductivities of four types of silicone rubber-based polymers for use in high voltage insulation systems of power components are reported. The field dependences of the conductivities obtained by two different techniques, namely by utilizing steady-state currents through materials' samples placed between metallic electrodes and by employing surface potential decay characteristics in an open circuit configuration, are compared and discussed. It is shown that the surface potential decay technique allows for a wider range of electric field strength and reduces the time span of the measurements. [ABSTRACT FROM AUTHOR]

The temperature and field dependencies of electric conductivities of two types of silicone rubber-based polymers intended for use in high voltage direct current applications are presented and discussed. The conductivities obtained with the standard method by measuring a current through the material sample placed between metallic electrodes in response to the applied voltage are compared with those deduced from the measured potential decay on pre-charged material surface in an open circuit configuration. The measurements were conducted in the range of the applied electric field strength (0.5–5) kV/mm and temperatures ranging from 22 °C to 70 °C. It is shown that the values of the conductivities obtained by the two methods are in agreement and their temperature dependences obey Arrhenius law yielding similar activation energies.

To design reliable high voltage cables, clean materials with superior insulating properties capable of operating at high electric field levels at elevated temperatures are required. This study aims at the electrical characterization of a byproduct-free crosslinked copolymer blend, which is seen as a promising alternative to conventional peroxide crosslinked polyethylene currently used for high voltage direct current cable insulation. The characterization entails direct current (DC) conductivity, dielectric response and surface potential decay measurements at different temperatures and electric field levels. In order to quantify the insulating performance of the new material, the electrical properties of the copolymer blend are compared with those of two reference materials; i.e., low-density polyethylene (LDPE) and peroxide crosslinked polyethylene (XLPE). It is found that, for electric fields of 10–50 kV/mm and temperatures varying from 30 °C to 70 °C, the DC conductivity of the copolymer blend is in the range of 10−17–10−13 S/m, which is close to the conductivity of crosslinked polyethylene. Furthermore, the loss tangent of the copolymer blend is about three to four times lower than that of crosslinked polyethylene and its magnitude is on the level of 0.01 at 50 °C and 0.12 at 70 °C (measured at 0.1 mHz and 6.66 kV/mm). The apparent conductivity and trap density distributions deduced from surface potential decay measurements also confirmed that the new material has electrical properties at least as good as currently used insulation materials based on XLPE (not byproduct-free). Thus, the proposed byproduct-free crosslinked copolymer blend has a high potential as a prospective insulation medium for extruded high voltage DC cables.

The space charge dynamics is very important for electrical breakdown of alumina based ceramics. In this paper, the charge trapping/detrapping characteristics of alumina based ceramics were studied by means of isothermal surface potential decay (ISPD) method. For alumina and zirconia toughened alumina (ZTA) ceramic samples, the ISPD curves charged by corona discharge as well as microstructure characterization were carried out. For the first time, crossover phenomenon and hollow shaped potential profile were observed and reported in alumina based ceramics, indicating a surface potential decay process dominated by charge injection and volume conduction affected by the trap states in materials. In addition, the comparative trapping characteristics were evaluated based on a charge detrapping controlled decay model. The correlation between trap distribution and microstructure of alumina based ceramics was investigated. It was proposed that different charge trapping characteristics of alumina based ceramic samples was caused by varied shallow trap density of grain boundary. [ABSTRACT FROM AUTHOR]

Insulating layer of photovoltaic (PV) modules is subject to irradiation-induced ageing that can affect their security, stability and lifetime. Early potential induced degradation phenomena were founded in the insulating Polyethylene Terephthalate (PET) backsheet of photovoltaic module. However, the designed lifetime of PET insulating backsheet is inconsistent with their practical service time. We have found that the corona discharge in the air provides consistent relative degradation behavior, and that crystallinity values can vary based on different electron avalanche duration. Surface charge evacuation phenomena of PET under varied corona discharge time were also tested. An increase tendency between the chemical degradation and the elevated electron irradiation was investigated. The insulating function and crystallinity properties correlated to its degradation factors as electron irradiation and corona discharge time will be discussed in this work. In this paper, the PET samples were polarized under a corona discharge configuration. Moreover, the surface potential induced by surface charge accumulation effect were tested. A DSC measurement was conducted on these samples. As a result, the bell shaped surface charge distribution and three DSC curves were provided. This paper will present the effect of potential induced aging and electron avalanche caused by corona discharge on the crystallinity of backsheet in solar photovoltaic system for sustainable energy. [ABSTRACT FROM AUTHOR]

This work presents a numerical model for studying charge dynamics during decay of pre-deposited surface charges on an enamel insulation comprising two layers of different materials. It is shown that the considered surface charge decay is dominated by charge injection from insulation surface into the bulk and the drift of injected carriers along the direction of induced electric field. These features allow for estimating charge carriers' mobilities in the studied insulation. The developed model incorporates experimental outcomes as well as the proposed effect of an internal interface between insulating layers on hindering charge transport through the bulk. The transient process of charge accumulation at the internal interface is exhibited and correlated with the well-known Maxwell-Wagner-Sillars polarization model. Contribution of charge injection at each insulation surface into the bulk to the measured potential decay is evaluated and compared. [ABSTRACT FROM PUBLISHER]

A model based on surface potential decay (SPD) measurement was developed to study the trap energy distribution of hole-type and electron-type traps in materials by considering two distinct energy levels (i.e., shallow and deep traps) and the detrapping process. An approximated Dirac function ?((E-Em)/kT) was also introduced to obtain a consistent unit of trap density. Besides, the space charge distributions (such as uniform, linear and exponent distribution) in positively and negatively charged materials were also taken into account. In order to verify our proposed model, the different SPD curves of low density polyethylene (LDPE), LDPE/zinc oxide (ZnO) microcomposite and nanocomposite were analyzed. The results show that the proposed model is effective to obtain the trap energy distribution in materials. The SPD curves in positively and negatively charged samples show a fast decay followed by a slow decay, which is agreed with our assumption of shallow and deep traps. Two peaks are clearly observed from the trap energy distribution. The trap energy distributions of hole-type and electron-type traps in these materials are distinct from each other. This implies some essential nature of hole-type and electron-type traps (i.e., intra-chain character for hole-type traps and inter-chain character for electron-type traps). In addition, compared to LDPE and LDPE/ZnO microcompoiste, the decreasing energy level and the increasing trap density of shallow traps as well as the decreasing trap density of deep traps in LDPE/ZnO nanocomposite may be attributed to the effect of the interaction zone surrounding nanoparticles. [ABSTRACT FROM PUBLISHER]

Gas‐insulated switchgear (GIS) spacers are made of epoxy resin. However, the surface charge accumulation has been a great concern to the safe operation of GIS, which causes the frequent flashover faults on spacers. In this study, micro‐silicon carbide (SiC) particles with non‐linear conductivity were added into epoxy matrix and the filler content varied from 0 to 14 vol%. Then, the bulk conductivity and surface potential decay (SPD) tests were conducted. The obtained results showed that the epoxy/SiC composites have obvious non‐linear conductivities and the non‐linear‐conductivity threshold decreases with the increasing filler content. The addition of SiC can effectively resist the rise of surface potential and enhance the surface charge dissipation process. From the trap energy distributions, it can be inferred that the deep traps of ∼0.9 eV should be the intrinsic traps of epoxy and the shallow traps of ∼0.8 eV are considered to be introduced by SiC. Furthermore, the simulation results confirmed that the sharp increase of carrier mobility in non‐linear region significantly reduces the remaining time and possibility of a de‐trapped charge being recaptured by traps before reaching the grounded electrode. Therefore, the high conductivity in non‐linear region contributes a lot to the increase of SPD rate. [ABSTRACT FROM AUTHOR]

The nonlinear conduction of polymeric insulation may solve the surface charge accumulation, avoiding the distortion of electric field and the flashover phenomenon. As the silicon carbide (SiC) powder is usually used to improve the nonlinear conduction of polymer composites, the epoxy/SiC nanocomposites are prepared and the dc conductivity, permittivity and isothermal surface potential decay characteristics are investigated. The experimental results show that the conduction of high filler loading is field dependent and is attributed to a new conduction mechanism. The permittivity is closely related to the interaction zone around nanoparticles. The isothermal surface potential decay characteristics are greatly affected by the charging polarity, charging level and filler loading. The investigation indicates that the nonlinear conduction plays an important role in the surface potential decay. [ABSTRACT FROM PUBLISHER]

The ability to retain localized charges at the surface or interface of dielectric materials is a universal property that applies to many different fields such as tribocharging, charge nanopatterning, nanoxerography, etc. Once the surface is charged, its stability and subsequent discharging rate will determine the potential applications of a given system. This decay rate is properly defined by the macroscopic equations which depend on dielectric constants and conductivities of the two media. Here, we derive the equations to model the decay of charge distributions localized at the surface/interface of materials and solve them avoiding additional approximations made so far. Addressing the problem in the Fourier space, we arrive to a compact generic equation which provides a useful tool to determine both the bulk and surface conductivities of a material. Furthermore, we show that Kelvin Probe Force Microscopy (KPFM) is a particularly suited method to exploit this tool. Monitoring the charge decay of previously injected charge patches on silicon dioxide (SiO 2), together with an appropriated data analysis, we verify the behavior predicted by our equations. This allows us to characterize the surface and bulk conductivities of SiO 2 layers as well as its dependence with the relative humidity. [Display omitted] • Surface charging of dielectric materials is a universal property. • The dependence of the surface charge decay rate with the system geometry is established. • Surface and bulk conductivities are obtained with Kelvin probe force microscopy. [ABSTRACT FROM AUTHOR]

Surface potential decay (SPD) characteristics of a corona charged polyethylene terephtalate (PET) are investigated experimentally.A negative corona discharge produced in a needle – grid – plate electrode system was employed to charge the surfaceof the film samples (thickness: 0.5 mm; surface: 50 mm x 50 mm). The temperature effect, initial potential and relativehumidity are presented. The variation domains for the three factors were respectively: 20 to 60°C; -1000 to -1800 V; 20 to80%. All surface potential decay measurements were carried out in a commercial climatic chamber, where relative humidityRH and temperature T were rigorously controlled. The aim of the present work is to demonstrate the effectiveness of the Experimentalmethodology for evaluating the effects of these factors. This investigation has showed that the surface potentialdecay is highly conditioned by temperature, relative humidity and charge density initially lay down on the material. Chargeinjection mechanism in material bulk seems to be the more probable hypothesis to explain charge flow in PET. More over,the experiment results confirm the influence and the role of thermal activation and electrical field on the potential decay

Charge transport behaviors of dielectric under electron radiation have an important influence on surface flashover performance. In this paper, charging process and model of dielectric during electron radiation are investigated based on the synergistic effect of electron movement on dielectric surface and charge transport properties in dielectric surface layer. For one thing, electrons accumulated in dielectric surface layer will form a reverse electric field acting against kinetic electrons flowing to dielectric surface, which affects the energy and density of electrons reaching the surface. For another, the changes of electron energy and density will further affect the dynamic processes of electron deposition, transport and accumulation in the surface layer. A dielectric charging model is proposed, and charge transport characteristics in dielectric surface and surface layer are obtained, including the temporal behavior of the incident kinetic electrons flowing to dielectric surface, the temporal behavior of secondary electrons and surface conduction charge, as well as the spatial and temporal behavior of the interior potential and electric field. Based on surface potential decay curves of polyimide under different electron energy levels (3-11 keV), the surface potential decay process and model are investigated. The surface trap distribution of polyimide shows different properties under different energy levels. The shallow trap level increases slightly with the increase of electron energy, ranging from 0.81 eV-0.85 eV, while the deep trap level remains unchanged about 0.94 eV. Besides, the amount of trap charge density gradually increases with the increase of electron energy. [ABSTRACT FROM AUTHOR]

Charge accumulation under high-voltage DC is a major concern in the transmission system as its presence distorts the local electric field. By performing chemical treatment on the polymeric insulation via fluorination process, the charge dynamics of the treated material can be modified. Surface fluorination treatment has been proven to be an effective tool to enhance the dielectric properties. The treatment slightly improves the surface conductivity value and enhances the surface potential decay rate, which helps to prevent the accumulation of surface charge and consequently improve the breakdown strength of epoxy samples. However, the authors suspected the introduction of a fluorinated layer on top of the epoxy sample may have the capacity to absorb moisture from the environment. The increase in the surface conductivity by the fluorination treatment may not come from the fluorine layer itself, but rather from the absorbed moisture in the surface layer. The loss of moisture from the surface may lead to a dip in dielectric performance of the treated materials. Hence, a study on the moisture effect on the surface fluorinated epoxy resin was designed. The fluorinated samples were characterised by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDX) to analyse the morphology as well as the concentration of elements in the treated materials. The samples then were dried in vacuum oven at 105 °C and/or inside nitrogen gas chamber at room temperature for 24 hours to forcefully dry out the absorbed surface moisture. The measurements of surface DC conductivity and surface potential decay were taken before and after the drying process. It has been found that the fluorination treatment on epoxy resins did give rise to high moisture content on the surface which plays an important contribution towards the dielectric enhancement properties. [ABSTRACT FROM AUTHOR]

Results of measurements of surface potential decay on coating layer of enameled wires are presented. In experiments, surfaces of winding samples were charged by dc corona of both polarities and decay of surface potential induced by charges deposited on the materials was recorded utilizing non-contact technique. The power-law type of time dependences of surface potential decay rates was obtained that indicated a dominant role of charge injection and/or dipolar polarization in the decay process. Furthermore, several decay mechanisms were employed for examining the experimental data, which revealed that potential decay was initially governed by the injection of charges due to electron transfer between the deposited charges and the material. Later on, the contribution of polarization to decay process was significant, while intrinsic conduction became the prevailing decay mechanism only at the latest stage as polarization was stabilized. [ABSTRACT FROM AUTHOR]

In the present paper the influence of both time and storage temperature on the surface potential decay of polypropylene (PP) composite films was investigated. We have investigated the 200 ?m PP composite films with different weight concentrations of the particles (ZnO or CuO) - 0 wt.%, 2 wt.% and 4 wt.%. The samples were charged in a corona discharge by means of a corona triode system for 1 minute under room conditions. Positive or negative 5 kV voltage was applied to the corona electrode and 1 kV voltage of the same polarity as that of the corona electrode was applied to the grid. After charging, the surface potential was measured using the method of the vibrating electrode with compensation. The results obtained show a significant change in the electret behavior of the composite films after the inclusion of ZnO or CuO particles with different concentration into the PP matrix. The possible surface potential decay mechanisms responsible for the electret?s behavior were discussed. It was established that the surface potential decay depended on the corona polarity, the particles concentration and the type of the particles. It has been experimentally demonstrated that the normalized surface potential of PP composite films with different concentrations of ZnO or CuO particles decays faster than the one of the pure PP films. [ABSTRACT FROM AUTHOR]

Sieving and air classification are not efficient enough for the extraction of the high-nutritional-value constituents of wheat. The aim of this article is to validate a simple electrostatic separation method of peeling and gluten, which are two such nutriments contained in finely ground wheat grains. The electrostatic separator is composed of metallic grounded belt conveyer and a rotating roll electrode connected to a high voltage supply. The electrostatic behavior of peeling and gluten powders was characterized using surface potential decay and direct charge measurements. These first set of experiments pointed out the conductive behavior of these powders: in contact with a grounded electrode, they lose their charge in less than 10 s. In a second set of experiments, mixtures of 50% peeling and 50% gluten powders were processed by electrostatic separation. Experimental design methodology was used to model the outcome of the separation process as function of two control variables: the high-voltage applied to the roll electrode and the speed of the belt conveyor electrode. In this way, it was possible to determine the optimal operational conditions for the recovery of high-purity peeling and gluten fractions. [ABSTRACT FROM AUTHOR]

Investigations of dielectric properties of a newly developed enamel wire insulation created by adding chromium (III) oxide (Cr2O3) filler to polyamide-imide enamel base are presented. Results of measurements of electrical conductivity and complex permittivity at various temperatures as well as surface potential decay are discussed and compared with corresponding properties of standard enamel insulation. Contributions of different polarization relaxation processes in both enamels are examined based on the obtained master curves of dielectric response. In addition, the properties of chromium oxide filler are characterized separately and utilized further for analyzing its impact on the performance of enamel wire insulation by means of computer simulations. The experimental and simulated results demonstrate that the introduction of chromium oxide yields changes in the electrical properties that allow for mitigating the voltage stress in a wound insulation system. Furthermore, a correlation between the obtained results and the earlier described improved resistance to partial discharge activity of the chromium oxide filled enamel is discussed. [ABSTRACT FROM AUTHOR]

The dielectric behavior of an insulating material is commonly characterized by exposing its surface to a DC corona discharge for relatively short duration and then recording the decay of the electric potential Vs at its surface, Vs = f(t). The representation of the surface potential decay (SPD) by using tdVs/dt = f(log t) plots has already been used to perform a finer analysis of the dielectric response of film insulators. The present paper takes advantage of this peculiar way of representing the SPD in view of characterizing the dielectric behavior of fibrous electrets negatively-charged from a triode-type (wire-gridplate) electrode system. The experiments were performed in ambient air (temperature: 20 ± 1 ?C), at various values of the relative humidity (range 25 % to 65%). This paper reports experimental data collected on a polypropylene (PP) film (sheet thickness: 250 μm) and two types of PP non-woven media (fabric thickness: 300 μm), characterized by different fiber diameters (20 μm and 4 μm). The initial surface potential and the dynamics of SPD of fibrous dielectric materials were found to be affected by the corona charging conditions (relative humidity of the ambient air, grid voltage and grid current), as well as by the properties of the fibers and the structure of the non-woven media. An appropriate model of SPD should take into account charge injection from the media-electrode interface, charge transport controlled by bulk mechanisms and local high electric field effects due to the porous structure of the media. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, silicon based planar technology and high performance fluorocarbon polymer polytetrafluoroethylene (PTFE) are combined to achieve PTFE thin film electrets on wafer. The PTFE film is fabricated onto SiO2 substrates and Pt substrates using spin coating and annealing processes, and its electret effect is demonstrated using negative corona charging method. PTFE electrets with different surface morphology exhibit different charge storage capability. Maximally, surface potential of −396 V is achieved on Pt substrates and −361 V is achieved on SiO2 substrates. The average retain rate of surface potential over 240 h is 90.6% for Pt substrates and 76.3% for SiO2 substrates. The proposed method presents the primary step toward integrated electrostatic devices. [Copyright &y& Elsevier]

Abstract: In this work, surface properties of polyimide (PI) films coated by thin layers deposited from pure hexamethyldisiloxane (HMDSO) vapours in low frequency powered plasma reactor have been investigated. The polymer thin layers were elaborated at different plasma treatment times. The surface characterization of the coated PI film is performed using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), refractive index, scanning electron microscopy (SEM), water droplet contact angle measurements and surface potential decay. The high carbon content revealed by ATR-FTIR analysis makes the coated surface PI films more hydrophobic. The water contact angle increased from 63° for untreated film to 115° after 10 min of HMDSO plasma coating. The coated PI surfaces were found to stay practically unchanged following storage of the samples in ambient conditions, indicating stable hydrophobic surface treatments. The increase of the refractive index indicates less porous structure. Scanning electron microscopy images showed a homogenous coating without crack. Surface potential evolution after corona charge deposition showed the retention of deposited charges at the surface of coated PI film. Correlation between these different analysis techniques results has been discussed. [Copyright &y& Elsevier]

To evaluate spacecraft charging level and predict surface and internal electrostatic discharging (ESD) probability, it is important to know the charge transport properties of high insulation materials, such as epoxy resin/glass composition (FR4), Teflon and polyimide. In present work, the charge transport properties of the space insulators are revealed by a bipolar charge transport (BCT) model combined with genetic algorithm (GA). It has been found that the BCT model can be used to simulate the experimental surface potential decay (SPD) results, and these two results are in good agreement with each other. The BCT model consists of charge injection, conduction, trapping, detrapping, and recombination processes. Stochastically initiating a series of charge transport parameters by GA, we can compute the SPD curves of materials by the BCT model. Used GA operates, the best fitting SPD curve of the experimental results can be obtained. From the comparison of the calculated and the experimental SPD results, we obtain the charge transport properties of FR4 and polytetrafluoroethylene (PTFE). [ABSTRACT FROM PUBLISHER]

Abstract: Xerographic method consists in monitoring of decay of the surface potential of the photoconducting layer under illumination. The charge carrier photogeneration quantum yield is determined basing on the initial potential decay rate. In this work the photogeneration quantum yield for theoretically simulated initial surface potential decay is analyzed for a case when simultaneous photogeneration and recombination occur. A model disordered organic photoconductor is considered in which the photogeneration probability is described by the Onsager model of geminate recombination and the cross-section for recombination exhibits power dependence on the electric field. Photogeneration yields calculated in the classical way and the yields calculated with assumed bimolecular recombination are compared. It is shown that for high bimolecular recombination probability correctly determining the classical xerographic method of photogeneration quantum yield is difficult. [Copyright &y& Elsevier]

Abstract: Surface potential decay method has been frequently used to characterize the charge state of insulating materials. The present paper aims at a critical evaluation of this method when used for the characterization of granular plastics, by comparing it with the electric field monitoring by means of non-contact vibrating probes, and with the measurement of the charge induced in a capacitive probe connected to a Coulomb-meter. The experiments were performed on corona-charged polyethylene, polycarbonate, polyamide, and acetyl – butadiene – styrene granular materials. The experimental results show that surface potential decays faster than the electric field or the charge measured with the capacitive probe. The dimensions of the probes and the capacitive coupling between them and the samples, may explain this difference. Part of the potential decay measured by the smaller-size probe of the electrostatic voltmeter is due to the surface conduction, while the measurements made with the larger-size electric field and capacitive probes are less affected by this phenomenon. [Copyright &y& Elsevier]

Abstract: The control of the residual electric charge carried by granular materials processed in various electrostatic installations is a prerequisite for the safe and efficient operation of the respective industrial equipment. The aim of the present work was to evaluate the neutralization efficiency of polyethylene granules exposed to an AC corona discharge from a wire-type electrode. The control variables and their domains of variations were the following: the amplitude and the frequency of the applied high voltage (16–18 kV, 20–400 Hz), the position of the corona electrode (3–7 cm above the ground plate that carries the sample) and the duration of the exposure to the corona discharge (4–10 s). The surface potential decay method was used for monitoring the charge carried by granular samples of PE before and after neutralization. Design of experiment methodology was employed to evaluate the influence of each of the above mentioned control variables and determine the optimum operation conditions. The efficiency of the neutralization was characterized by the ratio between the values of the surface potential before and after AC corona discharge exposure. The obtained results show that neutralization efficiency may be improved by increasing the frequency of the high voltage as well as by adequately correlating its amplitude with the inter-electrode spacing. [Copyright &y& Elsevier]

Abstract: PI nanocomposite films containing surface modified nanoparticles by employing silane coupling agent were prepared using in-situ dispersion polymerization process. The surface potential decay measurements on films were investigated over the different negative corona-charged voltages and times in a controlled environment where temperature and relative humidity were kept at 21 °C and 45%, respectively. There is a significant change in the surface potential decay characteristics after nano-fillers were introduced into polyimide. The surface potential decay pattern depends also on the amount of nano-fillers. The possible surface potential decay and corona resistance mechanisms responsible for the observed phenomena were discussed. [Copyright &y& Elsevier]

Abstract: In the present paper the surface potential decay after dc corona charging of gamma-irradiated low-density polyethylene (LDPE) has been studied. The irradiation was carried out in air, nitrogen gas and vacuum to investigate the effect of irradiation environment on the surface potential of LDPE. Samples with different absorbed doses were obtained by exposing samples to 60Co for various times at room temperature. It has been found that there is a significant change in the surface potential decay characteristics after different irradiation dose and the surface potential decay pattern depends also on irradiation environment. The possible surface potential decay mechanisms responsible for the above were discussed. The results are useful in the context of long-term performance of electrets. [ABSTRACT FROM AUTHOR]

New fractionation technologies are presently under investigation in order to enhance the wheat bran nutrient value. The explicit aim of this paper is to evaluate the possibility of using electric field forces for the separation of the fine particles generated from each wheat bran tissue during the milling process. Corona-charging and surface-potential-decay experiments were performed on samples of finely ground wheat bran and aleurone tissues (maximum size of 0.3 mm). Ground bran, which has a higher moisture content, more rapidly loses the charge imparted by corona discharge. For both kinds of samples, finer particles charged better than larger particles, and lyophilized samples were found to better preserve their charge than those not subjected to a freeze-drying process. An experiment carried out using a belt-type corona electrostatic separator validated the possibility of sorting these tissues based on the differences in their charge decay characteristics. Tribocharging experiments performed on the same tissues have also led to encouraging results: The charge/mass ratio of ground bran tissues was twice that of aleurone. These differences in the physical properties of the two types of tissues provide the technical basis for the development of electrostatic-separation technologies as part of more efficient bran-cracking strategies. [ABSTRACT FROM AUTHOR]

Abstract: The initial potential at the surface of the sample, as well as the temperature and the relative humidity of the ambient air are known to influence the surface-potential decay characteristics of corona-charged thin insulating films. The aim of the present work is to demonstrate the effectiveness of the Experimental Design methodology for evaluating the effects of these factors. Thus, a full factorial experimental design was carried out on a thin film of polyethylene terephthalate (thickness: 0.5mm; surface: 50mm×50mm). A negative corona discharge produced in a needle–grid–plate electrode system was employed to charge the surface of the film samples. The variation domains for the three factors were respectively: −1000 V to −1800V; 25 to 55°C; 50% to 80%. The surface-potential decay process was characterized by two output variables: the time needed for the potential to reduce to respectively 50% and 10% of the initial value. It was found that the former is more affected by the temperature, while the latter is more sensitive to the variation of the relative humidity. [Copyright &y& Elsevier]

Abstract: Corona discharge has a wide range of industry applications, such as charging the photosensitive layer and the toner particles in photocopying machines, modifying the wet-ability of plastic films, and conditioning the electrets for air filters. In all these situations, it is important to evaluate the surface charge density and compare it to the dielectric rigidity of atmospheric air. Experiments were carried out on 0.3mm and 0.8mm thick non-woven polypropylene fibrous media (average diameter of the fibres: 20μm) that were exposed to positive corona discharges from a wire–grid–plate electrode system. The electrode system was powered from a continuously-adjustable DC high-voltage supply, employed as constant current generator. The monitored variable was the surface potential detected by the probe of an electrostatic voltmeter. The controlled variables were the potential of the grid electrode and the pre-conditioning temperature of the samples. The results of the experiments enabled a crude evaluation of each factor effect. Research should continue, using the experimental design methodology, in order to establish the optimum operating conditions. [Copyright &y& Elsevier]

Abstract: TiO2:poly(N-vinylcarbazole) (PVK) bulk-heterojunctions (BHJ) have been elaborated from a blend of a TiO2 precursor with the polymer in solution. The TiO2 precursor is hydrolyzed with the surrounding air humidity in thin film. Titanium isopropoxide [Ti(iOPr)4] and Tetrakis (9H-carbazole-9-yl-ethyl-oxy) titanium [Ti(OeCarb)4] were used as TiO2 precursor. Photogeneration quantum yield in BHJ of TiO2:PVK were determined by the surface potential decay (SPD) technique. Photovoltaic effect was studied in ITO/PEDOT:PSS/TiO2:PVK/Al structures. It was found that the photovoltaic performance is strongly dependent on the homogeneity of the blends. The improved dispersion of the TiO2 phase obtained with the precursor bearing a carbazole group allows efficient electron transport and fill factor enhancement of the photovoltaic devices. [Copyright &y& Elsevier]

Surface potential decay (SPD) characteristics of a corona charged polyethylene terephtalate (PET) are investigated experimentally. A negative corona discharge produced in a needle - grid - plate electrode system was employed to charge the surface of the film samples (thickness: 0.5 mm; surface: 50 mm x 50 mm). The temperature effect, initial potential and relative humidity are presented. The variation domains for the three factors were respectively: 20 to 60°C; -1000 to -1800 V; 20 to 80%. All surface potential decay measurements were carried out in a commercial climatic chamber, where relative humidity RH and temperature T ?were rigorously controlled. The aim of the present work is to demonstrate the effectiveness of the Experimental methodology for evaluating the effects of these factors. This investigation has showed that the surface potential decay is highly conditioned by temperature, relative humidity and charge density initially lay down on the material. Charge injection mechanism in material bulk seems to be the more probable hypothesis to explain charge flow in PET. More over, the experiment results confirm the influence and the role of thermal activation and electrical field on the potential decay. [ABSTRACT FROM AUTHOR]

Abstract: Surface potential measurements after corona charging are reported on metal–insulator structures with artificial defects. On organic anticorrosion coatings, potential cartography shows clear evidence of bad adhesion areas. A detailed analysis has been carried out on printed circuit board composite epoxy fiberglass insulating plates with a calibrated cavity, on which potential decay and return data clearly exhibit a particular response compared with non-voided plates. This response is analyzed in terms of material polarization and charge injection from the interface. We conclude from this analysis that charge injection from the cavity is enhanced, whereas polarization is reduced in the cavity area. [Copyright &y& Elsevier]