Factors that influence the corona charging of fibrous dielectric materials

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 0.3 mm and 0.8 mm thick non-woven polypropylene fibrous media (average diameter of the fibres: 20 μm) 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.     

Electrical effect of soot depositions in a co-axial wire pipe flow

An investigation was performed to study the electrical effects on the soot deposition in a co-axial wire cylinder with cooled walls. Experiments were performed for applied voltages from 0 to ?5 kV or +5 kV and a diesel exhaust mass flow rate of 20 kg/h or Reynolds number of approximately 9000. The outer wall was cooled using water with a temperature of approximately 40 °C, and the experiments were performed for exposure times of 2 h. The soot deposition layer thickness was measured using a non-destructive neutron radiography technique at the end of each experiment. The results show that the electric field had a significant effect on the soot deposition and increases it by a factor of approximately 4 at the applied voltage of 5 kV before spark on-set. The soot thickness was similar for the positive and negative polarities and the results show that there was significant deposition on the wire as well as the outer wall for both polarities. Since soot deposition even occurs on both corona wire and grounded pipe below corona on-set voltages of the clean system, there may be a significant pre-charging of the diesel soot with both polarities in the diesel exhaust gas as has been observed by the recent measurements of Marieq [On the electrical charge of motor vehicle exhaust particles, Journal of Aerosol Science 37 (7) (2006) 858–874].     

Preparation of zeolite nanorods by corona discharge plasma for degradation of phenazopyridine by heterogeneous sono-Fenton-like process

The plasma-modified clinoptilolite (PMC) nanorods were prepared from natural clinoptilolite (NC) utilizing environmentally-friendly corona discharge plasma. The PMC and NC were characterized by XRD, FT-IR, SEM, EDX, XPS and BET, which confirmed the nanocatalyst formation. The catalytic performance of the PMC in the heterogeneous sono-Fenton-like process was greater than the NC for treatment of phenazopyridine (PhP). The desired amounts were obtained for experimental parameters including initial pH (5), PMC dosage (2 g/L), K₂S₂O₈ concentration (2 mmol/L), ultrasonic power (300 W) and PhP concentration (10 mg/L). Reactive oxygen species scavengers decreased the removal efficiency of the PhP. The treatment process followed pseudo-first order kinetic and seven degradation intermediates were identified by the GC–MS technique.     

Experimental study of the effect of wind on positive and negative corona from a sharp point in a thunderstorm

Corona discharge measurements made during a thunderstorm on a mountain at an altitude of almost 3300 m above sea level were analyzed for their dependence on the ambient electric field and the local wind speed. The corona current data were taken from an earthed needle point mounted at a height of 3 m above the ground. The coronating point was exposed to natural wind speeds of up to 14 m/s. Comparisons are made with empirical relationships dating back to the mid-1900s and new formulae are provided to describe the effect of wind on the magnitude of corona current measured under natural conditions.     

EHD atomization characteristics of a point-plate system with a porous point electrode

An electrohydrodynamic (EHD) atomization from a point-to-plate system, with a wet porous point as a corona electrode, has been studied. And the atomized water droplets from the wet porous point, as well as the water droplet traces, the water droplet charge-to-mass ratios, and the water droplet number concentrations, were investigated. It was observed that the wet porous point can atomize abundant amounts of water droplet, 2.8, 2.6 and 2.2 mg/min for negative, AC and positive corona, respectively. The migrated water droplet traces were observed. The positive wet porous point atomized very fine water droplets than those obtained with the negative wet porous point. Moreover, the water droplets atomized from the AC corona showed granular-like larger traces. A weak corona discharge can atomize water droplets very effectively. On the other hand, an intensive corona discharge can eject more water droplets. As a result with the wet porous point, the maximum corona-current-based and corona-power-based water droplet atomization yields of Y_C = 3.34, 3.32 and 3.25 μg/μAs and Y_P = 0.35, 0.40 and 0.27 mg/Ws have been obtained for the negative, AC and positive corona discharges.     

Research on the possibility of ignition of materials by electrostatic discharge in pure oxygen environment at different pressures

In spacecraft environments, spacesuits materials such as textiles, leather, or other materials are used in a pure oxygen environment. The materials are in serious risk of being ignited by electrostatic discharge (ESD) and may cause fire and even disasters or death of astronauts. In this paper, a well sealed chamber was first developed for ignition test. Then, ignition tests of four textiles and leather materials were carried out under oxygen pressures of 42 kPa, 101 kPa and 142 kPa using different ESD models. It is concluded that the materials are more easily ignited at higher oxygen pressure.     

Electret properties of ethylene–propylene random co-polymer

Thermally stimulated current (TSC) spectra were examined for ethylene–propylene (EP) random co-polymer at different charging voltages V_p with positive and negative polarities. Observed TSC spectra showed two well-separated TSC bands, B_L and B_H, which respectively appeared in the temperature regions below and above 100 °C. Observed V_p dependence of B_L was quite different from that of typical polypropylene homo-polymer: As V_p increased, B_L band grew keeping its peak position same at 65 °C, and the band shape unchanged, as if the traps responsible for the B_L band are a single set of traps with the same trap depth and capture cross section. The trap depth of B_L was about 1.9 eV and 1.7 eV for positively charged EP and talc-containing EP samples, respectively. EP samples also showed unique TSC bands above 100 °C: one is a narrow TSC band peaked at 120 °C and the other is an unusual TSC band which was non-vanishing even at 165 °C just before destruction of samples by their melting. Consequently, the utmost stable charge density in EP co-polymer above 100 °C was found to be 3.5 × 10^?4 C/m² and 6.0 × 10 ^?4 C/m² for positively and negatively charged samples, respectively. These equivalent surface charge densities are much larger than those of usual polypropylene homo-polymer.     

Factors that influence the surface potential decay on a thin film of polyethylene terephthalate (PET)

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: 0.5 mm; surface: 50 mm × 50 mm). 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 ?1800 V; 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.     

Characteristic measurement of spark transients due to finger touch

To understand a mechanism of spark transients, using a 12-GHz digital oscilloscope, we measured discharge currents due to a finger touch through a hand-held metal bar or a fingertip with an aluminum foil attachment from a charged human body with a charge voltage of 600 V. As a result, we found that the hand-held metal bar and aluminum foil attachment produce a one-shot discharge current with steeply rising time shorter than a 100 ps, while the fingertip without any aluminum foil attachments produces multiple-shot discharge currents with gently rising time larger than a 100 ps and significantly low amplitudes.     

Investigation on the microscopic features of layered oxide Li[Ni1 / 3Co1 / 3Mn1 / 3]O2 and their influences on the cathode properties

Three kinds of samples of Li[Ni_1 / 3Co_1 / 3Mn_1 / 3]O₂ were prepared respectively from direct solid-state reaction method, combustion method and co-precipitation route and their microscopic structural features have been investigated using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), magnetic susceptibility measurement and X-ray photoelectron spectroscopy (XPS). The microscopic features such as uniform distribution of transition metal ions at 3b-site and the site-exchange ratio between lithium and nickel were found to be significantly dependent on the synthetic routes. The electrochemical properties of three samples were monitored using 2016 coin-cell by galvanostatic charge–discharge cycling test and cyclic voltammetry, which showed that the microscopic structural features are deeply related with the electrochemical performance. The obtained results also suggested that the combustion method may become a much simple alternative synthetic route to the complicate co-precipitation method.     

Modelling of corona discharge in cylinder-wire-plate electrode configuration

Numerical computation of the electric field strength and ionic space charge density in electrode systems consisting of ionizing wire and non-ionizing cylinder, connected to the same DC high-voltage supply and facing a grounded plate, is a difficult problem, which is of interest to several electrostatic processes applications. In a previous study a simple numerical method has been proposed to calculate the spatial distributions of electric field and ionic space charge in a case of a continuum and uniform corona discharge originating at the surface of the wire. The aim of the present paper is to improve the physical model of the corona discharge in this particular electrode configuration, by assuming a more realistic law of charge injection on the wire circumference. The computations were carried out for an ionizing wire of radius r=0.1 mm, located at different distances h from a metallic tubular support of radius R=13.4 mm.The initial conditions of the corona discharge took into account the non-uniformity of the charge injection around the ionizing wire electrode. The computational results were compared with those obtained under the assumption of uniform corona discharge. The comparison pointed out that neither the non-uniformity of the electric field nor that of the charge injection can be neglected. They depend on the geometry of the electrode system and affect the distribution of the electric field and of the space charge density in the inter-electrode gap.     

X-ray photoelectron spectroscopy of CeO2–Na2O–SiO2 glasses

A series of (CeO₂)_x–(Na₂O)_0.3–(SiO₂)_(0.7−x) glasses, where 0.025 ≤ x ≤ 0.075, have been synthesized and investigated by mean of X-ray photoelectron spectroscopy (XPS). The Ce 3d spin-orbit doublet was curve fitted in order to quantify the proportions of each cerium oxidation state in these glasses. It was found that Ce ions are predominantly in the Ce(III) state in glasses with compositions x ≤ 0.075, while mixed Ce valences were found in the glass with composition x = 0.10. The O 1s spectra have also been curve fitted with two components, one from bridging oxygen (BO) and the other from non-bridging oxygen atoms (NBO). The measured number of NBO, based on the fact that only oxygen atoms in the site Si–O–Na⁺ contribute to the NBO peak, was found to be constant at ∼35% for all samples, in good agreement with the value calculated from the glass composition and inductively coupled plasma (ICP) suggesting that Ce ions enter the network as a glass intermediate. The thermal measurements done on these glasses agree well with the XPS findings.     

Band diagram for chemical vapor deposition diamond surface conductive layer: Presence of downward band bending due to shallow acceptors

The properties of surface conductivity (SC) of impurity-non-doped CVD diamond (001) samples were studied by various methods of sheet-resistance (R_S) measurement, Hall-effect measurement, XPS, UPS, SES, SR-PES, PEEM and 1D band simulation taking into account special emphases on deriving the information about the surface band diagram (SBD). The R_S values in UHV conditions were determined after no-annealing or 200 ～ 300 °C annealing in UHV. C 1 s XPS profiles were measured in detail in bulk-sensitive and surface-sensitive modes of photoelectron detection. The energy positions of valence band top (E_V) relative to the Fermi level (E_F) in UHV conditions after no-annealing or 200 ～ 300 °C annealing in UHV were determined. One of the samples was subjected to SR-PES, PEEM measurements. The SBDs were simulated by a band simulator from the determined R_S and E_V ? E_F values for three samples based on the two models of surface conductivity, namely, so-called surface transfer doping (STD) model and downward band bending with shallow acceptor (DBB/SA) model. For the DBB/SA model, there appeared downward bends of SBDs toward the surface at a depth range of ～ 1 nm. C 1 s XPS profiles were then simulated from the simulated SBDs. Comparison of simulated C 1 s XPS profiles to the experimental ones showed that DBB/SA model reproduces the C 1 s XPS profiles properly. PEEM observation of a sample can be explained by the SBD based on the DBB/SA model. Mechanism of SC of CVD diamonds is discussed on the basis of these findings. It is suggested that the STD model combined with SBD of DBB/SA model explains the surface conductivity change due to environmental changes in actual cases of CVD diamond SC with the presence of surface E_F controlling defects.     

XPS and SRUPS study of oxygen adsorption on Cd0.9Zn0.1Te (1 1 1)A surface

Synchrotron radiation ultraviolet photoemission spectroscopy (SRUPS) and X-ray photoelectron spectroscopy (XPS) have been applied to investigate oxygen adsorption on a cadmium zinc telluride (CZT) (1 1 1)A surface. The surface chemical composition and the surface oxidation process were monitored by recording the Te 3d, O 1s, Zn 2p, Cd 4d core level peaks, and the Cd MNN Auger peak. The CZT (1 1 1)A surface was effectively oxidized by dosing oxygen directly. The typical surface state of the clean CZT (1 1 1)A surface was identified. After oxygen exposure, this surface state disappeared and a signal due to the formation of O–CZT appeared. In addition, the work function of CZT decreased with the increasing oxygen exposure.     

Laser ablation fast pulse discharge plasma spectroscopy analysis of Pb,Mg and Sn in soil

Laser ablation fast pulse discharge plasma spectroscopy (LA-FPDPS) technique is a recently developed atomic emission analytical technique that is analogous to dual pulse laser induced breakdown spectroscopy (DP-LIBS). LA-FPDPS, however, uses a periodical oscillating discharge plasma generation method on samples instead of the second laser beam in DP-LIBS. Here we describe the electric characteristics and its application to the analysis of Pb, Mg and Sn in soil. Due to the fast discharge process, the peak power deposition rate is up to 1.5 MW, although the discharge energy is relatively small. The main energy deposition process only last for ~ 4 μs. From the measured spectra, calibration curves for Pb, Mg and Sn in soil were derived and the limits of detection were 1.5 μg/g, 34 μg/g and 0.16 μg/g respectively.     

Spectroscopic study of singlet oxygen photogeneration by lipophilic photosensitiser in liposomes

The time- and spectrally-resolved phosphorescence measurements of protoporphyrin IX (PpIX), haematoporphyrin (HpD) and singlet oxygen in liposomal samples under different oxygen concentrations were performed. We observed two different phosphorescence lifetimes of two distinct groups of photosensitisers (PSs). The group with shorter lifetime is located deep inside the nonpolar lipid bilayer, whereas the group with longer lifetime is exposed to H₂O due to its localisation near the bilayer surface. When the oxygen concentration in H₂O is increased about five times, a significant change in the slower decay component of the group of PS near the surface was observed from 3.8 to 1.3 μs (HpD) and from 3.3 to 1.2 μs (PpIX). On the other hand, the shorter phosphorescence components exhibit less-pronounced changes in lifetimes from 0.42 to 0.39 μs (HpD) and from 0.28 to 0.25 μs (PpIX). The singlet oxygen decay time decreases from 7.3 to 3.5 μs (PpIX) and from 8.0 to 3.5 μs (HpD) in H₂O. The results are discussed in the frame of a model, where an increase of the oxygen concentration in the aqueous medium is accompanied by only a slight increase of the oxygen concentration inside the lipid bilayer.     

Design and evaluation of a unipolar aerosol charger to generate highly charged micron-sized aerosol particles

In this study, a unipolar charger for generating highly charged microparticles was designed and its performance was evaluated both theoretically and experimentally. The measured particle charge number and corona current of the charger were in good agreement with the theoretical results from FLUENT. The experimentally determined average particle charge number of 1 μm PSL under an applied voltage of 8 kV was 128, which agreed well with the theoretically predicted and simulated values of 118 and 121, respectively. Computational calculations revealed the average charge of 10 μm particles to be 7560 at an applied voltage of 8 kV.     

Micro-force measurement of drag on a small flat plate in the presence of a corona discharge

The design of a micro-force sensor suitable for the measurement of corona drag and other low velocity drag studies in a small laboratory wind tunnel facility is described. Example drag data are given for dc corona discharge generated by sharp parallel electrodes mounted on a microscope glass slide with discharge parallel to the air flow. The arrangement simulates two-dimensional flow over a flat plate useful for theoretical analysis. Measurements of free stream wind velocities in the range 0–210 cm/s with attendant drag down to 10⁻⁷ N can be detected in this facility depending on the calibration. The force sensor utilizes two strain gages mounted on a 0.127 mm stainless steel “feeler gage” in a cantilever arrangement. A bridge circuit provides sensitivities in the range 40–250 N/mV using a gravitational calibration technique. Anomalous effects from suspension wires and the interaction of electrostatic forces with the surroundings are discussed.     

A DC corona discharge on a flat plate to induce air movement

This paper describes a DC surface corona discharge designed to modify the airflow around a flat plate. The electrode configuration consisted of two thin copper layers placed on each side of the plate's attack edge. Discharge optical measurements with a photomultiplier tube indicated that the light emitted by the plasma is pulsating at a frequency that increases with applied voltage. Moreover, with voltage higher than a threshold value, the electric discharge changes regime with brighter pulses. This discharge also induced an “ionic wind” whose velocity was measured with a pressure sensing probe (up to 1 m/s). Experiments with the particle image velocimetry system in a subsonic wind tunnel showed that this discharge can reduce the separated airflow on the flat plate for a flow of 14 m/s (Reynolds number of 187,000).     

Influence of ultrasonication times on the tunable colour emission of ZnO nanophosphors for lighting applications

This paper reports on the sonochemical synthesis of zinc oxide (ZnO) nanophosphors (NPr) at different ultrasonication times (5 min, 30 min, 1 h, 5 h, 10 h and 15 h) for near white light emission applications. X-ray photoelectron spectroscopy indicated that the O1s peak consists of two components. These were O1 (ZnO) and O2 (deficient oxygen; OH groups) centred at 529.7 ± 0.3 eV and 531.1 ± 0.3 eV, respectively. All samples showed UV and defect level emission (DLE). The DLE enhancement was due to the increase in oxygen related defects such as oxygen vacancies/interstitials. Due to the combination of near UV and DLE near white light emission in ZnO NPr was obtained. The emission could be tuned with different ultrasonic times. It was found that the ultrasonication time influenced the growth mechanism and luminescence properties of the ZnO NPr.