Corona Discharge In Air Research Articles

A quantitative laser Schlieren analysis of positive streamers in atmospheric air

A quantitative Schlieren analysis, using the shadow method in conjunction with a helium–neon laser, has been made of positive streamers in a point–plane corona discharge in air. Changes in the intensity profile of the laser beam, after it passed through the discharge gap, were measured and analysed to provide radial profiles of neutral density at different times following streamer onset. The profiles reveal that energy is transferred to the neutrals from streamer electrons in two stages. The first stage lasts for ca . 1 μs after streamer onset, during which time energy may be transferred directly from electrons and from rotationally excited molecules. The second stage lasts for ca . 100 μs, during which time energy may be transferred from vibrationally excited metastables. The resultant temperature rise causes reductions in neutral density of up to 13.5% below the atmospheric value.

Corona Corrosion of Aluminum in Air

Aluminum suffers severe pitting corrosion when used as an anode in negative corona discharges in ambient air. This paper gives a comprehensive account of the electrochemical interaction between a low electric field metal surface, especially aluminum, and the unipolar gaseous electrolyte created by an air corona. Introductory sections on coronas and corona corrosion give the necessary background. Physical and chemical analysis of the gaseous, liquid, and solid corrosion products of aluminum in air coronas demonstrate their close resemblance to the products formed in aqueous nitrate electrolytes.

Monte Carlo study of ionization zone electron kinetics in negative pin-plane coronas in atmospheric air

Monte Carlo simulation techniques are used to study the electron transport properties in the high electric field region near the pin in negative pin-plane corona discharges in atmospheric air. The results of the calculations show that the discharge electrons are nearly in equilibrium with the high local electric field near the pin tip. Consequently, a simpler computational model can be used to predict the voltage-current characteristics of these discharges. The results also show that ionization growth is very rapid for the pin-tip radii, gap lengths, and applied voltages which have been studied experimentally.

Simulation of trace species production by lightning and corona discharge in moist air

Numerical simulations of chemical processes initiated in moist air by lightning strokes and lightning coronas indicate that the amounts of major new species generated are not very different from the amounts previously found in dry air. Thus, the major new species produced globally in moist air are estimated to be: 2.4 megatonnes NO y −1, 0.28 megatonnes NO 2 y −1 and 220 tonnes N 2O y −1. The minor species, ozone and those containing hydrogen released by lightning from water in moist air are: 1.2 kilotonnes O 3 y −1, 25 kilotonnes HNO 2 y −1, 1.2 kilotonnes HNO 3 y −1, 0.32 kilotonnes H 2O 2 y −1 and 0.32 kilotonnes HO 2 y −1.

Electrothermographic behaviour of poly(methyl methacrylate) and leucomalachite green mixed system

The optimum charging parameters are found to be (a) corona voltage 6.0 kV (a.c.), (b) grid voltage 1.5 kV (d.c. + ve), and (c) charging time 30 sec. Corona discharge in air results in electrons, free radicals and ions being generated in the space between the corona wires and the grounded electrothermographic layer. In this case, where the grid potential is kept as positive, negative charge carriers (such as electrons and negative ions) are accelerated towards the layer. These carriers may either exchange charge with surface atoms of the layer, get trapped at surface states [7-9] and trap centres [10]; or may simply be attached to the surface by electrostatic attraction [111.

Surface treatment of metal surfaces by corona discharge

Abstract Aluminium and titanium surfaces have been treated by corona discharge in air and gave bonds of strength similar to those obtained by conventional chemical treatment.

Modification of the wettability of a poly(ethylene terephthalate) film treated by corona discharge in air

AbstractThe wettability of poly(ethylene terephthalate) films is an important criterion for their industrial use. The attainment of that property is realized by treatment of the material under corona discharge. The purpose of this article is to describe the influence of the principal parameters of the discharge on the modification of the surface properties; the influence was measured by physicochemical methods (ESCA, contact angle). The results prove that the most important physical parameters of the discharge are the wire‐cylinder distance, the current intensity, and the time of treatment. The analysis shows that the fixed species are oxygen and nitrogen in the form of carboxylic functions and amines or nitrogen oxides. In any case, the correlation between free surface energy and concentration of fixed chemical species shows that the surface properties depend on the chemical functions introduced into the material by the discharge.

An interferometric measurement of gas temperatures in corona discharges

An optical interferometer has been used to measure the increase in gas temperature in a point-to-plane corona discharge in air as a function of radial and axial position. For a corona current of 150 mu A, a 10 mm gap and a point radius of 0.35 mm, a maximum change in temperature of approximately 6K was observed. The authors' results suggest that under these conditions, where the corona voltage is approaching the spark breakdown voltage, the predominant ionisation process is two-step ionisation.

5305. A note on the creation of condensation nuclei by negative corona discharges in air at low pressure: N L Allen et al,J Phys D: Appl Phys,14 (12), 1981, L207–L209

5305. A note on the creation of condensation nuclei by negative corona discharges in air at low pressure: N L Allen et al,J Phys D: Appl Phys,14 (12), 1981, L207–L209

Experimental study on the onset of positive corona in atmospheric air

This paper reports the findings of a study into the gas physical processes which lead to the inception of the positive corona discharge in atmospheric air. A multiple avalanche process is observed to be a basic feature, and correlation with the works reported in the literature suggests that at corona onset the physical phenomena are independent of electrode radius of curvature ρ in the range 0.04<ρ (mm) <250. The various models used to simulate the precorona discharge sequence and to predict corona-onset field-strength values are then examined. It is concluded that the development of a rigorous physical-mathematical model of corona onset must await a full understanding of the avalanche-to-corona transition mechanism. Prior to this, a simple empirical approach is adequate for the prediction of corona-onset field strengths.

Low-Velocity Heat Transfer to a Flat Plate in The Presence of a Corona Discharge in Air

A study was conducted to determine the enhancement in convection heat transfer that could be achieved using the corona wind over a range of stream velocities. A heated flat plate mounted in a flow channel was placed in a Mach-Zehnder interferometer. Corona wires were placed above the active plate surface. Data were taken over a range of stream velocities. The results showed the expected large increase in heat transfer at low velocities and that this gain in heat transfer decreased to zero at high stream velocities.

Wettability of Wool Fibers

The critical surface tension of wool fibers was measured using the sink-float technique with various classes of test liquids. Nonpolar organic liquids and aqueous surfactants gave similar values of γ, but much lower values were obtained with butanol/water mixtures. Adsorption of butanol on the surface of the fibers is thought to be responsible for the low values of γ in the latter case. Removal of lipid material from the surface of fibers by extraction increases γ from 30 mN/m to 37 mN/m, similar to that obtained for horn keratin or polypeptide material. Exposure of fibers to a corona discharge in air at atmospheric pressure also increases γ.

A repulsive-field technique for obtaining the mobility-spectra of the ion species created in a corona discharge

A repulsive-field technique has been developed for obtaining the mobility spectra of a distribution of ions present in a dynamic gas environment. It has been applied to an investigation of the negative-ion spectra of corona discharges in ambient air, oxygen, and related oxygen-nitrogen mixtures. Spectra are presented as a function of the inverse mobility (1/K); the present resolution of the technique - (1/K) is ∼ 0.1 V sec/cm2. Future applications of the technique are discussed.

High-field transport in SiO2 on silicon induced by corona charging of the unmetallized surface

A study has been made of high-field electronic transport in thermally grown SiO2 in which the injection and transport of carriers were induced by charging the exposed surface of the insulator with ions extracted from a corona discharge. This technique totally avoids destructive breakdown through weak spots in the insulator. Auxiliary developments included a comparison technique for measuring the steady-state potential difference across the unmetallized insulator and a p-n junction method for determining the sign of the principal charge carrier in the oxide. Using a corona discharge in dry air, breakdown fields of approximately 6.5 and 13.5 MV/cm were obtained for charging with positive and negative ions, respectively. Electrons were identified as the current carriers for both polarities of applied field. Measurements of the discharge of the samples, made with a Kelvin probe, yield results that are consistent with Fowler-Nordheim tunneling of electrons from the silicon into the oxide, with an electron effective mass in the oxide m*ox=0.48m. Positive charge accumulation was observed in the oxide after charging with negative corona to fields above 11 MV/cm.

Mobile fluoride ions in SiO2

We have obtained evidence that fluoride ions are mobile in SiO2 at room temperature. The outer surface of a thin layer of the oxide is coated with a fluoride salt and charged by a negative corona discharge in air. From shifts in the C−V curve and changes in the properties of trapping states near the interface we infer that negative ions have moved through the oxide. This is confirmed by an analysis with a secondary−ion mass spectrometer.

Determination of the sign of carrier transported across SiO2 films on Si

A technique has been developed for determination of the sign of charge carrier transported across an insulating film on a semiconductor substrate, utilizing the charge-carrier separation properties of a shallow p-n junction diffused into the semiconductor. For thermally grown SiO2, unmetallized and contacted by a corona discharge in dry air, electrons are found to carry the current for both polarities of surface potential. Also demonstrated is electron-hole pair production in the Si by electrons entering from the oxide.

Spectroscopic investigation of impulse corona discharges

The spectra of corona discharges in air at atmospheric pressure, in a 0·6 m point-plane gap under positive impulse voltage, have been measured in the near-ultraviolet and visible regions. Two types of corona discharges have been investigated: the first corona which develops from the electrode tip; and the leader coronas which develop successively from the leader tip.The spectrum of the first corona appears to be due almost exclusively to molecular nitrogen (second positive system), while that of the leader coronas also contains some weaker radiation of molecular positive ions of nitrogen (first negative system) and oxygen (first and second negative system), together with some of the brighter lines of atomic oxygen. The radiation of molecular oxygen and atomic nitrogen does not appear with a measurable intensity.A comparison of the relative intensities of the N2 second positive and N2+ first negative bands with low-pressure data indicates that under high-pressure conditions the repartition of population in the various vibrational levels is affected by secondary deactivation processes (electronic and vibrational quenching). By taking into account such processes, the relative intensities of a number of these bands have been theoretically calculated for different electron energy distributions.A comparison between the present experimental and theoretical results shows that a Druyvesteyn energy distribution is more likely for the electrons in the avalanches developing in front of the streamer tip. Furthermore, this comparison makes possible the evaluation of the electron mean energy and the average field in these avalanches: they both turn out to be larger in the leader coronas than in the first corona. This difference in the electron mean energy is responsible for the different spectral characteristics of the first and leader coronas.

High electric fields in silicon dioxide produced by corona charging

We have applied high electric fields to films of SiO2 thermally grown on silicon. The films were not metallized and high fields were obtained by depositing charge directly onto the surface from a corona discharge in air. After terminating the discharge the surface potential was measured, using a vibrating capacitor plate mounted near the free surface. Both the surface potential and the current through the oxide decrease with time, rapidly at first and then more slowly. When the current level has dropped to 10−9 A/cm2 the surface potential is changing by only a few percent per minute and the field across the oxide has nearly a steady value, Es. We measure Es and compare it with the dielectric breakdown fields that have been reported by others. We distinguish between the operational quantity Es and the breakdown field as usually reported since there appears to be no destruction of the sample in our experiments. We find that Es is independent of the conductivity type and the doping level of the silicon, even when it is degenerate. When the free surface is charged negatively, Es is about twice as large as it is for positive charging.

Coherent ion plasma oscifiations in a d.c. corona discharge in rarefied air

Stable, phase coherent ion plasma oscillations are found superimposed on the d.c. potential and current of positive coaxial corona discharges in air at pressures of the order of 1/100 of one atmosphere. The frequency of these oscillations, typically several hundred kHz, is a function of air density, and varies with the concentration of gaseous trace contaminants.

Effect of Electric Charge on the Evaporation of Naphthalene Single Crystals

An electrically charged crystal of naphthalene shows characteristic evaporation etch pits not found on evaporation of an uncharged crystal. The charge is deposited on the crystal from a corona discharge in air. The effect of the charge is apparently to nucleate evaporation at sites where nucleation is unlikely in the absence of charge.