Relaxing Phenomena in Negative Corona Discharge: New Aspects

Two theories, explaining the time dependence of the negative corona discharge current in air, are confronted with new experimental results. The influence of the ozone concentration on the discharge current was experimentally confirmed in dry air and in mixtures of nitrogen with oxygen. Assuming that only the dissociative electron attachment to ozone molecule is a process being responsible for a reduction of the electron component in the total mean discharge current, the mean value of the electron attachment rate constant k = (3 - 5.5) × 10^?9 cm^?3 s^?1 was derived from the measured dependence of the discharge current on the ozone concentration. The calculated value of the rate constant k corresponds to the dissociative attachment of electron to ozone molecule via process e + O₃ → products (O^? or O^?₂ negative ions).     

The contribution of space charge in a high non-homogenous electric field to the creation of negative differential conductivity

The paper describes anomaly origination on current or voltage characteristics in time of positive potential on small curvature radius electrode rod against plane electrodes. An anomaly phenomenon occurred in the narrow voltage area in a high non-homogenous electric field close to the electrode (E > 10⁷ V m^?1). A mathematical – physical analysis of the observed processes in close proximity to the electrode with the above mentioned form is made. The differential equations, which analytically and theoretically describe this phenomenon, are compiled and solved. The space charge created by element particles (electrons, ions) which causes negative differential conductivity origination in narrow voltage area by their behaviour in electric field, plays a substantial role in this phenomenon. Current–voltage characteristics at both polarities of corona electrode were continuously measured at the study of static and dynamic processes occurring during discharge in the surrounding of a small curvature radius electrode. It was proved that an anomaly, in the form of negative differential conductivity (dI/dU < 0), appeared on a highly curved electrode at positive polarity in a narrow voltage area. This phenomenon was subjected to detailed experimental research including investigation of the influence of the shape and material of the electrode (output voltage), electrode temperature, influence of photoionization on the profile of the anomaly, the contribution of exoelectrons to particle distribution, and study of electrochemical potential of metal electrode. Oscillation of low ionized plasma at positive and negative polarity of small curvature radius electrodes has been analyzed. At the same time, the influence of the external forced electric field on the change of current–voltage characteristic profile was investigated. Theoretical justification of the anomaly phenomenon resulted from a change of energy conditions in the investigated place (the distance limit from the electrode is 10^?4–10^?6 m).     

Parametric study of radiofrequency helium discharge under atmospheric pressure

The parameters of radiofrequency helium discharge under atmospheric pressure were studied by electrical and optical measurements using high voltage probe, current probe and optical emission spectroscopy. Two discharge modes α and γ were observed within certain limits. During α to γ mode transition, a decrease in voltage (280–168 V), current (2.05–1.61 A) and phase angle (76^°–56^°) occurred. The discharge parameters such as resistance, reactance, sheath thickness, electron density, excitation temperature and gas temperature were assessed by electrical measurements using equivalent circuit model and optical emission spectroscopy. In α mode, the discharge current increased from 1.17 to 2.05 A, electron density increased from 0.19 × 10¹² to 0.47 × 10¹² cm^?3 while sheath thickness decreased from 0.40 to 0.25 mm. The excitation temperatures in the α and γ modes were 3266 and 4500 K respectively, evaluated by Boltzmann’s plot method. The estimated gas temperature increased from 335 K in the α mode to 485 K in the γ mode, suggesting that the radiofrequency atmospheric pressure helium discharge can be used for surface treatment applications.     

Optimization of Extraction System for Cold Cathode Ion Source

We have simulated ion trajectories with the SIMION 3D, version 7.0, package to optimize the extraction system of a cold-cathode ion source and compared the results with experimental data collected under the same operational conditions. The simulation determined the negative voltage applied to the extractor electrode and the extraction gap widths that maximize the ion-beam current for singly charged nitrogen ions with low emittance and small diameter. The experiment measured the input electrical discharge and output ion beam characteristics of the source at different nitrogen pressures. The extractor electrode voltage and the extraction gap width were determined at 8?×?10^?4?Torr nitrogen. The results of the simulation agreed well with the experimental data.     

The intercalation/deintercalation kinetic studies on the structure-integrated cathode material 0.5Li2MnO3 0.5LiNi0.5Mn0.5O2

A cathode material, 0.5Li₂MnO₃ 0.5LiNi_0.5Mn_0.5O₂, was prepared by citric acid-assisted sol–gel method and its electrochemical performance was investigated. It delivered a charge capacity of 270 mAh g^?1 and a discharge capacity of 189 mAh g^?1 in the first cycle. With the increase of current density from 14 to 28 mA g^?1, the discharge capacity dropped severely to 130 mA g^?1. Obviously, the rate capability of the material was inferior to most of the oxide cathode materials. The diffusion coefficient of this material was calculated to be 6.04?×?10^?12 cm² s^?1 from the results of cyclic voltammetry measurements. Moreover, diffusion coefficients between 3.13?×?10^?12 and 1.22?×?10^?10 cm² s^?1 in the voltage range of 3.8–4.7 V were obtained by capacity intermittent titration technique. This, together with the localized Li₂MnO₃ domains in the crystal structure, may validate the poor rate capability.     

Some Investigations of the Ignition and Development of Breakdown in Cylindrical Hollow Cathode Glow Discharges

The breakdown behaviour of a hollow cathode glow discharge is investigated in a cylindrical, hollow cathode structure having an internal diameter of 2 cm. The anode is a plane electrode across one end of the cathode cylinder. Pressures of argon between 20 and 107 Pa were used (0.15 to 0.80 torr), and applied voltages between 800 and 2500 V. It is shown that the statistical time lag for breakdown is in the range of ～ 1 ms and depends on the applied voltage, the gas pressure, and the history of operation of the discharge tube. The rise time of the discharge current ranges from about 10 ns at high pressure and voltage to about 200 ns at the lowest pressure and voltage used. The discharge propagates along the cathode axis at a speed of about 10⁸ cm s^?1. From the obtained data, a qualitative model of the first stage of the discharge is derived. Based on this model, a simple calculation gives values of Townsend modified first coefficient η at high values of E/N, 10⁴ < E/N < 8 · 10⁴ Td which fit well at the lowest E/N, where they approach the data of PENNING and KRUITHOF in argon. In contrast to the extremely short initial current-rise times, in the submicrosecond range, the discharge currents reach steady-state values only after about 300 μs.     

Deposition of ultrahard Ti–Si–N coatings by pulsed high-current reactive magnetron sputtering

We report on the results of investigation of properties of ultrahard Ti–Si–N coatings deposited by pulsed high-current magnetron reactive sputtering (discharge pulse voltage is 300–900 V, discharge pulse current is up to 200 A, pulse duration is 10–100 μs, and pulse repetition rate is 20–2000 Hz). It is shown that for a short sputtering pulse (25 μs) and a high discharge current (160 A), the films exhibit high hardness (66 GPa), wear resistance, better adhesion, and a lower sliding friction coefficient. The reason is an enhancement of ion bombardment of the growing coating due to higher plasma density in the substrate region (10¹³ cm^–3) and a manifold increase in the degree of ionization of the plasma with increasing peak discharge current (mainly due to the material being sputtered).     

Swift ion irradiation effect on high-k ZrO2- and Al2O3-based MOS devices

This paper describes the heavy ion-induced effects on the electrical characteristics of reactively sputtered ZrO₂ and Al₂O₃ high-k gate oxides deposited in argon plus nitrogen containing plasma. Radiation-induced degradation of sputtered high-k dielectric ZrO₂/Si and Al₂O₃/Si interface was studied using 45?MeV Li³⁺ ions. The devices were irradiated with Li³⁺ ions at various fluences ranging from 5?×?10⁹ to 5?×?10¹²?ions/cm². Capacitance–voltage and current–voltage characteristics were used for electrical characterization. Shift in flat band voltage towards negative value was observed in devices after exposure to ion radiation. Post-deposition annealing effect on the electrical behavior of high-k/Si interface was also investigated. The annealed devices showed better electrical and reliability characteristics. Different device parameters such as flat band voltage, leakage current, interface defect density and oxide-trapped charge have been extracted.The surface morphology and roughness values for films deposited in nitrogen containing plasma before and after ion radiation are extracted from Atomic Force Microscopy.     

DD reaction enhancement and X-ray generation in a high-current pulsed glow discharge in deuterium with titanium cathode at 0.8–2.45 kV

The DD reaction yield (3-MeV protons) and the soft X-ray emission from a titanium (Ti) cathode surface in a periodic pulsed glow discharge in deuterium were studied at a discharge voltage of 0.8–2.45 kV and a discharge current density of 300–600 mA/cm². The electron screening potential U_e = 610 ± 150 eV was estimated in the range of deuteron energies 0.8 keV < E_d < 2.45 keV from an analysis of the DD reaction yield as a function of the accelerating voltage. The obtained data show evidence for a significant enhancement of the DD reaction yield in Ti in comparison to both theoretical estimates (based on the extrapolation of the known DD reaction cross section for E_d ≥ 5 keV to low deuteron energies in the Bosch-Halle approximation) and the results of experiments using accelerators at the deuteron energies E_lab ≥ 2.5 keV and current densities 50–500 μ A/cm². Intense emission of soft X-ray quanta (10¹³–10¹⁴ s^?1 cm^?2) was observed at an average energy of 1.2–1.5 keV. The X-ray emission intensity and the DD reaction yield enhancement strongly depend on the rate of deuterium diffusion in a thin subsurface layer of Ti cathode.     

The profile of the Fe 372·00 nm line excited in a hollow cathode discharge

The profile of the Fe 372·00 nm line emitted in the negative glow of a hollow-cathode discharge is analyzed. The value of the discharge current was varied within the range 7–15 mA, the neon pressure being 1·22–4·40 Torr. The Lorenzian and Gaussian components of the recorded line profile were corrected for instrumental broadening. A correlation was found to exist between the Gaussian component and the cathode voltage drop. The half-width of the Lorentzian component shows the expected dependence on gas pressure. Under the operating conditions used, this component is approx. 10² times greater than the natural one. No dependence on the discharge current was observed. The emitted line profiles may be considered to be Voigt functions with the Voigt parameter varying in the range 3·2 × 10^-2 to 5.5 × 10^-2     

Dynamics of energy release in a low-voltage pulsed arc in air

The influence of the discharge conditions on the dynamics of energy release is considered for pulsed arcs in air at initial pressures from 10⁵ to 8×10⁵ Pa and a low-voltage capacitor voltage of up to 400 V. A novel method for determining the resistance of the discharge channel in the final stage of a spark discharge is proposed. The method is applied to estimating the discharge channel parameters.     

The preparation and electrochemical properties of the Li-excess cathode material Li1 + x (Mn0.7Fe0.3)1 − x O2 by coprecipitation method

The Fe-substituted Li₂MnO₃ cathode materials were synthesized by the coprecipitation method. The effects of the different precipitants of Na₂CO₃ and NaOH on the structure, morphology, and electrochemical performance were investigated by X-ray diffractometry, scanning electron microscopy, dQ/dV plots, and charge–discharge tests. The results indicate that the materials prepared using both precipitants possess layered α-NaFeO₂ structure with R-3m space group. However, the material prepared using Na₂CO₃ shows smaller primary particle size as well as higher discharge capacity. The cycling test shows that the initial discharge capacity is 206 mAh g^?1 in the voltage range of 2.5–4.8 V under current density of 30 mA g^?1 at 30 °C and 231 mAh g^?1 in the voltage range of 2.0–4.8 V. Meanwhile, the discharge capacity fades to 191 mAh g^?1 after 20 cycles. The activated Mn⁴⁺ was confirmed to contribute to the high reversible capacities.     

Fluorine Determination and Matrix Effects in DC and HF Hollow Cathode Discharges

Abstract

The InF bands excited in a hollow cathode discharge have been used for fluorine determination in solid samples (containing from 10^?6 to 10^?1% F) and solutions (at the F^? concentrations from 1 μg/ml to 1 mg/ml). The discharge operated at direct current (dc) or high frequency current (hf). A dependence of the InF band intensities on the fluorine concentration has been investigated. Matrix effects caused by some metals and halides have been studied and discussed.     

Ionenschallinstabilitäten in Edelgas-Gleichstromentladungen bei niedrigen Drücken. I. Meßanordnung und experimentelle Ergebnisse

An experimental study of self-excited ion acoustic waves with wavelengths greater than the radius of the discharge tube in a de-low pressure column is presented. The propagation of this type of waves was observed over a pressure range of 5 · 10^?4 torr ≦ p ≦ 10^?1 torr and currents of 0,02 A ≦ i ≦ 0,6 A in various gases (argon, neon, helium, and hydrogen) in cylindrical glass tubes with diameters of d = 2;4 and 6 cm. The Dispersion behaviour and the existence range were measured in dependence of the internal parameters of the discharge (characteristic velocities and collision frequencies) and the geometry of the discharge tube. It is shown, that the existence range depends not only on gas pressure and current but is influenced also by the geometry of the discharge tube. The minimum wavelengths which belong to the upper cut-off frequencies correlate with the radius of the discharge tube at currents higher than i ～ 0,2 A and increasing pressure.     

Electrical characteristics of etched ion-tracks in polyimide filled with silver nanoparticles

Silicon ions, of energy 150?MeV and fluence ～10¹²?ions/cm², were used to register latent tracks in 40?µm thick polyimide samples. Different sizes of tracks were obtained by etching the ion irradiated polyimide samples, in chemical solutions, by varying the temperature and etching period. Silver nanoparticles were diffused into the etched tracks by immersing the polyimide samples in silver solution and then irradiating with 6.5?MeV electrons at different fluences varying from 1?×?10¹⁵ to 5?×?10¹⁵?cm^?2. Results of morphological and elemental analysis, carried out by Scanning Electron Microscopy and Energy Dispersive X-ray. Analysis revealed that the conical tracks could be fully filled with silver nanoparticles at electron fluence of 5?×?10¹⁵?cm^?2. The minimum d. c. resistance of an array of tracks, filled with silver nanoparticles and measured across the polyimide film, was orders of magnitude higher as compared to that of silver wires of equivalent sizes connected in parallel. In addition, these silver nanoparticles filled tracks exhibited rectifying I–V behavior and frequency dependent a. c. resistance, characteristic of metal–polymer nano-composites. Possible mechanisms have been discussed, which can justify the asymmetric current–voltage characteristics in such nano-composites.     

Li+ transportation kinetics of FeF3 · 0.33H2O/C nanocomposite synthesized by one-step solid state method

A new cathode material for lithium ion battery FeF₃?·?0.33H₂O/C was synthesized successfully by a simple one-step chemico-mechanical method. It showed a noticeable initial discharge capacity of 233.9 mAh g^?1 and corresponding charge capacity of 186.4 mAh g^?1. A reversible capacity of ca.157.4 mAh g^?1 at 20 mA g^?1 can be obtained after 50 charge/discharge cycles. To elucidate the lithium ion transportation in the cathode material, the methods of electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) were applied to obtain the lithium diffusion coefficients of the material. Within the voltage level of 2.05–3.18 V, the method of EIS showed that \( {D}_{{\mathrm{Li}}^{+}} \) varied in the range of 1.2?×?10^?13?~?3.6?×?10^?14 cm² s^?1 with a maximum of 1.2?×?10^?13 cm² s^?1 at 2.5 V. The method of GITT gave a result of 8.1?×?10^?14?~?1.2?×?10^?15 cm² s^?1. The way and the range of the variation for lithium ion diffusion coefficients measured by the GITT method show close similarity with those obtained by the EIS method. Besides, they both reached their maximum at a voltage level of 2.5 V.     

Laboratory studies of back-discharge in fly ash

The back-discharge is a type of discharge that takes place in the presence of corona discharge and occurs at an electrode covered with a dielectric layer of resistivity higher than about 10⁸ Ω m. Back-discharge can be observed in electrostatic precipitators when dust covering the collection electrode has low conductivity. In this paper, the studies of back-discharge generated in ambient air, in point-to-plane geometry with the plate electrode covered with fly ash are presented. The discharge is characterised in terms of its visual forms, current–voltage characteristics, and light emission spectra. Three forms of back-discharge were investigated: glow discharge, streamers, and low-current back-arc discharge. The current of the back-arc discharge was only a few milliamps. The discharge was stabilised by a high series resistance. It was noted that the voltage of ignition of the back-discharge for negative polarity is lower than for a positive one. Spectroscopic measurements of emission spectra provided information on elements present in the discharge column. The elements present in the fly ash, including toxic metals, can be re-entrained into the gas as particles or can be emitted as ions or neutrals during the discharge, and can decrease the collection efficiency of electrostatic precipitators. These elements were detected in the emission spectra. The effect of the discharge on the fly ash layer was also discussed. It was observed that sinter-like leftovers remain in the dust layer after a back-arc discharge.     

Negative Ions in a Glow Discharge of Tetrafluoromethane

The Langmuir — probe measurements in a CF₄ — glow discharge reveal a large number of negative ions (10¹⁰ cm^?3) in the plasma between the planar C-electrodes. Under special conditions the density of them exceeds the electron density at several orders of magnitude and sustains a quasi — electron free plasma. The ratio depends on the residence time of the molecular gas in the discharge reactor. It is due to dissociative electron attachment to highly molecular gas components arising from the plasmachemical conversion of CF₄. F^? and CF₃^? are the most important negative ions.     

Generation of H− ions in a low-pressure xenon-hydrogen discharge. I

A theory of a low-pressure discharge in a xenon-molecular hydrogen mixture is developed. It is shown that, in such a discharge, at an interelectrode distance of L = 1 cm and a total plasma pressure of p ₀ ～ 1 Torr, the density of negative hydrogen ions produced via the dissociative attachment of thermal electrons to vibrationally excited molecules H₂ can reach a value as high as N_H ^? ≥ 10¹² cm^?3. According to calculations, the electron temperature in discharge operating regimes under study attains T _e ≈ 1?2 eV, which corresponds to the maximum of the e-v exchange rate constant of H₂ molecules. This ensures a relatively high rate of vibrational pumping of H₂ molecules in the discharge.     

Cold-hollow-cathode arc discharge in crossed electric and magnetic fields

A crossed-field cold-hollow-cathode arc is stable at low working gas pressures of 10⁻²–10⁻¹ Pa, magnetic-field-and gas-dependent arcing voltages of 20–50 V, and discharge currents of 20–200 A. This is because electrons come from a cathode spot produced on the inner cathode surface by a discharge over the dielectric surface. The magnetic field influences the arcing voltage and discharge current most significantly. When the plasma conductivity in the cathode region decreases in the electric field direction, the magnetic field increases, causing the discharge current to decline and the discharge voltage to rise. The discharge is quenched when a critical magnetic field depending on the type of gas is reached. Because of the absence of heated elements, the hollow cathode remains efficient for long when an arc is initiated in both inert and chemically active gases.