Influence of High Voltage Needle Electrode Material on Hydrogen Peroxide Formation and Electrode Erosion in a Hybrid Gas–Liquid Series Electrical Discharge Reactor

Formation rates of hydrogen peroxide and electrode erosion rates for a range of different electrode materials were determined in a gas–liquid pulsed electrical discharge reactor with a high voltage electrode needle in the liquid and a ground electrode suspended in the gas over the liquid. It was found that the H₂O₂ formation rates and efficiencies did not depend on the electrode material. Electrode erosion from lowest to highest followed the series: nickel chromium, thoriated tungsten, diamond-coated tungsten, stainless steel, tungsten carbide and tungsten copper alloy. Smooth crater-like morphology was found for nickel chromium, titanium and tungsten carbide and a much finer surface structure with small protrusions for the tungsten, tungsten copper and the copper. Doubling the electrode diameter lead to an increase in the H₂O₂ formation per eroded length by a factor of three but it also decreased the energy efficiency yield of H₂O₂ by more than 20%.     

Effect of Reactor Structure in DBD for Nonthermal Plasma Processing of NO in N2 at Ambient Temperature

In order to improve dielectric barrier discharge reactor structure, an experimental study was carried out into its effect on nitric oxide (NO) removal. Different structures were distinguished by electrode connection, diameter, material and shape of inner electrode, and dielectric material, respectively. The results show that breakdown voltage is lower when a high voltage is applied to the outer electrode in the coaxial reactor; NO removal efficiency decreases with a smaller inner electrode diameter and increases when tungsten is used as the inner electrode material rather than copper or stainless steel. When the inner electrode is screw shaped, it improves the discharge power and NO removal efficiency. A similar higher NO removal efficiency is found when corundum is used as the dielectric material instead of ceramic or quartz. Therefore, these findings should become the basis for modifications to the electrode structure in order to improve NO removal efficiency.     

Development of high-sensitivity radio gas chromatography--specific characteristics of a long path internal gas flow proportional counter (author's transl)

A long path internal gas flow proportional counter was devised was to be used as a high sensitivity detector for radio gas chromatography, and its performance characteristics were investigated. The long path counter tube used for this detector has a sufficiently long passage in comparison with the diameter. The counter tube for general use is made of brass or copper tube 1 cm in diameter, 100 cm in length with a mirror finish on all internal surface, and the center electrode is of tungsten wire 0.05 mm in diameter. For actual use, several of these counter tubes are connected in series in assembly to hold the total volume of a gas sample in the counting system over a desired counting period. Thus this flow detector as an integral type one and gives directly a counting rate. Experiments showed that the dynamic counting efficiencies of tritium and carbon-14 were about 90% and equal to the static counting efficiencies. Furthermore, with this detector, the counting rate does not appear to be affected by minor variations of the effective inner volume of the counter tube and the flow rate of counting gas.     

A study of a high repetition condensed arc source for the analysis of low alloy steels using different counter electrode sample configurations: II. A comparison between flat and dimple samples using a tungsten pin counter electrode

A high repetition condensed arc source was further investigated as a light source for the analysis of low alloy steel samples using a tungsten pin counter electrode. Experiments using different tangential and axial flow configurations as well as with only an axial flow, and using manganese as test element are described. With long pre-arc times necessary for sequential spectrometers, a build-up of material on the counter electrodes of different diameters occurred. To overcome this problem the use of counter electrodes with a fresh ground surface for every exposure was investigated. Modifications of the counter electrode holder and the necessary tools and jigs to achieve the effective change of the counter electrodes between exposures is described. Assessment of the performances of the different counter electrode sample configurations with various gas flows indicated that the use of only a tangential flow appears to be the preferred condition. The effect of relatively high phosphorous concentrations on the reproducibility of the analytical results for manganese is indicated. Burn patterns and sample build-up on the counter electrodes are discussed.     

Gas analysis by infrared spectroscopy as a tool for electrical fault diagnostics in SF6 insulated equipment

Infrared spectroscopy shows an enormous potential for the analysis of by-products generated from electrical discharges in sulfur-hexafluoride (SF₆) insulated equipment. Since by-product composition can be related to the fault genesis (arc, partial discharge or corona), the analysis of contaminated SF₆ provides a valuable diagnostic tool. The IR-spectrometric results from discharge experiments are presented, carried out with the application of SF₆ pressures around 300?kPa and an alternating voltage up to 30?kV. Under the discharge conditions used, the main by-products found are the sulfuroxyfluorides SOF₄ and SO₂F₂ with concentrations correlated to the discharge time. Due to its toxicity, special attention is also paid to S₂F₁₀. The experimental conditions and practical aspects for reliable quantitative analysis of reactive species are discussed.     

Gas chromatographic analysis of trace gas impurities in tungsten hexafluoride

Highly reactive fluorinated gaseous matrices require special equipment and techniques for the gas chromatographic analysis of trace impurities in these gases. The impurities that were analysed at the low-microg/l levels included oxygen, nitrogen, carbon dioxide, carbon monoxide, sulfur hexafluoride and hydrogen. This paper describes the use of a system utilising backflush column switching to protect the columns and detectors in the analysis of trace gas impurities in tungsten hexafluoride. Two separate channels were used for the analysis of H2, O2, N2, CO, CO2 and SF6 impurities with pulsed discharge helium ionisation detection.     

CoSe/TiN同轴纳米管阵列在染料敏化太阳能电池对电极中的应用研究

以钛网作为基底,采用阳极氧化、氨气氮化的方法制备了TiN纳米管,随后电沉积CoSe,制备了CoSe/TiN/Ti同轴纳米管阵列电极。循环伏安结果表明,CoSe/TiN/Ti电极对I-3具有高的电催化还原性能,这归因于高催化活性的CoSe和高导电的TiN的协同效应。以CoSe/TiN/Ti电极作为对电极组装染料敏化太阳能电池,电池的能量转换效率高达9.25%,比传统Pt/FTO对电极组装的电池(8.09%)高1%。这一结果为非Pt对电极纳米结构的设计提供了一个很好的思路。     

The Dependence of Gliding Arc Gas Discharge Characteristics on Reactor Geometrical Configuration

The dependence of gliding arc gas discharge characteristics, including gas flow field, arc column motion and volatile organic compounds (VOCs) decomposition performance, on reactor configuration parameters was investigated based on numerical simulation and laboratory experimental findings. For a given supply voltage (10 kV) and a certain nozzle outlet diameter (1.5 mm), increasing the electrodes gap (1–4 mm) or decreasing vertical distance between electrode throat and nozzle outlet (25–10 mm) will increase the gas flow rate through the electrode throat, the gas velocity in the plasma region, the arc column velocity, the maximum attainable position of the arc column and the electrical power consumption, also, higher VOCs decomposition rate and lower specific energy requirement are observed according to the n-butane and toluene decomposition experiments.     

Process analysis using ion mobility spectrometry

Ion mobility spectrometry, originally used to detect chemical warfare agents, explosives and illegal drugs, is now frequently applied in the field of process analytics. The method combines both high sensitivity (detection limits down to the ng to pg per liter and ppb_v/ppt_v ranges) and relatively low technical expenditure with a high-speed data acquisition. In this paper, the working principles of IMS are summarized with respect to the advantages and disadvantages of the technique. Different ionization techniques, sample introduction methods and preseparation methods are considered. Proven applications of different types of ion mobility spectrometer (IMS) used at ISAS will be discussed in detail: monitoring of gas insulated substations, contamination in water, odoration of natural gas, human breath composition and metabolites of bacteria. The example applications discussed relate to purity (gas insulated substations), ecology (contamination of water resources), plants and person safety (odoration of natural gas), food quality control (molds and bacteria) and human health (breath analysis).     

Electrical field distribution on the cross-linked polyethylene insulation surface under partial discharge testing

Cross-linked polyethylene (XLPE) insulated power cables are widely used in transmission and distribution networks. The enhanced localised electrical field/stress can result in surface discharges (SD), i.e. partial discharges on the surface of the dielectric. To measure discharges, very low frequency (VLF-0.1 Hz or lower) excitation has emerged as an attractive alternative to the conventional power frequency (PF- 50/60 Hz) testing as it significantly reduces the required reactive power from the test supply. As the discharge process mainly resulted from the enhanced electric stress; it is necessary to understand how the electric field distributes on the XLPE dielectric surface when it is exposed to a high voltage AC excitation. In this study, the distribution of surface electric field before, during and after a PD event at VLF and PF test voltage is investigated. Finite element analysis (FEA) based numerical simulation shows that the space charge dynamics cause the differences in the field distribution and supports the experimental results.     

Analytical capabilities of the microwave-coupled hollow-cathode discharge in emission spectroscopy

The intensity of spectra emitted by hollow copper cathodes with and without the superposition of 2450-MHz microwaves was studied under different operating conditions with argon as the filler gas. The hollow-cathode discharge was operated at 25–200 mA, with argon pressures ranging from 166 to 690 Pa. The intensities of the copper spectral lines are usually higher in the presence of microwaves, whereas the argon lines are weaker. The differences in the copper spectral lines with and without microwaves increase with increasing pressure of the filler gas and decreasing current. Analogous conclusions were reached for aqueous solutions of gold and silver ions placed in the cathode cavity and dried prior to discharge. The suitability of the method for improving the detection limits obtainable with the hollow-cathode discharge could thus be demonstrated.     

The effect of gamma radiation on the stability of miniature reference electrodes

The design and fabrication of four types of miniature reference electrodes and their long term stability in a radiation field are described. Miniature versions of a saturated calomel electrode (MSCE), a silver/silver chloride electrode (MAG), a tungsten/tungsten oxide (MWO) and a copper/copper ion (MCU) electrode were tested in a 10 kGy/h (1 Mrad/h) radiation field for up to 30 days total at 25 and 40 °C. The latter two (MWO and MCU) varied appreciably over time periods of several hours whereas the former two (MSCE and MAG) varied less than 1 mV over periods of 6–8 h and are deemed suitable as reference electrodes for corrosion studies of systems immersed in a radiation field at elevated temperature.     

Production of metal atoms,clusters and complexes in pulsed discharge-excited jets : Studies via mass-resolved laser multiphoton ionization

A pulsed, high-voltage, discharge-excited nozzle source has been developed and exploited to study the possibility of sputtering and entraining various metal atoms into the gas expansion from the discharge electrodes. By appropriate choice of electrode materials, atomic beams of copper, silver, tin and lead have been generated and spectroscopically characterized by 2 + 1 laser multiphoton ionization with mass analysis. Sufficiently high atomic densities are achieved with this nozzle system that metal clustering also takes place, producing dimers such as Ag₂, species of mixed composition such as AgSn and trimers, Ag₃. In addition, chemical reactions have been observed which can be initiated in the discharge and which lead to the formation of metal–ligand complexes when suitable molecules are seeded into the carrier gas. Mass spectral evidence for two such silver complexes is presented.     

Inorganic volatile fluorides obtained from electrical decomposition of sulfur hexafluoride in a quartz tube

Recent investigations on sulfur hexafluoride decomposition have shown the need of a rapid and efficient method for the qualitative and quantitative analysis of the reaction products. An analytical method for characterizing the gas mixture obtained from the decomposition of sulfur hexafluoride in a quartz reactor submitted to an r.f. discharge, is presented. A combination of gas-chromatographic, mass spectrometric and infrared spectrophotometric techniques has shown the presence of SF₆, SO₂F₂, SOF₄, SOF₂, SiF₄ and F₂ in the gas mixtures examined. For quantitative purposes a gas-chromatographic method has been found to be most suitable.     

Ionic Transfer during Anodic Dissolution of a Vertical Tungsten Electrode in Alkali under Natural Convection Conditions

The problem of anodic dissolution of a plane vertical tungsten electrode in alkaline solutions under conditions of natural convection is solved. Equations for the local (height-dependent) and average limiting currents of tungsten dissolution and the distribution of boundary layer thickness over the electrode height are derived.     

Electrode phenomena in a medium voltage spark

The surface of aluminium samples containing approximately 5 % copper has been studied by means of high speed photography while it was being struck by single medium voltage spark discharges under atmospheric pressure. The formation of cathode spots was found to be dependent on the condition of the sample electrode surface and changed during the duration of one single discharge. Cathode spots have been observed under the impact of oscillating and damped spark discharges.     

锂离子电池负极碳材料的表面改性与修饰Ⅱ.具有“核壳”结构的碳及其对电池性能的影响

以具有气相碳化形式的精制煤焦油沉积碳为壳层材料、人造石墨（ＡＧ）及中间相石墨微球（２８００℃）为核材料制备了核壳结构的碳及碳电极．核壳结构碳及核壳结构碳电极的充放电研究表明碳负极的稳定充放电容量及首次充放电效率都得到了较大的改善,循环伏安研究表明在０．７Ｖ（ｖｓＬｉ＋／Ｌｉ）左右用于形成碳电极表面钝化膜的溶剂的还原分解峰显著减小,显示了核壳结构碳材料电极对电极表面钝化膜的影响作用,Ｘ射线衍射研究揭示了石墨及石墨电极上的无定形碳壳层的存在     

Influence of Metallic Materials on SF<Subscript>6</Subscript> Decomposition Components under Positive DC Partial Discharge

Determination of the influence and mechanism of metallic materials on SF₆ decomposition under direct current (DC) partial discharge is one of the key aspects to improve SF₆ decomposition component analysis (DCA). In this study, three kinds of metallic materials, namely, aluminum, copper, and 18/8 stainless steel, were made into needle–plate electrons, and then used in the SF₆ positive DC partial discharge decomposition experiments. The influences of metallic materials on the five main decomposition components (i.e., CF₄, CO₂, SOF₂, SO₂F₂, and SO₂) were determined by gas chromatography–mass spectrometry. Results showed no significant correlation among the contents of CO₂ for the different kinds of metallic materials. However, the metallic materials considerably influenced the contents of the other four gases. The difference in SF₆ decomposition characteristics for the different metal electrodes was mainly due to the difference in anti-halogenation ability of metals and the passive film. Therefore, the impacts of different metallic materials should be considered when using SF₆ DCA for the condition monitoring and fault diagnosis of DC gas-insulated equipment.     

Conical tungsten tips as substrates for the preparation of ultramicroelectrodes

Here we describe a simple method to prepare voltammetric microelectrodes using tungsten wires as a substrate. Tungsten wires have a high tensile modulus and enable the fabrication of electrodes that have small dimensions overall while retaining rigidity. In this work, 125 microm tungsten wires with a conical tip were employed. For the preparation of gold or platinum ultramicroelectrodes, commercial tungsten microelectrodes, completely insulated except at the tip, were used as substrates. Following removal of oxides from the exposed tungsten, platinum or gold was electroplated, yielding surfaces with an electroactive area of between 1 x 10-6 and 2 x 10-6 cm2. Carbon surfaces on the etched tip of tungsten microwires were prepared by coating with photoresist followed by pyrolysis. The entire electrode was then insulated with Epoxylite except the tip, yielding an exposed carbon surface with an area of around 4 x 10-6 to 6 x 10-6 cm2. All three types of ultramicroelectrodes fabricated on the tungsten wire had similar electrochemical behavior to electrodes fabricated from wires or fibers insulated with glass tubes.     

Design and construction of a low-background,internal-source proportional counter

High-purity copper has emerged as a preferred construction material for ultra-low-background HPGe spectrometers and offers excellent bulk radiopurity along with good electrical, thermal, and vacuum properties. Recently, these materials and techniques have been applied to the construction of low-background internal-source gas proportional counters. This work describes the design, construction, and testing of an ultra-low-background internal-source gas proportional counter built primarily of high purity electroformed copper. Energy resolution of ~10% FWHM at 59.5 keV has been achieved, a low-energy threshold of ~3 keV has been reached, and gas gain stability over a 4-week period has been demonstrated. Progress toward low-background operation is described.