Development of ambient sampling chemi/chemical ion source with dielectric barrier discharge

The development of a new configuration of chemical ionization (CI)‐based ion source is presented. The ambient air containing the gaseous sample is sniffed into an enclosed ionization chamber which is of sub‐ambient pressure, and is subsequently mixed with metastable species in front of the ion inlet of the mass spectrometer. Metastable helium atoms (He*) are used in this study as the primary ionizing agents and are generated from a dielectric barrier discharge (DBD) source. The DBD is powered by an AC high‐voltage supply and the configuration of the electrodes is in such a way that the generated plasma is confined within the discharge tube and is not extended into the ionization chamber. The construction of the ion source is simple, and volatile compounds released from the bulky sample can also be analyzed directly by approaching the sample to the sampling nozzle. When combined with heated nitrogen or other desorption methods, its application can also be extended to non‐volatile compounds, and the consumption for helium can be kept minimum solely for maintaining the stable discharge and gas phase ionization. Applications to non‐proximate sample analysis, direct determination of active ingredients in drug tablets and the detection of trace explosive such as hexamethylene triperoxide diamine are demonstrated. Copyright © 2010 John Wiley & Sons, Ltd.     

The Breakdown Phenomena in Micrometer Scale Direct-Current Gas Discharges

This paper reports on experimental and theoretical studies of the direct current breakdown voltage characteristics for several gases (argon, nitrogen, helium, hydrogen, dry air, oxygen and carbon dioxide) in discharges with parallel-plane electrodes separated from 1 to 100 μm. The breakdown phenomena have been discussed in terms of field emission of electrons from the cathode. Based on the measured breakdown voltage curves, realistic values of the effective yields and the field emission thresholds for considered gases have been estimated. It was found that the secondary electron emission due to high electric field generated in microgaps depends primarily on the electric field E leading directly to the violation of the Paschen’s law. The effective yields due to the field emission for all gases are determined for the first time. Experimental data are supported by the theoretical predicitions that suggest departure from the scaling law and a flattening of the Paschen curves at higher pressures. The obtained results may provide better understending of the breakdown phenomena in microgaps.     

Effects of Air/H<Subscript>2</Subscript>O Discharge Plasma on Propane Combustion Enhancement Using Dielectric Barrier Discharges

Combustion provides about 80% energy for our daily life and industrial production. But thermal efficiency of traditional combustion technologies is low, which causes energy waste and serious environmental pollution. In order to improve the combustion efficiency, a combined method based on non-equilibrium plasma generated by dielectric barrier discharge and OH radicals coming from water-steam additive was proposed in this work, and plasma assisted propane combustion was examined and evaluated. The results indicated that when relative humidity (RH) was 20% and applied peak voltage was fixed at 8.75 kV, the relative intensity of OH radical and the flame temperature reached the maximum value at the flame root. At the same time, propane combustion was the most complete. In addition, we found that the erosion of the inner electrode was weakened by H₂O addition, and the symmetry of discharge current was changed from symmetry to asymmetry with the increase of RH. Compared with the pure air undischarged combustion, when the relative humidity was 20% and under the discharge conditions of 8.75 kV, the lean-burn extinction limit was extended to 0.4,which is far lower than the traditional lean-burn limit (0.51).     

Influence of Duty Cycle on Ozone Generation and Discharge Using Volume Dielectric Barrier Discharge

The influence of duty cycle on ozone generation and discharge characteristics was investigated experimentally using volume dielectric barrier discharge in both synthetic air and pure oxygen at atmospheric pressure. The discharge was driven by an amplitude-modulated AC high voltage–power supply producing T_ON (a single AC cycle) and T_OFF periods with a widely variable duty cycle. The experimental results show that the energy delivered to the discharge during each AC cycle remains roughly constant and is independent of feed gas, duty cycle and T_OFF. Both average discharge power and ozone concentration show an initial linear increase with duty cycle, and deviate gradually from linearity owing to an increase in gas temperature at higher duty cycles. Nevertheless, ozone yield remains nearly constant (45.7 ± 3.5 g/kWh in synthetic air and 94.7 ± 3.1 g/kWh in pure oxygen) over a wide range of applied duty cycles (0.02–1). This property can be conveniently employed to develop a unique ozone generator with a widely adjustable ozone concentration and simultaneously a constant ozone yield. Additionally, the discharges in synthetic air and pure oxygen have similar electrical characteristics; however, there are observable differences in apparent luminosity, which is weak and white-toned for synthetic air discharge, and bright and blue-toned for pure oxygen discharge.     

Nitric Oxide Conversion and Ozone Synthesis in a Shielded Sliding Discharge Reactor with Positive and Negative Streamers

Positive and negative streamer discharges in atmospheric pressure air were generated in a shielded sliding discharge reactor at operating voltages as low as 5 kV for a gap length of 1.6 cm. In this reactor, electrodes are placed on top of a dielectric layer and one of the electrodes, generally the one on ground potential, is connected to a conductive layer on the opposite side of the dielectric. The energy per pulse, at the same applied voltage, was more than a factor of seven higher than that of pulsed corona discharges, and more than a factor of two higher than that of sliding discharges without a shield. It is explained on the basis of enhanced electric fields, particularly at the plasma emitting electrode. Specific input energy required for 50 % removal from ~1,000 ppm initial NO could be reduced to ~18 eV/molecule when ozone in the exhaust of negative streamers was utilized. For sliding discharges and pulsed corona discharges this value was ~25 eV/molecule and it was 35 eV/molecule for positive shielded sliding discharges. Also, the ozone energy yield from dry air was up to ~130 g/kW h and highest for negative streamer discharges in shielded sliding discharge reactors. The high energy density in negative streamer discharges in the shielded discharge reactor at the relatively low applied voltages might not only allow expansion of basic studies on negative streamers, but also open the path to industrial applications, which have so far been focused on positive streamer discharges.     

An Array of Micro-hollow Surface Dielectric Barrier Discharges for Large-Area Atmospheric-Pressure Surface Treatments

A robust, commercial micro-hollow plasma source was used to generate atmospheric-pressure plasma, of surface area 18 × 18 mm, in ambient air, nitrogen and argon. An electrode system consisting of 105 micro-hollow surface dielectric barrier discharges was powered by sinusoidal high-voltage at a frequency of 26.7 kHz. The influence of the plasmas on the polycarbonate surface was investigated by means of surface energy measurements and X-ray photoelectron spectroscopy. It emerged that short plasma exposures led to significant increases in surface energy. It is suggested that this may arise out of incorporation of polar groups on the polycarbonate surface. A thermal camera was used to monitor the plasma source surface temperatures for the gases at flow rates ranging from 0 to 5 L/min. It was found that the temperature of the micro-hollow ceramic when operated upon in ambient air decreased significantly from 147 °C at 0 L/min to 49 °C at 5 L/min. In order to investigate further the thermal properties of the plasma, optical emission spectroscopy was employed to monitor the vibrational and rotational temperatures of the plasma generated in ambient air. CCD camera spectroscopic measurements estimated plasma thickness and temperature distribution at high spatial resolution.     

Scaling of Shielded Sliding Discharges for Environmental Applications

Shielded sliding discharges are nanosecond streamer discharges which develop along a dielectric between metal foil electrodes, with one of the foils extended over the entire rear of the dielectric layer. The electrode configuration not only allowed rearranging discharges in parallel due to the decoupling effect of the metal layer, but also to modify the electric field distribution in such a way that components normal to the surface are enhanced, leading to an increased energy density in the discharge plasma. By varying the electrode gap, the applied voltage, and the repetition rate, it is shown that by keeping the average electric field constant, the discharge voltage can be reduced from tens of kV to values on the order of a few kV, but only at the expense of a reduced energy density of the plasma. Varying the repetition rate from 20 to 500 Hz resulted in a slightly reduced energy per pulse, likely caused by residual charges on the dielectric surface. Measurements of the NO conversion to NO₂ and ozone synthesis in dry air showed that the conversion is only dependent on the energy density of the discharge plasma. Although reducing the pulse voltage from the tens of kV range to that of few kV, and possibly even lower, causes a reduction in energy density, this loss can be compensated for by increasing the electrode gap area. This and the possibility to form discharge arrays allows generating large volume discharge reactors for environmental applications, at modest pulsed voltages.     

Optical nitrogen-15 analysis of small nitrogen samples with a mixture of helium and xenon to sustain the discharge in an electrodeless tube

A spectrographic technique has been developed for the determination of the nitrogen-15 abundance, with a mixture of rare gases, helium, and xenon, to sustain the nitrogen discharge. The average natural abundance obtained with 0.2-μg samples of nitrogen was 0.370±0.005 at-%. Preliminary work indicates that this method is applicable directly to plant and liquid samples.     

The Processing of Pyrolysis Fuel Oil by Dielectric Barrier Discharge Plasma Torch

In present paper, an atmospheric-pressure low-temperature plasma treatment of pyrolysis fuel oil (PFO) was investigated in dielectric barrier discharge plasma torch reactor. The effect of the applied voltage and the volume of feedstock, as the main parameters, on the cracking of PFO were studied. By increasing the applied voltage from 10 to 16 kV, the production rate of hydrocarbons containing methane, ethylene, acetylene, propane, propylene, and C₄ rise 18 times. In this case, the production rate of hydrogen increases by approximately 14 times and reaches 7.27 × 10^?3 mol/min for 16 kV. In the feedstock volume investigation, based on limitation of reactor volume, the production rate of hydrocarbons decreased from 0.44 × 10^?3 to 0.15 × 10^?3 mol/min by increasing volume of feedstock from 1 to 5 cc.     

Low Cost Compact Nanosecond Pulsed Plasma System for Environmental and Biomedical Applications

Nanosecond pulsed non-thermal atmospheric-pressure plasmas are promising for numerous applications including air and water purification, ozone synthesis, surface sterilization, material processing, and biomedical care. However, the high cost of the nanosecond pulsed power sources has hindered adaptation of the plasma-based technologies for clinical and industrial use. This paper presents a low cost (<100US$) nanosecond pulsed plasma system that consists of a Cockcroft–Walton high voltage charging circuit, a compact nanosecond pulse generator using a spark gap as switch, and a plasma reactor. The nanosecond pulse power source requires only a 12 V DC input, hence is battery operable. Through the optimization of the experimental parameters, pulses with a peak voltage >10 kV, a 3 ns rise time (10 to 90 %), and a 10 ns pulse duration (full width at half maximum) at a pulse repetition rate of up to 500 Hz were achieved in the present study. It has been successfully tested to power three different plasma reactors to form pulsed corona discharges, dielectric barrier discharges, and sliding discharges. The energy efficiency of such a nanosecond pulsed sliding discharge system was assessed in the context of ozone synthesis using air or oxygen as the feed gas, and was found comparable to a previously reported non-thermal plasma system that used commercial high voltage pulsed power sources. This study demonstrated that this low-cost nanosecond pulsed power source can prove to be an energy efficient and simple supply to drive various non-thermal atmospheric-pressure plasma reactors for environmental, medical and other applications.     

Coupling electrospray corona discharge, charge reduction and ion mobility mass spectrometry: From peptides to large macromolecular protein complexes

We present the design and implementation of a home-built point-to-plane corona discharge probe, which rapidly and efficiently charge reduces biological ions generated by electrospray ionization (ESI). The molecules analysed ranged from small peptides such as Glu-fibrinopeptide B (1.5 kDa), small proteins such as myoglobin (16.9 kDa), polymers such as polyethylene glycol (PEG 10 k) which all showed intense singly charged ions; to large native multiprotein complexes such as GroEL (802 kDa) which show a broad range of charge-reduced species. The corona discharge probe operates at atmospheric pressure and was directly interfaced with a standard-ESI or nanoflow-ESI source of quadrupole ion mobility time-of-flight mass spectrometer. The corona discharge probe is completely modular and could potentially be mounted to any commercial or research grade mass spectrometer with an ESI source. The level of charge reduction is precisely controlled by the applied voltage and/or probe gas flow rate and when in operation, results in approximately a 50 % reduction in total ion current. We also present the combination of corona discharge and travelling wave ion mobility and assign helium collision cross-section values (Ω_He) to the charge reduced species of the native protein complex pyruvate kinase. It would appear that the Ω_He of the +20 charge state for pyruvate kinase is approximately 20 % smaller than the +35 charge state. Finally, we discuss the potential benefits and concerns of utilising charge reduced protein species as a means of extending the travelling wave collision cross-section calibration range over that which is already published.     

Preliminary investigation for the development of surrogate debris from nuclear detonations in marine-urban environments

The effect of ambient gas on measurements with microwave-assisted laser-induced plasma in microwave-assisted laser-induced breakdown spectroscopy (MA-LIBS) was studied with relevance for the analysis of nuclear fuel. A pelletized gadolinium oxide (Gd₂O₃) sample, which was used as a simulated nuclear fuel, was irradiated by a pulsed Nd:YAG laser (532 nm, 5 mJ) coupled with microwaves (2.45 GHz, 400 W) under various gases of air, Ar, and He. Microwaves can be effectively used to enhance laser-induced plasma emissions. The emission spectrums of Gd obtained by MA-LIBS in Ar and He gases are much better than those of the air case. Namely, the spectral lines can be clearly identified and are far from molecular bands. Furthermore, the emission intensity is highest with low background emissions. Linear calibration curves of Ca in the concentration range between 0 and 500 mg/kg as an impurity in Gd₂O₃ have been successfully obtained in all gases. The detection limits of Ca impurity in air, Ar and He gases were 2, 0.8 and 0.6 mg/kg, respectively, which are much lower than the required limits of Ca impurity in nuclear fuels.     

Development of double cylindrical dielectric barrier discharge ion source

This paper deals with the dielectric barrier discharge (DBD) ion source composed of the outer cylindrical dielectric tube and the inner grounded metallic tube electrode. The sample gas is supplied through the inner ceramic tube. In this ion source, the DBD plasma is localized in the DBD tube so that the sample gases can be ionized just outside of the ceramic tube by the DBD excited helium gas without being exposed in the plasma jet. Besides, ambient air does not take part in the ionization of the sample vapor because ionization takes place inside the DBD ion source. Thus, this method is totally free from contaminants in ambient air. It was found that this ion source is capable of soft, high-sensitivity, and reproducible ionization. Application of this technique to the analysis of methamphetamine, carbaryl and basil leaf was given.     

Intrinsic dosimetry of glass containers: a potential interrogation tool for nuclear forensics and waste management

Intrinsic dosimetry is the method of measuring total absorbed dose received by the walls of a container holding radioactive material. By considering the total absorbed dose received by a container in tandem with the physical characteristics of the radioactive material housed within that container, this method has the potential to provide enhanced pathway information regarding the history of the container and its radioactive contents. We report the latest in a series of experiments designed to validate and demonstrate this newly developed tool. Thermoluminescence (TL) dosimetry was used to measure dose effects on raw stock borosilicate container glass up to 70 days after gamma ray, X-ray, beta particle or ultraviolet irradiations at doses from 0.15 to 20 Gy. Two main peaks were identified in the TL glow curve when irradiated with ⁶⁰Co, a relatively unstable peak around 120 °C and a more stable peak around 225 °C. Signal strength of both peaks decayed with time. The minimum measurable dose using this technique is 0.15 Gy, which is roughly equivalent to a 24 h irradiation at 1 cm from a 50 ng ⁶⁰Co source. As a result of fading, this dose would be detectable for approximately 1 year post-irradiation. In a more detailed analysis, the TL glow curves were separated into five peaks centered near 120, 160, 225, 300, and 340 °C. Differences in TL glow curve shape and intensity were observed for the glasses from different geographical origins. These differences can be explained by changes in the intensities of the five peaks. This suggests that mechanisms controlling radiation induced defect formation from gamma, beta, X-ray, and UV sources may be similar.     

Softening Hard Water Using High Frequency Spark Plasma Discharge

Effects of high frequency spark plasma discharge as a time efficiency method in order to softening the natural hard water has been investigated experimentally. A very hard water sample with 331 ± 19 mg/l of CaCO₃ hardness was used. The current and voltage of each spike was about 9.6 A and 3.5 kV respectively at 16 kHz frequency with 35 μs pulse width. Hard water was treated for 2, 4, 6, and 8 min. The concentration of CaCO₃, Ca²⁺ ions, Mg²⁺ ions and pH as well as water conductivity was controlled before and after treatment. The concentration of CaCO₃ dropped by 70%, after 8 min treatment. During the treatment, the pH had a fluctuation about 1.5 and finally remained in neutral state. Also the elemental composition, crystalline structure and morphology of the precipitates were identified. Molecular dynamics simulation revealed that the ozone and hydroxyl play important roles in the softening of the hard water.     

Abatement of Gaseous Xylene Using Double Dielectric Barrier Discharge Plasma with In Situ UV Light: Operating Parameters and Byproduct Analysis

Ultraviolet (UV) light with a wavelength of 254 nm was applied to a double dielectric barrier discharge (DDBD) system to decompose of gaseous xylene. The results show that a significantly synergistic effect can be achieved with the introduction of UV light into the DDBD system. When UV light is applied, the system show a 21.8 % increase in its removal efficiency for xylene at 35 kV with an ozone concentration close to 971 ppmv. The CO _x (x = CO₂ and CO) selectivity of outlet gas rises from 6.54 to 76.2 %. The optimal synergetic effect between UV light and DDBD can be obtained at a peak voltage of 30 kV. The system is robust for humidity, which only slightly reduces the xylene removal efficiency at a high peak voltage (30–35 kV). With the increase of gas flow rate, the removal efficiency for xylene decreases due to a reduced residence time. In addition, the products of xylene degradation were also analyzed. The major products of the degradation were found to be CO₂ and H₂O while byproducts such as O₃ and HCOOH were observed as well.     

Pulsed Discharge Regeneration of Diesel Particulate Filters

A novel method for the removal of soot from a diesel particulate filter using pulsed electric discharges is presented. High voltage pulses of between 18 and 25 kV of nano to microsecond duration and with pulse energies of typically 100–200 mJ were applied to the filter via a series spark gap. Initial slow erosion of the soot layer proceeds via the formation of microdischarges. Subsequent spark discharges removed the accumulated soot more effectively from a larger filter volume. Average soot removal rates of ～0.1–0.2 g/min were achieved at 50 Hz breakdown frequency by optimizing both electrode geometry and breakdown voltage. On-engine long term testing of the technology showed soot removal by pulsed discharge to be reliable, efficient and uniform; a total of 100 g of soot was deposited and removed over 18 filter regeneration cycles.     

A Novel Dielectric-Barrier-Discharge Loop Reactor for Cyanide Water Treatment

A novel dielectric-barrier-discharge (DBD) loop reactor was designed for the efficient degradation of cyanide anion (CN^?) in water. The circulation of cyanide water as a falling film through plasma gas discharge zone enhanced gas–liquid mass and energy transfer and induced formation of H₂O₂ which was associated with the efficient destruction of CN^?. It was observed that among different discharge gases, the CN^? degradation rate decreased in the order of Ar > air > H₂/air mixture. Depending on discharge voltage, the treatment time for complete removal of 100 ppm CN^? in this DBD loop reactor is in the range 120–300 min. The dose of Cu²⁺ catalyst in combination with in situ production of H₂O₂ enhanced the destruction of CN^? apparently in this DBD loop reactor. The treatment time for complete degradation of 100 ppm CN^? decreased from 180 min with Ar DBD discharge alone to 40 min with 40 mg/L dose of Cu²⁺ ion in water, making it an efficient means to degrade cyanide water.     

Characteristics of Dielectric Barrier Discharge Ozone Synthesis for Different Pulse Modes

This paper features the pulse polarity effect on ozone generation efficiency by adjusting the applied voltage and the flow rate in a coaxial dielectric barrier discharge reactor. Results show that utilization of unipolar pulse has better performance when compared with the bipolar mode, but on the other hand, utilization of the positive pulse has slightly higher efficiency than that of negative mode. Meanwhile, changing the gas flow rate shows a minor effect on ozone generation. Utilization of bipolar pulse would decrease the breakdown voltage and ozone generation efficiency when compared with unipolar pulse while it would lead to higher ozone concentrations at fixed applied voltage. The maximum ozone yield reaches 186.9 g/kWh at 6 kV positive pulse with ozone concentration of 11.9 g/Nm³.     

Synthesis of CdO Ultradisperse Powders Using Atmospheric Pressure Glow Discharge in Contact With Solution and the Investigation of Intermediate Products

A new plasma-solution method of the CdO ultradisperse powders synthesis was described. The atmospheric pressure direct current discharge was excited in the ambient air by applying a high direct voltage to two pointed titanium electrodes placed above liquid anode and liquid cathode in the H-shaped cell. The discharge current was 40 mA and the total input power was about 40 W. The action of the DC glow discharge on the cadmium nitrate water solution in the absence of additional reagents and without electrodes-solution contact was shown to result in the production of the solids in the liquid phase. The kinetics of particles formation was studied using turbidimetry and nephelometry methods. Powders’ chemical composition and morphology was obtained using X-ray diffraction spectroscopy (XRD), electron-dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TGA), differential-scanning calorimetry (DSC) and scanning electron microscopy (SEM). It was found that as-synthesized powders are not the pure cadmium hydroxide but the mixture of the cadmium nitrate, hydroxy nitrate and hydroxide. Some assumptions regarding the mechanisms and pathway of the chemical processes both under the plasma action on the solution and during the calcination of as-synthesized powders were discussed.