Main Positive Ions Research Articles

Evaluating arsenic contamination in northwestern Bangladesh: A GIS-Based assessment of groundwater vulnerability and human health impacts

One of the biggest environmental worries in the world today is the risk of arsenic (As) contamination in groundwater. The Atomic Absorption Spectrometer (AAS) was used in this work to assess the As content in groundwater samples from 38 shallow (27 m) tubewells in northwest Bangladesh to determine the existing situation, potential source(s), and likely health risk of As and other important water quality parameters. The range of arsenic concentrations (μgL−1) was troublesome and greater than the WHO recommended level for drinking water, ranging from 0.50 to 164 (mean ± SD: 20.22 ± 36.46). In groundwater, the concentrations of Fe, and Mn vary from 0.04 to 52.75 mgL−1 (mean ± SD: 4.23 ± 9.68), and 0.23 to 3.27 mgL−1 (mean ± SD: 1.10 ± 0.67). The obtained groundwater samples have pH values ranging from 5.9 to 7.1, which indicates a somewhat acidic to neutral character. Major cations have an average abundance that is as follows: Ca2+ > Mg2+ > Na+ > K+, while major anions have an average abundance that is as follows: HCO3− > Cl− > SO42− > NO3−; Ca2+ and HCO3− are the main cation and anion, respectively. The groundwater in the Rajarampur village was deemed unfit for drinking or irrigation based on analyses of water quality performed using the entropy water quality index. The Ca–HCO3 type of water, in which Ca2+ and HCO3− are the main positive ions and negative ions, is suggested by the Piper tri-linear diagram. It was discovered that silicate weathering regulates the hydro-geochemical activities in groundwater using a bi-variate examination of several hydro-chemical variables. Four major clusters were observed for the water sample. According to reductive dissolution processes and principal component analysis, the arsenic in groundwater is geogenic in origin. Arsenic is discharged from sediment to groundwater by reductive dissolution of FeOOH and MnOOH, as shown by the modest connection between As, Fe, and Mn. The United Nations Environmental Protection Agency's (USEPA) suggested value for probable cancer risk assessment was 10−6, however the probable cancer risk assessment found a higher value, indicating that the population in the study region was at high risk for cancer. Remedial measures for arsenic mitigation include removing arsenic from groundwater after it is extracted, searching for alternative aquifers, and implementing various water-supply technologies such as dugwells, deep tubewells, pond-sand filters, and rainwater harvesting systems.

Simulation and Study of DC Corona Discharge Characteristics of Bar-Plate Gap

In this paper, the corona discharge process of the bar-plate gap at −1 kV DC voltage is simulated using a two-dimensional axisymmetric plasma module. We analyze the variation of air negative corona discharge current, and the distribution morphology of microparticles in different discharge stages in detail. The significance of plasma chemical reactions at some typical time and the distribution characteristics of heavy particles are investigated according to reaction rates. Results show that, in the current rising stage, the collision ionization reactions (e.g., R1 and R2) and electron adsorption reaction (e.g., R3) play a major role, which lead to the increase in charged particles and the formation of an electron avalanche. In the current drop stage, all reaction rates decreased, except for collision ionization and electron attachment, partial charge transfer reactions (e.g., R8, R10, R11, and R14), and composite reactions (e.g., R16, R17, and R18), which come into play and gradually reduce the number of charged ions in the gap. In the current stabilizing stage, the main chemical reactions are composite reactions (e.g., R16 and R17), then the corona discharge ends. For the heavy particle distribution, O2+ and O4+ are the main positive ions, O2− is the most abundant negative ions, and the neutral particles are mainly O.

Circuit simulation of current loss in magnetically insulated transmission line system in 15- MA Z-pinch driver

In this paper, a transmission line circuit model of a magnetically insulated transmission line(MITL) system is developed for a 15-MA Z-pinch driver. The current loss characteristics of multi-level MITL and the ion emission due to the expansion of anode and cathode plasma in the post hole vacuum convolute(PHC) and inner-MITL region are analyzed. The spatiotemporal distribution of current loss of the outer-MITL and ion current of the PHC and inner-MITL of the 15 MA driver are obtained. The results show that the first electron emission happens at the end of constant-impedance MITL and the beginning of constant-gap MITL, and the end of constant-gap MITL firstly achieves fully magnetic insulation. Electron emission occurs at the start of load current and its duration is about 30 ns, which is short for a single pulse and has little effect on the rising edge nor peak value of the load current. The waveform of the electron flow varying with time resembles a saddle shape, whose amplitude first goes up, then comes down, and increases again. The electron flow current decreases from upstream to downstream in constant-gap MITL in space. The starting time of the loss current of the PHC is synchronized with the gap closing time. The loss current amplitude increases rapidly, reaching 4 MA at the peak load current time and 6.5 MA in the end. In the inner-MITL region, the main positive ion species are protons and oxygen 2+. At the beginning, the ion loss current of protons is larger than that of oxygen 2+, and then the protons are quickly magnetically insulated due to the small charge-to-mass ratio. The ion loss current of the inner-MITL region mainly increases after the peak load current time, and its peak value is 2.1 MA. Given the input conditions, the stack is going to deliver current of about 18 MA, the hold voltage is about 2.3 MV, and the peak load current is about 13.5 MA.

Influence of water vapor concentration on discharge dynamics and reaction products of underwater discharge within a He/H2O-filled bubble at atmospheric pressure

In this study, a two-dimensional fluid model is proposed to simulate the underwater discharge in a He/H2O-filled bubble at atmospheric pressure. The molar fraction of water vapor is varied in the range of 0.01%–1% to investigate the dependence of discharge dynamics and reaction products on water vapor concentration (WVC). The numerical results show that most properties of the discharge sensitively depend on the WVC. The increase of WVC leads to an increase in the electron density and discharge propagation velocity, which is attributed to Penning ionization between He* and H2O. The main positive ion switches from He+ to H2O+, while the WVC increases from 0.01% to 1%. The dominant reactive oxygen species is OH, whose peak density is about two orders of magnitude higher than that of O. Besides, the densities of OH and O radicals increase with the increasing WVC. It is shown that the formation mechanism of O radicals is significantly affected by the WVC. The dominant reaction creating O radicals changes from the charge exchange between He2+ and H2O to the electron impact dissociation of H2O as the WVC increases from 0.01% to 1%. This study is helpful for better understanding the application of non-thermal plasmas discharges in water, such as biomedical, environmental engineering.

The effect of axial ion parameters on the properties of glow discharge polymer in T2B/H2 plasma

Glow discharge polymer (GDP) films were fabricated using plasma-enhanced chemical vapor deposition. The main purpose of this work was to explore the correlations of plasma parameters with the surface morphology and chemical structure of GDP films. The intensities of main positive ions and ion energy as functions of axial distances in T2B/H2 plasma were diagnosed using energy-resolved mass spectrometry. The surface morphology and chemical structure were characterized as functions of axial distances using a scanning electron microscope and Fourier transform infrared spectroscopy, respectively. As the axial distance increases, both the intensities of positive ions and high energy ions decreases, and dissociation weakens while polymerization enhances. This leads to the weakening of the cross-linking structure of GDP films and the formation of dome defects on films. Additionally, high energy ions could introduce a strong etching effect to form etching pits. Therefore, an axial distance of about 20 mm was found to be the optimal plasma parameter to prepare the defect-free GDP films. These results could help one to find the optimal plasma parameters for GDP film deposition.

The Radial Distribution of Ions and Electrons in RF Inductively Coupled H2/T2B Plasmas

A glow discharge polymer (GDP) was fabricated using trans-2-butene (T2B) and hydrogen (H2) via a plasma-enhanced chemical vapor deposition (PECVD) system. The uniformity of the GDP films was significantly affected by the radial distribution of the H2/T2B plasma parameters. The plasma properties while discharging by a multi-carbon gas source of mixed H2/T2B were investigated during the GDP deposition process. The main positive ions and ion energy distributions in inductively coupled H2/T2B plasmas were analyzed by energy-resolved mass spectrometer (MS), and the electron density and the effective electron temperature were mainly analyzed using a Langmuir probe. The MS results show that the main positive ions in the plasmas are \({\text{C}}_{ 2} {\text{H}}_{ 4}^{ + }\), \({\text{C}}_{ 2} {\text{H}}_{ 6}^{ + }\), \({\text{C}}_{ 3} {\text{H}}_{ 3}^{ + }\), \({\text{C}}_{ 3} {\text{H}}_{ 6}^{ + }\), \({\text{C}}_{ 3} {\text{H}}_{ 8}^{ + }\), \({\text{C}}_{ 4} {\text{H}}_{ 5}^{ + }\), \({\text{C}}_{ 4} {\text{H}}_{ 1 0}^{ + }\), \({\text{C}}_{ 5} {\text{H}}_{ 5}^{ + }\), and \({\text{C}}_{ 5} {\text{H}}_{ 7}^{ + }\) with mass-to-charge ratios (m/e) of 28, 30, 39, 42, 44, 53, 58, 65, and 67, respectively. For a normalized ion intensity, the relative intensities of saturated CH ions increase with increasing radial distance, while the unsaturated CH ions decrease with increasing radial distance. The ion energy distribution of \({\text{C}}_{ 2} {\text{H}}_{ 6}^{ + }\) (m/e = 30) presents a bimodal structure. Additionally, both the electron density and the effective electron temperature decrease with increasing radial distance.

Relaxation of heavy species and gas temperature in the afterglow of a N2 microwave discharge

In this paper we present a self-consistent kinetic model to study the temporal variation of the gas temperature in the afterglow of a 440 Pa microwave nitrogen discharge operating at 433 MHz in a 3.8 cm diameter tube. The initial conditions in the afterglow are determined by a kinetic model that solves the electron Boltzmann equation coupled to the gas thermal balance equation and a system of rate-balance equations for N2 (X 1 ∑ g + , v ) molecules, electronically excited states of N2 , ground and excited states of atomic nitrogen and the main positive ions. Once the initial concentrations of the heavy species and gas temperature are known, their relaxation in the afterglow is obtained from the solutions to the corresponding time-dependent equations. Modelling predictions are found to be in good agreement with previously measured values for the concentrations of N(4 S) atoms and N2 (A 3 ∑u + ) molecules, and the radially averaged gas temperature Tg along the afterglow of a microwave discharge in N2 under the same working conditions. It is shown that gas heating in the afterglow comes essentially from the energy transfer involving non-resonant vibration–vibration (V–V) collisions between vibrationally excited nitrogen molecules, as well as from energy exchanges in vibration–translation (V–T) on N2 –N collisions.

Microparticle charging in dry air plasma created by an external ionization source

In the present paper the dust particle charging is studied in a dry air plasma created by an external ionization source. The ionization rate is changed in the range 101-1020 cm-3s-1. It is found that the main positive ion of the plasma is O+4 and the main negative ones are O−2 and O−4. The point sink model based on the diffusion-drift approach shows that the screening potential distribution around a dust particle is a superposition of four Debye-like exponentials with four different spatial scales. The first scale almost coincides with the Debye radius. The second one is the distance, passed by positive and negative plasma components due to ambipolar diffusion in their recombination time. The third one is defined by the negative ion conversion and diffusion. The fourth scale is described by the electron attachment, recombination and diffusion at low gas ionization rates and by the recombination and diffusion of negative diatomic ions at high ionization rates. It is also shown that the electron flux defines the microparticle charge at high ionization rates, whereas the electron number density is much less than the ion one.

Langmuir probe measurements and mass spectrometry of plasma plumes generated by laser ablation of La0.4Ca0.6MnO3

The plasma formed in vacuum by UV nanosecond laser ablation of La0.4Ca0.6MnO3 in the fluence range of 0.8 to 1.9 J cm−2 using both Langmuir probe analysis and energy-resolved mass spectrometry has been studied. Mass spectrometry shows that the main positive ion species are Ca+, Mn+, La+, and LaO+. The Ca+ and Mn+ energy distributions are quite broad and lie in the 0–100 eV region, with the average energies increasing with laser fluence. In contrast, the La+ and LaO+ distributions are strongly peaked around 10 eV. The net time-of-arrival signal derived from the measured positive ion energy distributions is broadly consistent with the positive ion signal measured by the Langmuir probe. We also detected a significant number of O− ions with energies in the range of 0 to 10 eV. The Langmuir probe was also used to measure the temporal variation of the electron density and temperature at 6 cm from the ablation target. In the period when O− ions are found at this position, the plasma conditions are consistent with those required for significant negative oxygen ion formation, as revealed by studies on radio frequency excited oxygen plasma.

Numerical simulation of the gas phase composition in a glow discharge with an electrolyte cathode

The results of the numerical analysis of the gas phase composition in a system of a glow discharge with an electrolyte cathode are presented. The transfer of the dissolved substance from the solution into the gas phase has been taken into account. The obtained results show that H2O+ is the main positive ion and the concentration of the excited Na atoms in the plasma zone is sufficient for the resonance spectral line of the metal atom to appear.

Influence of working pressure on the state of H2/C4H8 glowing discharge plasma

The variations of the main positive ion components and their energies for the plasma of H2/C4H8 gas mixture under different working pressures are investigated using the glow discharge technique and plasma mass spectrometry diagnostic method, and the effects of work pressure on both the dissociation mechanism of the mixed gas H2/C4H8 and the forming process of the main positive are analyzed. The results show that both the intensity and energy of the C-H segment ions in H2/C4H8 plasma decrease with pressure increasing. The relative concentration of m/e 41(C3H5+) reaches a maximum when work pressure is 5 Pa. And when the pressure is 10 Pa, the relative concentration of m/e 39(C3H3+) is largest; when the pressures are 15 Pa and 20 Pa, the relative concentration of m/e 29 (C2H5+) is highest; when the pressure is 25 Pa, the relative concentration of m/e 57(C4H9+) is biggest. The component and its energy distribution of H2/C4H8 plasma are qualitatively analyzed. The results will serve as a reference to the optimization of parameters for glow plasma polymer coatings.

Characterization of neutral, positive, and negative species in a chlorine high-density surface-wave plasma

This article reports an experimental study of the influence of the plasma parameters on the concentration of neutral and ion species in a chlorine high-density plasma sustained by surface waves. The investigation focuses on the dependence of the concentrations of Cl, Cl2, Cl+, Cl2+, Cl−, and electrons on the gas pressure in the 0.1 to 10 mTorr range, and on the intensity of a confinement magnetic field. The results show that a high dissociation degree (up to 90%) can be achieved even with a very modest power level (250 W, power density of about 2 mW/cm3), provided the pressure is low enough (i.e., less than 1 mTorr). It was also found that Cl+ is the main positive ion and that electrons are the main negative charge carrier at lower pressure. When the gas pressure is higher than a few mTorr, Cl2+ becomes dominant with Cl− as the negative charge carrier. The behavior of the positive ion and neutral species concentrations is compared to the results of a simple model based on creation–losses rate equations for the various species. It is shown that for a given magnetic field intensity, there is a critical pressure above which diffusion can be neglected in comparison with ion–ion recombination and charge transfer.

Positive and negative ion emission from perfluorinated poly-ethers

Positive and negative ion ejection in the mass range below 200 Dalton is observed for perfluorinated poly-ether surfaces subjected to electron- and ion-beam irradiation. The exciting projectiles are Ar + ions of 300 and 4000 eV and electrons of 3000 eV. The main positive ions found are fragments of CF 3 + ions. Larger ions are found with lower probability. The main negative ion observed is F. The results show that the liquid–vacuum interface is formed by CF 3 groups from the polymer.

Production of hydrocarbons and nitriles by electrical processes in Titan's atmosphere.

Although lightning has not been observed in Titan's atmosphere, the presence of methane rain in the troposphere suggests the possibility of electrical activity in the form of corona and/or lightning discharges. Here we examine the chemical effects of these electrical processes on a Titan simulated atmosphere composed of CH4 in N2 at various mixing ratios. Corona discharges were simulated in two different experimental arrays. For the detection of reactive intermediates we used a mass spectrometer to study the main positive ions arising by bombarding low-energy electrons from a hot filament into low-pressure methane. The final stable products, generated by applying a high voltage in a coaxial reactor with either positive or negative polarity, were separated and detected by gas chromatography-Fourier transform infrared spectroscopy and electron impact mass spectrometry (GC-FTIR-MS). Lightning discharges were simulated by a hot and dense plasma generated by a Nd-YAG laser and the final products were separated and detected by GC-FTIR-MS. Corona discharges produce linear and branched hydrocarbons as well as nitriles whereas lightning discharges generate mainly unsaturated hydrocarbons and nitriles. Lightning discharges are about 2 orders of magnitude more efficient in product formation than corona discharges.

A time-dependent analysis of the nitrogen afterglow in and - Ar microwave discharges

This paper presents a theoretical analysis of the nitrogen afterglow induced by a microwave discharge in and - Ar. The initial conditions at the beginning of the afterglow are obtained by solving the electron Boltzmann equation, under the effective field approximation, coupled to the rate-balance equations for the ) levels, the electronically excited states of , the atoms and the main positive ions. The electric field for the maintenance of the discharge is self-consistently determined. Once the concentrations of heavy species in the discharge have been obtained, the relaxation in the afterglow of the above system of equations is investigated. It is shown that, as a result of the mechanisms leading to associative ionization by collisions between the electronic metastable species and , associated with the near-resonant V - E energy-exchange reaction , the characteristic emission of the system of can occur in the afterglow of a microwave discharge at p = 2 Torr after a time s. However, in the case of - Ar mixtures the state arises only for higher pressures and longer residence times (such as - s in a - 50% Ar mixture at p = 10 Torr). The predicted dependences on the pressure and gas-mixture composition of the temporal evolutions of [] and [] concentrations are shown to be in qualitative agreement with reported spectroscopic measurements.

Self-consistent electron and heavy-particle kinetics in a low-pressure - glow discharge

A homogeneous kinetic model of a low-pressure - positive column is developed. The model is based on the self-consistent solutions to the electron Boltzmann equation coupled to the rate balance equations for the vibrationally excited molecules (X ) and (X ), the electronically excited states of , and NO(), and species. Further, this set is still solved together with the continuity equations for the electrons and the main positive ions (, , , , ) in order to determine the maintenance reduced electric field. This formulation allows us to determine the concentrations of the various neutral and ionic species, the electron density and the vibrational temperatures, and , as a function of the gas pressure, discharge current, gas temperature, tube radius and fractional composition. The calculated results are shown to be in satisfactory agreement with published experimental data. The complex interplay kinetics is analysed in detail and the effects of the poor knowledge of some collisional and surface data on the results are discussed.

Tidal termolecular ionic recombination

Measurements by Mezyk et al. (1989,1991) have shown that the rate coefficient for Xe2++Cl-+Xe to XeCl*+2Xe is enhanced relative to that given by the universal curve that describes termolecular recombination of structureless atomic ions. This is attributed to Cl- exciting internal modes of Xe2+ during passage through the perihelion part of the orbit. The electrostatic tidal effect is simulated by the Monte Carlo technique, excellent agreement with the data of Mezyk et al. being obtained. It is reasoned that the tidal action cannot enhance the rate of termolecular recombination of small valence-bound ions like O2+ and O2- appreciably. However its influence is pervasive because complex ions are commonly present when the ambient gas density is enough for termolecular recombination to be of interest: for example, O4+ is the main positive ion if the ambient gas is pure oxygen. Enhanced mutual neutralization may obscure the experimental evidence.

The gas-phase ion chemistry of carbonyl compounds: Formyl fluoride and a binary mixture of H 2CO [sbnd]F 2CO or H 2CO [sbnd]Cl 2CO

The gas-phase ion chemistry of formyl fluoride has been studied by ion cyclotron resonance mass spectrometry. The most abundant ions observed in the positive ion mass spectrum were: HFCO +, HCO +, FCO + and CO +. The main positive ion—molecule reactions in HFCO were the protonation of the neutral molecule by HFCO + and HCO + with rates of (2.5 ± 0.2) × 10 −9 and (0.7 ± 0.1) × 10 −9 cm 3 s −1, respectively. Tertiary ions formed by reactions of the protonated molecule are CH 3F 2O + and the protonated dimer (HFCO) 2H +, which either stabilized by collision or dissociated by ejection of hydrogen, oxygen or fluorine atoms. The only primary negative ion formed by electron impact was FCO −. Its ionization efficiency curve showed a peak arising from resonant dissociative electron attachment. A secondary ion COF 2H − was formed by the reaction of FCO − with HFCO. Ion—molecule reactions in mixtures of H 2CO and F 2CO or Cl 2CO were also studied. Proton and halide transfer reactions were observed in both mixtures, but formation of protonated mixed dimers was not observed. The limits of the heats of formation of the ions CO(H, F) 3 − and CO(H, Cl) 3 − were estimated.

Mass spectrometric investigation of two-component systems of complex vapour composition by the isothermal evaporation method

The Isothermal Evaporation Method (IEM) and its application to the investigation of two-component systems is considered. The isothermal evaporation process should be carried out rather slowly (1–3% mole per hour). Under this condition the process can be considered as a sequence of equilibrium states. Ion current intensities are measured as a function of time. Taken in such a way the ion current time dependences are transposed into dependences of the partial pressures on the melt composition. The mathematical part of IEM which makes possible this transformation is based on two well-know equations, viz. Knudsen's equation and the Gibbs—Duhem equation. Using EIM the following two-component systems were studied: NaFMF n (where M = Be, Mg, Ba, Al, Sc, Y, La, Zr), KFAlF 3, LiFAlF 3 and LiFScF 3. In the equilibrium vapour of these systems four types of molecules were found: AB  NaBeF 3, NaAlF 4, NaScF 4, NaYF 4, NaZrF 4, LiAlF 4, LiScF 4 KAlF 4; A 2B 2(NaBeF 3) 2, (NaAlF 4) 2, (LiAlF 4) 2, (KAlF 4) 2; A 2B  Na 2BeF 4, Li 2AlF 4, possibly Na 2AlF 5; AB 2  NaV 2F 7. The mass spectra of the main positive ions, the relative ionization cross-sections, heats and entropies of dissociation of these molecules are given. Investigation of two-composition systems of complex vapour composition leads to the conclusion that some of the thermodynamic relations can usefully be written in a form which takes into account the complex vapour composition. Forms of Gibbs—Duhem's and Schreder's equations are considered. The relations which are true at the extreme points of the isothermal function ▪ are given. Examples illustrating the mass-spectrometric application of the given thermodynamic relations are given.

Effect of Halogens and Oxygen on the Emission of Thermal Positive Ions from the Tungsten Surface

Abstract The effect of chlorine, bromine, and oxygen on the emission of thermal positive ions from tungsten filaments has been studied. When a tungsten filament is heated in a vacuum, positive ion emission is always observed, and it cannot be removed completely by flashing the filament at high temperatures. This background ion emission increases greatly in halogen or oxygen. Main positive ions are K+ and Na+. The increase cannot be explained by the increase of the work function of tungsten by the formation of adsorbed layer of halogen or oxygen atoms. It is ascertained that the tungsten surface reacts with these gases and the reaction products evaporate as neutral particles. As the reaction proceeds, tungsten surface is removed successively and alkali metal atoms in the bulk are exposed to the surface and contribute to the positive ion emission.