Rate Of Ion Formation Research Articles

A model for a Langmuir sheath in a stagnating dense plasma with secondary ion formation

This simplified model provides solutions for the current-voltage characteristics of a sheath in a dense flowing plasma when surface chemistry contributes secondary ions. The problem is motivated by the recent discovery that strong transient signals in industrial ion current sensors are caused by chemical reactions with carbon in the steel being cut or welded by oxyfuel processes. The one-dimensional model considers a quasi-uniform dense plasma flowing towards and stagnating on an absorbing surface, above which there is a source of secondary ions. Because the secondary ions are formed directly in the plasma sheath, they have strong impacts on the current-voltage characteristic. With ionic Reynolds number, R, and integral length scale, α, secondary ion formation rate, Ω, and length scale, β, saturation currents are simply R + βΩ until β ≪ 1, at which point, new electrons cannot escape the sheath, and secondary ions have no effect. Floating potential, ϕ ∞, scales like exp(ϕ∞)∝R−3/4 , and secondary ions have little impact unless β 2Ω > 1. Even then, floating potential is only weakly affected by secondary ion formation. The integral length scale, α, is not found to strongly affect the results.

Stabilization of Solar Salt at 650 °C – Thermodynamics and practical implications for thermal energy storage systems

Thermal Energy Storage (TES) based on molten salts is thought to play a major role for the transition from fossil fuels to renewable energy carriers in the future. Solar Salt, a mixture of NaNO3–KNO3 is currently the state-of-the-art heat transfer and storage material in Concentrating Solar Power (CSP) plants which produce electricity from a Rankine cycle with steam temperatures up to 550 °C. To allow a technology transfer and adapt Solar Salt based TES systems to modern, high temperature Rankine cycles (e.g. Tsteam > 600 °C), the thermal stability of Solar Salt needs to be increased well above 615 °C. At these temperatures, the formation of nitrites, which depends on the oxygen partial pressure above the melt, needs to be suppressed effectively to prevent further decomposition into corrosive oxide ions. In this work, the thermodynamics of the nitrite-forming reaction at different oxygen partial pressure are explored in a temperature range up to 650 °C from isothermal experiments in the 100 g-scale and limitations of the ideal description are revealed. The measured apparent oxide ion formation rates at 100 g-scale were below previous findings. The activation energy found was 60 ± 15 kJ/mol and the preexponential factor 1*10−5±0.00005s−1. The effect of closing the storage system in terms of gas and salt phase at 645 °C are also explored to understand if and how pressure formation and oxygen release correlate. The results of this work finally contribute to an understanding of the decomposition reactions of Solar Salt at previously untouched temperatures.

Single-Source Precursors for the Controlled Aqueous Synthesis of Bismuth Oxyhalides.

Bismuth oxyhalides are a promising class of photocatalysts for harvesting solar energy. These materials are often synthesized in aqueous media with poor synthetic control resulting from the extremely fast nucleation and growth rates of the particles. These fast rates are caused by the rapid precipitation of bismuth salts with free halide ions. We have developed water-soluble precursors combining bismuth with either chlorine or bromine atoms in the same metal-organic complex. With the application of heat, halide ions are released, which then precipitate with bismuth ions as BiOX (X = Cl, Br). By controlling the halide ion formation rate, the nucleation and growth rates of BiOX materials can be tuned to provide synthetic control. The diverse potential of these precursors is demonstrated by synthesizing BiOX in three ways: aqueous colloidal synthesis, solid-state decomposition, and fabrication of films of BiOX via spray pyrolysis of the aqueous precursor solutions. These broadly applicable single-source precursors will enhance the ability to synthesize future BiOX materials with controlled morphologies.

Air ionization in self-neutralizing air-breathing plasma thruster

The paper describes an arc electron source for air ionization applications in a self-neutralizing air-breathing plasma thruster. The arc electron source is an electron source with a prominent level of electron energy control that is required for the air-breathing plasma thruster. The mean energy of the electrons in the arc electron source is controlled by changing the grid voltage in the range of 0 V–300 V. The Langmuir/Faraday probes were used to obtain ion/electron current, electron temperature, and electron density as a function of pressure and electron energy. Ion current measurements concerning distance from the source were obtained as a function of pressure and grid voltage. Optical emission spectroscopy was used to obtain electron temperature, spectral intensities, and ion formation rate. Additionally, a drift tube based on radial magnetic field electron confinement was designed to detect the presence of negative ions. It has been shown that both positive and negative ions can be produced thus providing conditions for a self-neutralizing air-breathing plasma thruster.

Low-temperature plasma technique for skin structure consolidation

Durability indicators of products operating in extreme conditions largely depend on their working part material properties, the properties of the surface layer in particular. For the purposeful formation of these properties, the method of the surface layer exposure to a gas discharge of low-temperature plasma formed by the interaction of microwave electromagnetic and electrostatic fields has been developed directly around the product surface. As a result of this impact, a significantly harder structure may form in the surface layer due to consolidation of the surface layer material. The paper presents a study performed to answer the question about the mechanism that leads to the consolidation. The results showed that this mechanism is mostly related to local thermal effect on the surface layer that occurs due to the neutralization of negative ions, molecules, and molecular complexes formed in plasma. Ion formation depends on the appearance of slow electrons with energy of about 0–3.5 eV in the plasma. Maximum mechanism impact is achieved while ensuring a high rate of negative ion and molecule formation and attaining their maximum concentration on the surface. In this regard, to ensure the formation of negative ions and molecules, it is necessary, firstly, to select a technological mixture of gases in which plasma effects the surface so that it contains atoms and molecules that have high electron affinity, and secondly, to control the energy level of the microwave electromagnetic field. Practical implementation of these recommendations allowed the average 2.0–2.3-fold increase of the real product endurance.

Modeling nightglow in atomic oxygen red and green lines under moderate disturbed geomagnetic conditions at midlatitudes

We present results of a study of mid-latitude auroras. The study is based on optical measurements and theoretical modeling. The modeling shows that precipitation can indirectly generate airglow in red and green lines of atomic oxygen by increasing rates of ion formation and heating of thermal electrons. This causes an increase in the rate of dissociative recombination and thermal-electron-collision excitation of the 1D and 1S levels.

Моделирование ночных свечений красной и зеленой линий атомарного кислорода для умеренно-возмущенных геомагнитных условий на средних широтах

We present results of a study of mid-latitude auroras. The study is based on optical measurements and theoretical modeling. The modeling shows that precipitation can indirectly generate airglow in red and green lines of atomic oxygen by increasing rates of ion formation and heating of thermal electrons. This causes an increase in the rate of dissociative recombination and thermal-electron-collision excitation of the 1D and 1S levels.

The mechanism of dissolution of minerals in acidic and alkaline solutions: Part VI a molecular viewpoint

The theory of dissolution proposed here and in this series of papers predicts that the order of reaction with respect to H+ ions in solutions should in the series 0.5, 1.0, 1.5…. Experimentally this is found to be the case. The mechanism of dissolution is based on the removal of material from the surface that results in the formation of cations and anions in parallel ‘partial’ reactions. These reactions result in the charging of the surface and the formation of a potential difference across the solid–solution interface. This potential difference in turn influences the rate of removal from the surface. The purpose of this paper is to discuss in further detail the particular mathematical form of the dependence on potential difference that has been chosen. Three plausible models are examined in order to understand the mechanistic steps of dissolution underlying the mathematical form of the potential dependence: (i) the Marcus model, (ii) ionic transfer model of Fawcett, and (iii) the ‘make-before-break’ model of Gileadi. This mathematical form for the potential dependence implies a somewhat surprising link between the dissolution of a metal and the dissolution of a mineral. This link is strengthened by demonstrating that both the rates of mineral dissolution and metal electrode reactions are correlated with the rate of water self-exchange. Since they are correlated with the same variable, they must be correlated with one another. It is proposed that mineral dissolution reactions and dissolution/deposition reactions at metal electrodes share similar reaction trajectories, and hence the similarity between functional dependencies of the rate of ion formation on potential difference across the Helmholtz layer.

On the use of electron capture rate constants to describe electron capture dissociation mass spectrometry of peptides.

Electron capture dissociation (ECD) tandem mass spectrometry (MS/MS) is a powerful analytical tool for peptide and protein structure analysis. The product ion abundance (PIA) distribution in ECD MS/MS is known to vary as a function of electron irradiation period. This variation complicates the development of a method of peptide identification by correlation of ECD MS/MS data with experimental and theoretical mass spectra. Here, we first develop a kinetic model to describe primary electron capture by peptide dications leading to product ion formation and secondary electron capture resulting in product ion neutralization. We apply the developed kinetic model to calculate product ion formation rate constants and electron capture rate constants of product ions from ECD mass spectra acquired using various electron irradiation periods. Contrary to ECD PIA distributions, the product ion formation rate constants are shown to be independent of electron irradiation period and, thus, may be employed to characterize ECD product ion formation more universally. The electron capture rate constants of product ions in ECD Fourier transform ion cyclotron resonance MS were found to correlate (with a correlation factor, R(2), of ca 0.9) with ion mobility cross sections of product ions in electron transfer dissociation. Finally, we demonstrate that the electron irradiation period influences the ratio of radical and even-electron c and z product ions.

The importance of reductive mechanisms for intestinal uptake of iron from ferric maltol and ferric nitrilotriacetic acid (NTA)

Intestinal iron absorption is thought to proceed with iron mainly in the ferrous form, yet the novel iron complex, ferric maltol is an effective oral preparation. Although possessing a high oil: water partition coefficient, ferric maltol does not diffuse across the intestine but donates its iron to the endogenous uptake system. Reduction of the ferric iron in the gut lumen appears to precede iron uptake both from ferric maltol and from ferric nitrilotriacetic acid (NTA) which is a non-penetrating iron ligand. Uptake of radiolabelled iron (59Fe) into isolated fragments of rat small intestine was inhibited by the ferrous chelator, bathophenanthroline sulphonate (BPS) and enhanced at low concentrations by the reducing agent ascorbic acid. Spectrophotometric evidence was obtained that ferrous ions are generated from these ferric complexes in the presence of ascorbic acid and other reducing agents. The rate of ferrous ion formation was independent of ferric maltol concentration at low ascorbic acid levels and decreased with increasing ferric maltol concentration at higher levels of ascorbate. Maltol has a high affinity for ferric ions and may delay reduction at higher concentrations. By contrast, a higher rate of ferrous ion generation was seen with ferric NTA and this increased with iron ligand concentration. Washings from the intestinal lumen also brought about ferrous ion formation from these ferric ligands. Gel filtration revealed these reducing factors to be of low molecular weight. The washings, however, interfered with 59Fe uptake into the isolated fragments, but when reducing fractions only from the filtered washings were used, enhanced iron uptake was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

New particle formation events in semi-clean South African savannah

Abstract. This study is based on 18 months (20 July 2006–5 February 2008) of continuous measurements of aerosol particle size distributions, air ion size distributions, trace gas concentrations and basic meteorology in a semi-clean savannah environment in Republic of South Africa. New particle formation and growth was observed on 69% of the days and bursts of non-growing ions/sub-10 nm particles on additional 14% of the days. This new particle formation frequency is the highest reported from boundary layer so far. Also the new particle formation and growth rates were among the highest reported in the literature for continental boundary layer locations; median 10 nm formation rate was 2.2 cm−3 s−1 and median 10–30 nm growth rate 8.9 nm h−1. The median 2 nm ion formation rate was 0.5 cm−3 s−1 and the median ion growth rates were 6.2, 8.0 and 8.1 nm h−1 for size ranges 1.5–3 nm, 3–7 nm and 7–20 nm, respectively. The growth rates had a clear seasonal dependency with minimum during winter and maxima in spring and late summer. The relative contribution of estimated sulphuric acid to the growth rate was decreasing with increasing particle size and could explain more than 20% of the observed growth rate only for the 1.5–3 nm size range. Also the air mass history analysis indicated the highest formation and growth rates to be associated with the area of highest VOC (Volatile Organic Compounds) emissions following from biological activity rather than the highest estimated sulphuric acid concentrations. The frequency of new particle formation, however, increased nearly monotonously with the estimated sulphuric acid reaching 100% at H2SO4 concentration of 6 · 107 cm−3, which suggests the formation and growth to be independent of each other.

Electrization of aerosol wetted in bipolarly ionized air

We studied the influence of the characteristics of the atmospheric ionization and physical-chemical state of condensation nuclei on the electric state of convective cells. Based on the results of experiments in an adiabatic chamber with a volume of 3200 m3, we found that, with increase in relative air humidity H from 40 to 95% with an equivalent ascent rate of 100–400 cm/s, excessive charges in amounts of about 103 or more elementary charges per cm3 may be accumulated on the nuclei. The sign of the charge depends on the chemical composition of the hygroscopic nuclei. For instance, media with insoluble nuclei (porous silica, etc.) typically have prevailing negative charges; those with soluble nuclei (sodium chloride, etc.) are dominated by positive charges. At H = 60−90%, the electrization of soluble nuclei can be interpreted in the diffusion-kinetic models of the ion charging of aerosols. Considerable negative volume charges, which appear on insoluble hygroscopic nuclei during a rise in humidity from 40 to 70%, are explained by the structuring of surface water films, which exhibit a resemblance to negative lightweight ions. At high values (H > 90%), it is necessary to take into account the resemblance of the wetted surfaces to positive lightweight ions. We showed for the first time that, at ion formation rates of 3 and 1010 ion pairs/(cm3 s), the differences in the volume charge and wetting rate of condensation nuclei are insignificant. It is concluded that, in many meteorological situations, the first stage of electrization of the convection-derived cloud media is the ion charging of the condensation nuclei.

Electron Capture Dissociation Implementation Progress in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Successful electron capture dissociation (ECD) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) applications to peptide and protein structural analysis have been enabled by constant progress in implementation of improved electron injection techniques. The rate of ECD product ion formation has been increased to match the liquid chromatography and capillary electrophoresis timescales, and ECD has been combined with infrared multiphoton dissociation in a single experimental configuration to provide simultaneous irradiation, fast switching between the two techniques, and good spatial overlap between ion, photon, and electron beams. Here we begin by describing advantages and disadvantages of the various existing electron injection techniques for ECD in FT-ICR MS. We next compare multiple-pass and single-pass ECD to provide better understanding of ECD efficiency at low and high negative cathode potentials. We introduce compressed hollow electron beam injection to optimize the overlap of ion, photon, and electron beams in the ICR ion trap. Finally, to overcome significant outgassing during operation of a powerful thermal cathode, we introduce nonthermal electron emitter-based electron injection. We describe the first results obtained with cold cathode ECD, and demonstrate a general way to obtain low-energy electrons in FT-ICR MS by use of multiple-pass ECD.

Electric field perturbation caused by an increase in conductivity related to seismicity-induced atmospheric radioactivity growth

The influence of conductivity perturbation in the lower atmosphere on the DC electric field over a seismic region is investigated. This perturbation is related to the emanation of radon and other radioactive elements into the lower atmosphere as the seismic activity increases. An increase in the level of atmospheric radioactivity results in the appearance of additional ionization sources. The altitude dependence of the ion formation rate is calculated. An ionization source changes the atmospheric conductivity because of the appearance of ions with an equilibrium number density. The perturbation of the atmospheric conductivity is calculated as a function of the altitude. Lower atmosphere conductivity changes disturb the electric current that flows in the global atmosphere-ionosphere circuit. This disturbance is caused by an external current over a seismic region. DC electric field perturbations on the Earth’s surface and in the ionosphere are estimated.

A Mechanistic Model for Copper Electropolishing in Phosphoric Acid

Copper electropolishing in phosphoric acid has been characterized using electroanalytical methods, primarily potential transient techniques. An uncommon voltage response, consisting of two distinct steps, was noted when the current was stepped to the limiting current. A slow (, depending on agitation) and relatively small initial potential increase was followed by a fast and large potential rise. The latter always reached the oxygen evolution potential , irrespective of the process conditions. While the first, slow potential transient can be correlated in terms of a diffusion process, the second, rapid potential rise suggests the buildup of a highly resistive component, most likely a surface film. The nearly instantaneous potential relaxation upon current interruption further supports the resistive film model rather than a transport-related process. A two-stage mechanism is proposed and analytically modeled. Accordingly, the cupric ion concentration at the anode increases during the initial stage of the dissolution process due to transport limitations, until a saturation level is reached and a resistive surface film forms. During the second stage, the continuing imbalance between the rate of cupric ion formation and transport into the bulk leads to increasing film thickness and, consequently, to a rapid buildup in resistance. The model quantitatively correlates the experimentally measured transients and is consistent with all other observations relating to the copper electropolishing process.

A novel potentiometric biosensor for selective l-cysteine determination using l-cysteine-desulfhydrase producing Trichosporon jirovecii yeast cells coupled with sulfide electrode

Trichosporon jirovecii yeast cells are used for the first time as a source of l-cysteine desulfhydrase enzyme (EC 4.4.1.1) and incorporated in a biosensor for determining l-cysteine. The cells are grown under cadmium stress conditions to increase the expression level of the enzyme. The intact cells are immobilized on the membrane of a solid-state Ag 2S electrode to provide a simple l-cysteine responsive biosensor. Upon immersion of the sensor in l-cysteine containing solutions, l-cysteine undergoes enzymatic hydrolysis into pyruvate, ammonia and sulfide ion. The rate of sulfide ion formation is potentiometrically measured as a function of l-cysteine concentration. Under optimized conditions (phosphate buffer pH 7, temperature 37 ± 1 °C and actual weight of immobilized yeast cells 100 mg), a linear relationship between l-cysteine concentration and the initial rate of sulfide liberation (d E/d t) is obtained. The sensor response covers the concentration range of 0.2–150 mg L −1 (1.7–1250 μmol L −1) l-cysteine. Validation of the assay method according to the quality control/quality assurance standards (precision, accuracy, between-day variability, within-day reproducibility, range of measurements and lower limit of detection) reveals remarkable performance characteristics of the proposed biosensor. The sensor is satisfactorily utilized for determination of l-cysteine in some pharmaceutical formulations. The lower limit of detection is ∼1 μmol L −1 and the accuracy and precision of the method are 97.5% and ±1.1%, respectively. Structurally similar sulfur containing compounds such as glutathione, cystine, methionine, and d-cysteine do no interfere.

A rapid method to evaluate potential vasodilatory activity of organic nitrates

The kinetics of interaction between organic nitrates (3,3-bis(nitroxymethyl)oxetane) and cysteine were evaluated by the rate of nitrite ion formation at various concentrations of reagents and pH. The activities of natural reducing agents, including cysteine, glutathione, and NADH, in generating the nitrite ion from organic nitrates (3,3-bis(nitroxymethyl)oxetane) were compared. Cysteine was shown to be the most potent reducing agent. Studying the effectiveness of nitrates (trinitroglycerol, 3,3-bis(nitroxymethyl)oxetane, and nicorandil) at a concentration of 3 mM showed that the rate of nitrite ion accumulation in the reaction with 10 mM cysteine is 1.66, 0.37, and 0.02 microM/min, respectively.

Formation of negative ions in collisions between fluorine ions and C60 molecule versus the kinetic energy of projectiles

We have measured the rate of negative ion formation in F+-C60 collisions at different projectile velocities (v • 0.1 a.u to 0.4 a.u.). The measured rate has been found to decrease from 9.6% to 7.1% for projectile energy increasing from 7.3 keV to 18.3 keV. The fragmentation patterns of C60r+multicharged ions charged r+ formed in the collisions have been analyzed.

A perturbation of DC electric field caused by light ion adhesion to aerosols during the growth in seismic-related atmospheric radioactivity

Abstract. The influence of variations in conductivity and external electric current variations in the lower atmosphere on DC electric field over a seismic region is investigated. The external current is formed with the occurrence of convective upward transport of charged aerosols and their gravitational sedimentation in the atmosphere. This effect is related with the occurrence of ionization source due to seismic-related emanation of radon and other radioactive elements into the lower atmosphere. An increase in atmosphere radioactivity level results in the appearance of additional sources of ionization, and altitude dependence of the ion formation rate is calculated. Ionization source varies the atmospheric conductivity and the external current through appearance of ions with equilibrium number density and their adhesion to aerosols. We have calculated the perturbation of conductivity and external electric current as a function of altitude. Variation of conductivity and external current in the lower atmosphere leads to a perturbation of electric current which flows in the global atmosphere-ionosphere circuit. Finally, perturbations of DC electric field both on the Earth's surface and in the ionosphere are estimated.

Characteristics of single metallic nanowire growth via a field-emission induced process

The growth and characteristics of metallic nanowires formed by field emission in the presence of organometallic precursors are studied. At low growth currents, single nanowires can be formed, which allows a systematic study of the growth characteristics, and wire morphology, structure, and composition. The major role of metal ion deposition in forming the metallic core is demonstrated experimentally, while the formation of the carbonaceous overcoat results from the deposition of neutral atoms from the precursor dissociation process. Transmission electron microscope analysis of tungsten nanowires shows that the core is polycrystalline, with columnar grains dominating the microstructure for thin wires, while larger diameter nanowires are straddled by multiple grains with a wider range of sizes. The axial and radial growth rates of tungsten nanowires as a function of growth current were studied and can be accounted for by assuming a situation in which the rate of ion formation just ahead of the growing tip is supply-rate limited. At higher growth currents, forking and branching phenomena were found to be increasingly probable, and hence, a key to the growth of single, well-defined nanowires is to keep the growth current low. Thermal decomposition of the precursor can also contribute to nanowire growth, and evidence for this mechanism was found in the cases of precursors where autocatalytic decomposition is known to result in metal deposition at relatively low temperatures.