Water Dissociation Products Research Articles

Development of a Zr-Nb-H-O reactive force field for molecular dynamics simulations of in-reactor corrosion

The corrosion of Zircaloy fuel cladding is one of the crucial issues during the operation of pressurized water reactors (PWR). In this work, a Zr-Nb-H-O reactive force field (ReaxFF) is constructed to study the corrosion mechanisms and irradiation effect of Zr-Nb alloys at the atomic landscape. This ReaxFF can describe the interactions between water dissociation products and Zr-Nb alloys, and the stability as well as diffusion properties of irradiation defects in Zr bulk. The molecular dynamics (MD) simulations based on the present ReaxFF show that Nb can thicken the suboxide layer during the corrosion process, as well as the promotion effect of irradiation on corrosion varies under different PKA (Primary Knock-on Atom) energies. The ReaxFF described here has the potential to be a new tool for understanding the in-reactor corrosion mechanism under the irradiation environment.

Theoretical Analysis of the Influence of Spacers on Salt Ion Transport in Electromembrane Systems Considering the Main Coupled Effects.

This article considers a theoretical analysis of the influence of the main coupled effects and spacers on the transfer of salt ions in electromembrane systems (EMS) using a 2D mathematical model of the transfer process in a desalting channel with spacers based on boundary value problems for the coupled system of Nernst-Planck-Poisson and Navier-Stokes equations. The basic patterns of salt ion transport have been established, taking into account diffusion, electromigration, forced convection, electroconvection, dissociation/recombination reactions of water molecules, as well as spacers located inside the desalting channel. It has been shown that spacers and taking into account the dissociation/recombination reaction of water molecules significantly change both the formation and development of electroconvection. This article confirms the fact of the exaltation of the limiting current studied by Harkatz, where it is shown that the current (flux) of salt ions increases when the dissociation reaction begins by a certain value called the exaltation current, which is proportional to the flow of water dissociation products. A significant combined effect of electroconvection and dissociation/recombination reactions as well as the spacer system in the desalting channel on the transport of salt ions are shown. The complex, nonlinear, and non-stationary interaction of all the main effects of concentration polarization and spacers in the desalting channel are also considered in the work.

Heating and ionization by non-thermal electrons in the upper atmospheres of water-rich exoplanets

Context. The long-term evolution of an atmosphere and the remote detectability of its chemical constituents are susceptible to how the atmospheric gas responds to stellar irradiation. The response remains poorly characterized for water and its dissociation products, however, this knowledge is relevant to our understanding of hypothetical water-rich exoplanets. Aims. Our work investigates the effect of photoelectrons, namely, the non-thermal electrons produced by photoionizing stellar radiation on the heating and ionization of extended atmospheres dominated by the dissociation products of water. Methods. We used a Monte Carlo model and up-to-date collision cross sections to simulate the slowing down of photoelectrons in O-H mixtures for a range of fractional ionizations and photoelectron energies. Results. We find that that the fraction of energy of a photoelectron that goes into heating is similar in a pure H gas and in O–H mixtures, except for very low fractional ionizations, whereby the O atom remains an efficient sink of energy. The O–H mixtures will go on to produce more electrons because the O atom is particularly susceptible to ionization. We quantified all that information and present it in a way that can be easily incorporated into photochemical-hydrodynamical models. Conclusions. Neglecting the role of photoelectrons in models of water-rich atmospheres will result in overestimations of the atmospheric heating and, foreseeably, the mass-loss rates as well. It will also underestimate the rate at which the atmospheric gas becomes ionized, which may have implications for the detection of extended atmospheres with Lyman-α transmission spectroscopy. Our simulations for the small exoplanets π Men c and TRAPPIST-1 b reveal that they respond very differently to irradiation from their host stars, with water remaining in molecular form at lower pressures in the latter case.

Quantitative Characterization of Oxygen-Containing Groups on the Surface of Carbon Materials: XPS and NEXAFS Study

The results of the comparative quantitative study of oxygen-containing groups adsorbed on the surface of carbonized sponge scaffold (CSS), highly oriented pyrolytic graphite (HOPG), fullerite C60 and multi-walled carbon nanotubes (MWCNTs) introduced into a high vacuum from the atmosphere without any pre-treatment of the surface are discussed. The studied materials are first tested by XRD and Raman spectroscopy, and then quantitatively characterized by XPS and NEXAFS. The research results showed the presence of carbon oxides and water-dissociation products on the surfaces of materials. It was shown that main source of oxygen content (~2%) on the surface of HOPG, MWCNTs, and C60 powder is water condensed from the atmosphere in the form of an adsorbed water molecule and hydroxyl group. On the CSS surface, oxygen atoms are present in the forms of carbon oxides (4–5%) and adsorbed water molecules and hydroxyl groups (5–6%). The high content of adsorbed water on the CSS surface is due to the strong roughness and high porosity of the surface.

To the Question of the Production of Silicon Carbide

The issue of qualified use of the whole granulomeres composition of petroleum coke is considered. The possibility of using petrochemical fines for the production of silicon carbide is shown. Various technologies for upgrading petro-coke fines are presented and their advantages and disadvantages are revealed. An optimal variant of the preparation of petrochemical fines, in which the main driver for the production of silicon carbide is proposed. The possibility of a significant increase in the reactivity and specific surface area of oil reducing agents due to precision sifting by refined petrochemical fines and removal of excess moisture from petrochemical fines is shown. Due to the evaporation of moisture and the action of water vapor on the carbonaceous material, a positive effect can be created, consisting in the vapor activation of the reducing agent, accompanied by an increase in its reactivity and resistivity. It has been established that the increased humidity of the reducing agent degrades the heat balance of the electric smelting because of the heat costs for evaporation and, in part, the dissociation of water, and also causes an increased consumption of the reducing agent due to its active oxidation with water vapor and water dissociation products.

Математическое моделирование влияния основных температурных эффектов на стационарный перенос ионов соли в диффузионном слое

This article is devoted to the construction of a new mathematical model, using a mathematical model of the system of Nernst-Planck-Poisson equations for electrodiffusion of four varieties of ions simultaneously (two salt ions, and H+, OH- ions) in the diffusion layer in electromembrane systems with a perfectly selective membrane and the heat equation, taking into account the Joule heating of the solution, endo- and exothermic nature of the reactions of dissociation of water molecules and recombination of ions. In addition, the model takes into account the dependence of the coefficient of equilibrium of the dissociation/recombination reaction on temperature. The mathematical model is a boundary value problem for the system of ordinary differential equations, the study of which allows determining the basic patterns of transport of ions of binary salt and water dissociation products taking into account the space charge, reactions dissociation/recombination of water and the corresponding temperature effects. The paper presents the conclusion of the formula for the amount of heat absorbed/emitted at each point $x$, during the course of the dissociation/recombination reaction of water. A boundary condition is derived at a point $x=\delta $ with allowance for the balance of heat fluxes at this point. The study determines the structure of the diffusion layer from the receiving side of the membrane, and, accordingly, the asymptotic solutions in each of the regions of the diffusion layer, to conduct their splicing. The conditions under which the practically irreversible dissociation of water with the maximum possible constant rate in the expanded space charge region are determined. In addition, the study shows that in the region of electroneutrality a narrow band (the recombination region) arises, where the recombination of water molecules prevails over their dissociation, and that the centers of the recombination and dissociation region, within the diffusion layer, are spaced from each other at a considerable distance.

Active Cryovolcanism on Europa?

Abstract Evidence for plumes of water on Europa has previously been found using the Hubble Space Telescope using two different observing techniques. Roth et al. found line emission from the dissociation products of water. Sparks et al. found evidence for off-limb continuum absorption as Europa transited Jupiter. Here, we present a new transit observation of Europa that shows a second event at the same location as a previous plume candidate from Sparks et al., raising the possibility of a consistently active source of erupting material on Europa. This conclusion is bolstered by comparison with a nighttime thermal image from the Galileo Photopolarimeter-Radiometer that shows a thermal anomaly at the same location, within the uncertainties. The anomaly has the highest observed brightness temperature on the Europa nightside. If heat flow from a subsurface liquid water reservoir causes the thermal anomaly, its depth is ≈1.8–2 km, under simple modeling assumptions, consistent with scenarios in which a liquid water reservoir has formed within a thick ice shell. Models that favor thin regions within the ice shell that connect directly to the ocean, however, cannot be excluded, nor modifications to surface thermal inertia by subsurface activity. Alternatively, vapor deposition surrounding an active vent could increase the thermal inertia of the surface and cause the thermal anomaly. This candidate plume region may offer a promising location for an initial characterization of Europa’s internal water and ice and for seeking evidence of Europa’s habitability.

PROBING FOR EVIDENCE OF PLUMES ON EUROPA WITH HST/STIS

ABSTRACT Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude region on Europa: spectroscopic detection of off-limb line emission from the dissociation products of water. Here, we present Hubble Space Telescope direct images of Europa in the far-ultraviolet (FUV) as it transited the smooth face of Jupiter to measure absorption from gas or aerosols beyond the Europa limb. Out of 10 observations, we found 3 in which plume activity could be implicated. Two observations showed statistically significant features at latitudes similar to Roth et al., and the third at a more equatorial location. We consider potential systematic effects that might influence the statistical analysis and create artifacts, and are unable to find any that can definitively explain the features, although there are reasons to be cautious. If the apparent absorption features are real, the magnitude of implied outgassing is similar to that of the Roth et al. feature; however, the apparent activity appears more frequently in our data.

Analytical model of Europa’s O2 exosphere

The origin of the exosphere of Europa is its water ice surface. The existing exosphere models, assuming either a collisionless environment (simple Monte Carlo techniques) or a kinetic approach (Direct Monte Carlo Method) both predict that the major constituent of the exosphere is molecular oxygen. Specifically, O2 is generated at the surface through radiolysis and chemical interactions of the water dissociation products. The non-escaping O2 molecules circulate around the moon impacting the surface several times, due to their long lifetime and due to their non- sticking, suffering thermalization to the surface temperature after each impact. In fact, the HST observations of the O emission lines proved the presence of an asymmetric atomic Oxygen distribution, related to a thin asymmetric molecular Oxygen atmosphere. The existing Monte Carlo models are not easily applicable as input of simulations devoted to the study of the plasma interactions with the moon. On the other hand, the simple exponential density profiles cannot well depict the higher temperature/higher altitudes component originating by radiolysis. It would thus be important to have a suitable and user-friendly model able to describe the major exospheric characteristics to use as a tool.This study presents an analytical 3D model that is able to describe the molecular Oxygen exosphere by reproducing the two-component profiles and the asymmetries due to diverse configurations among Europa, Jupiter and the Sun. This model is obtained by a non-linear fit procedure of the EGEON Monte Carlo model (Plainaki et al. 2013) to a Chamberlain density profile. Different parameters of the model are able to describe various exosphere properties thus allowing a detailed investigation of the exospheric characteristics. As an example a discussion on the exospheric temperatures in different configurations and space regions is given.

Study of electric mass transfer peculiarities in electromembrane systems by the rotating membrane disk method

This study examines one of the current issues of membrane electrochemistry: the study of ion transport patterns through membranes under high and ultra-high current densities. It focuses on the new mechanisms for their delivery to membrane/solution interface, the role of concentration polarization coupled phenomena and its impact on intensification of mass transfer in electromembrane systems (EMS). Furthermore, an experimental device consisting of a rotating membrane disk (RMD) with horizontally positioned ion-exchange membrane is described. The device's design makes it possible to simultaneously obtain current–voltage characteristics (CVCs) and dependences of effective transport numbers for ions of electrolyte and water dissociation products on the current density. Partial CVCs are calculated and limiting current densities and diffusion layer thickness are determined at various disk rotation rates. It was established that the coupled phenomena of the concentration polarization are the reason for the distortion of the classic CVC form with a horizontal plateau. Such behavior observes even under conditions when the diffusion-layer thickness is stabilized by the RMD method. It was described that in the studied asymmetric bipolar membranes (aBPM) the ratio of chemical reaction part (water splitting at bipolar border) and electrodiffusive part of overall masstransfer shifts towards chemical reaction at high rotation speed.

Oxygen reduction reaction at Pt single crystals: a critical overview

Oxygen reduction reaction (ORR) dynamics at platinum single crystal surfaces is reviewed, and experimental results in acid and alkaline solutions are discussed in the framework of theoretical studies. Special emphasis is devoted to point out the role of the surface charge, water structure and adsorbed oxygen containing species. Additionally, discussion about the possible relevance of hydrogen peroxide as an intermediate species is also included. It is shown that the ORR is a complex process affected by many different factors and so neither surface charge nor oxygen-containing species coverage alone are a determining factor of the electrode activity. Instead, adlayer structures and the relation between adsorbed water, H2Oads, water dissociation products, OHads or Oads, and PtO oxide species coverage affect the whole energetics of the adsorption processes and may determine the surface reactivity. Finally, if H2O2 is an intermediate product in the ORR mechanism, it would be crucial to find a suitable catalyst able to effectively reduce H2O2 at high potentials and inhibit its oxidation.

Critical Review of Water Radiolysis Processes, Dissociation Products, and Possible Impacts on the Local Environment: A Geochemist

Radiolysis of water is the process whereby water dissociates due to various types of ionizing radiation (α, β, and γ) into hydrogen and hydroxide radicals (instead of hydrogen and hydroxide ions as in ionization). During radiolysis, water breaks down to highly reactive radicals such as •OH, •H, eaq–, HO2, and O2–• and molecular species such as H2, O2, and H2O2. Yields of these dissociation products are largely dependent on factors including the type of radiation, vapour pressure of the system, and linear energy transfer. These dissociated radicals are highly reactive and can affect the local environment by changing redox conditions and, in turn, inducing and enhancing metal mobility in the environment. This article reviews the process of water radiolysis, dissociation products, and possible effects on the environment.

Study of pH correction process of chloride-bicarbonate dilute solutions by electrodialysis with bipolar membranes

The pH of a dilute chloride-hydrocarbonate solution and the concentrations of chloride ions and carbonic acid anions at the outlet of the alkaline and acid chambers of the electrodialysis cell formed by bipolar and anion-exchange membranes were determined. The decrease in the concentration of hydrocarbonate ions in the alkaline chamber with growth of current density was not equal to its increase in the acid chamber. This disbalance was caused by two concurrent processes: the electromigration ion transport through the anion-exchange membrane and the chemical reactions of hydrocarbonate ions with the water dissociation products formed on the bipolar and anion-exchange membranes. A mathematical model was suggested to describe the electrodialysis correction of the pH of a dilute chloride-hydrocarbonate solution. The experimental data on the correction of pH of the chloride-hydrocarbonate solution were well approximated by both the model that takes into account water dissociation on the anion-exchange membrane and the simplified model that neglects water dissociation. The experimental data agreed well with the results of calculations by the model in which the effective anion transport numbers were calculated only from ion concentrations and diffusion coefficients in solution. This reflects the outer diffusion character of the kinetics of ion transport through the anion-exchange membrane, with pH of dilute solutions corrected by electrodialysis.

Numerical simulation of the electrodeionization (EDI) process for producing ultrapure water

A steady-state model was established to simulate EDI process for producing ultrapure water (MixEDI), the dilute compartment of which is filled with mixed cation and anion-exchange resins. By calculating the mathematical model which includes water dissociation mechanism, ionic status of ion-exchange resin, concentration polarization status and the concentration distribution of water dissociation products are obtained. The influence of water dissociation on the current efficiency, removal rate and pH value of EDI effluent is investigated. The existence of water dissociation catalyst at anion-exchange membrane (AM) makes the water dissociation current of the AM much larger than that of CM. The result is that the amount of electro-regenerated cation-exchange resins is much larger than that of anion resins. This is the reason why the removal rate of salt cation much larger than that of salt anion in EDI for producing ultrapure water. Thus, at the target percentage removal, water dissociation at AM surface is excessive and the one at CM surface is insufficient. We assume that there is also some water dissociation catalyst at CM surface. It is found that the improved water dissociation at CM could increase the percentage removal of salt anions and the current efficiency.

Long-living plasmoids from an atmospheric water discharge

Ball-like plasmoids were generated from discharging a capacitor bank via a water surface. In the autonomous stage after current zero they have diameters up to 0.2 m and lifetimes of some hundreds of milliseconds, thus resembling ball lightning in some way. They were studied by applying high speed cameras, electric probes, calorimetric measurements, and spectroscopy. The plasmoids are found to consist of a true plasma surrounded by a cold envelope. Decreasing electron densities in the order of 1020–1022 m−3 were measured from Stark broadening in the initial (formation) phase. The electron temperature is estimated to be 2000–5000 K during most of the plasmoid's lifetime. The temperature of the neutral particles can exceed 1300 K. Calcium hydroxide molecular band emission is the major source of visible radiation in the autonomous phase. Chemiluminescence reactions between dissociation products of water and dissolved calcium are proposed as a source for this emission. The plasmoid's colder boundary layer consists of electric double layers that may be attributed to the characteristic shape of the balls.

Coupled convection of solution near the surface of ion-exchange membranes in intensive current regimes

Mechanisms responsible for the overlimiting ion transfer in membranes systems are discussed. The overlimiting transfer is shown to be due largely to the action of four effects coupled with the concentration polarization of the system. Two of these are connected with the water dissociation near the membrane/solution interface: the emergence of additional charge carriers (ions H+ or OH−) in the depleted solution layer and the exaltation of transfer of salt counterions. The latter effect is connected with the perturbation of electric field caused by the water dissociation products. The other two effects are two versions of coupled convection, which leads to partial destruction of the depleted diffusion layer. These include gravitational convection and electroconvection. The former is caused by the emergence of the solution’s density gradient. The latter develops via a mechanism of electroosmotic slip. In this work, methods of voltammetry and chronopotentiometry and pH measurements are used to study the transfer of ions through homogeneous membranes Nafion-117 and AMX as a function of the concentration of sodium chloride solutions in the underlimiting and overlimiting current regimes. In a 0.1 M NaCl solution, gravitational convection makes a considerable contribution to the transfer of salt ions near the membrane surface in intensive current regimes. The influence of this effect on the electrochemical behavior of membrane systems weakens with the solution dilution and with increasing relative transfer of the H+ and OH− ions that are generated at the membrane/solution interface. In conditions where gravitational convection is suppressed and the water dissociation near the membrane/solution interface is not great, the major contribution to the overlimiting growth of current is made by electroconvection. Topics for discussion in the paper include the mutual influence of effects on one another, in particular, the effect the rate of generation of the H+ and OH− ions exerts on the gravitational convection and electroconvection and the reasons for the different behavior of cation-and anion-exchange membranes in intensive current regimes.

Electric mass transfer of sodium chloride through cation-exchange membrane MK-40: A rotating membrane disk study

An experimental device consisting of a rotating membrane disk with horizontally positioned cation-exchange membrane MK-40 is described. The device’s design makes it possible to simultaneously obtain current-voltage curves (CVC) and dependences of effective transport numbers for ions of electrolyte and water dissociation products on the current density. Partial CVC are calculated and limiting current densities and diffusion layer thickness are determined at various disk rotation rates. At current densities below the limiting value, the disk’s CVC obey regularities of electrodiffusion kinetics. Upon raising the current density further, the salt ion fluxes increase due to a decrease in the effective diffusion layer thickness, which is caused by the emergence in the near-membrane region of a space charge and electroconvection. At high current densities there occur oscillations of the potential jump that are caused by hydrodynamic instability of the near-membrane solution layer.

Adsorption of water on thin V 2O 3(0 0 0 1) films

V 2O 3(0 0 0 1) films have been grown epitaxially on Au(1 1 1) and W(1 1 0). Under typical UHV conditions these films are terminated by a layer of vanadyl groups as has been shown previously [A.-C. Dupuis, M. Abu Haija, B. Richter, H. Kuhlenbeck, H.-J. Freund, V 2O 3(0 0 0 1) on Au(1 1 1) and W(1 1 0): growth, termination and electronic structure, Surf. Sci. 539 (2003) 99]. Electron irradiation may remove the oxygen atoms of this layer. H 2O adsorption on the vanadyl terminated surface and on the reduced surface has been studied with thermal desorption spectroscopy (TDS), vibrational spectroscopy (IRAS) and electron spectroscopy (XPS) using light from the BESSY II electron storage ring in Berlin. It is shown that water molecules interact only weakly with the vanadyl terminated surface: water is adsorbed molecularly and desorbs below room temperature. On the reduced surface water partially dissociates and forms a layer of hydroxyl groups which may be detected on the surface up to T ∼ 600 K. Below ∼330 K also co-adsorbed molecular water is detected. The water dissociation products desorb as molecular water which means that they recombine before desorption. No sign of surface re-oxidation could be detected after desorption, indicating that the dissociation products desorb completely.

Rate of Generation of Ions H+ and OH− at the Ion-Exchange Membrane/Dilute Solution Interface as a Function of the Current Density

Partial currents of water dissociation products through cation- and anion-exchange membranes that form thin desalination channels in electrodialyzers are measured. The investigations are performed in a broad interval of flow rates during desalination of dilute sodium chloride solutions at overlimiting currents. A water dissociation theory, which was developed for bipolar membranes, and a mass transfer theory that allows for the space charge formation at overlimiting currents are used to derive an expression, according to which the rate of generation of the H+ and OH− ions is defined by the ratio of the current density to its critical value at which water starts undergoing discernible dissociation.

Kinetic energy distributions and line profile measurements of dissociation products of water upon electron impact

The Doppler line profiles of H Ly‐α (1216 Å) and O I (1302 Å and 1152 Å) resulting from electron impact dissociative excitation of H2O have been measured with a high‐resolution (λ/Δλ = 50,000) ultraviolet spectrometer. The line profiles are used to calculate the kinetic energy distribution of the hydrogen atoms produced in dissociative excitation and ionization of H2O at electron impact energies 25, 35, and 100 eV. Three distinct populations of H(2p) atoms were found. The kinetic energy of hydrogen atoms is found to have contributions from a low‐energy component, with a mean energy of ∼0.2 eV at all the three electron impact energies. In addition, a medium‐energy component appears with a mean energy of ∼2.0 eV for 35 eV electrons, and a high‐energy component, ∼7 eV, for 100 eV electrons. The measurement of O I (1302 Å) and O I (1152 Å) line profiles indicate that the kinetic energy of excited O I atoms is very small (∼1 eV or less) at all electron impact energies. Most of the energy released in dissociation is found in the translational energy of the hydrogen atoms. The excitation functions of H Ly‐α, O I (1302 Å) feature of oxygen, and A(0) − X(0) molecular band of hydroxyl near 3050 Å from threshold to 600 V were also measured. The spectrum (1.0 Å FWHM) of the rotational structure of OH (A − X) from electron impact dissociation indicates a high degree of rotational excitation, which is almost identical to the rotational structure from dissociative recombination of H2O+. The results presented in this paper have important applications to planetary bodies, like comets, icy satellites of outer planets, Saturn's magnetosphere, and rings, all of which have H2O and its daughter products in large amount.