The effect of a carrier on the residence time of atoms in an arc discharge plasma

The residence time of impurity atoms in an arc discharge has been calculated using the solution of both steady state and non-steady state equations which describe four different mass transport models; conventional diffusion by itself; conventional diffusion together with the movement of ions in an electric field; conventional diffusion together with ambipolar diffusion and conventional diffusion together with both ambipolar diffusion and the movements of ions in an electric field. The best agreement between measured and calculated results is obtained using the model which considers only conventional and ambipolar diffusion. This model also adequately explains the effect of a carrier on the residence time of atoms in the arc discharge.     

A method for the solution of the mass transport equation in a free burning d.c. arc

A method is developed for the solution of a general form of the mass transport equation for a free burning d.c. arc. The spatial particle density distribution function is represented in form of a linear combination of appropriate basis functions in which the expansion coefficients are calculated using the variation principle. The method allows calculation of particle distribution at various levels of approximation, and also includes cases in which both radial and axial dependences of the diffusion coefficient as well as the directed transport velocity are taken into account. The results of some simple test calculations are presented.     

Molecular Mobility in a Poly(ethylene glycol)–Poly(vinyl pyrrolidone) Blends: Study by the Pulsed Gradient NMR Techniques

The molecular mobility in PEG–PVP blends as a function of the time of system storage and the PVP molecular mass is studied by the pulsed-field gradient NMR method. The distribution of PEG molecules over their mobilities is found in a blend containing 36 vol % of PEG with the molecular mass of 400 g/mol. As the storage time of the system increases, the spectrum of diffusion coefficient values varies, thereby indicating the redistribution of PEG400 molecules in the blend with PVP. An anomalous (partly restricted) diffusion of PEG400 molecules is discovered, reflecting the influence of PVP macromolecules on the motion of short PEG chains. It is shown that, during the redistribution of PEG molecules in the blend, they are involved in a complex with PVP, which is characterized by its own transport properties. The data obtained by the NMR relaxation technique are in agreement with the results of NMR diffusion measurements in the studied systems.     

Transport des CaO im Lichtbogenplasma

Transport of the excited CaO molecules, formed in the reaction between a small quantity of Ca atoms and oxygen in DC arc plasma, was followed by a high-speed camera. Axial transport velocities of substances were measured. The diffusion coefficient was determined from the distributions of the intensity of light and their time dependence (found by photometric measurements). The calculation of the diffusion coefficient was performed by using the equation corresponding to the spherical diffusion.     

Ionization interferences under various operating conditions in a 9, 27 and 50 MHz ICP,and a study of shifts in level populations of calcium through simultaneous absorption-emission measurements in a 9 MHz ICP

Radially resolved absorption and emission measurements were employed for a better understanding of the excitation mechanism of nebulized species operating under conditions favourable for the occurrence of ionization interferences in an atmospheric pressure 9 MHz ICP. Three monitored spectral lines of calcium were used to observe changes in ground and excited level populations of atoms and ions, in ion excitation temperatures using the two-line method. Observations were made at a fixed height, namely 25 mm above the rf coil and varying carrier gasflows from 2 to 51 min^?1 and were correlated with the position of the “initial radiation zone” (IRZ) in the plasma. Ionization interferences occurring only inside the IRZ indicate an excitation mechanism depleting ion ground level population and populating excited atom and ion levels. No changes in atom absorbances or excitation temperatures were observed ruling out ionization suppression as dominating mechanism. Indications are that increased collisional excitation for Ca ions and ambipolar diffusion may be the dominant excitation mechanism operating in the analyte channel. Recombination reactions (three body or radiative) or charge transfer reactions may be responsible for an increase of excited atom level populations. It is obvious that non-thermal processes are operating under conditions favourable for ionization interferences occurring in the ICP.     

Ambipolar diffusion in multicomponent plasmas

A recently described self-consistent effective binary diffusion approximation is applied to ambipolar diffusion in a neutral multicomponent plasma in zero magnetic field, where forced diffusion due to the electric field E plays an essential role. The field E is determined by the constraint that the net current flow produced by the diffusion fluxes must be zero. The resulting effective binary diffusion fluxes are the sum of those that would obtain for E=0 and ambipolar correction terms proportional to E. The formulation is .self=consistent with respect to both mass and charge, the net diffusional fluxes of which are both identically zero. The results may be further simplified due to the small mass of the electrons. The effective binary diffusivity D_e of the electrons no longer appears in the simplified expressions. They are therefore well suited to numerical calculations, where the large value of D_e, might otherwise have resulted in unacceptable stability or accuracy restrictions. The well-known effective doubling of ion diffusivities due to ambipolar diffusion occurs in simple situations but is not a general feature.     

Effects of halogen atoms on the mass spectra of some 3-phenylpropionyl halides

The mass spectra of the title compounds have been studied by use of deuterium labelling. The character of the halogen atom appears to have a marked influence on the fragmentation pathways. It is shown that the acyl halide group may react with the different active atoms in the molecular ion—the α- and β-hydrogen atoms—as well as with the phenyl ring.     

Thin Polymer Films by the Glow-Discharge Indirect Method

The growing mechanism and the structure of thin polystyrene film by the glow discharge-indirect method are discussed. A theoretical relationship between the growth rate of polymerized film and the discharge condition is deduced on the basis of Poll's model, taking the charge transport processes in the discharge space into consideration: 1) the ambipolar diffusion, 2) the recombination of charges forming the ion sheath, and 3) the effect of stray capacity. Substitution of possible values of physical parameters on the gaseous plasma into the theoretical relation give a reasonable growth rate which agrees well with the experimental results. From NMR, ESR, and dielectric experiments, it is suggested from the molecular and morphological structure of the film that small molecules and free radicals remain, but most of the film consists of a three-dimensional mesh structure.     

感应耦合等离子体中原子发射光谱的非局部热平衡(Ⅱ)──非沙哈电离平衡过程

感应耦合等离子体中原子发射光谱的非局部热平衡（Ⅱ）──非沙哈电离平衡过程杨原,王小如,应海,王志勇（厦门大学化学系近代分析化学研究所,厦门,３６１００５）关键词ＩＣＰ－ＡＥＳ,非沙哈电离平衡,双极扩散过程实验已经证实用于原子发射光谱（ＡＥＳ）的感应耦...     

Solute size effects on the solvation structure and diffusion of ions in liquid methanol under normal and cold conditions

We have performed a series of molecular dynamics simulations of alkali metal (Li+, Na+, K+, Rb+, and Cs+) and halide (F-, Cl-, Br-, and I-) ions in liquid methanol at two different temperatures to investigate the effects of ion size on the hydration structure and diffusion of ions in methanol under normal and cold conditions. Simulations are also carried out for some of the larger cations such as I+, (CH3)4N+, and (C2H5)4N+ and also neutral alkali metal atoms in methanol at both temperatures. With the increase of ion size, the diffusion coefficients of both positive and negative ions are found to show anomalous behavior. For cations, it is found that the maximum of the diffusion coefficient versus ion size curve occurs at the rather large cation of (CH3)4N+ unlike in water where the maximum occurs at the relatively smaller ion of Rb+. For halide ions, the anomalous behavior, i.e., the increase of diffusion with ion size, continues up to iodide ion and no maximum is observed. These results are in good agreement with experimental observations. The diffusion coefficients of neutral atoms are found to be greater in methanol than that in water and they decrease monotonically with solute size, whereas the diffusion coefficients of the corresponding ions are found to be smaller in methanol. Accordingly, an ion experiences a smaller Stokes friction and a higher dielectric friction in methanol than in water. These contrasting effects are believed to be responsible for the shift of the maximum of ion diffusion toward a larger ion size when compared with similar anomalous size dependence in liquid water.     

Numerical analysis of the behavior of hydrogen added into a free-burning arc

The objective of the present work is to investigate the behavior of hydrogen in an atmospheric-pressure free-burning argon are when a small amount of hydrogen is added into the arc. A two-dimensional model calculation is carried out under the assumption that the ionization reaction of argon is in equilibrium and the reactions among hydrogen molecules, atoms, ions, and electrons are not necessarily in equilibrium. This calculation gives the following conclusion. The hydrogen mass fraction of 0.001 is too small to affect the flow and temperature fields markedly, and the concentration ratios among the hydrogen species are in equilibrium in the greater part of the arc region except for same parts with a steep temperature gradient. The hydrogen mass Junction, however, is not uniform in the me and, especially in the high-temperature region near the cathodes, over three dynes mass fraction of the hydrogen accumulates and flows downstream to cause a high flux of hydrogen atom toward the anode. This phenomena can be explained by the large difference between the diffusivity of hydrogen atom and that of hydrogen ion in argon ion.     

Some considerations on the excitation mechanism in the inductively coupled argon plasma

The excitation conditions in the analytical observation zone of the inductively coupled argon plasma cannot be described by the model of partial local thermal equilibrium. After some general remarks on excitation models the paper analyses in tutorial fashion four alternative models proposed in the literature, featuring metastable argon atoms, radiation trapping, reaction rates and ambipolar diffusion.It is concluded that none is completely satisfactory, but that they are complementary rather than contradictory. Finally, some elements of the four models are integrated into a new model that considers the ICAP as a plasma decaying from conditions of heterogeneous disequilibrium to a situation of homogeneous thermal equilibrium.     

Dynamics of H2O and Na+ in nafion membranes

We investigate the transport properties of a model of a hydrated Na-Nafion membrane using molecular dynamics simulations. The system consists of several Nafion chains forming a pore with the water and ions inside. At low water content, the hydrophilic domain is not continuous and diffusion is very slow. The diffusion coefficient of both water and Na+ increases with increasing hydration (more strongly so for Na+). The simulations are in qualitative agreement with experimental results for similar systems. The diffusion coefficient is an average over the motion of ions or water molecules located in different environments. To better understand the role of the environment, we calculate the distribution of the residence times of the ion (or water) at different locations in the system. We discuss the transport mechanism in light of this information.     

Numerical Simulation of Nonequilibrium Species Diffusion in a Low-Power Nitrogen–Hydrogen Arcjet Thruster

Species distributions in a low-power arcjet thruster are investigated using a two-dimensional thermal and chemical nonequilibrium numerical model that incorporates the self-consistent effective binary diffusion coefficient approximation treatment of diffusion. Plasma flows in arcjet thruster with different input mole ratios of nitrogen to hydrogen are modelled. It is found that species separation due to nonequilibrium chemical kinetic processes occurs mainly in the regions where the dissociation and ionization of nitrogen and hydrogen species take place. The enrichment of nitrogen molecules at the fringes of the arc and hydrogen molecules near the anode wall of the thruster occurs mainly because the recombination processes of these two gases occur in different temperature ranges. In the expansion portion of the thruster nozzle, the gas residence times are of the same order as some chemical kinetic processes. Comparison between the nitrogen and hydrogen species profiles at the constrictor and thruster exit shows that the recombination of hydrogen ions and atoms are dominant kinetic processes near the thruster centreline, while the chemical reactions of nitrogen species are almost frozen in the high speed flow. The effects of temperature and pressure gradients on the species diffusion inside the arcjet thruster are also presented, with thermal diffusion found to have a much larger influence than pressure diffusion.     

Halogenation with CCl4 and CF2Cl2 vapours in arc emission spectrometry

Halocarbon vapour diluted with air or nitrogen was applied during the arc excitation of carbide forming elements in solution form, of metal samples (copper, aluminium) and powder samples (alumina, glass, RU-powder) on graphite supporting electrodes. Means were developed for the carrier vaporization of CCl₄ and for the introduction of the halocarbon vapour into the arc discharge. The gaseous agent was supplied continuously during excitation. This possibility was also subjected to some theoretical predictions. On applying CCl₄ with samples introduced in solution form, the volatilization rates of the most refractory elements (e.g. W) were found to increase at least 50 times on the basis of line intensities. Fractional distillation could be attained on constituents and matrices similar to those reported with solid agents, but the gaseous agents could be applied more easily and without contamination problems. The overall effect of halogenation on excitation processes was evaluated from line intensities integrated over the total evaporation time of a complex powder sample, with and without graphite powder dilution. A high intensification (a factor of 3–12) was obtained for the u.v. lines of the refractory constituents with halogenation, which was attributed to the increased efficiency of these elements in entering the excitation zone. Decrease in the intensities of barium atom and ion lines in the VIS range and a decrease of self-absorption were found as a consequence of halide formation in the arc fringe.     

Electrolyte-as-Cathode Glow Discharge Emission and the Processes of Solution-to-Plasma Transport of Neutral and Charged Species

Emission from an atmospheric-pressure glow discharge with alkali metal chloride solutions used as the cathode was studied. The relation between the discharge emission and the cathode sputtering process leading to the transfer of solution components to the plasma zone was analyzed. It was assumed that the appearance of neutral alkali metal atoms and halogens in the plasma zone is due to the dissociation of halide molecules from a covalently bound state, since the transition to this state becomes possible as a result of excitation of sputtered molecules to high vibrational levels.     

Mouvement des particules solides en fluidisation liquide solide

Solid motion in liquid fluidized beds has been analysed using a radioactive particle and two detection devices partly superimposed, dividing the beParticle velocity was determined by two different estimations, using the net flux across a zone frontier and the residence time between two successiveParticle dispersion coefficients, determined from residence time distribution, were also strongly increasing with increasing liquid velocity. It was co     

A study of the density of sputtered atoms in the plasma of the modified Grimm-type glow discharge source

The sputtering of atoms from the cathode of a modified Grimm-type glow discharge source was studied using hollow cathode lamps as primary sources. Absorption of copper atoms at a distance of 1.5 mm from the cathode was measured, using different discharge conditions, with helium, neon, argon, krypton and nitrogen as carrier gases. For conditions with voltages at and above 800 V, the greatest absorption (copper atom concentration) was obtained using argon as carrier gas. Absorption by copper and chromium, measured at varying distances from the cathode and at different discharge conditions, shows a maximum between 1 and 2 mm from the cathode. This phenomenon can only be explained by cluster sputtering or cluster formation in the plasma. By using the Doppler temperatures of the emission and absorption sources to calculate line profile halfwidths, measured absorbances can be converted to atom number densities.A diffusion model has been formulated to describe the diffusion of sputtered atoms through the plasma which is in a steady state. From the agreement obtained with experimental results, it is concluded that in principle this diffusion model can be used to predict the spatial distribution of sputtered atoms in the plasma.     

Effective thickness of the diffusion layer during hydrogen ion reduction in aqueous hydrochloric acid solutions

The process of mass transport during hydrogen ion reduction in aqueous hydrochloric acid solutions is examined both with and without excess supporting electrolyte. The study of this process is based on a numerical solution to a system of equations of material balance and the movement of particles in solution under the influence of forces for diffusion, migration, and convection. The homogeneous chemical reaction of water dissociation is also taken into account. The results of calculations show that a diffusion layer forms near the electrode during the passage of current in these solutions and that the effective thickness of this layer is the same at any instant for all particles participating in mass transport in solution in spite of differences in their diffusion coefficients. The value of the diffusion coefficient measured in these multicomponent solutions by the methods of chronopotentiometry and rotating disk electrode should differ little from that of hydrogen ions in spite of the fact that other particles with different diffusion coefficients participate in the mass transport.