Equilibrium Plasma Composition Research Articles

Plasma Properties of Electric Arc Discharge Burning Between Cu-W Composites Electrodes

Plasma of electric arc discharge burning between different types of composite Cu-W electrodes was investigated. Electrodes manufactured of Cu-W composite materials (30/70% by mass) by shock sintering technology at temperatures of 750, 850, 950, and 1050°C were used. Optical emission spectroscopy techniques were applied to determine the main plasma parameters. Specifically, the side-on spectra of plasma emission were registered using a space-resolved spectrograph with a CMOS camera as a sensor device. The plasma thermodynamics properties were calculated based on the equilibrium plasma composition, which was determined using experimentally obtained radial distributions of temperatures and atom concentrations of the metals.

Simplified method for calculation of equilibrium plasma composition

In this work, a simplified method for the evaluation of equilibrium composition of plasmas consisted of monoatomic species is proposed. Multicomponent gas systems resulting from thermal ionization of spatially uniform mixtures are assumed enough rarefied to be treated as ideal gases even after multiple ionization steps. The method developed for the calculation of equilibrium composition of these mixtures makes use of the fundamental principles of statistical physics. Equilibrium concentrations of mixture components are determined by integration of distribution functions over the space of momentum and summation over electronic energy levels. These functions correspond to the entropy maximum. To determine unknown parameters, the systems of equations corresponding to the normalization conditions are derived. It is shown that the systems may be reduced to one algebraic equation if the equilibrium temperature is known. Numeral method to solve this equation is proposed. Special attention is given to the ionized mixtures, generated from the atoms of a single chemical species and the situations, when in the gas only the first- or the first- and second-order ionization are possible.

Contribution to the evaluation of diffusion coefficients in plasmas containing argon and fluorine

The theoretical values of the numerical evaluation of the electron and ion diffusion coefficients in plasmas from mixtures of argon and fluorine are presented. The temperature dependence of the diffusion coefficients for low-pressure (from 0.1 to 1.0 kPa) and low-temperature (from 500 to 5000 K) argon plasmas with 20% and 30% of added fluorine are investigated. These values are results of the applications of the specific numerical model to the evaluation plasma composition and transport coefficients in argon plasma with fluorine as additive. It is assumed that the system is kept under constant pressure and that a corresponding state of local thermodynamical equilibrium (LTE) is attained. Since the LTE can be assumed, a Maxwellian electron distribution function will be adopted. The hypothesis of LTE, which is commonly used in most of the numerical evaluations, is analysed with the modified Debye radius .The binary electron and ion diffusion coefficients are calculated with the equilibrium plasma composition and with the collision frequencies. Strictly speaking, Maxwellian distribution function (in the state LTE) is not valid for low pressure, but in this case with the aid of the modified Debye radius, a Maxwellian is assumed correctly. It is shown that the electron diffusion coefficients are about four orders of magnitude larger than the corresponding overall diffusion coefficients of ions. Both diffusion coefficients are lower in argon plasma with 30% than with 20% of fluorine additives, in the whole temperature range examined.

Some transport characteristics in plasmas in the mixtures of xenon, argon and caesium

In the present paper, the xenon plasmas containing argon and caesium as additives and pertaining to the above-mentioned type (high-pressure, low-temperature) are studied, and a theoretical evaluation of their basic transport parameters are presented. The numerical calculations were based on the assumption that the system is kept under constant pressure and temperature and has attained local thermodynamical equilibrium (LTE). Particular attention is given to the evaluation of electron collision frequencies within the temperature interval from 2000 to 20000K, and for initial pressures ranging from 0.1 to 1.5 MPa in plasmas in the mixtures of xenon, argon and caesium. The equilibrium plasma composition was evaluated with the use of the modified Debye radius.It is found that the addition of as little as 1% of caesium profoundly alters the properties of the plasma. The presence of the added caesium in the thermal xenon and argon plasma is indeed quite significant for its transport properties, especially at temperatures below and around 10000K. Thus, electron number density, monotonically increasing with temperature (with pressure kept constant) much as in the pure noble-gas plasma, becomes considerably higher. The characteristics of the electrical and thermal conductivities are basically caused by the specificities of the processes of thermal ionization taking place in the system considered, as these processes determine the multiplier electron number density.

The influence of ethanol addition on the spatial emission distribution of traces in a vertical argon stabilized DC arc plasma

The plasma of a vertical argon stabilized DC arc at atmospheric pressure is applied as a spectrochemical source. The lateral distributions of relative spectral line intensities of some trace elements (Zn, Pt, Cd, Mg, Ca and Al) introduced into the plasma in the form of aqueous and ethanol-aqueous solutions were experimentally determined. These distributions were correlated with the calculated equilibrium plasma composition of the arc plasma. On the basis of the obtained results, an explanation of the influence of ethanol addition on the radiation densities from an arc plasma is given.

Some transport properties in plasmas containing argon and fluorine

In this paper some results of numerical evaluation of transport coefficients in plasmas in the mixtures of argon and fluorine are presented. These transport characteristics are given in the function of the temperature for low pressures ranging from 0,1 kPa to 1,0 kPa and for low temperatures between 500 K and 5 000 K in argon plasmas with 20% and 30% of the fluorine added. It is assumed that the system is kept under constant pressure and that a corresponding state of local thermodynamical equilibrium (LTE) is attained in it. The equilibrium plasma composition, necessary for the evaluations, was determined on the ground of the Saha equations for ionization processes and the law of mass action for the thermal dissociation of F2, combined with the charge conservation relation and the assumption that the pressure remained constant in the course of temperature variations. The ionization energy lowering, required in conjunction with the Saha equations, was obtained with the aid of a modified expression for the plasma Debye radius proposed previously. A previously derived expression for the modified Debye radius, offering the possibility to treat the plasmas considered as weakly non-ideal in the whole temperature range, is used. The cut-off at the Landau length rather than of the smallest of ionic radii is introduced. This alteration in the evaluation procedure brings different considerable changes in the final numerical results for the all relevant quantities.

Electron and ion mobilities in argon plasma with fluorine as additive

Results of the numerical evaluation of the electron and ion mobilities in plasmas from mixtures of argon and fluorine are given. The temperature dependence of the number densities of the components and their mobilities as a function of temperature for low-pressure (from 0.1 kPa to 1.0 kPa) and low-temperature (from 500 K to 5000 K) argon plasmas with 20% and 30% of added fluorine are evaluated. It is assumed that the system is kept under constant pressure and that a corresponding state of local themodynamical equilibrium is attained in it. The previously derived expression for the modified Debye radius, offering the possibility to treat the plasmas as weakly non-ideal in the whole temperature range, is used and the cut-off at the Landau length rather than at the smallest ionic radius is introduced. This alteration in the evaluation procedure gives different changes in the final numerical results for all the relevant quantities. It was found that the equilibrium plasma composition depends considerably on the presence of fluorine in the whole temperature range for both the pressures; the addition of fluorine significantly enhances the number densities of all relevant charged constituents. This fact influences the electron and ion collision frequencies as well as their mobilities.

Evalution of Plasma Composition and Mobilities in Argon Plasma with Chlorine as Additive

AbstractResults of numerical evaluation of equilibrium compositions and mobilities in plasmas formed in the mixtures of argon and chlorine are given. The temperature dependence of the number densities of the components and their mobilities in function of temperature for low‐pressure (from0, 1 kPa to 1,0 kPa) and low‐temperature (from 500 K to 5 000 K) argon plasmas with 20% and 30% of added chlorine are evaluated. It is assumed that the system is kept under constant pressure and that a corresponding state of local themodynamical equilibrium is attained in it. A previously derived expression for the modified Debye radius, offering the possibility to treat the plasmas considered as weakly non‐ideal in the whole temperature range, is used and the cut‐off at the Landau length rather than of the smallest of ionic radii is introduced. This alteration in the evaluatin procedure brings different change in the final numerical results for all the relevant quantities.It is found that the equilibrium plasma composition depends considerably on the presence of chlorine in the whole temperature range for both pressures; the addition of chlorine significantly enhances number densities of all relevant charged constituents. This fact influences of the electron and ion collision frequencies and their mobilities too.

Computer simulation of added Li influence on the ICP properties

The influence of added Li on the ICP characteristics is investigated by computer simulation. The transport and the thermodynamic parameters of Li in the temperature interval between 300 and 13,000 K are taken from the literature, while in the case of absence of those, the data were estimated. The HiFI computer program was used for calculation of spatial distributions of temperature, velocity, and electromagnetic fields for argon plasma with the presence of different quantities of Li up to 30%. On the basis of calculated temperature field and equilibrium plasma composition the spatial distribution of electron density was determined. It was found that the addition of Li considerably influences the spatial distributions of all analyzed plasma parameters at Li concentrations higher than 1%. It is shown that the electron density is the most sensible among all analyzed parameters of the presence of Li.

Equilibrium plasma composition in U-shaped DC argon-stabilized arc

The calculation of the equilibrium plasma composition of a U-shaped argon-stabilized dc arc burning at 1 bar is given. The calculation procedure, based on the minimization of Gibbs free energy, was applied in the temperature range 1000–9000 K, assuming a state of local thermodynamic equilibrium. The results obtained were compared with experimentally determined values of plasma parameters (temperature, electron density) and spectral line intensities, with consideration of the local thermodynamic equilibrium state in this arc source.

Optical Emission Diagnostics of an U‐Shaped Argon Stabilized d.c. Arc

AbstractThe radial distribution of parameters has been measured by using the optical emission spectroscopy of an U‐shaped argon stabilized low current arc at atmospheric pressure. All the measurements reported here were performed from a side‐on observation direction by applying the Abel inversion routine. Radial distributions of apparent temperatures (Texc., Te, Ti, Tg) and of electron number density (ne) for the plasma were measured, with and without presence of KCl (spectrochemical buffer). The measured data of ne are compared to the theoretically calculated values of the equilibrium plasma composition. On the basis of the measured data, the validity of LTE concept is considered. It was found that deviation from LTE increases to the plasma periphery.

Study of the matrix effect of easily and non-easily ionizable elements in inductively coupled argon plasma. Part 2. Equilibrium plasma composition

The matrix effect of easily and non-easily ionizable elements in an inductively coupled argon plasma is discussed in relation to the equilibrium plasma composition. The calculation procedure, based on the minimization of free energy, was applied in the temperature range 1000–9000 K, assuming the state of chemical equilibrium. The calculations were performed for ‘pure’ argon with water vapour and with the addition of Li, Ba and Zn. The influence of matrix elements on the emission intensities of Ca and Cd as analytes was also investigated.

Evaluation of electrical conductivity in high-pressure plasmas formed in xenon with sodium as additive

Results of a numerical evaluation of the electrical conductivity in high-pressure plasmas of intermediate degrees of ionization formed in xenon with, respectively, 1% and 10% of sodium are presented, for temperatures between 2000 K and 20 000 K, and for pressures ranging from the normal atmospheric value Patm = 0.1 MPa up to 2.5 MPa. The equilibrium plasma composition, necessary for the evaluations, was determined on the ground of the Saha equations combined with the charge conservation relation and the assumption that the pressure remained constant in the course of temperature variations. The ionization energy lowering, required in conjunction with the Saha equations, was obtained with the aid of a modified expression for the plasma Debye radius proposed previously. The electron elastic collisions with the charged particles were described by the Spitzer-Härm (or, rather, Rutherford) formula, and those with the neutrals were taken into account by a polynomial formula interpolating some selected experimental results. The evaluated electrical conductivity is found to increase with the pressure at fixed temperature (except in the mixture with 10% of sodium, in which case an indistinct maximum at p = 10 patm can be seen for 6000 K). This feature is opposite to what is found in pure xenon plasma and, except in the upper part of the temperature range analysed, agrees well with the behaviour of pure alkaline vapours. The numerical values obtained for the electrical conductivity are smaller than the figures resulting from the approximate formulae commonly used in numerical estimates of this transport coefficient in moderately non-ideal plasmas of intermediate degrees of ionization, much in accordance with the trends suggested by the experiment.

Spectroscopic study of the influence of iodine on metal halide discharges

A typical metal halide discharge with iodine as the halide was investigated by monitoring the emission radiation densities of atoms, ions, radicals and molecules. The influence of iodine on the spatial distribution of the excitation temperature and electron density was evaluated. Experimental data were used in conjunction with calculated equilibrium plasma composition to explain the mechanism of formation and excitation of different species in the system. Changes in mass and energy transport and in the main plasma parameters and the resulting excitation conditions can be attributed to the high evaporation rate and chemical reactivity of iodine. A direct spectroscopic method was developed for the determination of trace elements with high ionisation potentials and poor detection limits in the presence of iodine.

On plasma composition of a pulsed discharge in electrolyte

The equilibrium plasma composition for a system containing H, O, N, Na, and Cu is determined for the temperature range between 5000–20,000 K. This corresponds to the pulsed discharge plasma in electrolyte with energy dissipation which is near threshold. For computing the plasma composition of the system based on the minimization of free energy, the method of steepest descent was used. The plasma composition was calculated for different electrolyte contents, conductivity, and various external pressures.

Temperature determination for arcs in sulphur hexafluoride accounting for demixing

Methods of temperature determination for arcs in sulphur hexafluoride (SF6) are presented for the temperature range from 9000 to 20000K. Temperatures are derived from combinations of measured S I, S II, F I and F II absolute line intensities and computed equilibrium plasma composition data by means of iterative procedures. Demixing effects are accounted for as both the temperature and the fluorine to sulphur concentration ratio M are determined from the measured data. The methods are applied to experimental line intensity data obtained from steady-state wall-stabilised arcs in SF6 at atmospheric pressure, at axis temperatures of about 15000K. Simple approximation formulae are given for calculating the various partition functions at a pressure of p=1 bar for M=6, 12, 24 and 48; and at p=2, 4, 8 and 16 bar for M=6.