Mass spectrometric analysis of plasma composition of a D. C. arc burning in an air atmosphere

Summary The plasma composition of a d. c. arc burning in air was investigated by mass spectrometry. It has been found that the CO and CO₂ contents result from homogenous chemical reactions and that the content of carbon is about 1%.

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Massenspektrometrische Analyse der Plasmazusammensetzung eines Gleichstrombogens in Luft

Zusammenfassung Die zwischen den Luftbestandteilen und den Elektroden stattfindenden Reaktionen wurden mit Hilfe der Massenspektrometrie untersucht. Es ergab sich, da? die CO- und CO₂-Anteile von homogenen chemischen Reaktionen herrühren. Der Gehalt an Kohlenstoff betr?gt etwa 1%.

     

D.C. arc spectrochemical determination of rhenium in molybdenite ores

Rhenium is isolated as tetraphenylarsonium perihenate from solutions of molybdenite ores. It is excited in a mixture with an alumina/graphite buffer directly on the cathode in an oxygen atmosphere. Oxygen acts as a protective atmosphere and as a carrier to sweep into the discharge the highly refractory rhenium in the form of easily volatilized oxides Intensity ratios of Re 346473, 346046, 345188 and 3399 30 Å lines with Co 3453.50 Å internal standard line cover the range 0.1–3.2μg of rhenium on the electrode. The relative deviation of the method, computed by a routine regiession analysis program, is+16-—14% for the best analytical line The detection limit is 6·10^-8 g of rhenium Several Canadian and other molybdenites with a rhenium content from 8 to 250 p.p.m. have been analysed.     

Transport velocities of particles in the plasma of a d.c. arc in air

Axial transport velocities of materials injected into a d.c. arc plasma by a liquid jet method have been determined on the assumption that the motion is influenced by diffusion (due to gradients in the number density of particles), axial electric field and convection. The velocities were measured using both high speed cinematography and cross-correlated photomultiplier signal techniques. In the interpretation of the measurements, with both methods use had to be made of the motion of the constant concentration boundary of the injected material in the frames of reference relative to both the arc electrodes and the point of maximum material density. Particular attention was given to convection effects.     

Operating characteristics and energy distribution in transferred plasma arc systems

A specially designed plasma chamber was constructed to study the operating characteristics of a dc plasma-transferred arc of argon, struck between a fluid convective cathode and a water-cooled anode. The arc voltage increased markedly with arc length and with an increase in the inlet velocity of the argon flow past the cathode tip, and much less with an increase in current. Radiation from the plasma column to the chamber walls and transfer of energy to the anode were the two principal modes of transfer of the arc energy. The former was dominant in the case of long arcs and at high inlet argon velocities. At the anode, the major contribution was from electron transfer, which occurred on a very small area of the anode (～5 mm in diameter). Convective heat transfer from the plasma was somewhat less. In all cases, the arc energy contributions to cathode cooling and to the exit gas enthalpy were small. From total heat flux and radiative heat transfer measurements, it was estimated that the plasma temperature just above the anode was in the range 10,000–12,000 K. Preliminary experiments with an anode consisting of molten copper showed that the arc root was no longer fixed but moved around continuously. The arc was othwewise quite stable, and its operating characteristics differed little from those reported for solid anodes, in spite of the greater extent of metal vaporization.     

Axial distribution of analyte emission in inductively coupled argon plasma

Summary Using a spectrometer, ICP axial profiles of analyte emission for a large number of atom and ion lines with different excitation and ionization potential have been studied. Obtained experimental results for axial distribution of atom and ion lines can be correlated with some of the proposed models for excitation mechanisms of analytes in argon ICP. On the basis of experimental data it can be concluded that in the case of simultaneous multielement analysis the observation heights between 14 and 17 mm above the load coil can be recommended. Experimental data show that there is no simple correlation between maximum intensity of lines and their excitation and ionization potential. Experimental results for axial distribution for ionic lines show that there is agreement between measured axial profile and calculated Boltzmann distribution of excited ionic state population.

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Axialverteilung der Analytemission im induktiv gekoppelten Argonplasma

Zusammenfassung Die ICP-Axialprofile der Analytemission wurden mit Hilfe eines Spektrometers für eine große Anzahl von Atom- und Ionenlinien mit verschiedenem Anregungs- und Ionisierungspotential untersucht. Die erhaltenen Ergebnisse können zu einigen Modellen für den Anregungsmechanismus im Argon-ICP in bezug gebracht werden. Aus den experimentellen Daten wird geschlossen, daß bei der simultanen Multielementanalyse Beobachtungshöhen zwischen 14 und 17 mm über der geladenen Wendel zu empfehlen sind. Es ergab sich, daß zwischen der Maximalintensität der Linien und ihrem Anregungs- bzw. Ionisierungspotential keine einfache Beziehung besteht. Die Untersuchung der Axialverteilung bei den Ionenlinien zeigte, daß Übereinstimmung besteht zwischen den gemessenen Axialprofilen und der berechneten Boltzmann-Verteilung.

     

A new equipment for mass transport study in a free-burning d.c. arc in air

A method for injection of liquid substances into the arc plasma is proposed. This method, which is also applicable to other plasmas at atmospheric pressure, seems to be very convenient for the study of the transport properties of the injected elements. The results of time-resolved measurements of the intensity of characteristic radiation emitted by the injected substances are presented in terms of residence times of particles in the plasma. The effect of the polarity of the arc was also studied. The cathode retains the substance in the vicinity of this electrode.     

The axial density distribution of radiation emitted by traces in the plasma of a D.C.ARC

Summary The axial radiation density distribution was determined for elements of different ionization potentials present in traces in the arc plasma. The sample was evaporated from the lower electrode (anode), while the diameter and shape of the upper electrode (cathode) were varied. The cathode layer enrichment was found to be affected by the cathode shape.

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Axiale Verteilung der Strahlungsdichten der Spurenelemente im Bogenplasma

Zusammenfassung Die axiale Verteilung der Strahlungsdichten der Spurenelemente wurde mit verschiedenen Ionisierungspotentialen im Bogenplasma bestimmt. Die Probe wurde aus der unteren Elektrode (Anode) verdampft, wobei der Durchmesser und die Form der oberen Elektrode (Kathode) variiert wurden. Dabei wurde gezeigt, daß die Verteilung der Strahlungsdichten von der Form der Kathode abhängt.

     

Optimum excitation conditions in spectrographic analysis with the D. C. carbon arc

Summary A previously established expression for the transport mechanism in the arc is applied to the equation for the spectral line intensity. The possibility of a correlation between temperature and electron concentration in the arc is discussed and optimum temperatures are calculated, for which the intensity of an atom line reaches a maximum. The optimum temperature is shown to depend on (a) the excitation potential of the transition and the ionization potential of the element, (b) the magnitude of the electron concentration and its variation with arc temperature and (c) the occurence of transport processes in the arc.

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Zusammenfassung Mit Hilfe einer kürzlich gefundenen Beziehung für den Transportmechanismus im Gleichstrombogen wird eine vollstÄndige Gleichung für die LinienintensitÄt erhalten. Die Möglichkeit einer Korrelation zwischen Temperatur und Elektronenkonzentration im Bogenraum wird diskutiert und optimale Temperaturen werden berechnet, für welche die IntensitÄt einer Atomlinie maximal wird. Die optimale Temperatur hÄngt ab von a) der Anregungsenergie des Spektralübergangs und der Ionisierungsspannung des Elementes, b) der Grö\e der Elektronenzahl und ihrer Änderung mit der Temperatur, und c) dem Transportmechanismus im Bogenraum.

     

Calculation of thermodynamic and transport properties of a typical arc furnace plasma

Using a previously developed computer program, thermodynamic and transport properties of a typical arc furnace plasma are calculated in order to single out those species and / or reactions which exert a dominating influence on the properties of such complex mixtures. The results indicate that dissociation of molecular species in the arc furnace atmosphere has a strong effect on the specific heat and on the thermal conductivity of the mixture. The electrical conductivity is strongly affected by metallic vapors from the molten metal pool and the slag cover.     

Transport of uranium free particles in a d.c. arc plasma burning in air at atmospheric pressure

The transport parameter ψ was calculated for the free particles of uranium in a d.c. arc plasma burning in air. Using the “wire method” the volatilization rate (Q_w), the total concentration of free particles (_nt), the axial velocity (_vj) of uranium particles and the plasma cross section (S) were measured. The transport parameter was calculated for cylindrical symmetry of the arc. The total particle concentration calculated by the wire method was compared to values obtained by absolute intensity measurements of ion and atom spectral lines of uranium. This led to an estimate of the molecular concentration of uranium in the d.c. arc plasma.     

Spectrometric analysis of nitrogen in steel with D.C. arc in the vacuum ultraviolet

Summary A spectrometric determination of nitrogen in steel was performed with d.c. arc excitation in the vacuum ultraviolet region. Two nitrogen spectral lines, 1,742 Å and 1,745 Å, were utilized for the determination of nitrogen using C I 1,930 Å as internal standard in the wave-length region of 1,200–2,000 Å. In argon atmosphere (700 mm Hg, 28 A arc current) and in helium atmosphere (700 mm Hg, 30 A arc current) nitrogen could be determined below 50 ppm after a pre-arcing time of 100 sec. Better reproducibility could be obtained with the line 1,745 Å rather than with 1,742 Å.

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Zusammenfassung Zur Bestimmung von Stickstoff in Stählen wird eine UV-vakuumspektrometrische Methode mit Gleichstrom-Bogenentladung empfohlen. Zur Anwendung kommen die Stickstofflinien 1742 Å und 1745 Å mit der inneren Standardlinie C I 1930 Å. Unter Argon- (700 mm Hg; 28 A Bogenstrom) oder unter Heliumatmosphäre (700 mm Hg; 30 A Bogenstrom) konnten Stickstoffmengen unter 50 ppm nach einer Vorentladungszeit von 100 sec bestimmt werden. Die Linie 1745 Å ergab eine bessere Reproduzierbarkeit als 1742 Å.

     

Volatilization rate of free particles in a d.c. arc plasma,burning in air under atmospheric pressure

The volatilization rate (Q) of free particles (atom, ions and molecules) from the anode cavity into the discharge zone of d.c. arcs burning in air under atmospheric pressure was studied. In volatilization rate of particles of uranium, thorium and zirconium matrices was measured by two methods. The first is an indirect method, in which the residue in the anode cavity after the arcing period was chemically analysed (Q_ch and corrections for side losses of particles were applied. The second method is a direct one, in which aluminium wires were passed at uniform velocity through the plasma, in the vicinity of the anode. The wires coated by the free particles were analysed (Q_w) by neutron activation for uranium and spectrochemically for thorium and zirconium content. The two methods are compared.     

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.     

A high-powered A.C. plasma torch for the arc heating of molten steel in the tundish

Current user's requirements for excellent product quality means that producers must discover the isothermal casting conditions which trill lead to top operating performance in the continuous casting process. In response to this requirement. a high-powered A. C. plasma arc heating system was adopted for the No. 4 Continuous Caster (No. 4CC) put into operation at Kakogawa Works. This heating system is a single-phase A.C. plasma type with two torches. This report describes research on the molten steel heating technique utilized by the A. C. plasma system, the effects of tundish atmosphere on the characteristics of plasma electric potter, and the counter- measures devised to increase the arc voltage using a suitable torch structure.     

On the carrier effect mechanism in relation to mass transport processes in the arc discharge

The time of residence of impurity atoms in the arc discharge is calculated. Diffusion, ion motion in the electric field, and ambipolar diffusion are taken into account. It is shown for the first time that ambipolar diffusion contributes significantly to the total particle flow from the arc discharge zone. The effect of charge exchange on the speed of ion motion in the arc is estimated. The influence of a carrier on the residence time of atoms in the arc discharge zone is calculated. Attention is paid to the peculiarities of the mechanism of the carrier effect associated with halide compounds. An attempt is made to explain the influence of halide compounds on the residence time of atoms in the arc using the considered model of mass transport. The velocities of mass transport and the time of atoms in the discharge zone are calculated for the are with and without halide containing substances. The initial parameters of calculation (discharge temperature, electron density, degree of ionization, and coefficient of atom diffusion) are partly measured and partly taken from the literature. The results of the calculation are compared with experimental data published in the literature. The adopted mass transport model adequately accounts for the influence of a carrier on the residence time of atoms in the arc discharge zone.     

Penetration of plasma surface modification. II. CF4 and C2F4 low-temperature cascade arc torch

The depth of surface modification by low-temperature cascade arc torch is investigated. A stack of 10 sheets of nonwoven fabrics of polyester fibers is exposed to a low-temperature cascade arc torch containing CF₄ or C₂F₄, and the fluorination effect is examined by ESCA. It is shown that interaction of chemically reactive species, created in a low-temperature cascade arc torch, with the surface is not limited to the surface contacted by the torch (flame). The results indicate that the fluorination effect is observed on surfaces which are shadowed from the torch by overlying fibers. The highest degree of fluorination is found on the second layer, rather than on the first layer which the torch contacts directly. No significant differences in the trends of penetration of CF₄ and C₂F₄ treatment through porous samples are observed. However, ESCA data show principal differences in chemical structures of the surfaces treated with CF₄ (nonpolymer-forming gas) and C₂F₄ (polymer-forming gas). These results indicate that chemically reactive species induced by the excited species of argon rather than primary species created by the ionization process seem to play predominant roles in the surface treatment as well as the low-temperature cascade arc torch polymerization of perfluorinated compounds. © 1994 John Wiley & Sons, Inc.