Argon Plasma Torch Research Articles

Excitation and kinetic equilibrium in an argon inductively coupled plasma—II: Introduction of aerosol flow

The introduction of an aerosol flow (argon only) axially through an inductively coupled plasma is shown, by means of a relaxation method, to cause a deviation from excitational equilibrium across the entire plasma radius. Increasing this flow from 1 to 21 min appears to return the plasma to a state of excitational equilibrium, but the temperatures obtained are inconsistent with the validity of Saha's equation, indicating a non-Boltzmann distribution of the Ar I excited states. The effects of the introduction of aerosols containing various molecular samples through the centre of the plasma of an inductively coupled argon plasma torch on the state of kinetic and excitational equilibrium are then investigated. Aerosols of argon +4% H 2, 4% air, H 2O and 1% KCl in aqueous solution were introduced through the central channel of the plasma. Their effect on the state of kinetic and excitational equilibrium of the plasma is found to be relatively insignificant compared to that caused by the aerosol gas flow.

Effect of high-temperature annealing on the microhardness of silicon carbide crystals

The effect of annealing on the microhardness of silicon carbide crystals (type II) was studied in the high-temperature range 2000–2500°C, in an argon plasma torch, for 2 h. It is found that the hardness decreases with the increase of temperature. A nominal increase of hardness with increase in the annealing temperature was noted for anneals longer than 2 h. The decrease in microhardness is attributed to weakening of the Si-C bond and reduction in the Peierls force, at very high temperatures. Microstructure examination of the specimen after the anneals revealed some slip activity inside the indentations. It is found that these slip lines belong to the (0001) 〈112̄0〉 and (101̄0) 〈112̄0〉 slip systems.

Sample entraining 3-electrode argon plasma source for atomic emission spectroscopy

A new 3-electrode argon plasma torch has been designed to entrain a sample stream in the center of hot plasma in a manner similar to an induction coupled plasma. The design uses three concentric quartz tubes with electrodes running parallel to the tubes in the space between the sample and middle quartz tubes. Performance is better than a previous model developed in this laboratory. Advantages include a low cost power supply with no radio frequency noise, and a linear dynamic range of four orders of magnitude. Detection limits for five elements range from 0.1 to 2 mgl −1. Phosphate has a slightly enhancing effect on Ca emission.

Ignition mechanism of an induction‐coupled argon plasma torch at atmospheric pressure

Ignition mechanism of an induction‐coupled argon plasma torch at atmospheric pressure

Studies of flame and plasma torch emission for simultaneous multi-element analysis—I: Preliminary investigations

The need for rapid and relatively simple techniques for simultaneous multi-element analysis of solutions focusses attention on emission techniques using a high-temperature flame, a radio-frequency plasma torch or a plasma jet. This paper deals with the premixed nitrous oxide-acetylene flame and the inductively-coupled argon plasma torch as excitation sources for trace analysis of solutions. Experimental facilities encompass various commercially available burners (including a burner for a gas-shielded flame), an improved plasma torch using a new type of HF generator (52 MHz, 2 kW) and a new arrangement of an ultrasonic nebulizer, less conventional accessory optics, a medium monochromator (1-m Czemy-Turner), and a double-beam, dual-channel arrangement using two monochromators. Detection limits of representative elements were determined in both sources and the conditions favourable for simultaneous multi-element trace analysis were investigated. In many instances, detection limits lower than those published previously were attained. With the plasma torch, the ng ml region—and for many elements even the sub- ng ml region—is easily accessible. The paper includes a discussion of some fundamentals of detection limits. This is to connect the present approach, which stems basically from emission spectrographic analysis, more smoothly with common usage in flame spectrometrio analysis.

Criterion for establishing deviations from the local thermodynamic equilibrium in atmospheric pressure plasma jets

In this paper a dimensionless parameter is defined which allows the prediction of the thermodynamic state in the field-free plasma jet of D. C. operated plasma torches of various designs. This dimensionless parameterP is derived from the conservation equations applied to a two-step temperature and velocity model and contains only quantities which can be experimentally determined without using sophisticated equipment. Critical values ofP based on a critical electron density of 1016 cm−3 have been calculated for argon, hydrogen, nitrogen, oxygen, and helium and corresponding values of Pcrit have been determined experimentally for two different D. C. operated argon plasma torches using various diagnostic techniques. The experimental values corroborate the assumptions made for the calculation of Pcrit. ForP < Pcrit, substantial deviations from the local thermodynamic equilibrium (LTE) may occur.

Emission spectroscopy of trace impurities in powdered samples with a high-frequency argon plasma torch

A commercial high-frequency plasma generator and torch have been modified for application to the analysis of powdered samples. Many of the operating parameters have been investigated and the optimised system has been tested for the analysis of beryllium and boron in magnesium oxide. Two possible methods of sample introduction have been developed.

Absorption et emission du rayonnement continu emis par un jet de chalumeau à plasma d'argon entre 30 et 30.000 cm -1

The absorption and emission continuum in the jet of an argon plasma torch ( T⋍10.000°K, N e ⋍10 17 cm -3) has been investigated from the ultra-violet (σ=30.000 cm -1) to the far-infrared (σ=30 cm -1) regions of the spectrum. In the far-infrared, for σ<1000 cm -1, the radiation corresponds to free-free transitions and is associated with electron-ion collisions. In the ultra-violet and visible, radiation from the jet corresponds to free-bound transitions. For σ<300 cm -1, the plasma becomes optically thicker and behaves as a black-body near the plasma frequency (σ p =100 cm -1).

Diffusion Thomson et diffusion Rayleigh dans un jet de plasma d'argon

Experimental determination of electron density in the jet nozzle of an argon plasma torch by Thomson scattering of a ruby laser beam is reported. The results are compared with those obtained from other processes (absolute continuum, absolute intensity of the AI 4044 Å line). The experimental setup makes it possible to determine the absolute value of the differential scattering cross section; it is found to be in agreement with the theoretical value of σ′ = 0·47 × 10 −26 cm 2.

Electronic Structure of Rare-Earth Sesquisulfide Crystals

Single crystals of R2S3, R = Dy, Gd, Nd, and Y, have been grown by flame fusion in an argon plasma torch and by the Bridgman technique. The purification of R2O3 starting materials, synthesis and analysis of compound powders R2S3, crystal growth, analysis to determine if single crystals are produced, and measurement of electrical resistivity and thermoelectric power coefficient from 300° to 1300°K and discussed. The electrical measurements indicate highly degenerate semiconductor behavior with ρ and α increasing with temperature in contrast with previous reports for rare-earth tellurides and selenides. The presence of the rare-earth ions in their trivalent state and the absence of divalent ions have been confirmed independently by reflectance spectra from powders, by absorption spectra of single crystals, and by measurement of magnetic susceptibility of single crystals. The materials are unusual because they are semiconductors with the (4f)n levels of the rare-earth ions spanning the bandgap in ladderlike fashion. The free ion energy levels of Dy3+ were obtained by diagonalization of the electrostatic and spin—orbit matrices arising from a perturbation calculation, and least-squares fitting of the calculated levels to experimental values. The Dy2S3 spectra are correlated with DyF3 and Dy2O3 results.

Étude du spectre continu dans le visible d'un jet de chalumeau á plasma d'argon

The absolute emission continuum in the visible region, in the jet of an argon plasma torch, has been measured and the experimental results have been compared with theories of Kramers, of Biberman, Norman, and Ulyanov and of Schlüter. The last theory explains satisfactorily the decreasing intensity of the continuum in the ultraviolet and yields temperature values in agreement with results obtained from other processes (absolute continuum, broadening of the Hβ line when argon contains hydrogen as an impurity, absolute intensity of the AI 4044 Å line, temperature of neutral species).