[en] Studies of injected elements in an inductively coupled argon plasma working at atmospheric pressure show a departure from L.T.E. This is confirmed by the discrepancies between the ionization temperature and the excitation temperatures. The excitation of some lines of these elements can be explained through the action of metastable levels of neutral and ionized argon. An atomic absorption experiment using a two-line method has been set up in order to measure the metastable densities

[en] ICP (Inductively Coupled Plasma) generators at atmospheric pressure have quite widespread since thirty years. They are useful for elementary analysis, either for optical emission spectroscopy or for mass spectroscopy. Plasma know how is described. For both spectroscopies, the best choice is argon plasma, emitted by a HF (high frequency) inductive source, at a 1 to 2.5 kW power. Then the analytical properties are detailed. (D.L.). 8 refs., 3 figs., 1 tab., 1 photo

[en] We have used the pulsed afterglow technique in a hollow cathode titanium-argon plasma to study the mechanisms of production and loss of the neutral and ionized titanium species. From the measurement of the decay time of the ground state titanium atom Ti(a³Fsub(J)) density, determined by the optical absorption technique, we have deduced the value of the diffusion coefficient of titanium atoms in argon at 300 K, D₀(Ti-Ar) = 3.1 x 10¹⁸ atoms cm^-1 s^-1. The analysis of the emission intensity from the excited levels of titanium ion seems to point to the fact that the principal mechanism for the production of the (Ti⁺)* is a charge transfer process, involving Ar⁺ ions, rather than the Penning ionization by argon metastable atoms. The excited levels of the titanium atom are populated by electron-ion recombination involving the Ti⁺ ions. (orig.)

[en] Modelling of inductively coupled plasmas at atmospheric pressure has been developed for years, integrating fluid dynamics, electromagnetism and heat transfer. In this work, special attention has been devoted to radiation transfer. Two radiation models have been implemented: the net emission coefficient and the P1 model. These models have been run with different torch geometries and input powers. The parametric study shows that they are very sensitive to parameters such as the thermal and electrical conductivity of the gas and input power. The temperature distributions have been compared with the measurements available in the literature. The spectral P1 model is more accurate at the expense of the computing time. The radiative heat losses are below 5% in small torches such as those used in spectrochemical analysis, but can exceed 40% in large torches (40 mm diameter or more), becoming the main cooling mechanism

[en] Gettering treatments such as phosphorus diffusion and aluminium-silicon alloying have been applied to multicrystalline silicon wafers prepared from upgraded metallurgical feedstock. Purification of the feedstock results of plasma torch treatment and directional solidification. Minority carrier diffusion lengths L_n are close to 40 μm in the raw wafers and increase up to 150 μm after phosphorus plus Al-Si getterings. Improvements are limited by the presence of residual metallic impurities, mainly slow diffusers like aluminium, and also by the high doping level.

No abstract available

[en] Metallized-film capacitors have the property, even under high continuous voltage, to self-heal i.e., to clear a defect in the dielectric. The self-healing process is a consequence of a transient arc discharge. It has been previously shown that during the discharge, due to Joule effect, the metal is vaporized until the arc extinguishes. The discharge duration has been found to be inversely proportional to the mechanical pressure applied on the layers of metallized films making up a capacitor. The aim of this study is to understand the physical processes involved in this spontaneous extinction of the arc discharge. Emission spectroscopy has been used to provide information about the physical properties (temperatures, electronic and neutral particles densities, etc.) of the plasma induces by a self-healing. An analysis, based on the broadenings and shifts of Al atomic lines, of the experimental light spectra obtained has shown that the self-healing process leads to the generation, from the vaporized metal, of a high-density and relatively weakly ionized aluminum plasma. The plasma density increases with the pressure applied on the film layers and, consequently, the density power needed to extend the plasma zone increases as well and the arc discharge goes out faster as experimentally observed

[en] Microwave plasmas sustained at atmospheric pressure, for instance by electromagnetic surface waves, can be efficiently used to abate greenhouse-effect gases such as perfluorinated compounds. As a working example, we study the destruction and removal efficiency (DRE) of SF₆ at concentrations ranging from 0.1% to 2.4% of the total gas flow where N₂, utilized as a purge gas, is the carrier gas. O₂ is added to the mixture at a fixed ratio of 1.2-1.5 times the concentration of SF₆ to ensure full oxidation of the SF₆ fragments, providing thereby scrubbable by-products. Fourier-transform infrared spectroscopy has been utilized for identification of the by-products and quantification of the residual concentration of SF₆. Optical emission spectroscopy was employed to determine the gas temperature of the nitrogen plasma. In terms of operating parameters, the DRE is found to increase with increasing microwave power and decrease with increasing gas flow rate and discharge tube radius. Increasing the microwave power, in the case of a surface-wave discharge, or decreasing the gas flow rate increases the residence time of the molecules to be processed, hence, the observed DRE increase. In contrast, increasing the tube radius or the gas-flow rate increases the degree of radial contraction of the discharge and, therefore, the plasma-free space close to the tube wall: this comparatively colder region favors the reformation of the fragmented SF₆ molecules, and enlarging it lowers the destruction rate. DRE values higher than 95% have been achieved at a microwave power of 6 kW with 2.4% SF₆ in N₂ flow rates up to 30 standard l/min