A. Lefort

Experimental study of discharge with liquid non-metallic (tap-water) electrodes in air at atmospheric pressure

The discharge with liquid non-metallic electrodes (DLNME) was investigated. The discharge burnt steadily with a DC power supply between two streams of weakly conducting liquid (tap water) in open air at atmospheric pressure. The metallic current leads were inserted into the streams and were covered by a 5 mm thick water layer. The discharge burnt in volumetric (diffuse) form with fairly high voltage (~3 kV between leads) and low current density (~0.2-0.25 A cm-2). The plasma state in the inter-electrode gap was studied by spectroscopy, microwave sounding and electrical probe technique. The rotational and vibrational temperatures of N2 electronically excited molecules were measured. The absolute radiation values of different species were obtained as a function of position in the gap. The electric field E and the concentration of charged particles were obtained. The value of parameter E/Ng was estimated (Ng being the gas concentration). The density of water vapour in the discharge column was estimated. The results obtained show that DLNME generate molecular plasma at high pressure but out of thermal equilibrium. The properties of DLNME make it promising for various engineering applications, including those in plasma chemistry.

Work function measurements of contact materials for industrial use

The nature of the contact material is important for the characteristics of electric arcs and particularly for the electronic emission. Work functions of new industrial materials made with silver alloys and silver oxide alloys are not known at present. An experimental set-up is described which allows work function measurements from room temperature up to 700 K. The Fowler method was used for the measurement of the work function by the photoelectric effect. As a first application of the experimental device, work functions of metals (Ag, Cu, Ni, Sn and Zn) were determined. Furthermore, the influence of industrial surface treatment such as the application of electric arcs and repeated mechanical shocks on the Ag contact work surface was studied by SEM to observe their effect on electron work function. Breaking arcs in air cause a remarkable increase in the work function of the silver contact material by progressive formation of silver oxides.

Erosion of graphite electrodes

A macroscopic model is established to describe the erosion of anode and cathode graphite electrodes. Results concerning electrode temperatures, spot radii and mass losses are presented for a current range from 0 to 10000 A. A comparison with several experimental measurements of mass losses is given.

Theoretical study of column of discharge with liquid non-metallic (tap water) electrodes in air at atmospheric pressure

The discharge established between two liquid non-metallic electrodes (DLNME) is investigated. This d.c. discharge burns between two streams of tap water in open air at atmospheric pressure in diffuse form. In the plasma column two zones are defined: one close to the near-cathode and the other one close to the near-anode regions of the discharge. In each zone, the composition, massic enthalpy, volumetric emissivity of N2(2+) spectral band (376-380 nm), hydrogen spectral line (Hα) and triplet oxygen spectral lines (777 nm) have been calculated in non-equilibrium conditions. The comparison with experimental results allows determining the ratio between translational temperature of electrons and that of heavy species and an upper limit of the air humidity in both zones. This type of calculation describes satisfactorily the previously obtained experimental results

The calculation of monatomic spectral lines' intensities and composition in plasma out of thermal equilibrium; evaluation of thermal disequilibrium in ICP torches

The composition and monatomic spectral line intensities are calculated for several thermal disequilibriums in a plasma composed of water, cupric sulphate and argon. The monatomic excitation temperatures are determined experimentally from three chosen spectral lines of copper (510, 515 and 521 nm) in an ICP torch. By comparing the intensity of the argon spectral lines with that of the copper spectral lines, we evaluate the thermal disequilibrium for various excitation temperatures depending on the power input to the plasma.

The influence of thermal disequilibrium on a plasma consisting of insulator vapours

With the Gibbs free energy minimization method, we determine the molar fraction in a plasma out of thermal equilibrium consisting of ablated vapours of polymer (polyethylene and polyoxymethylene) in the temperature range 1000-6000 K. We indicate the formulae and the numerical method used to perform the calculation, taking the graphite phase into account. We show that there is an increase in the electronic mole fraction and a decrease in the mole fraction of negatively charged species when the plasma is out of thermal equilibrium. We clarify the role played by the vibrational temperature in determining the molar fraction and we show that the higher the vibration the higher the diatomic molar fraction. The calculation for vapours ablated from polyethylene has shown that it is possible to produce graphite in the presence of a plasma. The comparison of the two polymers studied has shown that polyoxymethylene produced less graphite than polyethylene does and that the polyoxymethylene insulator is bound to be less consumed by the plasma.

COMPARISON BETWEEN GIBBS FREE ENERGY MINIMIZATION AND MASS ACTION LAW FOR A MULTITEMPERATURE PLASMA WITH APPLICATION TO NITROGEN

This paper gives all the necessary physical equations to determine the composition and the thermodynamic properties in a multitemperature plasma utilizing two different methods: the first method is based on Gibbs free energy minimization and the second is based on the resolution of the mass action law. The lowering terms of the ionization potential and thermodynamic properties are given for a multitemperature plasma using the Debye-Hückel approximation. Numerical application is made to a nitrogen plasma.

Optical emission spectroscopy, thermodynamical and thermal disequilibrium aspects in an inductively coupled plasma torch. Experimental applications to - mixtures

The purpose of this article is to study experimentally and theoretically the spectral line ratios O 700.22 nm/N 746.87 nm with a sample gas mixture of and (notably for pure air) in an inductively coupled plasma (ICP) torch. We study theoretically the influence of the thermal disequilibrium on the composition and on the volumic enthalpy in a plasma produced in an ICP torch, and we show that the lower temperature in the plasma is set by the power supplied by the inductive coil. If the temperature (or heavy species temperature for plasma out of thermal equilibrium) is sufficiently low (<5000 K), we show that the thermal disequilibrium has no influence on intensity spectral line ratios (O 700.22 nm/N 746.87 nm). We compare these results with those obtained experimentally in the case of - mixtures, and we show that the determination of monatomic spectral line ratios (O 700.22 nm/N 746.87 nm) solely depends on the initial sample gas composition introduced in the ICP torch.

Theoretical calculation of composition, atomic and molecular spectral lines in Ar-SF6 plasma out of thermal equilibrium

In this paper we calculate the intensity emitted by different atomic lines and by the (B 3u--X 3g-) system of S2. We show the influence on intensity of the deviation from thermal equilibrium and of the hypotheses on different temperatures (atomic excitation temperature Texat, rotational temperature Trot, vibrational temperature Tvib, diatomic excitation temperature Texmol, translation temperature of free electrons Te-tr and translation temperature of heavy species Thtr). From this method, we show that from optical emission of atomic line and diatomic molecule spectra, the deviation from thermal equilibrium and consequently the composition of plasma can be determined.