Emission spectroscopy and the recording of electrical characteristics are used to study the influence of the granulometric composition of arc-quenching material. Six adjacent intervals of grain size are studied: each of them is 50 µm wide, and the upper limit of the global interval is lower than 1000 µm. The final dimensions of the fulgurite are found to be proportional to the granulometry. Concerning the electrical parameters, two groups are considered: the extinction time constant, the dissipated energy and the I2t value decrease with the granulometry, whereas the maximum value of the arc voltage increases with the granulometry. The rate of decrease of the temperature depends on the time interval observed: at the beginning of the arcing period, the decrease is fastest for the smallest granulometric parameters; and during the last part of the arcing period the trend is reversed. At the beginning of the arcing period, the electron number density increase varies between 1019 and 1020 cm-3 ms-1. When the electric current decreases, the electron number density decreases exponentially with a time constant value ranging from 0.40 ms to 0.25 ms.

International audienceCalculated values of viscosity, thermal and electrical conductivities of plasma formed in mixtures of silver (Ag) and silica (SiO2) are presented. The calculations, which assume local thermodynamic equilibrium, are performed for three pressures (1, 10 and 30 atm) in the temperature range from 4,000 to 30,000 K. All the data for the potential interactions and the necessary formulations to obtain values of transport coefficients are given in details. For atmospheric pressure, five mixtures (100% Ag, 75% Ag and 25% SiO2, 50% Ag and 50% SiO2, 25% Ag and 75% SiO2, 100% SiO2) in weight percentage are studied. In order to analyse the pressure influence on the transport coefficients, three samples of Ag–SiO2 mixtures (100% Ag, 50% Ag and 50% SiO2, 100% SiO2) in weight percentage are discussed for pressures of 1, 10 and 30 atm. In addition for the test case of oxygen plasma, we compare the computation code results with values obtained by other authors: discrepancies are found and explained

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