J.C. Sagás

Basic Characteristics of Gliding-Arc Discharges in Air and Natural Gas

Gliding-arc discharges have been utilized in plasma-assisted combustion processes, among various other applications, due to their properties of high electron density and chemical selectivity in a transitional regime. However, basic characteristics relative to the relations between the fundamental parameters of discharge, like mass flow rate, breakdown voltage, and frequency of repetition (number of discharge breakdowns per half cycle), have not been completely studied. In this paper, an ac-powered gliding-arc discharge having a reverse vortex flow configuration is built to carry on a basic investigation on discharges in air, natural gas, and mixture of both. Electrical measurements, optical emission spectroscopy, and mass spectrometry are the techniques used for these investigations. The results presented in this paper describe the dependence of the breakdown voltage, frequency of discharges, and conversion rates of methane and molecular oxygen with respect to the variation of the mass flow rate (directly related to the residence time) and discharge current.

SixCy Thin Films Deposited at Low Temperature by DC Dual Magnetron Sputtering: Effect of Power Supplied to Si and C Cathode Targets on Film Physicochemical Properties

A DC dual magnetron sputtering system with graphite (C) and silicon (Si) targets was used to grow stoichiometric and non-stoichiometric silicon carbide (SixCy) thin films at low temperature. Two independently DC power sources were used to enable the total discharge power be shared, under certain proportions, between the Si and C magnetron cathodes. The motivation was to control the sputtering rate of each target so as to vary the stoichiometric ratio x/y of the deposited films. The species content, thickness and chemical bonds of as-deposited SixCy films were studied by Rutherford backscattering spectroscopy (RBS), profilometry analysis and Fourier transform infrared absorption (FTIR), respectively. Overall, the present work reveals a new reliable plasma sputtering technique for low temperature growth of amorphous SixCy thin films with the capability of tuning the degree of formation of a-SiC, a-Si and a-C bonds in the film bulk.

Similarity Relations of Power–Voltage Characteristics for Tornado Gliding Arc in Plasma-Assisted Combustion Processes

Gliding arc discharges have been utilized in plasma-assisted combustion processes, among various other applications, due to their chemical properties. In this paper, an ac-powered gliding arc discharge having a reverse vortex flow configuration (tornado) was experimentally studied in air and in air-natural gas mixtures. A new method is proposed for the generalization of power characteristics of this type of discharge, based on similarity theory. The application of this method is demonstrated to be efficient for gliding arc discharges with tornado effect, using dimensional numbers. Regression dependences for discharges in air and in mixtures of air and natural gas were obtained in a form of simple power function equations (using the concept of equivalence ratio), which can be applied for the design of different gliding arc equipments for plasma-assisted combustion and related technologies.

Pulsed bias effect on crystallinity and nano-roughness of Ti6Al4V-N films deposited by grid assisted magnetron sputtering system

This paper reports the effect of pulsed bias in comparison with DC bias on reactive deposition of Ti6Al4V-N films, obtained by Grid Assisted Magnetron Sputtering. The results obtained by X-Ray diffraction (XRD), Energy Dispersive X-ray Fluorescence Spectrometer (EDX) and Atomic Force Microscopy (AFM) show that bias condition affects the crystalline texture and change the roughness and morphology of the films. The DC bias favors the film crystallinity, however the pulsed bias produces smoother films.