Spectroscopic study of plasma during electrolytic oxidation of magnesium- and aluminium-alloy

Abstract

We present the results of an optical emission spectroscopy study of Plasma during Electrolytic Oxidation (PEO) of magnesium- and aluminum-alloy. Plasma electron number density N e diagnostics is performed either from the H Β line shape or from the width or shift of non-hydrogenic ion lines of aluminum and magnesium. The line profile analysis of the H Β suggests presence of two PEO processes characterized by relatively low electron number densities N e≈1.2×10 15cm -3 and N e≈2.3×10 16 cm -3. Apart from these two low N e processes, there is the third one related to the ejection of evaporated anode material through micro-discharge channels. This process is characterized by larger electron density N e=(1.2-1.6)10 17cm -3, which is detected from the shape and shift of aluminum and magnesium singly charged ion lines. Two low N e values detected from the H Β and large N e measured from the widths and shift of ion lines suggest presence of three types of discharges during PEO with aluminum- and magnesium-alloy anode. On the basis of present and earlier results one can conclude that low N e processes do not depend upon anode material or electrolyte composition. The electron temperature of 4000K and 33,000K are determined from relative intensities of Mg I and O II lines, respectively. The attention is drawn to the possibility of N e application for T e evaluation using Saha equation what is of importance for PEO metal plasma characterization. During the course of this study, difficulties in the analysis of spectral line shapes are encountered and the ways to overcome some of the obstacles are demonstrated. © 2012 Elsevier Ltd.