Spectroscopic characterization of plasma during electrolytic oxidation (PEO) of aluminium

Abstract

We present results of an optical emission spectroscopic study of Plasma during Electrolytic Oxidation (PEO) of aluminium in citric acid and in sodium-tungstate water solutions. The line shape analysis of the first two hydrogen Balmer lines indicates presence of two PEO processes characterized by relatively low electron number densities Ne≈0.8×1015cm-3 and at 2.5×1016cm-3. Apart from these two Ne values, Ne≈6.0×1016cm-3 is determined from the width of the Al II 704.2nm line. Three considerably different Ne values imply presence of three types of discharge during PEO of aluminium. The electron temperature Te is determined from relative line intensities of the O II (Te≈38,300K) and W I (Te≈3300K) lines. The use of two databases of transition probabilities for O II lines introduces systematic difference of reported Te results. © 2011 Elsevier B.V.