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

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 N-e approximate to 0.8 x 10(15)cm(-3) and at 2.5 x 10(16)cm(-3). Apart from these two N-e values, N-e approximate to 6.0 x 10(16)cm(-3) is determined from the width of the Al II 704.2 nm line. Three considerably different N-e values imply presence of three types of discharge during PEO of aluminium. The electron temperature T-e is determined from relative line intensities of the O II (T-e approximate to 38,300 K) and WI (T-e approximate to 3300 K) lines. The use of two databases of transition probabilities for O II lines introduces systematic difference of reported T-e results. (C) 2011 Elsevier B.V. All rights reserved.