![]() In a number of papers the results of optical emission spectroscopic studies of plasma generated during the PEO process have been presented. The investigation and characterization of PEO microdischarges (plasmas) are important steps for understanding of the PEO process. 2 Due to these plasma processes, the roughness of the coating as well as its morphology, the coating microstructure and composition are modified to some extent, which can be controlled by process parameters. The oxidation mechanism becomes now more complex, including also plasma chemical reactions. They are of short duration, typically of a few microseconds, appearing stochastically in time and in space (on the surface of the coating). In the PEO processing, due to dielectric breakdown of an anode oxide film under high electric field, a plasma state is generated in the form of visible microdischarges or (plasma) sparks. In the conventional electrolytic oxidation process, the oxidation of the metal is a consequence of electrochemical reactions in the electrolyte (one phase) and on the electrode (the other phase), including the phase-boundary processes. ![]() 1 The thickness of the coating film varies from tens to hundreds of micrometers, which is influenced by the processing parameters like power supply, electric field strength and the type of the metals and electrolytes used in the PEO process. is a processing technique in which surfaces of metals are transformed into oxide coatings. Introduction Plasma electrolytic oxidation (PEO) of valve metals like Al, Ti, Zr, Ta, etc. After detailed analyses of a series of spectra obtained by applying different detection parameters, like exposure time, slit width, detection mode, and number of accumulations, we attributed the anomalous D 2/ D 1 intensity ratio to the effect of approaching a saturation condition of the charge coupled device detector and thus to an early indication of saturation occurrence. Assuming that the plasma is in local thermal equilibrium it is expected that the intensity ratio of sodium doublet components equals the ratio of the statistical weights of the atomic sublevels corresponding to the electronic transitions ( D 1: 3 2P 1/2–3 2S 1/2, D 2: 3 2P 3/2–3 2S 1/2) i.e. We found that the D 2 to D 1 intensity ratios were not constant, varying from 2 to 1.2. ![]() In this paper we present the results of intensity measurements of D 1 (589.5224 nm) and D 2 (588.9950 nm) sodium doublet spectral lines emitted from a short-lifetime plasma randomly appearing across the aluminum anode surface during its electrolytic oxidation from the water solution of boric acid with sodium tetraborate.
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