Analysis of Gaseous Products of Plasma Electrolytic Oxidation of Aluminum

The measurements of the volume and density of the anodic gas evolved in anodic-spark oxidation showed that the ratio of hydrogen to oxygen is about 1.6–1.8 at current densities of 1000–3000 A m−2. The fraction of anodic hydrogen is in the range of 1.17–1.38% among the total hydrogen released during the anodic-spark oxidation from both electrodes. Hypothetical reactions responsible for the appearance of hydrogen in the anodic gas are considered. It is shown that the oxide current output calculated in accordance with electrochemical regularities decreases with increasing current density, in the range of 11–18%. This is indicative of the enhancing role of thermochemical processes upon a higher intensity of sparks and an increase in their sizes.