Analysis of Gaseous Products of Plasma Electrolytic Oxidation of Aluminium

Measurements of the volume and density of anodic gas evolved during anodic-spark oxidation showed the ratio of hydrogen to oxygen to be about 1.6–1.8 at current densities 1000–3000 A×m^-2. The fraction of anodic hydrogen was 1.17–1.38% in the total amount of all hydrogen released during the anodic-spark oxidation from both electrodes. The hypothetical reactions responsible for the appearance of hydrogen in the anodic gas were considered. It is shown that the oxide current output, calculated in accordance with electrochemical regularities, decreases with increasing current density; it was in a range of 11–18%. This indicates a stronger role of thermochemical processes at a higher intensity of sparks and an increase in their sizes.