Using half wave rectification obtained from selemium rectifier, anodic oxidation of aluminium by oxalic acid process is investigated as follows:
1) Anodic corrosion and its protection of negative current.
2) Observation of wave forms of electric current by oscillograph.
3) Properties of oxide film anodized under various conditions of temperature and concentration of electrolyte.
Results are summarized as follows:
(1) In 0.5 and 3.5% concentration of electrolyte, anodic corrosion occurs when only half wave rectification is used. The lower the concentration of electrolyte, the higher the negative current necessary to protect its corrosion. It is about 0.1-0.2A/dm
2 (root mean square value) for 1A/dm
2 positive current (mean value). With an increase of negative current and a decrease of concentration of electrolyte, specific corrosion resistance becomes better. But specific abrasion resistance slightly falls with an increase of negative current.
(2) While the anodic oxidation is normally proceeding, distortion of wave form in oscillograph is observed, but this distortion disappears when anodic corrosion begins to occur.
(3) As a general tendency of the effect of temperature and concentration of electrolyte on the properties of oxide film anodized under constant positive and negative current, specific corrosion resistance becomes better with lower concentration and higher temperature, but specific abrasion resistance becomes better with lower temperature.
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