Stability of the anodic film on aluminium in relation to the nature of some anions

✍ Scribed by I. A. Ammar; S. Darwish; E. A. Ammar

• Publisher: John Wiley and Sons
• Year: 1973
• Tongue: German
• Weight: 666 KB
• Volume: 24
• Category: Article
• ISSN: 0947-5117
• DOI: 10.1002/maco.19730240304

✦ Synopsis

Abstract

Using a galvanostatic method of investigation the influence has been studied of various anions on the formation of anodic layers during anodization in borate solution. According to the results obtained sodium carbonate, phosphate, succinate and oxalate enhance the formation of the anodic oxide layer. Sulfite, sulfate, thiosulfate and nitrate lower the anode potential to a constant value which depends from the type of anion and may be extremely low in the case of halogen ions (chloride, bromide, iodide). This phenomenon is attributed in the case of the halides to a pitting type attack, while a duplex layer formation is assumed to take place with the other members of this group. The effect of the halides may be suppressed by the addition of phosphate ions, but rather high phosphate:halide ratios are required in order to achieve healing of the pits. The pores in the duplex layer may be sealed by a second anodization in borate, phosphate, benzoate or succinate solution.