Morphology and Boron Content of Anodic Aluminum Oxide Films Formed in Boric/Sulfuric Acid Baths

• Published in: Hyōmen gijutsu Vol. 45; no. 11; pp. 1152 - 1157
• Main Authors: MORISAKI, Shigeyoshi, NAGASE, Hirokazu
• Format: Journal Article
• Language: English; Japanese
• Published: Tokyo The Surface Finishing Society of Japan 01.01.1994; Hyomen Gijutsu Kyokai; Japan Science and Technology Agency
• Subjects: Anodic Alumina Film; Boron Content; PGA Analysis
• ISSN: 0915-1869; 1884-3409
• DOI: 10.4139/sfj.45.1152

The boric/sulfuric acid anodizing process has been developed in the U. S. as a replacement for chromic acid anodizing to meet stricter environmental regulations. A comparative study has been conducted on the microstructures of boric/sulfuric acid films and sulfuric acid films. The sulfur and boron contents of the oxide films were determined by prompt gamma ray analysis. The type of V-t and I-t curves, and the morphology of pores were not appreciably influenced by the presence of boric acid in the anodizing bath, but the rate of formation of the boric/sulfuric acid films increased slightly and the rate of their disolution in phosphoric acid solution decreased slightly. The concentration of boric acid did not influence the amount of surfur incorporated into the oxide films. After the pores were sealed, surfur content decreased significantly due to the dissolution of sulfur compounds to the sealing solution. The boron content of porous type films was negligible, in the order of ppm. This is in remarkable contrast to the barrier type films formed in borate solutions, where boron contents of the order of several per cent have been reported. The boron content increased with increasing concentration of boric acid in the electrolytes.