Studies on sealing of anodic oxide coatings of aluminum by gas adsorption method

Abstract

The sealing mechanism was studied on the pore structure of thin oxide coatings of aluminum which had been anodized in sulfuric or chromic acid bath. The sealing was made in boiling water or in a steam autoclave. The coatings were heated in vacuum at various temperatures of 20∼400°C, and the pore structure was examined by nitrogen adsorption isotherms at -196°C.
The following results were obtained:
(1) The pores of anodic oxide coatings were filled by sealing almost perfectly; but the pores of chromic acid coating were not sealed in boiling water at 100°C for 30min.
(2) The sealed anodic oxide coatings were dehydrated by vacuum heating at temperatures higher than 150°C and a large number of pores were formed on their surfaces. The pore size distribution curves of the coatings were different according to the methods of anodizing and sealing.