抄録
99.99% aluminum sheets were anodized with various inorganic acids, pKa values of which were mostly less than 2, by applying d.c. of 1.87-37.4A/dm2. The bath concentration was between 0.01M/l and the saturated aqueous solution and the bath temperature between 20°C and boiling point. Porous and uniform coatings were formed in sulfuric, phoshorous, phosphoric, hypophosphorous, EHDP, arsenic and chromic acid baths at certain electrolytic conditions, but integral color of the coating was not observed. The porous structure involving round cracks was observed at pittings which occurred in the bath of above acids. At high temperatures, the solvent action of the acids was strong, so that extremely thin coatings were obtained. With nitric or perchloric acid, caved pittings occurred and the porous structure was not observed around pittings. With periodic, iodic or boric acid, some insoluble matter was deposited on pittings. With telluric, phosphomolybdic or molybdic acid, the uniform and porous coating was not formed. Hunter's electrical method for measuring the thickness of barrier layer was found useful to evaluate the microstructure of the anodized surface precisely.
