FORMATION OF AL (TI, NB, TA)-COMPOSITE OXIDE-FILMS ON ALUMINUM BY PORE FILLING/

Aluminum specimens coated with porous anodic oxide films were dipped i n solutions containing Ti4+, Nb5+ or Ta5+ ions and heated in air mainl y at 400 degrees C to deposit Ti, Nb, or Ta oxide on the inner walls o f pores. After 0 to 7 cycles of the dipping and heating process, the s pecimens were reanodized in a neutral berate solution to fill the pore s with Al2O3. The incorporation of Ti, Nb, or Ta oxide in the anodic o xide films was examined by transmission electron microscopy, Rutherfor d backscattering spectroscopy, and impedance measurements. Incorporati on of Ti, Nb, or Ta oxide was found only in the outermost part of the anodic oxide film after reanodizing up to 400 V. The Al/Ti composite o xide films consisted of an outer Al/Ti-composite oxide layer, an inter mediate crystalline alumina layer, and an inner amorphous alumina laye r, while the Al/Nb -and Al/Ta-composite oxide films consisted of an ou ter composite oxide layer and an inner amorphous alumina layer. The pa rallel electric capacitance of Al/Ti-composite oxide film was 40% high er than those of the other two due to its small thickness and high die lectric constant. The formation mechanisms of the composite oxide film s during reanodizing are discussed in terms of the ion transport acros s the oxide film.