On the Anodic Oxidation of SAP (Sintered Aluminum Powder)

Abstract

Effects of Al₂O₃ on the anodizing of SAP in 15% H₂SO₄ aqueous solutions were studied by comparing the results obtained with the data for pure aluminum of different purity (99.99%Al and 99.49%Al). The specimens used were SAP 26 (1.2%Al₂O₃), SAP 45 (4.6%Al₂O₃), SAP 61 (8.0%Al₂O₃), SAP 82 (12.7%Al₂O₃).
Al₂O₃ contained in SAP gives remarkable effects on the anodic oxidation, and the results obtained are summerized as follows: (1) In the constant voltage anodizing, the leakage current density decreases with the increasing Al₂O₃ content of SAP, and the bath voltage increases for the constant current density anodizing. (2) In the constant current density anodizing, the bath voltage-time curves of SAP containing a small amount of Al₂O₃ show critical voltages, but not for the specimens of a high Al₂O₃ content. (3) In the constant voltage anodizing, the thickness of the anodic oxide films decreases with the Al₂O₃ content of SAP. However, no remarkable effect of the Al₂O₃ content was observed for the constant current density anodizing. (4) Oxide films formed on SAP containing a large amount of Al₂O₃ are dark grey or black in color when the specimen is anodized under a high current density. (5) There is no relation between the corrosion resistance of anodic oxide films of SAP and its Al₂O₃ content. (6) From the electron microscopic observation, it was found that pores observed on the anodic oxide films of pure Al are gradually diminished as the Al₂O₃ content increases, and that the surface of the films becomes smooth.