Abstract
This report deals with the investigations on formation of a thick anodic coating on aluminum in alkaline solutions (NH4OH-NH4F system bath: 2.5M-NH4OH, 0.1M-(NH4)2CO3' 0.2M-(NH4)2C4H4O6 (tartrate), 0.3M-NH4F, 0.005M-Al2(SO4)3' Na2CO3-NaF system bath: 0.1M-Na2CO3' 0.1M-Na2C4H4O6 (tartrate), 0.1M-NaF, 0.2M-NaAlO2' Na3PO4-NaF system bath: 0.1M-Na3PO4' 0.1M-Na2C4H4O6 (tartrate), 0.1M-NaF, 0.1M-NaAlO2) containing polyhydric alcohols or oxidizing agents. In the NH4OH-NH4F bath containing ammonium vanadate, a thick film (about 29μm) was obtained by anodizing for 30°C at a current density of 4A/dm2. In the Na2CO3-NaF bath, a thick film (about 13μm) was formed by anodizing for 30min at 30°C at a current density of 3.5-1.5A/dm2 when both glycerol and potassium hexacyanoferrate (111) are added to the bath. In the Na3PO4-NaF bath, a thick film (about 12μm) was formed with addition of both sorbitol and sodium chromate.
