ANODIC-OXIDATION OF ZIRCONIUM COVERED WITH A THIN-LAYER OF ALUMINUM

Anodic oxidation of Al-Zr bilayer samples (aluminium deposited on zirc onium) has been investigated by secondary ion mass spectrometry depth profiling and transmission electron microscopy of ultramicrotomed sect ions. Anodizing proceeds in the sequence of growth of amorphous anodic alumina and, when the aluminium layer is consumed, growth of crystall ine anodic zirconia on zirconium. Despite the outer anodic Al2O3 layer having a higher ionic resistivity than the inner anodic ZrO2 layer, f ingers of ZrO2 do not penetrate locally into the outer Al2O3 layer. Th e oxidation of the inner zirconium layer results from oxygen ions tran sported through the outer amorphous Al2O3 layer without zirconium bein g in direct contact with the electrolyte. These new findings and their impact on the detailed understanding of oxygen transport during the g rowth of crystalline anodic ZrO2 are considered. (C) 1997 Elsevier Sci ence S.A.