The study of the volume expansion of aluminum during porous oxide formation at galvanostatic regime

The volume expansion factor of porous alumina, formed by through anodizing of an Al foil of thickness 11.5 mum in the range of current densities of 4-35 mA cm(-2) in oxalic and sulfuric acid at 18-24 degreesC has been studied. The microstructure of anodizing samples has been observed using scanning electron microscopy. The thickness of obtained porous alumina films was measured by a mechanical profilometer with a computer signal-processing. The volume expansion factor of porous alumina varied from 1.35 to 1.65. Linear dependences were obtained for the volume expansion factor of porous alumina versus the anodizing voltage and the ionic current-density logarithm versus the inverse volume expansion factor. Unlike oxide formation in sulfuric acid, these dependences have two subsequential rectilinear regions in oxalic acid. This peculiarity of the dependences in oxalic acid was explained by formation of a region of the immobile negative space charge in the barrier Al oxide layer and its influence on the ionic transport. (C) 2003 Elsevier B.V. All rights reserved.