Dissolution of the Native Oxide Film on Polycrystalline and Single-Crystal Aluminum in NaCl Solutions

Abstract

The rate of dissolution, R dis , of the native Al 2 O 3 film on electrochemically polished, single-crystal ͓͑100͒, ͑110͒, and ͑111͒ orientations͔ and polycrystalline Al electrodes is reported. Measurements were made in 50 mM H 3 BO 3 /0.3 mM Na 2 B 4 O 7 •10 H 2 O solutions (pH ϳ 6.7) containing between 0 and 75 mM NaCl. R dis is determined by analysis of voltammetric curves recorded during film growth, using a model in which oxide growth is governed by high-field transport of ions within the film, while oxide dissolution at the oxide/electrolyte interface occurs by a potential-independent mechanism. R dis is observed to be dependent upon the surface orientation in the order: polycrystalline Al Ͼ Al(111) ϳ Al(110) Ͼ Al(100). Small enhancements in both the rate of ion transport within the oxide film and R dis at polycrystalline Al are attributed to lowering of activation barriers at grain boundaries. R dis is also shown to increase with increasing Cl Ϫ concentration, reaching a limiting value at ϳ40 mM, regardless of electrode crystallinity or orientation. The dependence of R dis on Cl Ϫ concentration is consistent with adsorption of Cl Ϫ at the oxide/electrolyte interface, followed by desorption of an AlCl x complex.

The Influence of Crystallographic Texture and Niobium Stabilisation on the Corrosion Resistance of Ferritic Stainless Steel

“…It is believed that this behaviour is not related to the crystallographic textures or alloying elements and that it is produced by the variation of grain size. More refined grains can help the uniform passive layer grow, due to the higher free energy associated with grain boundaries 25,[37][38] . In addition grain size distribution (S n ) has also effects: the passive layer may vary from being very uniform and compact at some locations to being very non-uniform at other locations if the grain size distribution (S n ) is large 25 .…”

Growth of Anodic Aluminum Oxide Films Without pH-Buffer

“…This is because the oxide film thickness increases during each cycle. The anodic behavior in borate can be accounted for in terms of the high field conduction model (16,18,19) without chemical oxide dissolution. Around pH 7 chromate, bicarbonate, nitrite (NO 2 2-), and sulfite (SO 3 2-) which display analogous voltammograms to Fig.…”

Theoretical Pore Growth Models for Nanoporous Alumina

“…As the volume expansion accompanying the oxidation reaction at the metal/oxide interface is fixed under a certain anodization condition, the required spaces to accommodate such volume expansion for maintaining good metal-oxide contact is then fixed, and so the ratio between the outward amount of aluminum ion current density and the inward amount of oxygen ion current density, should also be fixed during anodization, where where j Al,dis = |j Al,dis |. Strictly speaking, under different anodization conditions such as voltage, electrolyte type, concentration, or substrate grain orientation, β may change a little because the volume expansion ratio may change, but the change is expected to be small as the oxide density is usually around 3 g/cm 3 from experiments [4,168]. As a typical condition, we set β to be 3/7 in accordance with Siejka and Ortega's experimental results [162].…”