Anodization Behavior of Aluminum in Ionic Liquids with a Small Amount of Water

Abstract

We investigated the anodic oxidation of aluminum in ionic liquids (ILs) by the constant-voltage rising rate (C-V) method and constant-current density (C-C) method, with characterization by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The structure of the oxide layer and the reaction efficiency varied with the type of IL, the applied voltage, the forming method, and the water content. A homogeneous Al 2 O 3 film with a superior dielectric property was formed by the C-V method (100 mV/s) in 1-butyl-3-methylimidazolium benzoate (BMIm-BEN, water content 0.81 wt%) at 40 V. Although a homogeneous barrier-type Al 2 O 3 film was also formed in 1-butyl-3-methylimidazolium mandelate (BMIm-MAN, water content 0.34 wt%) at 40 V, some anion species existed in the film, and its jump-voltage characteristics was inferior to that of the film formed in BMIm-BEN. The relative permittivity of the film formed in BMIm-BEN was almost equal to that of the Al 2 O 3 film formed in adipate (1.0 wt%) aqueous solution, but the dielectric constant of the film formed in BMIm-MAN was 1.5 times larger. In contrast, a heterogeneous porous Al 2 O 3 film containing a large amount of anion molecules was formed in 1-ethyl-3-methylimidazolium acetate (EMIm-ACE, water content 0.79 wt%) at 40 V. Since the source of oxygen for anodic oxidation is the small amount of water in the ILs, the water content strongly affected the characteristics of the formed Al 2 O 3 layer.

Electrochemical treatment of aluminium alloy 7075 in aqueous solutions of imidazolium phosphonate and phosphate ionic liquids and scratch resistance of the resultant materials

“…The inclusion of IL anions in the anodized layer to form [Al 2 O 3−x (Anion) x ] species has been previously described [2]. A similar mechanism could have taken place in the present case.…”

“…The anodization processes of aluminium have been extensively studied, and some authors have reported on the formation of anodic porous alumina using ionic liquid (ILs) as electrolytes [1][2][3]. In these studies, several neat imidazolium IL were used as electrolytes for anodization of pure aluminium applying electric potential values of up to 40 V, finding that anion structure strongly affects the ability to form passive layers on the aluminium.…”

Is a 2D Nanostructured Surface Capable of Changing the Corrosion and Magnetic Properties of an Amorphous Alloy?

“…The formation of nanocells with four or five walls during the anodizing of silicon in IL with a water content of up to 2% was observed recently [24]. The anodization of aluminum in IL is accompanied by the formation of various nanostructures [25]. These facts made it possible to propose the possibility of producing nanocells on the alloy surface under study.…”