Influence of the anodization conditions and chemical treatment on the formation of alumina membranes with defined pore diameters

Porous anodic aluminum oxide membranes were fabricated via two-step anodization of aluminum in 0.3 M H2C2O4, 0.3 M H2SO4 and 0.17 M H3PO4 solutions. The parameters of the oxide film such as: pore diameter (Dp), interpore distance (Dc), porosity (P) and pore density (ρ) can be completely controlled by the operating conditions of the anodization. Additionally, the pore diameters and pore density can be controlled via a chemical treatment (pore opening/widening process). The effect of anodizing conditions such as the applied voltage, type of electrolyte and purity of the substrate on the rate of porous oxide growth are discussed. The obtained results were compared with the theoretical predictions and data that has been reported in the literature. The influence of the duration of chemical etching on the structural features of the oxide membranes was studied. On the based on qualitative and quantitative FFT analyzes and circularity maps, it was found that the nanostructures of anodized aluminum have the maximum order under certain specified conditions. The presence of alloying elements affects not only the rate of oxide growth but also the morphology of the anodic aluminum oxide. The rate of oxide growth depends on the electrolyte type and temperature. During chemical treatment of the oxide films pore diameter increases with the pore widening time and the highest pore widening was observed in phosphoric acid solution.

Development of Superhydrophilic 6061 Aluminum Alloy by Stepwise Anodization According to Pore-Widening Time

This study created alumina structures with the highest hydrophilic properties on 6061 aluminum alloy. The anodization process was applied to make various aluminum oxide structures. To create uniform alumina structures on top of a 6061 aluminum alloy surface, after conducting the first anodization in 0.3 M oxalic acid at 40 V at 0 ^oC, the alumina was removed using a mixture of chromic acid and phosphoric acid. Then, secondary and tertiary anodization was performed using the same electrolyte conditions as the primary anodization for 30 minutes at 40 V, respectively. Pore-widening (PW) of oxide film formed after the secondary anodic oxidation was performed for 20, 30, and 40 minutes in 0.1 M phosphoric acid solution. The PW time control allowed various oxide structures to be created, and reduced the area of the outermost surface in contact with water droplets. The smaller the initial area of water droplets, the better the hydrophilic phenomenon. The surface area can be represented as a solid fractional value. Surfaces with solid fraction values of less than or equal to 0.5 were superhydrophilic. This well-controlled anodization process with a pore-widening step can be used to create excellent superhydrophilicity on various metallic substrates, expanding their usefulness and efficacy.

Systematic Control of Anodic Aluminum Oxide Nanostructures for Enhancing the Superhydrophobicity of 5052 Aluminum Alloy

The recent increased interest in the various applications of superhydrophobic surfaces necessitates investigating ways of how this property can be enhanced further. Thus, this study investigated how superhydrophobic properties can be enhanced through the formation of anodic alumina nanostructures on 5052 aluminum alloy. A multistep anodizing process that alternates two different anodizing modes, mild anodization (MA) and hard anodization (HA), with an intermediate pore-widening (PW) process was employed. Multistep anodization was employed in two different ways: an MA → PW → HA process and an HA → PW → MA process. Both routes were conducted with PW durations of 40, 50, and 60 min. The well-defined nanostructures were coated with a self-assembled monolayer (SAM) of FDTS (1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane). The contact angle values of water droplets were maximized in the pillar-like nanostructures, as they have a less solid fraction than porous nanostructures. With this, the study demonstrated the formation mechanism of both nanoscale pillar and nanoscale hierarchical structures, the wettability of the superhydrophobic surfaces, and the relationship between PW duration time with wettability and the solid fraction of the superhydrophobic surfaces.

Preparation and morphology-dependent wettability of porous alumina membranes

This article presents the preparation and study of the wetting properties of porous alumina membranes (PAMs) with a thickness of 25 to 75 μm and with a different pore sizes. The fabrication process features, scanning electron microscopy and atomic force microscopy characterization results are presented. The comparative analysis of PAM surfaces (outer and inner) and the effect of morphology of these surfaces on the wetting properties are discussed. Both alumina surfaces show significant morphology-dependent wettability. Measurements of the interfacial contact angle were made on the as-fabricated amorphous membrane and after pore widening with a range of pore diameters from 25 to 100 nm. The possible applications of PAMs for various membrane technologies is shown.

Superamphiphobic aluminum surfaces that maintain robust stability after undergoing severe chemical and physical damage

Robust superamphiphobic aluminum surfaces with dual structures were successfully fabricated through combining chemical etching, anodization, and pore-widening treatment.