Effect of Aluminum Purity on the Pore Formation of Porous Anodic Alumina

Abstract

Anodic alumina oxide (AAO), a self-ordered hexagonal array, has various applications in nanofabrication such as the fabrication of nanotemplates and other nanostructures. In order to obtain highly ordered porous alumina membranes, a two-step anodization or prepatterning of aluminum are mainly conducted with straight electric field. Electric field is the main driving force for pore growth during anodization. However, impurities in aluminum can disturb the direction of the electric field. To confirm this, we anodized two different aluminum foil samples with high purity (99.999%) and relatively low purity (99.8%), and compared the differences in the surface morphologies of the respective aluminum oxide membranes produced in different electric fields. Branched pores observed in porous alumina surface which was anodized in low-purity aluminum and the size; dimensions of the pores were found to be usually smaller than those obtained from high-purity aluminum. Moreover, anodization at high voltage proceeds to a significant level of conversion because of the high speed of the directional electric field. Consequently, anodic alumina membrane of a specific morphology, i.e., meshed pore, was produced.

Upcycling Discarded Aluminum Cans into Nanoporous Membranes as an Eco-Friendly and Cost-Effective Strategy for Fabricating Polymer Nanoarrays and Self-Cleaning Surfaces

“…To validate these viewpoints, WDXS mappings are analyzed (Figure S8), revealing the presence of local tiny beads of impurities, such as Mg and Mn, in the aluminum even after the electropolishing process. This evidence confirms that the anodic oxidation process is indeed influenced by the remaining impurities. − Furthermore, the impurities also impact the growth rates of the oxidized layers. Figure a displays the pore lengths of the AAO membranes at different oxidation times, and the growth rates of the oxidized layers are determined by calculating the slopes of the three curves.…”

“…Besides, Figure S4 shows that the appearances of the AAO membranes made from high-purity aluminum sheets are more reflective than those of the T-AAO and S-AAO membranes . The morphological differences between the AAO membranes made from high-purity aluminum sheets and aluminum cans could be attributed to the metallic impurities in the aluminum cans. − …”

“…These results suggest that the interfacial metallic impurities at the metal/oxide interface, inducing disordered pore formations, retard the growth of the oxidized layer. Furthermore, the hydrolysis reactions of the metallic impurities, which release heat, are inhibited at 0 °C at the interfaces between the metal and oxide layers, agreeing with previous studies. − …”

Characterization of nanopores arrangement of anodic alumina layers synthesized on low-(AA1050) and high-purity aluminum by two-step anodizing in sulfuric acid with addition of ethylene glycol at low temperature

“…Many papers [37][38][39][40] proved that interpore distance are affected by type and concentration of electrolyte, applied voltage and reaction temperature. Although Kim et al [41] analyzed the impact of purity of aluminum on the interpore distance showing no effect, but the difference with purity of aluminum was rather slight (99.999% Al was comparable with 99.8% Al), thus any alloying element effect was negligible in this case. In this study the difference with purity of anodizing aluminum was relatively big: highpurity aluminum was 99.9995% Al and low-purity aluminum was 99.5% Al.…”

Synthesis of Nanoporous Anodic Alumina by Anodic Oxidation of Low Purity Aluminum Substrates

“…Very recently, Kim et al have also examined the effect of aluminum purity on the pores formation by comparison of the morphologies of anodic oxide layers obtained by two-step anodizing of the high purity (99.999 %) an low purity (99.8 %) substrates in oxalic acid and phosphoric acid electrolytes [62]. No direct effect of the substrate composition on the average interpore distance (D c ) was found, since the pore spacing is directly proportional to the anodizing potential (see further sections).…”