The effect of anode surface area on nanoporous oxide formation during anodizing of low purity aluminum (AA1050 alloy)

Abstract

Porous anodic alumina layers were obtained by a simple two-step anodization of low purity aluminum (99.5 % Al, AA1050 alloy) in a 0.3 M oxalic acid electrolyte at 45 V and 20°C. The effect of anode surface area on structural features of nanoporous oxide and process of oxide formation was investigated. An ordered structure composed of nanostripes or nanopores was formed on the Al surface during electrochemical polishing in a mixture of perchloric acid and ethanol. This nanopattern is then replicated during the anodic oxide formation. It was found that the pore diameter, interpore distance, and porosity increase slightly with increasing surface area of the aluminum sample exposed to the anodizing electrolyte. On the other hand, a slight decrease in pore density and cell wall thickness was observed with increasing surface area of the sample. The detailed inspection of current density vs. time curves was also performed. The obtained results revealed that the higher surface area of the anode, the local current density minimum, was reached faster during first step of anodization and the increase in current density corresponding to the pore rearrangement process was observed earlier. Finally, a dense array of Pd nanowires (∼90 nm in diameter) was synthesized by simple electrodeposition of metal inside the channels of through-hole nanoporous anodic alumina templates with relatively large surface areas (4 cm 2).

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

“…During prolonged anodization of as pre-textured aluminum the lowest resistance and the highest electric field are observed at the bottom of each concave. Hence, the pore nucleation occurs easier, so the lower rate of the barrier oxide growth and more rapid increase in current density are observed [36]. This dependence observed in our group for AA1050 is in excellent agreement with the results obtained e.g., by Li et al [50], and Wang et al [51] for anodization of high-purity substrates.…”

“…We also confirmed that the pattern formed on the Al surface by electropolishing is then replicated at the initial stages of first anodizing step (compare Fig. 3.3c, d), so the morphology of initial nanoporous oxide is strongly determined by the morphology of aluminum substrate used as a starting material for anodization [36]. It was also reported that the significant improvement of nanostructured oxide morphology can be also achieved by annealing of impure Al foils prior to anodizing that could be attributed to the reduction of amount of grain boundaries and smoothing of the Al surface during annealing [40].…”

“…In our recent work, we also studied the effect of electropolishing procedure on the surface morphology of the AA1050 substrate [36]. The process was carried out in a mixture of perchloric acid (60 wt%) and ethanol (1:4 vol.)…”

Sensitive Amperometric Sensing of Hydrogen Peroxide Using Ag Nanowire Array Electrode

“…at the constant potential of 20 V and 0 8C for 30 s. The porous anodic aluminum oxide (AAO) films were prepared by a two-step anodization under the constant cell voltage of 45 V in 0.3 M H 2 C 2 O 4 at 25 8C, as described previously [23][24][25][26][27]. The duration of the first and second anodizing steps was 1 h and 5 h, respectively.…”

Introduction to the special issue on 'Nanostructures by Valve Metal Anodization'

“…She introduced the Tafel equation and the concept of chemical potential, as well as a view of APA cell nucleation based on flakes of oxides. The comprehensive picture given by Dr. Runge may help to understand metallurgical issues [19] and side effects emerging during APA fabrication from Al alloys [20], which in the future could foster the use of recycled Al from e.g. beverage cans or food packaging.…”