Fabrication of a novel aluminum surface covered by numerous high-aspect-ratio anodic alumina nanofibers

Abstract

The formation behavior of anodic alumina nanofibers via anodizing in a concentrated pyrophosphoric acid under various conditions was investigated using electrochemical measurements and SEM/TEM observations. Pyrophosphoric acid anodizing at 293 K resulted in the formation of numerous anodic alumina nanofibers on an aluminum substrate through a thin barrier oxide and honeycomb oxide with narrow walls. However, long-term anodizing led to the chemical dissolution of the alumina nanofibers. The density of the anodic alumina nanofibers decreased as the applied voltage increased in the 10 to 75 V range. However, active electrochemical dissolution of the aluminum substrate occurred at a higher voltage of 90 V.Low temperature anodizing at 273 K resulted in the formation of long alumina nanofibers measuring several micrometers in length, even though a long processing time was required due to the low current density during the low temperature anodizing. In contrast, high temperature anodizing easily resulted in the formation and chemical dissolution of alumina nanofibers. The structural nanofeatures of the anodic alumina nanofibers were controlled by choosing of the appropriate electrochemical conditions, and numerous high-aspect-ratio alumina nanofibers (>100) can be successfully fabricated. The anodic alumina nanofibers consisted of a pure amorphous aluminum oxide without anions from the employed electrolyte.

The Alumina Film Nanomorphology Formed to Improve the Corrosion Resistance of Al-2.0 wt% Fe Alloy as Result of the Laser Surface Melting Technique Applied

“…It is a modern technique that is being used recently, therefore it is important to focus on this work. As well, the authors Nakajima et al [1] studied the formation behavior of the anodic alumina nanofibers via constant voltage pyrophosphoric acid anodizing. They have discussed extensively on aluminum oxide films fabricated via anodizing in various electrolyte solutions.…”

Effect of Anodizing Time on Multiscale Porous Structure of Ti–Al Alloy Microchannel Wall

“…Similar whisker-like projections were observed on the alumina films produced by anodizing aluminum. 18,19) During steady state growth of an anodic oxide film, its thickness is kept constant by the balance between the formation speed of the nanoporous structure at the growth front on the substrate and its dissolving speed in the electrolyte. When a difference of local dissolving speed is caused by an inhomogeneous composition distribution in the structural unit such as a nanotube or nanocell, the slower dissolving sites remain as projections.…”

“…When a difference of local dissolving speed is caused by an inhomogeneous composition distribution in the structural unit such as a nanotube or nanocell, the slower dissolving sites remain as projections. 19) The origin of the whisker-like projection on the nanoporous alumina film is the line of intersection between the wall planes of neighboring nanocells. 18,19) Such a projection sometimes grows to form a long nanofiber under specific conditions.…”

“…19) The origin of the whisker-like projection on the nanoporous alumina film is the line of intersection between the wall planes of neighboring nanocells. 18,19) Such a projection sometimes grows to form a long nanofiber under specific conditions. 19,20) This fact suggests an alternative approach to produce specialized nanostructures by controlling the dissolving behavior of the film surface contacting with the electrolyte instead of the formation behavior at the growth front on the substrate.…”

Nanostructural characterization of large-scale porous alumina fabricated via anodizing in arsenic acid solution

“…For example, anodizing in etidronic and phosphonoacetic acid solutions can occur at high potential differences (voltage), i.e., >200 V [31][32][33][34], and produces a large-scale ordered porous alumina and generates a bright structural coloration from the nanostructured surface. Anodizing in pyrophosphoric acid (H 4 P 2 O 7 ) causes growth of single nanometer-scale alumina nanofibers, and the nanofiber-covered aluminum surface exhibits rapid superhydrophilicity [35][36][37][38]. Further additional electrolytes for anodizing allow the fabrication of novel anodic aluminum oxides with characteristic properties.…”