Self-Ordering Behavior of Anodic Porous Alumina via Selenic Acid Anodizing

Abstract

The self-ordering behavior of anodic porous alumina that was formed by anodizing in selenic acid electrolyte (H 2 SeO 4 ) at various concentrations and voltages was investigated with SEM and AFM imaging. A high purity aluminum foil was anodized in 0.1-3.0 M selenic acid solutions at 273 K and at constant cell voltages in the range of 37 to 51 V. The regularity of the cell arrangement increased with increasing anodizing voltage and selenic acid concentration under conditions of steady oxide growth without burning. Anodizing at 42-46 V in 3.0 M selenic acid produced highly ordered porous alumina. By selective dissolution of the anodic porous alumina, highly ordered convex nanostructures of aluminum with diameters of 20 nm and heights of 40 nm were exposed at the apexes of each hexagonal dimple array. Highly ordered anodic porous alumina with a cell size of 102 nm from top to bottom can be fabricated by a two-step selenic acid anodizing process, that includes the first anodizing step, the selective oxide dissolution, and the second anodizing step.Key words: Aluminum; Anodizing; Anodic Porous Alumina; Selenic Acid IntroductionBarrier anodic oxide films and porous anodic oxide films on aluminum have been widely investigated by many researchers in the fields of surface finishing [1][2][3], electrolytic capacitor application [4][5][6], and micro-and nano-structure fabrication [7][8][9]. Recently, highly ordered anodic porous alumina with a cell size on the scale of 10-100 nm has been studied for potential use in various ordered-nanostructure applications [10][11][12][13][14][15][16][17][18][19][20][21]. Anodic porous alumina is typically fabricated on an aluminum substrate using electrochemical anodizing (or anodization) [22][23][24][25][26]. In several acidic electrolyte solutions, the porous alumina fabricated by anodizing is self-ordered when prepared at the appropriate electrochemical conditions, including appropriate concentrations, temperatures, and voltages (or electrochemical potentials) [27][28][29][30] [50], and acetylenedicarboxylic (HOOC-C≡C-COOH) [51] acids have also been reported as electrolytes used to fabricate porous alumina that has characteristic nanostructure morphologies.In addition to these acidic electrolytes, alkaline and neutral solutions used for porous alumina fabrication were reported by several research groups. Takahashi et al. reported that a porous anodic oxide film could be formed by anodizing in an H 3 BO 3 /Na 2 B 4 O 7 neutral borate solution at a high temperature [52]. Baron-Wiechec et al. investigated aluminum anodizing in a borax (Na 2 B 4 O 7 ) solution at 333 K and successfully obtained porous alumina [53]. Noguchi et al. investigated the anodizing behavior of aluminum in propylenediamine and choline alkaline solutions containing ammonium fluoride, ammonium tartrate, ammonium carbonate, and ammonium tetraborate, and obtained anodic porous alumina with nanopores that were 10-150 nm in diameter [54]. However, it is difficult to form a highly ordered porous alumina by anodiz...

Self-ordered Porous Alumina Fabricated via Phosphonic Acid Anodizing

“…In various electrolyte solutions such as phosphoric, selenic, and etidronic acids, highly ordered porous alumina with an ideal cell arrangement can be fabricated via anodizing under the maximum voltage applied, as reported previously [32,35,38]. However, phosphonic acid anodizing causes the formation of a disordered dimple array on the aluminum substrate, as described in Fig.…”

“…The self-ordering voltage is determined and limited by the electrolyte species used, and the use of several electrolytes such as sulfuric (U s = 19-25 V) [6,7], oxalic (40 V) [7,29,30], selenic (42-48 V) [31][32][33], malonic (120 V) [34], phosphoric (160-195 V) [35,36], tartaric (195 V) [34], phosphonoacetic (205-225 V) [36], and etidronic acids (210-270 V) [38,39] have been reported to date through the optimum exploration for the self-ordering of porous alumina. Therefore, highly ordered porous alumina possessing a required cell diameter can be obtained by the choice of an optimal electrolyte solution and anodizing conditions.…”

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

“…Typically, the two-step anodization of aluminium is conducted in sulfuric [14,15], oxalic [16,17] and phosphoric [18,19] acid aqueous solution at voltages in the range of [15][16][17][18][19][20][21][22][23][24][25] and 120-195 V, respectively. Depending on the anodization electrolyte, it is possible to obtain AAO membrane with cell diameter in the range of 25-75, 75-125, 375-525 nm in sulphuric, oxalic and phosphoric acid solution as electrolyte, respectively.…”

“…According to research published recently, it is possible to extend this range up to 530-670 nm in cell diameter by using etidronic aqueous solution as novel self-ordering electrolyte and anodizing Al foils at voltage in the range 210-270 V at 0-60°C [20]. What is more, additions of various modifiers to well know electrolytes [21] or to the new ones are recently reported in numerous papers [20,[22][23][24]. Usually the anodized aluminium is high purity (99.99%), but there are many papers about anodized aluminum alloys [21,[25][26][27][28][29], because they are generally less expensive and more accessible then highpurity aluminum.…”

Growth behavior of anodic oxide formed by aluminum anodizing in glutaric and its derivative acid electrolytes

“…It is a well-known experimental fact that anodic porous alumina can be formed by anodizing in these acidic electrolytes, which provide low acid dissociation constants. To date, sulfuric [12][13][14][15][16], selenic [17,18], phosphoric [19,20], and chromic[21] acids have been reported as useful inorganic electrolytes for fabricating anodic porous alumina. The ideal cell arrangement of porous alumina can be achieved via sulfuric, selenic, and phosphoric acid anodizing, whereas poorly ordered porous alumina is fabricated via chromic acid anodizing [22,23].…”