ISE active member2 Highlights Etidronic acid anodizing caused self-ordering behaviors between 165 and 270 V.Large-scale pore arrays measuring 470 nm in diameter could be fabricated.Hexagonal phosphorus-free distribution was measured in the porous alumina.A truly honeycomb alumina structure consisting of hexagonal pores was formed. 3 Abstract Ordered porous alumina (OPA) with large-scale circular and hexagonal pores was fabricated via etidronic acid anodizing. High-purity aluminum plates were anodized in 0.2-4.2 M etidronic acid solution at 145-310 V and 288-323 K. Self-ordering of porous alumina was observed at 165 V and 313 K in 4.2 M, at 205 V and 303 K in 1.0 M, and at 260 V and 298 K in 0.2 M, and the cell diameter was measured to be 400-640 nm.The ordering potential difference decreased with the electrolyte concentration increasing. OPA without an intercrossing nanostructure could be fabricated on a nanostructured aluminum surface via two-step anodizing. Subsequent pore-widening in etidronic acid solution caused the circular dissolution of anodic oxide and the expansion of pore diameters to 470 nm. The shape of the pores was subsequently changed to a hexagon from a circle via long-term pore-widening, and a honeycomb structure with narrow alumina walls and hexagonal pores measuring 590 nm in its long-axis was formed in the porous alumina. Transition of the nanostructure configuration during pore-widening corresponded to differences in the incorporated phosphorus distribution originating from the etidronic acid anions.4
Ordered anodic porous alumina with large-scale periodicity was fabricated via phosphonoacetic acid anodizing. Aluminum specimens were anodized in a 0.1-0.9 M phosphonoacetic acid solution under various electrochemical operating conditions, and optimum anodizing at 205-225 V exhibited self-ordering growth of the porous alumina. These self-ordering voltages during phosphonoacetic acid anodizing filled an undiscovered vacant region in the linear relationship between the self-ordering voltage and the cell diameter. The nanostructured aluminum surface formed via self-ordering phosphonoacetic acid anodizing produced a bright structural coloration with a visible light wavelength of 500-700 nm, which is useful for optical nanoapplications. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0021508ssl] All rights reserved. Self-ordered anodic porous alumina possesses a well-defined periodic porous structure with numerous nanopores that have high aspect ratios. [1][2][3] This characteristic nanoporous material is widely used for various novel nanoapplications, including electronic, optical, and sensing devices. [4][5][6][7][8][9][10][11][12] Ordered porous alumina can be fabricated by electrochemical anodizing in several acidic electrolyte solutions under appropriate experimental conditions such as concentration and applied voltage. The periodical size of the obtained ordered porous alumina, defined as the "cell size" or "interpore distance", is typically determined by the electrolyte species used.2,3,13 In self-ordered anodizing, the regularity of the pore arrangement in the porous structure can be accurately determined by a quantitative analysis based on Fourier transformation.14-19 Sulfuric, oxalic, and phosphoric acids were found early and have been commonly used as the standard self-ordering electrolytes to date. 13,20,21 However, the cell size of these ordered porous alumina is limited to the following narrow nanometer-scale regions: 50-60 nm in sulfuric acid, 100 nm in oxalic acid, and 405-500 nm in phosphoric acid.13 Therefore, the identification of novel electrolytes for self-ordered porous alumina with different cell sizes has been a recent challenge to extensively expand the nano-periodicity. Additional dicarboxylic acids with a large molecular structure, malonic and tartaric acids, for the fabrication of anodic porous alumina were reported by Ono et al., and self-ordering was achieved by anodizing with these acids for 300 and 500 nm intervals, respectively. Particularly, etidronic acid anodizing exhibited large-scale self-ordering behavior measuring 530-670 nm in cell diameter. Eti...
Introduction Anodizing of aluminum under appropriate conditions allows the formation of self-ordered porous alumina (porous type oxide film). Ordered porous alumina with large-scale cell sizes and pores is required for expanding the application field in nanotechnology. In the present investigation, we demonstrated anodizing at various conditions in a new electrolyte, etidronic acid, for large-scale ordered porous alumina. Experimental High-purity aluminum plates (99.999 wt%) were ultrasonically degreased and electropolished. The electropolished specimens were immersed in 0.2-4.2 M etidronic acid solutions at 288-323 K and then anodized at a constant cell voltage of 145-310 V for up to 24 h. After anodizing, the anodic oxide was selectively dissolved in a 0.2 M CrO3/0.51 M H3PO4 solution at 353 K to expose the aluminum substrate, and then two-step anodizing was carried out for the formation of highly ordered porous alumina. The specimens were examined by field emission scanning electron microscopy (FE-SEM) and image-aberration-corrected scanning transmission electron microscopy (STEM). Results Etidronic acid anodizing at 165-270 V and the appropriate temperature caused the self-ordering of porous alumina measuring 400-670 nm in cell diameter. Figure 1 shows an ordered aluminum dimple array fabricated in a 0.2 M etidronic acid solution at 298 K and 260 V for 24 h, and an ideal dimple array was successfully fabricated via etidronic acid anodizing. Ordered porous alumina through the vertical cross-section could be fabricated via two-step etidronic acid anodizing. Phosphorus-free oxide cell boundaries with a honeycomb configuration were measured by STEM-energy dispersive X-ray spectrometry (EDS). Figure 1. An SEM image of the aluminum dimple array fabricated via 0.2 M etidronic acid anodizing at 260 V for 24 h. Figure 1
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