• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.429-429
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• 2009

Nanoporous anodic alumina membranes (NAAM) with high-density through-hole pores fabricated by hard anodization of aluminum in 0.3 M oxalic acid under the applied voltage of 40 (mild anodization), 80, 100, 120 and 140 V were investigated. The current-time responses monitored using a PC-controlled anodization cell and the corresponding pore structures attainable from field-enhanced scanning electron microscopy (FE-SEM) were analyzed in order to establish the optimum fabrication process. The nanoporous structure can be produced for all the voltage conditions, while the stabilized through-hole pore formation seems to occur at 40, 80 and 140 V. The growth rate under 140 V hard anodization was over 30 times higher than under 40 V mild anodization (1.5 um/hr).

• Journal of Surface Science and Engineering
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• v.48 no.4
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• pp.142-148
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• 2015

The effect of equal channel angular pressing (ECAP) on the pitting corrosion resistance of hard anodized Al5052 alloy was investigated. The degree of internal stress generated in anodic oxide films during hard anodization was also evaluated with a strain gauge method. The pitting corrosion resistance of hard anodized Al5052 alloy was greatly decreased by ECAP. Cracks occurred in the anodic oxide film during hard anodization and these cracks were larger and deeper in the alloy with ECAP than without. The pitting corrosion was accelerated by cracks. The internal stress present in the anodic oxide films was compressive and the stress was higher in the alloys with ECAP than without, resulting in an increased likelihood of cracks. The pitting corrosion resistance of hard anodized Al5052 alloy was improved by annealing at the range of 473-573K after ECAP processed at room temperature for four passes. The compressive internal stress gradually decreased with increasing annealing temperature. It is assumed that the improvement in the pitting corrosion resistance of hard anodized Al5052 alloy by annealing may be attributed to a decrease in the likelihood of cracks due to the decreased internal stresses in anodic oxide films.

• Journal of Powder Materials
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• v.22 no.4
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• pp.240-246
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• 2015

Anodic aluminum oxide (AAO) has been widely used for the development and fabrication of nano-powder with various morphologies such as particle, wire, rod, and tube. So far, many researchers have reported about shape control and fabrication of AAO films. However, they have reported on the shape control with different diameter and length of anodic aluminum oxide mainly. We present a combined mild-hard (or hard-mild) anodization to prepare shape-controlled AAO films. Two main parameters which are combination mild-hard (or hard-mild) anodization and run-time of voltage control are applied in this work. The voltages of mild and hard anodization are respectively 40 and 80 V. Anodization was conducted on the aluminum sheet in 0.3 mole oxalic acid at $4^{\circ}C$. AAO films with morphologies of varying interpore distance, branch-shaped pore, diameter-modulated pore and long funnel-shaped pore were fabricated. Those shapes will be able to apply to fabricate novel nano-materials with potential application which is especially a support to prevent volume expansion of inserted active materials, such as metal silicon or tin powder, in lithium ion battery. The silicon powder electrode using an AAO as a support shows outstanding cycle performance as 1003 mAh/g up to 200 cycles.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.33-33
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• 2010

Recently, a self-organizing process that occurs during the anodization of aluminum in acidic electrolytes has attracted a vast amount of research attentions, coupled with the ever-increasing demand for the development of effective, inexpensive and technologically simple methods for the synthesis of low-dimensional nanostructures over a macroscopic area overcoming many of the drawbacks of conventional lithographic techniques. In this presentation, recent progress in the fabrication of ordered nanoporous anodic aluminum oxide (AAO), including conventional anodization techniques, newly developed pulse anodization, hard anodization processes, and generic approaches to three-dimensional pore structures with periodically modulated diameters. Discussion will also cover the applications of AAO for the development of structurally well-defined extended arrays of low-dimensional nanostructures, such as nanodots, nanotubes, and nanowires, which could be model systems in investigating a diverse range of research problems in chemistry and physics and also be starting materials in realizing advanced electronic devices.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.59-63
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• 2012

Studying the long-range ordering of nanopores on the anodic aluminum oxide (AAO) membranes under a hard anodization (HA) approach is crucial in producing well-aligned nanopores on the AAO membranes. Electro-polishing in a mixture of ethanol and perchloric acid for 5 min removed marks formed by rolling and produced flat surfaces on aluminum substrates. The AAO was formed by the first HA process, providing seeds for the subsequent production of uniform AAO nanopores. The second HA process carried out on the seeds produced well-aligned, uniform AAO nanopores. The AAO nanopores, varying in size and shape, were observed with voltages applied for HA. This study provides a route for controlling the size and shape of AAO nanopores by changing the applied voltages.

• Journal of dental hygiene science
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• v.11 no.5
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• pp.405-410
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• 2011

The aim of this study was to evaluate antibacterial effect of Cl coated titanium. To coat the Cl on the titanium, first, the titanium was modified by blasting treatment with hydroxyapatite and alumina powder. Anodization process was completed using electrolyte solution of 0.04 M ${\beta}$-glycerol phosphate disodium salt n-hydrate, 0.4 M calcium acetate n-hydrate and 1 M NaCl on the condition of 250 voltages for 3 min. Surface morphology and elements' observation were performed with scanning electron microscopy and energy dispersive spectroscopy and surface profiler was used to analyze the surface roughness. Antibacterial effect was evaluated by film adhesion method. The anodized titanium after blasting showed dimpled surface contained the Cl. Surface average roughness of these surfaces had significantly higher compared to polished titanium. Result of antibacterial test showed that anodized titanium after blasting had an enhanced antibacterial effect compared to the polished titanium. Therefore, these results suggested that titanium contained Cl by anodization after blasting had a rough surface as well as antibacterial effect.

• Journal of Surface Science and Engineering
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• v.55 no.6
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• pp.417-424
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• 2022

This research develops an easy-to-use, environmentally friendly method for fabricating functional 1050 aluminum alloy surfaces with excellent corrosion resistance. Functional aluminum surfaces with various nanostructures are fabricated by controlling the experimental conditions of anodizing process. The experiment used a multi-step anodizing process that alternates between two different anodizing modes, mild anodizing (MA) and hard anodizing (HA), together with a pore-widening (PW) process. Among them, the nanostructured surface with a small solid fraction shows superhydrophobicity with a contact angle of more than 170° after water-repellent coating. In addition, the surface with superhydrophobicity is difficult for corrosive substances to penetrate, so the corrosion resistance is greatly improved.

• Corrosion Science and Technology
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• v.18 no.6
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• pp.228-231
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• 2019

Aluminum and its alloys have been widely used in various fields because of low weight, high strength, good conductivity, and low price. It is well known that aluminum alloys that cause natural oxide film can inhibit corrosion in wet, salty environments. However, these oxides are so thin that corrosion occurs in a variety of environments. To prevent this problem, an electrochemical anodizing technique was applied to the aluminum alloy surface to form a thick layer of oxide and a unique oxide shape, such as a hierarchical pore structure simultaneously combining large and small pores. The shape of the structures was implemented using stepwise anodization voltages such as 40 V for mild anodizing and 80 V for hard anodizing, respectively. To maximize water repellency, it is crucial to the role of surface structures shape. And a hydrophobic thin film was coated by 1H, 1H, 2H, 2H-Perfluorodecyltrichlorosilane (FDTS) to minimize surface energy of the structure surface. Thus, such nanoengineered superhydrophobic surface exhibited a high water contact angle and excellent corrosion resistance such as low corrosion current density and inhibition efficiency.

• Corrosion Science and Technology
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• v.19 no.6
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• pp.310-317
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• 2020

This study investigated the damage to the specimen due to liquid droplet impingement erosion corrosion, which improved the corrosion resistance and durability via hard anodization of 5083-H321 aluminum alloy, which is widely used for small ships and marine structures. The experiment combined liquid droplet impingement erosion and electrochemical equipment with the flow rates in natural seawater solution. Subsequently, Tafel extrapolation of polarization curves was performed to evaluate damage due to the liquid droplet impingement erosion corrosion. The damaged surface was observed using a 3D microscope and a scanning electron microscope. The degree of pitting damage was measured using the Image J program, and the surface hardness was measured using the micro-Vickers hardness tester. The corrosion current density, area, depth, and ratio of the damaged areas increased with the increase in flow rate. The grain size of the damaged area at a flow rate of 20 m s-1 showed fewer and minor differences in height, and a smooth curved shape. The hardness of the damaged surface tended to decrease with increase in flow rate.