• Advances in nano research
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• 제10권3호
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• pp.211-219
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• 2021

The evaluation of the corrosion resistance of titanium with a TiO2 nanotubes top layer was carried out (TiO2 NT). These nanostructures were evolved into anatase nanoparticles without heat treatment in an aqueous medium, which is a novel phenomenon. This work analyzes the layer between the nanotube bottom and the substrate, which is thin and still susceptible to corrosion. The bottom of TiO2 nanotubes having Fluor resulting from the synthesis process changed between amorphous to crystalline anatase with a crystallite size of about 4 nm, which influenced the corrosion rates. Four kinds of samples were evaluated. A) NT by Ti anodizing; B) NTSB for Ti plates, either modifying its surface or anodizing the modified surface; C) NT-480 for anodized Ti and heat-treated (480℃) for reaching the anatase phase; D) NTSB-480 for Ti plates, first, modifying its surface using sandblast, after that, anodizing the modified surface, and finally, heat-treated to 480℃ to compare with samples having induced crystallization and passivation. Four electrochemical techniques were used to evaluate the corrosion rates. The surfaces having TiO2 nanotubes with a sandblast pre-treatment had the highest resistance to corrosion.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2002년도 춘계 학술발표강연 및 논문개요집
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• pp.93-93
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• 2002

• 한국재료학회지
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• 제23권1호
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• pp.72-80
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• 2013

Recently, consumption of magnesium alloys has increased especially in the 3C (computer, communication, camera) and automobile industries. The structural application of magnesium alloys has many advantages due to their low densities, high specific strength, excellent damping and anti-eletromagnetic properties, and easy recycling. However, practical application of these alloys has been limited to narrow uses of mild condition, because they are inferior in corrosion resistance and wear resistance due to their high chemical reactivity and low hardness. Various wet and dry processes are being used or are under development to enhance alloy surface properties. Various conversion coating and anodizing methods have been developed in a view of eco-friendly concept. The conventional technologies, such as diffusion coating, sol-gel coating, hydrothermal treatment, and organic coating, are expected to be newly applicable to magnesium alloys. Surface treatments for metallic luster or coloring are suggested using the control of the micro roughness. This report reviews the recent R&D trends and achievements in surface treatment technologies for magnesium alloys.

• Tribology and Lubricants
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• 제26권1호
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• pp.68-72
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• 2010

A ceramic coating is a surface treatment method that is being used widely in the industrial field, recently. Ni-P plating is also being used widely because of its corrosion resistance and low cost. An anodizing method is applicable to aluminum alloy. An anodizing method generates a thick oxide layer on the surface and then, that heightens hardness and protects the surface. These surface treatments are applied to various mechanical components and treated surfaces relatively move one another. In this study, tribological characteristics of Ni-P plating and TiAlN coating on anodized Al alloy are compared. The counterpart, anodized Al alloy, is worn out abrasively by Ni-P plating and TiAlN coating that have higher hardness. Abrasively worn debris accumulated on the surfaces of Ni-P plating and TiAlN coating, and then transferred layer is formed. This transferred layer affects the amplitude of variation of friction coefficient, which is related to noise and vibration. The amplitude of variation of friction coefficient of Ni-P plating is lower than those of TiAlN coating during the tests.

• 한국기계가공학회지
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• 제15권2호
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• pp.72-77
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• 2016

Airplane reservoirs made of Al7075 are coated with an anodizing layer to maintain precision, air tightness and corrosion resistance. It is commonly required that the inner surface roughness of the reservoir be less than an average $0.2{\mu}m$ to maintain stable oil pressure. Even though precision polishing is necessary to achieve this quality it is not easy. Inner surface roughness is not uniform and the quality of the product is irregular because most of the work is done by hand. The purpose of this study is to design an exclusive polishing machine and to determine the standard cutting condition and polishing condition necessary for good inner surface roughness and to improve workefficiency.

• 한국재료학회지
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• 제12권7호
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• pp.540-544
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• 2002

Hydration treatments were performed on the pure aluminum substrate at $100^{\circ}C$ followed by anodizing and heat treatments on the layers. The transformation behaviors of the oxide layers according to the hydration treatment were studied using TEM, XRD, RBS etc. Above $90^{\circ}C$ the hydrous oxide film could be formed, which were turned out to be hydrous oxides(AlOOH $nH_2$O). The anodization on the hydrous oxide film was more effective for the transition of amorphous anodic oxides to the crystalline $\Upsilon-Al_2$ $O_3$ comparing with the case for anodizing on the aluminum substrate without hydration treatment And additional heat treatments were also helpful for the acceleration of the transformation of the hydrous oxide to $\Upsilon-Al_2$ $O_3$. During the heat treatment the interface between $\Upsilon-Al_2$ $O_3$and the hydrous oxide layers migrated to the outer side of hydrous layer.

• Corrosion Science and Technology
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• 제20권2호
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• pp.45-51
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• 2021

In this work, we describe the effect of pulse anodizing duty ratio on the corrosion resistance of anodic films in magnesium AZ31B. The process involves the application of square pulse potential for a constant period with a duty ratio varying from 40, 60 and 80%. In several samples, a sealing treatment for 30 minutes was conducted after anodization in order to seal the pores available in the anodic layer. After anodizing, the surface morphology of the anodic layer was examined using a scanning electron microscope (SEM Hitachi SU3500). The corrosion characteristics of the sample were evaluated through an open circuit potential (OCP) and potentiodynamic polarization test using potentiogalvanostat. SEM observation shows that the increase of anodization duty ratio (α) results in a more uniform anodic layer, with fewer pores and cracks. The increase of duty ratio (α) decreases the OCP value from approximately -1.475 to about -1.6 Volt, and significantly improves the corrosion resistance of the anodic coating by 68%. The combination of anodization and sealing treatment produces an anodic coating with a very low corrosion rate of 4.4 mpy.

• Journal of Advanced Marine Engineering and Technology
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• 제28권2호
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• pp.300-308
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• 2004

The formation mechanism of anodic oxide films on Mg alloys when anodized in NaOH solution. was investigated by focusing on the effects of anodizing potential. Al content. and anodizing time. Pure Mg and Mg-Al alloys were anodized for 10 min at various potentials in NaOH solutions. $Mg(OH)_2$ was generated by an active dissolution reaction at the surface. and the product was affected by temperature. The intensity ratio of $Mg(OH)_2$ in the XRD analysis decreased with increasing applied potential. while that of MgO increased. The anti-corrosion properties of anodized specimens at each constant potential were better than those of non-anodized specimens. The specimen anodized at an applied potential of 3 V had the best anti-corrosion property. And the intensity ratio of $Mg_{17}Al_{12}$/Mg increased with aluminum content in Mg-Al alloys. During anodizing. the active dissolution reaction occurred preferentially in ${\beta}\;phase(Mg_{17}Al_{12})$ until about 4 mins. and then the current density increased radually until 7 mins. The dissolution reaction progressed in a phase(Mg) which not formed the intermetallic compound. which had a lower Al content. In the anodic polarization test of $0.017\;mol{\cdot}dm^-3$ NaCl and $0.1\;mol{\cdot}dm^-3\;Na_2SO_4$ at 298 K. the current density of Mg-15 mass% Al alloy anodized for 10 mins increased. since the anodic film that forms on the a phase is a non-compacted film. The anodic film on the phase for 30 mins was a compact film as compared with that for 10 mins.

• 한국재료학회지
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• 제14권12호
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• pp.876-884
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• 2004

This study was to investigate whether the bioactivity of the anodized and hydrothermally treated Ti-6Al-7Nb alloy were affected by the time of hydrothermal treatment. Anodizing was performed at current density 30 $mA/cm^2$ up to 300 V in electrolyte solutions containing $DL-{\alpha}-glycerophosphate$ disodium salt hydrate $(DL-{\alpha}-GP)$ and calcium acetate (CA). Hydrothermal treatment was done at $300^{\circ}C$ for 30 min, 1 hr, 2 hrs, and 4 hrs to produce a thin film layer of hydroxyapatite (HA). The bioactivity was evaluated from HA formation on the surfaces in a Hanks' solution with pH 7.4 at $36.5^{\circ}C$ for 10, 20, and 30 days. Anodic oxide films were porous with pore size of $1\sim4{\mu}m\;and\;3\sim4{\mu}m$ thickness. The anodic oxide films composed with strong anatase peak with presence of rutile peak, and showed the increase in intensity of anatase peak after hydrothermal treatment. It was shown that the intensity of anatase peak increased with increasing the time of hydrothermal treatment but was no difference in rutile peak. The corrosion voltage was the highest in the group of hydrothermal treatment for 2 hrs (Ecorr: -338.6 mV). The bioactivity in Hank's solution was accelerated with increasing the time of hydrothermal treatment.

• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2017년도 공동학술발표회
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• pp.258-258
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• 2017