• Journal of the Korean institute of surface engineering
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• v.17 no.2
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• pp.29-40
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• 1984

The structure of rapidly solidified Al-Si-based alloys and its relationship to subsequent anodic film growth in near neutral and acid solutions have been investigated. Solidification of the alloys proceeds via pre-dendritic nuclei, associated with rugosity of the casting surface, from which cellular-type growth, comprised of aluminium-rich material surrounded by silicon-containing material, emanates. Observation of ultramicrotomed sections of the alloys and their anodic films reveals the local oxidation of the silicon-rich phase and its incorporation into the anodic alumina film, formed in near neutral solutions. Such incorporation occurs but resultant isolation of the silicon-rich phase is not possible for anodizing in phosphoric acid, and a three-dimensional network of the oxidized silicon-containing phase, with continuing development of porous anodic alumina, is observed.

• Corrosion Science and Technology
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• v.8 no.4
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• pp.143-147
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• 2009

In biomedical implants and dental fields, titanium has been widely utilized for excellent corrosion resistance and biocompatibility. However, Ti and its alloys are nonbioactive after being implanted in bone. In this study, for the purpose of improvement in biocompatibility the anodic $TiO_2$ layer on Ti-xNb alloys were fabricated by electrochemical method in phosphate solution, and the effect of Nb content on the pore size, the morphology and crystallinity of Ti oxide layer formed by the anodic oxidation method was investigated. The Ti containing Nb up to 3 wt%, 20 wt% and 40 wt% were melted by using a vacuum furnace. The sample were cut, polished, and homogenized for 24 hr at $1050^{\circ}C$ for surface roughness test and anodizing. Titanium anodic layer was formed on the specimen surface in an electrolytic solution of 1 M phosphoric acid at constant current densities ($30mA/cm^2$) by anodizing method. Microstructural morphology, crystallinity, composition, and surface roughness of oxide layer were observed by FE-SEM, XRD, EDS, and roughness tester, respectively. The structure of alloy was changed from $\alpha$-phase to $\beta$-phase with increase of Nb content. From XRD results, the structure of $TiO_2$ formed on the Ti-xNb surface was anatase, and no peaks of $Nb_2O_5$ or other Nb oxide were detected suggesting that Nb atoms are dispersed in $TiO_2$-based solid solution. Surface roughness test and SEM results, pore size formed on surface and surface roughness decreased as Nb content increased. From the line analysis results, intensity of Ti peak was high in the center of pore, whereas, intensity of O peak was high in the outside of pore center.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.8
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• pp.655-659
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• 2010

Nanoporous titanium dioxide ($TiO_2$) is very attractive material for various applications due to the high surface to volume ratio. In this study, we have fabricated nanoporous $TiO_2$ thin films on Si by anodic oxidation. 500-nm-thick titanium (Ti) films were deposited on Si by using electron beam evaporation. Nanoporous structures in the Ti films were obtained by anodic oxidization using ethylene glycol electrolytes containing 0.3 wt% $NH_4F$ and 2 vol% $H_2O$ under an applied bias of 5 V. The diameter of nanopores in the Ti films linearly increased with anodization time and the whole Ti layer could become nanoporous after anodizing for 3 hours, resulting in vertically aligned nanotubes with the length of 200~300 nm and the diameter of 50~80 nm. Upon annealing at $600^{\circ}C$ in air, the anodized Ti films were fully crystallized to $TiO_2$ of rutile and anatase phases. We believe that our method to fabricate nanoporous $TiO_2$ films on Si is promising for applications to thin-film gas sensors and thin-film photovoltaics.

• Applied Chemistry for Engineering
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• v.9 no.7
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• pp.1047-1052
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• 1998

The porous alumina membrane was prepared from aluminum metal(99.8%) by anodic oxidation using DC power supply of constant current mode in aqueous solution of sulfuric, oxalic, phosphoric and chromic acid. Pore size and distribution, membrane thickness, morphology and crystal structure were examined with several anodizing conditions : reaction temperature, electrolyte concentration, current density and electrolyte type. It was found that ultrafiltration membrane was fabricated in electrolyte of sulfuric, and oxalic acid. On the other hand, microfiltration membrane was fabricated in electrolyte of phosphoric, and chromic acid. Also, it was shown that crystal structure of porous alumina membrane prepared in sulfuric, oxalic, and phosphoric acid was amorphous, whereas porous alumina membrane prepared in chromic acid had ${\gamma}$ type of crystal structure.

• Journal of Powder Materials
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• v.17 no.3
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• pp.216-222
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• 2010

Self-standing $TiO_2$ nanotube arrays were fabricated by potentiostatic anodic oxidation method using pure Ti foil as a working electrode and ethylene glycol solution as electrolytes with small addition of $NH_4F$ and $H_2O$. The influences of anodization temperature and time on the morphology and formation of $TiO_2$ nanotube arrays were investigated. The fabricated $TiO_2$ nanotube arrays were applied as a photoelectrode to dye-sensitized solar cells. Regardless of anodizing temperature and time, the average diameter and wall thickness of $TiO_2$ nanotube show a similar value, whereas the thickness show a different trend with reaction temperature. The thickness of $TiO_2$ nanotube arrays anodized at $20^{\circ}C$ and $30^{\circ}C$ was time-dependent, but on the other hand its at $10^{\circ}C$ are independent of anodization time. The conversion efficiency is low, which is due to a morphology breaking of the $TiO_2$ nanotube arrays in manufacturing process of photoelectrode.

• Korean Journal of Materials Research
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• v.29 no.10
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• pp.609-616
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• 2019

Oxide coatings are formed on die-cast AZ91D Mg alloy through an environmentally friendly plasma electrolytic oxidation(PEO) process using an electrolytic solution of $NaAlO_2$, KOH, and KF. The effects of PEO condition with different duty cycles (10 %, 20 %, and 40 %) and frequencies(500 Hz, 1,000 Hz, and 2,000 Hz) on the crystal phase, composition, microstructure, and micro-hardness properties of the oxide coatings are investigated. The oxide coatings on die-cast AZ91D Mg alloy mainly consist of MgO and $MgAl_2O_4$ phases. The proportion of each crystalline phase depends on various electrical parameters, such as duty cycle and frequency. The surfaces of oxide coatings exhibit as craters of pancake-shaped oxide melting and solidification particles. The pore size and surface roughness of the oxide coating increase considerably with increase in the number of duty cycles, while the densification and thickness of oxide coatings increase progressively. Differences in the growth mechanism may be attributed to differences in oxide growth during PEO treatment that occur because the applied operating voltage is insufficient to reach breakdown voltage at higher frequencies. PEO treatment also results in the oxide coating having strong adhesion properties on the Mg alloy. The micro-hardness at the cross-section of oxide coatings is much higher not only compared to that on the surface but also compared to that of the conventional anodizing oxide coatings. The oxide coatings are found to improve the micro-hardness with the increase in the number of duty cycles, which suggests that various electrical parameters, such as duty cycle and frequency, are among the key factors controlling the structural and physical properties of the oxide coating.

• Korean Journal of Materials Research
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• v.21 no.1
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• pp.21-27
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• 2011

A nano-porous structure of tin oxide was prepared using an anodic oxidation process and the sample's electrochemical properties were evaluated for application as an anode in a rechargeable lithium battery. Microscopic images of the as-anodized sample indicated that it has a nano-porous structure with an average pore size of several tens of nanometers and a pore wall size of about 10 nanometers; the structural/compositional analyses proved that it is amorphous stannous oxide (SnO). The powder form of the as-anodized specimen was satisfactorily lithiated and delithiated as the anode in a lithium battery. Furthermore, it showed high initial reversible capacity and superior rate performance when compared to previous fabrication attempts. Its excellent electrode performance is probably due to the effective alleviation of strain arising from a cycling-induced large volume change and the short diffusion length of lithium through the nano-structured sample. To further enhance the rate performance, the attempt was made to create porous tin oxide film on copper substrate by anodizing the electrodeposited tin. Nevertheless, the full anodization of tin film on a copper substrate led to the mechanical disintegration of the anodic tin oxide, due most likely to the vigorous gas evolution and the surface oxidation of copper substrate. The adhesion of anodic tin oxide to the substrate, together with the initial reversibility and cycling stability, needs to be further improved for its application to high-power electrode materials in lithium batteries.

• Journal of Technologic Dentistry
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• v.27 no.1
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• pp.79-88
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• 2005

This study was performed to investigate the surface properties of electrochemically oxidized pure niobium by anodic oxide and hydrothermal treatment technique. Niobium specimens of $10\times10mm$ in dimension were polished sequentially from #600, #800, #1000 emery paper. The surface pure niobium specimens were anodized in an electrolytic solution that was dissolved calcium and phosphate in water. The electrolytic voltage was set in the range of 250 V and the current density was 10 $mA/cm^2$. The specimen was hydrothermal treated in high-pressure steam at 300$^{\circ}C$ for 2 hours using an autoclave. Then, specimens were immersed in the Hanks' solution with pH 7.4 at 37$^{\circ}C$ for 30 days. The surface of specimen was characterized by scanning electron microscope(SEM), energy dispersive X-ray microanalysis(EDX), potentiostat/galvanostat test, and cytotoxicity test. The results obtained was summarized as follows; According to the result of measuring corrosion behavior at 0.9% NaCl, corrosion resistance was improved more specimens treated with anodic oxide than in hydrothermal treated ones. The multi-porous oxide layer on surface treated through anodic oxidation showed a structure that fine pores overlap one another, and the early precipitation of apatite was observed on the surface of hydrothermal treated samples. According to the result of EDX after 30 days deposition in Hanks' solution, Ca/P was 1.69 in hydrothermal treated specimens. In MTT test, specimens treated through anodic oxidation and hydrothermal treated ones showed spectrophotometer similar to that of the control group. Thus no significant difference in cytotoxicity was observed (P>0.05).

• Journal of the Korean institute of surface engineering
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• v.42 no.3
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• pp.109-115
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• 2009

Magnesium is one of the lightest metals, and magnesium alloys have excellent physical and mechanical properties such as high stiffness/weight ratios, good castability, good vibration and shock absorption. However their poor corrosion resistance, wear resistance, hardness and so on, have limited their application. To improve these defects, many techniques are developed. Micro arc oxidation(MAO) is a one of the surface treatments under anodic oxidation in which ceramic coating is directly formed on the surface of magnesium alloy. In this study, the characteristics of anodic film were examined after coating the AZ31B magnesium alloy through the MAO process. MAO was carried out in potassium hydroxide, potassium fluoride, and various concentration of sodium silicate in electrolyte. The morphology and chemical composition of the coating layer were characterized by SEM, XRD, EPMA and EDS. The hardness of anodic films was measured by micro-vickers hardness tester. As a result, the morphology and composition of anodic film were changed by concentration of sodium silicate. Thickness and Si composition of anodic film was increased with increasing concentration of sodium silicate in electrolyte. The hardness of anodic film was highly increased when the concentration of sodium silicate was above 40 g/l in electrolyte.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.6
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• pp.795-804
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• 2007

Statement of problem. Nano-scale calcium-phosphate coating on the anodizing titanium surface using ion beam-assisted deposition (IBAD) has been recently introduced to improve the early osseointegration. However, not much is known about their surface characteristics that have influence on tissue-implant interaction. Purpose. This study was aimed to investigate microtopography, surface roughness, surface composition, and wettability of the titanium surface modified by the anodic oxidation and calcium phosphate coating using IBAD. Material and methods. Commercially pure titanium disks were used as substrates. The experiment was composed of four groups. Group MA surfaces represented machined surface. Group AN was anodized surface. Group CaP/AN was anodic oxidized and calcium phosphate coated surfaces. Group SLA surfaces were sandblasted and acid etched surfaces. The prepared titanium discs were examined as follows. The surface morphology of the discs was examined using SEM. The surface roughness was measured by a confocal laser scanning microscope. Phase components were analyzed using thin-film x-ray diffraction. Wettability analyses were performed by contact angle measurement with distilled water, formamide, bromonaphtalene and surface free energy calculation. Results. (1) The four groups showed specific microtopography respectively. Anodized and calcium phosphate coated specimens showed multiple micropores and tiny homogeneously distributed crystalline particles. (2) The order of surface roughness values were, from the lowest to the highest, machined group, anodized group, anodized and calcium phosphate deposited group, and sandblasted and acid etched group. (3) Anodized and calcium phosphate deposited group was found to have titanium and titanium anatase oxides and exhibited calcium phosphorous crystalline structures. (4) Surface wettability was increased in the order of calcium phosphate deposited group, machined group, anodized group, sandblasted and acid etched group. Conclusion. After ion beam-assisted deposition on anodized titanium, the microporous structure remained on the surface and many small calcium phosphorous crystals were formed on the porous surface. Nanoscale calcium phosphorous deposition induced roughness on the microporous surface but hydrophobicity was increased.