• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.633-637
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• 2010

In this study, lithium manganese oxide spinel ($LiMn_{1.9}Fe_{0.1}Nb_{0.0005}O_4$) as a cathode material of lithium ion secondary batteries is synthesized with spray drying, and in order to increase its crystallinity and electrochemical properties, the granulated $LiMn_{1.9}Fe_{0.1}Nb_{0.0005}O_4$ particle surface is coated with lithium titanium oxide spinel ($Li_4Ti_5O_{12}$) through a sol-gel method. The granulated particles present a higher tap density and lower specific surface area. The crystallinity and discharge capacity of the $Li_4Ti_5O_{12}$ coated material is relatively higher than uncoated material. With the coating layer, the discharge capacity and cycling stability are increased and the capacity fading is suppressed successfully.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.10
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• pp.651-655
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• 2017

This work reports the surface morphology and transmittance of copper oxide thin films for semitransparent solar cell applications. We prepared the oxide specimens by subjecting copper thin films to an oxidation reaction at annealing temperatures ranging between $100^{\circ}C$ and $300^{\circ}C$. The color of the as-deposited specimen was red, but changed to purple at the annealing temperature of $300^{\circ}C$. The surface morphology and transmittance of the specimens were significantly dependent on the annealing temperature and thickness of the copper films. Copper oxide nanoparticles prepared from a 20-nm-thick copper film at an annealing temperature of $300^{\circ}C$ provided a maximum transmittance of 93%. The obtained optical characteristics and surface morphology suggest that copper oxide thin films prepared by an oxidation reaction can be potentially employed as color- and transmittance-adjusting layer in semitransparent thin solar cells.

• Journal of Surface Science and Engineering
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• v.41 no.6
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• pp.308-311
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• 2008

Oxide layers were prepared on Al2021 alloys substrate under a hybrid voltage of AC 200 V (60 Hz) combined with DC 260 V value at room temperature within $5{\sim}60\;min$ by plasma electrolytic oxidation (PEO). An optimized aluminate-fluorosilicate solution was used as the electrolytes. The surface morphology, thickness and composition of layers on Al2021 alloys at different reaction times were studied. The results showed that it is possible to generate oxide layers of good properties on Al2021 alloys in aluminate-fluorosilicate electrolytes. Analysis show that the double-layer structure oxide layers consist of different states such as ${\alpha}-{Al_2}{O_3}$ and ${\gamma}-{Al_2}{O_3}$. For short treatment times, the formation process of oxide layers follows a linear kinetics, while for longer times the formation process slows down and becomes a steady stage. During the PEO processes, the average size of the discharge channels increased gradually as the PEO treatment time increased.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2008.11a
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• pp.30-30
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• 2008

In this study, electrochemical impedance characteristics of anodic oxide layer formed on titanium binary alloy surface have been investigated. Titanium oxide layers were grown on Ti-$_XTa$ and Ti-$_XNb$(X=10, 20, 30 and 40 wt%) alloy substrates using phosphoric acid electrolytes.

• Journal of Surface Science and Engineering
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• v.47 no.4
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• pp.155-161
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• 2014

The present work is concerned with the formation behavior of anodic oxide films on Al7075 alloy under a galvanostatic condition in 20 vol.% sulfuric acid solution. The formation behaviour of anodic oxide films was studied by the analyses of voltage-time curves and observations of colors, morphologies and thicknesses of anodic films with anodization time. Hardness of the anodic oxide films was also measured with anodization time and at different positions in the anodic films. Six different stages were observed with anodiziation time : barrier layer formation (stage I), pore formation (stage II), growth of porous films (stage III), abnormal rapid oxide growth (stage IV), growth of non-uniform oxide films (stage V) and breakdown of the thick oxide films under high anodic voltages (stage VI). Hardness of the anodic oxide films appeared to decrease with increasing anodization time and with the position towards the outer surface. This work provides useful information about the thickness, uniformity, imperfections and hardness distribution of the anodic oxide films formed on Al7075 alloy in sulfuric acid solution.

• Korean Journal of Materials Research
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• v.27 no.9
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• pp.495-500
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• 2017

Oxide layers were formed by an environmentally friendly plasma electrolytic oxidation (PEO) process on AZ91 Mg alloy. PEO treatment also resulted in strong adhesion between the oxide layer and the substrate. The influence of the KF electrolytic solution and the structure, composition, microstructure, and micro-hardness properties of the oxide layer were investigated. It was found that the addition of KF instead of KOH to the $Na_2SiO_3$ electrolytic solution increased the electrical conductivity. The oxide layers were mainly composed of MgO and $Mg_2SiO_4$ phases. The oxide layers exhibited solidification particles and pancake-shaped oxide melting. The pore size and surface roughness of the oxide layer decreased considerably with an increase in the concentration of KF, while densification of the oxide layers increased. It is shown that the addition of KF to the basis electrolyte resulted in fabricating of an oxide layer with higher surface hardness and smoother surface roughness on Mg alloys by the PEO process. The uniform thickness of the oxide layer formed on the Mg alloy substrates was largely determined by the electrolytic solution with KF, which suggests that the composition of the electrolytic solution is one of the key factors controlling the uniform thickness of the oxide layer.

• Journal of Surface Science and Engineering
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• v.48 no.5
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• pp.194-198
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• 2015

A blade-abrading method was newly developed for the preparation of clean Mg alloy surface and reported for the first time in detail in this paper. The blade-abrading method includes abrading of the Mg alloy surface with a sharp blade or knife to remove the surface oxide and contaminants on the skin of Mg alloys mechanically, thereby providing very clean surface of Mg alloys. The clean surface prepared by the blade-abrading method in the air was found to be covered with thin and dense air-formed oxide films. Based on the experimental results obtained in this work, it is concluded that the newly developed blade-abrading technique is a very simple and useful pretreatment method which can provide clean and well-defined surface for the following surface treatments.

• Journal of Surface Science and Engineering
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• v.50 no.3
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• pp.147-154
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• 2017

This research was conducted to investigate the electrochemical properties of the thin air-formed oxide film-covered AZ31 Mg alloy. Native air-formed oxide films on AZ31 Mg alloy samples were prepared by knife-abrading method and the changes in the electrochemical properties of the air-formed oxide film were investigated in seven different electrolytes containing the following anions $Cl^-$, $F^-$, $SO{_4}^{2-}$, $NO_3{^-}$, $CH_3COO^-$, $CO{_3}^{2-}$, and $PO{_4}^{3-}$. It was observed from open circuit potential (OCP) transients that the potential initially decreased before gradually increasing again in the solutions containing only $CO{_3}^{2-}$ or $PO{_4}^{3-}$ ions, indicating the dissolution or transformation of the native air-formed oxide film into new more protective surface films. The Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) showed that there was growth of new surface films with immersion time on the air-formed oxide film-covered specimens in all the electrolyte. The least resistive surface films were formed in fluoride and sulphate baths whereas the most protective film was formed in phosphate bath. The potentiodynamic polarization curves illustrated that passive behaviour of AZ31 Mg alloy under anodic polarization appears only in $CO{_3}^{2-}$, or $PO{_4}^{3-}$ ions containing solutions and at more than $-0.4V_{Ag/AgCl}$ in $F^-$ ion containing solution.

• Journal of Surface Science and Engineering
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• v.30 no.3
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• pp.191-201
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• 1997

Non-passivated electrolytic tinplates withour conventinal chemical treatment self-oxidize in ambient atmosphere to from yellow stain on the outermost surface during the long-term storage. The degree of yellowness of the stain increased linerly with the oxide thickness due to the interfeefence color of the $SnO_2$ Even though the thickness of the oxide layer was very thin, less than 100$\AA$ , it exerts an undesirable influence on the can-making processes, particularly the stripping behavior after ironing. Investigations were carried out on the morphologies of the coating layer, the changes in oxide thickness during successive can-making processes and the averge friction coefficients with the different oxide thinkness. These oxide layers were broken up and distributed within the bulk tin coating during the ironing process. This redistribution of the oxide layer prvented smooth pressing-aside of the tin coating layer, resulting in an increase in the ironing friction coefficient. As the friction was increased, the residual stress along the can wall thinkness(i.e., the hoop stress) was also increased. Due to both the oxibe layer accumulation, which increased the friction coefficient, and the hoop stress, can stripping efficiency without roll-back is reduced.

• Applied Chemistry for Engineering
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• v.8 no.5
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• pp.830-836
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• 1997

The surface modification of iron oxide particle produced from steel-pickled acid by sodium-contained materials was studied. The molar ratio of $SiO_2$ to $Na_2O$ of sodium silicate was 1, 2, 3.5, respectively. The dispersion stability of iron oxide suspension as functions of amount of silica and pH was evaluated by surface charge and sedimentation velocity of iron oxide particle. Then the amount of sodium silicate was determined to provide a dispersion stability of iron oxide particle above pH 7. Finally, the surface modification of iron oxide particle with sodium silicate as silica-contained materials was done by wet ball milling. In the results of study, the dispersion stability of silica modified iron oxide particle was largely depended on amount of silica and pH together. The untreated iron oxide was unstable at pH 8, i.e. isoelectric point, but, the surface modified iron oxide particle with 0.8wt% silica was stable above pH 5. The dispersion stability was enhanced with 0.2wt% of anionic polyelectrolyte.