• Journal of the Korean institute of surface engineering
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• v.25 no.2
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• pp.82-89
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• 1992

The effect of interlayer coating of Ni and Ti on corrosion behavior was studied in TiN ion plated steel plate. Interlayer coating was carried out in a single and bi-layer to a various thickness combination prior to final TiN coating of $2\mu\textrm{m}$. Corrosion behavior was evaluated by anodic polarization test in 1N H2SO4 as well as salt spray test. Porosity of each coating was also tested by using SO2 test. Corrosion resistance was improved with increasing the thickness of Ni interlayer coating and Ni-Ti interlayer coating markedly enhanced the corrosion resistance. Ni/Ti interlayer coating of $2\mu\textrm{m}$/2$\mu\textrm{m}$ prior to $2\mu\textrm{m}$ TiN coating decreased the corrosion current density of active range by an order of 4 and that of passive range by an order of 1. This improvement was associated with the retardation of corrosive agent penetration with increasing coating thickness and inherent corrosion resistance of Ni and Ti interlayers, Ni/Ti interlayers coating were also very effective in improvement of corrosion resistance under salt atmosphere.

• Journal of the Korean institute of surface engineering
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• v.42 no.2
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• pp.86-94
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• 2009

Various types of multilayer coatings including Al/$Al_2O_3$ structure have been prepared on Nd-Fe-B permanent magnet to modify the morphology of the coating and to enhance the corrosion resistance of the magnet. Magnetron sputtering has been employed to make the multilayer coatings. $Al_2O_3$sputtering conditions were optimized in reactive sputtering by varying the deposition parameters. The formation of $Al_2O_3$ film was confirmed from the binding energy shift measured by electron spectroscopy for chemical analysis. 3 types of coating structures were designed and prepared by magnetron sputtering. The coating structures consist of (1) single Al coating, (2) modified coatings having oxide or plasma treated layer in the middle of coating structure, and (3) Al/$Al_2O_3$ multilayer coatings. Surface and cross-sectional morphologies showed that Al/$Al_2O_3$ multilayer grew as a layered structure, and that very compact Zone 3 like structure were formed. X-ray diffraction peak showed that the crystal orientations of multilayer coatings were similar to that of the bulk powder pattern. Hardness increased drastically when the Al thickness was around 1im in the Al/$Al_2O_3$ multilayer. From the salt spray test and pressure cooker test, it has been shown that the multilayer coatings showed good corrosion resistance compared to Al single or modified layer coatings.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.295-298
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• 2007

Reduction of optical losses in crystalline silicon solar cells by surface modification is one of the most important issues of silicon photovoltaics. Porous Si layers on the front surface of textured Si substrates have been investigated with the aim of improving the optical losses of the solar cells, because an anti-reflection coating(ARC) and a surface passivation can be obtained simultaneously in one process. We have demonstrated the feasibility of a very efficient porous Si ARC layer, prepared by a simple, cost effective, electrochemical etching method. Silicon p-type CZ (100) oriented wafers were textured by anisotropic etching in sodium carbonate solution. Then, the porous Si layers were formed by electrochemical etching in HF solutions. After that, the properties of porous Si in terms of morphology, structure and reflectance are summarized. The structure of porous Si layers was investigated with SEM. The formation of a nanoporous Si layer about 100nm thick on the textured silicon wafer result in a reflectance lower than 5% in the wavelength region from 500 to 900nm. Such a surface modification allows improving the Si solar cell characteristics. An efficiency of 13.4% is achieved on a monocrystalline silicon solar cell using the electrochemical technique.

• Journal of the Korean institute of surface engineering
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• v.41 no.5
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• pp.181-188
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• 2008

A.C. impedance properties of HA/Ti compound layer coated Ti-30Ta-($3{\sim}15$)Nb alloys have been studied by electrochemical method. Ti-30Ta binary alloys contained 3, 7, 10 and 15 wt% Nb were manufactured by the vacuum furnace system. And then specimen was homogenized at $1000^{\circ}C$ for 24 hrs. The sample was cut and polished for corrosion test and coating. It was coated with HA/Ti compound layer by magnetron sputter. The non-coated and coated morphology of Ti alloy were analyzed by X-ray diffractometer (XRD), energy X-ray dispersive spectroscopy (EDX) and filed emission scanning electron microscope (FE-SEM). The corrosion behaviors were investigated using A.C. impedance test (PARSTAT 2273, USA) in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Ti-30Ta-($3{\sim}15\;wt%$)Nb alloys showed the ${\alpha}+{\beta}$ phase, and $\beta$ phase peak was predominantly appeared in the case of increasingly Nb contents. The microstructures of Ti alloy were transformed from needle-like structure to equiaxed structure as Nb content increased. From the analysis of coating surface, HA/Ti composite surface uniformed coating layer with 750 nm thickness. The growth directions of film were (211), (112), (300) and (202) for HA/Ti composite coating on the surface after heat treatment at $550^{\circ}C$, whereas, the growth direction of film was (110) for Ti coating. The polarization resistance ($R_p$) of HA/Ti composite coated Ti-alloys were higher than those of the Ti and HA coated samples in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. Especially, corrosion resistance of Ti-Ta-Nb system increased as Nb content increased.

• Journal of the Korean institute of surface engineering
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• v.51 no.1
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• pp.34-39
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• 2018

Steel crucible used for molten Al has a problem of very limited lifetime because of the interaction between Fe and molten Al. This study was performed to improve the lifetime of steel crucible for molten Al by coating metallic Al and by further anodizing treatment to form thick and uniform anodic oxide films. The lifetime of the steel crucible was improved slightly by Al coating from 30 to 40 hours by metallic Al coating and largely to 120 hours by coating the surface with anodic oxide film. The improved lifetime was attributed to blocking of the reaction between Fe and molten Al with the help of anodic oxide layer with more than 20 um thickness on the crucible surface. The failure of the steel crucible arises from the formation of intermetallic compounds and pores at the steel/Al interface.

• Journal of the Korean institute of surface engineering
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• v.38 no.2
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• pp.79-82
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• 2005

This study investigated the effect of nitriding on the hardness and adhesion properties of $TiB_2$ coatings. Inductively coupled plasma (ICP) was used for both nitriding and deposition. By applying ICP, H13 steel was nitrided at a high rate of $50\;{\mu}m/hr$. After nitriding, a Fe4N compound layer or a diffusion layer was formed according to the hydrogen/nitrogen ratio. Both layers could improve the load-bearing capacity of the substrate by increasing the substrate hardness. The adhesion of the $TiB_2$ coatings increased to $\~30N$ after nitriding, but the hardness of the coating was lowered to 20-30 GPa. However, the adhesion of the $TiB_2$ coatings with a high hardness (>60 GPa) could not be improved substantially by nitriding due to the large difference in hardness between the coating and the substrate. The grain size of the $TiB_2$ coating was larger on the nitrided substrates, resulting in a decrease in the hardness of the coating.

• Journal of the Korean institute of surface engineering
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• v.45 no.2
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• pp.70-74
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• 2012

In thermal barrier coating (TBC) systems, the life of the coating depends on thermally grown oxide (TGO) layer because most of the failure of TBCs occurs when TGO growth increases. In order to inhibit TGO growth, process was additionally carried out before the heat treatment of the TBC coating layer at $1200^{\circ}C$ in air. In the additional process, heat treatment in vacuum furnace of < $10^{-5}$ torr was conducted for 7 h and 14 h before the heat treatment. The area and length of TGO, as well as the crack length in the TBC were characterized using a scanning electron microscope (SEM). The TGO thickness and crack of specimens pre-heat treated in vacuum furnace were reduced by 45% compare to those heat treated in furnace. Consequently, pre-heat treatment in a vacuum furnace process lead to effective inhibition of growth of the TGO.

• 연구논문집
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• s.24
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• pp.63-79
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• 1994

This article reports a experimental study of the method to achieve a bond joint at lower temperature in a short time. DC magnetron sputtering of Sn, Sn/Pb, Sn/In and Sn/Cu on copper substrate was provided as an interlayer for Cu to Cu bonding under the air environment. Various examination was conducted and investigated on the effect of experimental parameters such as coating materials, coating time(or coating thickness), bonding temperature and bonding time etc. Bonding was performed at the temperature of $210^\circC-320^\circC$ for 0sec and interfacial reaction between the coated layer and copper substrate was examined using optical, scanning electron microscope and x-ray diffractometer. From the obtained results, it was found that intermetallic compounds layer consisted of $\eta-phase(Cu_6Sn_5)$ and $\beta-phase(Cu_3Sn)$ was formed at the joint interface for almost all coating materials. But the dominant phase formed in the preetched Cu substrate coated with Sn was $\beta-phase$. A characteristic morphology looks like a reaction ring, which was believed as the strong interconnecting regions between two substrates, was found to be formed on the reaction surface of copper substrates. The morphologies and compositions of the intermetallics, which depends on the regions of the reaction surface, was appeared as greatly different. Based on above results, the new bonding process to make the joint at lower temperature for short time can be admitted as a feasible process.

• Corrosion Science and Technology
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• v.21 no.3
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• pp.221-229
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• 2022

To understand effects of cooling rates of coating layer on microstructures and corrosion behaviors of hot-dip alloy coated steel sheets (Zn-5%Al-2%Mg) in a neutral aqueous condition with chloride ion, a range of experimental and analytical methods were used in this study. Results showed that a faster cooling rate during solidification decreased the fraction of primary Zn, and increased the fraction of Zn-Al phase. In addition, interlamellar spacing became refined under a faster cooling rate. These modifications of the coating structure had higher open circuit potentials (OCP) with smaller anodic and cathodic current densities in the electrochemical potentiodynamic polarization. Surface analyses after a salt spray test showed that the increase in the Zn-Al phase in the coating formed under a faster cooling rate might have contributed to the formation of simonkolleite (Zn₅(OH)₈Cl₂·H₂O) and hydrotalcite (ZnAl₂(OH)₆Cl₂·H₂O) with a protective nature on the corroded outer surface, thus delaying the formation of red rust.

• Journal of Electrochemical Science and Technology
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• v.10 no.4
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• pp.424-432
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• 2019

Planar BiVO₄ and 3 wt% Mo-doped BiVO₄ (abbreviated as Mo:BiVO₄) film were prepared by the facile spin-coating method on fluorine doped SnO₂(FTO) substrate in the same precursor solution including the Mo precursor in Mo:BiVO₄ film. After annealing at a high temperature of 450℃ for 30 min to improve crystallinity, the films exhibited the monoclinic crystalline phase and nanoporous architecture. Both films showed no remarkably discrepancy in crystalline or morphological properties. To investigate the effect of surface passivation exploring the Al₂O₃ layer, the ultra-thin Al₂O₃ layer with a thickness of approximately 2 nm was deposited on BiVO₄ film using the atomic layer deposition (ALD) method. No distinct morphological modification was observed for all prepared BiVO₄ and Mo:BiVO₄ films. Only slightly reduced nanopores were observed. Although both samples showed some reduction of light absorption in the visible wavelength after coating of Al₂O₃ layer, the Al₂O₃ coated BiVO₄ (Al₂O₃/BiVO₄) film exhibited enhanced photoelectrochemical performance in 0.5 M Na₂SO₄ solution (pH 6.5), having higher photocurrent density (0.91 mA/㎠ at 1.23 V vs. reversible hydrogen electrode (RHE), briefly abbreviated as V_RHE) than BiVO₄ film (0.12 mA/㎠ at 1.23 V_RHE). Moreover, Al₂O₃ coating on the Mo:BiVO₄ film exhibited more enhanced photocurrent density (1.5 mA/㎠ at 1.23 V_RHE) than the Mo:BiVO₄ film (0.86 mA/㎠ at 1.23 V_RHE). To examine the reasons, capacitance measurement and Mott-Schottky analysis were conducted, revealing that the significant degradation of capacitance value was observed in both BiVO₄ film and Al₂O₃/Mo:BiVO₄ film, probably due to degraded capacitance by surface passivation. Furthermore, the flat-band potential (V_FB) was negatively shifted to about 200 mV while the electronic conductivities were enhanced by Al₂O₃ coating in both samples, contributing to the advancement of PEC performance by ultra-thin Al₂O₃ layer.