• 한국표면공학회지
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• 제42권5호
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• pp.191-196
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• 2009

Nanocrystalline Cu thin films were electrodeposited from sulfate baths and investigated systematically the influences of $Cu^{2+}$ concentration and additives on current efficiency, residual stress, surface morphology, and XRD patterns of electrodeposited Cu film. Current efficiency was nearly 100% at from 0.2M to 1.0 M $Cu^{2+}$ concentration. but it was linearly increased with $Cu^{2+}$ concentration at less than 0.2M. The residual stress was observed in range of 7.9 to 18.4 MPa and tensile stress mode. Dendritic and powdered form was obtained at below 0.1 M. As increased with $Cu^{2+}$ concentration in solution, the main peak in the XRD pattern shifted (111) and (220) from (200). In the other hand, all about 100% current efficiency observed in all additive concentration systems, and residual stress observed in range of 20.4 to 26.3 MPa tensile stress. The condition 5(Ultra make-up - 10 ml/l, Ulta A - 0.5ml/l, Ultr B - 0.5 ml/l) was good surface morphology, and fcc(111) peak in XRD patterns increased with increasing additive concentration.

• 산업경영시스템학회지
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• 제41권3호
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• pp.90-96
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• 2018

This paper proposed data driven techniques to forecast the time point of water management of the water reservoir without measuring manganese concentration with the empirical data as Juam Dam of years of 2015 and 2016. When the manganese concentration near the surface of water goes over the criteria of 0.3mg/l, the water management should be taken. But, it is economically inefficient to measure manganese concentration frequently and regularly. The water turnover by the difference of water temperature make manganese on the floor of water reservoir rise up to surface and increase the manganese concentration near the surface. Manganese concentration and water temperature from the surface to depth of 20m by 5m have been time plotted and exploratory analyzed to show that the water turnover could be used instead of measuring manganese concentration to know the time point of water management. Two models for forecasting the time point of water turnover were proposed and compared as follow: The regression model of CR20, the consistency ratio of water temperature, between the surface and the depth of 20m on the lagged variables of CR20 and the first lag variable of max temperature. And, the Box-Jenkins model of CR20 as ARIMA (2, 1, 2).

• 한국표면공학회지
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• 제49권2호
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• pp.119-124
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• 2016

Plasma electrolytic oxidation (PEO) is a promising coating process to produce ceramic oxide on valve metals such as Al, Mg and Ti. The PEO coating is carried out with a dilute alkaline electrolyte solution using a similar technique to conventional anodizing. The coating process involves multiple process parameters which can influence the surface properties of the resultant coating, including power mode, electrolyte solution, substrate, and process time. In this study, ceramic oxide coatings were prepared on commercial Al alloy in electrolytes with different KOH concentrations (0.5 ~ 4 g/L) by plasma electrolytic oxidation. Microstructural and electrochemical characterization were conducted to investigate the effects of electrolyte concentration on the microstructure and electrochemical characteristics of PEO coating. It was revealed that KOH concentration exert a great influence not only on voltage-time responses during PEO process but also on surface morphology of the coating. In the voltage-time response, the dielectric breakdown voltage tended to decrease with increasing KOH concentration, possibly due to difference in solution conductivity. The surface morphology was pancake-like with lower KOH concentration, while a mixed form of reticulate and pancake structures was observed for higher KOH concentration. The KOH concentration was found to have little effect on the electrochemical characteristics of coating, although PEO treatment improved the corrosion resistance of the substrate material significantly.

• 한국표면공학회지
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• 제52권2호
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• pp.78-83
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• 2019

Chloride baths for electrodeposited Ni thin films were fabricated by dissolving metal Ni powders with the mixed solution consisting of HCl and de-ionized water. Current efficiency, residual stress, surface morphology and microstructure of Ni films with the change of metal ion ($Ni^{2+}$) concentrations in the plating solution were studied. Current efficiency was measured to be more than 90% with increasing $Ni^{2+}$ concentrations in the plating solution. Residual stress of Ni thin film was increased from about 400 to 780 MPa with increasing $Ni^{2+}$ concentration from 0.2 to 0.5 M. It is gradually decreased to 650 MPa at 0.9 M $Ni^{2+}$ concentration. Smooth surface morphologies were observed over 0.3 M $Ni^{2+}$ concentration, but nodule surface morphology at 0.2 M. Ni films consist of FCC(111), FCC(200), FCC(220) and FCC(311) peaks in XRD patterns. Preferred orientation of FCC(111) was observed and its intensity was slightly decreased with increasing $Ni^{2+}$ concentration. The average grain size was slightly increased at 0.3 M $Ni^{2+}$ concentration and then slightly decreased with increasing $Ni^{2+}$ concentration.

• 한국표면공학회지
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• 제49권4호
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• pp.331-338
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• 2016

In this work, anodic oxidation behavior of AZ31 Mg alloy was studied as a function of $Na_2CO_3$ concentration in electrolyte by voltage-time curves and observation of surface appearances and morphologies after the anodic treatments, using optical microscopy and confocal scanning laser microscopy (CSLM). The voltage-time curves of AZ31 Mg alloy surface and surface appearances after the anodic treatments showed three different regions with $Na_2CO_3$ concentration : region I, below 0.2 M $Na_2CO_3$ where shiny surface with a number of small size pits; region II, between 0.4 M and 0.6 M $Na_2CO_3$ where dark surface with relatively low number of large size burned or dark spots; region III, more than 0.8 M $Na_2CO_3$ where bright surface with or without large size dark spots were obtained. The anodically treated AZ31 Mg alloy surface became significantly brightened with increasing $Na_2CO_3$ concentration from 0.5 M to 0.8 M which was attribute to the formation of denser and smoother surface films. Pits and porous protruding reaction products were found at relatively large size and small size spots, respectively, on the AZ31 Mg alloy surface in low concentration of $Na_2CO_3$ less than 0.2 M. The formation of pits is attributed to the result of repetition of the formation and detachment of porous anodic reaction products. Based on the experimental results obtained in this work, it is concluded that more uniform, denser and smoother surface of AZ31 Mg alloy could be obtained at more than 0.8 M $Na_2CO_3$ concentration if there is no other oxide forming agent.

• 한국표면공학회지
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• 제36권5호
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• pp.379-385
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• 2003

The surface morphology, the glossiness and the hardness of Zn-Cr and Zn-Cr-X(X:Co, Mn) alloy electrodeposits were investigated by using chloride bath with EDTA additive and flow cell system. The surface morphology of Zn-Cr alloy and Zn-Cr-Mn alloy changed from fine needle shape crystalline structure to colony structure of fine granular crystallites with increasing current density in the range of 20-100 $A/dm^2$. The surface morphology of Zn-Cr-Co alloy deposited from low Co concentration bath(2.5-10 g/$\ell$) was similar to that of Zn-Cr alloy, while that of Zn-Cr-Co alloy deposited from high cobalt concentration bath was fine granular crystalline structure in the same range of current density. The glossiness of Zn-Cr and Zn-Cr-Mn alloy increased noticeably with increasing current density, while that of Zn-Cr-Mn alloy decreased with increasing Mn concentration of bath in high current density region. The glossiness of Zn-Cr-Co alloy deposited from low Co concentration bath increased with current density while that of the alloy from high Co concentration bath decreased with increasing current density. The hardness of Zn-Cr and Zn-Cr-X alloy increased noticeably with current density.

• 한국표면공학회지
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• 제49권3호
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• pp.225-230
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• 2016

The present work was conducted to investigate the effects of NaF concentration in phosphate and silicate-containing alkaline electrolyte on the morphology, thickness, surface roughness and hardness of anodic oxide films formed on AZ31 Mg alloy by plasma electrolytic oxidation (PEO) method. The PEO films showed flat surface morphology with pores in the absence of NaF in the electrolyte, but nodular features appeared on the PEO film surface prepared in NaF-containing electrolyte. Numerous pores ranging from 1 to $20{\mu}m$ in size were observed in the PEO films and the size of pores decreased with increasing NaF concentration in the electrolyte. Surface roughness and thickness of PEO films showed increases with increasing NaF concentration. Hardness of the PEO films also increased with increasing NaF concentration. It was noticed that hardness of inner part of the PEO films is lower than that of outer part of them, irrespective of the concentration of NaF. The low hardness of PEO films was explained by the presence of a number of small size pores less than $2{\mu}m$ near the PEO film/substrate interface.

• 한국분무공학회지
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• 제20권4호
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• pp.236-240
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• 2015

This study aims to experimentally investigate the evaporation characteristics of nanofluid droplet on heated surface at boiling temperature of DI-water. In particular, textured surface was used to examine the effect of wettability on evaporation. At the initial stage of evaporation process, dynamic contact angle (DCA) of nanofluid droplet with 0.01 vol.% concentration on textured surface rapidly increased over its equilibrium contact angle by generated large bubble inside the droplet due to lower wettability. However, contact angle of nanofluid droplet with higher concentration on textured surface decreased with surface tension. In addition, total evaporation time of droplet on textured surface was considerably delayed due to reduction of contact area between droplet and solid surface. Thus, evaporation characteristics were highly affected by the nanofluid concentration and surface wettability.

• Bulletin of the Korean Chemical Society
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• 제30권4호
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• pp.902-906
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• 2009

It is found that that the coating N-acetyl cysteine (NAC) on gold surfaces may be used to design the distribution of either gold particle adsorbed to the $TiO_2$ surface or vice versa by adjusting the electrostatic interactions. In this study, we investigated electrostatic properties of the NAC-coated-gold surface and the $TiO_2$ surface. The surface forces between the surfaces were measured as a function of the salt concentration and pH value using the AFM. By applying the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to the surface forces, the surface potential and charge density of the surfaces were quantitatively acquired for each salt concentration and each pH value. The surface potential and charge density dependence on the salt concentration was explained with the law of mass action, and the pH dependence was with the ionizable groups on the surface.

• 한국세라믹학회지
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• 제33권8호
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• pp.921-927
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• 1996

The liquid-phase concentration from the interior to the surface region and its influence on the microstructural changes were investigated in pressureless sintered $\beta$-SiC Surface reaction-layer was formed by reaction of packing powder and volatile components on the surface during sintering which was induced the concentration of liquid-phase in the surface regions. The microstructural changes between the surface region and the interior were appeared in sintered specimen which was resulted from the difference of liquid-phase content during sintering. Microstructural changes were observd with the depth of about 250${\mu}{\textrm}{m}$ from he surface. The grain size and aspect ratio of SiC in the interior are larger than those in the surface region and the rate of transforma-tion of $\beta$-to $\alpha$-SiC during sintering is higher in the interior than that in the surface region.