• Corrosion Science and Technology
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• 제16권6호
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• pp.317-327
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• 2017

The change in the oxidation behavior of three types of B-added ultrahigh strength martensitic steels containing Ti and Nb induced by applying constant cathodic current was investigated. In a 3% NaCl+0.3% $NH_4SCN$ solution, the overall polarization behavior of the three alloys was similar, and degradation of the oxide film was observed in the three alloys after applying constant cathodic current. A significant increase in the anodic current density was observed in the Nb-added alloy, while it was diminished in the Ti-added alloy. Both Ti and Nb alloying decreased the hydrogen overpotential by forming NbC and TiC particles. In addition, the thickest oxide film was formed on the Ti-added alloy, but the addition of Nb decreased the film thickness. Therefore, it was concluded that the remarkable increase in the anodic current density of Nb-added alloy induced by applying constant cathodic current density was attributed to the formation of the thinnest oxide film less protective to hydrogen absorption, and the addition of Ti effectively blocked the hydrogen absorption by forming TiC particles and a relatively thick oxide film.

• 한국표면공학회지
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• 제53권6호
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• pp.351-359
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• 2020

Formation behavior and properties of PEO (Plasma Electrolytic Oxidation) film on AA2024 were investigated under application of pulsed current as a function of Na3PO4 concentration in 0.05 M Na2SiO3 solution by analyzing voltage-time behavior, in-situ observation of arc generation, observation of surface morphology and measurements of thickness and surface roughness. Arc generation voltage decreased with increasing Na3PO4 concentration. Color difference of PEO films between edge and inner part disappeared by addition of Na3PO4. It was also observed that size of nodules on PEO film decreased with increasing Na3PO4 concentration. Thickness of PEO films formed on AA2024 increased with increasing Na3PO4 concentration. Whereas, surface roughness of PEO films decreased with increasing Na3PO4 concentration up to 0.05 M of Na3PO4 which is attributed to the deceased size of nodules on the PEO films. However, the surface roughness increased with increasing Na3PO4 concentration more than 0.07 M of Na3PO4 which seems to be due to the formation of non-uniform PEO films with smooth surface and large size pores formed by orange-colored big arcs. The experimental results suggest that added sodium phosphate less than 0.2 M in an alkaline silicate solution can contribute to the formation of relatively thick and uniform thickness of PEO films under arc generation voltage lower than 300 V.

• 한국표면공학회지
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• 제54권4호
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• pp.184-193
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• 2021

This study demonstrates formation behavior and morphological changes of PEO (Plasma Electrolytic Oxidation) films on AZ91 Mg alloy as a function of pre-treatment time in 1 M HF solution at 25 ± 1 ℃. The electrochemical behavior and morphological changes of AZ91 Mg alloy in the pre-treatment solution were also investigated with pre-treatment time. The PEO films were formed on the pre-treated AZ91 Mg alloy specimen by the application of anodic current 100 mA/cm² of 300 Hz AC in 0.1 M NaOH + 0.4 M Na₂SiO₃ solution. Vigorous generation of hydrogen bubbles were observed upon immersion in the pre-treatment solution and its generation rate decreased with immersion time. It was also found that 𝛽-Mg₁₇Al₁₂ in AZ91 Mg alloy was dissolved and a protective thin film of MgF₂ was formed on the AZ91 Mg alloy surface during the pre-treatment process in the 1 M HF solution. PEO film did not grow on the AZ91 Mg alloy specimen when the surface was not pre-treated and irregular PEO films with nodular defects were formed for the specimens pre-treated up to 1 min. Uniform PEO films were formed when the AZ91 Mg alloy specimen was pre-treated more than 3 min. The growth rate of PEO films on AZ91 Mg alloy increased significantly with increasing pre-treatment time.

• 한국재료학회지
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• 제4권2호
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• pp.166-176
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• 1994

Ni기 초합금은 Co, Cr, Mo, W등의 고용 강화 원소와 AI, Ti, Nb, Ta 등의 $\gamma '$ 석출 강화 원소로 구성되어 있다. 초합금의 기계적 성질과 내산화성을 개선하기 위하여 희토류 원소를 재료 내부에 첨가하거나, 코팅 재료로써 사용하고 있다. 이들 희토류 원소는 $Al_2O_3, Cr_2O_3$등의 산화물의 종류에 따라 산화물의 성장 속도와 밀착성에 영향을 미친다. Hf함유 Ni기 초합금 AF115와 $AI_2O_3$ 함유 MA6000초합금 2종을 이온 코터를 이용, Yttrium 표면개질후, 온도 1273K-1473K에서 고온 산화 수 산호 피막의 성장 속도, 결정립, 내부 구조 및 내박리성에 미치는 Yttrium 의 영향을 조사하였다. AF115와 MA6000 초합금에 Yttrium코팅을 한 결과 내부 산화물의 성장에 현저한 변화가 있었다. Yttrium의 표면 개질에 의하여, AF115의 경우는 $AI_2O_3$ 주성분의 입계 집중과 Hf의 우선 산확 억제되고, 삼각 형태의 내부 산화물이 plate형으로 변화되었다. MA6000의 경우 $AI_2O_3$ 주성분의 산화층이$Cr_2O_3$주성분의 외부 산화층과$AI_2O_3$ 주성분의 내부층으로 변화되었다.

• 청정기술
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• 제23권2호
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• pp.158-162
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• 2017

철, 구리, 알루미늄, 니켈 등의 금속을 에칭하기 위한 에칭액으로 $FeCl_3$ 용액이 사용되며, 에칭 과정에서 $Fe^{3+}$가 $Fe^{2+}$로 환원되면서 에칭속도를 저하시키고, 에칭효율이 감소하게 된다. 또한 에칭 후 발생하는 염화철 에칭폐액은 환경적, 경제적으로 문제를 지니기 때문에 에칭액을 재생하여 재사용 할 필요가 있다. 본 연구에서는 $FeCl_2$ 용액에 HCl을 첨가한 후, 산화제로 $H_2O_2$, $NaClO_3$를 첨가하여 용액 내 $Fe^{2+}$를 산화시켰으며, 산화과정에서 산화-환원전위(ORP)와 산화율간의 관계를 조사하였다. ORP는 $H_2O_2$와 $NaClO_3$의 농도가 증가함에 따라 증가하였으며, 산화가 진행되면서 점차 감소하여 산화가 완료된 후에 일정한 ORP를 유지하였다. Nernst 식과 일치하는 결과를 보였다. 또한 충분한 양의 HCl 및 $H_2O_2$, $NaClO_3$를 첨가하였을 경우, 약 99% 이상 산화가 이루어짐을 알 수 있었다.

• 자원리싸이클링
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• 제26권2호
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• pp.18-24
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• 2017

$FeCl_3$ 용액은 금속의 에칭용액으로 사용되며, 사용 후 발생하는 $FeCl_3$ 에칭폐액은 환경적, 경제적으로 문제를 지니기 때문에 에칭액을 재사용할 필요가 있다. 본 연구에서는 $FeCl_2$ 용액에 HCl을 첨가 한 후, 산화제로 $H_2O_2$를 첨가하여 용액 내 $Fe^{2+}$를 산화시켰으며, 산화과정에서 산화-환원전위(ORP)와 산화율 간의 관계를 조사하였다. ORP는 HCl과 $H_2O_2$의 농도가 증가함에 따라 증가하였으며, 산화가 진행되면서 점차 감소하여 Nernst 식과 일치하는 결과를 보였다. 또한 충분한 양의 HCl과 $H_2O_2$를 첨가하였을 경우, 약 99% 이상 산화가 이루어짐을 알 수 있었다.

• 한국재료학회지
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• 제13권1호
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• pp.36-42
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• 2003

The oxidation behaviors of Y-Cr bilayer deposited on ferritic steel by magnetron-sputtering for application of the Fe-Cr alloys as interconnectors of planar-type solid oxide fuel cells (SOFCs) were studied. After oxidation at $800^{\circ}C$ for 40 hours, the major phase of $Y_2$$O_3$and the minor phase of $YCrO_3$, $Mn_{1.5}$ $Cr_{1.5}$ $O_4$and Cr$_2$SiO$_4$were formed in the Y/Cr bilayered samples, while the major phase of Cr$_2$O$_3$and the minor phase of $Y_2$$O_3$were formed as the major phase in the Cr/Y bilayered samples. The Log(ASR/T) that expresses electric resistance of the Y/Cr coated specimen with nonconducting $_Y2$$O_3$oxide showed high value of -2.80 Ω$\textrm{cm}^2$$K^{-1}$ / and that of the Cr/Y coated specimen with conducting $Cr_2$$O_3$oxide appeared to be -4.11 Ω$\textrm{cm}^2$$^{K}$ . The electric resistance of the Y/Cr coated specimen was largely increased due to the formation of high resistance oxide scales. However, the Cr/Y coated specimen did not show any increase in the electric resistance and had the long-term stability of oxidation because there was no formation of the secondary phases with low conductivity.

• 한국재료학회지
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• 제21권3호
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• pp.161-167
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• 2011

The stress-strain responses and oxidation properties of cold-rolled Zr-1.5Nb-O and Zr-1.5Nb-O-S alloys were studied. The U.T.S. (ultimate tensile strength) of cold-rolled Zr-1.5Nb-O-S alloy with 160 ppm sulfur (765 MPa) were greater than that of Zr-1Nb-1Sn-0.1Fe alloy (750 MPa), achieving an excellent mechanical strength even after the elimination of Sn, an effective solution strengthening element. The addition of sulfur increased the strength at the expense of ductility. However, the ductile fracture behavior was observed both in Zr-Nb-O and Zr-Nb-O-S alloys. The beneficial effect of sulphur on the strengthening was observed in the cold rolled Zr-1.5Nb-O-S alloys. The activation volume of cold-rolled Zr-1.5Nb decreased with sulfur content in the temperature region of dynamic strain aging associated with oxygen atoms. Insensitivity of the activation volume to the dislocation density and the decrease of the activation volume at a higher temperature where the dynamic strain aging occurs support the suggestion linking the activation volume with the activated bulge of dislocations limited by segregation of oxygen and sulfur atoms. The addition of sulfur was also found to improve the oxidation resistance of Zr-Nb-O alloys.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제41회 하계 정기 학술대회 초록집
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• pp.212-212
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• 2011

In addition to the catalysts' activity and selectivity, the deactivation of catalysts during use is of practical importance. It is crucial to understand the phenomena of the deactivation to predict the loss of activity during catalyst usage so that the high operational costs associated with catalyst replacement can be reduced. In this study, the activity of Ru catalysts, such as nanoparticles (3~6 nm) and polycrystalline thin film (50 nm), have been investigated under CO oxidation and oxidative/reductive reaction conditions at various temperatures with the ambient pressure X-Ray photoelectron spectroscopy (APXPS). With APXPS, the surface oxides on the catalyst are measured and monitored in-situ. It was found that the Ru film exhibited faster oxidation-and-reduction compared to that of nanoparticles showing mild oxidative-and-reductive characteristics. Additionally, the larger Ru nanoparticles showed a higher degree of oxide formation at all temperatures, suggesting a higher stability of the oxide. These observations are in agreement with the catalytic activity of Ru catalysts. The loss of activity of Ru films is correlated with bulk oxide formation, which is inactive in CO oxidation. The Ru nanoparticle, however, does not exhibit deactivation under similar conditions, suggesting that its surface is covered with a highly active ultrathin surface oxide. Since the active oxide is more stable as nanoparticles than as a film, the nanoparticles showed mild oxidative/reductive behavior, as confirmed by APXPS results. We believe these simultaneous observations of both the surface oxide of Ru catalysts and the reactivity in real time enable us to pinpoint the deactivation phenomena more precisely and help in designing more efficient and stable catalytic systems.

• 분석과학
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• 제16권6호
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• pp.431-437
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• 2003

가압경수로 사용후핵연료 (이산화 우라늄)의 리튬환원공정으로부터 생산된 우라늄 금속 전환체에 대한 금속 전환율을 건식방법인 열중량분석법 (T.G.A)으로 측정하였다. 전환체를 고체와 분말로 분류하여 측정한 결과 우라늄 금속 전환율은 각각 90.7~95.9 및 77.8~71.5 wt% 이었다. 금속 전환체의 건식저장 시 열적 산화 안정성을 확인하기 위하여 전환체내에 함유되어 있는 Mo, Ru, Rh 및 Pd 합금에 대한 산화 거동을 조사하였다. 합금을 $600{\sim}700^{\circ}C$의 공기분위기에서 산화시킨 결과 0.40~0.55 wt%의 무게증가를 보였으며 $750^{\circ}C$부터는 표면으로부터 산화가 진행되어 상변화가 일어났다. $900^{\circ}C$에서는 Mo의 휘발에 의한 영향으로 0.76~25.22 wt%의 무게 감소를 나타내었다.