• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1998.05a
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• pp.22-22
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• 1998

304 는 BWR(boiling water reactor)의 reactor 구조용 재료로 사용되고 있고, 합금 600 은 PWR(pressurized water reator) 의 증기 발생기 세관으로 쓰이고 있으며 모두 약 $280{\;}^{\circ}C$ 이상 의 원자로 냉각수에 노출되어 있다. 원자로 냉각수 분위기에서 두 합금의 공통적인 특정은 입계응력부식균열(IGSCC)에 민감한것과 IGSCC가 예민화(sensitization)와 관련이 있는 것이 다. 두 합금에서 일어나는 IGSCC는 원자력발전소의 부식피해중 가장 빈도가 높고 발생시 방사능 누출로 인하여 원전의 신뢰성을 저하시키고, 가동중단으로 인한 경제적 손실을 초 래하여 지난 20 년 동안 가장 심도있게 연구된 주제다. 304 은 크롬 탄화물의 업계 석출로 언하여 예민화된경우 IGSCC 에 민감한 반면 600 은 예민화된 경우 뿐만 아니라 용체화처리된 상태에서도 IGSCC에 민감하다. 오히려 600은 용 체화처리 후 700 C에서 15~20시간 시효처리를 하여 크롬탄화물을 업계에 석출 시커었을 때 IGSCC 저항성이 향상된다. 두 합금의 IGSCC 특정 중 큰 차이는 304는 임계균열전위 ( (critical cracking potential) 이 존재하여 부식전위(corrosion potential) 가 엄계균열전위보다 낮 은 경우 IGSCC 가 일어나지 않지만 그 반대인 경우 IGSCC 에 민감하게된다. 반면에 600 은 뚜렷한 임계균열전위가 존재하지 않고 양극 분극(anodic polarization) 뿐만 아니라 음극분극 시에도 IGSCC 가 일어난다. 이련 이유로 600의 IGSCC 가구로 피막파괴-양극용해(film rupture-anodic dissolution)외에 수소취성(hydrogen embrittlement)기구도 제안되고 었다. 원전의 냉각수는 고 순도의 물이지만 수 처리 과정과 웅축기 배관의 누수로 인한 산소, $Cu^{2+},{\;}S_xO_6{\;}^{2-}(x=3~6)$ 등이 유입되어 오염되는데 이려한 오염물질들이 수 ppm정도 소량 포함된 경우 응 력부식민감도는 상당히 증가된다. 산성분위기 흑은 산소, $Cu^{2+}$, 등이 소량 포합된 산화성 분위기 그리고 sufur oxyanion 에 오염된 고온의 물에서 600 의 IGSCC 민감도는 예민화도가 증가할 수록 민감하여 304 의 IGSCC 와 매우 유사한 거동을 보인다. 본 강연에서는 304 와 600 의 고온 물에서 일어나는 IGSCC 민감도에 미치는 환경, 예민화처리, 합금원소의 영향을 고찰하고 이에 대한 최근의 연구 동향과 방식 방법을 다룬다.

• Tribology and Lubricants
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• v.31 no.3
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• pp.79-85
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• 2015

RC delay is a critical issue for achieving high performance of ULSI devices. In order to minimize the RC delay time, we uses the CMP process to introduce high-conductivity Cu and low-k materials on the damascene. The low-k materials are generally soft and fragile, resulting in structure collapse during the conventional high-pressure CMP process. One troubleshooting method is electrochemical mechanical polishing (ECMP) which has the advantages of high removal rate, and low polishing pressure, resulting in a well-polished surface because of high removal rate, low polishing pressure, and well-polished surface, due to the electrochemical acceleration of the copper dissolution. This study analyzes an electrochemical state (active, passive, transpassive state) on a potentiodynamic curve using a three-electrode cell consisting of a working electrode (WE), counter electrode (CE), and reference electrode (RE) in a potentiostat to verify an electrochemical removal mechanism. This study also tries to find optimum conditions for ECMP through experimentation. Furthermore, during the low-pressure ECMP process, we investigate the effect of current density on surface roughness and removal rate through anodic oxidation, dissolution, and reaction with a chelating agent. In addition, according to the Faraday’s law, as the current density increases, the amount of oxidized and dissolved copper increases. Finally, we confirm that the surface roughness improves with polishing time, and the current decreases in this process.

• Corrosion Science and Technology
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• v.7 no.6
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• pp.315-318
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• 2008

The atmospheric corrosion performance of Al-alloying, Si-alloying and Al-Si-alloying steel were studied by wet/dry cyclic corrosion tests (CCT) at $30^{\circ}C$ and 60% relative humidity (RH). The corrosion electrolyte used for CCT was 0.052 wt% $NaHSO_{3}$ (pH~4) solution. The result of gravimetry demonstrated that Al-Si-bearing steels showed lower corrosion resistance than other rusted steels. But the rusted 0.7%Si-alloying steel showed a better corrosion resistance than rusted mild steel. Polarization curves demonstrated that Al-/Si-alloying and Al-Si-alloying improved the rest potential of steel at the initial stage; and accelerated the cathodic reduction and anodic dissolution after a rust layer formed on the surfaces of steels. XRD results showed that Al-Si-alloying decreased the volume fraction of $Fe_{3}O_{4}$ and $\alpha-FeOOH$. The recycle of acid accelerated the corrosion of steel at the initial stage. After the rust layer formed on the steel, the leak of rust destabilized the rust layer due to the dissolution of compound containing Al (such as $FeAl_{2}O_{4}$, $(Fe,\;Si)_{2}(Fe,\;Al)O_{4}$). Al-Si-alloying is hence not suitable for improving the anti-corrosion resistance of steel in industrial atmosphere.

• Applied Chemistry for Engineering
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• v.9 no.7
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• pp.1030-1035
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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 an aqueous solution of sulfuric acid. To prevent the chemical dissolution of alumina membrane, $Al_2(SO_4)_3$, $AlPO_4$ and $Al(NO_3)_3$ which could be considered to supply $Al^{3+}$ ions were added to electrolyte solution at a reaction temperature of $20^{\circ}C$ and cumulative charge of $150C/cm^2$. Effects of these additives on the formation of porous alumina membrane were evaluated under various electrolyte concentration(5~20 wt%) and current densities($10{\sim}50mA/cm^2$). The membrane surfaces which were prepared in electrolyte solution with all the additives except $Al_2(SO_4)_3$ were damaged. However, when $Al_2(SO_4)_3$ was added to the $H_2SO_4$ solution, an uniform surface of porous alumina was obtained. Also, it was shown that the pore size of membrane was nearly independent on the quantity of $Al_2(SO_4)_3$ added at same electrolyte concentration and current density.

• Nuclear Engineering and Technology
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• v.52 no.9
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• pp.2025-2033
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• 2020

Signature-based safeguards (SBS) is being developed to assist tradition nuclear material accountancy methods in tracking material in pyroprocessing facilities. SBS involves identifying off-normal scenarios that would result in improper movement of material in a pyroprocessing facilities and determining associated sensor response signatures. SBS investigations are undertaken in the computational space utilizing an electrochemical transport code known as enhanced REFIN with anodic dissolution (ERAD) to calculate the affect of off-normal conditions in the electrorefiner (ER) on material movement. Work is undertaken to experimentally validate the predictions and assumptions made by ERAD for off-normal occurrences. These experiments were undertaken on a benchtop scale and involved operating an electrochemical cell at 10 separate current densities for constant current operations to deposit U and Gd at a W cathode. These experiments were then modeled using ERAD to compare calculated predictions versus analytical experimental results it was found. It was discovered both the experimental and calculated results reflect a trend of increased codeposition of U and Gd with increasing current density. ERAD was thus demonstrated to be useful for predicting trends from anomalous operation but will require further optimization to be utilized as a quantitative design tool.

• Journal of Welding and Joining
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• v.16 no.6
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• pp.59-68
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• 1998

In this study, effects of solidification modes (primary $\delta$-ferrite, primary ${\gamma}$-austenite) on the pit initiation and propagation in the 304L and 316L austenitic stainless steel weld metals were investigated. The solidification mode of weld metal was controlled by the addition of nitrogen to Ar shielding gas. Through the electrochemical experiments (potentiodynamic anodic polarization and potentiostatic time-current transient test) and metallographic examination (microstructure and elemental distribution), the following results were obtained. The more the volume content of nitrogen in the shielding gas were, the lower critical current density for passivity was observed. In comparison with weldments solidified through the primary $\delta$-ferrite solidification mode and the primary ${\gamma}$-solidification mode, the former showed higher critical pitting potential and a longer incubation time for stable pit initiation than the latter. However, in the pit propagation stage the former exhibited a faster dissolution rate than the latter. These results were believed to ee related to the distribution of alloying elements such as Cr, Mo, Ni and S.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.39 no.4
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• pp.291-297
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• 2003

Al-brass is usually used as the tube material of vessel's heat exchanger for seawater cooling system because it has high thermal conductivity and good mechanical properties and high corrosion resistance due to cuprous oxide (Cu20) layer against seawater. However, Al-brass tubes of heat exchanger for vessel at the actual environment is reported that local corrosion such as stress corrosion cracking occurred by synergism effect between mechanical factor and corrosion environment In this paper, the effect of corrosion environment on the stress corrosion cracking of Al-brass in various NH4OH of 3.5% NaCl solution, under flow by constant displacement tester. Based on the test results, the behavior of polarization, stress corrosion crack propagation and dezincification phenomenon of Al-brass are investigated. The main results are as follows：(1) Increasing range of potential from open circuit potential to repassivation gets lower, as the contain rate of NH4OH gets higher. (2) As contain rate of NH4OH gets higher, SCC of Al-brass is become activation but the protection film(Cu20) of Al-brass is created in 3.5% NaCl solution. (3) According as content of NH4OH increases in 3.5% NaCl solution, the dezincifiction area is spread. It is concluded that dezincification occurred by localized preferential anodic dissolution at stress focusing region.

• Corrosion Science and Technology
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• v.17 no.4
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• pp.166-175
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• 2018

In this study, the electrochemical properties of CP-Ti (commercially pure titanium) and Ti-64 (Ti-6Al-4V) were evaluated and the effect of hydrofluoric acid on corrosion resistance and electrochemical properties was elucidated. Additive manufactured materials were made by DMT (Directed Metal Tooling) method. Samples were heat-treated for 1 hour at $760^{\circ}C$ and then air cooled. Surface morphologies were studied by optical microscope and SEM. Electrochemical properties were evaluated by anodic polarization method and AC-impedance measurement. The oxide film formed on the surface was analyzed using an XPS. The addition of HF led to an increase in the passive current density and critical current density and decreased the polarization resistance regardless of the alloys employed. Based on the composition of the oxide film, the compositional difference observed by the addition of HF was little, regardless of the nature of alloys. The Warburg impedance obtained by AC-impedance measurement indicates the dissolution of the constituents of CP-Ti and Ti-64 through a porous oxide film.

• Korean Journal of Metals and Materials
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• v.48 no.11
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• pp.1014-1020
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• 2010

In order to improve the purity on deposit in cobalt electrowining, a fundamental study using Pulse-Reverse Current (PRC) was carried out. Based on a sulfate solution, Cu, Ni, and Fe as impurities were added during cobalt electrowinning. There were four reverse waveforms and frequency conditions from 1 Hz to 10 kHz, and the purity of each condition was compared with the Direct Current (DC) purity. From the results, it was found that the anodic potential induced by reverse current affects selective dissolution of impurities. In this work, the case of the highest reverse peak current density ($I_r$) with a short reverse time ($t_r$) at 100 Hz showed a higher purity than that of the DC. This PRC condition also showed only a 4% low current efficiency comparable to the DC. We concluded that an optimized PRC for cobalt electrowinning could improve the purity with little loss of current efficiency.

• Corrosion Science and Technology
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• v.21 no.2
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• pp.138-146
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• 2022

The cavitation and potentiodynamic polarization experiments were conducted simultaneously to investigate the effect of cavitation amplitude on the super austenitic stainless steel (UNS N08367) electrochemical behavior in seawater. The results of the potentiodynamic polarization experiment under cavitation condition showed that the corrosion current density increased with cavitation amplitude increase. Above oxygen evolution potential, the current density in a static condition was the largest because the anodic dissolution reaction by intergranular corrosion was promoted. In the static condition, intergranular corrosion was mainly observed. However, damage caused by erosion was observed in the cavitation environment. The micro-jet generated by cavity collapse destroyed the corrosion product and promoted the repassivation. So, weight loss occurred the most in static conditions. After the experiment, wave patterns were formed on the surface due to the compressive residual stress caused by the impact pressure of the cavity. Surface hardness was improved by the water cavitation peening effect, and the hardness value was the highest at 30 ㎛ amplitude. UNS N08367 with excellent mechanical performance due to its high hardness showed that cavitation inhibited corrosion damage.