• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2002년도 춘계학술대회논문집
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• pp.135-139
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• 2002

Most of all the mechanical devices are becoming more high-speed and high-power as well as their used condition being more polluted. So, it is necessary for these devices to equip cooling system to overcome that kind of severe using condition. In this study, corrosion test was carried out in distilled and tap water for the investigation on the corrosion characteristics of Al-alloy that is using as material for radiator.

• Corrosion Science and Technology
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• 제16권4호
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• pp.167-174
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• 2017

Bicarbonate/carbonate and molybdate anions have been characterized for their inhibitive effect on pitting corrosion of carbon steel in simulated concrete pore solution by using electrochemical tests such as electrochemical impedance (EIS) and linear polarization (LP). It was revealed that bicarbonate/carbonate has a weak inhibitive effect on pitting corrosion that is approximately one order of magnitude lower compared to hydroxide. Molybdate is effective against pitting corrosion induced by the concentration of chloride as low as 113 mM and can increase the pitting potential of a previously pitted sample to the oxygen evolution potential by the concentration of molybdate as much as 14.6 mM only. The formation of a $CaMoO_4$ film on the surface hinders the reduction of dissolved oxygen on the steel surface, reducing corrosion potential and increasing the safety margin between corrosion potential and pitting potential further. In addition, pore-plugging by $FeMoO_4$ as a type of salt film within pits increases the likelihood of repassivation.

• 방사성폐기물학회지
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• 제8권3호
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• pp.247-260
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• 2010

한국원자력연구원 처분시스템개발과제에서는 처분용기 재료로 개발중인 저온분사코팅 구리에 대한 틈새부식(Crevice Corrosion) 시험을 실시하였다. 본 시험을 통하여 틈새에서의 부식의 발생여부와 발생되는 시점인 재부동태 전위(Repassivation Potential)를 측정하고자 하였다. 틈새부식 시험 방법으로 (1) ASTM G61-86 : Cyclic Potentiodynamic Polarization Measurements, (2) SWRI의 Potentiodynamic Polarization plus intermediate Potentiostatic Hold method, 그리고 (3) ASTM G192-08 (THE method) :Potentiodynamic- Galvanostatic -Potentiostatic Method 등의 3가지 방법을 소개하였다. 실제 저온분사 코팅구리의 부식시험에서는 ASTM G61-86에 따라서 틈새부식장치를 설치하고, 저온분사코팅구리가 KURT 지하수를 모사한 용액에서 어떻게 틈새부식이 일어나는지 살펴보았다. 전기적 부식조건으로는 Cyclic Polarization Test, Potentiostatic Polarization Test, 및 Electrochemical Impedance Spectroscopy 등을 사용하였다. 그리고 부식이 된 시편에 대해 Profilometer Measurement를 통해 실제 부식표면의 높낮이를 조사하여 틈새부식 유무를 관찰하였다. 최종적인 결론에서는 저온분사코팅구리는 틈새부식을 나타나지 않는다는 것을 확인할 수 있었다. 그리고 시험에 사용된 세종류의 구리에 대한 상대적인 부식평가를 한 결과, 부식전위를 나타내는 개방회로(Open Cell)에서의 전위는 구리의 제조방식과 상관없이 구리의 순도가 높을수록 높은 값을 보이는 것을 확인할 수 있었다. 결론적으로 KURT 심층지하수 조건에서는 구리는 틈새부식이 발생되지 않는다고 결론지었다.

• 수산해양기술연구
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• 제39권4호
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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.

• Journal of Electrochemical Science and Technology
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• 제7권1호
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• pp.58-67
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• 2016

The corrosion behavior of duplex stainless steel AISI 2205 was investigated in ethylene glycol-water mixture in the presence of 50 W/V % LiBr at different concentrations and different temperatures. Cyclic polarization, impedance measurements and Mott-Schottky analysis were used to study the corrosion behavior the semi conductive properties of the passive films. The results showed that with increasing in the ethylene glycol concentration to 10 V/V%, the corrosion rate of the steel alloy substrate increased. In higher concentrations of ethylene glycol, corrosion current of steel decreased. The results of scanning electron microscopy of electrode surface confirmed the electrochemical tests. Electrochemical experiment showed that duplex steel was stable for pitting corrosion in this environment. The increase in the ethylene glycol concentration led to increasing the susceptibility to pitting corrosion. The corrosion current increased as the temperature rise and also pitting potentials and repassivation potentials shifted towards the less positive values as the temperature increased. According to Mott-Schottky analysis, passive films of stainless steel at the different temperatures showed both n-type and p-type semiconductor behavior in different potential.

• 한국표면공학회지
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• 제38권6호
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• pp.227-233
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• 2005

Electrochemical characteristics of welded stainless steels containing Ti have been studied by using the electrochemical techniques in 0.5 M $H_2SO_4$+0.01 M KSCN solutions at $25^{\circ}C$. Stainless steels with 12 mm thick-ness containing $0.2{\~}0.9 wt\%$ Ti were fabricated with vacuum melting and following rolling process. The stainless steels were solutionized for 1hr at $1050^{\circ}C$ and welded by MIG method. Samples were individually prepared with welded zone, heat affected zone, and matrix for intergranular corrosion and pitting test. Optical microscope, XRD and SEM are used for analysing microstructure, surface and corrosion morphology of the stainless steels. The welded zone of the stainless steel with lower Ti content have shown dendrite structure mixed with $\gamma$ and $\delta$ phase. The Cr-carbides were precipitated at twin and grain boundary in heat affected zone of the steel and also the matrix had the typical solutionized structure. The result of electrochemical measurements showed that the corrosion potential of welded stainless steel were Increased with higher Ti content. On the other hand, reactivation($I_r$), passivation and active current($I_a$) density were decreased with higher Ti content. In the case of lower Ti content, the corrosion attack of welded stainless steel was remarkably occurred along intergranular boundary and ${\gamma}/{\delta}$ phase boundary in heat affected zone.

• Corrosion Science and Technology
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• 제21권2호
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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.

• Corrosion Science and Technology
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• 제23권4호
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• pp.255-265
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• 2024

Duplex stainless steels (UNS S32205, UNS S32750) are used in various environments. The potentiodynamic polarization tests were conducted at 30 ℃ in order to study the electrochemical corrosion behaviors of duplex stainless steels under different seawater concentrations (fresh water, seawater, mixed water). The results of Tafel analysis in seawater showed that UNS S32205 and UNS S32750 had the highest corrosion current densities at 6.12 × 10^-4 mA/cm² and 5.41 × 10^-4 mA/cm², respectively. The pitting potentials of UNS S32205 and UNS S32750 were comparable to or higher than the oxygen evolution potential in fresh water, mixed water, and seawater. The maximum damage depths and surface damage ratio caused by pitting corrosion increased with chloride concentration. The synergy effect of molybdenum and nitrogen enhances the concentration of Mo, Ni, and Cr at the interface of the metal-electrolyte. In particular, in the case of nitrogen, NH₃ and NH₄⁺ are formed to compensate for the pH drop in the pitting region, thereby strengthening the repassivation of the film. The excellent corrosion resistance of UNS S32750 is attributed to the strengthening effect of the chromium oxide film due to the presence of molybdenum and nitrogen.

• 콘크리트학회논문집
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• 제29권1호
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• pp.109-116
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• 2017

본 연구에서는 콘크리트 중의 철근부식의 보수로 전기방식법을 적용할 경우의 탈염, 부식복원 및 구조거동을 효과적이고 정량적으로 평가하였다. $160{\times}160{\times}1000mm$의 콘크리트 시편을 제작하였으며 피복두께 20 mm의 원형철근 3본을 매립하였으며 콘크리트 타설 시 염소이온 5.0%를 혼입하여 철근부식을 가속한 뒤 전기방식을 인가하였다. 전기방식 전류는 직류 $750mA/m^2$를 2, 4, 8주간 인가하였다. 결과로서 탈염효과는 인가 기간에 따라 증가하였으며 최대 탈염비는 8주간의 인가 시 64.7-83.7%로 측정되었다. 이는 시멘트계에서 염소이온의 50-60%가 고정화됨을 고려할 때, 일정량의 고정화된 염소이온 역시 탈염된 것으로 판단된다. 또한 부식상태는 8주간의 전기방식 이후에도 $6.5mA/m^2$의 부식 전류 및 330 mV (vs. SCE)의 부식전위를 나타내 여전히 부식이 존재함을 확인하였다. 구조거동에 있어 부식의 증가로 인해 콘크리트의 최대하중은 증가하였으나, 전기방식을 적용함에 따라 오히려 최대하중은 감소하였으나 Control시편보다는 상회한 값을 나타내 전기방식이 구조적 악영향은 없음을 확인하였다.

• Nuclear Engineering and Technology
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• 제27권4호
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• pp.453-462
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• 1995

사용후 핵연료 저장구조재의 구조적 안정성자 관련해서, 감마선 조사 생성물로 알려져 있는 $H_2O$$_2$를 전해질에 주입시키었을 때, $H_2O$$_2$가 저장구조재인 304L스텐리스강의 부식거동에 어떤 영향을 미치는가를 조사하였다. 실험결과, $H_2O$$_2$는 304L 스텐리스강의 부식전위를 상승시키고 Pitting 전위를 감소시킴으로써 부동태 영역을 줄이고 pitting 저항성을 감소시키는 것으로 나타났다. 이는 감마선 조사에 의한 부식 거동 변화와 유사한 결과라고 볼 수 있으며, 또한 산소농도증가에 의한 부식거동 변화와 유사한 결과로 해석되었다. 재부동태형성전위가 $H_2O$$_2$의 존재로 증가하는데, 이로써 응력부식균열임계전위는 약간 상승할 것으로 추론되었다. 그러나, $H_2O$$_2$ 농도가 6.3$\times$$10^{-6}$M 이하로 떨어질 경우, $H_2O$$_2$는 부식거동에 영향을 주지 못했다. 이는 대기압상태에서 용존된 $O_2$환원반응속도에 비해 $H_2O$$_2$환원반응속도가 작기 때문이라고 해석되었다. 중성용액보다 산성 및 염기성 용액에서, $H_2O$$_2$가 부식거동에 미치는 영향이 작아졌는데, 이는 산성용액에서는 높은 H$^{+}$ 농도 때문에, 염기성용액에서는 le Chatelier의 원칙 때문인 것으로 해석되었다.