• Journal of Advanced Marine Engineering and Technology
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• 제41권3호
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• pp.230-237
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• 2017

본 연구에서는 해상풍력 타워 지지구조물용 강재인 S355ML 강에 대하여 전기화학적 기법으로 전기방식 설계에 필요한 최적 방식전위를 규명하고자 하였다. 동전위분극 실험 결과, 양극분극 곡선 상에서는 부동태 구간은 존재하지 않으며, 음극분극 곡선 상에는 용존산소환원반응에 의한 농도분극 구간과 수소가스 발생에 의한 활성화분극 구간이 관찰되었다. 음극방식 시 방식전위에 해당하는 농도분극 구간은 약 - 0.72 V ~ - 1.0 V의 전위 구간인 것으로 확인되었다. 다양한 전위에서 정전위 실험을 실시한 결과 전류밀도 변화는 시간에 따라 안정화되는 경향을 나타냈다. 1200초 동안 정전위 실험 후 주사전자현미경과 3D 분석 현미경을 이용한 시험편 표면 분석 결과, 양극분극 전위에 해당하는 0 V ~ - 0.50 V의 전위구간에서는 양극용해반응에 의한 부식손상이 관찰되었다. 이에 반해 음극분극 전위 영역에서는 대체적으로 손상이 없는 양호한 표면을 유지하였으며 석회질 피막 형성을 확인할 수 있었다. 연구결과, 농도분극 영역에 해당하는 - 0.8 V ~ - 1.0 V의 전위영역이 S355ML 강의 외부전원법에 의한 음극방식 적용 시 최적 방식 전위 구간으로 사료된다.

• Corrosion Science and Technology
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• 제19권6호
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• pp.288-295
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• 2020

This study investigated the erosion-corrosion characteristics of 5038-H321 aluminum alloy in a natural seawater solution through various electrochemical experiments and flow rate parameters. Cathodic polarization experiments were conducted at flow rates ranging from 4 to 12 knots. Considering the concentration polarization section representing a relatively low current density, the range of the potentiostatic experiment was determined to be -1.6 to -1.0 V. The potentiostatic experiment was conducted at various potentials for 180 minutes in seawater. After the experiment, the corrosion characteristics were evaluated by observing surface morphology and measuring surface roughness. As a result, as the applied potential was lower, the amount of calcareous deposits increased and the roughness tended to increase. On the other hand, it was confirmed that the roughness was larger in the static condition than the flow rate condition due to the influence of the flow velocity. Variations in the chemical composition with flow rate variations were analyzed by energy-dispersive spectroscopy (EDS). In conclusion, the cathodic potential of AA5083-H321 in seawater was determined to be -1.0 V.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
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• pp.395-400
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• 2005

The ship hull part is always exposed to severe corrosive environments. Therefore, it should be protected in appropriate ways to reduce corrosion problems. So there are two effective methods in order to protect the corrosion of ship hull. One is the paint coating as a barrier between steel and electrolyte (seawater) and the other is the cathodic protection(CP) supplying protection current. In the conventional design process of the cathodic protection system the required current densities of protected materials have been used. However, the anode position of field or laboratory experiment for obtaining the required current density for CP is significantly different from anode position for real structures. Therefore, the recent CP design must consider the optimum anode position for potential distribution equally over the ship hull. The CP design companies in the advanced countries can obtain the potential distribution results on the cathodic materials by using the computer analysis module. This study would show how to approach the potential analysis in the field of corrosion engineering. The computer program can predict the under protection area on the structure when the boundary condition and analysis procedure are reasonable. In this analysis the polarization curve is converted to the boundary condition in material data.

• 해양환경안전학회지
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• 제18권6호
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• pp.569-576
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• 2012

일반적으로 중성용액 하에서 알루미늄 합금은 부동태피막($Al_2O_3$나 $Al_2O_3{\cdot}3H_2O$)을 형성한다. 그러나, 해수 환경에서 염소이온이 표면에 생성된 부동태 피막을 파괴하여 부식이 발생하게 된다. 본 연구에서는 해수환경 하에서 부식 문제점을 해결하기 위해 Al-4.5%Mg-0.6%Mn 알루미늄 합금에 대하여 정전위 방식 기술을 적용하였다. 분극실험결과, 개로전위보다 귀한 전위에서는 활성 용해 반응이 나타났으며 개로전위 보다 비한 전위에서는 용존산소 환원에 의한 농도 분극과 활성화 분극이 관찰되었다. 정전위 실험결과, 농도 분극에서 활성화 분극으로 전환되는 전위부터 적용 시간이 증가할수록 전착물이 많이 생성되었으며, 부분적으로 전착물과 모재의 계면사이에서 틈부식이 관찰되었다. 전체적으로 정전위 양극분극실험시, 활성용해반응이 발생하여 정전위 방식 기술을 적용하기 어려운 반면, 정전위 음극분극 실험시 방식 전위인 농도분극 범위내에서 적용 시간을 고려하여 최적 방식 조건을 -1.1 V~-0.75 V로 규명하였다.

• 한국표면공학회지
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• 제49권1호
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• pp.26-31
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• 2016

In this paper, the characteristics of a cavitation-erosion damage behavior on the STS 304 and hot-dip aluminized STS 304 under cavitation environment in sea water solution was investigated. The electrochemical experiments were carried out by potential measurement, anodic/cathodic polarization test, Tafel analysis, and also galvanostatic experiment in current density variables for the samples. The apparatus of cavitation-electrochemical experiment was manufactured in compliance with modified ASTM G-32 standard, with the conditions of sea water temperature of $25^{\circ}C$ and the measurement, amplitude of $30{\mu}m$. The damage behavior was analyzed by an observation of surface mophologies and a measurement of damage depth by a scanning electron microscope(SEM) and a 3D microscope, respectively, after electrochemical test. After polarization experiment under cavitation environment, much higher damage depths for the hot-dip aluminized STS 304 were observed comparing to the untreated STS 304. In addition, higher corrosion current density in hot-dip aluminized STS 304 presented than that of untreated STS 304 as a result of Tafel analysis.

• Corrosion Science and Technology
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• 제9권1호
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• pp.48-55
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• 2010

The many vessels are built with FRP(Fiber-Reinforced Plastic) material for small boats and medium vessels. However, FRP is impossible to be used for recyclable material owing to environmental problems and causes large proportion of collision accidents because radar reflection wave is so weak that large vessels could not detect FRP ships during the sailing. Hence, Al alloy comes into the spotlight to solve these kinds of problems as a new-material for next generation instead of FRP. Al alloy ships are getting widely introduced for fish and leisure boats to save fuel consumption due to lightweight. In this study, it was selected 6061-T6 Al alloy which are mainly used for Al-ships and carried out various electrochemical experiment such as potential, anodic/cathodic polarization, Tafel analysis, potentiostatic experiment and surface morphologies observation after potentiostatic experiment for 1200 sec by using the SEM equipment to evaluate optimum corrosion protection potential in sea water. It is concluded that the optimum corrosion protection potential range is -1.4 V ~ -0.7 V(Ag/AgCl) for 6061-T6 Al alloy, in the case of application of ICCP(Impressed current cathodic protection), which was shown the lowest current density at the electrochemical experiment and good specimen surface morphologies after potentiostatic experiment for Al-Mg-Si(6061-T6) Al alloy in seawater environment.

• 한국표면공학회지
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• 제46권6호
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• pp.271-276
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• 2013

The demand for stainless steel is continuously increasing with the development in offshore industry due to its excellent corrosion resistance characteristics. However, it suffers cavitation-erosion in application of high rotating fluid and the damage accelerates in combination with electrochemical corrosion because of Cl-ion in sea water. This paper investigated the complex damage behavior for 431 stainless steel, that is one of martensite stainless steels, through the hybrid test in sea water. Various experiments were carried out, including potential measurement, anodic/cathodic polarization experiment and Tafel analysis. Surface morphology was observed and damage depth was analyzed by SEM and 3D microscope after each experiment, respectively. The results revealed that more active potential was observed under cavitation condition than static condition due to breakdown of passive film and activation of charge transfer, and that higher corrosion current density was obtained under cavitation condition due to synergistic effect of corrosion and erosion.

• Journal of Advanced Marine Engineering and Technology
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• 제13권2호
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• pp.43-63
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• 1989

Various kinds of corrosion prevention methods have been developed. It is known that the method of electrochemical protection is more effective and economical than any other method on the large scale metal structures in corrosive solutions. Strong acid solutions such as nitric and sulfuric acid solutions are often used in industries, and the expensive stainless steel is almost exclusively used for the equipment that comes in contact with such acid solutions. However, it is more reasonable that carbon steel is used rather than stainless steel depending upon concentration of those acid solutions from the economical viewpoint. In this study, the typical strong acid solution such as nitric and sulfuric acid solutions are chosen for the experiment and the selected materials of specimen are the stainless steels of SUS 304L and SUS 316L, the carbon steels of SS 41, SM 50 and RA 32, and highly pure lead. Electrochemical protection diagrams can be drawn with data from the external cathodic and anodic polarization curves of SUS 304L, SUS 316L and SM 50 steels in 5-60% nitric acid solutions and from those polarization curves of SS 41, RA 32, SM 50 and SUS 316L steels, and highly pure lead in 2.5-98% sulfuric acid solutions at the slow scanning rate. The data obtained with using the determination method of the optimum cathodic protection potential, the Tafel extrapolation method and the characteristics of anodic polarization curves. The main results obtained from the diagrams are as follows: 1) In nitric acid solution : (1) Corrosion potentials exist in each of those corrosion zones on the stainless steels in the lower concentration than about 12% solutions and on the high tensile strength steels in the lower concentration than about 30% solutions, but the corrosion current (density) in each zone is small on the above mentioned former steels and large on the latter ones. (2) The stainless steels can be self-passivated in the higher concentration than 15% solutions, and the high tensile strength steels gives rise to the same phenomenon in the higher concentration than 35% solutions. (3) The stainless steels in the lower concentration than 60% solutions and the high tensile strength steels in the higher concentration than 35% solutions can be used without protection, but the latter steels must ve protected anodically in the lower conccentration than about 30% solutions. 2) In sufuric acid solution : (1) The carbon steels can be self-passivated in the higher concentration than 45% solutions, and the SUS 316L steel in higher concentration than 75% solutions and the lead in all concentration solutions also gives rise to the same phenomenon. (2) The lead in the lower concentration than 80% solutions and the SUS 316L steel in the higher concentration than 80% solutions can be used without protection. (3) The carbon steels in the higher concentration than 50% solutions also can be used without protecting economically, but the SUS 316L steel in the 20-70% solutions are considerably corrosive without protecting anodically.

• 한국수산과학회지
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• 제16권3호
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• pp.239-245
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• 1983

Electrochemical adsorption always was accompanied with solvent displacement and relative size factor(x) of adsorbate and solvent and hydrogen coverage(${\theta}$) on the lead anodic film electrode formed in phosphoric acid in NaCl solution and the sea water at $15{\sim}35^{\circ}C$ were studied by means of constant current-potential method and potentiodynamic cathodic polarization method. In this experiment, various constants and thermodynamic quantities calculated from the hydrogen coverage were also described to explain the reactivities of di-iso-butylnitrosoamine(DBNA) and proton ($H^+$) according to the changes of interactions between solute and solvent in the bulk phase and interphase. It was investigated that the average values of relative size factor and the coverage of hydrogen atoms studied with the electrode of lead anodic film formed in phosphoric acid solution in 60mM DBNA+0.5M NaCl and in 60mM DBNA+$6\%0$ sea water were about 11.0 and 0.2 respectively. Hydrogen evolution was electrochemical mechanism because of substitutional adsorption of aromatic substance with their delocalization of electrons, but in the case of non-charge transfer adsorption of aliphatic substance(DBNA) interacting relatively little with the electrode, it was combination mechanism.

• Corrosion Science and Technology
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• 제21권6호
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• pp.503-513
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• 2022

As part of eco-friendly policies, interest in hydrogen vehicles is growing in the automotive industry to reduce carbon emissions. In particular, it is necessary to investigate the application of aluminum alloy for light weight hydrogen valves among hydrogen supply systems to improve the fuel efficiency of hydrogen vehicles. In this research, we investigated mechanical characteristics of aluminum alloys after hydrogen embrittlement considering the operating environment of hydrogen valves. In this investigation, experiments were conducted with strain rate, applied voltage, and hydrogen embrittlement time as variables that could affect hydrogen embrittlement. As a result, a brittle behavior was depicted when the strain rate was increased. A strain rate of 0.05 mm/min was selected for hydrogen embrittlement research because it had the greatest effect on fracture time. In addition, when the applied voltage and hydrogen embrittlement time were 5 V and 96 hours, respectively, mechanical characteristics presented dramatic decreases due to hydrogen embrittlement.