• Corrosion Science and Technology
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• 제6권6호
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• pp.291-296
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• 2007

The corrosion of metals and alloys in flowing liquids can be classified into uniform corrosion and localized corrosion which may be categorized as follows. (1) Localized corrosion of the erosion-corrosion type: the protective oxide layer is assumed to be removed from the metal surface by shear stress or turbulence of the fluid flow. A macro-cell may be defined as a situation in which the bare surface is the macro-anode and the other surface covered with the oxide layer is the macro-cathode. (2) Localized corrosion of the differential flow-velocity corrosion type: at a location of lower fluid velocity, a thin and coarse oxide layer with poor protective qualities may be produced because of an insufficient supply of oxygen. A macro-cell may be defined as a situation in which this surface is the macro-anode and the other surface covered with a dense and stable oxide layer is the macro-cathode. (3) Localized corrosion of the active/passive-cell type: on a metal surface a macro-cell may be defined as a situation in which a part of it is in a passivation state and another in an active dissolution state. This situation may arise from differences in temperature as well as in the supply of the dissolved oxygen. Compared to uniform corrosion, localized corrosion tends to involve a higher wall thinning rate (corrosion rate) due to the macro-cell current as well as to the ratio of the surface area of the macro-anode to that of the macro-cathode, which may be rationalized using potential vs. current density diagrams. The three types of localized corrosion described above can be reproduced in a Jet-in-slit test by changing the flow direction of the test liquid and arranging environmental conditions in an appropriate manner.

• Corrosion Science and Technology
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• 제8권2호
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• pp.53-61
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• 2009

본 연구에서는 강교 도장재료로 사용될 수 있는 에폭시 하도 도료를 도포한 시험편을 촉진시험을 통해 열화시킨 후 도막의 외관 평가 및 EIS에 의한 평가를 실시하고, 그 2가지 방법에 대한 비교 분석을 실시하였다. 화상처리 기법에 의해 구한 총 열화 면적율과 열화도 평점 산정 결과를 상호 비교해 본 결과 녹이 발생한 경우가 그렇지 않은 경우보다 열화도 평점이 높게 나타났다. 이는 강교 도장의 열화도 평가 기준에서 단위 열화 면적율당 부여하는 열화도 평점이 박리의 경우보다 녹의 경우가 더 크기 때문이다. 열화 면적율과 EIS 측정 데이터를 비교해 본 결과 녹의 면적율 약 0.1% 이상, 블리스터링의 면적율 약 3% 이상만 되어도 도막의 임피던스는 약 $10^4{\Omega}{\cdot}cm^2$ 혹은 그 이하로 크게 저하되었다. 2개의 시험편을 제외한 모든 시험편에 대해 전하전달저항(charge transfer resistance, $R_{ct}$)과 이중층 정전용량(double layer capacitance, $C_{dl}$) 값이 나타났으며, 이 결과로부터 이들 시험편들은 도막과 강재 계면에 수분이 축적되어 부식이 진행되고 있음을 알 수 있었다. 열화도 평점과 EIS 측정결과를 상호 비교해 본 결과 저주파수(10 mHz)에서의 임피던스 값이 $10^6{\Omega}{\cdot}cm^2$ 이하로 떨어진 경우는 모두 열화도 평점이 10점 이상으로 나타났으며, NORSOK cyclic test 과정에 의해 열화시킨 경우 열화도 평점이 높지 않음에도 불구하고 임피던스는 가장 낮게 나타났다. 이것은 도장계와 열화조건이 주 시험편과 다르기 때문인 것으로 판단되며, 열화조건이 더 가혹하거나 복합적일 경우 외관 상태에 비해 도막의 저항이 더 크게 저하될 가능성이 있다고 생각된다.

• 대한금속재료학회지
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• 제48권6호
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• pp.514-522
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• 2010

Graphite epoxy composite material (GECM) shows high specific strength and its application in the aerospace industry is gradually increasing. However, its application would induce galvanic corrosion between GECM and metallic materials. This work focused on the effects of anodizing and thermal oxidation on galvanic corrosion in a 3.5% NaCl solution between GECM and aluminium and titanium. In the case of anodized aluminium, galvanic corrosion resistance to the GECM was greatly improved by the anodizing treatment regardless of area ratio. In the case of anodized titanium, the anodizing by a formation voltage of 50V increased corrosion resistance of titanium in galvanic tests. Thermal oxidation of titanium also improved corrosion resistance of Ti to GECM.

• 콘크리트학회지
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• 제11권2호
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• pp.221-230
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• 1999

콘크리트 구조물에 균열이 생겨 물과 산소의 침투확산이 용이해 지거나 또는 외부로부터 염소이온과 같은 염화물이 침투확산되어 콘크리트 중의 철근까지 도달할 경우 및 콘크리트의 중성화가 철근위치까지 진행될 경우 철근의 부동태 피막은 파괴되어 부식이 급진전 되며 콘크리트의 박리 및 탈락현상이 수반될 뿐만 아니라 구조물의 내구성이 크게 저하된다. 본 연구에서는 콘크리트 중의 철근부식을 억제하기 위한 한 방안으로 적용되는 전기방식의 이론적인 고찰과 콘크리트 내부에 다량의 염화물을 함유시키거나 또는 균열을 발생시킨 시험체에 대하여 외부전원법을 활용한 실내실험을 실시하여 철근의 방식효과에 대해 고찰하였다. 외부전원법에 의한 전기방식을 실시하여 복극량을 측정한 결과 대상 시험체 모두 NACE의 방식기준을 만족하였으며, 부식면적율의 측정결과 34 ~84%, 단면감소의 경우 84 ~ 86%의 방식효과를 확인하였다.

• Corrosion Science and Technology
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• 제12권3호
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• pp.125-131
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• 2013

The most common pipe wall thinning degradation mechanisms that can occur in the steam and feedwater systems are FAC (Flow Acceleration Corrosion), cavitation, flashing, and LDIE (Liquid Droplet Impingement Erosion). Among those degradation mechanisms, FAC has been investigated by many laboratories and industries. Cavitation and flashing are also protected on the piping design phase. LDIE has mainly investigated in aviation industry and turbine blade manufactures. On the other hand, LDIE has been little studied in NPP (Nuclear Power Plant) industry. This paper presents the development of prediction system for pipe wall thinning caused by LDIE in terms of erosion rate based on air-water ratio and material. Experiment is conducted in 3 cases of air-water ratio 0.79, 1.00, and 1.72 using the three types of the materials of A106B, SS400, and A6061. The main control parameter is the air-water ratio which is defined as the volumetric ratio of water to air (0.79, 1.00, 1.72). The experiments were performed for 15 days, and the surface morphology and hardness of the materials were examined for every 5 days. Since the spraying velocity (v) of liquid droplets and their contact area ($A_c$) on specimens are changed according to the air-water ratio, we analyzed the behavior of LDIE for the materials. Finally, the prediction equations(i.e. erosion rate) for LDIE of the materials were determined in the range of the air-water ratio from 0 to 2%.

• 한국구조물진단유지관리공학회 논문집
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• 제14권2호
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• pp.75-81
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• 2010

본 연구에서는 콘크리트 배합과 혼화재 첨가에 의한 콘크리트 물성 변화가 매립 철근의 부식을 평가하는 전기-화학적 기법에 미치는 영향을 확인하고 그 원인을 분석하였다. 연구 결과 자연전위법은 철근의 부식면적이 10% 이하일 경우 콘크리트 내부 물성에 영향을 받는 것으로 나타났으며, 혼화재가 혼입된 경우에는 높은 부식상태의 철근에 대한 정성적인 부식평가가 가능하였다. 또한 분극저항법은 부식량이 10% 이하로 미미한 경우에도 콘크리트 물성의 영향을 받지 않았으나, 혼화재가 혼입된 경우에는 비슷한 철근부식면적의 OPC보다 부식정도를 과소평가하는 것으로 나타났다.

• 한국건축시공학회지
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• 제4권1호
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• pp.119-126
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• 2004

Generally, reinforced concrete is one of the most commonly used structural materials and it prevents corrosion of steel bar by high pH of interior, But, as time elapsed, reinforced concrete structure become deteriorated by many of combined deterioration factors and environmental conditions. And, there are large number of deteriorate mechanism of the reinforced concrete structure and it acts complexly. It is recognized that steel bar corrosion is the main distress behind the present concern regarding concrete durability. In this study, to institute combined deterioration environments, established acceleration condition and cycle for combined deterioration environments has a resemblance to environments which are real structures placed. After that to confirm corrosion properties of reinforced concrete due to permeability with covering depth and types of surface cover under combined deterioration environments, measured carbonation velocity coefficients, chloride ion diffusion coefficients, water absorption coefficients, air permeability coefficients and electric potential, corrosion area ratio, weight reduction, corrosion velocity of steel bar. The results showed that an increase in age also decrease carbonation velocity coefficients, increase Chloride ion diffusion coefficients and increases water absorption coefficients. As well, an increase in age also increases corrosion of steel bar. Data on the development of corrosion velocity of steel bar with types of surface cover made with none, organic B, organic A, inorganic B, and inorganic A is shown. As well, permeability and corrosion velocity of steel bar with covering depth is superior to 10mm than 20mm. And it is confirmed permeability and corrosion properties of steel bar are closely related.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.225-228
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• 2006

To clarify the one body behavior of reinforcing bar and concrete, it is important to investigate bond characteristics between two materials. Bond strength is decided by applied force and interface area between reinforcing bar and concrete. And, the resultant force of chemical adhesive force, frictional force, and mechanical interaction are to be main factors. Property of concrete influences on chemical adhesive force and frictional force; bond strength is decreased by corrosion of reinforcing bar, as the result, durability is also decreased. In this study, to confirm bond characteristics with property of concrete, w/c ratio and blending of mineral admixture were selected as the main test parameters. The results obtained from this study will be used as the basic data for bond characteristics with corrosion.

• 한국항해학회지
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• 제22권3호
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• pp.65-72
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• 1998

최근에는 고장력강의 사용증대와 함께 구조부재가 경량화추세에 있으며 이상부식이 발생한 구조부재는 강도가 크게 저하되리라 예상되지만 지금까지 이에 관한 연구가 거의 없는 상태이다. 본 연구에서는 단소성대변형유한요소법을 적용하여 국부이상부식을 가진 판이 면내압축하중을 받을 경우에 압축최종강도에 미치는 부식부영역의 크기. 부식부의 판두께 감소량 및 세장비의 영향에 대하여 연구하였다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.67-67
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• 2018

The 5xxx series aluminum alloys are recently used in not only marine system but also automotive area because of a low density material, good mechanical properties and better resistance to corrosion. However, Aluminum alloys are less resistant than the purest aluminum such as 1xxx aluminum alloy. Electrochemical anodization technique has attracted in the area of surface treatment because of a simple procedure, a low-cost efficiency than other techniques such as lithography and a large volume of productivity, and so on. Here, The relationship between the corrosion behavior and the thickness of aluminum anodic oxide have been studied. Prior to anodization, The 5052 aluminum sheets ($30{\times}20{\times}1mm$) were degreased by ultra-sonication in acetone and ethanol for 10 minutes and eletropolished in a mixture of perchloric acid and ethanol (1:4, volume ratio) under an applied potential of 20V for 60 seconds to obtain a regular surface. During anodization process, Aluminum alloy was used as a working electrode and a platinum was used as a counter electrode. The two electrodes were separated at a distance of 5cm. The applied voltage of anodization is conducted at 40V in a 0.3M oxalic acid solution at $0^{\circ}C$ with appropriate magnetic stirring. The surface morphology and the thickness of AAO films was observed with a Scanning Electron Microscopy (SEM). The corrosion behavior of all samples was evaluated by an open-circuit potential and potentio-dynamic polarization test in 3.5wt% NaCl solution. Thus, The corrosion resistance of 5052 aluminum alloy is improved by the formation of an anodized oxide film as function of increase anodization time which artificially develops on the metal surface. The detailed electrochemical behavior of aluminum 5052 alloy will be discussed in view of the surface structures modified by anodization conditions such as applied voltages, concentration of electrolyte, and temperature of electrolyte.