• Journal of Conservation Science
• /
• v.26 no.2
• /
• pp.109-120
• /
• 2010

Four gilded bronze objects and a gilded silver object were examined for elemental diffusion between the gilding layer and the mating matrix. The gilded bronzes consist of three objects from three different historical periods, the Korean Three Kingdoms period, the Koryo and the Choseon periods and one from an unknown period. The gilded silver was from the Koryo period. The amalgam process seems to have been the major technique employed for all of them in gilding. The occurrence of substantial diffusion was observed in all but the anonymous object, particularly in the Choseon artifact where evidence was found that the diffusion phenomenon was intentionally utilized in gilding. The gold content in the gilded bronzes decreases gradually from surface to interior while the copper content increases to the interior, making it difficult to locate the boundary between the gilding layer and the matrix. This gradual change in composition must have resulted from elemental diffusion at elevated temperatures. The oxygen content negligible in the gilding layer precludes the possibility of corrosion being responsible for the varying composition. It is observed that non-uniform diffusion caused variation of colors in the surface of gilded bronzes. The change of colors induced by diffusion, which is always accompanied by the unique surface morphology and chemical compositions, is distinguished from the color change by corrosion. In the gilded silver object, diffusion of mercury was observed along with that of gold and silver.

• Journal of the Korean Electrochemical Society
• /
• v.6 no.4
• /
• pp.250-254
• /
• 2003

In this study, the IR drop theory was adopted to explain the initiation of crevice corrosion in the framework of IR drop in crevice electrolyte. Furthermore, the electrochemical polarization was measured to study the mechanism of crevice corrosion for type STS430 stainless steel. lest method adopts under condition that the size of specimen is $10\times20\times5mm,\;in\;1N\;H_2SO_4+0.1N\;NaCl$ solution, and the artificial crevice gap sizes are three kinds, the Micro capillary tube size is inner diameter 0.04 mm, outer diameter 0.08 mm. Crevice corrosion is measured under the applied voltage of passivation potential -200mV/SCE, resulted from anodic potentio-dynamic polarization to the external surface along the crevice. The potential difference was measured by depth profile by Micro capillary tube which inserted in the crevice. The obtained results of this study showed that 1) As artificial crevice gap size became narrow, the current density was increased, whereas no crevice corrosion was found in the crevice gap size $3\times0.5\times16mm\;in\;1N\;H_2SO_4+0.1N\;NaCl\;solution\;at\;20^{\circ}C$ 2) potential of the crevice was about from -220 to -358mV which is lower than that of external surface potential of -200mV The results so far confirmes that the potential drop(so-called IR drop) in the crevice is one of the major mechanisms the process of crevice corrosion for 430 stainless steel.

• Nuclear Engineering and Technology
• /
• v.25 no.4
• /
• pp.507-514
• /
• 1993

Titanium tubes have recently been used in condensers of nuclear power plants since titanium has very good corrosion resistance to seawater. However, when it is connected to Cu alloys as tube sheet materials and these Cu alloys are connected to carbon steels as water box materials, it makes significant galvanic corrosion on connected materials. It is expected from electrochemical tests that the corrosion rate of carbon steel will increase when it is galvanically coupled with Ti or Cu in sea water and the corrosion rate of Cu will increase when it is coupled with Ti, if this couple is exposed to sea water for a long time. It is also expected that the surface area ratios, R$_1$(surface area of carbon steel/surface area of Ti) and R$_2$(surface area of carbon steel/surface area of Cu) are very important for the galvanic corrosion of carbon steel and that these should not be kept to low values in order to minimize the galvanic corrosion on the carbon steel of the water box. Immersed galvanic corrosion tests show that the corrosion rate of carbon steel is 4.4 mpy when the ratio of surface area of Fe/ surface area of Al Brass is 1 while it is 570 mpy when this ratio is 10$^{-2}$ . The galvanic corrosion rate of this carbon steel is increased from 4.4 mpy to 13 mpy at this area ratio, 1, when this connected galvanic specimen is galvanically coupled with a Ti tube. This can be rationalized by the combined effects of R$_1$ and R$_2$ on the polarization curve.

• Corrosion Science and Technology
• /
• v.8 no.1
• /
• pp.27-39
• /
• 2009

Non metallic composite materials, for example, GECM(graphite epoxy composite material) show high specific strength because of low density. These kinds of non metallic composite materials improved the structural effectiveness and operation economics. However, if these materials contacted several metals, corrosion can be arisen since non metallic composite materials have electrical conductivity. This paper dealt with galvanic corrosion between graphite epoxy composite material and several metals. Base on the electrochemical galvanic corrosion test between GECM and metals, corrosion current of carbon steel and aluminium increased with time but corrosion current of stainless steels and titanium decreased and galvanic potential increased. This behavior shows the galvanic corrosion depends upon the presence of passive film. Also, galvanic effect of GECM coupled with ferrous alloys and non-ferrous alloys was lower than that of 100% graphite, which is attributed to lower exposed area of graphite fiber in the GECM than apparent area of the GECM specimen used for the calculation of galvanic current in this work.

• Applied Chemistry for Engineering
• /
• v.4 no.4
• /
• pp.692-700
• /
• 1993

Corrosivities and catalytic activities of platinum-transition metal alloy catalyses loaded on carbon substrate and were studied by electrochemical method using a unit cell. And the analysis of Pt-alloy catalyst was conducted by x-ray diffractometer. Among the catalysts, the Pt-Mo/carbon, Pt-Fe-Co/carbon and Pt-Fe/carbon catalyst showed more excellent cathodic current densities than others. It was found that most of cathodic current density for the Pt-Mo/carbon electrode was $120mA/cm^2$. The current density of the Pt-Fe-Co/carbon was much higher than that of Pt/carbon, reaching $200mA/cm^2$.

• Corrosion Science and Technology
• /
• v.9 no.3
• /
• pp.129-136
• /
• 2010

The corrosion behaviors of 316L stainless steel were investigated in simulated anodic and cathodic environments for proton exchange membrane fuel cell (PEMFC) by using electrochemical measurement techniques. Interfacial contact resistance(ICR) between the stainless steel and gas diffusion layer(GDL) was also measured. The possibility of 316L was evaluated as a substitute material for the graphite bipolar plate of PEMFC. The value of ICR decreased with an increase in compaction stress(20 N/$cm^2$~220 N/$cm^2$) showing the higher values than the required value in PEMFC condition. Although 316L was spontaneously passivated in simulated cathodic environment, its passive state was unstable in simulated anodic environment. Potentiostatic and electrochemical impedance spectroscopy (EIS) measurement results showed that the corrosion resistance in cathodic condition was higher and more stable than that in anodic condition. Field emission scanning electron microscopy (FE-SEM), and inductively coupled plasma(ICP) were used to analyze the surface morphology and the metal ion concentration in electrolytes.

• Journal of ILASS-Korea
• /
• v.16 no.2
• /
• pp.82-89
• /
• 2011

When pipe components made of carbon steel in nuclear, fossil, and industry plants are exposed to flowing fluid, wall thinning caused by FAC(flow accelerated corrosion) can be generated and eventually ruptured at the position of pressure boundary. The aim of this study is to identify the locations at which local wall thinning occurs and to determine the turbulence coefficient related to local wall thinning. Experiment and numerical analyses for the tee sections of down scaled piping components were performed and the results were compared. In particular, flow visualization experiment which was used alkali metallic salt was performed to find actual location of local wall thinning inside tee components. In order to determine the relationship between turbulence coefficients and local wall thinning, numerical analyses were performed for tee components in the main feedwater systems. The turbulence coefficients based on the numerical analyses were compared with the local wall thinning based on the measured data. From the comparison of the results, the vertical flow velocity component(Vr) flowing to the wall after separating in the wall due to the geometrical configuration and colliding with the wall directly at an angle of some degree was analogous to the configuration of local wall thinning.

• New & Renewable Energy
• /
• v.2 no.4 s.8
• /
• pp.102-106
• /
• 2006

에탄올은 금속, 고무 수지를 부식시키고 열화시키기 때문에 FFV 등 알코올 대응차량이 아닌 경우 에탄올 허용도가 제한되고 있으며, 물과의 상호용해성과 흡습성으로 수분혼입에 의한 상분리가 발생하여 혼합가솔린의 유통에서의 취급에 어려움이 야기되고 있다. 또한, 에탄올은 가솔린과 혼합되면 공비현상으로 인하여 50% 유출온도가 크게 떨어지고 증기압이 7kPa 정도 상승을 초래하는 점도 간과하지 않을 수 없다. 따라서, 자동차용휘발유에 에탄올을 혼입하여 사용할 경우, 가솔린기재를 적절히 선택하여 적정품질을 유지하여야 하며 무엇보다도 에탄을 혼입농도에 따른 저장탱크와 주유기 등의 부품에의 영향과 저장시의 상분리 문제를 충분히 규명하여 유통인프라에서의 적절한 대응책이 마련되어져야 한다. 유통 인프라 대응을 위해서는 우선 생산단계에서 수분 혼입을 최소화하기 위하여 저유소의 출하지점에서 서브옥탄가솔린과 에탄올을 라인브랜딩에 의해 제조하는 방법이 가장 타당하며, 수송부문에서는 탱크로리 등의 공급라인인 파이프와 실링 재질 등에 대해서 면밀한 검토가 필요하다고 할 수 있다. 주유소에서의 대응은 에탄을 혼합연료와 직접 접촉하는 연료계 등 부품재질을 내부식성의 재질로 변환시켜야 하며, 수분혼입을 최소화하기 위한 이중탱크 설치, 지하탱크 환기구내의 대기벨브 설치 등이 필요하며, 기타, 품질 및 수분관리 대책 등도 마련되어야 할 것이다.

• Corrosion Science and Technology
• /
• v.14 no.5
• /
• pp.226-231
• /
• 2015

In spite of highly advanced paint coating techniques, corrosion damage of marine metal and alloys increase more and more due to inherent micro-cracks and porosities in coatings formed during the coating process. Furthermore, flowing seawater conditions promote the breakdown of the protective oxide of the materials introducing more oxygen into marine environments, leading to the acceleration of corrosion. Various corrosion protection methods are available to prevent steel from marine corrosion. Cathodic protection is one of the useful corrosion protection methods by which the potential of the corroded metal is intentionally lowered to an immune state having the advantage of providing additional protection barriers to steel exposed to aqueous corrosion or soil corrosion, in addition to the coating. In the present investigation, the effect of flow velocity was examined for the determination of the optimum corrosion protection current density in cathodic protection as well as the corrosion rate of the steel. It is demonstrated from the result that the material corrosion under dynamic flowing conditions seems more prone to corrosion than under static conditions.

• Corrosion Science and Technology
• /
• v.9 no.1
• /
• pp.39-47
• /
• 2010

Galvanic coupling between GECM(graphite epoxy composite material) and metallic materials can facilitate corrosion of metals and alloys because GECM is noble and electrically conductive. Galvanic corrosion is affected by many factors including metallic materials, area ratio, surface condition, and corrosivity. This work aims to evaluate the effect of area ratio on galvanic corrosion between GECM and several metals. In the case of glavanic coupling of carbon steel and Al to GECM, corrosion rate increased with increasing area ratio. Corrosion rate of sensitized STS 316S stainless steel decreased a little at an area ratio 1:1 but increased at an area ratio 30:1. It is considered to be due to that area ratio affects galvanic corrosion more in less corrosion resistant alloys. However, in case of STS 316 and Ti, galvanic coupling reduces corrosion rate by the formation of passive film.