• Journal of Advanced Marine Engineering and Technology
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• v.39 no.7
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• pp.779-785
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• 2015

Cathodic protection is recognized as the most cost-effective and technically appropriate corrosion prevention method for the submerged zone of offshore structures, ships, and deep-sea facilities. When cathodic protection is applied, the cathodic currents cause dissolved oxygen reduction, generating hydroxyl ions near the polarized surface that increase the interfacial pH and result in enhanced carbonate ion concentration and precipitation of an inorganic layer whose principal component is calcium carbonate. Depending on the potential, magnesium hydroxide can also precipitate. This mixed deposit is generally called "calcareous deposit." This layer functions as a barrier against the corrosive environment, leading to a decrease in current demand. Hence, the importance of calcareous deposits for the effective, efficient operation of marine cathodic protection systems is recognized by engineers and scientists concerned with cathodic protection in submerged marine environments. Calcareous deposit formation on a marine structure depends on the potential, current, pH, temperature, pressure, sea-water chemistry, flow, and time; deposit quality is significantly influenced by these factors. This study determines how calcareous deposits form in sea water, and assesses the interrelationship of formation conditions (such as the sea water temperature and surface condition of steel), deposited structure, and properties and the effectiveness of the cathodic protection.

• Ocean and Polar Research
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• v.29 no.2
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• pp.135-153
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• 2007

Temporal (seasonal) and spatial distributions and variations of various physico-chemical factors (salinity, temperature, pH, DO, COD, SPM, POC, silicate, DIP, DIN) in surface and bottom waters were studied in the coastal environment with typical macro-tidal range and monsoonal weather condition, Gyeonggi Bay, west coast of Korea. Spacial distribution patterns of these factors were generally similar to each other, and appeared to be inversely related to the distribution pattern of salinity, suggesting that water quality of the study area was primarily controlled by the physical mixing process of Han-River freshwater with nearby coastal seawater. During flooding season, silicate- and nitrogen-rich Han River water directly flowed into offshore as far as $20\sim30\;km$ from the river mouth, probably causing serious environmental problems such as eutrophication and unusual and/or noxious algal bloom, etc. Except the surface water during summer flooding season, high concentrations of nutrients appeared generally in dry season, whereas low values in spring, possibly because of the occurrence of spring phytoplankton bloom. On the other hand, nutrient flux through the estuary seems to be primarily depending on river discharge, sewage discharge and agricultural activities, especially during the rainy season. Also, nutrients in this coastal waters are considered to be supplied from the sediments of tidal-flats, which developed extensively around the Han-River mouth, especially during fall and winter of dry and low discharge seasons, possibly due to the stirring of tidal flat sediments with highly enriched pore-water nutrients by storm. And also, COD and DIN concentrations in the study area consistently increased during the last 20 years, probably because of agricultural activities and increasing discharge of industrial and domestic wastes.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.164-164
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• 2017

해양환경 중 많이 사용되는 철강재료들은 그 가혹한 부식환경에 대응하기 위하여 일반적으로 피복 도장방식법이나 음극방식법이 적용되고 있다. 여기서 음극방식법은 선박 및 해양구조물의 해중부 부식에 대해 가장 효과적인 방식법으로 알려져 있다. 한편, 이와 같이 해수 중 철강재에 음극방식을 적용할 경우, 피방식체인 그 강재 표면에 해수 중 용존된 산소의 음극환원 반응이 일어나며 국부적인 알카리 표면 조건을 형성시켜 $Mg(OH)_2$와 $CaCO_3$의 막을 석출시킨다. 이와같이 음극방식 중 형성된 전착물은 방식해야 될 표면적을 감소시켜 방식전류밀도를 감소시키는 효과가 있는 것으로 보고되고 있다. 이렇게 석출된 전착물은 음극표면에 부분적으로 형성되고, 여러 가지 환경 조건 등의 영향을 받아 그 피막의 형성 정도도 가늠하기 어렵기 때문에 음극방식 설계 시 그 정도에 따른 영향을 고려-반영하기가 곤란하다. 또한 이 전착물은 그 형성 메커니즘에 관한 해석이나 강도, 균일한 밀착성, 장기적인 방식효과 및 효율성 등이 아직 충분히 입증되어 있지 않은 실정에 있다. 따라서 본 연구에서는 해수 중 다양한 전착 프로세스에 의해 제작된 전착물의 기간별, 도장코팅 종류별 특성변화를 분석 및 평가하고, 전착물에 의한 희생양극 소모전류 변화 측정 분석을 통해 전착막을 균일하고 치밀하게 형성시키기 위한 최적의 조건을 찾고자 하였다. 또한 석출속도, 밀착성 및 내식특성을 향상시키기 위해 해수 중 기체를 용해시켜 제작한 막의 특성을 분석-평가하였다. 본 연구에 사용된 강 기판은 일반구조용강(KS D 3503, SS400)으로 ${\varnothing}42.7{\times}1,000mm{\times}4.0t$의 형상으로 제작하였다. 인가된 전류밀도는 1, 3 및 $5A/m^2$이고 도장 코팅 종류별 전착 석출물의 형성차이 비교 분석을 위한 실험은 선박 및 해양구조물에 많이 사용되는 Universal Epoxy 도료 2종을 선정하여 진행하였다. 또한 Steel Wire Mesh의 영향을 알아보기 위해 Mesh를 설치하여 실험을 진행하였다. 기간별-도장 종류별 외관관찰, 전착물의 두께 측정, SEM, EDS 및 XRD를 통해 막의 모폴로지, 조성원소 및 결정구조를 분석하였으며, 전착물의 내식성과 내구성을 평가하기 위해 테이핑 테스트(Taping Test) 및 전기화학적 양극분극 시험을 실시하였다. 희생양극 소모율에 대한 전착물의 영향을 확인하기 위해 외부전원을 인가하여 전착 피막을 형성시킨 강 기판에 희생양극을 연결하여 희생양극 소모효율 측정 시험을 진행하였다. 전착물의 석출량은 시간 및 전류밀도의 증가에 따라 비례하여 증가하였으며, 음극전류 인가 시 금속과 용액 계면 사이의 확산층에서 발생한 $OH^-$ 이온으로 인해 금속과 용액 계면 사이 pH가 부분적으로 증가하여 $Mg(OH)_2$ 화합물이 많이 생성되는 것으로 확인되었다. 또한 Mesh의 부착으로 평활하지 않게 형성된 미세한 굴곡구조 및 표면적 증가로 인하여 단계적으로 피복되는데 필요한 시간이 지연되면서 $CaCO_3$에 비해 $Mg(OH)_2$ 화합물이 상대적으로 증가한 것으로 사료된다. $CaCO_3$(Aragonite) 구조는 견고한 피막으로 치밀하고 화학적 친화력이 높아 우수한 밀착성을 보였으며 전착물의 영향으로 양극 전류가 감소하였고, 이로인해 방식전류 절감효과를 얻을 수 있을 것으로 기대된다.

• Journal of Conservation Science
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• v.29 no.2
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• pp.187-196
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• 2013

This study is on the corrosion of iron objects caused by sulfides in undersea environment. The corrosion state of objects in seawater and their damage state after underwater and left in highly humid air were studied. The samples of this study were four iron objects which had been taken out from undersea mud layer located in Taean Mado, Chungcheongnamdo. SEM-EDS and XRD analyse on the objects to check whether they have sulfides or not. The result of analysis suggested that the major component of corrosion product generated in undersea deposit soil is sulfur(S) and iron sulfide(FeS) is formed as sulfide. However, there was no clear corrosion on the surface of objects which was exposed to sea water because of the impact of concretion which covered the surface. In order to check the damage status of iron objects after they had been taken out of sea water, exposure tests in high humidity environment and dehumidified environment were done on the corrosion products. The result of the test suggested that the oxidization of iron sulfide corrosion product makes iron sulfate ($FeSO_4$) and sulfuric acid ($H_2SO_4$) and they can cause secondary corrosion of iron objects. Therefore, it is believed that the iron sulfide corrosion product of iron objects taken out from underwater environment should be removed by all means and the keeping environment of the iron objects should also maintain dehumidified state.

• Journal of the Korea Organic Resources Recycling Association
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• v.8 no.1
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• pp.77-82
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• 2000

Seven constructed and three natural tidal flats were compared to evaluate state-of- the-art of creation and restoration technology for tidal flats. parameters studied were physico-chemical and biological characteristics of soils and rate of respiration. The natural tidal flats had higher contents of silts, nitrogen and organic matter compared to the constructed ones. The natural ones had reductive Bone below 2 cm whereas the constructed ones had oxidative zone from the surface to below 20 cm. The bacterial population in the soil of the constructed tidal flats was one to two magnitudes lower than that in the natural ones. Biomass of macrobenthos and microbial respiration rate, however, were not different significantly between the natural and the constructed tidal flats. The purification capacity by diatom+bacterial+meiobenthos and macrobenthos in the constructed tidal flats was higher than that in the natural ones due to deeper permeable layer for purification in the constructed tidal flats. There was an exceptional constructed tidal flat with similar physico-chemical and biological characteristics to natural ones. Shearing stress to the surface of the tidal flat by the flow of seawater was as low as that of natural ones. These hydraulic conditions seemed to be a controlling factor on structures and functions of tidal flats. The control of hydraulic condition seemed to be one of the most important factors to create natural-like tidal flats.

• Korean Journal of Environmental Biology
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• v.17 no.1
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• pp.1-9
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• 1999

Numerous observations revealed strong evidence of increased middle ultraviolet radiation or UV-B (280 ~ 320 nm) at the earth's surface resulting from stratospheric ozone depletion. UV is the waveband of electromagnetic radiation which is strongly absorbed by nucleic acids and proteins, thus causing damage to living systems. It has been recorded in the East Sea, Korea that solar UV-B impinging on the ocean surface penetrates seawater to significant depths. Recent researches showed that exposure to UV-B for as short as 2h at the ambient level (2.0 Wm$^{-2}$) decreased macroalgal growth and photosynthesis and destroyed photosynthetic pigments. These may suggest that UV-B could be an important environmental factor to determine algal survival and distribution. Some adaptive mechanisms to protect macroalgae from UV-damage have been found, which include photoreactivation and formation of UV-absorbing pigments. Post-illumination of visible light mitigated UV-induced damage in laminarian young sporophytes with blue the most effective waveband. The existence of UV-B absorbing pigments has been recognized in the green alga, Ulva pertusa and the red alga, Pachymeniopsis sp., which is likely to exert protective function for photosynthetic pigments inside the thalli from UV-damage. Further studies are however needed to confirm that these mechanisms are of general occurrence in seaweeds. Macroalgae together with phytoplankton are the primary producers to incorporate about 100 Gt of carbons per year, and provide half of the total biomass on the earth. UV-driven reduction in macroalgal biomass, if any, would therefore cause deleterious effects on marine ecosystem. The ultimate impacts of increasing UV-B flux due to ozone destruction are still unknown, but the impression from UV studies made so far seems to highlight the importance of setting up long-term monitoring system for us to be able to predict and detect the onset of large -scale deterioration in aquatic ecosystem.

• Korean Journal of Environmental Biology
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• v.25 no.4
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• pp.313-318
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• 2007

Monitoring for the quality of coastal water is necessary to improve its biological resources and to maintain healthy environments. We measured the concentrations of phenols, nine polychlorinated biphenyls (PCBs), tributyltin (TBT) in surface water at 5 stations and the concentrations of mercury (Hg), chromium (Cr (VI)), cadmium (Cd), lead (Pb) in surface water of 10 stations in Tongyeong marine ranching ground of Korea in August, 2003. The concentrations of analytes were determined as follows: phenols: 1.6$\sim$2.8 ppb, PCBs: not detected (ND), Hg: <0.1 ppb, Cr (VI): 0.01$\sim$5.32 ppb, Cd: ND$\sim$0.41 ppb and Pb: 0.43$\sim$2.60 ppb. These concentrations satisfied the standards of human health protection in coastal water by Ministry of Environment, Republic of Korea as follows: phenols; 5 ppb, PCBs: 0.5 ppb, Hg: 0.5 ppb, Cr (VI): 50 ppb, Cd: 10 ppb and Pb: 50 ppb. TBT was not listed in the standards. The concentrations of Sn in TBT analyzed in sea water of Tongyeong marine ranching ground were in the range of ND$\sim$0.0273 ppb which are similar with the values of 8$\sim$35 ng Sn $L^{-1}$ (0.008$\sim$0.035 ppb) in Chinhae Bay studied by Shim et al.. Therefore, the quality of sea water in Tongyeong marine ranching ground was safe enough to protect human health.

• Journal of the Mineralogical Society of Korea
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• v.25 no.2
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• pp.63-76
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• 2012

Tachylite, black basaltic glass formed by the rapid cooling of molten basalt, locally occurs at the Basaltic Agglomerate Formation (BAF), the lowest formation of Ulleung Island. The purposes of this study are to characterize the occurrence and mineralogy of tachylite and to elucidate its formation condition, with emphasis on its fracture pattern, which can serve as implications for the early volcanic activity of Ulleung Island. To this end, we investigated the occurrence pattern of tachylite in the field and carried out mineralogical analyses using optical microscope, XRD, EPMA, and SEM. Tachylite occurs at the chilled margin of basic dikes which are distributed in Naesujeon, Dodong and Jeodong seasides, Turtle Rock, and Yaerimwon, whose widths vary from several cm to 10 cm. It is evident that the outer surface of tachylite is dense and smooth, whereas the inner surface, if fractured, is characterized by conchoidal fracture. The matrix of tachylite consists of amorphous, glass and some fine-grained phenocrysts present in tachylite include biotite, anorthoclase, sanidine, plagioclase, hornblende, and Fe-Ti oxides. The fracture patterns characteristic of tachylite are subrounded, oval, or less commonly polygonal, bounded by joints to form globule or lump. Taking into account texture and mineralogy, tachylite is interpreted to have undergone little subsequent alteration at low temperature via hydration or hydrolysis that could form clay minerals after it was formed. Because tachylite with peculiar fractures occurs as dikes in a close association with BAF, its presence is considered as reliable evidence that when tachylite formed, the most part of BAF was still under subaqueous conditions, or at least saturated with seawater.

• Ecology and Resilient Infrastructure
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• v.2 no.1
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• pp.64-79
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• 2015

We investigated the tidal current, hydrographic data, and benthic environment of major sea cucumber (Holothuroidea, de Blainville, 1834) habitats in Baengnyeongdo, Jindo and Uljin to understand the optimal environmental or ecological habitat for sea cucumbers. The three study areas were characterized by a cold-water mass of temperatures ranging $12{\sim}18^{\circ}C$, with an active circulation between the surface and deep waters. According to an analysis of the tidal current map, a strong flow velocity of $100{\sim}120cm\;s^{-1}$ appeared in Baengnyeongdo and Jindo. The three sea cucumber habitats showed the common characters of a bottom sediment composed of sand-silt, a diverse seaweed colony and benthic organisms, and boulders and rocks which provide a hideout for the organisms. We aimed to draw the optimal habitat condition for sea cucumbers in Korea, and the result showed that the low water temperature, rapid water flow, active vertical mixing between surface and deep waters, bottom composed by sand-silt, large rocks, and diverse seaweed colony and benthic organism were important factors. The optimal habitat for Juvenile sea cucumbers was the intertidal areas characterized by a muddy bottom, reef, and seaweed. The optimal habitat for adult sea cucumbers was characterized by a place where sand and mud are mixed, and the body size of the sea cucumber was proportional to water depth, and the relatively large boulders and rocks compared to the intertidal area.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.116-116
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• 2018

부식은 재료와 사용 환경과의 상호작용에 의한 결과로서 일반적으로 두께의 감소와 균열의 발생 및 파손 등의 문제로 나타난다. 특히 사용환경 중에서 해수 분위기는 금속의 부식에 가장 유리한 조건이다. 따라서 해양환경 중 항만이나 조선 및 해양 산업 등에 많이 이용되는 강 구조물은 이에 대응하기 위하여 도장방식이나 음극방식을 사용하고 있다. 여기서 음극방식은 피방식체를 일정전위로 음극 분극하는 원리로써 외부전원을 인가하거나 비전위의 금속을 전기적으로 연결하여 방식하는 방법이다[1]. 한편, 해수 중에서 이와 같은 원리로 음극방식 할 경우에는 피방식체인 강재표면에 부분적으로 칼슘 또는 마그네슘 화합물 등의 생성물이 부착하는 현상을 볼 수 있게 된다. 이와 같이 수산화마그네슘($Mg(OH)_2$)및 탄산칼슘($CaCO_3$)을 주성분으로 하여 석출되는 석회질 피막(calcareous deposits)은 피방식체에 유입되는 음극방식 전류밀도를 감소시켜 주거나 물리적 장벽의 역할을 함으로써 외부의 산소와 물 등 부식환경으로부터 소지금속을 보호한다[2]. 그러나 석회질 피막은 소지금속과의 결합력, 막의 균일한 분포, 내식성 및 제작시간의 단축 등 해결해야 할 과제가 있다. 또한 여러 가지 환경 조건 등의 영향을 받아 그 피막의 형성 정도도 가늠하기 어렵기 때문에 음극방식 설계 시 그 정도에 따른 영향을 고려-반영하기가 곤란하다. 따라서 본 연구에서는 석출속도, 밀착성 및 내식특성을 향상시키기 위해 전착프로세스를 통해 해수 중 기체를 용해시켜 석회질 피막을 제작하고 막의 결정구조 제어 및 특성을 분석-평가하였다. 본 연구에 사용된 강 기판(Steel Substrate)은 일반구조용강(KS D 3503, SS400)을 사용하였으며, 외부전원은 정류기(Rectifier, xantrex, XDL 35-5T)를 사용하여 3 및 $5A/m^2$의 조건으로 인가하였다. 양극의 경우에는 해수에 녹아있는 이온 이외에 다른 성분들이 환원되는 것을 방지하기 위해 불용성 양극인 탄소봉(Carbon Rod)을 사용하였다. 이때 석출속도, 밀착성 및 내식특성 향상을 위해 해수에 주입한 기체의 양은 0.5 NL/min였으며, 기판 근처에 고정하여 음극 부근에서의 반응을 유도하였다. 각 조건별로 제작된 막의 표면 모폴로지, 조성원소 및 결정구조 분석을 실시하였으며, 석회질 피막의 밀착성과 내식특성을 평가하기 위해 규격에 따른 테이핑 테스트(Taping Test, ISO 2409)와 3 % NaCl 용액에서 전기화학적 양극 분극 시험을 진행하여 제작된 막의 내구성과 내식성을 분석-평가하였다. 시간에 따른 전착막의 외관관찰 결과 전류밀도의 증가와 함께 상대적으로 많은 피막이 형성되었고, 용해시킨 기체에 의해 더 치밀하고 두터운 피막이 형성됨을 확인할 수 있었다. 성분 및 결정구조 분석 결과 $Mg(OH)_2$ 성분의 Brucite 및 $CaCO_3$ 성분의 Calcite 및 Aragonite 구조를 확인하였으며, 용해시킨 기체의 영향으로 $CaCO_3$ 성분의 Aragonite 구조가 상대적으로 많이 검출되었다. 밀착성 및 내식성 평가를 실시한 결과 해수 중 용해시킨 기체에 의해 제작한 시편의 경우 견고하고 화학적 친화력이 높은 Aragonite 결정이 표면을 치밀하게 덮어 전해질로부터 산소와 물의 침입을 차단하는 역할을 하여 기체를 용해시키지 않은 3 및 $5A/m^2$ 보다 비교적 우수한 밀착성 및 내식 특성을 보이는 것으로 사료된다.