• Journal of the Korean institute of surface engineering
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• v.53 no.5
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• pp.219-226
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• 2020

This paper investigated the characteristics of anodized aluminum 6061-T6 alloy for corrosion and stress corrosion cracking(SCC) under natural seawater. The hard anodizing oxide film formed on the 6061-T6 was a uniform thickness of about 25 ㎛. The corrosion characteristics were performed with a potentiodynamic polarization test. SCC was characterized by a slow strain rate tensile test under 0.005mm/min rate. As a result, the anodizing film showed no significant effect on SCC in the slow strain rate test. However, the corrosion current density of base metal was measured to be approximately 13 times higher than that of the anodized specimen. Therefore, the anodizing film significantly improved the corrosion resistance of 6061-T6 alloy in natural seawater.

• Corrosion Science and Technology
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• v.19 no.6
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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.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.44 no.1
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• pp.1-7
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• 2011

This study examined Tetraselmis sp. JK-46 isolated from seawater from the East Sea. Deep seawater (DSW) had a greater effect on the growth of Tetraselmis sp. JK-46 than surface seawater (SSW). The crude protein, lipid, carbohydrate and ash contents of Tetraselmis sp. JK-46 cultured with DSW were 27.2, 37.1, 13.2 and 26.3 %, respectively, and these values were similar to the results for samples cultured with SSW. The contents of Mg, Ca, Fe and K in the DSW cultured samples were 7080.3, 1009.6, 251.2, and 2749.7 mg/100 g, respectively. The fatty acid compositions of Tetraselmis sp. JK-46 cultured with DSW and SSW were 53.7 and 49.0 % polyunsaturated fatty acids (PUFA) and 25.7 and 30.7 % saturated fatty acids (SFA), respectively. The total amino acid contents of the samples cultured with DSW and SSW were 7392.6 and 6376.0 mg/100 g respectively. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of Tetraselmis sp. JK-46 extracts increased with the concentration of the chloroform and ethyl acetate fractions. The half maximal inhibitiory concentrations ($IC_{50}$) of the chloroform and ethyl acetate fractions of DSW and SSW cultured samples were 1.2 and 2.6 mg/mL, and 3.1 and 3.3 mg/mL, respectively. The ethyl acetate fractions of DSW and SSW cultured samples has anticoagulant activity and the activated partial thromboplastin times (APTT) were 93.4 and 89.3 sec., respectively. The chloroform and ethyl acetate fractions showed antimicrobial activity against Bacillus subtilis, Escherichia coli and Candida albicans.

• Corrosion Science and Technology
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• v.11 no.6
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• pp.263-269
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• 2012

Copper alloys are commonly applied to ship's propellers, pumps and valves which are serviced in seawater due to their good castability and corrosion resistance. In the environment of high flow velocity, however, erosion damage predominates over corrosion damage. In particular, the cavitation in seawater environment accelerates surface damage to copper alloys, resulting in degradation of products and economic losses and also threatening safety. The surface was coated with WC-27NiCr by high velocity oxygen fuel(HVOF) spraying technique to attain durability and cavitation resistance of copper alloys under high velocity/pressure flow. The cavitation test was performed for the WC-27NiCr coating deposited by HVOF in seawater at the amplitude of $30{\mu}m$ with seawater temperature. The cavitation at $15^{\circ}C$ caused exfoliation of the coating layer in 17.5 hours while that of $25^{\circ}C$ caused the exfoliation in 12.5 hours. When the temperature of seawater was elevated to $25^{\circ}C$ from $15^{\circ}C$, more damage was induced by over 160%. Although WC-27NiCr has good durability, corrosion resistance and eletrochemical stability, the cavitation damage rate of the coating layer could remarkably increase at the elevated temperatures under cavitation environments.

• Journal of Ocean Engineering and Technology
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• v.26 no.1
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• pp.78-83
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• 2012

The abundant nutrients contained in deep seawater are delivered by natural upwellings from the deep sea to the surface sea. However, the natural upwelling phenomenon is limited to specific areas of the sea; in other areas, the thermocline separates the surface sea from the lower layer. Thus, the surface layer is often deficient in nutritive salts, causing the deterioration of its primary productivity and ultimately leading to an imbalance in the marine ecosystem. Without a consistent supply of nitrogenous nutritive salts, they are absorbed by phytoplankton, resulting in a considerable problem in primary productivity. To solve this issue, a floating type of artificial upwelling system is suggested to artificially pump up, distribute, and diffuse deep seawater containing rich nutritive salts. The key technologies for developing such a floating artificial upwelling system are a floating offshore structure with a large diameter riser, self-supplying energy system, density current generating system, method for estimating the emission and absorption of CO2, and way to evaluate the primary production variation. Strengthening the primary production of the sea by supplying deep seawater to the sea surface will result in a sea environment with abundant fishery resources.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.41 no.3
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• pp.163-169
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• 2008

This study investigated the quality of salted mackerel prepared with deep seawater concentrate and salt. The quality of the salted mackerel product prepared with deep seawater was compared to that prepared with surface and intermediate seawater salts, sun-dried salt, and refined salt. After preparing the salted mackerel products using the five salts, the products were stored at $4^{\circ}C$ for 35 days. Quality characteristics compared were the acid value (AV), peroxide value (POV), lipophilic browning, volatile basic nitrogen (VBN), pH, viable cell count, and sensory factors. The deep seawater salted mackerel product had the lowest AV, POV, browning value, and viable cell counts, compared to the others, while it had the highest score in the sensory evaluation.

• Corrosion Science and Technology
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• v.23 no.4
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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.

• Corrosion Science and Technology
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• v.19 no.5
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• pp.239-249
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• 2020

The characteristics of cavitation-erosion damage with changes in the amplitude of 5052-O aluminum alloy for ships were investigated in a seawater environment. In the cavitation-erosion experiment, the cavitation environment was created using a vibration-generating device with a piezo-electric effect. The amplitudes of 5 ㎛, 10 ㎛, and 30 ㎛ were created by changing the geometric shape of the cavitation horn. The resistance characteristics of cavitation-erosion damage were evaluated by weight loss and pitting area. The damaged surface was analyzed using scanning electron microscopy (SEM) and 3D optical microscopy. As the amplitude increased, the amount of damage and the area of the damaged surface increased, and the damage was concentrated at the center and edge of the specimen. The pit was created after the initial incubation period with increasing experimental time, and then the pits were merged to grow and propagate into craters, and eventually, the surface was detached and damaged. The cavitation-erosion damage after 30 minutes with amplitude of 10 ㎛ and 30 ㎛ was 1.48 and 2.21 times compared to 5 ㎛, respectively.

• Corrosion Science and Technology
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• v.22 no.2
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• pp.108-114
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• 2023

In this study, anti-corrosion effect was investigated through various electrochemical experiments after applying Al thermal spraying technology to AA5083-H321. Open circuit potential and anodic polarization curves were analyzed through electrochemical experiments in natural seawater. The shape of the surface was observed using a scanning electron microscope (SEM) and a 3D microscope before and after the experiment. Component and crystal structure were analyzed through EDS and XRD. As a result, the surface roughness of AA5083-H321 and the Al thermal sprayed coating layer increased due to surface damage caused by anodic dissolution reaction during the anodic polarization experiment. The corrosion rate of AA5083-H321 was relatively low because the Al thermal spray coating layer contained structural defects such as pores and crevices. Nevertheless, the open circuit potential of the Al thermal spray coating layer in natural seawater was measured about 0.2 V lower than that of AA5083-H321. Thus, a sacrificial anode protection effect can be expected.

• Journal of the Korean institute of surface engineering
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• v.45 no.6
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• pp.278-283
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• 2012

This investigation evaluated the effect of cavitation condition on electrochemical characteristics of 304 stainless steel, which is widely used for marine environment. The cavitation test with time were conducted on 304 stainless steel in seawater solution. Surface morphologies of specimen were observed by scanning electron microscope (SEM) and 3D microscope. Pitting depth, weight loss and damage rate were analyzed after each cavitation experiment. The surface damage was more severe as the current density increased. A dramatical increase in the damage depth and weight loss was observed after 7 hours of cavitation experiment.