• 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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• 제29권5호
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• pp.495-501
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• 2005

Al is a active metal that owes its resistance to a thin, protective, barrier oxide surface layer, which is stable in air and neutral aqueous solution. Thus Al alloys are widely used in architectural trim. cold & hot-water storage vessels and piping. However Al and most of its alloy may corrode with some forms such as pitting corrosion, intergranular corrosion and galvanic corrosion in the case of exposure to various industrial and marine atmosphere. Therefore a correct evaluation of corrosion resistance for their Al and Al alloys may be more important in a economical point of view. In this study. a relative evaluation of corrosion resistance for three kinds of Al alloys such as ALDC2, ALDC3, and ALDC8 series was carried out with electrochemical method. There is a tendency that corrosion potential is shifted to positive or negative direction by alloying components regardless of corrosion resistance. Moreover the data of corrosion properties obtained from cathodic Polarization curve, cyclic voltammogram and AC. DC impedance respectively showed a good correspondence each other against the corrosion resistance but variation of corrosion potential. passivity current density of anodic polarization curve and corrosion current density by Tafel extrapolation and Stern-Geary method didn't correspond with not only each other but also considerably the data of corrosion properties discussed above. Therefore it is suggested that an optimum electrochemical evaluation for corrosion resistance of Al alloy is to calculate the diffusion limiting current density of cathodic polarization curve, impedance of AC or DC and polarization resistance of cyclic voltammogram.

• 한국표면공학회지
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• 제18권4호
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• pp.153-163
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• 1985

In the electroless nickel plating bath which contained nickel sulfate, sodium hypophosphite, boric acid and triethanolamine, effect of their concentration on the rate of deposition was tested by gravimetric method and polarization method. The polarization method that polarize small range of voltage anodicaly and cathodicaly at the mixed potential in the electroless plating bath can calculate mixed current (depositing rate) from $i_{mp}=\frac {i}{\eta}\;\frac{RT}{nF}\;or\;i_{mp}=\frac{i}{\eta}\;\frac{1}{2.3}(\frac{b_a\;\;b_c}{b_c+b_a})$ Where $i_{mp}$ is the depositing current, i is the polarized current, ${\eta}$ is the polarized voltage, $b_a\;and\;b_c$ are the Tafel slop of anodic and cathodic polarization curves respectively. The calculated mixed current ($i_{mp}$) is proportional to the depositing rate obtained by gravimetric method and corresponded mostly to the real depositing rate by multifying supplementary constant. The polarization method can be used for founding inclination of reaction on various concentration of each composition. Decreasing or increasing concentration of triethanolaminc as a complexing agent , the depositing rate is decreased and when the bath contained 25-50mL/L of triethanoloamine, the depositing rate is increased. The depositing rate is increased with increasing the concentration of boric acid, and when the bath contained 0.5M of boric acid, the depositing rate is increased abruptly. The optimum composition of the electroless nickel bath was estimated 0.1M of nickel sulfate, 0.25M of sodium hypophosphite, 0.5M of boric acid, and 25-50mL/L of triethanalamine.

• 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.

• 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.