• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.4
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• pp.648-662
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• 1996

Electrode surface reaction on glassy carbon and synthesized graphite (PVDF mixed graphite) in sulfuric acid solution is investigated by impedance spectroscopy at cyclic polarization. The redox peak, which may be due to the change of chemical adsorped functional group on electrode surface or oxidation and reduction of oxygen, is represented on glassy carbon and graphite electrode in potentio-dynamic current curve. The oxidation and reduction of these surface functional group on glassy carbon and PVDF mixed graphite have a major affect on the impedance spectrum and Faraday impedance parameter at cyclic polarization.

• Transactions of Materials Processing
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• v.28 no.2
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• pp.71-76
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• 2019

Corrosion resistance is one of the essential properties required in steel bolts. The various types of coatings are used to improve the corrosion resistance of steel bolts. But, roll formed, subsequently Zn alloy electrodeposited and top coated steel bolt easily takes place the white storage stain or white rust under high humidity condition. To investigate the corrosion resistance of roll formed and subsequently the various types of coated steel bolts, their polarization curves were measured by potentio-dynamic tester in this study. Based on the measured polarization curves, the more times of chromate and top coating on roll formed steel bolt, the higher corrosion resistance was shown. The roll formed steel bolt, which was Zn-Ni electro-deposited, two times chromated, one time inorganic top coated, one time organic top coated and annealed, showed the best corrosion resistance.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.2
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• pp.90-95
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• 2006

Nitriding or carburizing of carbon steels results in good mechanical properties such as high surface hardness and wear resistance but it has no affection on the corrosion resistance. Corrosion properties of nitriding and carburizing steels could be deteriorated. So, recently, there have been great demand for oxi-nitriding to enhance both mechanical properties and corrosion resistance. In this study, the corrosion resistance of carbon steel, S35C, and free cutting steel, SUM222, are prepared by vacuum nitriding and vacuum post-oxidation were compared with those treated by nitriding. After vacuum post-oxidation, $5{\mu}m$ oxide layer was formed on the nitride layer with $20{\sim}30{\mu}m$ depth. Potentio-dynamic polarization curve in corrosion test showed that the corrosion potential after post oxidation was increased from 200 mV to 800 mV in S35C and from 600 mV to 1200 mV in SUM222. SEM analyses showed that pores was increased and surface roughness became rougher with post oxidation. However, the formation of $Fe_3O_4$ resulted in the enhanced corrosion resistance of steels.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.3
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• pp.453-459
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• 2003

In this study, the effect of heat treatment to the electrochemical polarization resistance for the Ti-6Al-4V alloy was measured. The solution heat treatments were carried out at $1066^{circ}E, 966^{\circ}$E$, followed by aging heat treated $550^{circ}E, 600^{circ}E, and 650^{circ}E$. The electrochemical polarization resistance behavior was measured by potentio-dynamic polarization in the 1N $HNO_3$ + 15ppm HF solution. The obtained results were as follows. 1. As solution heat temperature increased. the corrosion potential was increased, whereas passive current density and critical current density were decreased. 2. As aging heat temperature increased, the corrosion potential was almost constant, but passive current density was decreased 3. The results of composition test measured by EDS at grain boundary and near $\gamma'$ precipitates indicated that S, Cl. and Si which originated from base metal were segregated at the grain boundaries Al and Ti which were the main alloying element in $\gamma'$ were depleted at the $\gamma'$ precipitated. The depletion of Al and Ti in $\gamma'$ was caused to early breakdown of passive film.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.2
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• pp.142-146
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• 2012

In the geothermal power, the geothermal fluid such as water or steam is moved from the ground to turbine a pipeline. Because the geothermal fluid with high temperature contains Cl-and SO4-, It cause to diminish the system lifetime due to the increase in the corrosion of pipeline. In the present work, the characteristics of corrosion and its fatigue of the sus316 which is used in the pipeline are evaluated experimentally. From this study, the following results can be obtained; for the case of the corrosion environment, it is found that the corrosion rate is faster than that of the steam environment by 10 to 30 times, and the corrosion fatigue limit is underestimated compared to that of steam state.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.3
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• pp.447-452
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• 2003

Crevice corrosion is localized form of corrosion usually associated with a stagnant solution on the micro-environmental level. Such stagnant micro environments tend to occur in crevices (shielded areas) such as those formed under gaskets washers insulation material. fastener heads. surface deposits. disbonded coatings. threads. lap joints and clamps. Crevice corrosion is initiated by changes in located electrochemical reaction within the crevice such as a) depletion of inhibitor in the crevice b) depletion of oxygen in the crevice c) a shift to acid conditions in the crevice and d) build-up of aggressive ion species (e.g chloride) in the crevice. In this study. the mechanism of crevice corrosion for Type 430 stainless steel is investigated undercondition that the size of specimen is $15{\times}20\{times}3mm$, in 1N $H_2SO_4$ + 0.05N NaCl solution. and the artificial crevice gap size of 3 x 0.2 x 15 mm. Crevice corrosion is measured under applied potential -300mV(SCE) to the external surface. The obtained result of this study showed that 1) the induced time for initiation of crevice is 750 seconds. 2) potential of the crevice was about from -320mV to -399mV. which is lower than that of external surface potential of -300mV It is considered that potential drop in the crevice is one of mechanisms for the crevice corrosion

• Korean Journal of Metals and Materials
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• v.49 no.8
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• pp.601-607
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• 2011

The study investigated the influence of current density on the corrosion-protection properties of an AZ91 Mg alloy subjected to plasma electrolytic oxidation coating. The present coatings were carried out under an AC condition at three different current densities, i.e., 100, 150, and $200mA/cm^2$. From microstructural observations, the micro cracks connecting each micro pore were pronounced on the oxide surface of the samples coated at current densities higher than $150mA/cm^2$ since increasing the current density in this study led to an increment in the relative volume fraction of the MgO compound. Based on potentio dynamic polarization and immersion tests, the sample coated at a current density of $100mA/cm^2$ showed superior corrosion resistance.

• Corrosion Science and Technology
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• v.12 no.1
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• pp.40-49
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• 2013

Effects of magnesium and pH on corrosion of aluminum galvanically coupled to iron have studied by using potentio- dynamic and static tests for polarization curves, Mott-Schottky test for analysis of semiconductor property, and GD-AES and XPS for film analysis. Pitting potential was sensitive to magnesium as an alloying element but not to pH, while passive current was sensitive to pH but not to magnesium. It was explained with, instead of point defect model (PDM), surface charge model describing that the ingression of chloride depends on the state of surface charge and passive film at film/solution interface is affected by pH. In addition, galvanic current of aluminum electrically coupled to iron was not affected by magnesium in pH 8.4, 0.2M citrate solution but was increased by magnesium at the solution of pH 9.1. The galvanic current at pH 9.1 increased with time at the initial stage and after the exposure of about 200 minute, decreased and stabilized. The behavior of the galvanic current was related with the concentration of magnesium at the surface. It agreed with the depletion of magnesium at the oxide surface by using glow discharge atomic emission spectroscopy (GD-AES). In addition, pitting potential of pure aluminum was reduced in neutral pH solution where chloride ion maybe are competitively adsorbed on pure aluminum. It was confirmed by the exponential decrease of pitting potential with log of [$Cl^-$] around 0.025 M of [$Cl^-$] and linear decrease of the pitting potential. From the above results, unlike magnesium, alloying elements with higher electron negativity, lowering isoelectric point (ISE), are recommended to be added to improve pitting corrosion resistance of aluminum and its alloys in neutral solutions as well as their galvanic corrosion resistance in weakly basic solutions.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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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.

• Journal of the Korean institute of surface engineering
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• v.39 no.4
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• pp.190-197
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• 2006

The effects of blasting and acidic treatment on the corrosion characteristics of dental implant fabricated with Cp-Ti and Ti-6Al-4V alloy have been researched by using electrochemical methods. The fabricated implants were cleaned and sandblasted by $Al_2O_3$ powder and then acidic treatment was carried out in nitric acid solution. The surface morphology were observed using scanning electron microscope. The corrosion behaviors were investigated using potentiosat and EIS in 0.9% NaCl solution at $36.5{\pm}1^{\circ}C$. The potentio-dynamic test in 0.9% NaCl indicated that the corrosion potential of blasting and acidic treated implant was lower than that of non treated implant, but current density was higher than that of non treated implant. From the cyclic potentiodynamic test results of Ti implant, the passivation current density of blasting and acidic treated implant slightly higher than that of non treated implant. From A.C. impedance test results in 0.9% NaCl solution, polarization resistance($R_p$) value of blasting and acidic treated implant was lower than that of non treated implant. In case of blasting and acidic treated implant surface, the pits were observed in valley and crest of implant surface.