• Journal of the Korean institute of surface engineering
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• v.44 no.2
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• pp.44-49
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• 2011

The films formed on AZ31B magnesium alloy were prepared from alkaline solution composed of potassium permanganate and sodium hydroxide. The immersion tests were carried out at the different concentration of sodium hydroxide and pre-treatment method in 5 minute. The morphology and the phase composition of the film were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion behavior of the film in 5.0% NaCl solution was evaluated using potentiodyanmic polarization. Open circuit potential in developing film was examined with time. The thin and transparent film was mainly composed of MgO and $Mg(OH)_2$. The film with the best corrosion resistance was obtained at $70^{\circ}C$ bath temperature, 1.6 M concentration of sodium hydroxide and chemical pre-treatment.

• Journal of the Korean institute of surface engineering
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• v.49 no.6
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• pp.521-529
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• 2016

In this study, titanium nanotubes, prepared by anodization method, showing high surface and strong chemical stability in acidic and basic media, have been employed for the application to the electrodes for water splitting in KOH solution. Due to its high polarization resistance of $TiO_2$ itself, proper catalysts are essentially required to reduce overpotentials for water oxidation and reduction. Most of academic literature showed noble metal catalysts for foreign dopants in $TiO_2$ electrodes. From commercialization point of view, screening of low-cost catalyst is important. Herein, we propose molybdenum oxide as low-cost catalysts among various catalysts tested in the experiments, which exhibits the highest performance for hydrogen evolution reaction in highly alkaline solution. We showed that molybdenum oxide doped electrode can be operated in extreme acidic and basic conditions as well.

• Korean Journal of Metals and Materials
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• v.47 no.10
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• pp.652-659
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• 2009

Many ancient and historical artifacts were made by copper and its alloys. In the case of outdoor exposure artifacts, the surface could be suffered from corrosion and tarnish by the reaction with its environment. In order to preserve the artifacts, surface treatment would be needed and BTA coating has been usually applied to tin-bronze. This paper dealt with the evaluation of the properties of BTA coated film using a linear polarization method and AC impedance measurement. On the base of corrosion rate and film resistance for the specimen formed by coating process, optimum coating conditions are as follows; 3 cycles brushing or 3 cycles spraying coatings for natural dried process and 1 cycle brushing coating or 5 cycles spraying coating for hot-air dried process.

• 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.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.1
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• pp.43-48
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• 2012

This paper presents the characterization of micro-tubular SOFCs using three different anode current collecting methods of inlet current collection (IC), both current collection (BC) and total current collection (TC). The maximum power densities of SOFCs at $750^{\circ}C$ using IC, BC and TC were 56 mW/$cm^2$ (0.43 V, 0.13 A/$cm^2$), 236 mW/$cm^2$ (0.43 V, 0.55 A/$cm^2$) and 261 mW/$cm^2$ (0.43 V, 0.61 A/$cm^2$) respectively. It was confirmed by impedance spectroscopy that both the polarization resistance and the ohmic resistance were dramatically increased at SOFC with IC.

• Proceedings of the KSR Conference
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• 2000.11a
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• pp.535-542
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• 2000

Pure copper, Cu-1.1wt%Cd and ACSR(Aluminum Conductor Steel Reinforced) have been used as Catenary Materials in Electric Railway System. Since these materials may have chance to be exposed to the corrosive environments like polluted air, acid rain and sea water, it is important not only to investigate the corrosion characteristics but also to measure corrosion rates in various corrosive environments. In order to examine corrosion characteristics according to the dissolved oxygen content, pH, chloride ion concentration ion, and the addition of Cd to Cu, a series of tests such as potentiodynamic polarization. a.c impedance spectroscopy and galvanic corrosion tests were carried out in these materials. Results showed that the addition of Cd to Cu and chloride ion in the solution have an adverse effect on the resistance to corrosion. Additionally, Galvanic currents between Al and steel wires of ACSR were confirmed by using ZRA(zero resistance ammeter) method.

• Korean Journal of Materials Research
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• v.23 no.3
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• pp.206-210
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• 2013

In the segmented-in-series solid-oxide fuel cells (SIS-SOFCs), fabrication techniques which use decalcomania paper have many advantages, i.e., an increased active area of the electrode; better interfacial adhesion property between the anode, electrolyte and cathode; and improved layer thickness uniformity. In this work, a cell-stack was fabricated on porous ceramic flattened tube supports using decalcomania paper, which consists of an anode, electrolyte, and a cathode. The anode layer was $40{\mu}m$ thick, and was porous. The electrolyte layers exhibited a uniform thickness of about $20{\mu}m$ with a dense structure. Interfacial adhesion was improved due to the dense structure. The cathode layers was $30{\mu}m$ thick with porous structure, good adhesion to the electrolyte. The ohmic resistance levels at 800, 750 and $700^{\circ}C$ were measured, showing values of 1.49, 1.58 and $1.65{\Omega}{\cdot}cm^2$, respectively. The polarization resistances at 800, 750 and $700^{\circ}C$ were measured to be 1.63, 2.61 and $4.17cm^2$, respectively. These lower resistance values originated from the excellent interfacial adhesion between the anode, electrolyte and cathode. In a two-cell-stack SOFC, open-circuit voltages(OCVs) of 1.915, 1.942 and 1.957 V and maximum power densities(MPD) of 289.9, 276.1 and $220.4mW/cm^2$ were measured at 800, 750 and $700^{\circ}C$, respectively. The proposed fabrication technique using decalcomania paper was shown to be feasible for the easy fabrication of segmented-in-series flattened tube SOFCs.

• Corrosion Science and Technology
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• v.11 no.6
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• pp.275-279
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• 2012

Ni-W alloy deposits have lately attracted the interest as an alternative surface treatment method for hard chromium electrodeposits because of higher wear resistance, hardness at high temperature, and corrosion resistance. This study deals with influences of process variables, such as electodeposition current density, plating temperature and pH, on the internal stress of Ni-W nanocrystalline deposits. The internal stress was increased with increasing the applied current density. With increasing applied current density, the grain size of the deposit decreases and concentration of hydrogen in the deposit increases. The subsequent release of the hydrogen results in shrinkage of the deposit and the introduction of tensile stress in the deposit. Consequently, for layers deposited at high current density, cracking occurs readily owing to high tensile stress value. By increasing the temperature of the electrodeposition from $60^{\circ}C$ to $80^{\circ}C$, the internal stress was decreased. It seems that an increase in the number of active ions overcoming the activation energy at elevated temperature caused a decline in the concentration polarization and surface diffusion. It decreased the level of hydrogen absorption due to the lessened hydrogen evolution reaction. Therefore, the lower level of hydrogen absorption degenerated the hydride on the surface of the electrode, resulting in the reduction of the internal stress of the deposits. By increasing the pH of the electrodeposition from 5.6 to 6.8, the internal stress in the deposits were slightly decreased. It is considered that the decrease in internal stess of deposits was due to supply of W complex compound in cathode surface, and hydrogen ion resulted from decrease of activity.

• Corrosion Science and Technology
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• v.19 no.2
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• pp.82-88
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• 2020

This work examined the corrosion protection performance of benzoate loaded hydrotalcite/graphene oxide (HT/GO-BZ) for carbon steel. HT/GO-BZ was fabricated by the co-precipitation method and characterized by infrared spectroscopy, X-ray diffraction, and scanning electronic microscopy. The corrosion inhibition action of HT/GO-BZ on carbon steel in 0.1 M NaCl solution was evaluated by electrochemical measurements. The benzoate content in HT/GO-BZ was determined by UV-Vis spectroscopy. Subsequently, the effect of HT/GO-BZ on the corrosion resistance of the water-based epoxy coating was investigated by the salt spray test. The obtained results demonstrated the intercalation of benzoate and GO in the hydrotalcite structure. The benzoate content in HT/GO-BZ was about 16%. The polarization curves of the carbon steel electrode revealed anodic corrosion inhibition activity of HT/GO-BZ and the inhibition efficiency was about 95.2% at a concentration of 3g/L. The GO present in HT/GO-BZ enhanced the inhibition effect of HT-BZ. The presence of HT/GO-BZ improved the corrosion resistance of the waterborne epoxy coating.

• Corrosion Science and Technology
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• v.17 no.6
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• pp.279-286
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• 2018

Austenitic stainless steels used in nuclear power plants mainly use pipes made of seamless pipes, which depend on imports. The manufacturing process and high cost are some of the problems associated with seamless pipes. Therefore, in this study, the corrosion characteristics of the seamless pipe and the SAW pipe were assessed to determine the safety and reliability of the SAW pipe in a bid to replace the seamless pipe. Microstructure was analyzed using an optical microscope and the degree of hardness was measured using a Rockwell B scale. Intergranular corrosion resistance was evaluated by ASTM A262 Practice A, C, and E methods. The degree of sensitization was determined using a DL-EPR test. Anodic polarization test was performed in deaerated 1% NaCl solution at $30^{\circ}C$ and the U-bend method was used to evaluate the SCC resistance in 0.01 M $Na_2S_4O_6$ at $340^{\circ}C$ and 40% NaOH solution at $290^{\circ}C$. Weld metal of the SAW pipe specimen showed relatively high degree of sensitization and intergranular corrosion rate. However, annealing to SAW pipes improved the corrosion properties in comparison to that of the seamless pipe.