• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.667-673
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• 1998

Rebar corrosion in a simulated pore solution (SPS) with chloride ion was analyzed by Tafel and AC impedance method and corrosion effects of surface roughness and iron oxide layer were also investigated. Corrosion estimation of rebar by electrochemical impedance spectroscopy is very useful, and the measured value can be adapted to proposed electrochemical equivalent circuit model. Corrosion potential increased to the cathodic direction as the concentration of chloride ions increased and corrosion current had the same tendency as above. Surface films were analyzed with scanning electron microscope and Auger electron spectroscopy. Thermally oxidized layer by torch flame for 15 sec was very poor at anti-corrosive property. The corrosion rate of rebar increased as the surface roughness increased. Also, higher temperatures above RT of SPS in initial stage caused a rebar to be corroded faster.

• Journal of the Korean Institute of Gas
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• v.2 no.1
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• pp.40-46
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• 1998

Mathematical modeling on the corrosion of the steel casing and main pipe due to the protection current resulting from a cathodic protection system was carried out using boundary element method. The model is consisted of Laplace's equation with non-linear boundary conditions(Tafel equations) and the iterative technique to determine the miexed potential of the steel casing. The model is applied to the normal steel casing section as well as abnormal one with defects such as metal touch and insulation defects. From the modeling procedure, we can calculate the potential distributions and current density distributions of the system. The theoretical results of the qualitatiive corrosion aspect along the steel casing and main pipe agree well with the experimental results within the experimental conditions studied.

• Applied Chemistry for Engineering
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• v.3 no.3
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• pp.527-534
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• 1992

Raney nickel was used as catalyst in the hydrogen electrode for an alkaline fuel cell. The hydrogen electrode manufactured with the Raney nickel catalyst which was sintered at $700^{\circ}C$ was found to have the highest electrode performance. Using the Raney nickel powder of average particle size $90{\AA}$ for the electrode, the current density which had been measured was $450mA/cm^2$ at $80^{\circ}C$ using 6N KOH solution as an electrolyte. The effects of PTFE addition were investigated with CO-chemisorption, polarization curves and Tafel slope. CO-chemisorption had shown the optimum value when the Raney nickel was mixed with 5wt% of PTFE, but from the current density and Tafel slope at porous Raney nickel electrode, the appropriate value of PTFE addition was 10wt%. Recommendable Ni and Al portion for Raney nickel was 60 : 40 and loading amount was $0.25g/cm^2$. Also the influence of pressing pressure for manufacturing catalytic layer and for junction with gas diffusion layer was examined. The morphology of catalyst surface was investigated with SEM. The influence of reactivation time and heat-treatment temperature were also studied.

• Journal of the Korean Chemical Society
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• v.58 no.5
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• pp.437-444
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• 2014

The electrochemical corrosion and passivation of Co-RDE in borate buffer solution was studied by Potentiodynamic and electrochemical impedance spectroscopy. The mechanisms of both the active dissolution and passivation of cobalt and the hydrogen evolution in reduction reaction were hypothetically established while utilizing the Tafel slope, the rotation speed of Co-RDE, impedance data and the pH dependence of corrosion potential. Based on the EIS data, an equivalent circuit was suggested. In addition, the electrochemical parameters for specific anodic dissolution regions were carefully measured. An induction loop in Nyquist plot measured at the open-circuit potential was observed in the low frequency, and this could be attributed to the adsorption-desorption behavior in the corrosion process.

• Journal of the Korean Chemical Society
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• v.18 no.6
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• pp.391-399
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• 1974

Corrosion and passivation of metallic cobalt was studied by means of electrochemical experiments including potentiostatic and galvanostatic measurements and cyclic voltammograms. The mechanisms of active dissolution and passivation of cobalt at the metal/borate buffer solution interface are deduced from the Tafel slope, pH dependence of the Flade potential, and dissolution kinetic data. Hydroxyl group adsorbed on cobalt surface seems to participate in surface oxidation and formation of the passive layer. The growth kinetic data as measured by the current density suggests a mechanism in which the growth of the passive layer is determined by field-assisted transport of ions through the layer. Thickness of the passive layer was estimated by coulometry to be about 10${\AA}$ at the lowest passive potential and to grow gradually with anodic potential to about 20${\AA}$.

• Korean Journal of Materials Research
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• v.10 no.12
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• pp.831-837
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• 2000

To improve the catalytic activity of platinum on polymer electrolyte fuel cell(PEFC), platinum was alloyed with cobalt and nickel at various temperature. By XRD, it was observed the crystal structure of alloy catalysts were the ordered face centered cubic(f.c.c) due to the superlattice line at $33^{\circ}$. As heat-treatment temperature was increased, the particle size of alloys also were increased and the crystalline lattice parameters were decreased. According to the results from mass activity, specific activity and Tafel slope measured by cell performance test and cyclic voltammogram, the catalyst activities of alloys are higher than that pure platinum.

• Journal of the Korean institute of surface engineering
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• v.48 no.6
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• pp.354-359
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• 2015

Stainless steel has poor corrosion resistance in marine environment due to the breakdown of a passive film caused by chloride. It suffers electrochemical corrosion like pitting corrosion, crevice corrosion, and stress corrosion crack (SCC) in marine environment. In general, it indicates that the passive film of $Al_2O_3$ has better corrosion resistance than that of $Cr_2O_3$ in seawater. This paper investigated the damage behavior 304 stainless steel and hot-dip aluminized 304 stainless steel in seawater solution. Various electrochemical experiments were carried out including potential measurement, potentiodynaimic experiment, Tafel analysis and galvanostatic experiment. As a result of anodic polarization experiment, higher pitting damage depth was indicated at 304 stainless steel than hot-dip aluminized 304 stainless steel. In addition, relatively higher corrosion current density was shown at hot-dip aluminized stainless steel as a result of Tafel analysis.

• Journal of the Korean Chemical Society
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• v.57 no.5
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• pp.533-539
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• 2013

The electrochemical corrosion and passivation of Ni rotating disk electrod in borate buffer solution was studied with potentiodynamic and electrochemical impedance spectroscopy. The mechanisms of both the active dissolution and passivation of nickel and the hydrogen evolution in reduction reaction were hypothetically established while utilizing the Tafel slope, impedance data, the rotation speed of Ni-RDE and the pH dependence of corrosion potential and current. Based on the EIS data, an equivalent circuit was suggested. In addition, carefully measured were the electrochemical parameters for specific anodic dissolution regions. It can be concluded from the data collected that the $Ni(OH)_2$ oxide film, which is primarily formed by passivation, is converted to NiO by dehydration under the influence of an electrical field.

• Bulletin of the Korean Chemical Society
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• v.24 no.11
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• pp.1613-1617
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• 2003

In the phosphoric acid based etchant, the dissolution rates of Mo films were measured by microgravimetry and the corrosion potentials of Mo and Al were estimated by Tafel plot method with various concentrations of nitric acid. Dissolution rate of Mo increased with the nitric acid concentration and reached a limiting value at high concentration of nitric acid in ambient condition. Corrosion potentials of Mo and Al shifted to positive direction and the difference between potentials of both metals was about 1,100 mV and 1,200 mV with 1% and above 4% of $HNO_3$, respectively. For a Mo/Al bilayers, the dissolution rate inversion is the main reason for good taper angle in shower etching process. Taper angles are observed by scanning electron microscope (SEM) after wet etching process for Mo/Al layered films with different concentrations of $HNO_3$. In the etch side profile, it was found that Al corroded faster than Mo below 4% of $HNO_3$ in dip etching process, however, Mo corroded faster above 4%. Trend for variation of taper angle of etched side of Mo/Al layered film can be explained by considering the effect corrosion rates of both metals with various concentrations of $HNO_3$.

• Journal of the Korean institute of surface engineering
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• v.49 no.1
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• pp.26-31
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• 2016

In this paper, the characteristics of a cavitation-erosion damage behavior on the STS 304 and hot-dip aluminized STS 304 under cavitation environment in sea water solution was investigated. The electrochemical experiments were carried out by potential measurement, anodic/cathodic polarization test, Tafel analysis, and also galvanostatic experiment in current density variables for the samples. The apparatus of cavitation-electrochemical experiment was manufactured in compliance with modified ASTM G-32 standard, with the conditions of sea water temperature of $25^{\circ}C$ and the measurement, amplitude of $30{\mu}m$. The damage behavior was analyzed by an observation of surface mophologies and a measurement of damage depth by a scanning electron microscope(SEM) and a 3D microscope, respectively, after electrochemical test. After polarization experiment under cavitation environment, much higher damage depths for the hot-dip aluminized STS 304 were observed comparing to the untreated STS 304. In addition, higher corrosion current density in hot-dip aluminized STS 304 presented than that of untreated STS 304 as a result of Tafel analysis.