• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.11a
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• pp.260-265
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• 2004

The materials of ship screw propeller are commonly the manganese bronze. The seawater corrosion and cavitation of the screw propeller reduce tire propulsive performance of ship. In screw manufactory, tire corrosion rust of tire screw propeller is removed by a hand grinding. The grinding work makes the dust of the heavy metals from the manganese bronze. The dust makes indoor working environment poor. A friendly-environmental and automatic corrosion removing apparatus was developed for the improvement of screw processing and working environment. The corrosion rust of a screw propeller was remarkably removed by using apparatus. And the screw surface roughness was improved by a blasting effect of the apparatus performance test. Anode polarization curves on jour processing conditions, that is to say, grinding, blasting, wire-brushing, fine sand papering, were confirmed by a potentiostat. Especially, two kinds of medias, alumina and emery, were used in the blasting processing. Then, investigated tire cavitation erosion of specimen. This result proved that tire blasting work has considerably improved the corrosion resistance of a screw propeller.

• Journal of the Korean Chemical Society
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• v.55 no.2
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• pp.268-278
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• 2011

Corrosion of aluminum in 0.1 M HCl solution in the absence and presence of ${\beta}$-blocker inhibitors (atenolol, propranolol, timolol and nadolol) was investigated using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency increased with inhibitor concentration and decreased with rise of temperature. Potentiodynamic polarization curves revealed that they acted as cathodic inhibitors. Some thermodynamic parameters were calculated and discussed. All inhibitors were adsorbed on Al surface obeying Frumkin isotherm. All EIS tests exhibited one capacitive loop which indicates that the corrosion reaction is controlled by charge transfer process. The inhibition efficiencies of all test methods were in good agreement.

• Journal of Surface Science and Engineering
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• v.47 no.5
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• pp.215-220
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• 2014

Electrodeposition behaviors of Pd-Ni alloys were investigated from the polarization curves in a solution containing ethylenediamine as complexing agent. The microstructure and hardness of electrodeposited Pd-Ni alloys were also characterized. Codeposition of Pd-Ni alloys was successfully performed in the wide current density ranging from 2 to $5000A{\cdot}m^{-2}$ because the deposition potential of Pd became close to that of Ni in the ethylenediamine-contained solution. It was also found from X-ray diffraction patterns that the solid solution between Pd and Ni was formed with variation of the composition of alloys. The measured hardness of Pd-Ni alloys increased with increasing the contents of Ni due to solid solution strengthening and grain refinement. The electrodeposited Pd-Ni alloys also exhibited a crack free smooth surface morphology from the SEM observation.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.322-323
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• 2012

This study discussed the formation of phosphate conversion coatings on AZ31 Mg alloy (AZ31) from the zinc phosphating bath with various concentrations of sodium fluoride (NaF). The effects of NaF on the formation, structure, composition and electrochemical behavior of the phosphate coatings were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD) weight balances, open circuit potential (OCP) transients, potentiodynamic polarization curves and immersion test. The coatings were composed of two layers: an outer $Zn_2(PO_4)_3.4H_2O$ (hopeite) crystal layer and an inner amorphous of $MgZn_2(PO_4)_2$. NaF concentration is emphasized to be highly effective in the formation of the hopeite crystal and etching and coating rates. Potentiodynamic polarization and immersion test showed that the coatings formed in the zinc phosphating bath with addition of NaF have much higher corrosion resistance than bare AZ31.

• Journal of Electrochemical Science and Technology
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• v.10 no.3
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• pp.257-270
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• 2019

The inhibition performance of sodium gluconate (SG), cetyltrimethylammonium bromide (CTAB) and their mixture (SG/CTAB) on the corrosion behavior of ${\alpha}$-brass in 0.5 M $H_2SO_4$ solution has been investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Scanning Electron Microscope with Energy-Dispersive Spectrometer (SEM-EDS), Inductively Coupled Plasma Spectrometry (ICPS) and molecular dynamics (MD) simulation techniques. The results reveal that SG with 5ppm CTAB, noted SG/CTAB, acts as a good corrosion inhibitor and its inhibition efficiency reached 89% after 24 h immersion in sulfuric acid solution, but slightly decreased at higher temperatures. The polarization curves displayed that SG/CTAB acts as a cathodic-kind inhibitor. Electrochemical impedance spectroscopy (EIS) studies revealed that the addition of 5ppm CTAB to different concentrations of SG considerably increases the corrosion resistance of ${\alpha}$-brass. The SEM-EDS and ICPS analyses support the experimental results. Further, molecular dynamics (MD) simulations were used to understand the adsorption profiles of SG/CTAB on Cu(111) and Zn(111) surfaces.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.44.3-44.3
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• 2019

Massive stars, supernovae, and kilonovae are among the most luminous radiation sources in the universe. Observations usually show near- to mid-infrared (NIR-MIR, 1-5~micron) emission excess from H II regions around young massive star clusters (YMSCs) and anomalous dust extinction and polarization towards Type Ia supernova (SNe Ia). The popular explanation for such NIR-MIR excess and unusual dust properties is the predominance of small grains (size a<0.05micron) relative to large grains (a>0.1micron) in the local environment of these strong radiation sources. The question of why small grains are predominant in these environments remains a mystery. Here we report a new mechanism of dust destruction based on centrifugal stress within extremely fast rotating grains spun-up by radiative torques, namely the RAdiative Torque Disruption (RATD) mechanism, which can resolve this question. We find that RATD can destroy large grains located within a distance of ~ 1 pc from a massive star of luminosity L~ 10^4L_sun and a supernova. This increases the abundance of small grains relative to large grains and successfully reproduces the observed NIR-MIR excess and anomalous dust extinction/polarization. We show that small grains produced by RATD can also explain the steep far-UV rise in extinction curves toward starburst and high redshift galaxies, as well as the decrease of the escape fraction of Ly-alpha photons observed from HII regions surrounding YMSCs.

• Corrosion Science and Technology
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• v.20 no.2
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• pp.52-61
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• 2021

This study using experimental design and linear regression technique was implemented in order to predict the pitting potential of stainless steel in marine environments, with the target materials being AL-6XN and STS 316L. The various variables (inputs) which affect stainless steel's pitting potential included the pitting resistance equivalent number (PRNE), temperature, pH, Cl^- concentration, sulfate levels, and nitrate levels. Among them, significant factors affecting pitting potential were chosen through an experimental design method (screening design, full factor design, analysis of variance). The potentiodynamic polarization test was performed based on the experimental design, including significant factor levels. From these testing methods, a total 32 polarization curves were obtained, which were used as training data for the linear regression model. As a result of the model's validation, it showed an acceptable prediction performance, which was statistically significant within the 95% confidence level. The linear regression model based on the full factorial design and ANOVA also showed a high confidence level in the prediction of pitting potential. This study confirmed the possibility to predict the pitting potential of stainless steel according to various variables used with experimental linear regression design.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.475-483
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• 2021

Additively manufactured titanium alloy is one of the promising materials in advanced medical industries. However, these additively manufactured alloys show corrosion properties different from those of conventional materials due to their unique microstructure. In this study, the effect of surface roughness and masking conditions on the results of the potentiodynamic polarization tests on additively manufactured or conventional Ti-6Al-4V alloys in artificial saliva solution with or without fluoride was investigated. The results showed that the corrosion potential was slightly lower with a flat cell with an O-ring than with masking tape. The corrosion rate was decreased with decreases in the surface roughness. Localized corrosion involving delamination of the surface layer occurred at 7 ~ 9 V (SSC) on the additively manufactured alloy in solution with or without fluoride when the samples were finished with 1000-grit SiC paper, whereas localized corrosion was not observed in the specimens finished with 1-㎛ alumina paste.

• Corrosion Science and Technology
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• v.21 no.2
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• pp.89-99
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• 2022

A versatile method for performing non-cyanide electroless gold plating using thiomalic acid (TMA) as a complexing agent and 2-aminoethanethiol (AET) as a reducing agent was investigated. It was found that TMA was an excellent complexing agent for gold. It can be used in electroless gold plating baths at a neutral pH with a high solution stability, makes it a potential candidate to replace conventional toxic cyanide complex. It was found that one gold atomic ion could bind to two TMA molecules to form the [2TMA-Au⁺] complex in a solution. AET can be used as a reducing agent in electroless gold plating solutions. The highest current density was obtained at electrode rotation rate of 250 to 500 rpm based on anodic and cathodic polarization curves with the mixed potential theory. Increasing AET concentration, pH, and temperature significantly increased the anodic polarization current density and shifted the plating potential toward a more negative value. The optimal gold ion concentration to obtain the highest current density was 0.01 M. The cathodic current was higher at a lower pH and a higher temperature. The current density was inversely proportional to TMA concentration.

• 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.