• Journal of the Korean institute of surface engineering
• /
• v.49 no.1
• /
• pp.62-68
• /
• 2016

A chromium-free Ce-based conversion coating formed by immersion in a solution containing cerium chloride and nitric acid on AZ31 magnesium alloy has been studied. The effects of acid pickling on the morphology and the corrosion resistance of the cerium conversion coating were investigated. The corrosion resistance of the conversion coating prepared on AZ31 Mg alloy after organic acid pickling was better than that of inorganic acid pickling. The morphology of the conversion-coated layer was observed using optical microscope and SEM. Results show that the conversion coatings are relatively uniform and continuous, with thickness 1.0 to $1.1{\mu}m$. The main elements of the conversion coating of AZ31 Mg alloy are Mg, O, Al, Ce and Zn by EDS analysis. The electrochemical polarization results showed that the Ce-based conversion coating could reduce the corrosion activity of the AZ31 Mg alloy substrates in the presence of chloride ions.

• Corrosion Science and Technology
• /
• v.20 no.2
• /
• pp.85-93
• /
• 2021

The corrosion damage of materials in marine environment mainly occurs by Cl^- ions due to the breakdown of passive films. Additionally, various characteristics in seawater such as salinity, temperature, immersion time, flow rate, and biological activity also affect corrosion characteristics. In this study, the corrosion characteristics of stainless steels (STS 304 and STS 316L) and anodized aluminum alloys (AA 3003 and AA 6063) were evaluated with seawater temperature parameters. A potentiodynamic polarization experiment was conducted in a potential range of -0.25 V to 2.0 V at open circuit potential (OCP). Corrosion current density and corrosion potential were obtained through the Tafel extrapolation method to analyze changes in corrosion rate due to temperature. Corrosion behavior was evaluated by measuring weight loss before/after the experiment and also observing surface morphology through a scanning electronic microscope (SEM) and 3D microscopy. Weight loss, maximum damage depth and pitting damage increased as seawater temperature increased, and furthermore, the tendency of higher corrosion current density with an increase of temperature attributed to an increase in corrosion rate. There was lower pitting damage and lower corrosion current density for anodized aluminum alloys than for stainless steels as the temperature increased.

• The Korean Journal of Physiology and Pharmacology
• /
• v.25 no.5
• /
• pp.403-411
• /
• 2021

This study was designed to evaluate the gastroprotective activity of cirsilineol in hydrochloric acid (HCl)/ethanol-induced gastric ulcer model. Cirsilineol was administered at the doses of 20 and 40 mg/kg in HCl/ethanol-induced rats. The gastroprotective ability was verified by determining the ulcer score, total acidity, hemoglobin, inflammatory cytokines, lipid peroxides, and enzymatic antioxidants superoxide dismutase (SOD) and catalase (CAT) in gastric tissue and serum biochemical analysis. The results showed a favorable increase in the hemoglobin level, antioxidant enzymes (SOD and CAT), restored electrochemical balance (carbon dioxide & anion gap) while a noticeable decrease in ulcer index, total acidity, lipid peroxides, inflammatory cytokines (interleukin-1 beta [IL-1β], IL-6, and tumor necrosis factor alpha) in rats treated with the cirsilineol. The serum biochemical analysis on liver markers (alkaline phosphatases, alanine aminotransferase, and aspartate aminotransferase), kidney markers (urea, creatinine, albumin, globulin, total protein), and lipid profile (triglyceride, high-density lipoprotein, total cholesterol) were attenuated by cirsilineol treatment in rats. Histopathology showed enhanced gastric protection and preserved the integrity of gastric mucosa upon cirsilineol administration. These results ultimately suggest that cirsilineol has gastroprotective effects that prevent the development of gastric ulcer.

• Journal of Environmental Health Sciences
• /
• v.45 no.6
• /
• pp.646-657
• /
• 2019

Objectives: The purpose of this study was to suggest methods to investigate continuous monitoring of concentration levels and assess the exposure of individuals considering the actual time activity of residents for formaldehyde and particulate matter (PM₁₀, PM_2.5) in the indoor and outdoor air of a house, assess the health risks of children and adults based on the results of the exposure assessment, and provide basic data on studies for assessing exposure and health risks in Korea in the future. Methods: The concentration levels of formaldehyde and particulate matter were measured in a family home in Gyeonggi-do Province from April 25 to July 31, 2019, using electrochemical sensors (formaldehyde) and light scattering sensors (PM₁₀, PM_2.5). Risk assessment by the duration of exposure by time activity was performed by dividing between weekdays and weekends, and indoors and outdoors. Results: The greatest level of carcinogenic risk from inhaling formaldehyde was indoors during the weekdays for both children and adults. For children, the risk was at 7.5 per approximately 10,000 people, and for adults, the risk was at 4.1 per approximately 10,000 people. PM₁₀ and PM_2.5 also showed the greatest values indoors during the weekdays, with children at 1.7 people and 1.4 per approximately 100 people, respectively, and adults at 8.2 per approximately 1,000 and 1.8 per approximately 100 people, respectively. Conclusions: The risks of formaldehyde, PM₁₀ and PM_2.5 were shown to be high indoors. Therefore, consideration of exposure assesment for each indoor pollutant and management of indoor air quality is necessary.

• Journal of the Korean Electrochemical Society
• /
• v.23 no.2
• /
• pp.39-46
• /
• 2020

Composite electrodes for rechargeable batteries generally consist of active material, electric conductor, and polymeric binder. And their composition and distribution within the composite electrode determine the electrochemical activity in the electrochemical systems. However, it is not easy to quantify the physical properties of composite electrodes themselves using conventional experimental analysis tools. So, 3D structural modeling and simulation can be an efficient design tool by looking into the contact areas between particles and electric conductivity within the composite electrode. In this study, while maintaining the composition (LiCoO₂ : Super P Li^® : Polyvinylidene Fluoride (PVdF) = 93 : 3 : 4 by wt%) and loading level (13 mg cm^-2) of the composite electrode, the effects of LiCoO₂ size (10 ㎛ and 20 ㎛) and electrode density (2.8 g cm^-3, 3.0 g cm^-3, 3.2 g cm^-3, 3.5 g cm^-3, 4.0 g cm^-3) on the physical properties are investigated using a GeoDict software. With this tool, the composite electrode can be efficiently designed to optimize the contact area and electric conductivity.

• Journal of the Korean Electrochemical Society
• /
• v.11 no.3
• /
• pp.165-169
• /
• 2008

The effect of reduction of carbon dioxide by CODH(Carbon Monoxide Dehydrogenase) was compared on glassy carbon and gold working electrodes. In case of gold electrode, the choice of the optimum applied potential is very important since $H_2$ evolution can be mixed with $CO_2$ reduction. On the other hand, efficient $CO_2$ reduction was observed up to -650 mV vs. NHE on glassy carbon in neutral solution due to the larger overpotential for $H_2$ evolution on glassy carbon surface than that on gold surface. The optimum potential for $CO_2$ reduction was found to be $-570{\sim}600\;mV$ vs. NHE. The current efficiency of $CO_2$ to CO decreased dramatically at more negative potential according to the activity of enzyme decrease and the hydrogen evolution.

• Transactions of the Korean hydrogen and new energy society
• /
• v.19 no.1
• /
• pp.18-25
• /
• 2008

The membrane electrode assembly(MEA) was prepared by a nonequilibrium impregnation- reduction (I-R) method. Nafion 117 and covalently cross-linked sulfonated polyetherether with tungsto- phosphoric acid (CL-SPEEK/TPA30) prepared by our laboratory, were chosen as polymer electrolyte membrane(PEM). $Pt(NH_3)_4Cl_2$, $RuCl_3$ and reducing agent $(NaBH_4)$ were used as electrocatalytic materials. Electrochemical activity surface area(ESA) and specific surface area(SSA) of Pt cathodic electrode with Nafion 117 were $22.48m^2/g$ and $23.50m^2/g$ respectively under the condition of 0.8 M $NaBH_4$. But Pt electrode prepared by CL-SPEEK/TPA30 membrane exhibited higher ESA $23.46m^2/g$ than that of Nafion 117. In case of Pt-Ru anodic electrode, the higher concentration of Ru was, the lower potential of oxygen reduction and region of hydrogen desorption was, and Pt-Ru electrode using 10 mM $RuCl_3$ showed best properties of SSA $34.09m^2/g$ with Nafion 117. In water electrolysis performance, the cell voltage of Pt/PEM/Pt-Ru MEA with Nafion 117 showed cell property of 1.75 V at $1A/cm^2$ and $80{\circ}C$. On the same condition, the cell voltage with CL-SPEEK/TPA30 was the best of 1.73 V at $1A/cm^2$.

• Journal of the Korean Electrochemical Society
• /
• v.12 no.1
• /
• pp.47-53
• /
• 2009

In this study, highly ordered AAO (Anodic Aluminum Oxide) with nanopores was prepared by commercial grade Al substrate containing 3.5 wt.% impurities through two step anodizing method. Nanopores of prepared AAO arrays were used as templates for preparing nanofiber. $TiO_2$ was deposited by using DP (deposition-precipitation) method into AAO pores to grow nanofiber. Au particles were loaded on this $TiO_2$ nanofiber which was grown vertically. Prepared 2 wt.% $Au/TiO_2$ nanofiber was characterized by XRD, SEM and Raman. The crystal structure was analyzed by the XRD. SEM was used to observe pore size and pore wall thickness. Photocatalytic activity of co-oxidation was compared with $TiO_2$ and $Au/TiO_2$ nanofiber on AAO arrays.

• Journal of the Korean Electrochemical Society
• /
• v.4 no.3
• /
• pp.87-93
• /
• 2001

Pressure-balanced external Ag/AgCl electrode has been extensively used for both Pressurized Water Reactor (PWR) and Boiling Water Reactor (PWR) environments. The use of KCI-based buffer solution often becomes the source of electrode potential drift due to slow leakage through its porous plug, typically made of zirconia. It is reported that results of our effort to improve the stability of electrode potential by using high purity water as the filling solution in which $Cl^-$ ion activity can be established and maintained at the solubility of AgCl even with the sustained leakage for a long period. Stability tests have been made in boron and lithium mixture solution at $288^{\circ}C$. The electrode potential remained stable within 10 mV over one week period. And after a thermal cycle between 288 to $240^{\circ}C$ the potential shift of Ag/AgCl electrodes did not exceed 15 mV By using the limiting equivalent ionic conductances and Agar's hydrodynamic theory, the thermal liquid junction potential (TLJP) of the electrode has been predicted. The calculated values for the water-fiued Ag/AgCl electrode potential, in which the chlorine concentration in the filling solution was derived from the measured data at ambient temperature, had a good agreement with the experimental values.

• Polymer(Korea)
• /
• v.35 no.1
• /
• pp.35-39
• /
• 2011

In this work, mesoporous carbons (CMK-3) were prepared by a conventional templating method using mesoporous silica (SBA-15) for using catalyst supports in polymer electrolyte membrane fuel cells (PEMFCs). The CMK-3 were chemically activated to obtain high surface area and small pore diameter with different potassium hydroxide (KOH) amounts, i.e., 0, 1, 3, and 4 g as an activating agent. And then Pt-Ru was deposited onto activated CMK-3 (K-CMK-3) by a chemical reduction method. The characteristics of Pt-Ru catalysts deposited onto K-CMK-3 were determined by surface area and pore size analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and inductive coupled plasma-mass spectrometry (ICP-MS). The electrochemical properties of Pt-Ru/K-CMK-3 catalysts were also analyzed by cyclic voltammetry (CV). From the results, the K3g-CMK-3 carbon supports activated with 3 g KOH showed the highest specific surface areas. In addition, the K3g-CMK-3 led to uniform dispersion of Pt-Ru onto K-CMK-3, resulted in the enhancement of elelctro-catalystic activity of Pt-Ru catalysts.