• Journal of Conservation Science
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• v.30 no.1
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• pp.95-101
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• 2014

Silver objects tarnish with black from reaction with sulfurous acid or hydrogen sulfide of atmospheric. Blackening of silver objects results from formation of silver sulfide($Ag_2O$) on the surface. Silver sulfide usually is usually removed by conservation treatment. There are several cleaning methods such as chemical, electrochemical and micro-abrasion cleaning, but all of them consume silver. This study investigated the safe and effective parameter of laser cleaning by test on silver coupons. Laser cleaning is a selective process for the removal of specific substances. At first, laser cleaning applied to plain silver coupons, which were not corroded, to find out the safe range of laser energy density. From results, plain silver coupons were not changed at 1064nm below $4.00J/cm^2$ and at 532nm below $2.39J/cm^2$. The corrosion layer(silver sulfide) of artifical corroded silver coupons was removed at 1064nm with $2.39J/cm^2$ by 5~10 pulses and at 532nm with $1.19J/cm^2$ by 5~10 pulses. The removal thickness of corrosion layer was about 13-25nm per a laser pulse using AES analysis. In addition, laser cleaning tested the tarnish silver rings based on the results of silver coupons. As a result of test, the black surface were clean successfully and gave luster of silver, which showed the application possibility of laser cleaning for silver objects.

• Advances in environmental research
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• v.9 no.3
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• pp.191-214
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• 2020

The rise in population and industrialization accounts for the generation of a huge amount of wastewaters. The treatment of this wastewater is obligatory to safeguard the environment and various life forms. Conventional methods for high strength wastewater treatment coming out to be ineffective. Advanced oxidation processes (AOPs) for such wastewater treatment proved to be very effective particularly for the removal of various refractory compounds present in the wastewater. Ozone based AOPs with its high oxidizing power and excellent disinfectant properties is considered to be an attractive choice for the elimination of a large spectrum of refractory compounds. Furthermore, it enhances the biodegradability of wastewaters after treatment which favors subsequent biological treatments. In this review, a detailed overview of the AOPs (like the Fenton process, photocatalysis, Electrochemical oxidation, wet air oxidation, and Supercritical water oxidation process) has been discussed explicitly focusing on ozone-based AOPs (like O₃, O₃/H₂O₂, O₃/UV, Ozone/Activated carbon process, Ozone/Ultrasound process, O₃/UV/H₂O₂ process). This review also comprises the involved mechanisms and applications of various ozone-based AOPs for effective municipal/industrial wastewaters and landfill leachate treatment. Process limitations and rough economical analysis were also introduced. The conclusive remarks with future research directions also underlined. It was found that ozonation in combination with other effective AOPs and biological methods enhances treatment efficacies. This review will serve as a reference document for the researchers working in the AOPs field particularly focusing on ozone-based AOPs for wastewater treatment and management systems.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.8
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• pp.823-830
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• 2008

The feasibility study for the application of the photoelectrocatalytic decolorization of Rhodamine B(RhB) was performed in the slurry photoelectrochemical reactor with powder TiO$_2$. The photoelectrocatalytic process was consisted of powder TiO$_2$, Pt electrode and three 8 W UV-C lamps. The effects of operating conditions, such as current, electrolyte, air flow rate and electrode material were evaluated. The experimental results showed that optimum TiO$_2$ dosage and current in photoelectrocatalytic process were 0.4 g/L and 0.02 A, respectively. It was found that the RhB could be degraded more efficiently by this photoelectrocatalytic process than the sum of the two individual oxidation processes(photocatalytic and electrolytic process). It demonstrated a synergetic effect between the photo- and electrochemical catalysis. Photoelectrocatalytic process was affected to air flow rate and optimum air flow rate was 2 L/min. The electrode material and NaCl effect of decolorization of RhB were not significant within the experiment conditions.

• Journal of Ocean Engineering and Technology
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• v.21 no.5
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• pp.33-38
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• 2007

The welding methods have been applied in the most structural products from multi-field of automobile, ship construction and construction, and so on. The structure steel must have enough strength of structure. In this study, SS400 steel and STS304 steel were used to estimate the corrosion characteristics of the weld thermal cycle simulated HAZ. To evaluate the corrosion characteristics, also, the materials with two conditions were used in 3.5% NaCl. The one is to the drawing with diameter of ${\Phi}10$ and the other is to the residual stress removal treatment. The electrochemical polarization test and immersion test were carried out. From test results, corrosion potential, corrosion current density, weight loss ratio and corrosion rate were measured. In the kinds of SS400 steels, corrosion potential of weld thermal cycle simulated specimens after the heat treatment showed somewhat the direction of noble potential. And in the base metal to be drawing weight loss ratio and corrosion rate occurred higher than the other kinds. In the kinds of STS304 steels, the result of base metal to be drawing was similar to results of SS400 steels, too. Two kinds of $750^{\circ}C$ and $1300^{\circ}C$ of weld thermal cycle simulation after the heat treatment were rather higher than the other kinds in weight loss ratio and corrosion rate.

• Journal of Environmental Science International
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• v.18 no.1
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• pp.61-72
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• 2009

Fabrication and oxidants production of 3 or 4 components metal oxide electrode, which is known to be so effective to destruct non-biodegradable organics in wastewater, were studied. Five electrode materials (Ru as main component and Pt, Sn, Sb and Gd as minor components) were used for the 3 or 4 components electrode. The metal oxide electrode was prepared by coating the electrode material on the surface of the titanium mesh and then thermal oxidation at $500^{\circ}C$ for 1h. The removed RhB per 2 min and unit W of 3 components electrode was in the order: Ru:Sn:Sb=9:1:1 > Ru:Pt:Gd=5:5:1 > Ru:Sn=9:1 > Ru:Sn:Gd=9:1:1 > Ru:Sb:Gd=9:1:1. Although RhB decolorization of Ru:Sn:Sb:Gd electrode was the highest among the 4 components electrode, the RhB decolorization and oxidants formation of the Ru:Sn:Sb=9:1:1 electrode was higher than that of the 3 and 4 components electrode. Electrogenerated oxidants (free Cl and $ClO_2$) of chlorine type in 3 and 4 components electrode were higher than other oxidants such as $H_2O_2\;and\;O_3$. It was assumed that electrode with high RhB decolorization showed high oxidant generation and COD removal efficiency. OH radical which is electrogenerated by the direct electrolysis was not generated the entire 3 and 4 components electrode, therefore main mechanism of RhB degradation by metal oxide electrode based Ru was considered indirect electrolysis using electrogenerated oxidants.

• Resources Recycling
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• v.27 no.3
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• pp.93-99
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• 2018

Effective extraction of platinum group elements by dissolving waste platinum scrap from the display industry and solvent extraction, was studied. The extracted platinum solution was prepared as a precursor solution for diesel automotive exhaust gas purification catalyst and its catalytic activity was tested. The behavior of aqueous species of platinum was investigated through solution chemistry and based on the existence and behavior of these chemical species, the possibility of extraction and separation was established. By dissolving waste scrap by electrochemical method, the dissolution time of scrap was shortened and the extraction efficiency was increased. Through separation and removal of rhodium component, solvent extraction by TBP, and stripping by hydrochloric acid, Pt-Chloride-$H_2O$ solution was prepared. And then, an platinum amine complex solution through amination reaction with this solution as a raw material was prepared. The possibility of producing high-value platinum compounds from platinum group waste scrap was investigated by preparing platinum amine complex solution and then examining the catalytic activity with this amine precursor on the combustion reaction of carbon black.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.3
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• pp.339-344
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• 2008

Titanium dioxide nanotubes were fabricated by self-organized electrochemical potentiostatic anodization of titanium thin film with an electrolyte solution of sodium sulfate 1M and sodium flouride 0.5wt% aqueous solution at 20$^{\circ}C$ for 20min. Field Emmision Scanning Electron Microscopy(FE-SEM) and X-ray Diffractometer(XRD) were used to evaluate the micromorphology and crystalline structure of the titanium dioxide nanotube thin film. Titanium dioxide nanotube were fabricated with diameters approx. 100nm and tube length from appox. 1 $\mu$m. Titanium dioxide films formed through anodization and annealing process at 450$^{\circ}C$ contained a phase of anatase. Also, this study was performed to evaluate the application of titanium dioxide thin film for treating humic acid dissolved in water. The reaction tended to follow the Langmuir-Hinshelwood kinetics with zero order. Comparative experiments with thin film and anatase powder showed the same zero order kinetics when 0.3g of powder had been used.

• Applied Chemistry for Engineering
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• v.23 no.3
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• pp.297-301
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• 2012

Microbial fuel cell (MFC) is the major of bio-electrochemical system which can convert biomass spontaneously into electricity through the metabolic activity of the microorganisms. In this study, we used an activated sludge as a microbial inoculum and then investigated the feasibility of using dairy wastewater as a possible substrate for generating electricity in MFC. To examine the performance of MFC as power generator, the characteristics on cell potentials, power density, cyclic voltammetric analysis and sustainable power estimation were evaluated for dairy wastewater. The maximum power density of $40\;mW/m^2$was achieved when the dairy wastewater containing 2650 mg/L COD was used, leading to the removal of 88% of the COD. The results from this study demonstrate the feasibility of using MFC technology to generate electricity while simultaneously treating dairy wastewater effectively.

• Journal of the Korean institute of surface engineering
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• v.49 no.5
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• pp.431-438
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• 2016

This research investigated the relationship between the corrosion damage characteristics of offshore wind steel substructure and the time of current density application by electrochemical accelerated short-term corrosion test. The galvanostatic corrosion was conducted on the steel specimens in natural seawater with a constant current density ranging from $1mA/cm^2$ to $200mA/cm^2$ for 1 ~ 180 min. Macro and micro observation was carried out on the surface of the corrosion damaged area using SEM and 3-dimensional analysis microscope. The weight loss of the specimens before and after was calculated as the difference between the initial weight prior to corrosion and weight after removal of the corrosion product. It was shown that during galvanostaic corrosion process, the corrosion behavior could be characterized by the onset of pitting corrosion in the early stage and the uniform corrosion in the late stage, showing damage development in the depth direction with the time of current application. The result of the 3D analysis revealed that both damage depth and surface roughness increased with increasing time of current application. The weight loss curves with time showed that a coefficient of determination ($R^2$) was relatively high for the relationship between the time of current application and weight loss. As a result, the degree of corrosion can be controlled by simply varying the time of current application.

• Corrosion Science and Technology
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• v.17 no.4
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• pp.154-165
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• 2018

During the process of sulfur dioxide removal, flue gas desulfurization equipment provides a serious internal corrosion environment in creating sulfuric acid dew point corrosion. Therefore, the utilities must use the excellent corrosion resistance of steel desulfurization facilities in the atmosphere. Until now, the trend in developing anti-sulfuric acid steels was essentially the addition of Cu, in order to improve the corrosion resistance. The experimental alloy used in this study is Fe-0.03C-1.0Mn-0.3Si-0.15Ni-0.31Cu alloys to which Ru, Zn and Ta were added. In order to investigate the effect of $H_2SO_4$ concentration and the alloying elements, chemical and electrochemical corrosion tests were performed. In a low concentration of $H_2SO_4$ solution, the major factor affecting the corrosion rate of low alloy steels was the exchange current density for $H^+/H_2$ reaction, while in a high concentration of $H_2SO_4$ solution, the major factors were the thin and dense passive film and resulting passivation behavior. The alloying elements reducing the exchange current density in low concentration of $H_2SO_4$, and the alloying elements decreasing the passive current density in high concentration of $H_2SO_4$, together play an important role in determining the corrosion rate of Cu-bearing low alloy steels in a wide range of $H_2SO_4$ solution.